AOA indicator - who can tell me more ?

[MAKG1]

Differences in thrust and weight cancel that, to first order. Beyond that, you'll have to consider shape.

The sight pictures (and critical AoA) in a 172 vs a 182 are remarkably similar given a 30% or so weight difference.

 

[gismo]

I imagine you have all heard about thought given by the FAA as to imposing the use in the future of AOA indicators.

I have read about them and understand their operation but have never seen them in a plane I flew myself.
Are they really that interesting as a safety device ?
What do you think about making them mandatory ?

Thanks for your answers

My personal opinion is that if we had AoA in all trainers, learning to fly would be significantly different (and better). To really understand what your wing is doing you need to visualize the AoA and without a direct readout of AoA pilot's tend to associate pitch angle, stick force, or g-load with AoA, none of which are even close under some circumstances.

As to the notion that any good pilot can easily "feel" how close they are to the critical AoA (stall) under all flight conditions I say BS. Sure under typical conditions (level flight, trimmed for at least 1.3 Vs, below MGW, reasonably smooth air, etc) there are obvious clues that a pilot should recognize. But throw in hot summer day bumpy air, a bit of mistrimming, and a fairly steep turn near the ground and how close you are to the critical AoA is far from easy to discern.

With AoA you can know before you roll into a turn how much stall margin you have and from that get a pretty good idea of whether or not you'll need to lower the nose if you want a quick turn. When things get dynamic you can go from what feels like a safe margin above stall to a wing drop quickly with a lot less warning than you usually get with a deliberate stall.

That said, while having an in-cockpit indication of AoA can go a long way towards understanding the wing's behavior, I think that by itself the indicator isn't likely to reduce the occurrences of inadvertent low altitude stalls. For that some sort of verbal warning as you get close and way too close to stall is what I think it takes.

But the biggest advantage for me is that with AoA I can extract maximum performance whenever I want without making mental adjustments to indicated airspeed for weight, g-loading, power, or configuration. I hardly more than glance at my airspeed during landings, I pick a target AoA based on wind and runway conditions and hold that while the airspeed may vary by 10-15 KIAS due to weight and my target AoA.

 

[gismo]

I wouldn't consider the Cheyenne a light plane. I realize the bigger the plane gets the less feel you have for it.

I'm saying I am vehemently against it being a 91.205 requirement in the vast majority of part 91 aircraft.

I'll admit that I'm undecided WRT putting AoA in my Porterfield for various reasons including the desire to keep the panel fairly original, loss of useful load (currently only 400 lbs) and the fairly benign stall behavior. Then again it has no stall warning system and tends to mush rather than exhibit a clean break so a stall is harder to sense.

 

[gismo]

One advantage of the AoA indicator on LSA with Dynon is that the pitot heat automatically supports the AoA pitot as well. As far as I know, again, the Alpha Systems one does not include heat.

Probe heat is a $100 option on Alpha Systems AoA products. I have a heated probe on the Baron and wouldn't want it any other way since I seem to end up in light ice fairly often.

 

[wabower]

For similar reasons I'm thinking the L-2 probably won't be sporting one either. I didn't see a chapter in the installation manual for spoiler-equipped airplanes.

I'll admit that I'm undecided WRT putting AoA in my Porterfield for various reasons including the desire to keep the panel fairly original, loss of useful load (currently only 400 lbs) and the fairly benign stall behavior. Then again it has no stall warning system and tends to mush rather than exhibit a clean break so a stall is harder to sense.

 

[gismo]

For similar reasons I'm thinking the L-2 probably won't be sporting one either. I didn't see a chapter in the installation manual for spoiler-equipped airplanes.

I doubt that spoilers have much if any effect on the critical AoA. More likely spoilers just reduce the amount of lift available for a given AoA and airspeed. I found the same to be true of the spoiler like effect windmilling props have on a twin engine airplane. The prop wash disrupts the airflow behind the engines enough to raise the stall speed noticeably but the AoA at stall is the same with full and idle power.

 

[kmead]

I installed an AOA system in a Malibu 2 years ago. The system was not ready for a pressurized aircraft. They made changes to the equipment that allowed us to install the system later on. The system never worked right and wouldn't adjust. The owner quit trying to make it work.

The FAA came back later and consider the installation a minor installation which eliminated many hassles.

 

[gismo]

I installed an AOA system in a Malibu 2 years ago. The system was not ready for a pressurized aircraft. They made changes to the equipment that allowed us to install the system later on. The system never worked right and wouldn't adjust. The owner quit trying to make it work.

The FAA came back later and consider the installation a minor installation which eliminated many hassles.

Was this one of the Alpha Systems? AFaIK the installation of their electronic models has the pressure sensors and associated electronics in a box that gets mounted outside the pressure vessel so the only thing inside are wires and circuitry. The primary issue in that case would be proper sealing of the wire's penetration which shouldn't affect the operation of the AoA indicator at all.

 

[wabower]

I signed the shop up as a dealer, so we get Alpha's stuff. The pressurized system is as you describe, but is probably different (new and improved) vs the one mentioned for the Malibu. And it's true that the unit has been changed to require only a wire into the pressure vessel as well as the "minor repair" classification than makes the installations much simpler.

Was this one of the Alpha Systems? AFaIK the installation of their electronic models has the pressure sensors and associated electronics in a box that gets mounted outside the pressure vessel so the only thing inside are wires and circuitry. The primary issue in that case would be proper sealing of the wire's penetration which shouldn't affect the operation of the AoA indicator at all.

 

[gismo]

I signed the shop up as a dealer, so we get Alpha's stuff. The pressurized system is as you describe, but is probably different (new and improved) vs the one mentioned for the Malibu. And it's true that the unit has been changed to require only a wire into the pressure vessel as well as the "minor repair" classification than makes the installations much simpler.

Are you on Mark's online list of dealer/installers?

 

[Ted]

That said, while having an in-cockpit indication of AoA can go a long way towards understanding the wing's behavior, I think that by itself the indicator isn't likely to reduce the occurrences of inadvertent low altitude stalls. For that some sort of verbal warning as you get close and way too close to stall is what I think it takes.

The verbal warning is one of the features I like about the Alpha product. We're now thinking about that for the 310, and wire it into the audio panel so we can get the warnings.

 

[Jim Logajan]

I see two theories, which aren't mutually exclusive:

(1) AoA indicators should reduce landing loss-of-control accidents because fewer pilots would feel the need to come in faster on final than is needed or safe.

(2) AoA indicators wouldn't substantially reduce accidents due to stalls because stall horns and buffeting already provide an equivalent measure of warning.

I don't know how many people dispute (1), but if it is true then the validity of (2) isn't as important since (1) should justify their wider use.

 

[wabower]

Dunno, haven't looked. Will do so.

QUOTE=gismo;1173545]Are you on Mark's online list of dealer/installers?[/QUOTE]

 

[gismo]

I see two theories, which aren't mutually exclusive:

(1) AoA indicators should reduce landing loss-of-control accidents because fewer pilots would feel the need to come in faster on final than is needed or safe.

(2) AoA indicators wouldn't substantially reduce accidents due to stalls because stall horns and buffeting already provide an equivalent measure of warning.

I don't know how many people dispute (1), but if it is true then the validity of (2) isn't as important since (1) should justify their wider use.

IME verbal warnings are much harder to ignore than lights, buzzers, and horns. And when you hear "Too Slow, Too Slow!" it's not likely you'll think it's the gear horn or autopilot disconnect warning. In addition, a stall warning only gives it's warning a few percent above stall while the AoA system provides a visual indication of how close you are as well as a two level audible warning with the first coming when an immediate correction isn't as critical.

And speaking of gear warning, I've been trying to convince Mark that he should include an AoA based gear warning in his products as it wouldn't require more than $1 for parts and a tiny bit of software. Seems to me the combination of AoA indication, two level verbal stall warning, and a nearly infallible verbal gear warning would be killer.

 

[Ted]

And speaking of gear warning, I've been trying to convince Mark that he should include an AoA based gear warning in his products as it wouldn't require more than $1 for parts and a tiny bit of software. Seems to me the combination of AoA indication, two level verbal stall warning, and a nearly infallible verbal gear warning would be killer.

I would be 100% for this. Most people forget what a gear buzzer sounds like, and it's usually so similar in tone to the stall warning that the easy confusion would be to think that the stall horn is blipping, which you'd expect. "WARNING GEAR UP" would go a long way, I think.