Bitten by the flutter bug - RC Groups
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Nov 05, 2008, 10:45 PM
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AndrewBurns's Avatar

Bitten by the flutter bug

Hi all, I've recently been reading up on some techniques for improving my launch. I've started running a few paces before the throw, trying to keep my arm locked and extended etc and I was seeing some improvement today. That was before I started to really put my back into it.

I've always known my current glider has a big problem with flex and flutter in basically every surface and structure. The tail boom is very week and the control surfaces have a large amount of slop when built as per the instructions (if I were to make it again I'd do so many things differently...). However today on my highest power launches I noticed a sudden huge increase in drag and a loud whipping/flapping noise just at the point of release. It honestly felt like a tip strike but without the impact. On recovery I noticed that the aluminium pushrod on the outer flapperon was totally buckled. I bent it back into shape and was able to reproduce the same damage every full power throw without releasing the aircraft so I know it wasn't landing damage.

I plan to try reinforcing the pushrods by binding some wooden skewers to them with CA and thread. However I'm more concerned about the integrity of the entire wing during high power launches. I've seen my ailerons flutter before when launching into 20+ knot wind however this felt different, out of the corner of my eye it looked like the entire wing was warping in a torsional fashion.
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Nov 07, 2008, 10:15 PM
philkiteflyer's Avatar
Hi Andrew, how'd you get on with this problem? I'm surprised no-one has responded. My first action would be replace the pushrods with carbon but that may cause more damage than it fixes. With a stiffer pushrod all that flutter is transferred to your servos which could cause gear damage.

I am new to DLG but have been modelling off and on for 30+ years. Looking at your photos the glider is EPP wings and pod and was probably only designed as a 'Starter' type plane. It may be that you have reached the upper limit of it's design performance, and you have 'out-grown' this plane.

That would mean you will have to look for a 'next level' model. Yeah! a good excuse for spending money

Also, 20+ knots is a pretty strong wind ! ! Are you flying off the flat or off a slope?

Phillip C

PS: heres my build log progress of a wooden DLG.
Nov 08, 2008, 05:53 AM
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AndrewBurns's Avatar
Heh I already decided it was time to get a nice glider, I ordered a Blaster 2 and it came snapped in half I'm just not allowed to have nice things. It's getting replaced but it will likely be a few weeks at least until the new one arrives hopefully not in shattered kit form.

The only slope near me is a veeeery gentle hill, I was flying there for the 20 knot wind just to see if it would generate any decent slope lift, it didn't really though I was able to surf above some trees for a few minutes.

I've been following that build thread for a little while, it's looking really nice. I've been considering getting a foodsaver or something and having a go at rolling my own, putting all my uni edumacation to work for once :P Just need some free time (don't we all).

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