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C of G

Elderly Minimoa

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Geoff Daunt19/03/2019 18:16:09
96 forum posts

Hi Glider Guiders, l have been given an elderly Minimoa type Glider, which was past from club member to member over many yrs for a refurb but no one got around to it.

l now have it. I guess it was built 20+ yrs ago.

the wings had bellcrank operated ailerons and Tissue covered with the wing covered in nylon and dope in poor condition.

l have removed everything and replaced with modern servos and covered in a vintage type oracover.

The wingspan is 3M with a cord of 245 mm.

There is a big chunk of lead in the front of Fuselage but l have no information on Cof G.

25% of Cord is 61.25mm and 1/3 is 81.66

Putting on my Balencer at 70mm it is still very tail heavy with Battery and Servo in place

So something is wrong , if it has ever flown !!!!

For a maiden flight would you go for the 25% figure or something less??

Any general advice appreciated.

flight119/03/2019 18:43:26
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600 forum posts
33 photos

Well 25% is very far forward and would make it harder to round out on landing. I always start out on 28% on an unknown wing and then work my way back each flight until I is right for me.

On a known section I do 30% to start, so that would be 73.5 going by the cord you have given and yes it is always surprising how big the bit of lead that goes in the nose

so going by your 70mm sound close to ok

Edited By flight1 on 19/03/2019 18:45:23

Simon Chaddock19/03/2019 18:55:57
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5370 forum posts
2818 photos

I wonder what was the weight of its original battery.

The wing has in effect quite a bit of sweep so I would expect the CofG to be a bit further back than might be expected.

The 2.4 m Replikit Minimoa described on RC Ggroups ended up with the CofG at 40% root cord as a "safe" figure!

I would only go that far back after some flight testing.

Edited By Simon Chaddock on 19/03/2019 18:56:36

flight119/03/2019 19:04:28
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600 forum posts
33 photos
Posted by Simon Chaddock on 19/03/2019 18:55:57:

I wonder what was the weight of its original battery.

The wing has in effect quite a bit of sweep so I would expect the CofG to be a bit further back than might be expected.

The 2.4 m Replikit Minimoa described on RC Ggroups ended up with the CofG at 40% root cord as a "safe" figure!

I would only go that far back after some flight testing.

Edited By Simon Chaddock on 19/03/2019 18:56:36

Yes i was talking about mean aerodynamiccord of the wing. The root cord is very diffent so please don't con fuse these

use this calculator to get a idea

Frank Skilbeck19/03/2019 19:55:19
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4358 forum posts
101 photos

Might be worth asking on scalesoaring.co.uk several Minimoa builders on there.

Geoff Daunt20/03/2019 18:07:16
96 forum posts

Hi All , many thanks for the replies. Just joined the Scalesoaring association and asked the question. Will post any interesting reply.

Geoff Daunt26/03/2019 10:56:01
96 forum posts

Hi All, just to conclude l got a referral to ‘rcplanes.online/cg_calc.htm from scale soaring

This is a C of G full auto calculator... just input the measurements and hey presto.

it had been suggested that it would be close to 50% of cord due to the swept back wing construction.

The figure came out at 120mm from L E, so in my case about 48 %.

Happy days 👌👌

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