Matirx, Hope your friend gets his Synergy sorted out...

I got a reply from Alvin Braeckman in Germany just before with some very usefull information regarding the Synergy 90 3D Tail Flutter issue, I have copied it here fo all to see:

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Patrick

Hello - hope your fine and your Synergy is still living.

I have read about your problems reg. the tail flutter. It took me a very long time to understand what was happening on a few kits.

Here as the modifications we introduced since you bought your plane

1) full, plain Balsa stab - this to avoid the problem with Balsa quality (I have seen that a few stabs were up to 30% lighter than the other ones - this could be one reason for flutter

2) introduction of 2mm carbon bracing for the stab (even if the stab is plain, we feel that there is a need for bracing as we do not want the fuselage to break)

3) introduction of carbon rods to slide over the elevator linkages

4) we now build into the fuselage some light ply reinforcments into the fuselage (we have seen that the 3x3 mm Balsa reinforcments are not enough to resist modelers abuses

5) servo recommendation - do not use cheap standard servos as the quality of the plastic case is very soft.

to resume : it is VERY important that the linkage to the elevator is very stiff - so please slip some carbon tubing on the 2 mm steel linkage - brace the elevator with carbon rod - and install if yet not done good quality servos. (if you do not have carbon tubes or rods or even want a plain stab - just tell me I send you everything by letter)

The basi problem is that Cristophe decided to have very efficient elevators. Therefor he decided to keep the surface straigt with a very thick trailing edge. This configuration is very prone to flutter (especially with the size of the movable parts) - therefor we must insist on extremely stiff linkage (replacing the horns and other parts of the kit is NOT the issue)

Best regards
Alvin

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I agree with Alvin that the tail linkages must have NO play and particular attention should be paid to ensure this. I feel this is the number one reason for tail flutter on this design.

I also agree that the problem is not with the supplied linkages, but I still feel happier knowing I have some slightly stronger horns with bigger bases.

I am running JR DS-811 Servos on the elevators which have a small ammount of movement in the gear train, I am guessing this will get worse in time so I am looking at upgrading to a better servo.

Thanks again Alvin for the ongoing support.

I had another successful day of flying my synergy without incident today so hopefully this will be the start of a trend.

Happy Flying
Patrick