Dafydd Llewellyn

I see my arithmetic was wrong in post # 90; the density of air at around half a mile density altitude is about 92.5 % of the standard sea-level value, 0.0766 pounds per cubic foot. So the average air density in the hypothetical cubic mile of air will be 0.0708 pounds per cubic foot. A cubic statute mile contains 1.472 x 10^11 cubic feet, so it weighs 1.0422 x 10^10 pounds. One ton = 2240 pounds, so one cubic mile of air weighs about 4.6 million tons. So the end answer of my post #90 is not 14 mm/sec, but 0.45 mm/sec (Shouldn't do those calculations late at night . . .).

Look at http://galileo.phys.virginia.edu/classes/311/notes/aero/node2.html ; note that there is an upwash ahead of the cylinder, as well as a downwash behind it. The picture is for an "ideal" fluid; in reality there is a large separated wake on a spinning cylinder, but the same upwash and downwash effects occur, and so it will in fact generate lift. The same is true for an airfoil that is generating lift; that becomes very obvious when one uses a pivoting-vane pitot some way ahead of the wing leading edge. The air does indeed move faster over the top when lift is being produced. The process is not perfect, because air has a finite viscosity, so the molecules do not exactly match up at the trailing edge, but the effect is small compared to the lift it generates. If you're looking at smoke puffs passing close to the airfoil surface, this will be visible. The "Kutta-Joukowski" condition is an approximation; in reality the circulation is never quite strong enough to fully comply with this, and the discrepancy gets larger, the closer the airfoil gets to its stall angle; a wool tuft at the trailing edge will point rearwards at cruise, but will wrap itself around the trailing edge and point forwards as the stall angle is approached. Remember that in an actual flight situation, the air as a whole is not dragged along en masse noticeably by the aeroplane passing through it; however the drag force on the aeroplane is equal (and opposite) to a change in momentum of the air - actually a small slice of air - so, yes, some air is dragged along, but viscosity slows it down; and the overall movement is vanishingly small; a cubic mile of air near sea level weighs around 150,000 tons, so an aeroplane weighing one ton, with a lift-drag ratio of 10, flying at 100 miles per hour through the middle of it, will apply a force of 224 pounds to that block of air for 31 seconds; if the force were uniformly distributed over the whole cubic mile, the air would gain a velocity of 224/150,000 ft per second every second; so after 31 seconds it would be moving at about 9/16 of an inch (14 mm) per second. So for practical purposes, the air stays still; and so it would in fact if the aeroplane had zero drag. The small difference between the velocity of the air passing below the wing, and that passing above it, produces a sheet of tiny vortices in the "slip" zone in the thin wake of the wing; the viscosity of the air quickly damps them out, so it's all over very quickly.

By the time fatigue cracking is visible, it's generally too late - unless the structure is designed to be "damage-tolerant". I do not know of any recreational aircraft that has been certificated as meeting the damage-tolerant criteria. So relying on finding fatigue cracking in critical flight structure as a means of fatigue management is tantamount to a form of Russian Roulette.

I've stayed out of this ridiculous argument, because I explained it all in an article that was written for the RAA magazine in March 2010. Ian, here's another reason to provide a subject index; this damn fool argument keeps cropping up. Bernoulli bk.docx Bernoulli bk.docx Bernoulli bk.docx

See also http://www.faa.gov/documentLibrary/media/Advisory_Circular/ac23-13A.pdf The FAA introduced the requirement to address fatigue life issues in GA aeroplanes at their initial Type Certification, in FAR 23.572, which was first introduced in 1969, and did not get really specific until 1973, when the FAA published Report AFS-120-73-2. In Australia, fatigue considerations were introduced earlier than this, via ANO 101.22 Appendix 2, which was applied unilaterally to imported aircraft types (as they almost all were) by Airworthiness Directives. Some of these ADs may still be in force, for older types of aircraft. This was done by the Australian Authority, because many overseas Authorities did not address fatigue issues in smaller aircraft at that time; for example, aeroplanes certificated under the old U.S. standard, CAR 3, had no promulgated fatigue lives unless the Australian Authority imposed them via AD. This situation has largely changed by now; most airworthiness authorities do require fatigue issues in the primary structure to be addressed in the original certification - but this is notably missing in the watered-down standards for recreational aircraft, for the most part. So nowadays, the fatigue life aspects for FAR 23 aeroplanes, and others whose certification standard required this, will be found in the "Airworthiness Limitations" section of the aircraft's Approved Maintenance Manual. For older types, check the ADs, both those issued in Australia and those in the country of origin.

If you ask whether the grass is available, this could be interpreted as asking CASA whether it is suitable - which will result in the response being to cover CASA's potential liability. If you say "Request use of grass", this may not trigger the backside-covering response. The reaction of a controller is not unusually "Go away and crash somewhere else". You could, I believe, request the use of a taxiway, if there is one suitably oriented for the wind, and there's no other traffic. Remember, you are in command of the aircraft, not the controller.

I didn't say it would; my bet is that it will end up like the Mt. Lindsay Highway. Unless /until the QLD Govt is prepared to tunnel under Cunningham's Gap, that's always going to be a secondary, fair-weather road. The Toowoomba Range requires rather less of a tunnel, I expect.

I'm about 29 NM SSE of it, which will presumably put me under a reduced CTA lower limit when they put in an ILS. But if you have forgotten the lesson from the big wet a couple of years ago, I haven't; the Toowoomba Range hill, the Cunningham's Gap hill, and the Clifton-Gatton road - which is really a goat track - were all closed for months; and whilst they have been patched up, it will only take another spell of really wet weather to close them all again. The geology means they will never be really satisfactory roads; Cunningham's Gap was still being kept open by a bunch of freight containers, last time I looked. There are three major highways converging on Toowoomba / Warwick - the Newell, the Hume, and the Great Western. The Toowoomba Bypass, which will go under the Toowoomba ridge in a tunnel, will be the only way traffic on those roads can get to Brisbane when bad weather closes the others - and in time nobody will bother with the upkeep on them. The traffic from the Newell and the Hume highways will pass about 50 metres from the eastern end of the Wellcamp strip. Guess what that means for any company trucking export produce to Brisbane along any of those highways. The basis for the airport won't be passenger traffic - that's just the gingerbread. I used to assist Heavy Lift, who operated two 727-200 flights a week out of Brisbane to New Guinea - always full of freight; and they were small beer in the Brisbane freight traffic. The Brisbane freight terminals will have to go when Brisbane gets a second runway - and despite Zoos, that's on the cards; and the freight people know it - they won't get caught with their pants down. Wellcamp has very little to do with Toowoomba itself; Toowoomba may get some benefit from having a licenced airport rather than an ALA, but trying to make sense of Wellcamp from a purely Toowoomba perspective is just plain silly. Wellcamp is just far enough to the SW of Toowoomba to not be closed by low cloud on the Toowoomba scarp. Wagner is a crazy as a fox. The rest of you are sillier than rabbits, except for Geoff, as far as I can see.

It's taken GFA a long time to come around to it, but it does have an "Independent Motor-Glider Operator" rating nowadays.

On the whole, I'd prefer the engine to have a scavenge pump.

Yep, that's how you land a Bonanza in a crosswind. If it's a reasonably strong crosswind, you need to roll a lot of into-wind aileron as you kick off the drift. With a Bonanza, it's easy to get this right, because you can tell when it's about to quit flying - timing is everything with this method.

Not all aircraft of my experience are best landed by the wheeler technique - including most tricycle types; they are susceptible to "wheelbarrow" type loss of control, and are best landed by the crab method.

I had one of those engines, in a Pug 405 wagon. It gave peak torque at 2400 RPM, as I recall, and peak power at about 2800 RPM, so it would have worked quite well as a direct-drive motor - except that the crankshaft lacked the double main bearing at the output end, that is necessary in an aircraft engine to safely handle the gyroscopic loads from the propeller. It was far better than the rest of the car; but it was best to avoid lugging it below about 2200 RPM - which would suit a propeller load very well. It was still running well when I scrapped the car for other reasons, at around 330,000 Km. The Jabiru engine was originally designed to have an installed weight no greater than a Rotax 582. It achieved that goal.

Ta - you had me wondering. I suppose it depends upon what one visualises by the term "test cell" - mine is definitely not one of the "gold plated" variety; but it's proving to be not a lot less work than building a small aircraft. It happened because I had a torque stand (i.e. a piece of hardware that mounts an engine in such a way that one can measure its torque) laying around, that we had built for calibrating engine test clubs up to 400 HP; plus a steel-lined cargo container, plus a set of instruments in a light-proof box so they can be recorded using a video camera. And I live on a rural property, with the neighbours sufficiently far away that the noise won't bother them. That provided the opportunity, and Ian Bent provided the need, so . . . One cannot conduct the certification endurance running on a dynamometer, because it must be done with "a representative propeller"; and previous experience starting with the Jabiru 1600C, showed that it needs fine control of engine temperatures, because the run must be conducted with the engine on its red-line temperatures, so it works out that one has to be able to control each cylinder to within about 2 degrees C. As always, the devil is in the detail, and the details of making sure the instruments are not telling lies is very tedious. The rules for instrument calibration and auditability of the results put some obstruction in the way of simply (!) recording it all digitally directly into a computer; so the video recording method, whilst extremely tedious to analyse, does provide an unarguable basis for auditing. One needs to measure things in terms of certified test weights and things that can be measured accurately, otherwise one ends up in a morass of "how did you calibrate the thing you used to calibrate the thing you used to calibrate the instrument?"; and designing around those issues means one has to sometimes do things in what may appear to be archaic ways.

And your meaning is?

I've seen this on the engine in my test cell; however if you let it stand for 1/4 hour, (probably less with a hot engine - but it needs time for the oil to drain back into the sump) the oil drains out of the dipstick tube and you can get an accurate reading. The 912 is a "dry sump" engine (like the Gipsy) and it uses crankcase pressure to blow the oil back into the oil tank; it does not have a scavenge pump (as did the old Gipsy Major). The oil system is entirely different to that of the Jab (or for that matter, any wet-sump Lycoming or Continental).

Instructors stop flying well before the crosswind gets that strong; they'd be fools not to, but that's a luxury one has when you're landing where you took off; one cannot always afford it if you are flying from A to B in something that has limited fuel margins. You can get local effects that result in a stronger crosswind at your destination than you expected; there are lots of locations for which you cannot get a TAF. If the conditions are marginal it's always advisable to have an alternative up your sleeve. In strong wind conditions it is also important to consider the effect of obstructions in the vicinity that can cause variations in the wind direction and velocity near the ground; if the strip is located on open ground that is flat or sloping downhill gently away from the strip, the wind will usually be consistent all the way to the ground. But if the strip is downwind from a ridge or a hill, or trees, or even hangars or other sizeable buildings, there can be very considerable turbulence or major airflow disturbances that can occasionally exceed the control authority of the aircraft. Unless you have local knowledge of the effects of wind at your destination, be wary of such situations. A "slot in the trees" may shelter the strip, but a "gappy" treeline or an isolated hanger or two can make things decidedly unpleasant. Hilly country can generate large-scale eddies in the lee of the hills that can cause a stall/spin; I've seen two cases of this, one close to my home, with a loaded agricultural aircraft, which burned to an unrecognisable heap; and one with a glider attempting an outlanding; the pilot survived with a crushed vertebra, only because he managed to impact on a patch of soft sand - the glider went into the ground up to the wing leading edges, and then bounced back out.

I did my PPL on Chippies, and I thought I could handle most conditions with them. Then I purchased an Auster III, to fly to & from work between Bankstown and Mittagong. It had an enormous position error, and no POH (ex-military); I managed to float the full length of the Bankstown 29 strip on my first attempt at landing there, because the cockpit placard showed an approach speed that was 15 kts too high. Also, the crabbed approach method that worked for the Chippie did not work for the Auster, because you could not judge when it would stop flying. It took me about 45 hours to master the thing - the correct speed, the correct technique (fly it in one wing low and fly it onto the ground tail up in that attitude). One day I left my wife in labour with our first child (at her direction) and went to work; couldn't stand the suspense by mid-day, so flew back to Mittagong, to be confronted by a windsock, bar taut at 90 degrees to the strip, with the last bit of it vibrating madly. I decided I was going to land the thing or break it; the landing worked, and I've never had a crosswind landing problem since. Once you know how, a taildragger has better crosswind capability than most tricycle undercarriages. In really strong conditions, you may run out of rudder as it slows down, after the tail comes down, and it will then turn into wind; so it's prudent to allow room for that. But if it's that strong, better to land across if there's room enough.

And if the wind is REALLY strong, it's possible (with care) to land ACROSS the strip. I've had to do this on occasion in my Auster. Tends to get people excited at a controlled aerodrome, though I've seen a Caribou practicing this at Richmond.

If Gympie Aircraft Maintenance are still in business, they should be able to help you.

If you are talking about a Gazelle, neither SCAT nor SCEET are permissible. See attached Skyfox induction.doc Skyfox induction.doc Skyfox induction.doc

Roll on, affordable ADSB . . .

Aeroplanes fly because of the principles involved; helicopters fly in spite of them . . .

I'd make the same assumptions - but if it's a gliding field that uses winch launching, it is quite possible to achieve a launch that goes above 2000 ft; so make it 3000 ft in those cases . . .

Cynic - how can you be so cynical after the experience with fuel cells? They were "just around the corner" in the '80s as I recall. Remember, the definition of a pessimist is - an optimist with experience.