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Old Sep 03, 2010, 10:45 PM
Culper Junior
eastern pa
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Question
High Alpha/Angle of attack

Just a simple question-are High Alpha and a high Angle of attack one and the same? Could a particular kind of flight attitude be described by both definitions and be correct? Or are they different flight modes?
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Old Sep 03, 2010, 11:06 PM
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Alpha is just the Greek name for the letter A. So high alpha just means high angle (of attack).

The terms AOA, Alpha and Angle of Attack and Pitch attitude are r synonymous. Although in different airframe communities or different facets of industry one might be more fashionable than another.
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Old Sep 03, 2010, 11:15 PM
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It is a nose high attitude that puts the airplane in a difficult situation for a beginner. The plane will be near stall attitude or actually under stall, being held up by the propeller thrust acting like a heli rotor.
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Old Sep 03, 2010, 11:33 PM
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Quote:
Originally Posted by hercdriver7777 View Post
Alpha is just the Greek name for the letter A. So high alpha just means high angle (of attack).

The terms AOA, Alpha and Angle of Attack and Pitch attitude are r synonymous. Although in different airframe communities or different facets of industry one might be more fashionable than another.

Not to be overly picky, but "Pitch attitude" isn't a synonym of the others. Pitch is the angle between the fuselage datum line and the horizon, where as AoA (or alpha) is the angle between the wing and the airflow. Those two values can differ if in climbing or decending flight, or when the airframe encounters lifting/sinking air, or if the wing has a non-zero angle of incidence (angle between the airframe datum on the wing) built in.


Regards,
George
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Old Sep 04, 2010, 12:13 AM
Shore Huckin'
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+1 on gmohr...BTW..what are you? An aerodynamicist
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Old Sep 04, 2010, 01:57 AM
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People also use High Alpha to describe knife edge which refers to the fuz, whereas AOA and Angle of Attack refer more to the state of the wing, perhaps actually pitch angle would be ok to use with KE.
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Old Sep 04, 2010, 02:13 AM
Shore Huckin'
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Threshold,

Just to parse you a little. HAKE (high alpha knife edge) is a type of knife edge...not all knife edge flight is high alpha.

High alpha knife edge is with nose high while knife edge can be with fuselage nearly horizontal with the ground. HAKE is flown slower with less throttle and more rudder while KE is higher speed and less rudder.

Gmohr, correct me if I'm wrong here. Pitch angle should actually be zero in linear KE flight. The "high alpha" in high alpha knife edge is actually refering to the yaw angle (or angle of attack of the fuselage rather than the airfoil). I don't think just because the plane in rotated 90 degrees in knife edge flight that the actual axes are relabeled.
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Old Sep 04, 2010, 06:46 AM
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Quote:
Originally Posted by gmohr View Post
Not to be overly picky, but "Pitch attitude" isn't a synonym of the others. Pitch is the angle between the fuselage datum line and the horizon, where as AoA (or alpha) is the angle between the wing and the airflow. Those two values can differ if in climbing or decending flight, or when the airframe encounters lifting/sinking air, or if the wing has a non-zero angle of incidence (angle between the airframe datum on the wing) built in.


Regards,
George
No worries. Good point.
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Old Sep 04, 2010, 08:00 AM
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Quote:
Originally Posted by Threshold View Post
People also use High Alpha to describe knife edge which refers to the fuz, whereas AOA and Angle of Attack refer more to the state of the wing, perhaps actually pitch angle would be ok to use with KE.
When you're flying KE, the fuselage effectively becomes the wing, in the sense that that's the part of the plane which is now producing lift. So I would say that doesn't really count as a different usage of AoA. I suppose you could generalize the definition of AoA by replacing "wing" with "lift producing part of the plane", as in

Angle of Attack: The angle between the main lift producing part of the plane (wing when upright or inverted, fuselage in knife edge) and the airflow.
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Old Sep 04, 2010, 08:15 AM
Irg
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don't some people refer to HAKE as "high beta"?
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Old Sep 04, 2010, 08:49 AM
Scott Stoops
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Quote:
Originally Posted by Irg View Post
don't some people refer to HAKE as "high beta"?
Yes. Alpha is a pitch based term, while beta is a yaw based term.

Scott
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Old Sep 04, 2010, 09:15 AM
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So it's AABBA and your doing the cha cha ?
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Old Sep 04, 2010, 10:45 AM
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Quote:
Originally Posted by KE Spin View Post
Threshold,

Gmohr, correct me if I'm wrong here. Pitch angle should actually be zero in linear KE flight. The "high alpha" in high alpha knife edge is actually refering to the yaw angle (or angle of attack of the fuselage rather than the airfoil). I don't think just because the plane in rotated 90 degrees in knife edge flight that the actual axes are relabeled.

This depends on the frame of reference that you chose. Typically though, we're using the earth axis as our frame, so "pitch" is the angle of the fuse datum line measured against the horizon. So in level KE flight, that datum is pitched up to provide lift, using the fuse side as a lifting body. Even though the plane has 90 deg of roll, it is still said to have, say, 15 deg of pitch. The axes "labels" are in reference to earth, not the airframe. A good illustration is a plane in a level climb with 10 deg of pitch. Roll that plane 15 deg left, and we'd still say it has 10 deg of pitch. Roll it the next 75 deg, and it still has 10 deg of pitch, etc..

It is possible to redefine the frame of reference to any arbitrary set of axes, so this isn't a hard rule, just a convention.

One other cool point to think about... in this instance, we've been talking about "pitch" with regard to "attitude", which is earth centric. We can also use the term "pitch" to describe rate of change of the plane's orientation, in which case the frame of reference is airframe centric. So if the pilot of that KE flying plane suddenly pulls a couple of G's, we can say that the plane has a "pitch rate" of 30 deg/second, while at the same time having a constant "pitch attitude".


Quote:
Originally Posted by KE Spin View Post
+1 on gmohr...BTW..what are you? An aerodynamicist
Nope, but I've been told I have a slight obsession with details

Regards,
G
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Old Sep 04, 2010, 07:04 PM
Shore Huckin'
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Looks like Scott and Gmohr have out shined the rest of us mere mortals so I declare a tie between them :-)

So, Scott and Gmohr, here is the tie breaker:

I'm driving along in my car at the speed of light. It starts getting dark so I turn on my headlights....What happens?
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Old Sep 04, 2010, 08:53 PM
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I yield
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