AOA indicator - who can tell me more ?

[Pat Flyer]

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

 

[bnt83]

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

#1 Not really. Another piece of expensive equipment to break.

#2 As long as they aren't retroactive, go for it.

 

[zaitcev]

I flew a Remos GX with an AoA indicator based on a 2-intake pitot. It displays a colored strip in the Dynon.

The AoA indicators are good for safety, but I oppose making them mandatory for the reson of added cost. It seems like a cheap enough item, but everything adds up. Aviation is expensive enough as it is. I know someone is going to argue that insurance rate is going to be adjusted to compensate, but that's hogwash. It's not going to happen.

BTW, you have to train yourself to rely on AoA indicator. But once you've done, flying it INOP is flying a partial panel.

I'm concerned that FAA is going to include them into MEL if installed. That would be the worst. One more thing to ground you at a remote location.

 

[LifeInverted]

Learning to fly off an AOA indicator was probably the best training experience for me yet. It look a lot of time to get used to flying off it almost exclusively (USN) and it definitely takes a mental switch to revert from flying AOA to flying airspeed again as Pete alluded to. Depending on the type of AoA system you have you can even fly by AoA as opposed to airspeed should you have some sort of pitot-static malfunction. If you're 'on speed', you know you can't stall. If you know how to use it properly, it is an amazing tool.

That being said, I flew for 5 years prior to the Navy without one, and I don't think the FAA should make them mandatory whatsoever

 

[stratobee]

They are 50 years long overdue. They should have been standard a long time ago. If we'd had them available and had trained to use them for stall avoidance rather the the useless airspeed, a lot more people would be alive today. In fact, if AF447's pilots had trained and had a habit of using that (it was available to them onboard), then 216 souls onboard that plane would probably have been alive today. And many, many others in similar accidents.

 

[EdFred]

Sorry, if you are in a light plane, and can't tell by feel when the plane is going to stall you shouldn't be flying. Unnecessary equipment.

 

[wabower]

Many of the stall-spin accidents occur when cross-controls damp the normal aerodynamic warnings. I have an AOA installed in the plane and consider it a useful tool. Absolute need to have would probably be a bit overstated, but so would the Aspen and some of the other stuff I really like.

Sorry, if you are in a light plane, and can't tell by feel when the plane is going to stall you shouldn't be flying. Unnecessary equipment.

 

[Ted]

Sorry, if you are in a light plane, and can't tell by feel when the plane is going to stall you shouldn't be flying. Unnecessary equipment.

In the Cheyenne II it was a mandatory item after several pilots had Airbus-like crashes where they stalled into the ground unaware. The power and other aerodynamic features were such that it wasn't as obvious as one would expect to be in on near a stall condition, even during what were otherwise normal flight conditions.

I didn't play around with it much, but have considered one for the 310 since all the people I talk to who have them have given favorable reports.

 

[EdFred]

Many of the stall-spin accidents occur when cross-controls damp the normal aerodynamic warnings. I have an AOA installed in the plane and consider it a useful tool. Absolute need to have would probably be a bit overstated, but so would the Aspen and some of the other stuff I really like.

Cross controlled won't spin ya - if we are talking cross controlled as in a slip. Overcontrol will do it to ya though.

 

[EdFred]

In the Cheyenne II it was a mandatory item after several pilots had Airbus-like crashes where they stalled into the ground unaware. The power and other aerodynamic features were such that it wasn't as obvious as one would expect to be in on near a stall condition, even during what were otherwise normal flight conditions.

I didn't play around with it much, but have considered one for the 310 since all the people I talk to who have them have given favorable reports.

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.

 

[Ted]

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 suppose I consider myself not in a position to say whether I think they should be mandatory on new make aircraft or not. Does Cirrus have them out of curiosity?

 

[EdFred]

I suppose I consider myself not in a position to say whether I think they should be mandatory on new make aircraft or not. Does Cirrus have them out of curiosity?

Oh crap, you don't want every plane to have a chute too, do ya?

 

[Ted]

Oh crap, you don't want every plane to have a chute too, do ya?

Nope, the reason I asked is because Cirrus likes to talk about having all the nifty whiz-bang gismos.

 

[wabower]

Raise the nose to level flight and report back.

Cross controlled won't spin ya - if we are talking cross controlled as in a slip. Overcontrol will do it to ya though.

 

[Ted]

Raise the nose to level flight and report back.

"Reporting live from a smoking hole in the ground..."

 

[MAKG1]

An AoA indicator -- especially a vane type that measures it directly -- would be useful. But I don't see that as "cheap." Anything outside the aircraft subject to aerodynamic stresses requires some actual engineering.

Using two pitot tubes won't be much more accurate than just a stall warning.

 

[zaitcev]

Nope, the reason I asked is because Cirrus likes to talk about having all the nifty whiz-bang gismos.

It's quite surprising, but older Cirrii (before G4) did not come with AoA indicators. I think these days they have a vane-type one, but I'm not sure.

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.

I thought a little bit about it and it could be fine if manufacturers replaced the stall warning devices with AoA indicators. This could make them more cost neutral, although of course in case of Cessna it's quite hard to go simpler than the stall horn. Advantage: LSA!

 

[LifeInverted]

"Reporting live from a smoking hole in the ground..."

 

[poadeleted20]

Are they really that interesting as a safety device ?

Absolutely yes. You'd have a single instrument which tells you when you're approaching a stall, when you're at proper approach or climb speed for the conditions, when you're at max range glide or cruise speed, etc. No doubt many stall/spin and landing accidents would have been prevented if there had been an AOA indicator in the plane.

What do you think about making them mandatory ?

I think it's a great idea -- it would make it a lot easier for us instructors to each people how to fly their planes safely, effectively, and efficiently. There is at least one aftermarket AoA device available which can be installed for around $700 total parts and labor.
http://www.liftreserve.com/

 

[poadeleted20]

Sorry, if you are in a light plane, and can't tell by feel when the plane is going to stall you shouldn't be flying. Unnecessary equipment.

AoA gauges are not just about stall. Can you "feel" when you're at best glide speed? Best approach speed? Vx? Vy? Max endurance? Max range? I've got some 8000 hours in light planes, and I can't, and I'm sure virtually none of the folks I've given training to (generally pretty good pilots to start with) can't. An AoA gauge makes that all dirt-simple, and several of those flight modes are where people get killed because they didn't understand that target airspeeds vary with conditions. OTOH, the AoA for those flight modes is constant.

 

[35 AoA]

Reference my username. It is a good piece of gear. It is vital in the carrier landing environment, but its use isn't just specific to grey jets with tailhooks on the underside. I think that for light aircraft, the benefit is recognizing via a gauge, that you have exceeded critical AoA. For larger aircraft, that have varying gross weights with fuel burn, it is a much more accurate measure of things like approach speed, best rate of climb, max range and max endurance airspeed. For my aircraft, as an example, my max range airspeed is whatever 4.2 AoA gives me (at least close ballpark). Max endurance is 5.6 AoA. Those are numbers I constantly reference. Doesn't matter if I have 12k lbs of gas, or 2k. Max range varies from about 315 at max internal fuel to about 270 indicated at 4k or so lbs of gas. If I were to use one reference number (like most light civils), I would be needlessly burning gas. 8.1 AoA gives me my ideal approach speed, which really only corresponds to the ideal drag index for a carrier approach, and the hook to eye perspective that is needed to catch a wire at the boat, but it could also be applied in other ways to a really accurate approach speed for land based aircraft as well. Just some thoughts.....

 

[pericynthion]

What principle do the military AoAs work on? Is it a vane, a pitot-type-thing or something else?

 

[Ted]

So the next question: Which ones do folks recommend for light aircraft? Wayne? Lance?

 

[wabower]

Alpha offers a heated vane. I didn't buy it.

It's quite surprising, but older Cirrii (before G4) did not come with AoA indicators. I think these days they have a vane-type one, but I'm not sure.

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.

I thought a little bit about it and it could be fine if manufacturers replaced the stall warning devices with AoA indicators. This could make them more cost neutral, although of course in case of Cessna it's quite hard to go simpler than the stall horn. Advantage: LSA!

 

[wabower]

I have the Alpha with two separate annunciators for demo purposes. I prefer the traditional vertical chevron/bullseye that is most like some of the jets I'm accustomed to flying, but all of them provide the same information.

So the next question: Which ones do folks recommend for light aircraft? Wayne? Lance?

 

[hkyplr18]

AOA for light aircraft, nah. For reasons stated by others..

AOA for Heavy/turbine aircraft absolutely!

You could (theoretically) fly around all day at any weight and land at any flap setting without having an airspeed indicator. I use AOA over IAS quite often when landing in a jet, especially for short strips. Having a device that shows you what the wing is doing is important in something that has a very high wing loading.

 

[bqmassey]

I have no experience with AoA indicators, but after learning a little bit of aerodynamics beyond the Pilot's Handbook of Aeronautical Knowledge, I really like the idea of them. It sounds like they're a superior instrument for nearly everything that we use the ASI for.

The ASI's primary use could be limited to navigation and structural concerns.

 

[MAKG1]

I have no experience with AoA indicators, but after learning a little bit of aerodynamics beyond the Pilot's Handbook of Aeronautical Knowledge, I really like the idea of them. It sounds like they're a superior instrument for nearly everything that we use the ASI for.

The ASI's primary use could be limited to navigation and structural concerns.

Not that simple. While you can stall at any airspeed, you can't avoid stalling at any airspeed.

 

[bqmassey]

Not that simple. While you can stall at any airspeed, you can't avoid stalling at any airspeed.

I don't believe that's the case.

 

[MAKG1]

I don't believe that's the case.

OK. How will you use this gauge to fly a Cessna 172 at 20 knots?

 

[bqmassey]

Straight-and-level flight? You won't. That would require an angle-of-attack that exceeds critical angle of attack, at least in any Cessna 172 I've flown.

 

[bqmassey]

I think the ASI would have to be the primary instrument on the take-off roll, too. With the ground interfering with the weight/lift relationship, the ASI would be your best indication as to when to rotate. You could switch to the AoA for climb as soon as the wheels are off the ground.

Without the ASI, you could pick the nose up and hold it at your climb AoA as soon as the nose gets light enough, but you would hang out there causing drag while waiting for the aircraft to accelerate.

 

[jnmeade]

I've used them and like them a lot. The one on my Dynon doesn't really stand out in the glass panel. I would prefer that it was closer to a HUD display that let you look out the windshield and see it at a glance. As more airplanes come with glass and we get better and better technology, more and more planes will come with them, standard.

 

[35 AoA]

What principle do the military AoAs work on? Is it a vane, a pitot-type-thing or something else?

It varies, but on my aircraft, they are dual probes that stick out the side of the fuselage just forward of the cockpit.

You can see it in this pic just forward of that red cylinder (the gun safing mechanism) as a little metal probe that sticks out sideways. The pitot probe is just forward and below that

 

[Ted]

AOA for light aircraft, nah. For reasons stated by others..

AOA for Heavy/turbine aircraft absolutely!

You could (theoretically) fly around all day at any weight and land at any flap setting without having an airspeed indicator. I use AOA over IAS quite often when landing in a jet, especially for short strips. Having a device that shows you what the wing is doing is important in something that has a very high wing loading.

I'm thinking I could see the benefit in a piston twin, especially for landing. I have a rather wide range of weights that I land with that comprises a difference of around 20% of gross weight, and I also end up landing at short runways. Having never used one, it seems in theory that it would help for short field operations when light (or heavy) to come in at the right airspeed. In my case, I'm used to landing heavy so when light I often will float longer than I would like to, despite being right at the bottom of the white arc. When heavy, it seems a lot of people come in too slow and crash.

 

[hkyplr18]

I'm thinking I could see the benefit in a piston twin, especially for landing. I have a rather wide range of weights that I land with that comprises a difference of around 20% of gross weight, and I also end up landing at short runways. Having never used one, it seems in theory that it would help for short field operations when light (or heavy) to come in at the right airspeed. In my case, I'm used to landing heavy so when light I often will float longer than I would like to, despite being right at the bottom of the white arc. When heavy, it seems a lot of people come in too slow and crash.

I think it would be good in a twin. My reasoning would be that your useful load has such a wider margin compared to something like a Cessna 150 yet your flight manual only gives you 1 airspeed to use for landing. In something like a Cessna 310 where you might have 1000lbs difference between flying heavy and flying light, you are still only given 1 published landing airspeed or an airspeed range to shoot for in the POH. Since we don't have/use VRef speeds in our smaller GA airplanes an AOA would give you true ref over the numbers and would surely decrease the landing distances.

 

[wabower]

The arithmetic to determine the lighter speeds is simple. Stall speed decreases by a percentage equal to half of the percentage of GW decrease. In my T-210, decreasing GW by 25% (4k# to 3k#) decreased VSO by ~12.5% (from 61 to 54) and removed the float. For many of my trips, 3k# was a normal landing weight.

I think it would be good in a twin. My reasoning would be that your useful load has such a wider margin compared to something like a Cessna 150 yet your flight manual only gives you 1 airspeed to use for landing. In something like a Cessna 310 where you might have 1000lbs difference between flying heavy and flying light, you are still only given 1 published landing airspeed or an airspeed range to shoot for in the POH. Since we don't have/use VRef speeds in our smaller GA airplanes an AOA would give you true ref over the numbers and would surely decrease the landing distances.

 

[boilert]

The past 3 military aircraft I've flown (T-6, T-1, and KC-135) all have them. The T-6 also had a stick shaker, and the T-1 had a shaker plus giant red STALL lights and a horn when you exceeded something like 90% of the stall angle of attack. IIRC, the T-6 and T-1 had vane systems while the tanker uses a probe similar to the one shown by 35 AoA on the Hornet.

In my opinion, if you fly any sort of aerobatic light plane or large, transport-type aircraft, you should absolutely have one. We can argue over where to draw the line with respect to that. For aerobatic planes, I think it adds an extra dimension of safety, because you can literally stall an aircraft at any airspeed and orientation. Did I think it was possible for an aircraft to stall on the backside of a loop, pointed at the ground? Not until an instructor demo'ed it.

For transport aircraft, ESPECIALLY automated ones, it has multiple uses. I think the best way to crosscheck what the autopilot is doing is to reference the AOA. Like others have mentioned, I can tell at an instant if I am flying best range or endurance based upon what the gauge is telling me. I always cross-check to see if my approach speed corresponds with the appropriate AOA as well. This may create quite a few arguments, but in a situation like both the Air France and Colgan crashes, an AOA gauge would have saved the day. In fact, when I am practicing engine failures, takeoff-continued scenarios nearing the edge of the jet's performance envelope (heavyweight, high temps, etc.) in the sim, my crosscheck is mainly back and forth between the airspeed indicator and the AOA in order to prevent a stall at what is the normal takeoff attitude and get away from the ground.

Should it be in all planes? No, but I think you can make a very good case why it should be in a lot more.

 

[Pat Flyer]

Thanks to all for these answers. I have been flying a C172 with nothing but the classic instruments and love it. But, stalls on last turn do happen even to experienced pilots.
Besides, the replies about best AOA for range and endurance really rings a bell. In most of our single pistons you are not goong anyplace fast. But range is often the key to wonderful journeys within safety margins.

Keep the answers coming I'm learning.

 

[bqmassey]

Do certain AoA figures, like max range and minimum sink, truly not change at all with different weights, or is the change small enough to be insignificant?

A heavy airplane flying straight and level at a certain AoA will be flying faster than a lighter plane at the same AoA. Parasitic drag would be a bit higher and induced drag lower, but I don't think the difference in induced drag at the lower and higher speed would necessarily offset the difference of the parasitic drag at the lower and higher speed.

It seems to me that the total lift/drag curve, even when based on AoA, might look a little different as aircraft weight changes.

Am I wrong?