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  1. Those that are going, or maybe going to AirVenture 2019 at Parkes don't forget to mark that you are going in the event entry here at Recreational Flying: This will enable members of the site to be able to perhaps organise a catch up with each other in person at the event
  2. 10.1 Control in pitch In section 6.3 we learned that movement of the elevators provides a pitching moment about the lateral axis, that initiates a change in the aoa. Once the new aoa is established, then — provided the elevators are held in that deflected position by pilot pressure on the control column or a trim device — the pitch moment returns to zero and the aircraft maintains that aoa (and there is a direct relationship between aoa and IAS). In the manoeuvring forces module we established that aoa and power combinations provide (a) increased speed or climb and (b) decreased speed or descent — or varying degrees of either. Thus, control in pitch (i.e. of aoa) combined with throttle control allows an aircraft to take-off, climb, cruise at various speeds, descend and land. However, control in pitch involves more than initiating a discrete pitching moment to effect an aoa change and subsequent attitude change. In section 1.10 we found that to sustain a turn, an additional force must be continuously applied towards the centre of the curve or arc — the centripetal force. This is achieved by an increased aoa — greater than the normal for a particular straight and level airspeed — held with control column back-pressure. The increased aoa provides the centripetal force, and that force keeps the aircraft constantly pitching 'up' in the longitudinal plane, into the direction of turn. 10.2 Control in yaw Aircraft perform much better if their longitudinal axis is accurately aligned, in plan view, with the flight path; i.e. with the relative airflow. Also, an aircraft flying with a constant angle of slip is part way to ending up in an unusual flight attitude. Thus, the primary task of the fin and rudder combination is to act as a stability and trim device so that the directional stability system will restore flight to the proper state of zero sideslip angle. If the rudder has no trim tab, as would be the case with most light aircraft, then the pilot would have to keep the aircraft in trim by applying pressure to one rudder pedal. This pressure will vary with airspeed and the sideslip angle. This trimming task also includes the use of rudder to overcome adverse yaw when initiating a turn, and to keep the turn balanced or 'coordinated'. The very simple flight instrument provided to indicate slip — or skid in a non-coordinated turn — is the balance ball. A metal ball is enclosed in a short, transparent, slightly curved tube where movement is somewhat damped by the restriction of the tube. When the aircraft is flying with zero sideslip, the ball will be centred at the bottom of the curve; when the aircraft is slipping into (or skidding out of) the turn, the inertial forces will move the ball left or right in the direction of the slip. To trim the aircraft, the pilot applies pressure on the rudder pedal on the side to which the ball has moved; i.e. 'steps on the ball'. When the aircraft is slipping, the pilot will also feel those inertial forces apparently pushing his/her weight in the same direction as the ball, hence the expression 'flying by the seat of your pants'. The amount of pilot-induced yaw, at a given airspeed, is dependent on the degree of rudder deflection. If the pilot holds the rudder deflection, the aircraft will continue yawing and sideslipping. But, as the aircraft rotates about the normal axis, the wing on the outside of the rotation must be moving a little faster — and the inner wing a little slower — so there will be a small lift differential. The differing lift moments will raise the outer wing and lower the inner wing and the aircraft will enter a banked turn. A pilot would not initiate a sustained turn by using rudder alone, but there are occasions when it is appropriate and effective to alter the aircraft's heading a few degrees by using just rudder — or perhaps rudder plus a little opposite aileron to stop the bank. Such occasions are when finally aligning the aircraft with the runway centre-line or compensating for small changes in wind direction when landing. We will cover this in the 'Circuit, approach and landing' module. Having said that, there is still an occasion where a rapid 180° change in direction is achieved solely with rudder; see the following. The ultimate use of rudder to yaw the aircraft is demonstrated when the pilot of an aerobatic aircraft executes a 'stall turn' or 'hammerhead'. The former term is perhaps a misnomer, because the wing does not reach the critical aoa during the manoeuvre. The manoeuvre involves pulling the aircraft into a full-power vertical climb then, as the airspeed decays to somewhere near the normal stall speed, applying full rudder so that the aircraft is yawed 180°, about the normal axis, into a vertical descent. The slipstream supplies the energy to the rudder for the turn. The interesting thing is that, although the aircraft is at or below normal stall speed, the wings are nowhere near the critical aoa as, towards the end of the climb, the control column is held forward of the neutral position — and because of the low aoa and low V², the wings are not producing much aerodynamic force*. The length of the vertical 'up-line' depends on the aircraft's power/weight ratio — and thrust power and momentum are reducing quickly. Of course, if the pilot delays too long before applying full rudder, the weight vector will take over and cause the aircraft to slide vertically backwards — a tailslide. *In fact the wing could be at the 'zero lift' aoa where the aerodynamic forces on both sides of the wing are equal and opposite. 10.3 Control in roll We discussed how ailerons produce a rolling moment in section 4.10, so what happens when the ailerons are normally deflected, by the pilot moving the control column to the left or right? Initially the aircraft will start to roll, and if the control column is then returned to the neutral position the roll will cease but the bank angle reached will tend to remain. To level the wings, the column has to be moved to the opposite side — then returned to neutral once the wings are again level. Which indicates there always tends to be a sort of 'neutral stability' in the lateral plane. However, that situation doesn't exist because, as we found in section 7.4, other forces come into play when the aircraft is banked — creating sideslip, then yaw and eventually a turn. So the prime reason for introducing a roll is as the first step in turning. However, before going on to the turn, let's just look a little further at the effect of aileron deflection while elevator and rudder are held in the neutral position, when the aircraft's velocity is high; i.e. pure roll. The simplest aerobatic manoeuvre is the aileron roll, which (in aircraft that have been certificated for aerobatics) is usually accomplished by first gaining some extra kinetic energy, applying full power and raising the nose so that it is pointing 20° or so above the horizon with the balance ball centred. The control column is then firmly moved left or right to the full extent of travel and held there, while the elevators and rudder are both held in the neutral position; i.e. the roll is produced solely by the aileron deflection. The aircraft will then continue to roll about its longitudinal axis — because the ailerons being positioned towards the wingtips produce a strong rolling moment about the axis — more or less at a steady rate of roll, until the accumulated extra energy is exhausted. If the column was not moved to its full extent, the aircraft will still roll, but the rate of roll will be slower yet still steady. The time to complete a full 360° roll is very much dependent on the aircraft design and that roll rate dictates how many complete rolls can be produced before the aircraft ends up with the nose pointed well below the horizon — because of the combined effects of slip, yaw and the full 360° inclination of the lift vector. The rate of roll for a competition-class aerobatic aircraft is around 360° per second; for the more mundane aerobatic aircraft, it is around 60° per second, which will probably produce only one full 360° roll. A properly executed roll will result in a continuing 1g load throughout the manoeuvre. 10.4 Control in a turn We come then to the question 'how do you turn an aircraft?' Well, you can make the aircraft's nose turn just a few degrees without banking by just applying pressure on the rudder pedal in the direction you want the nose to move and at the same time moving the control column a little sideways in the opposite direction to stop the consequent bank. Applying pressure to the rudder in one direction with opposite aileron is cross-controlling. Normally, this is a very sloppy way to fly but also a habit that can lead to trouble — particularly in low-speed descending turns, such as that made in the approach to landing. Although not directly related to turns, this extract from an RA-Aus incident report illustrates how easy it is to get into difficulties if you don't realise you are cross-controlled at low speeds. "The student had completed two solo circuits and landings without incident. During the third the landing appeared normal, the aircraft touched down without bouncing but then veered left and the left wing lifted. The student applied full power but the aircraft failed to climb normally and appeared to be staggering and slowly orbiting to the left. The aircraft only gained about 40 feet height then gradually descended, striking the ground nose low and left wing low. The student was not injured. It was found that he had maintained full left rudder when he applied full power and was using aileron to counter the yaw — the aircraft basically sideslipped into the ground." The normally recommended way to initiate a level turn (to the left) is to move the control column to the left until the required bank angle is achieved, then return the control column to neutral. At the same time as applying aileron, just sufficient bottom (left) rudder is applied to balance the turn so that there is no slip or skid and the balance ball stays centred. Also, the amount of rudder required increases as airspeed decreases. As the aircraft banks, the lift vector departs from the vertical, so the aoa must be increased sufficiently that the vertical component of lift always exactly balances weight. This means increasing back-pressure on the control column as bank is applied. As aoa increases, induced drag increases. So, to maintain V² throughout the turn, power must be increased. Thus a properly balanced, constant rate and constant-speed turn implies a smoothly coordinated application of aileron, rudder, elevator and power. In some aircraft, particularly slower aircraft with high aspect ratio wings, it is necessary to lead the turn with quite a bit of rudder (because of aileron drag) before adding aileron. In other aircraft it is quite easy to initiate and continue a turn without using rudder at all, but the turn will be uncoordinated — i.e. the balance ball not centred — and such conditions are not desirable. During a banked level turn, the outer wing is moving very slightly faster than the inner wing and will consequently produce more lift; the bank will tend to increase and the turn to wrap-up even though the ailerons are in the neutral position. In order to maintain the required bank angle it is necessary to apply a slight opposite pressure to the control column, which is known as 'holding off bank'. This is relative to level and climbing turns, but different physics apply to descending turns. In a climbing turn, the outer wing has a slightly greater aoa than the inner wing, and thus additional lift. Combined with its slightly faster speed, this reinforces the tendency for the bank angle to increase and the need to hold off bank. The reason for the higher aoa of the outer wing is because of a difference in relative airflow. Imagine an aircraft doing one complete rotation of a continuing climbing turn. Obviously all points on the airframe are going to take the same time to achieve the higher altitude; however, the upward spiral path followed by the outer wingtip must have a larger radius than that followed by the inner, and therefore the path followed by the outer wingtip is not as steep as that followed by the inner. The less steep path of the outer wing (i.e. the relative airflow) means that the aoa of the outer wing will be greater than that of the inner. You might have to think about it a bit! The reverse occurs in a descending turn — the steeper path of the inner wing in the downward spiral means that it will have a larger aoa than the outer wing, which may compensate, or overcompensate, for the faster velocity of the outer wing. In order then to maintain the required bank angle it is necessary to apply an inward pressure to the control column; i.e. in a descending turn the bank must be 'held on'. If the pilot tends to hold off bank in such a turn, there will be an excess of 'bottom' rudder and the aircraft must be skidding. Whenever an aircraft is slipping or skidding, the wing on the side to which the rudder is deflected will stall before the other, with a consequent instantaneous roll in that direction. So the situation we've described — holding off bank in the descending turn with excess bottom rudder — means that should the aircraft inadvertently stall — a cross-controlled stall — it is going to roll further into the bank and enter an incipient spin. Hence the old adage — 'never hold off bank in a gliding turn'. A cross-controlled stall typically occurs in the turn onto final approach for landing. If you must fly cross-controlled when banked, then it is better to fly with an excess of top rudder, as in the sideslip manoeuvre. Thus, if the aircraft should stall, the roll will be in the direction of the upper wing; i.e. towards an upright position. And never apply an excess of bottom rudder in an attempt to tighten any turn, particularly when the airspeed is low for the bank angle employed and/or height is low. This is discussed further in the 'Safety: control loss in turns' module. A breaking turn is a defensive flying manoeuvre, which every pilot should be able to perform rapidly and automatically to avoid collision, particularly in the circuit. It involves very rapid transition, usually into a steep descending turn, but a steep climbing turn may be necessary. A level turn is an unlikely choice, but whatever turn is chosen you must be able to perform it instinctively while your head is continually swivelling to ascertain the location of other aircraft — without falling out of the sky by inadvertently applying back-pressure on the control column and thus exceeding the critical aoa. Before we go on to the sideslip, another very simple aerodynamic demonstration — but only for aerobatic aircraft whose engine and airframe are able to take the loads, and absolutely never for any other aircraft — is the flick roll. The flick or snap roll asymmetric aerobatic manoeuvre is an accelerated stall combining a rapid increase in aoa with a full yaw. It is brought about — when cruising straight and level at a speed less than Va — by pulling the control column firmly back as far as it will go while applying full left or right rudder. The wing in the direction of the applied rudder stalls first and the aircraft flicks into a 360°, roughly horizontal, roll. The roll will continue while the rudder and elevators are held at their limits (and cease when they are returned to the neutral position) but the aerodynamic drag produced by the manoeuvre slows the aircraft quite rapidly and the aircraft will enter a vertical spin if the roll is held too long. The faster the entry speed, the higher the torsional stress on the rear fuselage and empennage, the engine mountings and perhaps even the engine crankshaft; but the slower the speed, the greater the likelihood of immediately entering a spin, and recovery technique is dependent on several variables. The roll is usually a lot snappier in the opposite direction to propeller rotation. Flick rolls may be executed only in aerobatic aircraft designed to withstand the extreme stresses. Such a simple control action, whether or not while turning, demonstrates how easily misuse of rudder can end up in an unusual and dangerous attitude, and where the possibilities increase as speed decreases. And be aware that you don't have to actually push on the rudder pedal, you can easily achieve misuse by inadvertently slipping one foot off the rudder bar at a critical time — the turn onto 'final approach' for example. 10.5 Sideslip as a manoeuvre Types of sideslip vary in degree — from inadvertently flying cross-controlled in the cruise (i.e. one wing slightly low and compensating with opposite rudder) to a fully-fledged cross-controlled turn where the aircraft is steeply banked in a descending turn with full opposite rudder applied. All sideslips reflect uncoordinated flight and result in increased drag. Note: in aerodynamic terms, any time it is evident that the aircraft's longitudinal axis is at an angle to its flight path (in plan view) then the aircraft is sideslipping (i.e. its motion has a lateral component), and the angle between the flight path and the axis is the sideslip angle. Aerodynamicists don't generally distinguish between sideslip and 'slip' or 'skid', but many pilots use 'slip' as the general term, 'skid' to describe slipping away from the centre of a turn and 'sideslip' to describe a particular type of height-loss manoeuvre. The sideslipping manoeuvre is only for the pilot who has a very good feel for their aircraft because, among other things, the ASI will most likely be providing a false airspeed indication. High sideslip angles combined with high aoa must be avoided. There seem to be as many definitions of the types of slip as there are exponents of sideslip techniques, but the safe execution of all sideslips requires adequate instruction and continuing practice. Here are some types: The straight or steady-state sideslip approach to landing The helmet and goggles crowd who, very sensibly, like to fly biplanes and other open-cockpit aircraft not equipped with flaps, need a manoeuvre for use on the landing approach to a short strip that enables them to lose height quickly without increasing airspeed and which provides a good view of the landing area. The answer has long been the cross-controlled steady state sideslip; a manoeuvre designed to lose height over a short distance, dumping the potential energy of height by converting it to drag turbulence rather than kinetic energy. Such sideslips may also be a requirement when executing a forced landing, and the same type of slipping approach may also be necessary for those aircraft where, in a normal approach, the pilot's view of the runway is obstructed by the nose. Once established on the approach descent path at the correct airspeed, the aircraft is banked with sufficient opposite (top) rudder applied to stop the directional stability yawing the nose into the relative airflow and thus turning. Slight additional backward pressure on the control column may be needed to keep the nose from dropping too far. The aircraft sideslips in a moderate to steep bank with the fuselage angled across the flight path, giving the pilot a very good view of the landing area. The greatly increased drag, from the exposure of the fuselage side or 'keel' surfaces to the oncoming airflow, enables an increased angle of descent without an increase in the approach airspeed. The execution of a sideslip to a landing varies from aircraft to aircraft and it may not work particularly well where there is a lack of keel surface — an open-frame aircraft like the Breezy, for example. The sink rate is controlled by aileron and power is held constant, usually at idle/low power, and the sideslip must be eased off before the flare and touchdown. When recovering, care must be taken to coordinate relaxation of the back-pressure, leveling of the wings and straightening of the rudder — otherwise the aircraft may do its own thing or stall, particularly in turbulent conditions. The straight sideslip is limited by the maximum rudder authority available; there will be a bank angle beyond which full opposite rudder will not stop the aircraft from turning. Although this manoeuvre usually comes under the proprietorship of the 'stick and rudder' people, the use of the sideslip, by the captain of a Boeing 767, undoubtedly saved the lives of many people in an extraordinary incident that occurred in 1983 when, due to a train of errors — as are most accidents/incidents — an Air Canada 767 ran out of fuel at 41 000 feet. The captain subsequently glided the aircraft to a safe landing on an out-of-service runway, which was being used for a drag racing event at the time. The aircraft was sideslipped through several thousand feet to lose excess height on the approach. For more information about this magnificent demonstration of airmanship (following an execrable demonstration of preflight procedure by many people; keep the old adage in mind — "proper pre-flight procedure precludes poor performance"!) google the phrase 'Gimli glider'. The sideslipping turn Slipping whilst turning is a manoeuvre often used in non-flap equipped aerobatic aircraft where it is desirable to perform a curving landing approach. This is also a useful emergency manoeuvre if it is necessary to increase the sink rate during a turn — such as the turn onto final approach in a forced landing when an overshoot of the landing site is apparent. It is just a sideslip where insufficient top rudder is applied to stop the aircraft turning while slipping. The rate of turn and the rate of sink are controlled by the amount of bank and the amount of rudder but it is an uncoordinated descending turn. Dangerously high descent rates are achieved if the bank angle applied exceeds the full rudder authority. Fishtailing Fishtailing is a series of sideslips where the wings are held level in the approach attitude with (alternating) aileron while the aircraft is repeatedly yawed from side to side by applying alternate rudder; the increased drag increases the sink rate and is possibly used as an emergency measure if overshooting a forced landing. The manoeuvre is generally not recommended, because uncoordinated control use at low levels may lead to dangerous loss of control. Also, excessive alternating rudder reversals may overstress the fin/rear fuselage. Sideslip to a crosswind landing In a sideslip to a crosswind landing, the aircraft is always banked with the into-wind wing down so that the sideslip can be smoothly decreased to a forward slip (below) before the roundout. Most aircraft tend to be slower in the slip, so the nose will need to be a bit lower than that needed to maintain the normal approach speed. A smoothly executed sideslip approach requires much practice, but displays considerable finesse to a ground observer. The forward slip crosswind approach A 'forward' slip is a moderate sideslip application designed only to compensate for crosswind during approach and landing. The slip can be applied throughout the final approach or just in the last stages, and it usually follows a full sideslip approach in crosswind conditions. The into-wind wing is lowered with sufficient bank so that the slip is exactly negating the crosswind drift, while opposite (top) rudder is applied to stop a turn developing and to align the aircraft's longitudinal axis with the flight path — and the runway centreline. If drifting off the path, just add or remove some aileron pressure and, at the same time, add or remove some rudder pressure to maintain direction. An approach speed 2–3 knots above normal is set up, the sink rate (which will be greater than usual because of the inclined lift vector) is controlled by the power setting, the into-wind main landing gear will touch down first and the aircraft is held straight with rudder by pivoting on that one wheel until ground speed has reduced to a safe level. The forward slip is the particularly recommended technique for crosswind landings in high-wing taildragger aircraft. Incidently, a useful technique for a high-wing taildragger in a significant crosswind is to also perform the take-off run on one main wheel. If there is any real difference between the straight sideslip and the forward slip it is just the amount of pressure applied to the controls. In a sideslip, the aileron pressure dictates the angle of descent and the rudder pressure dictates the amount the fuselage is deflected across the flight path. In a forward slip, the aileron pressure is just enough to compensate for the crosswind drift and thus maintain position on the extended runway line, and the rudder pressure just enough to keep the fuselage aligned with both the landing path and the flight path. There is one manoeuvre for certified aerobatic aircraft that demonstrates what might be considered a reversal of all we have stated in this module. This is the 'four-point slow roll' or 'hesitation roll' where the aircraft is rolled through 360° in level flight around a point on the horizon, but the roll is paused for a second or two at each 90° point; i.e. when the wings are first vertical, when the aircraft is upside down, when the wings are again vertical and when the aircraft returns to normal attitude. The roll is started (to the left) with normal aileron and a bit of left rudder, then as the roll progresses through the first 90° top (right) rudder is increasingly applied to negate the yaw, and also to hold the nose up. During the slight pause at the 90° position the aircraft is being held in a nose-up attitude by the rudder whilst the elevators are used to stop the nose wandering to the left or right across the horizon, and the ailerons are neutral. Some lift will be generated by the fuselage having an aoa because the nose is being held up. Then the roll is restarted until, at the 180° position, the aircraft is inverted and the nose is held up by a large forward movement of the control column and the aoa is negative; i.e. the lift is being generated by a reversed aerofoil. And so the roll continues. Of course, all the control movements involve gradual increase/decrease in pressures throughout the sequence. 10.6 Spins The 'stall/spin' phenomenon When an aircraft is held in a turn, and near the critical aoa with excess bottom rudder applied (i.e. a cross-controlled skidding turn, which often happens when the pilot tries to 'hurry' the turn with bottom/inside rudder instead of increasing bank) the lower, partly blanketed, wing will be producing less lift than the upper wing. Any tightening of back-pressure on the control column (or any inadvertent back-pressure applied when, for instance, looking over your shoulder; or even any encountered turbulence or wind shear) may take the aoa past the critical angle. The lower wing will drop sharply in an 'uncommanded' roll, and thus become more deeply stalled than the upgoing wing — which may not be stalled or just partly stalled. The high aoa of the lower wing causes greatly increased induced drag, yawing forces in the same direction as the lower wing come into action, the nose swings down and the aircraft enters an incipient (i.e. partly developed) spin condition, where it is about to start autorotation (below). All of this happens quickly, and in some aircraft very quickly indeed. If the aircraft is properly weight-balanced (i.e. weight less than MTOW and cg within the defined fore and aft limits), this is readily countered by quickly easing stick back-pressure to reduce aoa below critical aoa — which immediately restores full control — applying sufficient rudder to stop further yaw, adding full power and rolling the wings level with aileron while keeping the balance ball centred. However, if the slew, exacerbated by the yaw, is allowed to develop past perhaps a 45° movement in azimuth, then there is a stall/spin situation. You sometimes hear about this when an unaware pilot allows such to develop close to the ground — often when performing a climbing turn after departure from an airfield; or in a turn-back to the runway following engine failure after take-off; or when in the descending turn from base leg on to the final approach to landing where, because of illusory ground reference cues, there may be a tendency to increase the rate of turn by applying additional bottom rudder whilst maintaining the bank angle with opposite aileron — 'holding off bank' as mentioned in section 8.4. Ultralights, with their very low wing loading, normally display quite benign stall characteristics when slowly decelerated to stall speed in straight and level flight. But they may exhibit quite nasty behaviour in an accelerated stall or when a stall is initiated during a turn; and such are the usual unintentional stall/spin modes. Under these circumstances the height lost in the incipient spin — the initial entry to autorotation — may be 100 to 400 feet. Thus, an incipient spin condition is highly dangerous when occurring in the circuit pattern or in any other low-level flight situation. See the flick roll box above and read the sections dealing with 'limiting climbing turns during take-off' and 'accelerated stalls'. There may be uncertified light aircraft where characteristics, such as rolling inverted in a relatively mild stall/incipient spin situation, are evident. However, a commercially manufactured aircraft with such characteristics should not receive a CASA Certificate of Type Approval. Autorotation — the fully developed spin With adequate training, an incipient spin is readily anticipated and easy to correct — provided the aircraft weight and balance are within the stated limits. But, if the correction is not done before the nose has swung maybe 90° or so, it may develop into autorotation where the aircraft is descending in a stabilised, usually nose-down, rotation — rolling and yawing in the same direction at a constant airspeed at or slightly above Vs1 — a full-blown spin with each 360° rotation taking only 2–4 seconds in a very light aircraft. The height loss during each rotation — 200 to 400 feet or more, depending on the stall speed and the steepness of the spin — plus the considerable height loss during the pull-out from the recovery dive, is insignificant at a reasonable height but will be critical at lower levels. In a normal turn the aircraft's longitudinal axis is more or less aligned along the flight path — which is the periphery of the turn — the cg moves along the flight path and the inner wing is pointing towards the centre of the turn. But in fully developed autorotation the vertical axis of the spin is located somewhere in the 90° sector between the lateral and longitudinal axes and not so far from the aircraft's cg — perhaps less than two fuselage lengths. Thus, the aircraft is not turning in the normally accepted meaning of the word; it is 'spinning' around that vertical axis, while it's also rolling and yawing about the aircraft's cg; and also pitching somewhat. The lower wing is more deeply stalled than the higher producing less lift but, being on the back slope of the CL curve, more induced drag so providing the asymmetrical yawing and rolling moments. Those aerodynamic forces produced by the wings drive the spin while the resistance of the rear fuselage and empennage reaches a point where it prevents the yaw from developing further; the aircraft's inertia resists change in angular momentum so producing the stable autorotation condition. Usually the structural loads are only a little above normal during autorotation. In a steep spin, the nose is pitched down perhaps 50–60°, the aoa of the lower wing is 20–30°, there is a fair bit of bank and the roll motion dominates. The spin axis will be perhaps somewhere near one or two fuselage lengths forward (more or less) of the aircraft's cg — further away for a steeper spin. The cg will be following a helical flight path. In a flat spin, the nose is pitched down perhaps 10–20°, with an aoa around 60–70° due to the high vertical component of the relative airflow. With very high induced drag and little bank, the angular rotation winds up and yaw motion dominates. The spin axis will be much closer to the aircraft's cg, perhaps even within the airframe, and particularly so if the cg is in an aft position. The closer the spin axis is to the cg, the harder it is to break out of the spin. If the axis coincided with the cg, break-out would be impossible — unless the aircraft was equipped with a ballistic parachute recovery system. Most very light tractor-engined aircraft spin steeply to moderately steeply, so spin recovery early in autorotation is usually — but not always — straightforward: close the throttle, ailerons to neutral, stop the yaw (by applying full rudder opposite to the rotation direction apparent through the windscreen or shown by the turn indicator (not the balance ball/needle), then unstall the wings to stop the spinning (generally by applying full forward stick rather than just moving it to or past the neutral position until the spin stops). Control movements must be carefully sequenced and positive. The aircraft will be in a steep descent when the spin has ceased; the aerodynamic loads during the subsequent pull-out from the descent may lead to an accelerated stall if the aircraft is nearing the surface and the pilot applies extreme back-pressure. The height loss just during the pull-out stage may exceed 400 feet, so that the total loss of height during spin entry and recovery could easily exceed 1000 feet. The problem for a pilot who is conscious of the need to avoid stall conditions when in the circuit by always maintaining a safe speed near the ground, and has had ample training in stall and incipient spin recognition and recovery, occurs when a spin is inadvertently induced at altitude. If that pilot has never previously encountered full autorotation then the disorientation associated with the first experience can be frightening. The pilot may also experience a ground rush illusion where the surface features rapidly spread out to fill the entire field of view and the ground appears to rapidly rise; the reaction is to freeze or to pull back on the control column, which just ensures that the aircraft is held in the stalled condition even though there may be ample height available to recover. The photo at left was taken about 1949 and shows what happened when a student pilot got himself into a spin, evidently retained back-pressure on the control column and allowed the Tiger Moth to spin all the way to the ground from above 2000 feet. The spin developed into a flat spin, with relatively low vertical and horizontal speed, enabling the pilot to walk away with minor injuries. Also the Tiger Moth had a tough steel tubing fuselage frame, which absorbed much of the impact energy. You can see that the fuselage aft of the engine compartment firewall seems practically undamaged. The pilot of any aircraft will not be exposed to the risk of an unintentional stall/spin if they always remain situationally aware, maintain an appropriate energy balance, does not indulge in very low-level manoeuvring and, above all, flies the aircraft. Don't practice stalling below 3000 feet agl; and remember spins result from a loss of lateral and directional stability at the critical aoa, and the only way to get into a spin is to first exceed the critical aoa. Also, sufficient forward stick movement will immediately decrease aoa below the stall angle and restore full control in any stall or near-stall condition; but not in autorotation where opposite rudder and full forward control column movement is necessary because (1) the aoa developed will be well past the critical aoa and (2) the control surfaces will not be as effective as usual — the fin and rudder could be screened by the tailplane and thus in a low energy, turbulent airstream. Intentional spinning Stall/spin events occurring at a safe altitude are insignificant; they may become nasty accidents when they occur at lower levels. But intentional spins can be fun in an aerobatic aircraft that has been certificated for intentional spinning and, given sufficient height, quite easy to recover from — provided the cg position is within the forward and aft limits. The challenge is in aiming for a precise number of turns, half-turns or quarter-turns and the exact direction the aircraft will be heading at recovery. Spin characteristics are very complex and vary greatly between aircraft. Generally the intentional spin is induced from level flight by closing the throttle, bringing the aircraft to the point of stall in a nose-up attitude, holding ailerons in the neutral position then applying full rudder in the direction you want the aircraft to rotate and, at the same time, pulling the stick right back. Hold the neutral aileron, full rudder and back stick. The reason for the excessive control movements is to ensure a swift and definite entry into autorotation. The higher the nose is held above the horizon at the point of stall the more violent will be the spin entry. Aircraft that tend to spin with the nose pitched well down will recover more quickly than aircraft where the spin attitude is relatively flat. However, if allowed to continue past two or three full turns, then centrifugal forces become well established — which tend to make all parts of the aircraft rotate in the same horizontal plane. Then, a nose-down spin may turn into a flat spin, which will then speed up rotationally, the rate of descent decreases, spin radius decreases and break-out will take longer, or may not be possible because it may be impossible to lower the nose. The spin axis may be very close to the pilot which would be very disconcerting. Recovery control forces required usually increase as the spin winds up; also, after initiating recovery action, the spin may increase a little before the action takes effect. Engine power — and its associated effects — also tends to flatten the spin. The flatter the spin, the closer the spin axis is to the cg and the greater the aoa, maybe 75° or more! Also, at such angles, the rudder may be completely blanketed by the fuselage/tailplane, making that control quite ineffective. Structural stresses increase as the spin progresses. A flat spin might be induced if, at the point of stall, full opposite aileron is applied with full rudder. If an aircraft stalls when inverted, it may enter an inverted spin if the control column position was held well ahead of neutral at the stall. It only happens during aerobatic routines — such as a poorly executed entry into a half-roll off the top of a loop, or messing up a stall turn. The recovery from an inverted spin involves correcting the yaw and increasing stick back-pressure until rotation ceases, then rolling level when speed has increased sufficiently; but the great danger in an inverted spin is pilot disorientation. One thing is certain — NEVER, NEVER intentionally spin an aircraft that has not been through the complete spin certification process; they may be incapable of recovery from fully developed autorotation, or the recovery attempt may result in a violent manoeuvre that overloads the airframe. Spin restrictions are not confined to non-aerobatic aircraft; for example, intentional spins were prohibited in the Seafire 47 and Sea Fury, very fast naval fighters of the late 1940s early 1950s, because of the time to recover (if recovery was possible) and the consequent extreme height loss. Spin recovery confidence building Developed spin recovery training is not included in the RA-Aus Pilot Certificate syllabus or the General Aviation Private Pilot Licence syllabus, but stall and incipient spin awareness and recovery are normal parts of the syllabi. A spin is usually classified as an aerobatic manoeuvre and, as all RA-Aus registered aircraft are prohibited from such manoeuvres, they shall not be allowed to enter an intentional developed spin. More to the point, no ultralight (and rather few light non-aerobatic aircraft) has ever been through the complete flight test schedule for spin recovery. However, gaining some experience and confidence in recovery from full autorotation can be readily and cheaply obtained by practicing a half-dozen spin recoveries with an instructor in a two-seat glider or powered aerobatic GA aircraft. It is probably better experience in the glider, as you are also exposed to the fact that every glider landing is achieved easily without using any chemical energy; on the other hand, a GA aircraft provides more opportunity to also explore the basic aerobatic manoeuvres — rolls, loops and stall turns. Incidently, 30 minutes thermalling in a glider will also demonstrate the absolute need to coordinate rudder and aileron in every turn — the ailerons on the long slender wings provide a large adverse yaw moment. These intentional spins should not be made from level flight, as described above, but should be made from those flight situations where unintentional spins are most likely to occur; i.e. in climbing and descending turns. These defensive flying lessons will also expose the student to the fact that it is very easy to invoke an accelerated stall during the pull-out after breaking out of the spin, if excessive control column back-pressure is applied — which is an automatic reaction if the ground is rising up to smite you! Spin recovery training in a spin-certified aircraft does invoke a recognition of the behaviour of that aircraft type immediately prior to an incipient spin event, but these warning signs will vary between aircraft types — or even aircraft of the same type. However, knowing how to recover from a stall/spin situation is of no help if it develops at a height that does not provide sufficient height for recovery — circuit height, for example. At such heights the aircraft must always be operated at a safe airspeed (1.5 × Vs1) and restricted to gentle manoeuvres. The 'falling leaf' manoeuvre During World War I, a very simple manoeuvre called the 'falling leaf' was developed as an incipient spin training exercise consisting of repeated entries into incipient spins while the ailerons are held in the neutral position. Although simple, the exercise requires precise timing — so that speed remains at and just above stall — and a good 'feel' on the controls plus very good 'hands and feet' coordination. It involves the initiation of an incipient spin by bringing the aircraft to the point of stall in level flight, then pulling back on the control column whilst applying full rudder. As the wing drops, the control column is moved forward to the neutral position to unstall the wings, then opposite rudder is applied and held, which actions stop the yaw and the incipient spin. Then the control column is pulled back again to stall the wings whilst the rudder is held in the same position; thus an opposite-direction incipient spin is started. Those sequences are repeated so that as the aircraft mushes down, in and out of the stalled condition, it slips from side to side in a series of small arcs, supposedly as a falling leaf may descend. Nowadays the falling leaf is classified as an aerobatic manoeuvre, thus performing the exercise in an ultralight is prohibited. Obviously before any falling leaf exercise is attempted the pilot must receive appropriate spin recovery training. The falling leaf term is also used to describe the technique of 'walking or pedalling down' a stalled aircraft by picking up a dropping wing with opposite rudder and then leaving the rudder applied a little longer than necessary so that the other wing starts to drop. In the latter technique, which is also a good developmental exercise in smooth air, the aircraft shouldn't be allowed to display much lateral movement during the descent. One of Bob Hoover's popular airshow demonstrations, the 'Tennessee Waltz', is a graceful falling leaf manoeuvre. Again, this exercise should not be attempted unless the pilot has appropriate spin recovery training — and ample height because of the substantial height loss in all falling leaf manoeuvres — but all these types of control exercises do provide an excellent means of familiarising yourself with the feel of your aircraft at low speed and its particular stability foibles. Picking up a dropping wing with rudder There is occasionally some debate about the merits of using the secondary effect of rudder to pick up a dropping wing when flying at or near the stall. The dropping wing has not been arrested by roll stability because it is partly or fully stalled. (The reason for proposing use of rudder rather than aileron is because if the dropping wing is near the critical angle of attack the use of aileron will increase the camber of that section of the wing taking it into, or further into, the reducing lift zone of the wings CL curve.) As demonstrated in the falling leaf, using only the rudder to 'pick up' the wing does nothing to remove the stall condition, and excessive input will lead to the opposite wing dropping and the aircraft entering an opposite-direction incipient spin. This technique of picking up a dropping wing with opposite rudder should not be applied during normal stall recovery, unless there is ample height for recovery from an induced spin. The wing must be unstalled by moving the control column forward so that normal aileron control actions can be taken and rudder used to check any yaw. The aircraft manufacturer's recommendations for stall recovery should be followed. But in their absence, the recommended technique in normal stall recovery is always to unstall the wings by easing forward on the control column — which is immediately effective — use sufficient rudder to check any further yaw, at the same time apply full power and then level the wings with aileron. For further information see Standard recovery procedure for all stall types However, when in the final stages of landing, and just above the surface in ground effect (should you want the aircraft to touch down in a stalled condition), gentle application of rudder using opposite yaw to pick up a dropping wing coupled with a slight easing of control column back-pressure may be an alternative to applying power for a go-around. But it depends very much on the particular wing — form, washout, flap setting, slats and slots — on how the stall develops along the wing and on the pilot's knowledge of the particular aircraft. It also depends on how crosswind is being countered. In some aircraft, the use of aileron to pick up the dropped wing will increase induced drag on the lower wing, and the consequent adverse yaw may swing the aircraft towards the ground. The spiral dive As explained above, a spin and a turn are completely different beasts. Also, in a spin, the airspeed is relatively low and constant, the vertical speed is relatively low (2000–4000 fpm) and the angular rotation is fast. In a diving turn or 'spiral dive', the rotation is slower because of the wide (but tightening) turn radius, and the airspeed and height loss both increase rapidly. In the lateral stability section, the possibility of entering a spiral dive condition was mentioned. In a well-developed steep spiral dive — the 'graveyard spiral' — the lift being generated by the wings (and thus the load factor) to provide the centripetal force for the high-speed diving turn, is very high and the turn continues to tighten. The pilot must be very careful in the recovery from a fully established spiral dive, or excessive structural loads will occur. See recovery from a spiral dive. 10.7 The stick force gradient An aircraft's control systems must provide the pilot with handling qualities appropriate to the task in hand plus adequate feedback of the aerodynamic forces being generated by the control surfaces — particularly the elevators. To avoid inadvertent airframe overstress it is required that the pilot must always apply an increasing pressure to the control column if increasing the elevator's aerodynamic force and thus the load on the airframe. Increasing back-pressure if the manoeuvre is a turn or a pull-up, increasing forward-pressure if a push-down. That control column pressure requirement is known as the 'stick force gradient' and the pressure applied is specified as the 'stick force per g'. The stick force that can be applied to achieve a particular elevator deflection depends on the length of the control column and the degree of travel available in the fore-and-aft arc; i.e. the stick's mechanical advantage. If the stick travel is short then the force required to deflect the elevators will be greater and the control system will probably feel too sensitive. Also the cg position affects the stick force required to increase the aerodynamic load; an aft cg reduces the stick force, a forward cg position increases the stick force required. To reduce the possibility of inadvertent application of airframe loads exceeding the design positive load limit, the control system must be set up so that the stick force required to reach that limit must be at least a specified minimum value. FAR 23.155 specifies that value as the aircraft's mtow/140 or 15 pounds (6.8 kg), whichever is greater. Take for an example a 600 kg mtow aircraft: 600/140 = 4.3 kg stick force, but as the 6.8 kg minimum is greater, then FAR 23 would require 6.8 kg force as the minimum — for 'control column' systems. However it would not be difficult for the average male to apply a 7 kg one-handed pull on the control column. FAR 23.155 states that the stick force need not be greater than 35 pounds (16 kg). There is a different FAR 23.155 standard for 'control wheel' systems. FAR 23.155 also requires that 'There must be no excessive decrease in the gradient of the curve of stick force versus maneuvering load factor with increasing load factor.' Even design by professionals may not provide a guarantee that the aircraft is safe. Read this United States Federal Aviation Administration special review team report [pdf format] which identified issues with a LSA category aircraft's wing structure, flutter characteristics, stick force gradients, airspeed calibration, and operating limitations. The control system must be set up so that the stick force required to increase load by 1g (the stick force per g) is always greater than a minimum value. Perhaps 1–2 kg force would cover the recreational aircraft range from the lightweight minimum aircraft to the 600 kg light sport aircraft. The lower the value the more sensitive the aircraft is to elevator inputs. If the stick force per g was 2 kg then the pilot would apply a back pressure of 2 kg to increase the load from 1g to 2g for a 60° banked level turn. Once applied that force must be held-on by the pilot; i.e. if the pilot has to ease-off pressure to hold the aircraft in a constant rate 2g level turn then the aircraft is exhibiting signs of instability. Things that are handy to know Top rudder refers to the relative position of the rudder pedals — 'top' being the rudder pedal opposite the lower wing. Thus, if the aircraft is banked and turning to the left, then pressure on the right rudder pedal will apply top (or outside) rudder; pressure on the left rudder pedal will apply bottom (or inside) rudder. Stuff you don't need to know The Wright brothers were the first to realise that control in each of the three axes was necessary for sustained stable flight. They added vertical tail rudders to their canard configuration 1903 Flyer and arranged simultaneous rudder deflection with the wing warping control (the trailing edge of one outer mainplane was pulled down by cords to increase camber while the other was pulled up) thus providing a lateral stability system and countering adverse yaw when initiating a turn. Glenn Curtiss was the first to patent the use of ailerons [but not the first to use] in place of wing warping in the hope of beating the Wright patent for three-axis control/stability systems. A long and bitter patent battle among the United States aircraft manufacturers (that had inhibited U.S. aircraft development and manufacture for 10 years) ended in early 1917 when the U.S. Congress forced all manufacturers into pooling their patents by threatening to seize all their patents. When the USA entered World War 1 in 1917 the nation was forced to purchase 10 940 combat aircraft from Europe while only 5064 mainly training aircraft were supplied to the U.S. army and navy by U.S. manufacturers. View the Wright Brothers 1906 patent. Note that the patent uses the term 'aeroplane' in lieu of 'mainplane' or 'wing'. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)
  3. The first flight across Bass Strait took place 100 years ago this year and a new book aims to celebrate the seemingly forgotten pilot who met that challenge. Bridging the Strait by Pirrie Shiel salutes World War I veteran Lieutenant Arthur Long, whose pioneering flight was in part motivated by a desire to win an impromptu Strait Race for Tasmania. It all happened quite suddenly — Long was in Launceston in December 1919 when he heard that a Victorian pilot was planning an attempt to fly to Tasmania. Photo: Long's biplane safely on the ground at Highfield, surrounded by schoolkids from Stanley. (Supplied: Queen Victoria Museum and Art Gallery) "He decided, 'No, a Tasmanian should do this first'," Ms Shiel said. "He took off from Launceston in his Boulton Paul biplane on December 15 and flew to Stanley, the closest point to Victoria. "There were such buffeting winds that it took him three and a half hours to get to Stanley. "He landed in a paddock close to Highfield House but realised it wasn't the day to make the attempt so he decided to stay with the Ford family until the weather was suitable. "Luckily, the next day it was suitable, so off he took." Photo: Long took off from a paddock near Highfield House to start his historic first flight to Victoria. (ABC Northern Tasmania: Rick Eaves) Historic flight began at dawn The 23-year-old pilot took off from Highfield at 6.35am on December 16, 1919 and set a course for King Island. From there, he hoped to see Airey's Inlet lighthouse on the Victorian coast. Long had rigged up a self-filling oil mechanism whereby he would pull a rope and a can of oil would pour into the engine. When the rope broke, he was forced to make a landing in a paddock at Torquay, manually pouring the oil in as he kept the engine running. Photo: Author Pirrie Shiel has written about Long in her book, Bridging the Strait. (ABC Northern Tasmania: Rick Eaves) He could not restart the engine without someone giving the propeller a big spin. Long took off again and finally landed at Port Melbourne, 4 hours and 10 minutes after leaving Stanley; he averaged just 112kph flying at a 500m altitude. "There wasn't a big crowd there to greet him. There wasn't much time for fanfare before he left," Ms Shiel said. "There was a bit later on. Maybe more people knew but were afraid he wouldn't get there. Photo: Long with Mrs Nelson, the first female passenger to fly from Hobart to Launceston. (Supplied: Weekly Courier) One reason Long is not better remembered is that once he had landed in Victoria, he did not return home. He set up an aviation company flying out of Glenroy but 18 months later was bankrupt. "That marriage didn't last long but he did keep flying for himself and flew with the RAAF during World War II, although not overseas. He died in 1954." Photo: Long takes a break with photographer Stephen Spurling II after an aerial shoot. (Supplied: Weekly Courier) An inspiring uncle Long was born in 1896 at Ti Tree, near Brighton, in southern Tasmania. Like so many others, he headed off to WWI, serving for three years on the ground for the Australian Imperial Forces, fighting in France and Egypt before joining the Australian Flying Corps. Ms Shiel believes Long was inspired to fly by his uncle and best friend from his youth in Hobart, Audubon Palfreyman, one of about 200 Australians recruited by the Royal Flying Corps. "The British felt the young Australians were somehow well suited as pilots," she said. "Audubon was successful, a captain, but sadly was one of the numbers who didn't make it back to Australia. "The Palfreyman family were very well known in Hobart. They had the big drapery, a chemist and a Palfreyman was also one of the founders of the Henry James jam factory on the waterfront. "There was actually a demonstration, an early flight, in Hobart just before war was declared in 1914. "The boys probably had the opportunity to see that and be inspired." Innovative flyer Photo: Long, a WWI veteran, became the first person to fly across Bass Strait at age 23. (Supplied: Weekly Courier) During the latter part of WWI, Long flew a number of low-flying bombing missions over France and Belgium, targeting retreating troop trains and aerodromes. On one occasion, he was flying so low that shrapnel from one of his own bombs tore through the canvas of his biplane and injured his leg. When the war ended, Long commissioned his own biplane from the Boulton Paul company and had it shipped in pieces to Tasmania. His ground-breaking flights in that aeroplane included flying a photographer over the Central Highland lakes to do survey work for the Hydro Electric Commission. He did the earliest passenger flights — one passenger at a time — between Hobart and Launceston, as well as the first newspaper delivery from Hobart to the north coast of Tasmania. "The idea was to get The Mercury newspaper to the north coast even before the Launceston Examiner but he got lost," Ms Shiel said. "There was low cloud and he got disorientated and ended up over Maria Island so it became a rather long flight. "The story goes that when Arthur Long was flying over the Tasmanian landscape in that year, people reported that their animals behaved strangely when this noisy new bird flew over." (source: ABC News)
  4. Key points: A pilot shortage means the Royal Flying Doctor Service is having trouble finding suitable aeromedical pilots Aeromedical pilots are required to have logged 4,000 flying hours, half of that as a pilot-in-command The RFDS hopes to attract those pilots not interested in flying for big airlines Photo: Pilot Cameron Whatley has always wanted to fly with the RFDS. (ABC North West Queensland: Kelly Butterworth) Queensland's Royal Flying Doctor Service (RFDS) is trading training for loyalty in a new program to bring in more pilots. Their aviation mentoring program is giving young pilots an opportunity to upskill and gain the extremely high number of flight hours needed to become aeromedical pilots. RFDS aeromedical pilots are required to have completed 4,000 flying hours, with 2,000 as pilot-in-command, including 200 hours as a pilot-in-command at night. Mount Isa senior base pilot Dave Keavy said the high number of flying hours required to work with the RFDS, paired with a global pilot shortage, made finding pilots difficult. "With the current pilot shortage, [the RFDS] are finding it very difficult to find people who have the sort of hours that they need," he said. "Generally [pilots], when they've got those sort of hours, they've been sucked up by the airlines." Photo: RFDS pilot Dave Keavy has been flying for 37 years and says he fits the mould for an aeromedical pilot. (ABC North West Queensland: Kelly Butterworth) Mr Keavy has been a pilot for 37 years and said he fitted the mould for the usual aeromedical pilot. "The average RFDS pilot is older, usually in their mid 40s, so I'm on the far end of that," he said. "Generally it is the guys who haven't had aspirations with the airlines and have been working in regional Australia for quite some time. "They're the sort of guys [or women] we look for to [move] into our program." Photo: Three new Royal Flying Doctor Service PC-24 jets were delivered to the RFDS in December. (Supplied: RFDS) Looking for a change of course The program has given 35-year-old Cameron Whatley, who grew up near Miles, the one job he had always coveted with the RFDS. Now living in Cloncurry and working from the Mount Isa RFDS base, Mr Whatley is one of two pilots in Queensland taking part in the program; the other is Cairns-based Andrew Hotham. "I've been flying since I was approximately 14," he said. "There was a trial introductory flight at the local airport in Chinchilla and I've been flying ever since." Photo: RFDS Qld CEO Meredith Staib says the program will ensure continuity of their "world-class service". (ABC North West Queensland: Kelly Butterworth) After working for a pastoral company in northern Australia, Mr Whatley wanted to move his career up to flying bigger aircraft. He said the only immediate options were either commercial operations or working for the airlines, which he did not want to do. "I like the type of flying that the RFDS does," he said. "I had put a couple of applications in before, but this one came up through their website and I came through on it." 'Giving back' to aviation says CEO Once Mr Whatley has completed the required hours and achieved the skills to become an aeromedical pilot, he will be expected to continue with the RFDS in that role for between three and five years. RFDS Queensland CEO Meredith Staib said the program was as much about attracting and hiring quality pilots as it was about moving the industry forward. "I hold a firm belief that everyone in the aviation industry has an obligation to give back to the sector, and that's what we're doing with the program pilots," she said. "Realistically, the RFDS is only a small player in the global aviation market but undeniably we make a huge difference to individuals and communities right across the state. "By developing a program such as this, we can ensure we can continue to provide our world-class aeromedical service for generations to come." (source: ABC News)
  5. Admin

    09. Stability

    9.1 Concepts of stability and trim The aircraft's response to disturbance is associated with the inherent degree of stability; i.e. self-correction built in by the designer — in each of the three axes — that eventuates without any pilot action. Another condition affecting flight is the aircraft's state of trim — or equilibrium where the net sum of all forces equals zero, i.e. the aerodynamic forces are balanced and the aircraft maintains a steady flight condition when cruising, climbing or descending. Some aircraft can be trimmed by the pilot to fly 'hands off' for straight and level flight, for climb or for descent. But very light aeroplanes generally have to rely on the state of trim built in by the designer and adjusted by the rigger, although most have a rather basic elevator trim device, but no rudder or aileron trim facility. If natural trim is poor — and perhaps it flies with one wing low — inherent stability may maintain equilibrium with that wing-low attitude and not restore the aircraft to a proper wings-level attitude. In which case, the pilot has to maintain a slight but constant control column deflection to hold the wings level, which can be quite annoying. It is desirable that longitudinal trim doesn't change significantly with alterations in power, nor does directional trim change significantly with alterations in airspeed. An aircraft's stability is expressed in relation to each axis: lateral stability — stability in roll, directional stability — stability in yaw and longitudinal stability — stability in pitch. The latter is the most important stability characteristic. Lateral and directional stability have some inter-dependence. Degrees of stability An aircraft will have differing degrees of stability about each axis; here are a few examples: When disturbed a totally stable aircraft will return, more or less immediately, to its trimmed state without pilot intervention; however, such an aircraft is rare — and undesirable. We usually want a sport and recreational aircraft just to be reasonably stable so it is comfortable to fly. If overly stable they tend to be sluggish in manoeuvring and heavy on the controls; i.e. significant control force is required to make it deviate from its trimmed state. If it tends toward instability the pilot has to continually watch the aircraft's attitude and make the restoring inputs, which becomes tiring, particularly when flying by instruments. Some forms of instability make an aircraft unpleasant to fly in a bumpy atmosphere. The normally stable or positively stable aircraft, when disturbed from its trimmed flight state, will — without pilot intervention — commence an initial movement back towards the trimmed flight state but overrun it, then start a series of diminishing damping oscillations about the original flight state. This damping process is usually referred to as dynamic stability (or the tendency over time) and the initial movement back towards the flight state is called static stability. The magnitude of the oscillation and the time taken for the oscillations to completely damp out is another aspect of stability. Unfortunately a statically stable aircraft can be dynamically unstable in that plane; i.e. the oscillations do not damp out. The neutrally dynamically stable aircraft will continue oscillating after disturbance, but the magnitude of those oscillations will neither diminish nor increase. If these were oscillations in pitch, and if there were no other disturbances and the pilot did not intervene, the aircraft would just continue 'porpoising'. The negatively stable or fully unstable aircraft may be statically unstable and never attempt to return towards the trimmed state. Or it can be statically stable but dynamically unstable, where it will continue oscillating after disturbance, with the magnitude of those oscillations getting larger and larger. Significant instability is an undesirable characteristic, except where an extremely manoeuvrable aircraft is needed and the instability can be continually corrected by on-board 'fly-by-wire' computers rather than the pilot — for example, a supersonic air superiority fighter. The best piston-engined WWII day fighters were generally designed to be just stable longitudinally, neutrally stable laterally and positively stable directionally. 9.2 Longitudinal stability Longitudinal stability is associated with the restoration of aoa to the trimmed aoa after a disturbance changes it; i.e. if a disturbance pushes the nose up the tailplane will counter with a nose-down pitching moment. In section 6.2 we discussed the provision of a tailplane to act as a horizontal (longitudinal) stabiliser. Before we go any further we need to look at another structural aspect of the airframe. Angle of incidence Angle of incidence is a term that is sometimes mistakenly used as synonymous with wing angle of attack; however, the former cannot be altered in flight except in weight-shift control aircraft (hang gliders and trikes). Angle of incidence, usually just expressed as incidence, is within the province of the aircraft designer who calculates the wing aoa to be employed in the main role for which the aircraft is being designed, probably the aoa in performance cruise mode. The designer might then plan the fuselage-to-wing mounting so that the fuselage is aligned to produce the least drag when the wing is flying at the cruise aoa. Wings that incorporate washout will have differing angles of incidence at the wing root and at the outer section. A notional horizontal datum line is drawn longitudinally through the fuselage, and the angle between that fuselage reference line [FRL] and the wing chord line is the angle of incidence. Incidence should be viewed as the mounting angle of the fuselage rather than the mounting angle of the wings — see 'Stuff you don't need to know'. Incidence may also be called the 'rigger's incidence' or some similar expression carried over from the earlier days of aviation. For ultralight aircraft, incidence is something that should be checked at regular inspections by a qualified person Longitudinal dihedral An angle of incidence is also calculated for the horizontal stabiliser with reference to the FRL. The angular difference between wing and stabiliser angles is called the longitudinal dihedral, although it is probably more correct to say that the longitudinal dihedral is the angular difference between the two surfaces at their zero lift aoa. The angle of the line of thrust is also expressed relative to the FRL. Positive longitudinal dihedral — where the wing incidence is greater than that of the stabiliser — will help control a stall by ensuring that, if the aircraft approaches a stall, the wing will stall before the tail, giving the tail a chance to drop the nose. The tailplane of most very light 3-axis control aeroplanes is mounted in a position where the wing downwash may effect the angle of attack of the tailplane and that downwash angle increases as the wing angle of attack increases. It is the horizontal stabiliser area and moment arm that provides the restoring moment to return aoa to the trimmed state. However, bear in mind that the moment arm, which supplies the restoring leverage and thus the stability, is affected by the cg position. If the cg lies outside its limits, the aircraft will be longitudinally unstable. We learned in section 2.6 that when flying with level wings, at a particular weight, each aoa is associated with a particular IAS. We might as well take advantage of that by arranging the longitudinal dihedral so that the built-in state of trim produces a particular indicated airspeed. In some ultralights a designer/rigger might pick Vbg — best power-off glide speed — as the natural airspeed so that, lacking pilot input, the aircraft will naturally attempt to adjust its aoa to the Vbg aoa, whether power is on or off. Oscillating motions It is possible that an aircraft, properly trimmed for continuing level flight, may develop a 'phugoid' motion if affected by a sharp disturbance. A phugoid cycle is a pitch increase followed by a pitch decrease without any discernible aoa change, i.e. a short climb during which speed decreases and the nose drops into a short descent during which speed increases and the cycle starts again. The aircraft is trading kinetic energy for an increase in the potential energy of height, using the latter to return to the trimmed airspeed in the descent; the cycle time for one oscillation in a very light aircraft might be 20 seconds or so. The oscillating motion issometimes described as 'porpoising'. If the pilot doesn't intervene and the aircraft is phugoid stable the phugoid cycles will damp out after a few diminishing oscillations. If the aircraft is phugoid unstable the oscillations will diverge and the pilot must intervene. The longitudinal dihedral and the tail moment arm affect phugoid stability. 9.3 Directional stability Directional stability is associated with the realigning of the longitudinal axis with the flight path (the angle of zero slip) after a disturbance causes the aircraft to yaw out of alignment and produce slip; remember yaw is a rotation about the normal (vertical) axis. In section 6.3 we discussed the provision of a fin to act as a directional stabiliser. The restoring moment — the static stability — provided by the fin is the product of the fin area and the moment arm. The moment arm leverage will vary according to the cg position — the aircraft's balance. The area required for the fin has some dependency on the net sum of all the restoring moments associated with the aircraft fuselage and undercarriage side surfaces fore (negative moments) and aft (positive moments) of the cg. For instance, the Breezy has, except for the pilot's body, very little lateral moment ahead of the cg because of the open frame fuselage; thus a small fin provides all the moment necessary for directional stability. But if the pilot and passenger were enclosed in a cockpit or pod, with a much greater side surface, then the negative moments would be greater and consequently the fin area would have to be greater. If the pilot removes his/her feet from the rudder pedals the rudder, will 'float', aligning itself with the relative airflow and thereby reducing the restoring moment of the fin. The directional stability of very light aircraft with a lot of forward keel area — such as those with a cockpit pod and a 'boom' in place of a rear fuselage — may be 'conditional'; i.e. it is sensitive both to the position of the cg within its normal range and to the amount of sideslip. This is because the negative lateral forces of the pod are very much greater than the positive lateral forces of the boom and fin. Thus, beyond a certain angle of slip the moments change, positive stability is changed to neutral stability and yaw becomes locked in. It might also be associated with the fin stalling at high sideslip angles. The most noticeable symptom to the pilot is aerodynamic rudder overbalance (or 'rudder force reversal' or 'rudder lock') — where the rudder moves to full deflection without any additional pilot input, or doesn't return to the neutral position when the rudder pedal pressure is released, or the pedal force has to be reversed as sideslip angle is increased. It may require significant opposite rudder input, and probably an increase in airspeed, to return to the normal state. The areas of side surface above and below the cg also affect other aspects of stability. The term 'weathercocking' refers to the action of an aircraft, moving on the ground, attempting to swing into wind. It is brought about by the pressure of the wind on the rear keel surfaces, fin and rudder, which cause the aeroplane to pivot about one or both of its main wheels. It is usually more apparent in tailwheel aircraft because of the longer moment arm between the fin and the main wheels; although if a nosewheel aircraft is 'wheelbarrowing' with much of the weight on the nosewheel, then there will be a dangerously long moment arm between the nose wheel pivot point and the fin. 9.4 Lateral stability Lateral stability refers to roll stability about the longitudinal axis; in section 4.10 we established that ailerons provide the means whereby the aircraft is rolled in the lateral plane. However, unlike the longitudinal and normal planes where the horizontal and vertical stabilisers provide the restoring moments necessary for pitch and yaw stability, no similar restoring moment device exists in the lateral plane. But let's imagine that some atmospheric disturbance has prompted the aircraft to roll to the left, thus the left wingtip will be moving forward and down, and the right wingtip will be moving forward and up. Now think about the aoa for each wing — the wing that is moving down will be meeting a relative airflow coming from forward and below, and consequently has a greater aoa than the rising wing. A greater aoa, with the same airspeed, means more lift generated on the downgoing side and thus the left wing will stop going further down or perhaps even rise a little, although pilot action is usually needed to get back to a wings level state. This damping of the roll is known as lateral damping. So roll stability, except when at or very close to the stall, is intrinsic to practically all single-engined light aircraft. (When the aircraft is flying close to the stall, the aoa of the downgoing wing could exceed the critical aoa and thus stall, which will exacerbate the wing drop and might lead to an incipient spin condition. See the stall/spin phenomenon.) But — and there always seems to be a 'but' — when the aircraft is banked, other forces come into play and affect the process. If you re-examine the turn forces diagram in the manoeuvring forces module, you will see that when an aircraft is banked the lift vector has a substantial sideways component; in fact, for bank angles above 45°, that sideways force is greater than weight. So we can say that any time the aircraft is banked, with the rudder and elevators in the neutral position, an additional force will initiate a movement in the direction of bank; i.e. creating a slip. We know from the section 7.3 that the aircraft's directional stability will then yaw the nose to negate the slip and the yaw initiates a turn, which will continue as long as the same bank angle is maintained. There are several design features that stop the slip and level the wings, thus promoting lateral stability. For instance, placing the wing as high as possible above the cg increases so-called 'pendular stability', (The stability due to the high wing is not really pendulum stability such as that applicable to powered parachutes.) Wing dihedral* is usually employed with low-wing monoplanes (and to a lesser degree of tilt with high wings), where the wings are tilted up from the wing root a few degrees. A swept-back wing format is used with trikes. Another design method is anhedral, where the wings are angled down from the wing root, but it is unlikely to be used in light aircraft, although the powered parachute wing utilises an anhedral arc for stability. (*'Dihedral' is a mathematical term denoting the angle between two intersecting planes.) Spiral instability An aircraft with positive spiral stability tends to roll out of a turn by itself if the controls are centred. Some light aircraft with little or no wing dihedral and a large fin tend to have strong static directional stability but are not so stable laterally. If slip is introduced by turbulence or by the pilot, such aircraft — left to their own devices — will gradually start to bank and turn — with increasing slip and nose drop — and hence increasing turn rate and rapid increase in height loss. Neutral spiral stability is the usual aim of the designer. The turning process starts slowly in aircraft with slight spiral instability but leads to spiral divergence which, if allowed to continue and given sufficient height, will accelerate into a high-speed spiral dive. This often occurs when a pilot without an instrument flight rating strays into cloud where all visual cues are lost. In that condition it is known as the 'graveyard spiral'. Inadvertent entry into a fatal spiral dive, leading to inflight breakup, can happen even with experienced IFR pilots, see this Australian Transport Safety Bureau report. It is evident that directional stability and lateral stability are coupled (i.e. rotation about one axis prompts rotation about the other) and to produce a balanced turn; i.e. with no slip or skid, the aileron, rudder and elevator control movements and pressures must be balanced and coordinated. Dutch roll Induced motion in the lateral plane generally brings about a coupled motion in the directional plane, and vice versa. Dutch roll is a phenomenon in level flight where a disturbance causes a combined yaw and roll followed by a return to the level flight condition then a yaw and roll to the other side: the oscillations continuing until damped out. In a very light aircraft the time for each cycle might be 5 to 10 seconds. The motion is quite uncomfortable, viewed from the cockpit the wingtips complete a circular motion against the horizon as does the nose. Pilot intervention is by use of rudder. 9.5 Trim and thrust We have covered above the reaction of the aircraft to changes in relative airflow whether induced by the pilot or minor atmospheric turbulence. We know from sections 1.8 and 1.9 that if an aircraft is properly trimmed for cruise flight and we increase thrust then it will climb; and if we reduce thrust it will descend. But how this eventuates is not at all straightforward. The reaction to changing power, without the pilot touching the control column, depends on whether the cg is above, below or inline with the line of thrust; in the Breezy, the cg is below the thrust line. The thrust line is best located so that it passes close to the vertical cg position to minimise the initial pitching moments associated with power changes. The placement of the horizontal and vertical stabilisers, in relation to the propeller slipstream and to the wing downwash, affects flight performance and particularly flight at slow speeds — because then the total air velocity within the slipstream tube is nearly double that outside the tube; also the slipstream is rotating, and will thus impart a sideways moment to the fuselage and vertical stabiliser. Effects on individual aircraft types vary according to the designer's inbuilt compensations: for example, if the horizontal stabiliser operates in the wing root downwash airflow, then when the wing root stalls and the downwash becomes turbulent the stabiliser might undergo an abrupt change in aoa (and thus in its stability restoring moment). Or if the horizontal stabiliser operates substantially outside the downwash but if it is in the path of the turbulent flow from the stalled wing, it will then lose part of its aerodynamic force. If a modification is made to that design, even a seemingly minor change, the consequential effect on stability may be quite surprising. To illustrate the point, I suggest you read an "airworthiness report regarding (among other factors contributing to general stability problems) a small change made in relocating the exhaust manifold of a Thruster that, at a particular aoa, promoted turbulent flow over the upper wing surface, which then extended to the horizontal stabiliser, and reduced the stabilising moment imparted by that surface. Stuff you don't need to know The term 'decalage' (French = gap or shift forward/back) relates to the difference in the angles of incidence of the upper and lower mainplanes of a biplane. Decalage is now occasionally used as synonymous with longitudinal dihedral. The angle of incidence has some effect on the pilot's view over the nose. A very few naval aircraft designs have included 'variable incidence wings' where the angle of incidence could be changed by the pilot during flight, within a range of say 2–15°, using electric motors. Such aircraft included leading edge slats as a high-lift device.The idea was to take full advantage of the high maximum CL and consequent low speed, during the landing approach, without having the fuselage cocked up at a high angle blocking the view. As aoa increased and the aircraft slowed, the pilot wound the fuselage down, so that it remained more or less level during the approach and thus provided a better view of the flight deck! Variable incidence wings were also used with one of the post-WWII Supermarine amphibian designs. STRICT COPYRIGHT JOHN BRANDON AND RECREATIONAL FLYING (.com)
  6. Since the dawn of aviation, planes have primarily been powered by carbon-based fuels such as gasoline or kerosene. These contain a lot of energy for their weight, providing the vast power required to lift large commercial airliners on journeys across the globe. But with oil resources declining and penalties on greenhouse gas emissions increasing, the future of aviation is dependent on finding an alternative power source. Is electricity the answer? A first step is to develop “more electric aircraft” – jet-powered planes that maximise the use of electricity for all the other aircraft systems. The idea is to significantly reduce fuel consumption by improving overall energy efficiency. In practice, this means reducing the weight of the aircraft, reducing drag with improved aerodynamics and optimising the flight profile to use less fuel. But though these improvements can save on fuel, that alone isn’t enough. The shift to more sustainable aircraft requires major, longer-term solutions. Such significant innovations have often been driven by military requirements. The jet turbine engine was developed during World War II and the US Air Force’s Chuck Yaeger first broke the sound barrier in the Bell X-1 as part of the Cold War race to achieve supersonic speeds. The drive for new technologies led to massive improvements in performance and reliability, which has since filtered through to commercial aviation and made mass intercontinental air travel a reality. Left: the Bell X-1, the first supersonic aircraft. Right: a British Airways Concorde jet, the only commercial supersonic plane. Left: US Air Force. Right: Aero Icarus via Wikimedia Commons Concorde was the ultimate expression of this transformation from military to high-performance commercial aircraft, but despite its phenomenal performance it was plagued by complaints of excessive noise and pollution. Modern jet air travel still consistently raises such environmental concerns and, while the military has an obvious incentive to design the fastest aircraft, its motivation to go green is less obvious. We may need to look elsewhere for the next big innovation. Cleaning up the skies? Solar-powered endurance aircraft have received a lot of attention recently, with the Solar Impulse team attempting to make the first round-the-world flight. But solar power, while an interesting technical challenge, is not a particularly realistic option for mass transit of passengers. As can be seen from the Solar Impulse aircraft, the power output from the Solar Panels on a very wide wingspan is able to transport only the aircraft and the pilot for any significant distance. Solar Impulse landing at Brussels Airport. Brussels Airport, CC BY-SA Battery storage is the key limiting factor for electric aircraft. If electric aircraft are held back by either weight or fuel restrictions, it’s probably down to the battery. Aircraft typically have a longer fuelling time than a car, so rapid recharging is possible and effective, as current jet aircraft take about the same time to refuel (and also for passenger and cargo turnaround) so electric charging of about 1hr is reasonable, however the critical problem is energy density – how much energy does the battery provide for its weight? Typical lithium-ion batteries in use today have a maximum energy density of around 1,000,000 joules of energy per kilogram, and while newer research promises the possibility of higher densities, these are not available commercially. A million joules sounds like a lot. However, compare this with 43 million joules per kilogram for aviation fuel. Swapping the fuel tanks for a battery weighing 43 times as much isn’t a viable option – clearly there’s a significant storage problem to be solved before electricity can power large aircraft over long distances. The future for electric air travel So where does electric power fit in the long-term vision for consumer air travel? Despite the obvious technical challenges, The Airbus prototype E-Fan aircraft is to be put into production. The E-fan is a very light two-seater plane powered by two electric motors, with a relative speed and carrying capacity far lower than those required by commercial carriers. However, within the next decade, this technology may extend to short-range commuter and business aircraft – especially targeting routes that still use conventional propeller propulsion. Airbus has medium-term plans for such an aircraft, with a target capacity of perhaps 60 passengers – making it a suitable platform for short-haul commuter flights. Safety and reliability must be addressed before electric aircraft are adopted by commercial airlines. Much as the electric car still has to achieve a critical level of public confidence, perceived reliability will have a significant impact on consumer trust in new aircraft. If prototypes such as the E-Fan can build public confidence, this may mark a “tipping point” in overcoming the technical challenges inherent in any new form of transportation, especially in aviation which has a track record of rapid innovation. Advances – particularly in new materials, storage and power electronics technology – may offer the prospect of purely electric commercial aircraft within the next two decades. (source: The Conversation)
  7. As Russia's aerospace industry gets ready to stretch its wings at the MAKS air show in Moscow, we take a look at Russian aircraft programmes that would surely have been world-beaters – if they hadn’t been cancelled. 1. MiG Skat flying wing UAV Russia’s only extant flying-wing shaped, armed unmanned air vehicle (UAV) concept emerged briefly at the MAKS-2007 show, then just as quickly vanished without a trace. The MiG design bureau displayed the Skat to a select group of journalists inside one of the hangars dotting the Zhukovsky air base, which also hosts the show. The journalists saw and photographed a relatively small vehicle, approximately the size of the Lockheed Martin RQ-170 Sentinel. Displayed around the aircraft was a collection of weaponry, including the Kh-31 air-to-surface missile, which could be stored in an internal weapons bay. The Skat has not been seen since. The Russian press quoted a former director of MiG, saying the project was cancelled. In 2013 MiG signed a contract to develop unmanned combat air vehicles for the Russian air force, saying it planned to use lessons learned from the Skat for the follow-on project. MiG Scat Pycckue/wikimedia commons 2. Mil Mi-54 medium twin-engined helicopter Military helicopters were the forte of the Soviet Union, and the Mil design bureau appeared ready for the post-Communist era. The company displayed a model of a new medium-twin civil helicopter called the Mi-54 at the first MAKS event in 1992. Powered by a pair of Saturn/Lyulka Al-32 engines, the 10-12-seat helicopter was set to challenge Western rivals such as the Sikorsky S-76. But Russia’s economic circumstances in the 1990s proved fatal to many worthy projects, with the Mil-54 just one example. However, the concept was revived amidst the helicopter production boom of the last decade. Mil displayed a rotor-less cabin mock-up of the Mi-54 at the MAKS-2007 show. By 2010, though, Mil had moved on, telling Flightglobal the project was suspended. Mil-54 in traditional Russian "Khokhloma" livery, MAKS 2007; probably a wooden mock-up Yuriybrisk/wikimedia commons 3. Sukhoi S-21 supersonic business jet Sukhoi’s S-21 predated the creation of the MAKS air show, which began in 1992. Three years earlier Sukhoi had announced a partnership with Gulfstream to develop a supersonic business jet design. The first flight was originally planned in 1993. But Gulfstream’s marketing analysis concluded that more time was needed. Customers wanted something grander than an aircraft that was then only slightly better than the Concorde, which was still flying. So the project was extended to achieve first flight by the end of the 1990s. Russia’s decade-long economic crisis then wreaked havoc on Sukhoi’s finances. By 1993, Gulfstream had dissolved the partnership and started working on its own supersonic business jet project. The S-21 continued to be displayed by Sukhoi at MAKS for several years, but the design concept was eventually replaced by a series of new models. Sukhoi S-21 SSBJ Vitaly Kuzmin/wikimedia commons 4. Sukhoi KR-860 Kryl’ya Rossii double-deck airliner Does the world even need a 1,000-seat airliner? Perhaps not, but the world was a different place in the late 1990s. Sukhoi proposed a concept – the KR-860 – that would trump anything being entertained by the contemporary Airbus A3XX and Boeing 747X projects. The KR-860 was to offer 12-abreast, triple-aisle seating on the main deck, with nine-abreast, twin-aisle seating on the upper deck. Passengers would enter and exit through conventional fuselage doors or a ventral escalator. The outer-wing section would fold to allow the KR-860 to access the same airports as the 747. Those who attended the 1999 air shows in Paris and Moscow were privileged to see a 1/24-scale model of the beast, but that was the last anyone saw of the project in public. Sukhoi KR-860 Sukhoi/wikimedia commons 5. Sukhoi Su-47 Berkut fighter Sukhoi finally unveiled the Su-47 Berkut at MAKS-2007, but by then it was already too late for the forward swept wing fighter. Within four years Sukhoi would be working on a new design for a fifth-generation fighter, which would emerge in 2010 as the T-50. The S-47 Berkut would continue to see service in Sukhoi’s fleet as a test bed for technologies in development for the T-50. But the S-47 concept – conceived in the mid-1980s – was already past its expiration date, and with it expired the dream of an operational fighter employing a forward swept wing and forward canard. Sukhoi Su-47 Berkut in 2001 Leonid Faerberg/wikimedia commons 6. Tupolev Tu-334 regional airliner Tupolev’s answer to the Sukhoi Superjet beat its erstwhile competitor to a MAKS debut by two years in 2007. The 102-seat Tu-334 was the basis of Russia’s original plan to replace thousands of Tu-134 and Yakovlev Yak-42 regional jets. It featured a shortened fuselage from the Tu-204, a T-tail and aft-mounted engines. Though launched in the early 1990s, only two aircraft were built by the time the Tu-334 made its MAKS debut eight years ago. By then its time had almost run out. The Superjet was unveiled at the MAKS-2009 show, and United Aircraft Corp cancelled the Tu-334 around the same time. Tupolev Tu-334 at МАКS 2007 Зимин Василий/wikimedia commons 7. Tupolev Tu-444 supersonic business jet If the market wanted a supersonic business jet, surely Tupolev would have its say? The maker of the original Soviet supersonic transport, the Tu-144, and supersonic bombers such as the Tu-160 would not be left out of the conversation. The MAKS-2003 show featured the unveiling of the Tu-444 supersonic business jet concept, resembling a scaled-down Tu-144. It emerged as upstart bids by companies such as Aerion and Supersonic Aerospace International (SAI) proposed Mach-busting concepts. There may still be a market for the likes of the Tu-444, but no one, including Tupolev, seems to be in any hurry to find out. Tupolev Tu-444 Tupolev/wikimedia commons 8. Vega Lutch UAV Unmanned or optionally manned versions of popular sport aircraft are frequently unveiled at major air shows, never be glimpsed in public again. So it was with the Vega Lutch strike unmanned air vehicle (UAV), a proposed unmanned derivative of the Sigma 5 sport aircraft. Vega unveiled the aircraft at the MAKS-2011 show, but thereafter it disappeared. It is perhaps in service somewhere, but it is no longer in public view. Vega Lutch at MAKS-2011 Doomych + wikimedia commons 9. Yak-58 Some stories can still have happy endings. Yakovlev – now a division of Irkut – launched the Yak-58 as the Cold War ended, proposing a twin-boomed, single-engined general aviation aircraft for the post-Communist era. But tensions between Russia and Georgia – where the Yak-58 was developed – stymied the company’s hopes to fill hundreds of orders. The project was abandoned after 1997. Nearly 20 years later, there are new hopes for a Yak-58 revival. Russian media reported earlier this year that a decision to restart Yak-58 production could be announced at MAKS-2015. Might have been a Yak-58 (source: Flight Global)
  8. Eighty years ago, the Navy’s last flying aircraft carrier crashed off the coast of California and sank to the bottom of the Pacific Ocean. The sinking of USS Macon (ZRS-5), a lighter-than-air rigid airship, resulted in few deaths but its loss ended the Navy’s quest to use airships as long-range scouts for the fleet. While the idea died, the wreck Macon lives on as an important archaeological site and this week Naval History and Heritage Command, National Oceanic and Atmospheric Administration (NOAA) and several non-profits came together to explore the wreckage, mapping out pieces of the airship and its four biplanes and studying the change in its material condition over time. Their hope: to understand life aloft in the floating aircraft carrier, to piece together a clearer map of the wreck site and to research how quickly the remains of the airship are being consumed by the sea. USS Macon Life and Legacy USS Macon (ZRS-5) in 1933 or 1934. As early as 1916 the Navy had begun designing lighter-than-air (LTA) rigid airships, and by 1926 the focus had shifted to airships that could support aerial scouting missions. The first flying aircraft carrier, USS Akron (ZRS-4), was commissioned in 1931 – and after several incidents in two years, the airship crashed and sank off the coast of New Jersey in 1933, killing 73 of 76 men onboard, including Rear Adm. William A. Moffett, the first chief of the Navy’s Bureau of Aeronautics and the chief proponent of bringing LTA aircraft to the fleet. Macon was commissioned a month and a half after the Akron crash. The airship was commanded by one of the only Akron survivors, Lt. Cmdr. Herbert Wiley, and was based in California. The second-in-class dirigible had a slightly longer service life. The airship stayed mission-ready and participated in many fleet exercises in its two years. Macon demonstrated its concept of operations, launching and recovering as many as five single-seat Curtiss F9C Sparrowhawk biplanes via a “trapeze” that the crew used to recover the planes. The planes often had their landing gear removed while operating from the airship, leaving little room for error for the pilots. Curtiss F9C-2 Sparrowhawk hangs from USS Macon (ZRS-5). On Feb. 12, 1935, the airship hit a storm off the coast of Point Sur, Calif. A tailfin was sheared off, and in trying to respond the crew set off a chain of events that led to them losing control of the airship and falling nose-up into the ocean, according to a post in the Naval History Blog. The aircraft fell slowly enough that the crew could put on lifejackets – which were onboard the Akron. One crew member jumped from the airship at too high an altitude and died, and another died when he returned to the sinking ship to retrieve personal items. The other 74 crew members were rescued. However, the rigid airship program was beyond saving. Bruce Terrell, chief archaeologist and historian at NOAA’s Office of National Marine Sanctuaries’ Maritime Heritage Program, told USNI News on Tuesday that the Macon, for all it lacked in longevity, shed a lot of light on how the Navy perceived the threats to the U.S. in the Pacific. “it’s showing the pre-World War II mindset of the Navy. And as early as the turn of the century, the Navy was focused on Japan, watching Japan, because their military was increasing so fast and they kind of were getting clues as to the Japanese government’s designs on South East Asia and the islands,” he said. “Macon was envisioned as basically a scout for the fleet, Macon and Akron. … it kind of shows how the Navy was looking at scouting for the fleet, protecting the fleet. And Macon was kind of the highest expression of the technology, but as this was happening seaplanes with longer and longer range capability were being developed, radar was starting to be developed, newer technologies were coming along. So I think the Navy, at that point when Macon finally crashed, it was like, okay, we’re cutting our losses here. … But I think the concept was proven after Pearl Harbor – the big what-if question is, if Macon had been operational and successful, might Macon and the little scout aircraft, might they have spotted the Japanese fleet before they could hit Pearl Harbor?” Exploration and Mapping Mission On Tuesday morning, scientists, archaeologists and other experts gathered aboard the 211-foot Exploration Vessel Nautilus at the wreckage site; at the ship’s command hub, the Inner Space Center at University of Rhode Island’s Graduate School of Oceanography; and at NOAA headquarters in Maryland. Broadcasting the whole operation live online, the team prepared for its 12-hour mission: to find the boundary of the wreckage site, to create a photomosaic of the site, take 3D video of small portions of interest and to retrieve a small piece of aluminum for metallurgical study. The layout of the Macon site is already fairly well understood. Explorations in 1991 and 2006 photographed and identified the bulkiest items on the ocean floor – engines, fuel tanks, ovens, tires, and the four biplanes still relatively intact, among others – and even retrieved some items for study and display. But Terrell explained that this exploration will provide even greater detail, thanks to technological advances. New high-definition sonar will give researchers a better look at some of the smaller items, which are key to shedding light on what daily life was like aboard Macon. “We’re already getting a better sense of how Macon wrecked and came to rest on the seabed, but I think [this exploration is] going to help us identify actual objects more. It’s just a cumulative process that’ll be going on for years,” he said. A finer look at those items in the wreckage will help answer several questions, Terrell added. “We want to know basically what’s there, identify objects, things like that. We want to know how it wrecked, how all that happened,” he said. “But then we want to understand the more human story. Now with Macon, there were two losses, a radioman and a steward; we know the radioman jumped from too high and broke his back, so they may have recovered his remains. But the steward ran back into the galley and was never seen again, so we may have a military grave there. But then the other human question we want to answer is, since there were people onboard, we want to know basically how the workspaces were arranged on Macon, how this big complex ship in the sky actually operated – how they interacted with each other, how they communicated, what kind of personal effects may have been onboard. We know we’ve got a lot of the galley there, it would be interesting to know how they cooked and ate their food up there in the sky.” To answer the questions, the team took the Ocean Exploration Trust’s Nautilus and its dual-body remotely operated vehicle system, composed of primary ROV Hercules and and secondary vehicle Argus. The pair are outfitted with lighting, cameras, sensors and sonar to document what they encounter at the bottom of the ocean. The Nautilus crew launched the ROVs just after 8 a.m. EST, and it took the vehicles about an hour to reach the search site, more than 1400 feet below the water’s surface. The first step was to find an accurate perimeter for the photomosaic – Terrell said the one created in 2006 did not include the full wreck site. The mission covered Field A, which is the back two thirds or so of the Macon – including the Sparrowhawks, the ovens from the galley, engines and more – and Field B, which is the smaller front section of Macon. Hercules and Argus then “mowed the lawn” for about five and a half hours in Field A and for more than three hours for Field B, taking photos every few seconds to create the photomosaic. The ROVs were able to take 360-degree video of a biplane, take some measurements of corroded parts of a plane wing, and measure how much sediment had built up since 1935. The last item on the mission agenda was to pick up a piece of aluminum girder to bring back and study. Terrell told USNI News on Wednesday that the first piece the ROV’s manipulator arm picked up “turned to dust” when moved. The scientists located another similar-sized piece but found that an object was obstructing access to it. Upon trying to move the piece sticking out of the ground, they found it was another piece of girder – half of which had been exposed to the water and half of which had been buried in the ocean floor and protected. Right as time expired for the mission, the scientists brought up the girder, found it fit in their protective box, and were able to call the mission a success, Terrell said. Expedition’s Lessons Learned A view of the command center screens of the expedition on Aug. 18, 2015. USNI News Photo For those involved in the mission, Tuesday’s expedition was part of an obligation to monitor and preserve the wreck site to the best of their ability, given the great environmental challenges associated with artifacts under 1,400 feet of saltwater. Macon and its scout planes will eventually be corroded away, and these organizations want to continue to document their condition now and into the future. “We’re really extending the life of this airship and her biplanes and documenting the past 80 years she spent under water, which is the majority of her life,” NOAA archaeologist Megan Lickliter-Mundon said while broadcasting from Nautilus. But she noted Tuesday afternoon that the artifacts may be corroding faster than expected. One of the biplane’s wing collapsed since the 2006 expedition, which scientists knew would happen eventually but didn’t expect so soon. Gaining a better understanding of aluminum in the Macon frame and the Sparrowhawks will help scientists predict how long the wreckage will remain intact and may inform future expeditions. Alexis Catsambis, archaeologist and cultural resource manager at Naval History and Heritage Command, said Tuesday that the Navy has a good understanding of how materials from older shipwrecks – wood, iron, copper alloys – react to their underwater environment. But with 20th Century materials like aluminum alloys, “we haven’t quite figured out as a discipline how to best conserve the material, how those materials react with their environment and with other materials. And so this is an opportunity to learn through the sample that we collect about the rate of degradation of certain aluminum alloys and hopefully how to best help preserve them,” he said. At the Naval History and Heritage Command, “we are charged with managing the sites, with researching the sites, with conserving and curating artifacts that are recovered from them, and ultimately public outreach,” he said, and this mission taps into each of those missions. He said the Navy hoped to retrieve a piece of aluminum from the Macon frame, perhaps one or two feet long, for testing and eventually to loan out to a museum. Russ Matthews – whose family’s Edward E. and Marie L. Matthews Foundation helped pay for the expedition, along with the Oceangate Foundation – said Tuesday that bringing this “odd branch of aviation evolution that went nowhere” into the public discourse was important to him. He said the history of the dirigible program “reads like science fiction,” and he hopes that research teams can continue to learn more about the program and preserve and document artifacts for future generation. (source: usni news)
  9. I do sincerely hope the changes have been worth it for everyone
  10. Hi, just want to let you know that site development will slow down a bit now for about 6 weeks, I am back working again...income, YEAH but work is about 1.5hrs away in Geelong so no time for anything during the week but the site is stable so please enjoy what it offers
  11. Sorry guys but I shouldn't have created this poll as whilst I was trying to find out what you wanted so I could give it to you, I didn't realise that Option 2 in the poll would not make the site sustainable. Users would not know about the conversations and posts in 80% of the site i.e. the actual conversations and posts made in all the other sections of the site as these can not be listed in their own blocks, only in the one main block. So to have all discussions and new posts listed we also have to have new items in there as well, just like we have new forum threads in there. Consider each new item in say the Aircraft section, the Tutorials section etc are like new forum threads, a new thread is shown and then any new posts are shown in Whats New...if that makes sense I have had to change it back to the Whats New having everything listed and I don't know of an alternative other than those few people and as mentioned before, create their own Whats New page as previously explained...but then by only showing the forums threads and posts would miss out on all the other discussions and posts made over the other 80% of the site
  12. I have changed the Whats New page to a block layout now keeping each section of the site in their own blocks...still a little work to do on it but you will get the idea when you see it
  13. Oh, well as pointed out many times he can create his very own Whats New page just showing forum posts and nothing else however when a person does this they will miss out on any new and great things that may be added to existing sections of the site.:
  14. What do you mean all pushed off and only 1 item left???????? This is what I see and it is correct and is not really different from what you see:
  15. That screenshot is ok, I can't see content being pushed off the screen
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