Flutter

[Torsten Spitzner]

Most of us may have heard that distinct sound of control surface flutter, which usually ends in abrupt disaster This is a .60 Hobbico Trainer that I aquired as an engine test bed. It always had that flutter sound and I'd often shout out to the previous owner to "slow down".

When I actually saw what flutter looks like, this model was immediately grounded for a complete rebuild.

 

[John Lee]

Wise choice!

 

There can be multiple contributing factors and solutions but an easy first step in effecting a cure is to seal the gap between the control surface & main plane with a strip of covering material or adhesive tape.

 

Those of us who flew the early generation of the Mick Reeves Gangster will recall it occurred on most of those models. That was solved by stiffening the ailerons with a lamination of thin ply.

[SIMON CRAGG]

Remember it well!.

 

Also, try and make sure there is no slop at all in the servo arm / clevis / ball link etc. Square trailing edges seems to help as well.

[Simon Chaddock]

The full size remedy is to add balance weights ahead of the hinge line. Done correctly the surface will not flutter even it becomes disconnected.

Just saying. 

[John T]

A few years ago I was lucky to get a 'V' tailed electric thermal soarer down in one piece after flutter cracked one half of the tail.  It was only the plastic covering holding it together!

I made a new tail and covered it with traditional tissue doped on in the hope the extra torsional rigidity would help, and never had a problem again with flutter.

[Martin Harris - Moderator]

Not something to take chances with. I witnessed a fairly large aerobatic model encounter flutter - it removed one aileron but landed safely but worse, the violence of it actually cracked the main spar!

 

A controlled full size flutter test (and brave test pilot)

[J D 8]

      First the throttle link to the engine went awol, and engine which was to much for this model went flat out. It kept flying for couple of minuets with the elevator fluttering until its link broke.

  With only aileron and rudder left it was now in a steady decent and all I could do was steer to a safe crash hoping fuel would run out. [it did not]. All my fault should have done a better job on the control links of this old Ezee Pzze which later examination after showed they had gone brittle.

[gangster]

4 hours ago, John Lee said:

Wise choice!

 

There can be multiple contributing factors and solutions but an easy first step in effecting a cure is to seal the gap between the control surface & main plane with a strip of covering material or adhesive tape.

 

Those of us who flew the early generation of the Mick Reeves Gangster will recall it occurred on most of those models. That was solved by stiffening the ailerons with a lamination of thin ply.

I built numerous gangsters 52 and 63 back in the day. I always fitted a strip of trailing edge outboard on the Ennis ie aelerons stopped before tip of the wing. It was very effective 

[Rich Griff]

Thanks for the heads up about the "gangster" problem, didn't know about that !

 

I have never experienced a control surface flutter as far as I know, but I have heard it.

 

Jon made and was flying a fast model throwing it all over the sky. Flying down wind into wind diving at a shallowish angle increasing speed we heard the sound. He shouted out it's got flutter and it crashed quite spectacularly.

 

Elevator flutter due to high speed...

 

An hour later his biplane crashed, loss of control due to battery drop out.

 

He was having a bad day.....

[Rich Griff]

Hi gangster, please could you repost your cure for the gangster flutter problem, seems predictive text itise has happened ?

 

Thanks.

rich

[Andy Stephenson]

The first time I had flutter was on the ailerons of a Frank Vandenburg Vertigo. The plan said to fit 12gauge aileron torque rods. The plane landed but with a stripped servo gear. The torque rods were pulled out and 10 gauge ones fitted and that cured the problem.

[Martin McIntosh]

It is almost always due to lousy, sloppy linkages, especially with those awful strip ailerons from the days of expensive servos and systems which could not cope as well  as today with two aileron ones.

[Torsten Spitzner]

Yip, the Hobbico had seriously worn out torque rods on strip ailerons. It now has flaps and a servo on each aileron. It's also a completely different model now. Maybe on a rainy day I'll post the rebuild...

[Jesus Cardin]

I has just the same problem with a Carl Goldberg Piper Cub with its strip ailerons. Solution was to switch from a single ailerons servo to a servo for each aileron.

[Chris Freeman 3]

Also important that the control surfaces are not thinner than the main surfaces, I always try to have slightly thicker control surfaces as this creates a smoother airflow over them reducing flutter and also giving better control. Any slop in the fittings and servos increase the chance of flutter.

[Andy Stephenson]

Strip ailerons that reach all the way to the wing tip are also liable to flutter due to tip turbulence. This why you will see some designs where the wing tip extends back beyond the aileron.

[john davidson 1]

Perth College built a model as a project and asked to fly it at our field, all fit to go with a buddy lead. A few seconds into the flight came the dreaded BBrrp and the ailerons separated, mind you the instructor said it was a good lesson in aerodynamics!

[Don Fry]

On 15/07/2023 at 19:25, Martin McIntosh said:

It is almost always due to lousy, sloppy linkages, especially with those awful strip ailerons from the days of expensive servos and systems which could not cope as well  as today with two aileron ones.

In my case, a Basic 3D, plan build, built too light. Right horizontal stabiliser, and elevator, exploded in a hooligan manoeuvre.

[john stones 1 - Moderator]

Never had it.

[Don Fry]

2 hours ago, john stones 1 - Moderator said:

Never had it.

That’s why you are not paranoid. The sight of your creation, a seconds low buzz, and you are a passenger, is not good. 

[john stones 1 - Moderator]

4 minutes ago, Don Fry said:

That’s why you are not paranoid. The sight of your creation, a seconds low buzz, and you are a passenger, is not good. 

 

Yep I've seen it Don, just not on my models.

[Geoff S]

11 minutes ago, Don Fry said:

That’s why you are not paranoid. The sight of your creation, a seconds low buzz, and you are a passenger, is not good. 

 

It's probably even worse if you are literally a passenger 🙂

[gangster]

On 15/07/2023 at 13:38, Rich Griff said:

Hi gangster, please could you repost your cure for the gangster flutter problem, seems predictive text itise has happened ?

 

Thanks.

rich

Ah I don’t know what happened to my post. The cure was not to have ailerons right to the wing tip. Simply put saw the last two inches off the ailerons and glue in place as fixed trailing edge. i.e don’t have strip ailerons right to the wing tips.