AOA indicator

The most important thing is not either of those two instruments, its your ass, and situational awareness. Most folks get into stall/spin trouble by not having a clue that they are flying on or approaching the edge. An instrument only helps when theres time to scan it, but your ass can tell you immediately whats going on.
Dan

Whittle... :-D

Dan - 5J

On 4/30/2016 8:01 AM, kirk.stant wrote:
On Friday, April 29, 2016 at 6:18:00 PM UTC-5, 2G wrote:

Gliders are flown substantially differently than most other aircraft: we circle just above stall speed at high bank angles. A stall warning would be going off continuously and would be more annoying than anything. Above 30 degrees bank angle I find it impossible to stall the glider anyway; a stall will usually occur because of a gust. I don't know what an AOA indicator would add because AOA varies from the inner wing tip to the outer wing tip. The MOST important thing to do is to maintain coordinated flight. Maybe you could put an audible warning on the yaw string!

Tom
Tom, in many respects gliders are flown just like fighter planes - either fast or hard turning, at varying g loads and weights. Which is why AOA is often used instead of airspeed in those conditions. This is not a stall warning system, but an indication of what the actual AOA of the plane is. It can be an averaged indication - the critical AOA will be the same once calibrated. Momentary excursions due to gusts are handled just like on the airspeed indicator - you ignore them!

Amazing how almost everyone who actually hasn't used a real AOA system dismisses the concept out of hand. Kinda reminds me of the Brits before WW2 who totally dismissed Frank Whittle's ideas about jets (after all, he was just a lowly Flight Lieutenant) and as a result missed out on possibly having jet fighters during the Battle of Britain...

Cheers,

Kirk
66

--
Dan, 5J

On Saturday, April 30, 2016 at 9:07:40 AM UTC-5, kirk.stant wrote:
On Friday, April 29, 2016 at 6:18:00 PM UTC-5, 2G wrote:

The MOST important thing to do is to maintain coordinated flight. Maybe you could put an audible warning on the yaw string!

Tom

I don't agree. The MOST important thing is to not exceed stalling AOA. Below that, yaw (within limits) adds drag (or may help a bit - see discussions about slipping turns while thermalling) and may be less efficient; but you can still control your glider - exceed the critical AOA, and you are a passenger until you reduce it.

Airspeed indicators are required (which are indirect AOA indicators). Yaw strings or slip balls are not.

Kirk
66

I think you got it right, Kirk. Not all of us can be fighter pilots but we all can learn about AOA and how critically important it is in most flight regimes. Every couple of years I read my "Stick and Rudder" by Langewiesche.. He was a very smart man and put things together 70 years ago that are still a mystery to many of us.

On Saturday, April 30, 2016 at 10:01:15 AM UTC-4, kirk.stant wrote:
Amazing how almost everyone who actually hasn't used a real AOA
system dismisses the concept out of hand.

Some years ago, I was asked to evaluate an AOA sensor (vane type,
mounted on a Duo, with an audio warning). Even in a relatively
smooth thermal, it squawked often for no good reason (I'm pretty
familiar with the Duo and my thermalling doesn't really suck bad).
With sensitivity turned down, it didn't give indication until
too late to be helpful (yes, I know, I already stalled).

I don't know whether it is possible to make something that
is helpful safety-wise. With a gear-down interlock it won't
help the guy thermalling low.

For what its worth from somebody who has tried one in a glider,
Best Regards, Dave

I don't know if using AoA for safety would really work in a glider unless it was mounted and calibrated to remove gusts and other abnormalities. One idea would be a speed sensor matched with AoA over a 10 second gap below 1000'agl. Then all it does is say "speed speed" like bitching Betty.

I guess it's important to point out that the is a big difference in pitch and AoA in our type of Ops.

I think they could be useful matched to a Johnson type of drag meter.

I.e. Flap setting vs speed in different thermal strengths.
AoA to fly on long skinny glides and near the ground.
AoA to fly with underpowered turbos
AoA to fly in wave

I guess at some point we will move to HUD's. Once we do that there will be a plethora of stuff available to us. I guess the speed to fly will be a pipper based on track and macready, perhaps it will default to AoA at stable critical times such as the classic low level stall spin.

Just a thought from someone who flew the death pencil "Metroliner" and the AoA was pretty important.

Justin

Originally Posted by Dave Nadler

On Saturday, April 30, 2016 at 10:01:15 AM UTC-4, kirk.stant wrote:
Amazing how almost everyone who actually hasn't used a real AOA
system dismisses the concept out of hand.

Some years ago, I was asked to evaluate an AOA sensor (vane type,
mounted on a Duo, with an audio warning). Even in a relatively
smooth thermal, it squawked often for no good reason (I'm pretty
familiar with the Duo and my thermalling doesn't really suck bad).
With sensitivity turned down, it didn't give indication until
too late to be helpful (yes, I know, I already stalled).

I don't know whether it is possible to make something that
is helpful safety-wise. With a gear-down interlock it won't
help the guy thermalling low.

For what its worth from somebody who has tried one in a glider,
Best Regards, Dave

I may be weird, but I see four scenarios in which an audio AoA meter would be helpful enough to me that I'm tempted to prototype one:

1. Aerotow, increasingly raucous warning as AoA approaches stall. Recognized by landing gear down, acceleration profile corresponding to aerotow, dynamic pressure has been close to zero since last time landing gear was up.

2. Winch launch, gentle progressive audio warning if AoA goes above or below optimal (calibrated best L/D AoA?), increasingly raucous warning as AoA approaches stall. Recognized by landing gear down, acceleration profile corresponding to winch launch, dynamic pressure has been zero since last time landing gear was up.

3. Thermaling, gentle progressive audio warning if AoA goes above or below optimal (calibrated minimum sink AoA?), option to provide stall AoA warning if it's not annoying. Recognized by landing gear up, appropriate dynamic pressure, acceleration magnitude greater than 1G for 10 seconds or so.

4. Approach, gentle audio warning if AoA goes above or below calibrated approach AoA, increasingly raucous warning warning as AoA approaches stall. Recognized by landing gear down (combined with gear warning if dive brakes open), dynamic pressure has not approached zero since last time landing gear was up.

AoA measurement filtered by a few seconds of moving average combined with gust filtering. If it's quiet, I'm almost certainly doing OK, only annoying if I get out of the envelope for a given scenario. Fairly trivial to program using a pair of available cheap high resolution digital interface differential pressure sensors and a two port probe. Recognizing the difference between aero and winch launch will likely take a bit of cleverness.

On Saturday, April 30, 2016 at 12:57:10 PM UTC-5, Dave Nadler wrote:

Some years ago, I was asked to evaluate an AOA sensor (vane type,
mounted on a Duo, with an audio warning). Even in a relatively
smooth thermal, it squawked often for no good reason (I'm pretty
familiar with the Duo and my thermalling doesn't really suck bad).
With sensitivity turned down, it didn't give indication until
too late to be helpful (yes, I know, I already stalled).

Nice to know someone is trying, but it sounds like the AOA sensing mechanism needs developing - if the overall AOA of the Duo's wing was jumping around that much, I would think performance would suffer!


I don't know whether it is possible to make something that
is helpful safety-wise. With a gear-down interlock it won't
help the guy thermalling low.

As always, the devil is in the details - how to measure and display useful information.

If you think about it, we already use a coarse AOA indication while thermalling - nose position relative to the horizon. We then crosscheck against airspeed (and "feel") and adjust accordingly. That really wouldn't change with a working, glider-optimized AOA system, it would just allow better calibration of our "feel" vs what is really happening - and provide a useful warning if we misjudge and get too slow.


For what its worth from somebody who has tried one in a glider,
Best Regards, Dave

Interesting. Thanks.

Kirk
66

On Saturday, April 30, 2016 at 8:43:09 PM UTC-4, Skypilot wrote:
...calibrated to remove gusts and other abnormalities...

Except that's when a wing stalls...

One idea would be a speed sensor matched with AoA over a
10 second gap below 1000'agl.

It takes less than 10 seconds to spin into the ground.

...I guess at some point we will move to HUD's...

To interfere with our vision of thermal clues and traffic?

Always trade-offs...
Hope that helps clarify,
Best Regards, Dave

On Saturday, April 30, 2016 at 7:07:40 AM UTC-7, kirk.stant wrote:
On Friday, April 29, 2016 at 6:18:00 PM UTC-5, 2G wrote:

The MOST important thing to do is to maintain coordinated flight. Maybe you could put an audible warning on the yaw string!

Tom

I don't agree. The MOST important thing is to not exceed stalling AOA. Below that, yaw (within limits) adds drag (or may help a bit - see discussions about slipping turns while thermalling) and may be less efficient; but you can still control your glider - exceed the critical AOA, and you are a passenger until you reduce it.

Airspeed indicators are required (which are indirect AOA indicators). Yaw strings or slip balls are not.

Kirk
66

Well, I definitely take issue with "ASI are indirect AOA indicators". This falls into the category of "it either is or it isn't" category.

I am not dismissing AOA indicators since I have never flown with one. I think I will put one on for my next flight (a yaw string taped to the side of the canopy).

You are very dismissive of the roll of gusts: a former FAA administrator was killed by one (and his inability to deal with it). You also did not comment on my comment about not being able to stall a glider above a 30 degree bank angle. Recovering from a straight-ahead stall is a ho-hum event at best; dealing with stall-spins is a totally different animal.

Tom

2G makes some very valid points. Let me add, A slow shallow turn is the killer of many a not-so-wise pilot. The steeper the turn the safer for the following reason;
At steep bank angles as we all know a guy has to hold a whole hell of a lot of back pressure. This high back pressure tells any fool that he had better be carefull with these high AOA's.
Secondly, in this configuration, try increasing the bank angle, the aircraft will not immediately spin but will fall inward trying to drop its nose attempting to gain the speed needed or lesson the AOA it needs to keep flying. The aircraft WANTS to keep flying and will do what is needed on its own if allowed.

In my opinion while a "working" AOA would be somewhat helpfull, both an AOA and an airspeed can lead to a false sense of security. But understanding the dynamics of turning flight is the best key to real safety. Langshweger or however you spell/pronounce his name in the classic "Stick and Rudder" knew this 60 years ago.
Dan