Finding cg on plane
 

I have a couple planes that i bought as fixer uppers but i dont know where the center of gravity should be for them. Is there a general rule of thumb? With other builds it says to play your fingers some where from the leading edge of the wing and balance the weight to those points. how would i figure this out on my planes?

RE: Finding cg on plane
 

Normal rule of thumb. Balance on the spar. However if is a swept wing all bets are off.

RE: Finding cg on plane
 

Another rule of thumb that has worked for me is to place the CG approx 1/3 the width of the wing at the root,this works for tapered wings and sheeted wings where you cant see the spar.

RE: Finding cg on plane
 

what is the spar? whats a swept wing? is a tapered wing a tear drop shaped wing?

RE: Finding cg on plane
 

The spar is about 20 to 25% back from the leading edge of the wing. On some wings the front part from the leading edge is sheeted to the spar. The spar will go the entire length of the wing. Swept wing is one where the leading edge is not straight from one side of the wing to the other. The tip of the wing will be farther back towards the tail than the wing at the fuselage.

RE: Finding cg on plane
 

Do a search here for the CG Calculator and just follow the instructions. You just put in the information required and it spits out the CG. Beats the heck out of all that thinking stuff. I have used it on a few of my odd ball planes and it works very well.

RE: Finding cg on plane
 

trainer25,

Just measure your models and input the data into this on-line calculator:

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

A proper balancer is better than two fingers.

http://www3.towerhobbies.com/cgi-bin...FB%3E+machines

http://www.rcuniverse.com/forum/m_94...tm.htm#9438910

RE: Finding cg on plane
 

The Spar is the supporting beam that runs through the "center" of the wing from one side to the other. It gives the wing it's strength.

Swept wing is a wing that angles back from the center to the tip.. meaning it is not straight out from the fuselage, but is "swept back" from the fuselage rearwards with the tip somewhat behind.

Teardrop shaped wing, well, that's a horse of a different color.. perhaps a bit more advaced for here, but there is a different name for it, more technical, but I can't remember what that is.. someone I'm sure will chime in with that info.

CGr.

RE: Finding cg on plane
 

And here is the answer to the question you didn't ask. If you're new to the hobby, you will improve your chances of success 1000 times over by connecting with a club and getting some flight training. Just having a good airstrip to fly from is worth the price of membership.

RE: Finding cg on plane
 

I always use a formula to get a starting CG with any plane, even if the kit or plans specifies one. I assume the CG calculator, above, works from the same formula, and I would advise you to use it. Rules of thumb, like 1/3, work well enough for many planes, but not for all planes. If the stab is curvy, get the area by cutting from a rectangular piece of cardboard and use a balance to calculate area.

Once I have the CG figure I want to balance to, I cut two thin pieces of masking tape, measure, and stick to the wings spanwise, and then put my fingers on them. It's too hard to tell where your fingers were otherwise, but you don't need balancing machines. With this method I can tell right away if it is tail heavy or nose heavy.

Jim