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Rate/Radius of Turn

Old 02-11-2010, 08:31 PM
  #31  
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Originally Posted by Kasserine06 View Post
...Edited for brevity...
Wow, I guess I should have fully read the forum first or skimmed it better. I just realized that I basically copied you word for word. Go me!

X2 for your post/explanation method.
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Old 02-11-2010, 08:32 PM
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Originally Posted by ryan1234 View Post
I'm not sure I understand what it is you're asking, but I'll try to start from scratch and explain as best as I can...

We know that... during a steady, coordinated turn that lift is inclined to produce a horizontal component of lift equal to the centrifugal force in the turn. ... a steady turn is achieved by producing a vertical component of lift equal to the weight of the airplane. If either one of these values do not equal the respective value (i.e. horizontal lift does not equal centifugal force, etc) the airplane will be out of symmetry and some type of acceleration (either positive or negative) will occur (i.e. uncoordination, etc).

I think what you're trying to get at is static stability and dynamic stability. If it is please let us know... that's a whole 'nother topic.
I am responding to UAL who said:

"The horizontal force from the horizontal component moves the airplane at the same rate as the change in direction of flight (and therefore, relative wind), such that there is never any yaw."

What I am confirming is that horizontal lift changes the direction of motion (flightpath), but without a sideforce, the aircraft will not turn, it will only fly sideways. There needs to be something to turn the aircraft around the vertical axis and horizontal lift by itself will not move the aircraft in a circle. The change in the relative wind due to horizontal lift causes a side force to act on the side of the aircraft (behind the c.g.) which causes the plane to turn into the relative wind around the vertical axis.

The turn around the vertical axis has to occur after the change in relative wind, since it is the cause of the other.
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Old 02-11-2010, 09:07 PM
  #33  
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Originally Posted by gestrich19 View Post
I am responding to UAL who said:

"The horizontal force from the horizontal component moves the airplane at the same rate as the change in direction of flight (and therefore, relative wind), such that there is never any yaw."

What I am confirming is that horizontal lift changes the direction of motion (flightpath), but without a sideforce, the aircraft will not turn, it will only fly sideways. There needs to be something to turn the aircraft around the vertical axis and horizontal lift by itself will not move the aircraft in a circle. The change in the relative wind due to horizontal lift causes a side force to act on the side of the aircraft (behind the c.g.) which causes the plane to turn into the relative wind around the vertical axis.

The turn around the vertical axis has to occur after the change in relative wind, since it is the cause of the other.

Ok I'm sure UAL will be able to better answer this, but until then I'll take a stab at it...

Just a note as a basis to start: the aerodynamic sideforce equals zero during a coordinated turn. The rudder deflection (to maintain steady, coordinated flight) neutralizes the sideforce.

What is turning the airplane is the constant force of lift acting completely 'upwards' in relation to the aircraft's reference. The sum of the lift and thrust vectors are what make the 'turn'. Part of the lift force happens to be in a horizontal direction.

Last edited by ryan1234; 02-12-2010 at 08:08 PM.
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Old 02-11-2010, 10:48 PM
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Originally Posted by ryan1234 View Post
What is turning the airplane is the constant force of lift acting completely 'upwards' in relation to the aircraft's reference. The sum of the lift and thrust vectors are what make the 'turn'. Part of the lift force happens to be in a horizontal direction.
Incorrect or not, here is an analogy to help you see where I am coming from. If you were pushing a shopping cart forward, with wheels that caster, while I was pulling the middle side of the cart, 90 degrees to your force, the cart would not turn in a circle like an aircraft does -- the cart would only be moving in a steady new direction to the left or right of the original path. If its not obvious, I am comparing the redirection of the lift vector with "me pulling on the cart".

This is why I thought the weather vane effect was needed as the redirection of lift only explains the change in flight path to me --not actual rotation around any axis.

To confuse matters, the center of pressure is usually located aft of the center to gravity therefore lifting pressure wouldn't rotate you in the direction you want to go anyways.
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Old 02-11-2010, 10:54 PM
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Originally Posted by gestrich19 View Post
horizontal lift changes the direction of motion (flightpath)
Reread this a few times and really think about it: Is "horizontal lift," in this discussion, a force?

Did you have an answer?

...

...

Ok now let me give you a briefing on vectors. Lift is a force, actually a vector component of aerodynamic force, but we can ignore that. When you divide up a force into its relevant vector components, you are determining the directional application of that force. These directions will be split into, for this discussion, the X and Y axis.

For instance, if we place a block on the table and push on it, perpendicularly with another block, we have now applied a force. This force would have no vector components. However, if we push on that same block, this time at 45 degrees, it will have two vector components. One component on the X and one on the Y axis.

In that second application, at 45 degrees, we are left with an x force and a y force. Similarly, when lift force, in a bank, is broken up, we have a vertical (y) force and horizontal (x) force. Like the block, moving at an angle from these two separate forces, the aircraft will do just the same.

So the answer to the question is, yes horizontal lift is a force. While it is merely a vector component, and not the actual force itself, it has the same properties of any force. That is, it causes some action to happen. Since we know a force causes an action to happen and we know the horizontal force exists then we know the aircraft will turn (the action) because of it.



There needs to be something to turn the aircraft around the vertical axis and horizontal lift by itself will not move the aircraft in a circle.
No there doesn't and a simple experiment can prove it. Take one of your model aircraft and make it fly around a turn while looking at it from a birds eye (top down) view. Do you see any rotation around the vertical axis? If you are doing it coordinated, you won't.



The change in the relative wind due to horizontal lift causes a side force to act on the side of the aircraft (behind the c.g.) which causes the plane to turn into the relative wind around the vertical axis.
You keep repeating this, stop. It is wrong. Consider this: by your definition, a B2 (flying wing) wouldn't be an non-flyable aircraft. We both know that isn't true.
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Old 02-11-2010, 11:04 PM
  #36  
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Originally Posted by gestrich19 View Post
If you were pushing a shopping cart forward, with wheels that caster, while I was pulling the middle side of the cart, 90 degrees to your force, the cart would not turn in a circle
It would, if you continued to apply the same force constantly. You are discussing on pull of say 5 pounds. Well how bout you keep pulling with a constant 5 pound force. This would result in you constantly walking 90 degrees to the force ryan is applying to push the cart. The result would be a constantly changing direction otherwise known, a circle. Go test it and see.


This is why I thought the weather vane effect was needed as the redirection of lift only explains the change in flight path to me --not actual rotation around any axis.
There isn't a rotation around any axis to be explained.


To confuse matters, the center of pressure is usually located aft of the center to gravity therefore lifting pressure wouldn't rotate you in the direction you want to go anyways.
Not relevant, see above. Remember, the displacement of the AC vs the CG is countered by TD force. You increase TD force in a level turn don't you?
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Old 02-11-2010, 11:48 PM
  #37  
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Hi All.

I'm seeing a great deal of misinformation and misunderstanding on this thread. The definitive work on all this is "Aerodynamics for Naval Aviators", by Harry Hurt, Phd. This is available from the GPO, of possibly from your local FBO. Harry (now deceased) was a professor at the USC Institute of Safety and Systems Management. He was teaching a course on accident investigation, and doing the aerodynamics portion from notes that he pulled out of his pocket. A Navy Captain talked to him after class and told him that if he would put the aerodynamics into book form that he would make sure that it got published.

This is a work that I think that we all need to read and understand. The propulsion chapters are a little bit dated, but the aerodynamics of a spin or a stall do not change.

Joe
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Old 02-12-2010, 01:30 AM
  #38  
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Right or wrong, the same concept I am explaining is done much better justice in "Stick and Rudder" and also expanded below in "The Illustrated Guide to Aerodynamics" by Hubert Smith, Ph.D (1992)

The tilted lift vector also has a horizontal component, lift times the sine of the bank angle, which is tending to pull the airplane into the direction of the bank. This pull should result in the airplane just moving sideways, and would, except that the vertical fin provides weathercock stability and thus aligns the longitudinal axis with the resultant motion.
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Old 02-12-2010, 07:04 AM
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Originally Posted by shdw View Post
It would, if you continued to apply the same force constantly. You are discussing on pull of say 5 pounds. Well how bout you keep pulling with a constant 5 pound force. This would result in you constantly walking 90 degrees to the force ryan is applying to push the cart. The result would be a constantly changing direction otherwise known, a circle. Go test it and see.
If you are implying that two constant forces applied at right angles to each will form a circular path, then which direction does the circle form? To the left or right? Remember that the cart pusher is applying constant force as well.
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Old 02-12-2010, 07:40 AM
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Originally Posted by joepilot View Post
Hi All.

I'm seeing a great deal of misinformation and misunderstanding on this thread. The definitive work on all this is "Aerodynamics for Naval Aviators", by Harry Hurt, Phd. This is available from the GPO, of possibly from your local FBO. Harry (now deceased) was a professor at the USC Institute of Safety and Systems Management. He was teaching a course on accident investigation, and doing the aerodynamics portion from notes that he pulled out of his pocket. A Navy Captain talked to him after class and told him that if he would put the aerodynamics into book form that he would make sure that it got published.

This is a work that I think that we all need to read and understand. The propulsion chapters are a little bit dated, but the aerodynamics of a spin or a stall do not change.

Joe
Hey Joe,

Would you be a little more specific about the misunderstand/misinformation in this thread?
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