Conference vmszoo::rc

    
    	Next time when your hinging the aileron put a hinge about 1/2
    inch from the end. I definately sounds like flutter. Check all
    surfaces. Also check your servo gear train. Flutter can eat gears.
    One fix is to rehinge the surfaces. An alternative to try first
    is to go out and buy some clear vinyl tape and seal the aileron
    hinge gap. This usually fixes the problem. 
    	Like I said next time add the extra hinge at the end. Also
    laminating two pieces of aileron stock helps produce a stiffer
    piece than one piece alone. Try the tape I think it should solve
    your problem. Also seal the rudder and elevator. Also reduce the
    control surfaces throws after you seal the hinge gaps. You'll
    find that sealed surfaces are more effective.
    
    						Tom

        I do not know how you have your wing attached, but if it is
    held on with rubber bands, a possibility is that the rubber bands
    are making the sound.  This can make a real loud racket.
    
    Ken

    Along the same lines, I have a Super Kaos 60 with K&B pumper.  On
    full bore level flight it has a tendency to wiggle back and forth
    like the rudder is glitching.  Is this rudder flutter or is this
    a characteristic of this plane?  Whats the cure? 

    Thanks for the suggestions so far. The ailerons and elevator hinge
    gaps have been sealed since I built the plane. I used Ultracote
    folded into the hinge gap and ironed on. I didn't seal the rudder
    hinge gap.The hinges are the solid plastic type, no hinge pins, so 
    they are pretty stiff.
    
    There is a hinge near the end, but not as close as 1/2 inch. The
    servo is new and very little play, and there is very little play
    at the aileron horns. However, the outboard ends can be twisted
    fairly easily (the ailerons are not very stiff).
    
    It is a bolt on wing, with a very stiff saddle (no foam tape, just
    epoxolite to make a smooth matching surface).
    
    I'm suspicious that the ailerons are just twisting to cause the
    flutter, but how do I prove it? I'd like to be pretty sure before
    I go as far as replacing the ailerons or anything more drastic.

    Any more ideas, folks?
    
    Dave

    
    	The only way I know f proof is by an educated ear.   One final
    suggestion short of cutting off the ailerons and making new ones'
    is to remove the bottom covering of the ailerons and laminate some
    1/64 plywood to the aileron then recover.
    
    
    							Tom

    Here is something that might work. I've never tryed it on a model
    but full scale aircraft designers sometimes use the same princeaple.
    The frequency that the control suface resonates depends on the
    stiffness of the suface (the twistable aileron tips in your case)
    and the mass (actually moment of inertia) of the surface. Increasing
    the stiffness or decreasing the mass should increase the resonant
    frequency. So.. if you attach a small weight to the aileron tips
    then go out and recreate the conditions which caused the flutter,
    if the tone (i.e. frequency) of the flutter is lower or it isn't
    there anymore, then the weights on the aileron tips affected the
    flutter and therefore it is the ailerons which are fluttering.
    This should work for any surface so they could be tested one at a
    time to find out which one is fluttering. If you actually try this
    be very sure to attach the weights securely so that the high speed
    airstream can't pull them off and check your CG. Also, I would
    seal the rudder hinge gap.

    GES
    

    One method I've seen for adding a counterbalance to the control
    surface is to install a typical control horn out at the tip of
    the control surface so that the holes that normally a clevis
    would be attacked to are adjacent to the hinge line. Take a small
    length of 1/16 wire  (2") and bend a right angle in the wire app.
    3/4 of an inch from one end. Add a small wheel collar to the wire
    and then make two more right angle bends.
                          Front view                     Side View
    	IE.              _______                              .
    		        |                                     |
    			|                                     |
    			|         __<----Wheel collar         |
    			 --------|  |--                      (.)
    				  --   |                      /
    				       |                     /
    				       |                    /
    				       |	           /
                                       |                  /
    				       |                 /
                                                          
    
    		Slide the upper part of the wire thru the control horn
    bottom hole and then back thru a higher hole. Adjust the wheel collar
    to secure the wire and then add weighht to the wire that extends
    forward of the hinge line. They used common fishing sinkers as 
    weight.
    
    							Tom

    Well, it wasn't much work so this weekend I replaced the ailerons.
    I took a number of the suggestions that I received here and elsewhere:
    
    o Stiffer aileron stock
    o Laminated top and bottom with 1/64 ply (they're stiff now!)
    o Extended the wing tips the width of the ailerons so the ailerons 
      are more protected from turbulence at the tips
    o 4 hinges per aileron, instead of 3, one about 1/4 inch from the
      outboard ends.
    o Filled the gap with ultracote (had done this before, anyway)
    
    Today was the test flight. The results were encouraging - a high
    speed pass in front of me resulted in only minor noise, which I'm
    sure isn't the ailerons this time. I think it's the ultracote on
    the wing itself is flopping because it's not stuck down well to the
    ribs. Forming a very nice drum/resonator. I'll work on that next 
    and see if it's completely cured.
    
    Dave

>Up again, and, you guessed it - aileron flutter. Down again. This time, we
>find  the  torque rods haven't worked themselves loose. The torque rod is 4"
>long  from  servo  to aileron, so it can twist, like a Macpherson strut in a
>car.

    Really, you mean Torsion Bar. A MacPherson Strut is the shock absorber,
    It only goes up and down (actually, it does twist, since it provides the
    upper pivot point for steering, but it's supposed to do that, there's no
    torque at all, it's anchored at the top, but free rotate at the bottom).
    I don't suppose that makes any difference to your problem though. 

    If you can get the wing apart easily, you might try using a push-pull
    NyRod at the center of the aileron, rather than the current torque rod
    at one end. That would eliminate the torque-twisties altogether, and,
    since the actuating force on the aileron would be applied at the center,
    instead of the end of the strip, you are effectively halving the length
    of the aileron, and so reducing the ability to flutter by half
    (actually, it'de be doubling the fundamental frequency of vibration). 

Ajai,

I have a GP Trainer 40 that had serious problems with the ailerons. Basically
they were extremely ineffective. I tried sealing the gap - no effect. Adjusting
things so there was a little washout - no effect. Lengthen the throws - no
effect. And on and on. I took a long hard look at the plane and finally came up
with a solution that fixed the problem. In fact the ailerons are now so
effective that I have reduced the throws to almost nothing.

My evaluation of the problem on the T40 (it applies to the T60 also - I'm 
helping a friend build one) is that the ailerons simply aren't big enough 
for the extremely thick, symmetrical airfoil of the T40/60 wing. They 
never get close to clear air to do their job. The airfoil is 2+ inches thick 
and the ailerons are less than half of this wide.

I replaced the stock 3/8 X 1 rectangular ailerons with 3/8 X 1&1/2 inch tapered
aileron stock and viola - super effective ailerons. Now, I'm no expert, so my
evaluation of the problem may not make aerodynamic sense, but the problem is
definetly solved.

Hope this is of some use. My T40 is a fun plane now that it works.
Good Luck,
Randy

        Re:             <<< Note 239.1468 by DIENTE::OSWALD "Randy Oswald" >>>

                I saw Ajai's  plane  yesterday  and noticed how thick and
        short the ailerons are.    Also  the  fact  that  they flutter so
        easily indicates to me that the airflow around them must be wuite
        turbulent.  There is a poor  transition from the trailing edge of
        the wing to the aileron, which would help create turbulence, so I
        believe Randy's solution is the way to go.  Tapered ailerons that
        trasition  well  from  the  trailing  edge  should  eliminate the
        tendency to flutter.
        
                      _ 
                     / |
        |  _====____/==|
        |-/____________|
        |    |        o \
             O           \ 
                          O
         Hang in there! o_|_
                          |
             Anker      \_|_/

    Randy,
    
    Your T40 seems to have come with narrow ailerons, strangely enough!
    
    My T60 has 1 1/4" ailerons, and Charlie -Chuck-Yeager-Ace Watt, my
    test pilot and instructor, had no complaints about the effectiveness
    of the ailerons. Your 1 1/2" wide modification is pretty close to
    mine, so...
    
    We heard a distinct, low frequency buzz a number of times, with a
    number of experts watching intently, so I don't think there was any
    mistake in the verdict.
    
    Anyhow, I have currently covered the hinge line gap with film on both
    sides of the wing, hacked off the aileron from the wing tip until the
    first hinge - about 3" in all - and stuck it to the wing. The idea is
    that there is no movable surface present to be fluttered by the wing
    tip vortex. A second thing that happens is that I now have a hinge
    supporting the extremities of the ailerons, per the GP guys advice.
    
    That's 3 pieces of advice rolled into one, so let us see what happens.
    
    Yo Test pilot, let go fer it!
    
    ajai
    
    

From:	PNO::CASEYA       "RC-AV8R" 28-JUN-1989 10:58:03.40
To:	HPSRAD::AJAI
CC:	CASEYA
Subj:	FLUTTER

Ajai,

First, congratulations on the successful first flights on yer' T-60; second,
condolences on the flutter problem.

I'm not sure I ever encountered flutter on a T-60, though I'm sure it could
happen to _any_ airplane, under the right circumstances.  Flutter can result
from any number of causes: sloppy/loose linkage(s); sloppy hinges; too wide a
hinge-line gap; etc.

My most recent encounter with flutter was with the ol' Yeller' Peril which, 
after I don't know how many hundred flights began to exhibit aileron flutter. 
The cause was sloppy linkages resulting from the normal wear of hundreds of 
flights.  Since the Jungmeister has 4-ailerons, I wanted to avoid having to
completely rebuild the linkages (which were plenty safe, just sloppy).  So, I
decided to try sealing the already pretty tight hinge-line gaps first on the
advice of a local pattern and race pilot.  If this failed, I figgered' I was
doomed to tear into the 4-ailerons' associated linkages.

I sealed each gap from underneath by flexing the aileron to full up deflection,
then applying a strip of clear 3M upholstery repair tape (available in most any
hardware store) the length of the gap and adhered to the trail edge of the wing
as well as the lead edge of the aileron.  In this way, the movement of the sur-
face is not restricted but it is stiffened considerably.  This solved the flut-
ter problem on the ol' Peril, I'm happy to say.

The fellow who recommended the fix to me swore he could fix _any_ flutter prob-
lem using this technique so you may wish to give it a try on the T-60.  You
might opt to use Monokote instead of the tape I mentioned but I think the key
is adding stiffness to the surface as well as sealing the airflow through the
gap which, I think, is the realm of the tape more than Monokote.

By all means keep me/us informed of yer' progress.  And, hang in there...there
are always a few teething problems to sort out with a new bird.

Adios, amigo,	Al

    RE: .-1, ERIC,
    
    I'm tickled we could help you solve yer' problem!  Be sure and update
    us as to yer' progress and results.  
    
    Chuck Collier and I went out Saturday AM to put some Top Gun practice
    flights on his Jug and the ol' MiG-3.  Chuck was instantly plagued by
    aileron flutter which mystified us both as everything'd been
    rock-steady on the previous flights.  I put three flights on the MiG
    and slaked a little rust off in the process.  Everything went fine and
    the MiG is ready to go, but those $#@*^&% rubber pushrods (Gold 'n Rods) 
    got me again; on the first flight, I noticed I had _gobs_ of up trim in
    the elevator while preparing to start the engine.  Those blasted
    pushrods had expanded from the 90F temperature as they always do (and
    the mfgr has the unmitigated gall to claim they are "temperature-
    compensated"...now I'm here to tell you that, IMHO, that's nothing
    short of a bald-faced lie!
    
    Anyhoo, I had to guess at how much down trim to dial in and I guessed
    too much; takeoff roll proceded pwefectly 'til I got to full-throttle,
    at which time, the tail came up past level and no power on heaven or
    earth could stop its going over on the nose.  But, no harm done save
    for a broken prop, scratched spinner and slightly dented ego.  I
    replaced the prop, reset the trim and had no further problems, making
    3 letter-perfect takeoffs and landings (which are always my first
    concern when competition draws near).  So I've goat a spinner to
    repaint...big deal, that'll take all of an evening or two but I'm
    gonna' cut outhe prop clearances, prime and paint a backup spinner in
    the process so, if this ever happens again, I don't have to advertize
    my stupidity for the remainder of the meet.
    
    But, back to Chuck.  He tried a few things at the field but the flutter
    persisted through 2 subsequent flights so we went back to his place and
    tried to sort things out.  We took out a minute amount of play in the
    aileron linkage but Chuck'd convinced himself that the new nav lights
    and lenses he'd added since the 1/8 AF Fly-In must be setting up some
    turbulence.  I doubted this and said so but hey, you gotta' try
    everything that might help, right.  We were back at the field about two
    hours later and tried it again...NO JOY!  The flutter was still there
    just as bad as before.  Then I overheard a guy in the pits telling
    someone he'd read that flutter was primarily the function of having the
    CG of the control surface itself too far back...a light went on when I
    heard this.  I asked Chuck, "Didn't you tell me you outlined the
    ailerons and flaps with brass tubing to clean up the contours?"  "Yep!"
    he said, "I sure did...looks nice, doesn't it?."  "Rip 'em off," I
    commanded.  "Whaaaaa....??" Chuck responded, he's eyes wide in
    disbelief.
    
    I was taking a helluva chance here but felt I was right so I explained
    that the ounce or so he added to the very trailling-edge of the
    each aileron was more than enough to shift the surfaces' CGs back and
    induce the flutter.  Chuck wasn't a happy camper as, with the aid of a
    scalpel, he peeled the tubing off of bothe ailerrons.  I balanced one
    of the pieces on my finger, testing its weight up and down, and offered
    that it was plentty heavy enough to be the culprit (I hoped).  We
    refueled, fired up the monster Zenoah G-62 and Chuck taxied once more
    for takeoff.  (I had my fingers crossed [both hands] behind my back,
    not totally convinced that I might not have to run for my life if the
    problem persisted.)
    
    Chuck made yet one more rule-book takeoff and retracted the gear.  The
    moment of truth was at hand as Chuck dropped the nose, getting the
    aircraft stepped and making a max-speed pass...we watched, we listened
    and EUREKA!  NO FLUTTER!!  Numerous successive passes proved it was no
    fluke and we rejoiced that this ominous problem had been put to bed.  I
    never liked the idea of using tubing for this purpose in the first
    place but NOW I have a good reason for that dislike.  Chuck's happy and
    we BOTH learned something first-hand. 
						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)

    Re: .-1, Kay,
    
    Chuck outlined the very edge of his aileron and flap trailing edges
    with ~1/16" brass tubing to straighten/smooth out the overall wing 
    contour at the trailing edge.  The tubing was not cut in any way
    (except in length) and was CA'd right to the surfaces' trailing edges.
    Also, he reasoned that this provided him with a hard dam, if you will, 
    whereby he could apply fillers to the aileron/flap surfaces and block-
    sand the waviness out of them without getting the trailing edges too
    thin.  I told him I wasn't crazy about the idea when he did it but never
    guessed it would have the near-disastrous effect it had.  I've seen this 
    done using 1/16" dowel but the stuff is hard to find and I'm not sure its
    weight might not've been enough to've caused the same flutter problem
    Chuck experienced using the tubing.  Lay yer' left ear on yer' left
    shoulder as you look at the terminal drawing below and I think you'll
    get the idea.  
    
    					o  <---- 1/16"brass tubing
    				       / \
    				      /   \  <---- aileron (or flap)
    		   hinge-line ---->  /_____\
    
    The lesson learned is to watch the weight in the aft 3/4 of the
    aileron's width and keep it light to avoid flutter.  I know I'm gonna'
    watch this especially closely from now on.
    
    						 __
				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)