AOA indicator

On Saturday, April 23, 2016 at 3:19:47 PM UTC-7, kirk.stant wrote:
On Saturday, April 23, 2016 at 11:59:42 AM UTC-5, wrote:
We all have stall warning horns/lights in ag spray planes. Almost everyone has disconnected them. Another useless instrument when it comes to flying that is necessarily stick and rudder.
Dan

Dan, while I tend to agree that most stall warning indicators are of marginal use if you are current and have lots of experience in a particular plane, remember we are talking about glider pilots - most do not fly that much each year, and many may fly several different types frequently.

Heck, if you are comfortable in your plane, hardly any instrument is really needed. But if I could only have one - it would be a good AOA indicator :^)!

Kirk
66

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

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

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 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 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

QUOTE=Dave Nadler;924639]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..."

I always thought they stalled when the Critical Angle of Attack was exceeded. Therefore if you could remove the inaccuracies of a vane type AoA it would be good.

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


Yes but I cant help but feel if you never ended up in a fully developed spin below 1000' it might be a good start. I suspect that at the end of a 5 hour task having a system that says "hey numpty, you are thermalling below 1000', you are in ery little lift and I have noticed that you keep increasing your AoA, if you continue to do this we might enter a spin from which you may not be able to recover from before we hit the ground. Why don't you unload the wing a little and increase speed to give yourself a nice tight circle with a reduced AoA



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

"To interfere with our vision of thermal clues and traffic?"


Yeah because no cockpit I have ever seen has flarm, moving map or instruments below the coaming. I mean no pilot looks at all that stuff when they should have their heads outside do they ???. Yet one simple piper could give you track, speed to fly and selectable FLARM



kind regards

Justin

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 5:01:15 PM UTC+3, kirk.stant wrote:
Amazing how almost everyone who actually hasn't used a real AOA system dismisses the concept out of hand.

Not me. I'd love one. I merely stipulate that it needs to measure the actual AOA (whether by a vane or differential pitot pressures I don't care), and not *assume* the AOA because of some guesstimated data input to a PDA or "vario" or whatever.

I'm a computer programmer with experience doing embedded stuff. As a result, I have much less faith in them than many others do!

Also, it's FAR easier to optimise something -- that is, to find the maximum or minimum of a smooth function -- than it is to precisely predict the location of a discontinuity such as a stall.