AoA keep it going!

On 20 Dec, 14:42, "kirk.stant" wrote:

Ian, we appear to be comparing apples and oranges - you are talking
about not stalling on final, while I am talking about being able to
accurately thermal, and incidentally have a better instrument for
flying accurate approaches.

I wonder how much "flying at Clmax" matters in good thermalling
compared with "being in the right bit of the thermal"?

Obviously, my opinion is colored by having actually flown airplanes
with excellent AOA systems, and by my wish to optimise my soaring for
XC and racing. I really think that within a few years someone will
come up with a simple, low drag, accurate AOA system that will be
adopted by the same group of pilots who eagerly adopted radios, TE,
audio varios, glide computers, GPS, PDA moving maps, transponders,
ELTs, traffic detection devices - all those "unecessary" gadgets that
clutter up our cockpits but, in my opinion, make soaring safer, more
efficient, and more fun.

If it does these things I'll be all for it. If it costs less than
twenty quid I may even buy one. As a matter of interest, how do you
define "efficient" here?

Ian

Ian wrote:
On 20 Dec, 14:42, "kirk.stant" wrote:

Ian, we appear to be comparing apples and oranges - you are talking
about not stalling on final, while I am talking about being able to
accurately thermal, and incidentally have a better instrument for
flying accurate approaches.

I wonder how much "flying at Clmax" matters in good thermalling
compared with "being in the right bit of the thermal"?

Minor correction: you should be thermaling at min.sink, which is the
point at which Cl^3/Cd^2 is maximized.

This is not in general the same as Cl max. Min.sink is usually at a
slightly lower AOA than CL max because Cd is rising steeply with
increasing AOA in the Cl max region. As a result, by the time you've
slowed to Cl max you've passed min.sink and your sinking speed has
started to increase.

Since the polar is usually flatter on the faster side of min.sink I
think you're better off thermaling somewhere between the min.sink and
best glide speeds, preferably nearer the former. Best glide is the speed
where Cl/Cd is a maximum.


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martin@ | Martin Gregorie
gregorie. | Essex, UK
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