jaav

I have a SPAD that has bad aileron flutter, I can see it and hear it only on one wing.
When it happens the wing drops RH .
At a level flight its OK only when banking using rudder or ailerons or speed if thats what you call it.
It done it again on finals for landing but droped the wing had no height left and hit the deck....

there is no free play in controlls and only one wing......

Any ideas thanks..

MTK

a FEW THINGS ARE POSSIBLE CULPRITS. Sorry on the caps.

Aileron linkage that is too soft and an aileron that's heavy for the speed the model flies at. Inadequate servo torque to hold the aileron again at speed. Alternately too large aileron area for the servo torque. Make sure that the servo is adequate for the job and the linkage is at least 1/8" carbon tubing. I use 5/32" carbon tubing linkages on ailerons on my 2 meter Pattern models and keep these short. At most 4-4 1/2" long. Shorter is better

The one that thing that cures flutter is to balance the surface statically. That is, install a length of carbon tubing at the aileron LE at an angle pointing forward 45 degrees or so, above or below the wing. Add weight to the tip of the tubing until the surface balances better. With no connection to servo, the surface should tend to return to center on its own. I hate adding dead weight to a model anywhere and ailerons are worse than most areas but you may not have much choice.

The other thing that helps a little is to seal the aileron gap. This essentially stiffens the aileron response to servo motion and as such tends to dampen flutter resonance.. Some guys used to add a length of music wire at the aileron tip, embedding the wire through the aileron and into the wing facing. This also stiffens the aileron response and changes flutter freq to beyond the model's flight envelope

MattK

jaav

Thanks Mat for your reply,

it flutters at low and high speed, I dont have to use the Ailerons to make it flutter.
When it happens and drops the wing I can correct it by applying a left stick to level out and increase the speed and it will come back.

i can roll the plane and there is no sign of it.

The RH controll rod had a slight curve in it but swapped it to the LHS made no diff.

I dont understand how to balance the surface. Is the rod running length ways (horizontal) or through the top and botttom (vertical 45deg) I can understand the vertical one as used in full scale.

To make the rods shorter I can fit another servo if you think the harmonics is making the rods flutter.

Thanks Jim West Aust.

Villa

Hello jaav
I also build and fly SPADS. I suggest you use a separate servo for each aileron, because they are very large. Move the servos out on the wing so the rod is near the center of the ailerons. Move the servos closer to the aileron to shorten the rods so they are stiffer. Put about a 10 inch long stiffener rod, such as a bamboo skewer or a carbon hollow rod, into the flute of the ailerons, centered under the aileron bracket to which the servo rods connect. You cn get more help in the SPAD forum, below. You can see my latest SPAD there, http://www.rcuniverse.com/forum/m_8007330/tm.htm. Mine has no aileron flutter, but it did have elevator flutter. In my case, I reduced the elevator area a little.

CrateCruncher

My Feedback: (1)

Wow, I've never talked to anyone in Broome before. Thats a first!

Not to get book-ish, but the aileron starts to buzz because air turbulence in flight matches the "natural frequency" of the aileron and linkage causing the amplitude to grow dramatically as the system absorbs energy from the air. The match in frequency we call "resonance". Stiffening the aileron system will increase its natural frequency above and beyond any ability of the turbulence to match it and create a resonant condition. OK, thats the theory......

What everyone else has mentioned is all good advice and what they are essentially saying is "stiffen the system". Looking at the photo of your model I can see that the aileron linkage to the servo is rather floppy piece of music wire with a kink in it - shorten or at least stiffen that and for heaven sake lose that kink! As MTK mentioned, carbon tube with a piece of 4-40 threaded rod JBWelded in each end makes a very stiff pushrod. Also, looking at the aileron I see its a strip type with the linkage at one end. if you hold one end of the aileron you can probably twist the entire thing into a helix from the other - attaching your servo link to the middle of that instead of at one end will increase the stiffness too by shortening the lever arm. You might even consider replacing the ailerons with something that has better rigidity or gluing another strip of aileron stock to the one thats already there.

Finally, there is one thing that no one else has discussed and its a long-shot but worth mentioning. The fact that you are only having trouble with the right side suggests there may be something upstream causing an inordinate amount of turbulence feeding directly into that RH aileron. Exhaust? Good luck! Let us know how you fixed it.

Tall Paul

I had a foamie sloper that I could induce flutter in any time I wanted, and stop it also.
A very loose system from the servo to the aileron, including the hinges will generate flutter.

kd5boc

I had some flutter this weekend. One of the aileron hinges came loose from the wood. Check those too.

Tom

MTK

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Quote:
Also, looking at the aileron I see its a strip type with the linkage at one end. if you hold one end of the aileron you can probably twist the entire thing into a helix from the other - attaching your servo link to the middle of that instead of at one end will increase the stiffness too by shortening the lever arm. You might even consider replacing the ailerons with something that has better rigidity or gluing another strip of aileron stock to the one thats already there.
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Strip ailerons could be a problem especially when using soft stock to keep weight under control. If you find yourself with a kit that uses very soft wood, don't discard the wood. Just apply carbon mat or veil material to the aileron surface before you finsih it. It will add a fraction of the weight of heavier, stiffer balsa stock and improve stiffness at least 3 fold. I apply carbon mat with nitrate dope. The great thing about this material is you may then finish with iron on plastic if you want to, directly over the carbon mat. You will need substantially less heat than usual since nitrate is really and industrial adhesive that gets tacky around 200 F

MattK

Huntster

Loads of great examples. There are so many ways to create Flutter..... I had on my Ultra Sport 40..... She hauls booooty..... She has a crazy effect on my knees when she flies so fast, they start shaking. But.... When I first started bringing her up to speed on high speed passes I could hear the flutter and I also had to back off... I built this plane for speed and I had the controls tight.

I brought her home and sealed the gaps between ALL the surfaces and now she is slick a can be....

Looking at your set up I would say that you are getting your flutter from your "trim" bend you put in your Aileron control rod. Replace that rod with a straight one that has threads on ONE end so you can adjust it to fit and you might get rid of your flutter.... Separate servos might work as well... But I am willing to bet your issues with with that rod and the kink you put in it... That works well with the small park fliers, as they don't fly as fast and don't have the control surface loads that the larger planes have on them.... Keep her flying!!!!

jaav

Well thanks all for you info.
Shes ready for the air again, New chassis.
The ailerons are now driven by 2 servos and at the middleof the aileron. the control rods are now adjustable straight rods and are about 4" long unlike the 8"s before.

have a fly cam mounted, tides out at 6am on sunday (10 metre tides) so hopefully I'll have some good photos of Cable Beach.

Will let you know how the flutter goes......
Thanks Jim.......

JimCasey

My Feedback: (1)

It seems as if the participants in this thread assigned little if any significance to the fact that you reported this is a SPAD.

SPADS have NO aileron gap. There are no hinges to come loose.
They can have sloppy linkages.

Flutter is caused by sloppy linkages or flex. Aileron gap itself is not so bad, but it is a place where the ailerons can flex because of aerodynamic loads. That's why sealing the gap helps: it stiffens the mechanism. SPADS don't have aileron gap, but they DO have is very flexible ailerons. And the mounting for the control horns is usually not very rigid in normal SPAD practice. Grab the tips of your ailerons and push them up and down. See what I mean?

Somebody mentioned balancing. Balancing doesn't stiffen the mechanism, it just changes the phase relationship of the flutter so it tends to be self-cancelling. However, going to the trouble of balancing the control surfaces on a SPAD is a little like the proverbial polishing of a tu... -er, you know.


I had a SPAD once that fluttered. It looked scary, but it did not hurt anything. SPADtanium (coroplast) is pretty hard to hurt that way.

The dual servos are overkill but should stiffen things up a lot. If it still flutters, taper the ailerons outboard of the servo. If they are 1 1/2" wide, taper to 3/4" and see if that helps.
Be sure the mounting for the control horns is stiff. Don't use the little setscrew thingies that go in your servo horns, especially not with the plastic retainer rings. Use Z-bends at the minimum, or (preferred) a clevis soldered to one end and an adjustable clevis on the other end of each pushrod. Just be careful that everything fits snugly.

If you'll cut one rib to fit the inside of each wingtip and glue them into place, you may find that it stiffens the wing structure a lot. 1/8 balsa would be easier to work with for this than coroplast, but whatever you choose will be fine.

jaav

Thanks Jim..
Todays flight was perfect. Was throwing her around and had no problems at all.
Slight trim on the elevator and she was neutral. Had a 7-8knt sea breaze at dawn with the camera running. Its intresting to see how much the fuse flexes in the rolls.

Thanks all for your help. Ill know next time.....We all learn something every day..

jim G.

Huntster

GREAT!!!!! Would love to see the video of the flight! and the beach!!!! Have been thinking of bringing my bird to the beach for a video shoot.

My best guess just looking at your supplied pix, as I said before was probably just the "trim" bends, the V shapes bend in the middle of the push rod, was your issue. that might have been removing the stiffness you need to prevent the surface from flapping..... "Flutter".... Shoot you could have even rigged your camera on board and tried to induce a mild case of the flutters and see what was happening during your flight.

As I said before with my US40 I had flutter and I did two things to try and prevent it. Fill the gaps between your surfaces, You got that covered with the SPAD design.

I also moved my control rods closer to the end of the control horn which helped with the leverage of the control rods on the surfaces. It stiffened the controls just a little... My bird has been clocked at 118MPH so there is little room for play... I also tend to fly a little low..... 3 to 4 foot passes of the field and some in the 2 foot range and one on film at 2 inches... That didn't last too long as the prop split in half.... Now if only I could find the cure to that....

MTK

That's me. And I admit ignorance as to what the hell a SPAZ is. If it's some kind of flexible thingy, then I agree. Balancing ailerons would not help fix the flexible aileron. Carbon veil will

Matt Kebabjian

jaav

Just have to get the landing right, Id love to idle back to base..

Hey guys here is the video link..http://au.youtube.com/watch?v=S8DHYcgc8W0

Tall Paul

This SIG Senior Kadet ARF made a fluttering noise during a Cuban 8.
The dihedral brace was bent waaaaaaaaay beyond reason!

ChiefK

Doesn't look like the wing had 16 degrees of dihedral in the "before" picture. Maybe the brace was not properly set and it shifted to the 16 degree point with the stress of the cuban 8.

ChiefK

MTK

Was it wing flutter? I actually kinda like the wing with larger amount of dihedral. Bet it flies at least as well

MattK

Tall Paul

The ailerons went crazy for a very short time.
3-channel Kadets usually have a lot more dihedral, but not THAT much!

gittarpikk

If that is where you run your antenna, the trouble may be simply to low a signal to noise ratio (dropout) and the wing drop is the receivers response to such.

My observation is on landing (when you seem to have the most trouble) The antenna is pretty mush behind the wing, and very near the rudder and elevator servos.


Run the antenna from a hole in the wing (or tape it to wing) at a point right behind the wing servo and run it up to the top of the vertical stab (fin). you can tape it there or use a bit of fuel line and a pin to mount it. I'll bet this takes care of it