Hi, I'm assuming(?) that like all aircraft designers you performed your flutter testing on the ground thru the use of GVT ground vibration tests, and not by flying? ----- Original Message ----- From: <wdec...@cox.net> To: "KRnet" <kr...@mylist.net> Sent: Tuesday, March 23, 2004 8:54 AM Subject: Re: Re: KR> Balancing Ailerons
> Exactly my point. Ailerons are part of the dynamic system on the wing that can induce flutter, and it does so if the frequency at which the aileron flutters meets the frequence of the wing. Typically you try to make the wing as stiff as possible to increase the harmonic frequencies, and you try to decrease the harmonic frequencies of the ailerons to keep them below the harmonics of the wing. > > During my time at the Technical University Braunschweig I was involved building the SB-13 glider, which does not have a tail (I just tried to check out a link that would show a picture, but had to find out that something on the web page of the Academic Glidergroup does not work. I'll post it as soon as I find another one). During the development phase of this glider we built a 1:3 scale model, on which we experienced some extreme cases of fluttering. So we started doing calculations on this and found, that we had at least two different modes of flutter. The main reason for the occurance of flutter was the fact, that the tail was missing on this design, as the tail with it's long arm works as a great dampener, thus eliminating the oscillations created by a combination of warping and swinging of the main wing. The solution was to increase the stiffness of the wing so that the harmonic frequency of the wing (including the warp modes) was high enough that it flutter could not be induced within the speed enveloped we designed the aircraft for. > > Bottom line is, that you may still experience flutter, even if you perfectly balance your ailerons, if they are build light and if their harmonic frequencies coincide with the wings harmonic frequency. > > Just adding to the whole confusion about fluttering, but as it was pointed out before, it is indeed an extremely complex area. "Oscillations" was a mandatory class in my studies, and almost everybody in my class hated it!! > > Wolfgang > > > > From: Ross Youngblood <ross...@operamail.com> > > Date: 2004/03/23 Tue AM 04:16:25 EST > > To: KRnet <kr...@mylist.net> > > Subject: Re: KR> Balancing Ailerons > > > > I think Wolfgang's description regarding Eigen Frequencies > > is saying the same thing. Flutter is mechanical oscillation > > with positive feedback. I recall learning about Eigenvalues > > in linear algebra... but did not study aerospace or mechanical > > engineering... I suspect that reducing the "Eigen Frequency" is > > another term for trying to keep any harmonic oscillation low enough > > so that it doesn't feeback onto itself and cause the plane to damage > > itself. (i.e. prevent flutter). > > > > > > On Mon, 22 Mar 2004 19:31:01 -0600, Mark Jones <flyk...@wi.rr.com> wrote: > > > > > Wolfgang, > > > The reason to balance the ailerons is not to achieve equal control > > > balance > > > between the two ailerons yet to achieve balance on the pivot point of the > > > aileron hinge to help eliminate flutter. Flutter is sudden and is seldom > > > recoverable before it destroys the control surface. Do a search in the > > > archives on flutter and you will have a nights worth of reading. > > > > > > Mark Jones (N886MJ) > > > Wales, WI USA > > > E-mail me at flyk...@wi.rr.com > > > Visit my KR-2S CorvAIRCRAFT web site at > > > http://mywebpage.netscape.com/n886mj/homepage.html > > > > > > > > >> Hi Netters, > > >> > > >> I followed the balancing discussion for some time now, and to through > > >> some > > >> more fuel into the fire (or to just post a dumb question): Shouldn't the > > >> Ailerons balance each other, since if the left one goes down the right > > >> one > > >> goes up? I personally do not recall that we used balancing weights on > > >> the > > >> gliders we build at the glider group in Germany. > > >> > > >> There was only one reason to add counterweights to ailerons, and that > > >> was > > > to > > >> increase inertia of the system as to reduce Eigen-Frequency of the whole > > >> system to a manageable frequency. Schleicher Aircraft used an interesing > > >> method in the ASW-19, by putting lead into the top of the control stick. > > >> > > >> You may forgive me if the self balancing of the ailerons is not possible > > >> with the KR-2, as I am not yet fully familiar with the control > > >> mechanics. > > > I > > >> got my plans only a few weeks ago and still in the study phase. > > >> > > >> Wolfgang > > >> > > >> > > >> > > >> _______________________________________ > > >> to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > > >> please see other KRnet info at http://www.krnet.org/info.html > > > > > > > > > > > > _______________________________________ > > > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > > > please see other KRnet info at http://www.krnet.org/info.html > > > > > > > > -- > > Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/ > > > > _______________________________________ > > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > > please see other KRnet info at http://www.krnet.org/info.html > > > > > _______________________________________ > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html
