[NSRCA-discussion] flutter again

[Ed White]

George,

Based on the size and the description foamy I've been thinking surface flex.  When you say stiffeners "longitudinally" what do you mean? Chordwise or spanwise?  Either may actually be of less help than you think.  It depends upon the mode shape of the mode that is getting excited in flutter.  It may be a question of torsional stiffness in which case chordwise or spanwise stiffeners may not help that much.  It depends upon how the stiffeners are tied to each other, if there is a closed torque box.  The ideal would be +/- 45 deg stiffening. Classical flutter occurs when two vibration modes of the structure couple together to extract energy from the airstream.  Usually the modes are associated plunge (flapping) of the wing and with pitch (torsion) of the wing or any kind of flexing of the control surface.  Control surface flutter may be due to a vibration mode that occurs because the control actuator is not stiff enough or because the control
 surface itself is not stiff enough. The vibration modes that couple may be complicated and not always the usual modes.  Also, the closer in frequency these modes are to begin with, the easier it is to get them to flutter.  You may have two wing modes, or a wing and aileron mode that are just close to each other and flutter easily.

It may not be an aileron stiffness issue at all, it may be a wing torsional stiffness issue.  The fact that you have aerodynamic counterbalances and you said you weighted them leads me to wonder if it is not a wing issue.  Perhaps some strategically placed +/- 45 reinforcing tape to stiffen wing in torsion?

Ed




________________________________
 From: George Kennie <geobet4evr at gmail.com>
To: General pattern discussion <nsrca-discussion at lists.nsrca.org> 
Sent: Friday, September 13, 2013 5:10 PM
Subject: Re: [NSRCA-discussion] flutter again
 


I build in stiffeners into the surfaces in both the balance tab and longitudinally so I don't think there's a flex problem.



On Fri, Sep 13, 2013 at 6:01 PM, Michael Ramsey <milehipilot at gmail.com> wrote:

Probably 5.0V.
>
>I'm sure that you've seen what the bottom of the aileron looks like on an F3P model. Would an external frame of carbon fiber help your design here?
>
>
>
>
>On Fri, Sep 13, 2013 at 4:56 PM, George Kennie <geobet4evr at gmail.com> wrote:
>
>They're running on the BEC voltage. The ailerons are individually powered.
>>
>>
>>
>>On Fri, Sep 13, 2013 at 5:52 PM, Michael Ramsey <milehipilot at gmail.com> wrote:
>>
>>But they are aircraft servos right? What voltage are they running on?
>>>
>>>Paddles are normally used to reduce stick loads on ailerons that are linked to a single servo (or control stick). I don't believe dual servo setups benefit from aileron paddles. 
>>>
>>>
>>>
>>>
>>>On Fri, Sep 13, 2013 at 4:49 PM, George Kennie <geobet4evr at gmail.com> wrote:
>>>
>>>I'd be surprised Michael. These are Solar servos and I think they're either one or two micro/sec and there is no slop anywhere
>>>>
>>>>
>>>>
>>>>On Fri, Sep 13, 2013 at 5:43 PM, Michael Ramsey <milehipilot at gmail.com> wrote:
>>>>
>>>>Could what you're experiencing have anything to do with the deadband specification of the servo?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>On Fri, Sep 13, 2013 at 4:34 PM, George Kennie <geobet4evr at gmail.com> wrote:
>>>>>
>>>>>The plane with the tape hinges was modified with balance tabs that I made up at the exact weight of the total surface and added an additional sub small surface at a different incidence and nothing changed.
>>>>>>
>>>>>>
>>>>>>
>>>>>>On Fri, Sep 13, 2013 at 5:30 PM, Tom Simes <simestd at netexpress.com> wrote:
>>>>>>
>>>>>>On 09/13/13 13:27, George Kennie wrote:
>>>>>>>> It's an original foamy design with 3D size surfaces, Michael.
>>>>>>>> It's a progression of my Rad-Tad series
>>>>>>>
>>>>>>>Have you considered taping on some quickie aerodynamic balancing tabs to
>>>>>>>see if the behavior changes?
>>>>>>>
>>>>>>>--
>>>>>>>Tom
>>>>>>>
>>>>>>>======================================================================
>>>>>>>   "Z80 system stack overflow.  Shut 'er down Scotty, she's
>>>>>>>         sucking mud again!" - Error message on XENIX v3.0
>>>>>>>
>>>>>>>Tom Simes                                       simestd at netexpress.com
>>>>>>>======================================================================
>>>>>>>
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