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
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