hi im currently building a p51 from plans i got free in a magazine but nowhere on the plans does it mention where the balance point should be!.the plane has a wingspan of 42 inches shes 37 inches from tail to spinner.weight should be between 2and a 1/2 lbs to 3 lbs when finished.can anyone help me work out where to balance her?.

Most planes fly well with the balance point between 25% and 33% of the wing chord. The farther forward (in this range) the balance point is, the more stable the plane will be.

Dr.1

thanks for your help ill try to work with that!!.

A quick followup here -- it's 25% to 33% of the AVERAGE chord. On that P-51, you can get "eyeball close" by just going halfway out the wing. And, if it's designed with a spar, chances are the designer put the spar pretty close to the balance point, so if it balances at the spar or just ahead of the spar, it will probably fly OK.

With swept-back or more complex wing designs, there's more to it and there are formulas (formulae?) you can use, but that should be enough for now. Good luck!

Duane

what formulae for these wings?

cheers mate much appreciated,im glad you didnt blind me with science lol

Formulae?
cut a planform of the entire model from a piece of stiff paper -- balance at about 50% -60% from front
fly it.
Close?

Hypersonig,

Let's start with the basics. Which end is the front?

Now, THAT'S what I'M talkin' about, hypersonig!! What is that thing anyway? Sort of an aeronautical cousin to the Jackalope? A jetalope?

Some of you guys say you work designing real airplanes???!! Next time I've got to go see my sister in MPLS I think I'll strap one of my R/C birds to my back.

martno1fan, read the stickey threads at the beginning of this forum and try the calculators at:

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

You can't just guess. For a P51 CG should be 8-12% of MAC ahead of the neutral point. Less than 8 you better be super pilot. Even 8-12 you better be pretty good. But don't worry, I'm big on math, but not much beyond +-*/

And if you don't understand that (you will after checking out the calculator), you need to start reading at least 25% as much as you build.

thanks for the link mate ill give it a go tonight,glad you didnt blind me with science lol!!!.oh by the way did you know you put them wings on back to front lol?.also might i add its good there werent so many different opinions on this.

Withdrawn by author rather than be edited.

Sadly, Simons is incorrect with that procedure.
It requires a mathemathical approach..
http://perso.wanadoo.fr/scherrer/mat...glish/mce.html
And:
http://users.adelphia.net/~pjburke1011/cg.htm

The suggested formulas are for calculating the wing's MAC only.
But how to determine the balance point (CG) for the bird shown above?

Are there some in-flight tests one can do to check on balance. I know at some point it is a matter of taste, but I bet some people have very specific flight characteristics they look for.

Nominally, 25 to 30% of the m.a.c. is the usual place place to start, but that thing is kinda canardy, so its balance point will be ahead of that.
A balsa chuck glider will give a ballpark location.