C of G calculation

[John Edwards]

Can anyone tell me how to calculate the C of G for a biplane with staggered wings -

e.g. A Tiger Moth ?     I am contemplating such a model (not the Tiggie) from a plan

 but it does not have the C of G indicated.     Neither Martin Simons'  book nor the

BMFA News article seem to cover this aspect , both referring to monoplanes only.

[Brian Parker]

Several factors need to be considered to determine the C of G of a biplane. Without knowing the model it is impossible to be exact.

As a rough guide..From the plan view, consider both wings as a total  wing then C of G will be around 22% of chord.

ie...

No stagger...treat as a single wing.

With stagger...add the amount of stagger to the other wing to determine the chord.

For swept wings..consider a part of the total wing and determine as you would for a single wing.

[John Edwards]

 Thanks Brian for you information.   The bipe is an old design by Vic Smeed which I am               

adapting for electric RC.

Chord of both wings =  5"

Stagger (overlap)  =  2.125"

Combined chord therefore =  7.125" so the C of G at 22% =  1.425" from the L/E of the

top wing.   This places the C of G  0.7"  in front of the L/E of the lower wing.   Does this

sound OK?

[Brian Parker]

That may give a slightly forward (but safe) starting point, the final position could be slightly back.

 

Ex-free flight models usually need their wings beefing up a little for powered flight.

[Roy Hill]

Hi john, the Gordon whitehead book---scale models for everyday flying, covers all typesof airframe c/g positions ,its been my model bible for#########years! i could scan the article ,but i,me not sure how to send it------help?? hope you sort it---roy