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Old 24th Feb 2000, 14:40   #1 (permalink)
Acker Demick
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Question Angle of attack instrument?

I am supervising a project by an undergraduate aeronautical engineer - he is looking at the practicalities of a low-cost angle of attack instrument for light aircraft. It would be very helpful to get the opinions of instructors on the following:

Suppose that the GA fleet were all fitted with a reliable/accurate angle of attack instrument. Would this be of any value in PPL training? If yes, how would you make use of it? Also, what would be the benefits (if any)for qualified pilots in, say, routine flying, instrument flight, bush flying, aerobatics .... anything else that occurs to you.

All comments welcome.

AD
 
Old 26th Feb 2000, 06:56   #2 (permalink)
Oktas8
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AD: looks like everyone's stumped by the enormity of the idea.
I am a low hour instructor, so don't take my ideas as world-shaking truth. But I can't imagine it would be much use in PPL training, as students are taught to look outside as much as possible, not at the instruments.
Might make unusual attitude flying (& mountain flying) a bit safer for the inexperienced pilot. I doubt that veterans would use it though - they have developed other sensory cues to use.
I imagine light twins doing instrument takeoffs & approaches might use it, but you'd have to ask someone with relevant experience.
Try the other forums?
 
Old 26th Feb 2000, 11:47   #3 (permalink)
Luftwaffle
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It might be useful to show a student that the angle of attack for certain performance "speeds" was constant under conditions when the actual speed varied. But a trainer POH doesn't specify angles of attack corresponding to Va or best glide, so the student still has to learn to use the speeds.

I've seen two types of GA AoA indicators advertised, one with an external vane like on a 737 and one that measured the differential pressure between pinholes.
Here's one of the vane ones, complete with the manufacturer's arguments for its usefulness, and advantages over other designs: http://www.riteangle.com/
 
Old 27th Feb 2000, 13:58   #4 (permalink)
spooky
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Quote:
Originally posted by Luftwaffle:
It might be useful to show a student that the angle of attack for certain performance "speeds" was constant under conditions when the actual speed varied. But a trainer POH doesn't specify angles of attack corresponding to Va or best glide, so the student still has to learn to use the speeds.

I've seen two types of GA AoA indicators advertised, one with an external vane like on a 737 and one that measured the differential pressure between pinholes.
Here's one of the vane ones, complete with the manufacturer's arguments for its usefulness, and advantages over other designs: http://www.riteangle.com/
All good stuff, but anything more in the cockpit to confuse the poor student and he/she will be even more distracted from looking out---- I think one of the most important activities when flying in uncontrolled airspace. There's my twopence worth (I'm a very old lapsed instructor who won't be paying to revalidate-good luck all)

 
Old 27th Feb 2000, 14:12   #5 (permalink)
Gear up Shut up
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Can't see that it would be of benefit for a student.

The aircraft I fly is fitted with 2 and is directly connected to ADCs (Air Data Computer) allowing afore mentioned to compare speed and attitude. It is given as an indication on the EFIS with reference to Vstall. The centre point being 1.3Vs which is actually Vref for the given weight at that time for landing.

We tend to fly above that anyway allowing for the elements; ie gusts and windshear, as anything below would be considered dangerous.

To be honest I've never really looked at it as the speeds are bugged on the ASI so are part of your normal scan anyway. Infact this is the first time I have really considered its relevence, I think its more for the a/c computers than the pilot.

Well that's my bit of waffle don't really understand it to be truefull!
 
Old 27th Feb 2000, 16:20   #6 (permalink)
grade_3
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Another low-time Instructor here, but you did ask for all comments

I think that it would be a nice "gimmick" to have when teaching some sequences (i.e. that the wing *really does* stall at a certain AoA, not IAS etc.). That in itself would be nice, but it isn't absolutely necessary. Showing the gliding attitude might be another where it is useful.

But as to the benefits to trained pilots, once the training is done there really isn't that much information that an AoA vane can give you that other stimulus can not. Light planes are pretty forgiving little things, on the whole, and so long as you fly the right attitude and power etc. then you shouldn't really need another instrument telling you what you can already feel through the seat of your pants.

Mind you, calling out an AoA check on short final would sure sound impressive!

grade_3
 
Old 28th Feb 2000, 02:16   #7 (permalink)
StrateandLevel
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Can be useful on a research aircraft flying at high angles of attack, I have used one with a yellow scale, calibrated in "bananas"
really it just gave a relative indication high 10 bananas or low one banana.

For PPL training, no use whatsoever.
 
Old 28th Feb 2000, 02:34   #8 (permalink)
BEagle
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AoA isn't really much use in a GA application. However, it would be very useful to have an AoA audio tone at Cl max for aerobatics or max rate turns!! Buffet nibble bleeds energy, so just short of that value of AoA would be quite helpful in some hard manoeuvring applications.
An AoA gauge is probably the simplest instrument in the world to construct - or at least that's what I was told at Cranfield in 1971!! Not much of a research project, I'm afraid!! Now a basic weight and balance display based on strain gauges in the undercarriage - that would be very helpful and might save lives. I did the theoretical calculations back in the 70s but never got round to finishing the project

[This message has been edited by BEagle (edited 27 February 2000).]
 
Old 1st Mar 2000, 22:23   #9 (permalink)
ryan
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BEagle,

You say that and AoA gauge is the simplest instrument to construct, if thats the case, why has it never been done before, why is it not fitted to any general aviation aircraft?

It is easy to make and fit on to a jet aircraft, but a single prop is a different matter. The propellor disturbs the air over the fuselage, and the flow over the wing is affected by angle of attack anyway. There is therefore no logical place to put a sensor.

I would be interested to know what you were told at Cranfield in 1971?

Ryan

PS What did you do at Cranfield?
 
Old 1st Mar 2000, 23:20   #10 (permalink)
Acker Demick
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Ryan,
if I can chip in here - one arrangement we have looked at is a vane mounted on a longish (about one chord) probe sticking out of the wing leading edge, and far enough outboard to be well clear of the propwash. This works fine in wind tunnel tests, but would probably be very vunerable to handling damage on the ground.

AD

------------------
If God had meant us to fly he would have given us more money
 
Old 2nd Mar 2000, 00:28   #11 (permalink)
BEagle
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Ryan - yes, it's much more difficult on a single prop aircraft due to slipstream effects from the propeller. The probe and gauge are simple - but, as you so rightly say, the aircraft installation will be difficult. I suspect the reason no-one's bothered before is probably because there's no real benefit for the cost in a light aircraft. Personally I'd really like a single engine prop ac to have an AoA gauge from which I could deduce the alpha values for Cl max and also for (Cl/Cd)max for best still-air range and ((Cl**3/2)/Cd)max for best endurance.
The type of probe they showed us at Cranfield was the twin-slot type which naturally aligns itself with the free-stream and hence gives a value of alpha based upon its rotation relative to a calibration reference datum - you could blow on it and it would rotate!! I was doing my 2 week flight test course as part of an Aero Eng degree using the de Havilland Dove aircraft. I'd also learned to fly with the Bedfordshire Aviation Centre in 1968 at Cranfield.

[This message has been edited by BEagle (edited 01 March 2000).]

[This message has been edited by BEagle (edited 01 March 2000).]
 
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