AoA keep it going!

Kirk,

Could you summarize for me _how_ you used the AOA indicator in those
aircraft, which aircraft and under what conditions ?

I am curious to the actual use(s).

Thanks
Todd Smith
3S

Sure. I used AOA in T-38s (a little - not much flight time in those)
and in F-4s (about 2000 hours in those). In my current job, I fly a
variety of F-15 simulators (the real thing, not PC games) and use AOA
all the time. Have also a few flight in F-16s and a lot of time in
F-16 simulators, which use AOA in the approach and landing
configuration.

In a nutshell, AOA is used anytime optimum performance is required
from the wing - be it turning, flying an approach, flying for max
range, recovering from a dive, etc. Since fighters can vary weight a
lot due to fuel burn and store (weapons) configuration, it's
impractical to try to use airspeed other than as a general guide to
your energy state - your airspeed tells you how much instantaneous
energy you have to maneuver, then you fly at the AOA that matches the
type of turn you want - less AOA is conserves energy, more AOA turns
faster, etc. If you are flying for max range or max endurance, again
there is a recommended AOA to fly at - it will stay the same while
the actual airspeed changes based on gross weight, configuration, and
altitude. Finally, in the pattern, you figure out the approximate
airspeed and AOA based on fuel and stores remaining, then crosscheck
the two - if they agree, it's easier to fly AOA on most jets (F-4
especially, F-15 less so).

Now, compared to gliders, these are all extremely low aspect ratio,
and that will exaggerate AOA effects. But the aerodynamic priciples
are the same.

Finally, someone questioned about whether it's better to thermal
efficiently or in the best part of the themal. The answer, IMHO, is
that you should strive to do both. Right now we have wonderful
instruments to help us find the best lift. But we still use a crude
instrument to fly efficiently. Well, actually, most people probably
thermal more by feel and attitude than by staring at the airspeed
indicator.

End of war story.

Cheers,

Kirk

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.


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

kirk.stant wrote:
In my
experience, light power planes not really more susceptible to approach
stalls than gliders,

By approach stalls, so you mean stall on final approach? I thought that
was a rare accident gliders, and that most stalls during landing
occurred in the turns.

but there are more distractions - including that
noisy thing in the front just waiting to quit! Yet they mandate stall
warnings.

I don't know the reason that it's mandated, but that noisy thing up
front does change things significantly. For example, under power in my
motorglider, the nose attitude at 50 knots can vary from below the
horizon to above the horizon; the attitude while gliding at 50 knots is
constant and consistent. So, I suggest determining a safe AOA is harder
in powered aircraft, and this makes a stall warning more valuable.

--
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

John Smith wrote:


The solution is simple: Just don't get slow on your turn to final.

Thank you, John. Go to the head of the class.

Now, what is "slow"?



Jack

On 20 Dec, 01:55, J a c k wrote:
John Smith wrote:
The solution is simple: Just don't get slow on your turn to final.

Thank you, John. Go to the head of the class.

Now, what is "slow"?

That depends on the day. If wind shear is likely it will be
significantly higher than on a calm day. Which means, of course, that
on a windy day the safe AoA for the final turn will be significantly
lower than on a calm day ...

Ian

On Thu, 20 Dec 2007 01:55:25 GMT, J a c k
wrote:


Now, what is "slow"?

The simple fact that you arre still able to write this proves that you
know what "slow" is...


Bye
Andreas

"Andreas Maurer" wrote in message
:



Now, what is "slow"?

The simple fact that you arre still able to write this proves that you
know what "slow" is...






Or he is lucky!



Larry

01-- Zero One wrote:
"Andreas Maurer" wrote in message
:

Now, what is "slow"?

The simple fact that you arre still able to write this proves that you
know what "slow" is...




Or he is lucky!


Oh, I am--very lucky--and have been for a long time.


Jack

On 24 Dec, 07:26, J a c k wrote:

Oh, I am--very lucky--and have been for a long time.

As Arnold Palmer is reported to have said:

"It's a funny thing, but the more I practice, the luckier I get."

Ian