RE: MiG-29 Stab Flutter Cause?
 

Thanks for the reply ,Shaun. I know you fly mostly YA and any suggestions from you are money in the bank as far as I'm concerned. I feel more confident now and soon hope to take my first test hop in a few weeks.


Thanks again,
John

RE: MiG-29 Stab Flutter Cause?
 

Now this makes more sense. This would lead me to believe structure being the issue and not balance. Perhaps if you balanced the stabs in this situation it might have saved the airplane but you still would have an airplane with a weak rear fuse structure, you just wouldn't know about it ;-). I have never liked static balancing just solely for the weight penalty you ensue. Add all that weight to the rear and then double that weight in the front, just doesn't seem like a good trade off. I guess I have also never had to think about the fuse being inadequately stiffened. Man, all this thinking is taking the fun out of this hobby! :D:D

RE: MiG-29 Stab Flutter Cause?
 

Hi Ian,
There are numerous reasons for flutter, and several different modes of flutter. Mostly, we modellers experience control surface flutter. And yes you are quite right in part that the stiffness of a structure has a big impact on its flutter resistance. The stiffness of the linkages (or more correctly the absence of slop) also plays a very big part. Finally, keeping any thing that may be suseptible to flutter as light as possible will help to reduce the susceptibility to flutter.
However, allow to me to give you an example of the limits of your argument. This is the story (somewhat truncated) of the development of a high performance German sailplane, the Glasser Dirks DG 600. Now full size sailplanes do not just float around aimlessly, they race, and they are amazingly fast. This was to be the worlds first production sailplane with a full carbon composite structure, not just a carbon spar. The main benefit was the ability to design a much thinner wing that would fly faster with lower drag. Now normally sailplanes have very heavy metal built into the LE of the control surface for mass balance, but this wing was so thin that there was insufficient room to get enough metal in to make it balance.
They decided that carbon, being very stiff, would not flutter so they did a test flight, and pushed the machine carefully towards the VNE point. However, before they got close to VNE, a S mode phugoid set up in one wing. 400 milliseconds after onset of the flutter the wing failed about 12" from the root. They considered this to be a very bad thing. The pilot survived by using his parachute.
They then decided to try external mass balancing, but the extra drag caused by the fairings destroyed the machines peformance. So the considered making the wing much stiffer. And here is the rub. When they ran the math, they realised that they needed a material much stiffer than carbon! A solid diamond spar perhaps? Had they had the services of Superman to knock them up a few spars using coal as a raw material, the aircraft would then still have been so heavy as to be useless. So they figured out how to utilise mass balances into the bellcranks working horizontally.
The point is that there is a limit to what you can do with even world class engineering and design, and when you are at that limit it is time to reach for the tried and tested pragmatic solutions that work.
Mass balancing!
John

RE: MiG-29 Stab Flutter Cause?
 

And I see your point John and agree, however again, mass balancing, for me anyways, adds weight, more weight than say a proper rigid structure to mount a stab to I would think. I guess why you don't see a lot of other planes failing out there is for this reason. They must have adequate rear fuse support to overcome these issues. The one that comes mostly to mind for me are the Hornet's. Their stabs have so much weight behind the pivot point yet I have never seen a Tam's hornet fail from a stab or flutter issue, nor any manufacturer for that matter. Good discussion, Im likin it!

RE: MiG-29 Stab Flutter Cause?
 

DG-300

[youtube]http://www.youtube.com/watch?v=kQI3AWpTWhM[/youtube]
[link=http://www.youtube.com/watch?v=kQI3AWpTWhM]http://www.youtube.com/watch?v=kQI3AWpTWhM[/link]

RE: MiG-29 Stab Flutter Cause?
 

Static balance is in a way senseless since there is already much of the down force onto the leading edge of these full flying stabs.  The faster your plane the stronger that down force.

btw, sorry about the crash!

I wonder if you could post a picture of the pivot location in relation to the entire stab?

RE: MiG-29 Stab Flutter Cause?
 

Yes that was testing the 300 at close to VNE, and that was certainly flutter. But it is a well balanced aircraft and as you can see the result is that flutter is pretty mild and non destructive. Exceed VNE however......

RE: MiG-29 Stab Flutter Cause?
 

Just love the sound it makes, though I'd hate to hear it myself... someone suggested the pilot flipped a switch marked "Bird Mode!" :D

RE: MiG-29 Stab Flutter Cause?
 

Well if you are ever flying a real aircraft and you hear that sound, you will also make a similar sound shortly afterwards. But it won't come from your mouth:D

RE: MiG-29 Stab Flutter Cause?
 

:D :D :D