Hello
I have 1.20 Carl Goldberg ultimate with a Moki 1.35, flies like heaven (4 ailerons, two servos, one in neach half (bottom wing)
I have had it for the last 3 years with no problems at all.
About a month ago I landed terrible dead stick and the firewall came off, i glued the whole thing with 30 minutes epoxy and fixed it.
A week ago went out and flied again , eprfectly, at the 3rd flight I had aileron flutter, pretty noise, landed, traied it again andthe same thing abou 3/4 full throttle.
I sealed the ailero-wing gaps with monokote, today tested and had exactly the same thing, started to almost half roll, landed tested on gound, nothing found except my monokote seals were almost dettached.
I glue some lead in the ailerons to change the mass , and exactly the same.
I am thinking that I am just missing balancing my prop, about the linkages, they are the same I have always had, as mentioned before I have not had anything like that in 3 years with this plane it just started 2 weekends ago.
Any suggestion would be highly appreciated
regards from Brazil
Omar

Hi!
Flutter is due to a too weak aileron set-up and too much speed !
Check your ailerons so that they are stiff (the balsa that is) and then check the linkage. It's vital for any set-up that you adhere to the general law that says: shortest possible servo arm and longest possible aileron/rudder arm and no flex!! That's very important!!!! Othervise you build in flex in the system!

Then ...the Moki engine is just too big and powerful for that plane...that's the main problem! Too much speed! Use a .91-1.20 fourstroke and everything will be fine.

If the crash was the moment when this started, I would look for a bad hinge or a crack in the wing or aileron. Flutter that didn't remove the aileron from the plane shouldn't have torn up your hinge seals, but if a hinge has failed allowing the aileron to pull away from the trailing edge of the wing that would explain it.

jaka
thanks for the answer
As mentioned before I have had the same plane-engine configurarion and I never had any problem, anyway I will work on vibrations,meaning balacing the prop and review the engine soft mount
Regards

Have you checked your hinges? That would be my first guess on a plane that has flown well before and suddenly started fluttering.

A crack in the wood structure that connects servos and ailerons or other control surfaces could have been developed during the crash.
The structure works as part of a push-pull system, as counterpart of the linkage and servo.
A strong linkage plus a weak structure base equals a weak system.

Feel how firm each surface is when you try flexing it by hand.

Also, servos may be worn out the gears in these years.

I believe that engine vibration and flutter are not related.

The only good solution that I know is balancing the control surface aft and forward the hinge line:

http://www.centennialofflight.gov/es...rol/TH28G5.htm

If you added the lead behind the hingeline you just made things worse remove it immediately, but back to mass ballancing in a moment.

First assure that there is no damage as outlined by Jester to any of the structure, linkages and hinges. Next carefully inspect the servo and rotate them power off to full throws carefulling feeling for any stripped teeth from the flutter episodes.

Now if everything is solid (gap seals will not do anything to help) make four simple mass ballances as pictured, One for the bottom of each aileron. You do not have to ballance the surfaces completely or anywhere near it a simple thumb sized fishing weight will do about one and a half inchs forward of the hingeline.

This will stop the problem everytime unless there is now structural damage.

John

Hi!
That will not help! The problem is a too flexible aileron linkage (aileron, steelrodds,servo drivetrain, and so fort)!
If you grab the aileron with your hand it should not be possible to move it when the radio is on!

Prop out of balance will not cause flutter.....since the flutter starts at 3/4 throttle and above...you have a bad hinge, loose clevis pin, or servo gear slop, or a loose servo.....
Just to make things clear...flutter will sound like a buzz....you may, or may not see the surface move while it is in flutter......
Oh and by the way as this is a bipe with only 2 aileron servos have you checked the pushrod and the connections between the lower and upper ailerons?
Bottom line get this fixed before you fly it again....flutter can cause the destruction of the airframe instantly

You are wrong. Not only will it help, it will stop it. The only reason you do not know that is you simply have never done it. I have, and I have done it not only with a wide variety of model aircraft that have actually demonstrated flutter in flight (I am and talking hard core flutter ya know that which not only sounds like a machine gun but it also visable).

These all were some of mine and other fellows particularly at the warbird races which were lucky to survive the first dramatic episodes.

Jaka the other contributing factors you mentioned are indeed contributing factors however its a far more complex problem and that is only a scratch on the surface. Flutter analysis is a entire aeronautical engineering discipline in itself in which whole careers are committed.

Jaka it may be of interest you to know that virtually all full scale aircraft use controls surfaces that do indeed feature mass balancing to some degree.

Now in addition Jaka it agine may interest you to know that back in the eighties when the Fun fly aeroshaft airplanes (these aircraft were the progenitors of the modern 3D types) became all the rage, that the hugh control surfaces combined with the rubberband like fuselages (aeroshaft), The aero elasticity became absurd and of course those airplanes would always flutter anytime full throttle was used other than a perfectly up vertical line.

It was during that time after I had suffered complete controll separations on at least six airplanes and that I started extensive tests with mass balance on a fun fly type, a published design called a Richochet, Not my design. These included balance all the way up to 100 percent of all surfaces and I repededly found that balance anywhere above 20 twenty percent in every case eliminated all trace of flutter and full power could be used in virtually all attitudes except straight down.

These results have also been evident with later types of airplanes that I have used the simple balances on also.

Jaka it works and works well at the speeds most of our flying is conducted and it works most dramatically For any airplane that has demonstrated and survived the onset of flutter where all else has failed. I can only surmise Jaka that you do not know that because you have never and won,t try it.


John

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Dag yo! Jaka got owned.

Mass balancing makes perfect sense, but it may not be the issue because the plane has flown right for 3 years. With any troubleshooting procedure, the first question to ask is, "Has it ever worked right?" Here the answer is, "Yes." The second question to ask is, "Has anything changed or happened since it last worked right?" In this case, a light crash has happened. Logically, it makes sense to look for damage caused by the crash as the culprit.

Thanks everyone for the contrbutions it looks like I will be busy this week.
Iwill check the linkages of the ailerons (maybe increase diamater as i am not sure i am using 4-40)
About the surfaces balancing , this the first time I hear about it, although the pictures are explicaive, is there any good matwrial to read abount it so I understand the process and also what should I buy for doing it?
Thanks again averyone
Omar

No matter what is causing the problem now, John Buckner is right on the money, mass balancing will stop the the surface from starting into flutter mode in the first place.

Bob

Hi!
Sorry but it will not! The problem is a too weak aileron set-up (Linkage, balsa surface, servo gear play, kvick links etc). I have tried using massbalancing i pylonracing but it did not fix the flutter tendencies. Stiffer flying surfaces did.

LOL, I guess I should have stated, mass balancing done properly will stop flutter in the first place...

Bob

Here you have some reading:

http://findarticles.com/p/articles/m...1/ai_n8825915/

http://www.cs.wright.edu/~jslater/SD...ter_banner.pdf

The concept behind the mass balance is that a control surface that has the CG by the hinge cannot flutter.

Flutter is produced by the acceleration of the "heavy" control surface alternatively until it reaches the max deflection in both directions in a rapid succession and with great force (mass of the control surface times the acceleration).

The acceleration is a function of the air turbulence; however, we can control the mass that oscillates by moving the CG towards the hinge, which is what balancing does.

Strong linkages help hold the oscillation, slow speeds and hinge tape reduce the air turbulence, but those remedies do not eliminate the cause.

Okay,i was going to stay out of this post at first,because it seamed that all the advice being given was reasonable and could help. But it seam's as this post goes on,everyone is overlooking the one thing to me that is the most obvious. I have built and flown,numerous Carl Golberg Ultimate bipes over the years. If built exactly according to the plans,they are light and fly great! Only draw back is,that after a year or two of flying they tend to get structurely weak in the wings! Any slightest rough or bumpy landing will and usually does cause seperation of the trailing edge of the from the wing ribs. It's not easily seen or felt because only one or two ribs let lose. They also tend to break the outer wing strut mounting ribs. All of these will cause the flutter you are getting. It's not caused by you linkages being lose,the aileron hinges being bad, or servos going bad ( providing all those were checked and confirmed as okay). Your flutter is coming from the fact that the wing panel is actually moving,while in flight. The most obvious give away,was your saying,that it got so bad you had to trim it out to land. Surface flutter of any kind,CANNOT be trimmed out!

I learned this lesson the hard way on the ultimate's! lol Since my autopsy of my first one,showed the defects,i built the rest of them reinforcing the trailing edge's. And have since never had a repeat of the first.

Hope this info help's

Art

For those times when all else fails assuming the airplane has survived: Four Forty threaded rod ends some nuts, washers and a few fishing sinkers with the hole in the middle.

John Buckner's method is the way to do it for a good retro or initial fit. If the TE gets loose, as outlined by abacro, then the system of the TE and aileron will flutter because the mass balancing is set up for the aileron only. The 'system' of the TE and aileron will flutter in this case. Your wing may not be torsionally rigid enough, too. The whole wing and aileron may be going thru oscillations. Make sure the cabanes and struts are secure. If you cut into your wing and make repairs go ahead and make the LE of the ailerons thicker than the TE of the wing where ailerons hinge. This helps if you get flow separation on wing ahead of the aileron. Keep the TE of ailerons squared off. There are many methods to make this work. I like to make Frise type ailerons and include static mass balancing in the fwd part of the aileron. It helps reduce adverse yaw, decreases drag of weights hanging in the breeze and reduces chance of flutter. I am also 'guilty' of making mass balances on the outer end of ailerons as seen on many fullscale counterparts with the cutouts in the wings to let them pass. They look cool, too! Good luck and remember to pull power in nose down attitudes- just kidding- you can do whatever you want, right?

Thanks averyone for the help
I will get bussy saturday and check out my wings
It´s good to mention that to avoid rigidness (if that´s a word) iI built the wings in foam core balsa so I should not get the torsional issue or slackness in the TE.
I will chek them out anyway and keep you posted what happenes next.
regards