Hinge positions to reduce flutter
03-04-2003 | 03:03 AM
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From: Chesapeake, VA
Hinge positions to reduce flutter
I have a question I was wondering about.
Friend of mine said that to reduce the chances of flutter in a given control surface, let's say the ailerons, that some of the hinges should be spaced differently apart.
In my 35% Extra I spaced the 2 tip most hinges about twice the normal distance between the hinges of the rest. So in other words I did this:
llllll ll (not to scale
)
My thoughts and his were similar, the different connecting points between wing and aileron would act as a tuning fork or such, dampening any oscillations.
Obviously this isn't the most techincal way to put it, but does this strategy yield any results?
Friend of mine said that to reduce the chances of flutter in a given control surface, let's say the ailerons, that some of the hinges should be spaced differently apart.
In my 35% Extra I spaced the 2 tip most hinges about twice the normal distance between the hinges of the rest. So in other words I did this:
llllll ll (not to scale
) My thoughts and his were similar, the different connecting points between wing and aileron would act as a tuning fork or such, dampening any oscillations.
Obviously this isn't the most techincal way to put it, but does this strategy yield any results?
03-04-2003 | 03:22 AM
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From: Mary Esther, Florida, FL
Hinge positions to reduce flutter
Silvanskii:
Yes it makes a difference in the susceptibility to harmonically induced flutter. Improper horn location also has an effect - don't put the horn at the center or 1/4 surface span position.
When the aileron flutters and says "Goodbye,"
. You can watch, you can cuss, or you can sigh.
Bill.
Yes it makes a difference in the susceptibility to harmonically induced flutter. Improper horn location also has an effect - don't put the horn at the center or 1/4 surface span position.
When the aileron flutters and says "Goodbye,"
. You can watch, you can cuss, or you can sigh.
Bill.
03-04-2003 | 04:59 PM
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From: Kanata,
ON, CANADA
Flutter
From my recollections of aerodynamic courses many years ago, the best way to get away from flutter include statically balancing control surfaces and have some aerodynamic balancing. I dont recall anything about horn position but it could have some effect. Using hinges that support the surface adequately is probably more important than horn position.
03-04-2003 | 11:20 PM
#4
Senior Member
Hinge positions to reduce flutter
I don't know about the hinge "mis-spacing" idea, but it got me thinking/drifting - Not versed in this area, so pipe-up if I'm conjuring up some invalid concepts in my mental meandering.
First lets assume that a flimsy control surface or sloppy linkages are not the problem.
Assuming a relatively slender panel, e.g. an aileron, when flutter occurs, is the entire aileron fluttering uniformly about the hingeline, or is it actually rapidly "micro-flexing" about its chord axis (like a vibrating beam) with maximal deformation occurring near the TE? I believe the latter is the case, at least for slender surfaces - I hear a lot more cases of aileron flutter than rudder or flap.
Is flutter strictly structural resonance, which is a function of mass and stiffness, or is there also some aerodynamic influence like vortex shedding off the TE? If the surface is resonantly flexing about its chord axis, could varying the stiffness or mass along the length of the panel make the surface less prone to flutter all at once along its full length? Such a surface could be made by "simply"
making it from different grades of wood or composite lay patterns. Seems like the surface would then be prone to flutter only at localized points at a given airspeed, but not the whole surface going into flutter. Not sure if that's right; I think there will still be a resonant frequency that can be triggered at some airspeed where the whole surface goes into flutter despite the variable section properties.
First lets assume that a flimsy control surface or sloppy linkages are not the problem.
Assuming a relatively slender panel, e.g. an aileron, when flutter occurs, is the entire aileron fluttering uniformly about the hingeline, or is it actually rapidly "micro-flexing" about its chord axis (like a vibrating beam) with maximal deformation occurring near the TE? I believe the latter is the case, at least for slender surfaces - I hear a lot more cases of aileron flutter than rudder or flap.
Is flutter strictly structural resonance, which is a function of mass and stiffness, or is there also some aerodynamic influence like vortex shedding off the TE? If the surface is resonantly flexing about its chord axis, could varying the stiffness or mass along the length of the panel make the surface less prone to flutter all at once along its full length? Such a surface could be made by "simply"
making it from different grades of wood or composite lay patterns. Seems like the surface would then be prone to flutter only at localized points at a given airspeed, but not the whole surface going into flutter. Not sure if that's right; I think there will still be a resonant frequency that can be triggered at some airspeed where the whole surface goes into flutter despite the variable section properties.
