Screamin_Injun

I thought it was just normal because I was outflying my air frame, but should my plane shudder at all? I have a BUHOR, (I put the pics on this forum ), and at about 25mph she starts to stutter pretty badly. I have a .46 O.S. on her and I basically have to fly at a little under half throttle at level, straight flight. The plane to me is plenty fast, and I have enough power to pull her nearly straight up for as long as I can see her. But in fairly sharp dives the flutter is so bad I completely lose lift and must wag her back and forth to "slow" her down enough to pull her up. I have her trimmed well, she will fly as far as I want her to in level flight without me even touching the stick, so I know its not that. Any suggestions?

Woodsy

checked the prop/spinner balance?
is everyhing tight, engine mount, servoes etc, etc?

Screamin_Injun

Yup, she's tight a button. Balanced great, everything lock-tighted down. I do a flight check before every flight and all that stuff is good to go. I have a prop nut (the ones that look like spinners but are a solid piece of aluminum) so theres no imbalance there. Any other thoughts? :stupid: Just keep in mind that unless I speed her up to over 25mph, she soars by me as quiet as a lark.

jbowyer

My Feedback: (1)

The design of the aielerons may be the problem. Cut the ends of each aieleronn at an angle and see if that helps, it did mine. the angle should start at the aieleron end and end about 2" to 3" over from the end.

J. Bowyer

Screamin_Injun

Your talkin about the outside edge of the ailerons correct? Not by the fuselage.

jbowyer

My Feedback: (1)

Both ends worked for me, but at a minimum the outside ends.

J. Bowyer

Screamin_Injun

Well, the cutting off of the ends of the ailerons helped a little but I still have to "hold back" on my speed to keep her flying smoothe. Jeeze this is driving me crazy! :spinnyeye

Silly me

That is one problem all big spad have, I always use 2 servos in the wings and make my control horn base a long as possible and as far to the middle of the aileron as possible, so I have a control surface with as little flex as possible. Some skewers in the ailerons and make sure all the hings lines is easy to move as possible so the control surface moves at the hings rather than flexing in the general direction.

One more thing, is it the wing or the whole plane that is fluttering????

If its the whole plane, that it might be the flex in the fuse swell

I build a BUHOR a while ago and it was running with a old and lazy asp40 spinning a 11x4, and I think that was the max mine could handle on a level flight.

Its a great plane to learn dead stick landings with, as it almost doesn't need a motor to fly.

Screamin_Injun

It starts out in the trailing edges of the wings. If I push it hard some times the tail sorta "wags". I can see the fuselage twist when I am throwing her back and forth so it could be that it's just a big ass plane! LOL.

Captain351

You are probably going to find this hard to believe but your problem is likely caused by the stiffness of the coro hinges. I nave started slitting the hinges on all my Spads now and have had no flutter problems since.

Think of it as if you were using regular hinges how many and where would you put them. Then lay it out using a ruler and poke holes through the center of the hinge on each side of where these imaginary hinges should go. Then using a razor knife cut slits from hole to hole between these imaginary hinges. Now their not imaginary anymore.

Screamin_Injun

Thanks for the tips. I cut off 5 inches of outside aileron off and it helped oodles. If I get any more made wobblies Ill use your hinge idea.

Capt_Kc

I used to fly a airmadillo with a 46fx on it. It would flutter like crazy on me in downward slopes. I took some music wire and place a 3/4 inch 90 degree bend on each end (it should be about 12 inches between each bend). Take the two ends that are bent and where the aileron is hinged, push the 3/4 ends into the the ailerons. The 12 inches will rest in the hinged area. This won't effect the hinge. This stopped most of my flutters.

McIntoshj

If you goto this web site it will give a bunch of tips on flutter problems along with all kinds of building tips.

http://mywebpages.comcast.net/TipsTr.../tip_index.htm

Just copy it in the address window.
It is the website form Tattoo.

Good luck,
Jason

trroscoe

My Feedback: (39)

My DPS did the same thing. I trimmed the outboard corner off of the ailerons and it helped some. The other thing that I did is use some clear 2 inch tape to cover the open ends of the coro wing. This completely stopped the tail wag at high speed. I have an OS 46 FX on my DPS and I can fly it at full throttle with no problems. My plane has a bigger wing than the plans call for. I stretched it out to 56 inches and stretched the fuse to 36 inches. This plane flies very good and the vertical with the FX is great. Try taping the wing tips and you will be surprized at the difference.

Rick

Screamin_Injun

Heck, Ill try that too. Never thought about that. Thanks man.

adrian-RCU

FLUTTER
By Ed Moorman
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."

trroscoe

My Feedback: (39)

Try cutting your ailerons about 5 inches in from the outbaord edge to the outboard point of the hinge. Just cut the corner of the aileron off. Just like it shows on the SPAD web site in the aileron flutter modification page. Believe me it works. My DPS was almost unfliable. It would tail wag so bad at anything above 1/3 throttle. It scared the heck out of me to fly the thing. I previoulsy was flying a DEB that I built to plans and didnt have to do anything to it for it to fly great. I was looking forward to the DPS flying great until I took off the first time. The plane was all over the sky. I landed and cut the corners off of the ailerons and took off again. It was better but not great it would still tail wag at anything over 1/2 throttle. I had read something about closing up the open wing tips to stop this. I had some clear tape in my flight box so I taped up the ends of the wing. What a difference the plane now flies great and is the one that I fly the most. I can fly around at full throttle and have no problems. Try it.

Rick

*Crash*Johnson*

My Feedback: (7)

YO Adrianne...

So if I had a square flagpole my flag wouldnt flutter?

Screamin_Injun

I was thinking the same thing. Call me stupid, but I thought the flag fluttered because it was fabric and this thing called "wind" moved it...lol.

Ok, I give up on this fluttering thing. I have made sure my linkage was stiff. I added wooden supports the length of the wing to support it. I covered the ends of my wings with coro. I trimmed off 5 inches off the ends of my ailerons. Im just starting to think its cause I have a huge ass plane! LOL. No doubt all those things helped. My plane doesn't flutter now until its going alot faster. Thanks for the help guys.