Aileron Flutter on the Knife
 

...63 flights on my Knife ARF - it's helped me advance quite a bit on my vertical hovering - i don't come close to touching the tail to the ground (and don't ever plan to) but i can now get some pretty long hovers on calm evenings (which was my original purpose in purchasing the Knife) - i can also do some halfway decent low altitude, high-Alpha knife edges with it...

...the problem? - my aileron flutter seems to be getting worse - now i'm getting it even at lower throttle settings - i'm thinking about going to 4-40 linkages on my ailerons - anyone else tried this?...

Aileron Flutter on the Knife
 

Gary,

For what it's worth, I'm having no flutter issues on my Knife at all. Here are a few things that may be different in our planes...

1) I'm running the same equipment you are (46FX, etc.), but mine's a kit instead of an ARF. I added just a little extra reinforcement in the ailerons when building them up... not much though.

2) Because mine's a kit, it's probably lighter than yours at (I'm at 4lbs 5oz. all up dry weight).

3) I've sealed my aileron hinges as well as all other control surfaces... always do.

4) I used the stock linkage and CA hinges.

5) My throws may not be as aggressive on my ailerons... somewhere around 20 to 25 degrees. I know some guys are setting them at 30 plus degrees.

6) I fly pretty slow most of the time, never high throttle unless I'm in vertical climb.

I looked around a lot when I was building my Knife to see if flutter was an issue with these huge ailerons. I couldn't find anyone having any trouble. Are you sure you don't have some broken glue joints or cracked balsa in your ailerons?

Neo

Aileron Flutter on the Knife
 

...my ARF (with a bunch of added tail weight) weighs around 4 lb. 13-14oz. - i didn't seal the hinges, but there's very little gap - Dubro 2-56 linkages - i have a lot of throw...but i'm getting flutter at half throttle, neutral ailerons...

...maybe it's just vibration, but it sounds like flutter - not even a hard landing yet...but i'll check for broken glue joints - except for vertical, i fly it only at low throttle settings...

Aileron Flutter on the Knife
 

you could also have too large a hole on your servo arm. Are you useing Z bends?. Check this out in addition lok at your servos...are they fair new or aold....Gator

Aileron Flutter on the Knife
 

...i used the Dubro 2-56 w/Great Planes control horns because i thought there was too much slop in the kit supplied linkages/control horns...Z-Bends at the servos, Dubro metal clevises at the control horns...

...brand new Futaba standard servos w/ball bearings on the ailerons...

Aileron Flutter on the Knife
 

...maybe i need better servos? - i'm not sure if they're 3001's or 3004's - they came with my new Futaba 9C...

Aileron Flutter on the Knife
 

it also could be your covering on the plane resignateing to the vibes of th engine. If you stand infron of the stab and run it wide open ...do you hear it then?.....Gator

Aileron Flutter on the Knife
 

...just in the air, i think - i'll have to try that...

Suggestions
 

Seam up the seams regardless of how small that they are with regular scotch tape. Clean the areas first with alcohol.

Check for slop in the linkages as stated earlier.

If the ARF has heat shrinkable covering, re-shrink it, it may be loose covering and resonance as stated earlier.

If the problem still exists, this is a trick that I learned pylon racing, get some surgical tape from the drug store. I get the clear stuff. Be sure that it has a texture to it, and put a short piece on the trailing edge of the wing at the end of the aileron. This breaks up the airflow right there at the end of the wing just before it hits the end of the aileron. Creating this air disruption will stop the flutter.

If you are hearing the flutter at low speeds and can not physically see it as the aircraft goes by on a low pass, I would suspect that it is the covering resonating, not flutter. You might also want to check the balance of your prop and if you are using a nose cone, balance it as well. The resonance with magically disappear. :D
Kevin :D

Aileron Flutter on the Knife
 

Surcace oscillation can be very dangerous, I have saw planes actually loose the affected panel. :(
Possible Causes:
Excessive Hinge Gap
Excessive "Slop" in the Push rod Connections
Control Horn Slack (Slop)
There were a lot of good post above on possible fixes. :)
I even use toothpicks while building in the hinges using soda & thin CA to reinforce and wires in the tail feathers with soda & thin CA to secure with the use of extra small diameter supports.
The covering will cause issues as well.
I was given a Tiger ARF FF ( had loose covering-I tightened it with a hairdryer).
For instance the Morris ARF was heavier than my kit version of the Knifes (2) I had built previously. I have built the Hotts-Knife-Profile Mustang all good planes.

Aileron Flutter on the Knife
 

...DuBro aluminum prop nut/spinner, covering has been re-shrunk but will check again...will try the scotch tape & surgical tape tricks - thanks...

Aileron Flutter on the Knife
 

...put scotch tape on the bottom of the aileron hinge line - 50 to 75% better! - really helped - still getting some flutter even in vertical hover...

...do i need to put tape on top of the hinge line, too?...haven't reshrunk the covering on the ailerons yet either...

...i wouldn't think i'd be getting flutter from the elevator or rudder? - using stock pull-pull cables...