Dafydd Llewellyn

Aileron snatch!!!!. Now how will I remember that??Both the aircraft are LSA not type certified (I believe).The difference between the two has always confused me to be honest. Oh that reminds me, you may be able to answer this.

For Type certification under 95.55 the VS is meant to be less than 45 kts. The J160 doesn't come close to that figure. Having been involved with Jab production can you explain this? Ive always been curious.

 

Cheers

I didn't do the flight testing of the J160; my part of it was finding compliance with the structural aspects. However, I think you will find the requirement is Vso, i.e. the stall speed in the landing configuration, not Vs (strictly, Vs1) which is the stall speed with the flaps etc retracted. The J160 was certificated, as I recall, against JAR- VLA, which also requires Vso not greater than 45 Kts CAS. Note - calibrated airspeed, not indicated airspeed. There had been sufficient wrangles with CASA over the testing of stall speed by that time, that people were being very precise about it; I got sufficiently annoyed about it that I developed a form of calibration airspeed sensor that gave roughly double the pressure difference of a normal pitot/static system - I called it the "2Q" head - and had it wind-tunnel calibrated. Alan Kerr used a differential pressure transducer and a micro-manometer to calibrate it before & after the stall test flight, and the results were digitally recorded, so we reckoned the error was less than 1/4 of a knot. CASA issued the Type Certificate - you can download it from the CASA website - so evidently they agreed that it complied with the JAR-VLA 45 knot requirement. Rod Stiff wanted to shave that as close as possible, because one knot increase in stall speed means about 2.5 knots increase in cruise speed.

 

 

Thanks dafydd. Thats great information. Having tested several homebuilts I do have an Idea of what your saying. However my original question was about steering with the rudder 'only' when too fast, which Oscar later corrected and said he was too slow.We have done lots of 'ribbon testing' on our aircraft to observe the airflow approaching and during the stall. Almost all have indicated this reverse flow you speak of and is a curious factor that i like to demonstrate, particularly with aifoils that promote :"grabbing" of the aileron at the point of stall. Aircraft like the foxbat, which has a very strong Aileron grab tendency (my term) which bangs the stick hard over at the break. Also the piper sports, which has a very rear cof g at the best of times (33% MAC i think) is another aircraft that tended to misbehave in this fashion. Approaching the stall when the separation point would move forward past the aileron there was a strong pull on the ailerons. The interesting thing is it didn't always pull the same way..Its a feature of that particular aeroplane that I dont like, when you increase the AofA the aileron feedback changes significantly, and you even feel forced feedback (again, not a technical term, my description) which feels like someone else on the controls pulling the aileron into the turn direction..Not nice, I dont like having a ghost on the controls with me..

Ps. Please note, im only a pilot not an engineer so i can only relate what i feel to my limited knowledge of the mechanics.

 

Cheers

It's called "aileron snatch" and an aircraft that exhibits it would not pass type certification. My question is, how did these aircraft get to market with that fault? I consider the system that allows this to be deficient.

All this is, of course, quite off your original topic; if you're well above the stall speed, it's not dangerous in my view to correct lateral drift on mid- final using crossed controls - though I think it preferable to use the crabbing technique in that situation. However I do use the cross-control method on mid-final, to assess the crosswind strength; my personal criterion is that if it takes more than half the available rudder or aileron throw to counter the drift with the fuselage aligned with the runway, it's time to find another runway.

 

 

Just curious oscar, why would you need to use rudder to stay level when being tugged too fast.?

Whilst I hesitate to add more fuel to this fire, the above question begs an answer, which may help clarify things:

A test-pilot's approach to stall behaviour requires that one brings the aircraft to the stall, and then sit there and observe what happens - but catch it before it goes into a spin. In the pre-certification flight testing of the CA21 skyfox, the original Jabiru, and the Seabird Seeker, I spent a lot of time investigating stalling the aircraft at its extreme CG positions, in every configuration, straight and in turns, at all power levels. They all showed the same basic characteristic, i.e. they became very vague in their aileron response, and would undergo a mild wing drop, which would recover itself and maybe go the other way. In the case of the CA 21, that would repeat, getting a bit more severe each time, until after two or three cycles the airoplane would spear off into an incipient spin. In the case of the Jabiru, the wing-rock would continue more or less indefinitely, and the Seeker would damp out after one or two cycles - mostly. Whilst in this phase, one could (sometimes) pick-up a small wing drop with rudder whilst holding the stick back, but the ailerons were ineffective at best - but essentially they all went out of control laterally, before there was any G-break (nose drop) - which meant they were fundamentally non-compliant. Finding a fix for this meant I got more practice in stall recovery and post-stall behaviour than I really needed.

 

All three of them used a rectangular wing planform - which is known to be a feature that promotes initial stalling in the centre of the wing; two of them has washout; and all three used a wing airfoil that stalled by progressive separation from its trailing edge - i.e. a so-called "docile stall" airfoil; this could be seen by the behaviour of a wool tuft at the wing trailing edge - at 5 kts above the stall, it was laying on the top of the wing, pointing forward. They were also all high-wing aircraft.

 

What the textbooks on wing design do NOT point out, is that an aft-stalling airfoil gets reverse-flow on the top surface as it approaches the stall; and this extends further and further as you slow down. It eventually reaches the aileron hinge line, and by that time, the ailerons are definitely NOT working the way they are supposed to.

 

Now, I have only theoretical reasoning based on these observations to go on, but what I think happens is that these aircraft all develop a patch of separated flow on the top of the wing, starting at the trailing edge close to the fuselage, just as the textbooks say they should. However it may start on either wing first; and if it does, that wing will drop a bit. That causes sideslip which "blows" the separated patch across to the opposite wing, so the wing-drop reverses - etceters ad nauseum. This is the mechanism of the "falling leaf" manoeuvre, and the original Markey Ultrabat (VH-ANT) exhibited exactly that when I test-flew it, so the behaviour is not confined to high-wing aircraft.

 

It followed that wing modification that managed to contain the separation bubble, should correct this behaviour - and indeed they did, on the Seeker.

 

However, if you have an aircraft that behaves this way, it is quite possible to "correct" a mild wing-drop with rudder - though in many cases the aircraft will do that itself, but rather more slowly and somewhat erratically. Most aircraft are elevator-limited at the stall, at least at forward CG, and will only get to the beginnings of wing stall - so if you happen to be flying one of these, and the CG happens to be in the right place, you can sit there with the stick hard back and pedal it all day; but don't project that behaviour to all aircraft, or the same aircraft at full aft CG, or you may get a really big surprise.

 

Once I had modified the Seeker to contain the stall bubble, it stopped exhibiting the rock & roll behaviour - but it then became obvious that the aileron response was reversed from about 5 kts above the stall down. So it then got VGs across the full span - and in that configuration, the stall speed went down about eight knots - and the stall was then so violent it put the aircraft on its back & took 600 feet to recover despite my being ready for it. It took several further iterations to get it where it is to-day - i.e. almost impossible to stall or induce a wing drop. That's another story, and proprietory information; but I do speak from practical experience. I think few of the contributors to this thread would have gone to the trouble of weighing their aircraft with the pilot aboard before & after the flight, to make sure the test was done at precisely the aft CG limit - and therefore they have experienced only a limited sample of what their aircraft can actually do. It is dangerous to draw conclusions on such limited experience.

 

 

Trouble with the side if the fuselage is that it usually is in the prop slipstream so static pressure error increases with high power and low airspeed.

I agree that having to put an engine on an aircraft is a B nuisance; but it's difficult to avoid if you want to use the aircraft to go places. With the normal range of recreational aircraft, the slipstream effect on the static error, for flush static ports on the fuselage sides is usually small enough to ignore. They are better down the back, because there is a pressure rise just behind the propeller disc, that increases with power, but provided the ports are more than one propeller diameter downstream, that's usually negligible, too.

One can be cunning, and try to find the spot on the fuselage where the pressure rise behind the propeller balances out and reduction in static pressure from the added slipstream velocity, but that's likely to be somewhere near the wing, so the wing pressure field interferes, so not really worth the effort.

 

 

Stone the B crows! How many times does it need to be said before you buggers will grasp it? Once more:

 

The wing starts to stall when it is trying to carry more load than it can bear at the airspeed - i.e. its angle of attack is too large. To unstall the wing, the pilot must first UNLOAD it. That needs no more than a small movement of the stick, IF YOU ACT FAST ENOUGH. You do not need to generate a large excursion from the flight path to unload the wing; all you have to do is to change the curvature of the flight path to momentarily reduce the G load. This works in any attitude. IT IS IMPOSSIBLE TO STALL THE WING AT ZERO G, NO MATTER HOW SLOW THE SPEED. SO GIVE THE STICK A JAB IN THE DIRECTION THAT GETS ZERO G, AND IT WILL UNSTALL.

 

How big a jab is necessary, depends on the "stall hystereris" of the wing airfoil; some airfoils unstall almost instantly, others need their angle of attack reduced more substantially to re-establish unstalled airflow. But we're talking about maybe 7 (seven) or less degrees reduction in the angle of attack, so if you act whilst the aircraft is still mainly moving ahead, whilst it's still thinking about starting to fall, you can achieve this with very little divergance from the flight path.

 

If the pilot sits there playing with the rudder, before he unloads the wing, the loss in lift due to the initial stall will start the aircraft (or just the wing on the stalled side) falling through the air, which further increases the angle of attack and so the stall rapidly deepens. In that case, unloading the wing will take an armful of stick motion - and if autorotation sets in, a bootfull of rudder also. So yes, use the rudder to keep it straight whilst you unload the wing; but the words the instructor uses are important here; you should NOT be trying to "pick up the wing" with rudder whilst ignoring the stick; in fact doing so will only postpone the inevitable a few tenths of a second.

 

The correct way to think about stall recovery is "unload the wing whilst keeping it straight". The standard instructor patter needs to be changed - which seems to be about as easy to do as convincing people that the Earth was not flat.

 

Now, having momentarily unstalled the wing, the aircraft will usually have gained a knot or two, so it will not immediately fall back into the stall - all the pilot has to do is refrain from re-imposing the load that caused the initial stall, until the speed has increased sufficiently. The amounts to merely easing-off a trifle from whatever he was doing before.

 

As Oscar pointed out, glider pilots learn to do this as a reflex action; but the same is possible in any small aicraft that reacts quickly to control inputs. The response that matters here, is how fast you can reduce the G-load by a jab on the stick. LEARN TO USE YOUR BACKSIDE FOR SOMETHING MORE THAN SITTING ON; how hard you are pressed into the seat is the measure of how close you are to stalling, at any given speed. A quick jab on the stick can easily lift you out of your seat - and that will definitely unstall the wing. After that, it's up to you.

 

YOU STALL THE AIRCRAFT BY PULLING MORE G THAN THE WING CAN HANDLE AT THE SPEED YOU ARE FLYING (and 1G may be more than it can handle) - SO THE FASTEST WAY TO GET OUT OF A STALLED CONDITION IS TO REDUCE THE G LOAD.

 

Before the ATPL holders get their bit in, in a large aircraft the situation can get out of hand because the control responses are not fast enough. That's why those aircraft usually have devices to prevent them from getting into a stall in the first place. I'm talking about what the Americans call "small airplanes" here.

 

 

Dynamic + static?

Yes, a pitot head registers the total pressure, i.e. pitot plus static.

 

 

ok, Dafydd reminded me of a blindingly obvious point - the pressure field under the wing is caused at the expense of the local dynamic pressure, so the pitot reading IS lowered in that location. Trying again:EITHER a combined pitot/static head should be nearly a full chord ahead of the wing, OR you need to get a pressure map for the airfoil (or grope around in the air until you find a location that works), and put it in the unaffected zone; OR(2) you need to stick it close under the wing - a la Piper - and tweak it - a la Piper - until it works.

 

4412 / Clark Y both have a pressure-passive zone, and about 0.15 chords fwd and 0.15 chords down (if more than ~40% outboard - or lower if inboard of 40%) should work through the positive AoA range; 0.2C fwd and 0.2C down should work anywhere along the wing, out of slipstream...

 

since any mods to the system normally require you to do a calibration with a pivotting pitot / trailing static, most people just do an accurate calibration on their existing system, and call it quits.

Under the wing - anywhere between about 15% chord and 50% chord - 40% if it has flaps - and about one propeller diameter beyond the slipstream (and well clear of the wake of the lift strut) - is an excellent place for the pitot head - but NOT for a static source. The wing acts as a flow-straightener for the pitot, as far as angle of attack is concerned. The Jabiru pitot on the lift strut leading edge is as good as any. A simple thin-wall tube, cut off square and de-burred, will give dead accurate pitot pressure up to about 0.4 Mach, up to about 15 degrees either side of pointing dead into wind.

 

The best place for the static source is on the side of the fuselage, somewhere where it has no curvature (or as little as possible) in the direction of flow, and well clear of the wing pressure field and the wing wake. This requires a pair of static ports, one either side, connected together. Only if you cannot find such a place, should you resort to a tubular static head, and it will generally need an adjustable collar, to minimise its error. The way to measure the static source error, is to compare it with a trailing-cone static in flight. For guidance on making a trailing-cone static source, see CASA AC 21.40.

 

 

On the Gypsy Moth the ASI is on a interplane strut and is a bit of flat tin on a piece of wire that bends back across a scale. You have to look right out to the side. My god it was tough in those days. Women threw themselves at us The expectation was high..... Nev

Simple? How many hours do you think it took to build the NPL (New Physics Laboratory) wind-tunnel so they could calibrate that thing?

 

 

when flying my Savannah, i rarely look at the ASI, only when about to grab flap, when climbing at about 60kts or the windscreen starts to vibrate near 100kts. engine failure its 55kts.i can change the ASI just be opening and closing the window vents, as the static source is just behind the pressure instruments in the panel. cruise speed is 5100rpm, climb is full power, cruise descent at 4000rpm. finals and landing is all done by feel, and where the stick position is, gives me an accurate picture of AoA when flying behind the drag curve on steep approaches and short landings... rudder to keep the ball centred at all times..

And a piece of string you can feel to see if it's raining?

 

 

Of course Matty Weber at Luskintyre is a champion with R&T and because of that is pretty much booked out for over 12 months. Sigh. You'd thinkni would have got my act together by now and done mine.Daffyd, after that enlightenment about the leading edge structure I am getting inspection holes cut in my wings to check the structure. Mine was rebuilt on 1998 but unfortunately the builder has since deceased so I don't know what they used to rebuild the wing.

I only know of one aircraft that had the pressed (actually hand-formed) nose ribs, and even then it was only on one wing. I think I still have the template for the form block; the block itself may still be somewhere at what used to be Ian Aviation at Archerfield. We hand-formed the LE ribs from 0.050 inch 6061 T4, I recall, using a shrinker (the 6061 was unclad, so the shrinker marking was not an issue). I may still have the EO for it on file. The airraft was VH-WED, as I recall. It's the sort of thing one would consider in a major rebuild of the wing. There's an AD for cracking of the vertical leg of the formed T section from which the ribs were made; it was twisted to form the rib shape, from material that was made by rolling thin strips of metal, and they eventually crack due to stress corrosion where this forming was done - and after that the buckling strength of the rib is severely reduced. You are wise to check for it; now all those wings are covered with dacron, nobody looks there any more . . .

 

 

...that's not an easy question! Here goes:That'd be my first choice. A combined pitot-static head, as far outboard along the wing (but not near the ends of any lift struts) as practicable, and ~0.15 chords ahead of the LE would be my second. Note that putting a shroud on a pitot gives up to ~30 degrees of misalignment without significant error, although the shroud supports have to be faired and well behing the dynamic (pitot) port.

If you use a combined pitot-static source under the wing, the static part of it needs to be "tuned" so that the pressure it gets is reduced just the right amount to compensate for the pressure rise caused by the wing circulation. The one on the Piper PA 28 was so tuned (it's one of the more clever aspects of the PA 28 - must have taken a few hours in a wind-tunnel to get it right; it's probably also affected by the airfoil the designer chose). If you make the mistake of using a standard pitot-static head - which is designed for use elsewhere - in such a location, the ASI will read low.

I would consider o.15 chords ahead of the leading edge a bit too close - unless you are trying to get a low indicated stall speed.

 

The overall errors one finds in an airspeed system, are the reason why the Flight Manual airspeeds are always given in IAS - i.e. they incorporate those errors.

 

 

Hi Bob, sorry if I've missed this in previous post , so how far below the wing and what longitudinal position is the best for the pitot tube and is the static port best located with it. I know the RV's have them half way in the aft fuselage on both sides interconnected but I'm told even that system has to be 'tuned' .I hope know one minds the thread drift.....?

cheers

 

JimG

Unless you want to go to a lot of trouble calibrating it - as Piper evidently did with their underwing device on the PA 28 - the static ports / head should be well clear of the wing pressure field. The least troublesome spot is half-way along the rear fuselage - but only if the rear fuselage is a straight-generator shape. For most plastic fantastics, the rear fuselage shape is not suitable. Inside the rear fuselage is often used for the "alternate static" source for GA aircraft that require one - though it usually has a bit more error than a flush port, if you can find a suitable location for one, due to suction around the cabin and leaks around doors etc. The static port location gets more critical, the faster the aircraft goes.

 

 

I also agree I just wasn't clear on who you were targeting.

I was trying to get a general message across to the readers of the thread.

 

 

And bear in mind they you should be able to safely pilot a simple plane around a circuit with a failed AIS. Beware the wasps and their instant mud in the pitot. Try it with an instructor as backup. You are allowed to be a little fast . Nev

That's not difficult to do provided the aircraft has adequate stick force Vs speed characteristics (another one of those things that causes sweat, blood & tears in certification). Don't try it in a BD-4 or a Lancair 360.

 

 

I think Rag and Tube are very good, too.. On the matter of the 0-360 engine fit, wouldn't that be a bit of a hot -rod (overpowered) . There was a six cylinder powered one at Bankstown which may have been an O-300. Continental but would exceed Vne in level flight easily. It was Black and Yellow from memory. J1 of some kind (3 seater) Nev

No, I wouldn't describe it as a hot-rod; the reduction in propeller diameter about compensated for the 25 extra nominal horsepower. Having towed gliders out of paddocks with an original J5G, there wasn't much to choose between them for performance. The Lycoming version benefitted mainly by being able to lose the 25 lb of so block of cast iron above the tail-wheel, as well as the direct benefit of the lighter engine weight. The empty weight reduced by about 75 lbs, as I recall. The problem with the original engines was that most of the Cirrus Majors had by then spent years between 598 and 599 engine hours (the TBO was 600 hrs, and parts were no longer available) . . .

The one you saw was probably an 0-470 engine conversion done by Aerosmith in the 1960s.

 

 

Thats fair enough Bob, but from an instructing point of view we have to point out that the IAS does read erroneously on the dangerous side in aggressive sideslips on that particular system. While on others it reads the other way.i wonder how this design standard would be applied to an aeroplane with an approach speed of say 40 kts. The error "allowable" by the standard would be greater than 10% of the IAS.. Interesting..

Yep, the design standards ain't perfect. That's why having an understanding of them is so important.

 

 

Aahhh yes of course, the static port is a bit strange up there on the tail.

Yep, if the IAS rises with yaw, this is almost certainly - (I would say, definitely, having studied pitot head behaviour extensively) unless the yaw puts the pitot head in the slipstream - due to the static system being affected by cross-flow.

 

 

The only time I've used Mogas ( except in a 912 )was when I shandied it, and didn't use it on take off .Not in a Jab by the way. I know LAME's who just won't use it. ever. I've heard of Grumman Ag cats using it in a radial but also heard the gum deposits are excessive. This was 18 years ago. Perhaps the newer Mogas from Singapore is better but it varies in quality from time to time. IF there is any possibility the engine you use could suffer from preignition ot detonation, why use it at all? Avgas into the future is not assured and something else will have to be available . Some oil companies already make a racing fuel and if demand is there, aviation might get a look in. Sorry another several day old hold up in the posting Nev

I used the old leaded Super in my PA28-140 on occasion (the fuel system was legally modified to reduce the risk of vapour-lock - tho nowadays I'd have gone about it differently) because it had a low-compression Lyc 0-320 that was certificated for 80/87 Avgas. Seabird certificated the original 360 model Seeker for the same fuel, because it also used a low-compression variant of the Lyc 0-360. However, that grade of MOGAS had neither aromatic hydrocarbons nor alchohol in it; it was essentially similar to 80/87 AVGAS except for its higher vapour pressure (which makes it more prone to vapour-lock), 50 % higher methyl bromide to tetra-ethyl lead ratio, and a much less precise quality control requirement. In those days, when you purchased a drum of AVGAS, it came with a Release Note - and the distributor came & collected it if you had not used it within 3 months. A shandy of Super-grade Mogas and 80/87 Avgas worked pretty well in the low-compression engines, the main issue was vapour lock, except in high-wing aircraft with the fuel in the wings.

Those days are long gone; and the issue that most people are unaware of with motor fuels, is that they are all pumped through the one pipeline; the fuel companies pump one product for a while, then a different product for a while, etc - and the result is a slug of contaminated fuel where the two batches are mixed in the process. That slug of fuel ends up (mostly) in the 91 RON tank. But it means the precise QA of any of the fluids that are transported that way (and most of them are), is somewhat suspect - and well below AVGAS standards. The least-worst of them is almost certainly 95 RON.

 

Modern car engines cope with this variability by their "smart" electronic fuel injection systems, wish oxygen sensors and knock sensors etc. I do not know enough about fuel chemistry to comment on the reasons for the freedom from deposits that we enjoy nowadays - tho I suspect ashless dispersant oils have a lot to do with that. The issue of reliability of electronic ignition systems for aircraft use will have to be overcome - it's not an easy one - because it's obvious that the QA issue for aircraft is too small a concern for the fuel companies now that there are no airline or military users of the product, so it will have to be addressed by the machinery that uses the fuel, rather than by the supply system, in future. This SHOULD mean that the cost of fuel should come down, to compensate for the increased cost of the engines, which are NOT thumped out by the million. Wanna bet it will?

 

 

Just back to what you were saying earlier Dayfydd jabiru specify that mogas min 95ron be used I'm not ignoring the specified fuel

Good for you! I did not say it HAS to be 100LL; I said, it is stupid to ignore what the engine was type-certificated for. And illegal to disobey whatever is written in the Flight Manual, BTW; RAA aircraft are NOT exempted from that regulation. So if you are following the Flight Manual, fine; it's not you I was talking to. I agree TCDS VE 501 issue 2 lists both 100LL Avgas and 95 RON mogas for the Jab 2200C.

 

 

Let's remember the topic is "steering-on-final-with-rudder". Yes, many aircraft fly differently. Yes, unstalled rate 1 turns with rudder may feasible, and this pilot, being lazy and slack, uses them (in his plane) most of the time in high cruise, but NEVER in circuit.After late final I believe it would take really good understanding of the aircraft behaviour, and your own skill, to get the bloody stick forward. I know of at least two cases of damage hereabouts due to that. Several instructors have told me NEVER even ease the stick forward at low level. Hold it back, let it settle, or, if you are too high, give it more power. But what would I know - I'm a relative greenhorn.

 

But I DO fly finals balanced or slip. Slip I use if too high (or if far too high I fly balanced "S"s or "8"s towards the field until I am low enough - or go round, depending on whether farm or airfield, the circumstances and the field rules), and I also use slip to get and stay aligned for a cross-wind landing. From base and onwards I make ALL turns with increased descent (sort of 'diving into them' somewhat, just in case I was already a bit too 'slow'). Coming over the hedge, I also lower the nose for a few more knots as I round out rather than risk a wind-sheer pancake (which I have found can lead to unwanted workshop time and bills).

 

I'm NOT saying fly like I do. Don't. I'm not an instructor, and your plane will be different. But these things I have been variously taught, they might be useful discussion topics with YOUR instructor(s).

 

P

I have no objections to the basic thread topic, or the discussions relating to it. I, too, slip off excess height and use a mixture of crab and slip techniques, according to the aircraft type; how else can you land in a crosswind (is there any other kind?) unless your aircraft has "cross-wind" landing gear (a few Austers did - they are quite startling to watch, landing in a crosswind). However the off-topic debate on "picking up a wing with rudder" is misleading. In a properly-conducted landing, the wheels should be no more than about six inches off the ground when the stall warning sounds (at least 5 knots above the actual onset of stall, in a certificated aircraft - indeed, most aircraft are running out of elevator due to the ground effect, and the wing is not likely to stall.) However, you need to read the fine print in the flight manual - some aircraft - the DH Chipmunk for one - had slipping verboten with the flaps extended; a restriction like that generally means it can have a vicious stall in a strong slip condition; most aircraft do - the saving factor is that the sideslip makes the ASI read low, due to the cross-flow on the pitot head, so pilots who watch the ASI will have a hidden margin. This effect is sufficiently large, in a Super Cub, that the flap speed can be exceeded without the pilot being aware of it, with resulting damage to the flap hinges.

Me for dive brakes . . .

 

 

What do you mean Dayfydd ?

I mean, people here are ignoring the fuel that is specified in the engine TCDS. That's the fuel for which the engine detonation testing was done.

I have repeatedly pointed out that there is roughly a ten-point difference between MON (Motor octane number) as used in Avgas, and RON (Research octane number) as used for Mogas. So 91 RON is roughly equivalent (in regard to detonation) to 80/87 octane Avgas (no longer made, but some Lycomings were certificated for it). The old leaded "super" used to be a very close equivalent to 80/87 Avgas, but with a higher vapour pressure. Since that went off the market, there has not been a grade of Mogas that is anything like equivalent to 100LL. If there were, it would be called something like 110 RON.

 

If people persist in being so bloody-minded stupid about the fuel they use, they have no right to blame the engine manufacturer for the problems that result. The RON rating method was an advertising ploy introduced by the fuel companies to disguise the drop in fuel quality that resulted from the no-lead legislation.

 

(The no-lead legislation itself, was introduced so that catalyctic exhaust devices to clean-up the oxides of nitrogen (which produce brown smog) would not have their platinum catalyst "poisoned" by the lead bromide. The Rah-Rah about babies suffering brain damage from lead poisoning was political eyewash - the lead plumbing in British towns supplied far more lead than the vehicle exhausts.)

 

The message is: RTFM, you idiots.

 

 

I'm glad I'm not an engine manufacturer, if what is being said on this thread is typical.

 

 

I hesitate to put a word into this highly erudite discussion; however it does seem to me that there is a lot of generalising going on here, that may not help clarify things for inexperienced pilots.

 

One thing that pilots seem to take for granted, is that all aeroplanes inherently fly the same - sure there are minor differences in control feel etc, but setting those aside, the fundamentals are pretty much the same. This seems to lead to an unstated assumption that that's the only way an aeroplane CAN behave. I have to point out that that is very far from the truth.

 

Certificated aeroplanes all behave pretty much the same, because the design standards demand this, and people spend bood, sweat & tears in achieving this. Modern design standards demand that the dihedral effect is sufficient that IN UNSTALLED FLIGHT the aeroplane will lift the low wing when the ailerons only are released from a fully crossed-control condition; and that the aircraft will yaw towards the low wing when the rudder only is released in a fully crossed-control situation.

 

The practical result is that there is generally sufficient dihedral effect IN UNSTALLED FLIGHT to allow one to roll the aircraft into a rate 1 turn, and roll it out again, with rudder alone; and also sufficient weathercock stability that it is possible to make sloppy, gentle turns with ailerons alone. I had to require an increase in the wing dihedral for the CA 21 Skyfox, the original Jabiru, and the Seabird Seeker, to achieve this. As a result, David Eyre was able to land the prototype Seeker safely despite an aileron disconnect. Do NOT assume this will be the case with a non-certificated aeroplane.

 

However, this behaviour cannot be expected beyond the stall; and the debate about whether one should fool about trying to pick-up a wing at the stall with rudder, is bloody dangerous. The message is, UNSTALL THE DAMN THING - don't sit there trying to show how clever you are with your feet. Teaching people to "pick up a wing with rudder" is bordering on criminal, IMHO. GET THE BLOODY STICK FORWARD! is what should be taught.

 

Now, can we please have an end to this nonsense?

 

 

Possibly - but since NACA did all the research on light singles in the '20s and '30s, why can't Cessna read? Designing for spin resistance was done to death - remember the Ercoupe?

Very true - one can't help thinking that the professional engineers in the design dept. might be able to read, but the sales people couldnt - and guess who won?

However, the category weight limit is simply too low to build a Cessna-style aeroplane with sufficient useful load. In a sense, Cessna shot themselves in the foot - the GAMA manufacturers seem to have been determined to keep the recreational airplane sector tied down to such restrictive MTOW that they would not be a threat to their baseline trainers. Seems they succeeded. Poetic, actually - if extremely short-sighted.

 

 

I should've added: unless he was convinced the airspeed system was identical to an approved type and you could copy and paste the PECs to your AFM.

Yes. But I don't think there's any requirement to do this, for a VH experimental aircraft. However, given the critically small safe flight envelope of the Skyfox, knowing that the ASI system is telling the truth is a life & death matter. I never cease to be amazed that people make such heavy weather of ASI system calibration; a trailing-cone static and a pivoting-vane pitot are things anybody can make for not much over $10. Sure, you need two ASI instruments whose errors are known, but that's no big deal for an experimental aircraft, you don't need a certificate from an approved instrument shop; a simple manometer check of the instruments will suffice. You can do the flight recording with a kneepad & pencil.

I use an instrument box that straps on the spare seat, and records the instruments by a video camera. With that setup, the ASI calibration is all over in about 5 minutes of flying - it hardly needs more than an extended circuit. It takes a bit longer, and is not quite so precise, by pad & pencil, but still quite OK for the purpose.