adrian-RCU
Posts: 1687
Joined: 10/28/2002
Last Login: 9/19/2011
From: tel avivna, ISRAEL
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please guys flutter is a huge problem on the new big control s  ervices 3d type planes, because we fly them to fast, put standard servo,s and expect them to do the job and then we blame the plane. here on rcu a lot of experienced people will tell you all about this so take time to read before you go out and have lot's of bad luck with your new plane.
on flutter
We have all seen a flag fluttering in a breeze so we all know what flutter is. The control surfaces on your RC plane can do the same thing. Actually, the whole wing can flutter, too. Flutter is caused by 1. speed, 2. poorly designed or constructed control surfaces and 3. loose, sloppy control hook-ups. Flutter is bad. Flutter is destructive. You may not have seen it on an RC plane, but it is waiting out there to get you. Be aware it can happen.
The onset of flutter is heard as a buzzing or vibrating sound. It is a distinctive sound and virtually everyone at the flying field who hears it will look up. When you fly faster than the buzzing speed, things start breaking or falling off. Clevices, solder joints and servo arms will fail. The servo shaft the arm attaches to will shear off. Hinges will fail and control surfaces will fall off. Whole wings and fuselages will break. All it takes is speed and a little slop in the controls.
Here are my words on flutter:
NEVER, NEVER, NEVER ROUND OFF ANY TRAILING EDGES!
I don't care if the kit plans show it, they are WRONG! If a so-called "expert" tells you to round off any control surface trailing edge, he is an idiot. If the "expert" tells you he rounds his trailing edges off and has never had flutter he is still an idiot, but one who has the skills to build a tight system and who is lucky he has never flown past the flutter threshold airspeed for his planes. These people are doing a great disservice to the modeling community, especially the newcomers who they influence and who, though lack of skills like the "expert," will probably get flutter and may destroy an airplane. You can quote me on that!
Go look in any basic aerodynamics book and look up flutter. It will agree with me. When it comes to control surfaces, STRAIGHT LINES AND SHARP CORNERS DELAY FLUTTER, while CURVED LINES AND ROUNDED CORNERS PROMOTE FLUTTER. Go ask a pylon racer. He'll tell you about inlaying 1/64 ply in the trailing edge of the ailerons so he can sand it to a sharp edge. If you can't make the control surface a straight like to a sharp trailing edge, leave it square and sharp on the corners. Sharp corners preclude flutter while rounded edges promote flutter. NEVER ROUND OFF ANY TRAILING EDGES.
Look at a flag pole. They are rounded and every flag flutters. It's not because cloth naturally flutters, it's the pole.
As for the numerous ARF kits which are sold with rounded of trailing edges, let's look at the economics of the situation. Most people who are not knowledgeable about aerodynamics and flutter automatically think a squared off trailing edge is bad. They erroneously think, "Curves are nice, curves are sexy, curves have to be better." Just looking at a squared off trailing edge, you would have to think it would produce a lot of drag and slow your plane down several miles per hour. I think many people believe a plane with squared off trailing edges won't even fly so they certainly don't want one. It is my opinion the marketing staff insists no one will buy the plane if the ailerons have squared off trailing edges, so good aerodynamic practice is over ruled and the trailing edges are rounded off. Hooray for marketing!
To compensate for this, the building instructions may say, "Keep speed down," "Do not dive at full power," or the sneakier one, "Use long control horns and put the clevice in the furthest out hole." This is to minimize the effect of any slop in your controls. But many fliers will not do this and will end up blowing ailerons off the wing or shaking the tail off the plane.
For trailing edges, here are the choices, and I speak as an engineer and a long time modeler who has sadly and personally verified each of these.
1. Best: A straight line to a sharp trailing edge. This is best and has the least tendency to flutter. It's like commercial aileron stock or trailing edge stock. Don't get me wrong here, these can still flutter, but they will do so at a higher speed than the others. You must still eliminate springy pushrods and sloppy connections.
2. Second best: Straight lines on both sides to a square, flat trailing edge. Squared off trailing edges , too, are very flutter resistant. Think of the elevators of a giant which are made from 3/8 square sticks. DO NOT ROUND OFF THE TRAILING EDGE. Leave the corners square and sharp. I do all mine this way. I recall seeing a magazine article where the designer of a certain Extra 300 kit which specifies rounded trailing edges spoke about the plane. He said to be sure to use the longest control horn and have tight controls. All this does is hold the flutter off until a higher speed. Leave 'em square. It's easier and it works. If you already have the TE rounded off, glue some 1/64 ply vertically on the trailing edge, fill in the gap with Model Magic and Monokote over it. This will give you a sharp, square corner.
3. Next to worst: Sharp trailing edge, but a curved surface. Not very good from a flutter standpoint. These will hold up better than just rounded trailing edge. You probably had to carve some to get this shape and you actually wasted your time. Use long control horns and as tight a connection as you can get. Next time, leave it square or use a sanding block or a plane and carve in a straight line to the trailing edge.
4. The very worst: Completely rounded trailing edges. Think back to the flag pole. If you build up a giant tail surface and round off the trailing edges, you are looking for flutter. If you don't get flutter, it is because you aren't fast enough and you have a really tight control setup. DO NOT DO THIS.
OTHER THINGS YOU CAN DO
Use long control horns and long servo arms, and use the outer most holes. If you have any slop in your control system, the longer arms minimize the angular movement which can allow flutter to start. If you need more control throw, get one of the extra longer servo arms available.
Use stiff pushrods or pull-pull cables, especially on rudder. Tight pull-pull cables take all the slop out of a system. Very good for flutter prevention. Brace the pushrods inside the fuselage if you can.
As a last resort, you can counter balance the control surface."
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All Forums >> RC Airplanes >> 3D Flying! >> u can do 46 wing problem 
u can do 46 wing problem - 
u can do 46 wing problem - 
