Flutter

Did you dumb-thumb it or was luck just not on your side. Whatever the reason, tell us all about your (or other's) crashes here.

Flutter

Postby cuban8 » Wed Nov 07, 2012 10:08 pm

Talking to my mate at our club meet last night, he told me about the loss of his new model on its first flight. I won't name the model but it was a scale (ish) aerobatic job with a 38cc petrol motor. After a few gentle circuits he pulled the model up into climb whereupon a wing snapped off at the root with predictable results. On inspecting the wreckage, the carbon wing joiner/spar had failed at the wing root to fuselage junction.
He subsequently spoke to the UK supplier who immediately asked "did you have the endpoint settings on your ailerons less than 50%?) My friend was using very good quality digital servos and yes, he had reduced the movement of the large ailerons for initial flights by setting a low endpoint value. "Ah!" said the supplier, "that's your problem, we've seen this a few times" and explained how having a very low endpoint setting on digital servos had led to the model's demise by aileron & wing flutter ultimately leading to the broken carbon spar.

My friend told the supplier that he'd taken great pains (as always with him) to install the control rods in such a manner to reduce all mechanical slop to a minimum with quality hinges and pushrods, so was initially surprised at the diagnosis. Anyway, it turned out that the advice to not set low endpoint settings was in fact in the model's manual (that my friend overlooked) but sportingly the supplier agreed to send him a replacement kit.

I don't understand the suppliers explanation re endpoint and digital servos, as I thought digital servos worked harder to lock their commanded position, irrespective of control input, rates, or endpoint.
Perhaps I'm missing something here, so if anyone can put me right I'd be obliged.
cuban8
 
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Re: Flutter

Postby Bullet-Bait » Sat Mar 23, 2013 1:56 pm

I've just recently started to do a bit of IMAC and Pattern flying and the guy that is teaching me the ropes and has been flying these disciplines for a very long time told me that the absolute best way to set control surface throws is mechanically. Any time we use an electronic system to achieve the same goal we are not giving a servo the best mechanical advantage. However, it is sometimes not possible to get the exact amount of throw we want mechanically and that is the only time we should use End Points, for the finer adjusts.
I myself never really understood it but he's been around along time and I take his word for it. Just maybe your friend learnt this lesson the hard way?
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