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Old Mar 22, 2012, 04:03 PM
rcta15 is offline
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cg help needed on kfm glider build? motor question added


ok here is a 'not to scale' but all measurements are accurate representation (all be it very crude) of a glider i have built.
i am having a prob with the cg location, i have gone for the thickest part of the kfm wing and the i get the cg at 75mm from leading edge, but it just dont look right?
i have tryed the online cg locator gives me a cg location near the trailing edge??
can someone please advise if they can.
Many thanks in advance RCT

wingspan is 1603 not 1630 sorry my bad
Last edited by rcta15; Mar 23, 2012 at 07:25 AM. Reason: wingspan fault
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Old Mar 22, 2012, 05:01 PM
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It looks like it's about 38% of wing chord which would be too far aft for me if I was setting up a plane. I likek to start at 25%, Now that's just me, and lots of guys like cg at 30% of chord. This all for a conventional type plane like yours. I don't know why the calculator might say otherwise. Generally with a KFM2 or 3 and the 50% top step, cg will be foreward of the step.
Old Mar 22, 2012, 05:08 PM
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OK. Going by the old Rule of Thumb the testing CG should be at 25% of the wing cord, that is 30mm from the leading edge. The CG can then be moved back to around 1/3 of the cord to 65mm.
Or: Using a calculator I get testing at 33mm and final at 52mm.
That'll get you going.
Good luck with it all.

Hah! My bro got in first!
Old Mar 22, 2012, 05:11 PM
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thanks to you both that has helped loads, now to get back to building.
RCT
P.s. its a kfm9 foil
P.P.S. made a mistake in the wingspan it should read 1603 not 1630.
Old Mar 22, 2012, 06:35 PM
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Quote:
Originally Posted by Whiskers View Post
OK. Going by the old Rule of Thumb the testing CG should be at 25% of the wing cord, that is 30mm from the leading edge. The CG can then be moved back to around 1/3 of the cord to 65mm.
Or: Using a calculator I get testing at 33mm and final at 52mm.
That'll get you going.
Good luck with it all.

Hah! My bro got in first!
Bingo-correct! Whiskers hit the CG on the head!
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Latest blog entry: RC Slimer from Ghostbusters!
Old Mar 23, 2012, 07:28 AM
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which motor would be good for this glider?


now AUW so far is 900g ish so i was looking at either of these two motors what do you think?


http://www.giantcod.co.uk/epower-gt2...-p-405956.html because i need some extra weight up front, still might need say 40g extra on the nose i think.

or this one...

http://www.giantcod.co.uk/221720t-86...-p-402409.html but will need to add extra weight for this one.

i am leaning towards the first one but not to sure, will want to put a nice big folding prop on it as well.
can i please ask for everyones advice on this matter please?
many thanks RCT


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