how to cure flutter
10-14-2003 | 03:42 PM
#2
Senior Member
RE: how to cure flutter
There is no simple cure because there could be many different causes. Most often it is because of excessive play in the pushrods or pivot points and/or a soft (flexing) push rod. If there is any slop anywhere in the control system, it can lead to flutter. Also, if the moveable surface is flimsy or easily warped, that can lead to flutter. If there is large gaps between the two surfaces, it may help to trigger the onset of flutter but sealing the gap only delays onset, doesn't cure flutter. If you have stiff and rigid moveable surfaces, stiff push rods and aligned hinges, you probably will never get flutter although everything has a resonance point, and if you hit that point with excessive speed or vibration , you can and will get flutter.
10-14-2003 | 05:46 PM
#3
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From: Corrientes, ARGENTINA
RE: how to cure flutter
Hello, see more about flutter in this link
http://members.cox.net/moorman1/Flutter.htm
http://members.cox.net/moorman1/Flutter.htm
10-14-2003 | 09:35 PM
#5
Senior Member
RE: how to cure flutter
Flutter has several causes..
Chief cause is a loose control system.
From the splines on the servo output gear to the horn attachment on the control surface, each individual part must be used properly.
Reusing a servo horn after a severe crash... frequently these horns get a hairline fracture from the center to the edge. This fracture permits the servo horn to rotate -on- the servo spline in flight under load. The result can be flutter as the splines strip, or the horn can re-grab the output splines at a completely different location relative to the previously set neutral.
Next the pushrod connection at the servo horn should be as far out from the axis of the servo output gear as possible. This provides a long and therefore stiffer position for the pushrod.
The pushrod should be stiff enough to not bend in flight. The shorter the better, and braced along its length if shortness isn't possible.
The pushrod connection at the control surface should also be as far from the surface as it can be. This minimizes the effects of slop in the fit of the pushrod in the horn, and provids a long moment arm to prevent the surface from fluttering.
The control horn must be mounted securely to the surface, which itself should not be of soft material.
The hinges between structure and the surface must be good. No large gaps or floppy material.
The control surface shouldn't have a wide chord AND heavy construction. The more mass hanging off the hinges the more likely it is to flutter.
Also, long slender surfaces with the control connection at one end, typical of strip ailerons must have the torque rod securely attached in the wood. and the wood should not be light weight.
The Goldberg Tiger II for example always has aileron flutter using the kit torque rods.
Adding another aileron servo with each partway out the wing, a short pushrod and secure control horn installation fixes that problem.
.
A tight stiff control system won't flutter.
Chief cause is a loose control system.
From the splines on the servo output gear to the horn attachment on the control surface, each individual part must be used properly.
Reusing a servo horn after a severe crash... frequently these horns get a hairline fracture from the center to the edge. This fracture permits the servo horn to rotate -on- the servo spline in flight under load. The result can be flutter as the splines strip, or the horn can re-grab the output splines at a completely different location relative to the previously set neutral.
Next the pushrod connection at the servo horn should be as far out from the axis of the servo output gear as possible. This provides a long and therefore stiffer position for the pushrod.
The pushrod should be stiff enough to not bend in flight. The shorter the better, and braced along its length if shortness isn't possible.
The pushrod connection at the control surface should also be as far from the surface as it can be. This minimizes the effects of slop in the fit of the pushrod in the horn, and provids a long moment arm to prevent the surface from fluttering.
The control horn must be mounted securely to the surface, which itself should not be of soft material.
The hinges between structure and the surface must be good. No large gaps or floppy material.
The control surface shouldn't have a wide chord AND heavy construction. The more mass hanging off the hinges the more likely it is to flutter.
Also, long slender surfaces with the control connection at one end, typical of strip ailerons must have the torque rod securely attached in the wood. and the wood should not be light weight.
The Goldberg Tiger II for example always has aileron flutter using the kit torque rods.
Adding another aileron servo with each partway out the wing, a short pushrod and secure control horn installation fixes that problem.
.
A tight stiff control system won't flutter.
