BALANCE

[matt jarvis]

If you up scale from a  smaller plan, is the balancing point on the new larger build the same ?

 

I have completed a build like this and need to balance the plane.

The wingspan is 55" and the balancing point is 8.5 cm from the leading edge of the top wing.

 

With the 1800 lipo installed, the plane balances with a small amount of nose up with my fingers under  the planse balancing points.

 

Should I use the balancing points from the plan with a little added weight to the nose?

 

[Lindsay Todd]

Hi Matt, the balance point does not change with scale i.e all dimensions will be times the scale factor including the balance point. But for instance say at 1/10th scale the balance point was on the main spar of the wing, at 1/4 scale it would still be on the main spar.

 

Linds

 

[Simon Chaddock]

Matt

Nice looking model. A Hawker Fury?

As Lindsay says the balance point will remain geometrically the same but this assumes all the other parameters are the same.

The required CofG does depend on the wing and tail incidences, the prop thrust line and even the wing section.

If you have faithfully reproduced the larger scale the same balance point would be a good place to start with.

[Martin Harris - Moderator]

I'd agree that these factors all affect the flight characteristics but I don't recall any C of G calculations taking them into account with the exception that radically different wing sections might affect movement of the centre of pressure with increasing angles of attack leading to a more critical stability margin but a proportional C of G position should work perfectly well in this case.

Edited By Martin Harris on 04/09/2010 20:08:27

[sparks59]

I agree with the earlier posts. But this is a useful link on the topic of Cof G if you happen to have made any changes.

 

http://www.geistware.com/rcmodeling/cg_super_calc.htm

 

sparks

[matt jarvis]

Thanks for the advice.

Should I balance from under the top wing or turn the biplane over?

Answer to your question Simon.

This is a Hawker Nimrod mk II , built from the westwings Hawker Hart plan  802  squadren fleetairarm 1939.

[Lindsay Todd]

Hi Matt, personally I would balance from under the top wing as this keeps the centre of mass low and gives better pendulem effect plus its probably easiest in this case to see that the model is sitting level. I am a great advocate of keeping things simple just make sure you support the model on some part of the structure than film covering for obvious reasons.

 

cheers

 

Lindsay

 

[Martin Harris - Moderator]

Although I don't know the plan, they usually show the C of G on the wing position (although the real point is some way down the fuselage) which I think is the case from your first post.  On this layout you'll need to balance it from under the top wing to maximise the pendulum effect.  Earlier you mentioned it balancing nose up - please make sure it's level or a little nose down.

 

If you had a low wing monoplane, you'd need to balance it inverted as the C of G would be above the balance point the right way up.

Edited By Martin Harris on 04/09/2010 23:19:34

[Simon Chaddock]

Thanks Matt

I was not too far out. The Nimrod was the Navy version of the Fury!