AoA keep it going!

The inside wing; it travels a lesser distance while
sinking the same amount as the outside wing.

No one seems to have observed that the AoA is instantaneous
whereas the ASI indicates what the aircraft was doing
moments ago. The AoA is especially useful for helping
students understand relative wind and its consequences;
this cannot be done with the ASI.

At 02:18 22 December 2007, Denis wrote:
fred a écrit :

A favorite question I use for instruction... Which
wing in a turn has
the greatest angle of attack?

Would you be so kind to give us the answer please ?

Nyal Williams wrote:
The inside wing; it travels a lesser distance while
sinking the same amount as the outside wing.

No one seems to have observed that the AoA is instantaneous
whereas the ASI indicates what the aircraft was doing
moments ago.

I don't think this is true: all the ASI I've had or checked seemed to
respond in less than a second. Surely that's fast enough to keep up with
the glider? Just try blowing gently into a pitot and see how quick the
needle is. If takes "moments" to respond, you should check the indicator
and the pitot line.

The reason we are told to "fly attitude and don't chase the airspeed" is
it takes the glider a while settle down to a steady speed, not because
the ASI is slow.


--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

"Eric Greenwell" wrote in message
news:gi2bj.303$pi7.43@trndny02...
Nyal Williams wrote:
The inside wing; it travels a lesser distance while
sinking the same amount as the outside wing.

No one seems to have observed that the AoA is instantaneous
whereas the ASI indicates what the aircraft was doing
moments ago.

I don't think this is true: all the ASI I've had or checked seemed to
respond in less than a second. Surely that's fast enough to keep up with
the glider? Just try blowing gently into a pitot and see how quick the
needle is. If takes "moments" to respond, you should check the indicator
and the pitot line.

The reason we are told to "fly attitude and don't chase the airspeed" is
it takes the glider a while settle down to a steady speed, not because the
ASI is slow.

Eric,

Just a short observation. If you had an AOA you would notice an AOA
increase as you open your spoilers while maintaining a constant speed and a
decrease as you closed them.

Wayne

Eric,

Just a short observation. If you had an AOA you would notice an AOA
increase as you open your spoilers while maintaining a constant speed and a
decrease as you closed them.

Wayne


Why not? Surely the glider would be sinking quicker so the AoA would
increase when you open your spoilers?
--
Mike Lindsay

Mike Lindsay wrote:
Eric,

Just a short observation. If you had an AOA you would notice an AOA
increase as you open your spoilers while maintaining a constant speed and a
decrease as you closed them.

Wayne


Why not? Surely the glider would be sinking quicker so the AoA would
increase when you open your spoilers?

I agree that, once stabilized at the original airspeed with brakes open
the AOA will be a bit higher to compensate for loss of lift, but the AOA
variation during the transition may depend on the glider type.

Some gliders pitch down automatically and accelerate when the brakes are
opened (G103). Others raise the nose slightly and decelerate as the
brakes are opened, so require a good shove on the stick to hold the
airspeed constant (Puchacz). Ditto an ASW-20 as you select landing flap.
The waggling of the AOA needle may be quite different in these cases.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Wayne Paul wrote:
"Eric Greenwell" wrote in message
news:gi2bj.303$pi7.43@trndny02...
Nyal Williams wrote:
No one seems to have observed that the AoA is instantaneous
whereas the ASI indicates what the aircraft was doing
moments ago.
I don't think this is true: all the ASI I've had or checked seemed to
respond in less than a second. Surely that's fast enough to keep up with
the glider? Just try blowing gently into a pitot and see how quick the
needle is. If takes "moments" to respond, you should check the indicator
and the pitot line.

The reason we are told to "fly attitude and don't chase the airspeed" is
it takes the glider a while settle down to a steady speed, not because the
ASI is slow.

Eric,

Just a short observation. If you had an AOA you would notice an AOA
increase as you open your spoilers while maintaining a constant speed and a
decrease as you closed them.

True, but the ASI is still indicating correctly, not lagging as Nyal
seemed to suggest.

So, do we fly the same AOA with the spoilers open as when they are
closed? Supposed they are just "cracked" open, half open, fully open -
do I need to know a different AOA for each spoiler position?

And if I use landing flaps for the landing instead of the thermal flap
setting, do I need to yet another list of AOA for different spoiler
settings?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Sat, 22 Dec 2007 06:39:08 GMT, Eric Greenwell
wrote:

Nyal Williams wrote:
The inside wing; it travels a lesser distance while
sinking the same amount as the outside wing.

No one seems to have observed that the AoA is instantaneous
whereas the ASI indicates what the aircraft was doing
moments ago.

I don't think this is true: all the ASI I've had or checked seemed to
respond in less than a second. Surely that's fast enough to keep up with
the glider? Just try blowing gently into a pitot and see how quick the
needle is. If takes "moments" to respond, you should check the indicator
and the pitot line.

The reason we are told to "fly attitude and don't chase the airspeed" is
it takes the glider a while settle down to a steady speed, not because
the ASI is slow.

That's precisely his point. Change the AoA, and the drag changes.
Change the drag, and the glider accelerates (positively or
negatively). Then the airspeed changes, and only then does the ASI get
a chance to tell you about it.

"Fly attitude and don't chase the airspeed" really means "fly AoA and
don't chase the airspeed", but if you don't have an AoA indicator, you
have to use the attitude as a substitute for AoA. And it's a
second-rate substitute.

rj

Ralph Jones wrote:
"Fly attitude and don't chase the airspeed" really means "fly AoA and
don't chase the airspeed", but if you don't have an AoA indicator, you
have to use the attitude as a substitute for AoA. And it's a
second-rate substitute.

Please pardon me if I sound a bit cranky, but how can attitude be a
"second-rate substitute" for something that we don't even have?

And what would a "first-rate substitute" be?

Not a single poster here has flown with an AOA meter in their glider,
except a few using yarn taped to the side of their canopy. Is that what
we should be using instead of attitude and airspeed?

"Show me the money".

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Eric Greenwell wrote:
Not a single poster here has flown with an AOA meter in their glider,
except a few using yarn taped to the side of their canopy. Is that what
we should be using instead of attitude and airspeed?

Actually, I have flown with the factory supplied AoA meter (differential
pressure) in my DG-600, but I could never get the darn thing calibrated
properly...

Marc

On Sun, 23 Dec 2007 03:23:59 GMT, Eric Greenwell
wrote:

Ralph Jones wrote:
"Fly attitude and don't chase the airspeed" really means "fly AoA and
don't chase the airspeed", but if you don't have an AoA indicator, you
have to use the attitude as a substitute for AoA. And it's a
second-rate substitute.

Please pardon me if I sound a bit cranky, but how can attitude be a
"second-rate substitute" for something that we don't even have?

And what would a "first-rate substitute" be?


You could probably design one, but okay, I concede the grammatical
point. Let's put it this way: The ASI is to a good AoA meter as Hormel
Potted Meat Food Product is to Underwood Deviled Ham.

rj