What is "Angle of Attack"? Can you throw with it?

[un4fR4y3d]

Who here's an expert on aerodynamic physics terminology or likes to express ideas about it?

Can you throw a disc with an angle of attack? I am a little confused by how the term is used by Canadian Professor Vance Morrison in his description of a "Java Class for Calculating the Trajectory of a Frisbee." He says that in his studies, he simulating throwing a frisbee with various angles of attack, seven degrees and more.

Frisbee thrown at 10 degrees "Angle of Attack"

According to Wikipedia, however, 'angle of attack' is a measure of the chord of the disc to the direction of travel. Discs are generally thrown with very little or ideally no angle between the chord and the direction of travel. The angle, or pitch, is measured by the chord of the disc to the earth.

The arrow is the vector representing the velocity of the air in the free stream around a stationary two-dimensional section of airfoil. The upper red line is the chord line of the airfoil and the lower red line is parallel to the arrow. The angle α is the angle of attack.
-- Wikipedia, Angle of Attack.

I am interested in knowing if they have different terms in Canada or if there might be other reasons or explanations why it might not be in error to simulate frisbee flight using physics based on an angle of attack.

 

[Stringbean]

Nose up, nose down, flat, hyzer angle, anhyzer angle... all are in reference to the "angle of attack".

 

[un4fR4y3d]

Well, if angle of attack is a measure of the difference between the chord and the direction of travel, it has a specific meaning.

I think people are misusing the term; that in reality, we minimize the angle of attack or reduce it to zero and we rarely ever discuss or talk about angle of attack. It's not relevant to disc golf except when describing the flight characteristics of a frisbee from an aerodynamic perspective. Angle of attack is much more relevant to aircraft -- aircraft have a wing attached to a body that can be turned to a different angle than the direction of travel. This is what causes directional lift. Frisbees mostly have aerodynamic lift, but, to have any significant directional lift, someone would have to hold the frisbee at an angle to the direction of travel in order to maintain any significant angle of attack.

Pitch, nose up, nose down ... these are absolute references of the chord of the disc in relation to the ground. Angular momentum will cause a disc to have a slight angle of attack, but, a disc will not fly with an angle of attack any greater than a few degrees. If thrown at a few degrees angle of attack, the disc will wobble in the pitch direction until it stabilizes.

It's easy to think angle of attack is relevant or important to disc golf. We are all familiar with wings and would naturally think that the same terms would apply to disc golf. Actually, Angle of Attack is a real drag in disc golf.

When people misuse the term, it makes it unclear as to what they are talking about. As an example, people have applied mathematical formula for calculating the amount of lift produced when a Frisbee is thrown with x initial velocity at a a given angle of attack. Such formulas work when applied to aircraft when an aircraft is launched/thrown with wings at an angle of attack to the direction of travel, but, are probably not valid for calculating the flight of a disc (although they produce nice data that looks like the flight of a frisbee).

Perhaps what is going on here is that the disc golf community is appropriating the term outside of it's scientific meaning and using it in a more general sense to describe the angle between the intended flight path and the ground. The measure of the chord to the direction of travel is an important measurement in disc golf and we should have terms that clearly distinguish between the hyzer/anyhyzer angle and the pitch (or chord to ground angle). 'Pitch Angle' 'Vertical Angle' 'throwing angle' 'angle of throw' describe the angle I am talking about. However, for technical discussions of the flight of a frisbee, we still need a term that precisely defines the angle of attack. To avoid confusion, I suggest that we use some words other than "angle of attack" to describe the pitch or throwing angle, for lack of better terms.

 

[JR]

No physicist here so i will not put words into their mouths about what their definition and usage of the words angle of attack is. A disc thrown with nose up will often stay nose up not stabilize our of wobbling. In fact a nose up throw does not need to wobble at all. The nose up angle along with spin adds hss to the disc. And nose down flips the disc more than a flat throw. Because the moment of inertia times the vector defined by the nose angle i think physicists do call it the angle of attack, but what do i know, equals the force that resists flipping.

 

[un4fR4y3d]

Dang. Discs seem to have a lot of attitudes. (it's a pun, grin dammit)

I understand that one might want to put a tiny touch of nose up or nose down attitude/pitch/angle to the direction the disc is released in. That little tiny touch is technically termed the angle of attack. But, one wouldn't release a disc with a 7.5, 10, or 12 degree angle of attack as an aircraft might be released with wings fixed at a 7.5, 10, or 12 degree angle of attack. I don't think you would want to apply mathematical physics for calculating the lift produced by wings at an angle of attack to the direction of travel ... you'd want to apply the mathematical physics of aerodynamic lift as the primary lift force because a disc does not have the same flight characteristics of a fixed wing aircraft.

I am just saying for general discussion, using 'angle of attack' to describe the pitch of release is ok for informal discussion, but, when trying to accurately describe and explain the physics of disc golf flight, it should only be used to describe the angle between the chord and direction of travel.

 

[Stringbean]

Wouldn't nose up or nose down still apply? Usually those are the terms used in informal discussion.

 

[un4fR4y3d]

ah, nose up and nose down refers to angle of attack! thanks that's brilliant; now I understand JR's comment better though I'm still puzzling over what 'hss' is:

The nose up angle along with spin adds hss to the disc. And nose down flips the disc more than a flat throw.

 

[Stringbean]

High speed stability.

 

[Stringbean]

Blake has an excellent article on the homepage on this topic.

http://www.discgolfreview.com/resources/articles/angles.shtml