CG on Speed Contest Planes

Mark Boesen Wed Mar 12, 2014 12:19 pm

Couple weeks ago somebody mentioned that their speed plane, or the one(s) they had built all came out tail heavy...or was it nose heavy? I'm thinking of cheating down the fuselage length or build it with a longer nose I can trim down, or both?

Thanks

roddie Wed Mar 12, 2014 12:57 pm

Mark Boesen wrote:Couple weeks ago somebody mentioned that their speed plane, or the one(s) they had built all came out tail heavy...or was it nose heavy? I'm thinking of cheating down the fuselage length or build it with a longer nose I can trim down, or both?

Thanks

I'm pretty sure most models were nose heavy... (being so small) but it's very hard to guesstimate before painting/finishing... without everything in place.

I tried to anticipate this by having alternate push-rod materials (carbon-fiber vs. .062" music-wire) and wheels (main and tail) of different weights to try. You can also design a "V" style music-wire main-gear, to pivot slightly fore/aft to trim; before you anchor it.. and after most everything else is done.

batjac Wed Mar 12, 2014 7:23 pm

It is a bit difficult to know exactly where your balance point is. My two methods of rough calculating are to 1) make the nose a little longer at first, so I can cut it back if necessary, and 2) do rough balance with the wood cut out and the components stacked up in their approximate position, so I can move things back and forth before I start gluing.

CG on Speed Contest Planes DSCN1209_zps9a835b2d

The Rough Mark

Mark Boesen Wed Mar 12, 2014 10:18 pm

Ok, thanks...it's always a good idea to at least know about where 'north' is.

This does make sense, the last time I built from scratch a slab wing (with flaps) 1/2a profile it too came out nose heavy.
So with this I think I'll build the Shoestring with the same scale fuselage as wing and go with a long nose and bob down as needed.

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