Welcome Guest [Log In] [Register]
Welcome to Felbridge Flyers. We hope you enjoy your visit.


You're currently viewing our forum as a guest. This means you are limited to certain areas of the board and there are some features you can't use. If you join our community, you'll be able to access member-only sections, and use many member-only features such as customizing your profile, sending personal messages, and voting in polls. Registration is simple, fast, and completely free.


Join our community!


If you're already a member please log in to your account to access all of our features:

Username:   Password:
Add Reply
Eindecker Flutter - re-posted
Topic Started: Jul 3 2017, 07:58 AM (43 Views)
CliffW

Hello

The latest newsletter mentions:

"Ian Dinan had his Eindekker going which he has to keep the motor no more that half throttle to stop the elevator fluttering - you need to get that sorted Ian or it will self destruct."

30 odd years ago my day job was preventing and curing flutter on full size aeroplanes - at British Aerospace.
If this model still has a problem, I may be able to help?
If I can see some pictures of the tailplane and elevators - top, bottom, side, front view - I may be able to suggest some solutions.

I encountered flutter of all 4 ailerons on my DB Scout biplane in a dive and fixed it by mass-balancing - see picture (if I have managed to include it). There are other more elegant solutions, but this suited my purpose as the weights aren't noticeable under the upper wing of a biplane. They work by moving the centre of gravity of the ailerons forward of the aileron hingeline - so when the wing bends (accelerates) upwards the ailerons move training edge upwards to oppose the motion, and the same for downward motion. The full-size Messerschmidt 109 aileron has a similar installation.

Posted Image
Best wishes

Cliff
Attached to this post:
Attachments: IMG_0531.jpg (30.86 KB)
Edited by CliffW, Jul 3 2017, 08:05 AM.
Offline Profile Quote Post Goto Top
 
IanD

Thanks cliff for the interesting info on Flutter.
Update on the Eindecker; The cause of the tail flutter was a fractured tailplane where it joins the fuselage.
The sheet balsa used on the Tailplane of this Balsa USA kit was rather thin and must have easily cracked as a result of
storage in my rather cramped garage. (caused by too many models !)
Was easily repaired and reinforced with triangle balsa strip. Better than new and no more tail flutter !

I have added weight to the nose and have a large amount of Rudder linked to Aileron movement to make turns better.
However turns are still not quite right I am going to have to add in more rudder manually !

Plenty of power with the OS52 FS on a 13x6 APC prop, half throttle is all it needs on a calm day.
But beware of the thinner silicon fuel tubing, the walls can crush on modest curves as I found to my cost one day when the engine kept cutting mid flight.
It was not until I did an inspection to find out why the motor was suddenly cutting that I found the Silicon tubing was starting to deform on the bend from the fuel tank to the engine
causing less fuel throughput. Thicker walled tubing solved the issue.

Happy flying,

Ian D













Offline Profile Quote Post Goto Top
 
CliffW

Hello Ian

I'm glad you found the problem and all is now well.

Flutter arises when aerodynamic forces, flexible structure (or rotating controls) and mass (weight) distribution conspire to work together to cause oscillations that generally become more severe as speed increases - until the forces break the structure.
Stopping flutter involves working out what is going on and then changing one of the three contributors.
It's a bit like putting out a fire by removing the fuel, the oxygen and/or the heat.

Trying to change the aerodynamics is difficult (and can give alarmingly unexpected results!)
The easier options are changing the mass distribution (usually by adding weights) or
stiffening the structure, which is what you have done.

Best wishes

Cliff

Offline Profile Quote Post Goto Top
 
1 user reading this topic (1 Guest and 0 Anonymous)
« Previous Topic · Club Chat · Next Topic »
Add Reply