LoonyBob

Fouga would give you a good kicking for that!

I'd love to see the report; I had my gossip (much later) from a couple of members of NSW DCA at the time...

The Certification flight testing used to involve three turns of a developed spin; then it became three rotations after dropping a wing... the DCA started to have arguments with the FAA back in the '60s, according to my sources... I think NZ also had a disagreement on the topic.

Aerobatic manouvres were prohibited in AUF-registered aeroplanes... let us just say that I had to resort to unconventional measures to get out of the rotor and away from the ground!

The Taylorcraft & Austers used Linseed oil (as Kensla said, it's Approved). VH-WRB had no corrosion whatsoever inside it after the bowser incident at Bathurst (I thinkthat was WRB?). but it wa sonly about 33 years old then. Be aware! In Tymes of Olde, Boiled Linseed oil was ordinary linseed oil, brought to the boil & simmered to drive all the moisture off/reconfigure the volatiles; and it dried as a completely impervious film. Bunnings "Boiled Linseed" is linseed oil cut with a thinner, and dries porous. A good artist supplier will sell fair dinkum boiled linseed; pricey, but not compared to the alternatives. Linseed has the advantage of being self-healing. i've used unboiled linseed, both straight and 50/50 with fish oil, in car sills (which are ventilated), and either stops any further rusting for a decade or so.

Gliding in a small thermal, the inner wing nibbles the edge of stall a lot; but one never allows it to develop, for a stall decreases the rate of climb! I have had the fun of flying a T83 into strong rotor (off an adjacent hill) about 500m short of the airstrip threshold, which rolled it against full aileron. I aborted the approach...

The FAA flight test guide rests largely on RAeS/ARL and German data from pre-WW2; again, the FAA FTG is not a comprehensive first-principles study, but a guide for flight testing. It is just this failure to distinguish between an incipient and full spin, that eroded the original Certification requirement to recover from a developed spin. The Empire Air Training Scheme training material on spins and how to feed them, is much more comprehensive, but very hard to find! I repeat, I strongly recommend all RAAus pilots who have not practices deliberate spinning yet, to get the experience from a gliding club with an appropriate aircraft.

I agree that a Mirage, especially fully fueled, would act a good deal more like a gyroscope than does a cruciform aeroplane; but the Mirage gains its lift pretty much exclusively from vortex lift (forget Prandtl for a moment!), and so cannot experience a local separation of flow normal to the leading edge. It's a different beast in many ways. Precession is a reaction to an imposed torque normal to the axis of rotation, and occurs at 90deg to the applied torque, still in the plane of rotation; in an aeroplane, that would mean that the rudder would produce a pitch reaction, and vise versa. This is seen not to happen in cruciform aeroplanes. Non- Mirage flyers, consider a non-delta aeroplane just after pitch-down. The fuselage major axis is closely aligned to what is about to become the axis of rotation; the wing is almost normal to same. The integral of the squares of the distances of the wing elements from the axis of rotation is enormously greater that those of the fuselage; the wing inertia is considerably more critical, and remains so until the spin flattens. In said inclined state, a lift differential from tip to tip will start to drive a rotation, rather than support the aeroplane, because the lift is near normal to gravity. Correct spin recovery control input for test flying involves STARTING by centralising controls, and then - depending upon the results of a study of the physical details of (at least) the control surfaces, lifting and stabiliser surface geometry, location and execution, and the rear fuselage - either maintaining neutral pitch input and applying anti-spin rudder, or maintaining neutral rudder input & moving the stick smoothly to the full nose-down position. If recovery does not initiate, and height allows, cycling the stick is commonly the next step, followed perhaps by applying in-spin aileron, or cycling the rudder, or various combinations of the above. If the spin continues, one normally recentralises the controls, and (in a small aeroplane) moves the seat to the full-fowards position, possibly removing the harness and getting as far forwards as practicable. At some point, one deploys the (anti) spin 'chute, and then flies back to base, trying to figure out wtf can be changed on the aircraft to make it behave. I understand that when John Thorp (of NSW Region DCA, not the designer bloke) was investigating the unrecovering Chipmunk mystery, he followed very much this routine (I don't know if he had a spin chute fitted, but he didn't deploy one); after spinning the first Chippie, he flew to base and reported that the aircraft was unrecoverable by normal means, and that the fleet was (would remain?) grounded until he had cleared each aircraft. He went on to spin every Chippie on the Australian register, and cleared each and every one with the new stick grip removed and the old one returned to service. Apparently, the conformal grip reduced the stick foward travel by a few mm, which was enough to make the difference.

I was of the same view, until I gained the shotfirer's licence; by that time, I had acquired a wide base of knowledge on backyard preparation of a range of explosives and detonators, from publicly available sources. A shotfirer is responsible for maintaining the safety of the public w.r.t. explosives; and it was shown that keeping quiet about the nuts & bolts was of great import, because the record shows that terrorists, even more than criminals, don't use homemade explosives in IED, in the vast majority of cases. The fact that terrorists have not yet used any of the methodologies that I dreamed up after 11/9, does not support your position. Remember, Baader/Meihoff were journalism students; science was beyond them...

The load (forces) on VGs are very small; ~2gm at 80kt for those pictured. Double sided tape is certainly the go for short/medium term experimental attachment, which is where most of my experience lies. I wouldn't be too touchy about the exact orientation; Vortex Generators are little wingtips, which generate a tip vortex, best with an AoA of ~30 degrees to the local flow. Square or delta, they all work pretty much the same. When they are fitted as opposing pairs, the vortii(??) are meant to pump air on to the surface between/"behind" the VGs. The spacing is actually more important than the AoA. VGs on the HS to increase its Clmax are old news. Since VGs on the underside do nothing to help stall/spin recovery, a bigger HS (or restricted CG range) is normally preferred. The Savannah's rear fuselage provides both a bit of stall recovery and a bit of spin damping, i wouldn't get too excited.

Create your own market, BRILLIANT!!!

Okay, "powervalves" have become a thing; but their purpose is to allow engines with porting for huge power at high revs, to not stumble in the midrange. And yes, this does reduce the blowthrough (and emissions) under those conditions; but they don't change the fundamentals, unfortunately. I'm a big fan of 2-strokes that do NOT use crankcase compression, but I'm going to have to build my own!

I think stronger emission laws are eating the profitability of 2-strokes... I'd love to know how they get that power! Maybe it's more peaky than a Rotax?

Call me reactionary, but - it is inherently unstable, and requires fly-by-wire. Any failure that involves both assymetric lift and some fault in the artificial stability system will tend to be catastrophic. There's some good footage of the occupants of an F4 ejecting when the ASS failed on takeoff... what's the maintenance overhead on military aircraft with ASS fly by wire? ICAO targets a once per million flying hours possibility of a catastrophic (causing death or serious injury) failure in an SRE aeroplane; in a good year, we achieve ~1 in 850,000 for structural & systems failures not caused by human errors in operation/maintenance. We all know DO 160 does not garauntee perfect avionics... Given the failure modes and effects spread of that thing, I do not as yet see a probability of failure that I'd put my neck on.

Heat engines are heat engines. Are we talking about uniflow two-stroke supercharged outboards, or disc-valved crankcase compression two strokes, or reed valve crankcase compression two strokes, or piston ported crankcase compression two strokes, or some form of four stroke? All crankcase compression two-strokes* must open the exhaust port before the inlet/transfer port, and so they must close the exhaust port last. This allows some of the charge to escape into the exhaust. If said charge does not yet contain fuel (a la Sarich "Orbital Engine Combustion technology", which is a rehash of airblast injection from pre-WW1), the only penalty is a depressed scavange pressure. However, as the crankshaft bearings must be lubricated by an oil mist, some oil escapes. If the charge contains fuel, the only practicable system is, as Scott used in 1908, to reflect the previous exhaust pressure wave** within the exhaust, such to reverse the terminal exhaust flow at certain (narrow) bands in the rev range. In such circumstances, the escaping charge (fuel, oil & air) is rammed back into the cylinder, avoiding wastage and achieving a slight supercharge. However, between the "ram" bands, the opposite effect takes place - the resonance draws extra charge out of the cylinder, and subcharges the cylinder. *A very few early two-strokes used the crankcase compression to feed a manifold to timed valves at the combustion chamber, but the large clearance volume led to very low volumetric efficiencies. **A travelling normal shockwave (a supersonic phenomena) (a) attenuates greatly at an open pipe end, which entry into a muffler simulates, and (b) constitutes a feeble ghost of a piston. Assuming a constant gas density and velocity adjacent to both sides of the open end, it is usual to assume a ~50% reflectivity. The first return to an open exhaust valve should be expected to have a noticeable pumping effect, but note that this first return would occur while the port was still discharging gas at a high rate (well before blow-through), and so would not automatically be of benefit. After 32 traverses of the zorst pipe (whilst waiting for blowthrough to start), assuming no losses in transit, the intensity would be reduced to 1/65,536th of its original value. Use of a resonance box, to reduce said attenuation, will help things, but not greatly at less than WOT... The pressure wave, however, would be reflected very efficiently, though it would suffer edge attenuation by boundary layer formation, more than the shockwave does. However, after 32 traverses, boundary layer attenuation would be of the order of 15% loss. Four strokes can also benefit, by using the odd numbered waves (which have negative pressure) to aid scavange. For a poppet valve engine (912/14/15/17/213?), the end of the valve guide and the stem would somewhat attenuated the closed end reflection, but even if the overall losses were ~50%, the WOT initial pressure is of the order of 4 bar... The pressure wave effect is also present on the inlet side of the engine, although much less powerful; nevertheless, the "D" type Jag was able to lift its peak volumetric efficiency from ~87%(from memory) to over 120% by extending the inlet runner length (including the tract within the head) from ~8" to 48". This also reduced the volumetric efficiency between the power bands, but by tweaking the runner length, they were able to put the power bandes where the circuit and gearing needed them. It is interesting to note that a conventional set of "headers" for a car engine, terminate in a 3-1 or 4-1 transition, before the muffler / "open end". This means that the shock and pressure waves are shared between 3 or 4 cylinders, not returned in toto to the cylinder of origin. The McLaren TAG engine used a device that destroys (consumes) shockwaves, and swallows pressure waves almost completely, yet produced ~850hp from 1.5 litres...

How controllable is it with an assymetric failure?

Turbs, you appear to miss the point: the PHYSICS of GAS FLOW, SHOCKWAVES, and INTERNAL COMBUSTION ENGINES has NOT changed since the 1930s. If you think it has, please point to the post-1930 "Law" of physics that did was not known prior to that.

Your first sentence would be spot on, if the HS was nowhere near the VS. The textbook guidance, based upon 1930's research, is that between a line projected up at 30 degrees aft of vertical from the HS LE at the root, and a line projected up at 60 deg aft of vertical from the HS TE, the dynamic pressure is ~25% of the free stream value, and so HS in this area is ~25% as effective as it should be in stopping a spin. This was a significant incentive to try "T" tails, but they have their own issues... I agree that one should never need to exceed 2.5G, but numerous people have committed their unintentional spins at low level, and the ground tends to encourage avoidance manouvres. The airbatiC has plenty of keel area, so spins quite nicely... a nice aeroplane all round. Blanik (G)VB, when I flew it, tended to drop the nose past 90 degrees when stalled from slow straight-ahead flight, and it took a few turns to get back to a stable-ish ~50deg nosedown. It wasn't really coming down all that fast, but it certainly felt like it! (VP was altogether more gentlemanly...) The Cessna fin spar bulkhead was a steady money-earner for maintenance organisations, so I'm not really surprised... there might have been some shed vorticity at work, too. The F-18 (developmental) had similar issues in a high-G pullout, and I don't think the original F-16 finpost was great shakes either.

Physics is not black magic.

The only L13s not grounded now, have the Transavia /Llewellyn life extension mod. Glad at least one is still being used!

Not so much for a four stroke... sonic in hot exhaust gas is around 1,400 fps, so at 5,400rpm - 90 revs/sec, 45Hz - 1 wavelength will be 31.1ft; a 2ft pipe will experience ~15.56 traverses, whereas a 2ft 1" pipe will experience ~15.0 traverses. The muffler end of the pipe will reverse the sign of the shockwave, and so will the still-open exhaust valve on the cyinder end, for the second and possibly third traverse. Normally, as long as the first (inverted) return arrives while the exhaust valve is still open, it will help scavange, with a small power reward. If you have longer engine pipes (say 6ft effective), or much higher rpm, the shockwave is less attenuated; but still the major work the shockwaves do, is help pump the gas out - until they hit the muffler! In any crankcase-compression two-stroke, a returning compression wave is required, both to stuff spilled fuel-air mixture back into the cylinder, and to achieve some boost in the process. The Rotax 2-stroke zorsts are set up for snowmobiles, and are goodly at avoiding "falling off the pipe". The Ultrabats used custom exhausts, which (with pumper carbs) substantially improved the performance; they were of simple design, using basic physics. If the carb was out of tune, they did fall off the pipe quite drastically. Skippy's muffler is NOT designed to benefit the gas flow or resonance in any way, and - as Nev observed - the pipes are of different length anyway. The traditional way to form thin-walled steel tube (zorst) is to fill it with dry sand, and plug the ends; then heat to dull red, and gently and slowly bend it. Wander around with the flame so you don't stretch any hot spots too thin, or - if on the compression side - don't incur a wrinkle. Ifr you do get a wrinkle, you can shrink it by the normal panel-beating trick of heating a spot, then chilling it with a wet rag. 4130 is piss easy to form freehand, even without sand in smaller diameters, but prolly not great for zorsts. SS is meant to be easier than mild steel to heat form, but it doesn't conduct heat as well, so tends to hot spot. Why not make up a dummy out of car bog and pvc, then hand it to your fabricator?

In a developed, rather than incipient, spin, the outer wing has unstalled and is driving the spin; this is what "developed" means. The ICAO airworthiness standards for spinnable aircraft were taken to require recovery from three turns of developed spin, but manufacturers pressured Safety Authorities to accept three turns of incipient. The aircraft you neme can all recover from a developed spin. Pushing the nose down tends to increase airspeed, which both helps unstall the in-spin wing, and reduced the VS blanketting from the HS. It also reduces the polar moment of inertia of the fuselage, which reduces the force required to stop spinning. However, like an ice dancer pirouetting and pulling in their arms, the stored rotational inertia causes a short-term increase in rate of rotation. The wing polar moment is the major factor, and masses along the wing - fuel, U/C - make spin recovery much more challenging. NACA's research into spinning twin-engined aircraft (which drew heavily on Luftwaffe experience) was interesting; in most cases, pilots ended up using differential thrust to bring them out, after applying full foward elevator and rudder as suited the specific aircraft. Any aircraft which is to be deliberately spun, requires control surfaces demonstrated to considerably higher speeds, and an airframe to a considerably higher load factor than Utility Category, due to the likelyhood of overspeed and adrenaline-fuelled pullout of the resulting dive. Blaniks are fun to spin, provided those Red Bull loonies have not been at them...

Might this result in a glimmer of sense for airspace allocation??? Badgery's Creek is 14nm from YSBK; the RPT could fly along a corridor passing between Wedderburn and Holsworthy, then 090/270...

Electric props tend to have slow actuation (the forces can be quite high), and I do know that an early version of a well-known German VP prop on a 503, used to "hunt" when using a CS controller, and sometimes allowed engine overspeed at the end of climbout. Hydraulic actuators give both more force & more damping...

Under static conditions, propellors are running with a very high degree of recirculation, which remains significant up to 20~30kts foward speed (light aircraft). Recirculation gives a weird spanwise inflow velocity distribution on the blades, and so a weird lift (thrust) distribution - not very representative of flying conditions.. A look at fixed pitch props on TC'd aircraft (Cherokees, 172s etc) shows that a maximum static RPM of ~85% of full power RPM, will allow a healthy RoC, and WOT level flight without engine overspeeding; a 65% cruise of 1.5~1.6 Vs1 is typical, but 75% gives not much increase, as the prop is becoming depitched. This can be tweaked by adding a bit of pitch - a "cruise" prop - at the expense of a longer TOD. Fitting a CS prop to such a beast will give markedly better TO performance, simply because the engine is allowed to develop near full power for the entire TO roll and initial climb. At the top end, the CS prop will not change the airframe's power needs, but should offer 5~8% better cruise. Whilst Cherokee 172s are somewhat draggy, RAAus machines range from very draggy to very clean; however, a static WOT RPM of ~85% of full power RPM is a good starting point. Note that most fixed pitch props for TC'd aircraft have "overtwisted" blades (twisted beyond optimal performance for the speed range in question), because (a) tradition [most propellor makers still don't use blade element theory!], and (b) it tends to meet the overspeeding requirements for certification without much difficulty. Most (all?) composite RA blades are a tad undertwisted, which limits the propellor's efficient speed range. In summary: a CS prop will yield near-optimal TO performance for any aircraft, though not much if Vs1 >= 30kts; and should give optimal cruise, but not huge increases, subject to blade twist. A VP prop is a step in the right direction. The D18 gets a ground roll of ~110m, a healthy climb, and will cruise at Vno on a fixed pitch prop. The climb and fuel burn can be improved by drag reduction, and reducing the TO roll by ~15m is not worth the weight of a "live" prop...