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Old June 26th 18, 05:19 AM posted to rec.aviation.soaring
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Default Discus 2 Optimal CG location

On Tuesday, 26 June 2018 16:16:40 UTC+12, wrote:
On Tuesday, 26 June 2018 15:36:52 UTC+12, Ben Coleman wrote:
Wheel will be a bit different location if spring is different strength or deformed (and/or glider is different empty weight) but correct measurement of arms and moments makes it irrelevant.

Cheers Ben


Yes, that is our conclusion too. I have heard some people chock the landing gear extension somehow.

FWIW, we have measurements of 140 and 4285. The SH manual says 128 and 4278 (128+4150).

The 12mm makes a significant difference to the CG calculation - 90% aft vs 84% aft with the factory arms.

The lesson is to be a little careful of the factory arms, even in a glider with no damage history.

The 90% aft value ties in well with Bif's value above and it does feel good for thermalling, but you quickly start wishing for less aft weight when the trim is fully forward and you still need plenty of forward stick pressure when running.


I should add that the MM uses the same arms for loaded and empty CG calculations.