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AOA indicator



 
 
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  #111  
Old May 2nd 16, 03:08 AM posted to rec.aviation.soaring
kirk.stant
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Default AOA indicator

On Sunday, May 1, 2016 at 8:20:34 PM UTC-5, wrote:

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


Dan, please explain how a "working" AOA indicator could lead to a false sense of security? I know how a working airspeed indicator can, and I also (from personal experience - war story) know how a "not-working correctly" AOA indicator can lead to a false sense of security; which is why you are taught to cross check the two to make sure they are both working and make sense..

Last comment on AOA vs Airspeed. AOA is a control instrument, like an attitude indicator or yaw string. Airspeed is a performance instrument, like the altimeter and variometer.

Kirk
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  #112  
Old May 2nd 16, 03:09 AM posted to rec.aviation.soaring
kirk.stant
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Default AOA indicator

On Sunday, May 1, 2016 at 7:36:58 PM UTC-5, 2G wrote:

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.



No. Airspeed is exactly that - how fast your glider is moving through the air. I can be at 60 knots and zero angle of attack, or at 60 knots and stalling angle of attack (depending on the plane). But your glider will only stall at the stalling AOA, period. The reason we use ASI is tradition and ease of measurement, and the fact that in most flying airspeed is a suitable stand-in for AOA - assuming you know the speeds for various wing loadings, bank angles, configurations etc... But if you forget that you are heavy, and bank a bit too much, and slow down a bit too much, and your plane will stall (yes, most gliders may not), and you remember the wrong airspeed, or you are in a new-to-you plane or you are tired and forget...airspeed can lie - AOA cannot. Period. Luckily for us, gliders are usually extremely forgiving, and we can get by on "feel". Most of the time. Apparently power planes are not so forgiving, which is why almost all require at least a basic AOA system: a stall warning indicator! The Pawnees I tow with definitely have a big red light in the middle of the panel hooked up to a vane on the leading edge - tripped when approaching stall AOA. Interestingly, the Supercub I also tow in does not - I guess cub pilots were either better trained or less valuable ;^)


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).


It's a fun little experiment. But not very practical in the real world for a bunch of reasons.

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.


Not at all, I've had my share of upsets in gusty thermals. And the fix is the same whether you fly airspeed or AOA/Attitude: fly faster by lowering your AOA to give you more pad above stall. As far as not being able to stall a glider above 30 degrees of bank, so what? That just means that you are elevator limited, but you still want to fly as close to optimum AOA as possible, and it's nice to know what that is. Or do you just pull till the stick is in you lap and live with whatever it gives you? Somehow, I don't think that is an efficient way to thermal. Oh, and some gliders will stall very nicely at steep bank angles, by the way; the fabulous 2-32 comes to mind!

A stall only becomes a spin if you are unprepared for it and respond incorrectly. Knowing why you are about to stall is a good start, IMO. If you are focusing on airspeed to determine if you are stalled or flying, you are focusing on the wrong parameter - you need to decrease your AOA before you can fly, regardless of airspeed!

Cheers,

Kirk
66
  #113  
Old May 2nd 16, 03:38 AM posted to rec.aviation.soaring
[email protected]
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Default AOA indicator

As to an AOA leading to a false sense of security, the key word is "working" as we have discussed all of the variables that need to be accounted for to have a usefull gayge for sailplane application. But given someone developes an AOA that accounts for them, there is the gust factor. This is the one variable that in my opinion can not be eliminated. Since they occur so instantaneously, if a guy is relying on the AOA or for that matter the airspeed indicator to tell him hes in trouble, its already too late.

Secondly, while the pawnee and most other spray planes have a stall warning based upon airflow they are worthless. So much so that as I stated in an earlier post, most duster pilots either disengage them or ignore them.

The very first thing I do when flying an unknown aircraft or one I have limited experience in, I take her up and run a stall series. I want to directly know what she is like in slow flight and what she tells me around the slow end of the envelop. I also want to know how she actually stalls. Case in point that wonderfull 2-32. She breaks sharply and rapidly with not much warning, as does my old pilatus. In fact I do this with every aircraft I am tasked with flying. Pawnees vary in their behavior. I once flew one which would fall off rapidly and suddenly to the right if just a little right rudder was held in near the stall, but was as gentle as a pussy cat when flown on the edge to the left. She had to have been crooked due to all her previous accidents and repairs.

What I am attempting to do in each of these excercises is teach my butt and flight senses to memorize the symptoms and behavior of the craft way before or irrespective of what the flight manual numbers say or for that matter what the airspeed says. Our pawnee back at my home club in FL is a good 20 mph off. Reading 80 mph indicated is in actuality 60 mph. If a guy doesnt "feel" what that pawnee is doing and just goes by the indicated airspeed he is gonna be in deep ****.
Dan
  #114  
Old May 2nd 16, 03:48 AM posted to rec.aviation.soaring
[email protected]
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Default AOA indicator

Rereading some of the earlier posts, you brought up the same point I am trying to makeOn Wednesday, April 13, 2016 at 9:56:34 AM UTC-5, Soartech wrote:
Too many skilled pilots continue to spin in which makes me wonder if their ships don't give any hint of approaching stall or what else is going on.

"I think a lot of pilots, both low-time and skilled, spend way too little time exploring the corners of the envelope of their gliders - both high and low speed, negative to positive Gs, shallow to steep banks.

Get high and practice trying to kill yourself in the pattern, to the point that you recognize instinctively a dangerous condition and apply the right corrective actions. This is a basic flying skill, NOT an intellectual exercise! "

Kirk
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  #115  
Old May 2nd 16, 04:26 AM
Skypilot Skypilot is offline
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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
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Last edited by Skypilot : May 2nd 16 at 04:40 AM.
  #116  
Old May 2nd 16, 09:31 AM posted to rec.aviation.soaring
Bruce Hoult
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Default AOA indicator

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.
  #117  
Old May 2nd 16, 05:53 PM posted to rec.aviation.soaring
Dan Marotta
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Default AOA indicator



On 5/1/2016 8:09 PM, kirk.stant wrote:
you need to decrease your AOA before you can fly, regardless of airspeed!

Some folks just don't get the above simple statement and will argue the
point to the death (hopefully figuratively). Frankly, I'd love to
replace my ASI with a good AoA, but I don't see anything available that
would fit the bill, not to mention the sometimes not so thoughtful FAA
that would bust you for not having an ASI. And yes, Virginia, you
/_can_/ fly in a 90 deg bank without stalling (for a little while, at
least). Note that I didn't say, "level", a word often left out in these
discussions.
--
Dan, 5J

 




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