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COG advise please

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Bill Brown 305/03/2013 22:48:01
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363 forum posts
234 photos

Hi,

I need to know how many times through a build you would check if your COG is moving in the right direction or is this something that is checked on final stages of construction, i know that most plans and models give a measurement for the "sweet spot" upon where the inverted model should balance upon finger tips or more sophisticated apparatus, and would this test be done with engine fitted and perhaps an average fuel load ?

I know that i may be talking gobbledegook to some of you well experienced people but i am at the moment confused by it.

Bill (the confused)

Gary Binnie05/03/2013 22:57:05
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498 forum posts
23 photos

Hi Bill,

You don't really get an idea of the C of G until near the end of a build.

Very few models come out nose heavy so keeping it light at the back end is important.

Cheers

Gary

Danny Fenton05/03/2013 23:04:26
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8382 forum posts
3405 photos

Hi Bill, I for one do have a trial fit of things just to get a rough idea, but obviously it has to be very late on in the build. I include everything that I can. My models are electric so include fuel wink 2 But if it were ic I would balance without, and let the fuel bring the c of g forward for flight.

If my model isn't fairly nose heavy before covering and paint, then I know it will probably need lead up the front, if a cell shift wont cure it. Covering and paint have a dramatic impact on the c of g in my experience, unless its a long nosed model like a Mustang of course...... so until its finished you don't really know.

I think when you are building you know when you are adding to much weight to the tail, it becomes second nature to make everything as light as possible behind the c of g. I think Dave Platt states, 10g for a sheet of 1/16" x 3" x 36" is the heaviest he will use for the back end of a model. Leave epoxy in the bottle and make the joints do the work by being a good fit.

Cheers

Danny

Tim Hooper05/03/2013 23:12:06
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2801 forum posts
2346 photos

BIll,

You raise a very valid question. In my case I leave the servo and battery installation until as late as possible in the uild process, and then site them as required to achive the stated CG without using any of that nasty lead stuff.

tim

Percy Verance10/03/2013 14:05:08
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5675 forum posts
108 photos

Sound advice indeed from Mr Platt. Keeping the tail end of any model light is always a good thing.

A nose heavy model flies badly. A tail heavy model flies once...........

Edited By Percy Verance on 10/03/2013 14:05:31

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