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Pete in Northiam

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Pete in Northiam

Having seen several F3-RES gliders hit wing flutter on the bungee and watched as tailplane flutter led to the sad demise of an F5-RES under power on Saturday, I thought it was about time I got past my own limited understanding and read more about the causes and cures. I found the link below a useful summary of the physics of causes and fixes. If you want to skip the maths, look at the pictures then jump to page 9 for a summary of the problem and possible fixes.

I've posted this to the Facebook group too as I know not everyone is on BARCS.

https://www.kimerius.com/app/download/5784128815/Aerodynamic+Flutter.pdf

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Not sure I understand any of that 🤣

My take on flutter - speed and lack of stiffness in surfaces and linkages is your enemy.

Our quest of low wing loading kinda works against us, as typically means more fragile.

Launching - the steeper the climb the less speed and reduced risk of flutter.  I see people launching to the horizon on bungee which accelerates the model.  Release aiming as close to vertical as possible.

The best solution I think is 2 models.  1 lightweight one for light conditions, one heavier/stronger one for windier conditions.

But clearly I don't listen to my own musing 🤣

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17 hours ago, cirrusRC said:

Not sure I understand any of that 🤣

My take on flutter - speed and lack of stiffness in surfaces and linkages is your enemy.

Our quest of low wing loading kinda works against us, as typically means more fragile.

Launching - the steeper the climb the less speed and reduced risk of flutter.  I see people launching to the horizon on bungee which accelerates the model.  Release aiming as close to vertical as possible.

The best solution I think is 2 models.  1 lightweight one for light conditions, one heavier/stronger one for windier conditions.

But clearly I don't listen to my own musing 🤣

Launch to the horizon - That's me! 🤣.

But so far no flutter on the Magic 2. I sort of agree on the two model thing but my next project will be an attempt to have a design that will cope with all conditions. We shall see 🤔

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Plastic film covering adds little torsional stiffness.  Most Fx-RES designs use tubular carbon spars or wooden D-boxes to counter this stiffness problem within the rules.  It may be worth remembering that doped tissue is stiffer in torsion than a plastic heat-shrink film of the same weight.

As often happens, a 'simple looking' model formula turns out to reveal problems that 'more modern' models have already solved.

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