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-   -   Not understanding AoA indicators... (https://www.airlinepilotforums.com/safety/84956-not-understanding-aoa-indicators.html)

Yoda2 11-24-2014 07:39 PM

I just read another interesting article. For anyone interested, look up "Aero 12 - Angle of Attack - The Boeing Co." (This is from Boeings quarterly news)

Fluglehrer 11-24-2014 07:44 PM

Modern GA training aircraft are designed to have little further aft movement of the yoke past the critical AOA position. In this sense they are close cousins to the Ercoupe, and I think it somewhat hinders the instructor from training stalls. I find it very difficult to stall a Warrior or a C152 power-off/level flight and keep it stalled.

Yoda2 11-24-2014 09:07 PM


Originally Posted by Fluglehrer (Post 1770570)
Modern GA training aircraft are designed to have little further aft movement of the yoke past the critical AOA position. In this sense they are close cousins to the Ercoupe, and I think it somewhat hinders the instructor from training stalls. I find it very difficult to stall a Warrior or a C152 power-off/level flight and keep it stalled.

The Warrior stalls pretty docile, though I always thought a 150/152 stalled with a fairly noticeable break. I wouldn't exactly refer to those aircraft as modern either! Did you learn to fly in a Bleriot?

E2CMaster 11-24-2014 09:28 PM

Wright flyer.

And while yes, you can do math to get an approximate stall speed vs AOB, why do public math? Especially in the pattern.

Also remember, stall speed is predicated off of a slow decel rate as well.. You whip it over to 60 and pull, and it's going to stall at a higher speed, even without an abrupt pullup.

Of course, do this with an AOA gauge, and you can see the transient high AOA before speed and AOA come back to jiving with each other.

In dynamic flying, I trust my ass more than airspeed, and I trust AOA more than both of those combined.

Airliners and most GA never get all that close to stall speed in normal operation. I think (don't have proof) that the 1.3 Vso = Approach speed came from all the safety factors they have to put into making sure approach speed stays well above stall, with all possible airspeed and aircraft weight/cg computation errors, plus allowances for gust and turns.

I'd be comfortable flying at around 1.1 Vso with an AOA gauge on approach. I used to do it somewhat regularly. In a big plane. To a moving target.

Speed is energy. Energy dissipates from planes in three main ways.
Aerodynamic Drag (friction)
Brakes (more friction, with a bonus of heat retained on the airframe and possible fire if bad enough)
Reverse Thrust

Any kinetic energy not absorbed by one of the above tends to get arrested by the ground, which is technically a form of braking, oftentimes called a crash.

Landing slower, but above stall is generally safer and easier on the equipment. Hence why we normally land and takeoff into the wind.

I have no problem taking King Airs with AOA systems into absurdly short fields. (granted, VMCa usually becomes my limiting factor before AOA, but yeah, slower is better when landing rough and short)

Fluglehrer 11-24-2014 09:33 PM


Originally Posted by Yoda2 (Post 1770598)
I always thought a 150/152 stalled with a fairly noticeable break.

C-152 power-on often has a wing-drop. Power-off clean it will just oscillate as the nose barely drops and it immediately recovers with the yoke held full aft. This type of "designed-in safety" doesn't help to teach what a plane handles like in a full stall, although it does keep most everyone alive...at least until they get a license and move to another aircraft.
I guess you're right, the C-152 and Warrior are both old. But, the only modern GA trainers besides the Diamonds are the LSA type aircraft. Our Van's RV-12 is great for teaching stalls, far better than the C-152/Warrior.

Fluglehrer 11-24-2014 10:11 PM


Originally Posted by E2CMaster (Post 1770603)
Also remember, stall speed is predicated off of a slow decel rate as well.. You whip it over to 60 and pull, and it's going to stall at a higher speed, even without an abrupt pullup.

Of course, do this with an AOA gauge, and you can see the transient high AOA before speed and AOA come back to jiving with each other.

E2CMaster, I have no idea what you are talking about here. When you "whip it over to 60 and pull" it will stall at about 140% of your normal stall speed, assuming you are in a level turn. The level turn is just so you aren't pulling more than 2 g's (load factor at 60 deg bank) which I guess you would be exceeding if you had an abrupt pullup instead of maintaining level flight. The abrupt pull-up or any stick pulse past the position of critical AOA will stall your wing, and it will do it immediately, you don't have to wait at all for anything to catch up.

Teaching students the stall-speed/bank angle relationship is just so students know why we don't bank excessively when trying to keep from overshooting final (You can do the math on the ground, that's where I teach all my math). You can bank 90 deg and not stall as long as you don't pull, and if that's what you are saying, I understand. That was my point about the stick/AOA relationship. The plane will always stall when the stick/yoke reaches a certain aft position -- whether you are fast, slow, level, banking, inverted, "maneuvering dynamically", or just slowly decelerating. The AOA gauge will confirm that.

Fluglehrer 11-24-2014 10:56 PM

Every plane (except a few, most notably the Airbus) has an "AOA gauge" -- the yoke or stick. Until you get to a deep stall, that relationship between stick position and AOA is very direct.

I still rely on buffet to indicate a stall, but many planes don't give you much buffet. Many swept-wing transport aircraft will just have a hard time keeping the wings level during a stall, but won't give typical GA-like buffet, and just about all jets rely on artificial feedback/feel -- the loss of which is one reason a DC-10 crashed at O'Hare on takeoff in May 1979. Here's an interesting case of USAF test pilots (who knew they were going to be flying in a slow-speed regime that day) stalling a plane for thousands of feet before they realized it: Cargo Jet Nearly Fell During Test - Chicago Tribune

The A-10 has a straight wing, but had very little change in buffet when you exceeded the critical AOA -- the nose track just abruptly slowed way down, which was easy to tell and self-critiquing during BFM.

I think if the pilot of AF447 had a better understanding of why planes stall and how to recover, he wouldn't have been pulling back on the stick the whole time as he descended 35,000 ft to the ocean. If he had trained with an AOA gauge early in his career, it may have cemented the relationship enough for him to have known what he was actually doing.

Cubdriver 11-25-2014 08:32 AM

The only substantial argument against across the board AoA adoption I have read here today is the one about it being a cockpit distraction. All the other ideas are problems that can be solved or mitigated. The military does not find it much of a cockpit distraction from what I understand, and going out on a limb a little bit I think if you require AoA in all new primary training aircraft and thoroughly revamp the FAA primary pilot training liturgy the same way it was revamped for glass cockpits a few year ago, you could remove a lot of distracting material and replace it with AoA awareness techniques in lieu of a bunch of other training tasks. At any rate, tests can be done with and without the AoA instruments in ground sim to see whether they are distracting or not.

I would vote for a suite of 4 gauges rather than one, because until you know left & right AoA values for both tail and main wing you really do not have an adequate picture of the global lift regime. I also feel the present crop of dumbed-down retrofit AoA gauges without number scale are the right approach. It's too much like an idiot light in a passenger car, just another black box warning to disregard. A fairly accurate number band with color designations is the best presentation in my view, and it can be digitally enhanced to include attitude corrections the same way virtual attitude indicators shout messages to the pilot in unusual attitude scenarios. I would not argue for mandated inclusion in existing aircraft due to expense mostly, but you have to start somewhere.

BoilerUP 11-25-2014 08:35 AM


Originally Posted by Cubdriver (Post 1770799)
The only real and substantial argument against across the board AoA adoption I have read here today is the one about it being a cockpit distraction.

I think there's an extremely valid argument against "across the board AoA adoption" in the sense of a value proposition for a retrofit mandate for the existing fleet.

If Part 23 gets revised to require AoA in the future, more power to it and it would be a good thing IMO. But requiring Joe Sixpack to put an AoA on his Cherokee 140 would be of questionable public benefit for the expense induced.

cardiomd 11-25-2014 03:48 PM

Great posts, Fluglehrer.

I'd add that in my 182, it will drop a wing very aggressively with a nose-high power on stall. Have to be prepared, and this is one of the reason that high performance endorsements are needed - if you are not quick with the rudder you will be pointed toward the ground in a half spin, (which it will come out of into a dive).

Secondly in addition to below (all of what you described is Flying 101 well, maybe Flying 102) I'd have the student practice the falling leaf to get a good hang of the rudder control. It is actually a lot of fun too.


Originally Posted by Fluglehrer (Post 1770558)
Simple things that flight instructors can teach to help prevent stalls and understand AOA without needing an AOA gauge:

1. Explain the relationship of bank angle to stall speed increase in a level turn (these are within about 1% accuracy, and easy to compute)
30 deg = 10% stall speed increase
45 deg = 20% stall speed increase
60 deg = 40% stall speed increase

2. Have the student note where the yoke/stick is when the aircraft stalls. This will be the yoke position required to exceed the critical AOA at any speed and weight (assuming configuration stays the same). Also note the difference in yoke position to stall the aircraft with flaps up vs flaps down.

3. Practice accelerated stalls with the student after noting the yoke position required to exceed the critical AOA. This will reinforce point #2.



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