I'm studying material for the CFI test(s) and have a question regarding the Magnus effect on pages 3-5 through 3-7 in the PHAK (FAA-H-8083-25A).
The concept is introduced to illustrate how viscosity and friction affects the flow of a fluid around a rotating cylinder. I get it. The surface friction and viscosity of the fluid cause a lower pressure due higher velocity over the top of the rotating cylinder as the molecules are pulled in the direction of rotation. At one point in the discussion the rotating cylinder becomes a proxy for an airfoil without any explanation.
Just exactly how is a rotating cylinder analogous to an airfoil on a fixed non-rotating wing aircraft?
I have a pretty decent understanding of Bernoulli's principle, so no need to go there.
I'm studying material for the CFI test(s) and have a question regarding the Magnus effect on pages 3-5 through 3-7 in the PHAK (FAA-H-8083-25A).
The concept is introduced to illustrate how viscosity and friction affects the flow of a fluid around a rotating cylinder. I get it. The surface friction and viscosity of the fluid cause a lower pressure due higher velocity over the top of the rotating cylinder as the molecules are pulled in the direction of rotation. At one point in the discussion the rotating cylinder becomes a proxy for an airfoil without any explanation.
Just exactly how is a rotating cylinder analogous to an airfoil on a fixed non-rotating wing aircraft?
I have a pretty decent understanding of Bernoulli's principle, so no need to go there.
Would you please elaborate? Why is it analogous when the circulation is caused by the rotation?
My understanding up until now had been that since the path of the flow of air over the curved upper surface of a wing is longer than the lower surface, a relatively lower area of pressure develops on the upper side due to the increased velocity.
The rotating cylinder analogy was used to illustrate how molecules cling to surfaces and each other due to friction and viscosity. I'm just having a hard time understanding the leap from a rotating cylinder to a non rotating wing. It seems to me that phenomenon of friction and viscosity exist on both sides of a wing.
Maybe I'm overthinking this and should just move on.
Would you please elaborate? Why is it analogous when the circulation is caused by the rotation?
My understanding up until now had been that since the path of the flow of air over the curved upper surface of a wing is longer than the lower surface, a relatively lower area of pressure develops on the upper side due to the increased velocity.
The rotating cylinder analogy was used to illustrate how molecules cling to surfaces and each other due to friction and viscosity. I'm just having a hard time understanding the leap from a rotating cylinder to a non rotating wing. It seems to me that phenomenon of friction and viscosity exist on both sides of a wing.
Maybe I'm overthinking this and should just move on.
My stuff has better puns.The circulation itself causes the lift. If you designed an airfoil with no circulation (say, symmetric with zero angle of attack), there would be no lift.
See http://www.av8n.com/how/htm/airfoils.html#sec-circulation for some nice discussions and diagrams.
No prob.Thanks for the links. Good stuff. I hope I can have your permission to use it. Thanks for trying to help me out.
Wow! What a fantastic website! Thanks for helping.
Magnus effect is the only reason to brake wheels from rotating after takeoff.
When they rotate they are producing lift DOWN.
No. They are rotating in the correct direction for positive lift.
I just hate the rumbling sound and vibration. Never thought of it in terms of lift produced, and I doubt it's a significant amount, anyway.
And it is definitely not the only reason. Cessna retracts can rub the wheels on the frame holes if they are still spinning during retraction, due just to centrifugal distortion of the tire.
Wrong again!
Any airplane that needs to have its wheel stopped in retraction have "snubbers." Otherwise, it is a maintenance problem.
No. They are rotating in the correct direction for positive lift.
However, it is turbulent flow. You may have noticed that some airframes shudder right after takeoff due to that and stiffness that is just right to excite that mode. Particularly if the airplane doesn't have wheel pants. The Magnus effect is not zero with wheel pants, but the flow becomes much less turbulent.
And it is definitely not the only reason. Cessna retracts can rub the wheels on the frame holes if they are still spinning during retraction, due just to centrifugal distortion of the tire.
I was not asked about that term during either my initial ride in 1973, or my reinstatement ride in 1977, or my second reinstatement ride in 1990, so you probably would have been OK long after 1968.I would guess that if you went into any FSDO and asked a group of Ops Inspectors about Magnus Effect, 90+ percent would not know what you were talking about. Glad I got my CFI in 1968.
Not in the lift diagrams I've ever seen.
I was not asked about that term during either my initial ride in 1973, or my reinstatement ride in 1977, or my second reinstatement ride in 1990, so you probably would have been OK long after 1968.