Anyone flying the Cedar Hobbies SPORT FUN STICK 40 plane. I have had nothing but aileron flutter problems. I have covered the gaps replaced the rods and everything is tight. It starts up at half throttle and has torn the servo in the left wing right out. That does not happen any more. It just starts fluttering and I cut the throttle and bring it in. I am at the point of thing of replacing the ailerons with ones half there width. Just to see if that will get rid of the problem. If you have one of these and had the same problem what did you do to solve it? Thanks for looking.

I can't find the site to see what your plane looks like, but it sounds as though you are flying it faster than its design will tolerate. If it is a large control surface 3D type design, you should probably be propping it with no more than 4" pitch. If that is not the case, disregard this transmission.

It is not listed on the site anymore. I have a OS 50 SX and have been running it at 1/3 to 1/2 throttle. It has a APC 12 x 4 prop. Even lower to see if I can find the problem. The company is www.cedarhobbies.net the control surfaces are over sized.

Without much to go on, one thing I try and do is use the outer holes on the control horn and one closer to the output on the servo. You get more torque that way. Sealed gaps are a good practice, as is reinforcing the servo mounting rails. I had trouble with a bipe and solved it with higher torque servos and nothing more, other than to watch my speed on down lines.

What kind of servos are you using

could it be the ailerons themselves that are fluttering, made from too light (soft) balsa?

I am using the Fatuba S3004's. Yes, it could be the aileron material. It has many lighting holes in them and are not as stong as I would like. I am picking up new stock at the hobby shop to replace them. These are 3" ailerons and I will be putting in 2 inch stock solid. Also I have just moved the elevator & rudder servo's back on the tail of the plane. Replacing all rods with 4-40 ones and try it again. Thanks for the ideas. I have 19 planes and this is the first one that has ever had a flutter problem.

With a large control surface you want a servo and linkage system with enough "holding" power to prevent flutter.

The idea is to have the servo immobilize the control surface in the commanded position, even though airflow is working against this.

You are using relatively weak aileron servos, and I'll bet there is some play in the linkages.

The combination of the two permits the aileron to wiggle as the plane speeds up, in a harmonic fashion.

As things progress the servo can no longer hold the aileron in place and the aileron ( or any other surface ) can rip out.

Use a stronger servo or a digital one, with bigger linkages to help.

I agree with all this post. Good advise. I would add for your consideration, that when a control surface area is increased, the length of the control horn, the length of the servo arm, the gauge of the rod, and the strength of the servo are all effected. Standard arms, horns, rods, and servos no longer are sufficient.

I went to the hobby store today and got 4-40 rods and Futaba s3010 servo's. So everything is installed and ready. I replaced the OS 50sx with another new one and have to break it in. Once that is done I will find out if the changes corrected the flutter problem. Will keep you updated. Thanks for all the ideas again.

I once did a twin engine Ultra Sport 1000 and increased the ailerons to 2" and they would flutter like mad in a dive...Being cheap..just added one more servo to each wing but around 12" apart..No more problems.
Just a thought.
Twinman

I took the plane out again today with all the new modifications. It start fluttering on the first flight. But I saw what was happening this time.

Piroflip2 was correct it was the right aileron and it is the material being to soft. I will have to make another set of stronger wood. That will finally solve the problem. Thank you every one for all the ideas.

I flew the Fun Stick from Cedar Hobbies today and the flutter is all gone even at high speed. I replaced the ailerons with 1/4" x 3" solid balsa with no lightening holes. I reinforced the horn area with CA before covering. It is tight as can be. Thanks for all the changes.

The flutter returned and I had to reduce the size of the ailerons by 1/2" and round over the ends. Now the plane is solid and no flutter at hign speed and dives. Just wanted to keep looks updated to fixes to the flutter question.

Flutter is one of those aerodynamic phenomena that is partially a black art. Stiffer controls and surfaces do help. It is still a fact that wide control surfaces flutter more easily than narrower control surfaces. Also, as you have noted, flutter occurs at higher speeds. Most 3D planes can not fly very fast or they will flutter. This is just a fact of life with a 3D plane.

Another thing that has not been mentioned is the trailing edge of all control surfaces need to have sharp corners. For the wide controls, leave, or make, the trailing edge square. A straight line taper from the leading edge of the control surface to a sharp trailing edge is best. Pylon racers generally insert some 1/64 ply in the TE so they can have some strength when they taper to a sharp edge. Next best is to leave the TE corners square and sharp. I know it looks nice to round them off, but rounded corners are the worst for flutter.

It is my opinion that many manufacturers do things to planes to promote sales and if they kept the square TE, potential buyers might think they were cheap for not taking the time to round off the TEs and maybe not buy the plane. If the plane with the rounded TE does get flutter, their answer will be, "You were flying too fast."

The same thing happens with Sticks and other high wing sport planes. These planes need anhedral to counter roll due to rudder just as low wing sport planes need dihedral or sweep. The manufacturers are afraid, in my opinion, to use anhedral for fear that people will think the plane is unstable and not buy it. Just take any Stick up, even the flat wing Ultra Stick, and put in rudder. It rolls like a trainer. It has nothing to do with stability unless the plane is a trainer that you want to recover by itself. They will tell you how to use mixing to fix the problem.

The photo shows the aileron on an old Morris Hobbies TopCap profile. Their planes were popular when 3D first started and they were the first to hover and harrier. Their planes were designed and extensively tested in the US.

That's interesting. I didn't know that.

Why is this ( for my own edification I ask, not that I doubt that you are correct )?

I would normally expect that the squared off edges would cause mini vortexes at the edge, as the sharp "break" typically creates a low pressure area that the higher pressure flowing air gets sucked into.

With the rounded corners I would have expected that there would be some tendancy for the airflow to adhere to the contours, leading to a slightly smoother flow.

Hey Ed. You need to dust off that trusty old TopCap. I suggest a good hard aerobatic routine for the big chunks.

Ed,

I 'm sure your right and I definitely like the way you explained it so even I can understand it. I have never had a flutter problem but I also don't fly fast. If I do experience it in the future now I know what to do to fix the problem. Very good explanation.

Thanks,

Gibbs

I had a Saito .91 and Krazy Legs gear on the Top Cap and it used to do a nice climbing flat spin. Maybe I need to get it going again.

The rounded TE doesn't give the airflow a specific location to "hang on to". So the airflow can more easily fluctuate, side to side and up and down around and along the TE.

But most often a defined line of change will help to reattach separated airflow. Trip strips near the abscission line of a wing will often reattach airflow that has separated from the wing. They also help to hold flows that are about to break away. The energy that is building in that flow and would contribute to it's separation is disrupted by the disturbance in that flow.

One of the best profiles for an aileron is to taper it to follow the line of the profile, but have a definite "top" and "bottom" edge to the TE. The taper reduces the weight of the structure, yet you still have the square TE. The heavier the surface, the more prone to flutter.

The abscission line is the location along the span where the laminar airflow from the LE of the wing separates from the surface. The abscission layer is that air after it has gone from laminar to turbulent. It can reattach, but it won't go back to being laminar. There can and will be laminar layers above the abscission layer. The abscission layer can change in thickness and often will as a function of the pressure it experiences and the addition of more air going turbulent. The changes in those pressures are one of the suggested triggers for surface flutter.

It's also a theory that a rounded TE allows the top flow and bottom flow to "push and shove" right at the TE. But that a sharply defined "bobbed tail" TE causes the converging airflows to not meet at the TE, but farther aft, in "empty air". When the convergence is away from the surface's TE, the energy of the meeting is removed from having a direct effect on the surface. And flutter is avoided.

If you look at the TE from the side (as you'd see an airfoil printed on paper), a rounded TE provides a smooth large arc for the top and bottom airflows to meet. The pressures can cause the meeting point to move up. When that happens, the area that is effectively the top of the surface changes is area while the lower surface changes in the opposite amount. So you've got the virtual top of the wing changing in area, while the bottom changes opposite. But the change can cause change. The shifting "fronts" build up and then get blown back. When they're pushed back, momentum often causes the difference in virtual areas to go in the opposite directions. And that new relationship gets blown back. And the fluctuation of areas gives a fluctuation of pressures, which "fluctuate" the bloody aileron. And the sucker flaps. OK, it flutters.

Cut out the nice comfortable, round curve on the TE, and the air on the top and the air on the bottom no longer have a nice round, smooth curve to push back and forth around. They're suddenly confined to meeting along a very sharp line. And the pushing and shoving suddenly has nowhere to move up or down, and is even more suddenly left behind by that wing. Which has flown off, leaving the turbulence of meeting top and bottom air, in it's wake.

Excellent explanation.

That makes a lot of sense, and helps explain why having a small low pressure zone is actually advisable.

I'd love to see it in a wind tunnel.

Anyone have an RC wind tunnel?

BTW, there are TWO things that help reduce the flutter tendency of a surface.

One is the thing we've just been talking about, the squared off trailing edge.

Another is to taper the surface to a narrower trailing edge. That often works by itself, just like squaring often works by itself when modifying an existing surface. Why? Because it takes away a large ill-defined area where the top and bottom airflows have room to fluctuate. Reduce the space where fluctuation can work, and there is less pressure variances from top to bottom.

But of course, tapering also lightens. And the mass of the surface contributes greatly to what speed the flutter starts. So there are two very significant reasons to taper. Also, tapering does not reduce the area of the surface like hacking off a rounded TE can.

I would add a third way. counter-balancing the surface, especially on larger planes.

Stick some tape across the corner of the outboard corner of the aileron. It will solve the problem.

Ed S