im new to flying and i was just wondering if there is any good tips on how to find the c of g on a plane without the use of a proper gauge?
at the moment i mark the c ogf g point on the plane and use my middle fingers to pick it up, this however is hard to do and probabaly totally inaccurate.
i have heard that you can tell if its nose heavy or tail heavy by doing a spin and if it spins rapidly that means its nose heavy is this true?
also some planes you must invert to get the c of g why is this?
and should it be done with a full tank or half ect..?

any help welcome thanks

I use my index fingers against the fuse. CG should be checked with a empty tank. And always remember it is always safe to be nose heavy, if it is tail heavy odds are it will only fly once.

You can make a very simple CG machine. Get a 1"x4" board. Drill two holes in it about 6" apart. Stick a wooden pencil in each hole. Now place the plane on erasers of the pencils in the location were the CG is supposed to be. Adjust as needed to get the CG back to where it's supposed to be.

No need to spend a lot of money, you can make this one with stuff you probably have on hand.

Ken

Hold the airplane so the wing is on top. The CG is not all that critical anyway, just get in the middle of the range and go fly. Then adjust the CG to get the flight characteristics you desire.

I think this statement is meant to say that the CG is not critical if you are in the manufacturers recommended range. The CG itself is VERY critical. I always go to the front of the recommended CG for maidens, and move it back from there to suit my needs. A nose heavy plane flies sluggish, a tail heavy plane flies once.

You have gotten several good replies on locating C. G.There are many ways of doing so. doing so with plane upside down has no bearing on it it's just easier to do so on some. No the speed at which it spins has nothing to do with C.G. Always checked with tank empty. Usually placement of battery will enable you to make adjustments.

Low wing planes must be inverted to check the CG

You should start thinking about the CG when you first open the box regardless if it is a kit, scratch built, or an ARF. Besides the simple balance of the model, how the mass of the components are distributed affects the flight characteristics. The technical term is the polar moment of inertia, but in laymans terms having the weight farther away from the CG increases the polar moment around each axis. So it takes more force from the controls to start movement, and takes longer to start and stop movement.

I got give a CoG measuring device and all it really served to do was show that my fingers were actually a lot more accurate than I thought they were so trust your fingers they'll not be that far out !!!!

Two good articles on Balancing:

http://www.rcuniverse.com/magazine/a...?article_id=84

http://www.rcuniverse.com/magazine/a...article_id=601

I have a fancy CG device but just use my fingers.

Actually my fingers are just a preliminary device so I can get the plane in the air

Flying the plane tells the true story and I readjust the CG according to true flying characteristics

There is a variety of methods and CG devices from simple finger tips to pencils in a board, fancy sometimes expensive 'CG Machines to even hanging techniques with plumb bob pointers. This is definately not a case where one size fits all. All the methods have their advantages and disadvantages and this is directly related to the airplane configuration and size, even the builders physical condition can have an effect on which method he may want to use for any given airplane.

I have used all the methods and the choice depends on the airplane of course. The most common that works fine for many airplanes is the Great Planes CG Machine, I recently supplimented one of those with the New Sig balancer (in the picture) which I really like but I do confess its biggest appeal to me is that it is a 'Real' kit just like an airplane that took a few days to properly build.

Now don,t get me wrong I still use sometime just fingertips and this brings us to the reason I responded: When using fingertips and you have a desired point where you have made a mark on the airplane with which is your target balance point. Instead of just marking the point make tiny little pip of epoxy on the surface or even a pinhead inserted in the wing.

This makes it very easy and accurate to ballance with nothing more than your fingertips. Your finger will feel the pip and be in the perfect location.

Of course this is no help if you trying to locate the existing CG and measure it. Less common but also useful as your set up skills progress. For this the CG devices with scales are more functional for the average airplanes.

John

Hi!
I just use my index finger to measure C of G and have done so for 33 years on all my planes, from pylon racers to scale planes. You don't have to hold the plane inverted to get a good grip of the where the C of G is supposed to be...Why?
Just be in the proper range and fly the plane and then you adjust it from there.

As Jan says, the important thing is how it flies.

You need to be able to identify nose heaviness and tail heaviness in flight

Nose heavy planes don't fly well

tail heavy planes fly only once unless you are mighty lucky

A nose heavy plane seems to reset a good landing flair and will not do a true spin.

A tail heavy plane resists coming out of a spin and gets so squirrelly on approach to landing that you can never get the attitude right for landing. it will oscillate up and down on you

don't mean to steal the thread, but I'm balancing a nitroplanes cessna 182 "40", instructions say to balance 22mm from center of wing, 73-78mm from back from the LE. my problem/question is, my great palnes balancer won't go that wide. can I balance next to the fuse or just go as wide as the balancer will go?
thanks

If you are using the Great Planes balancer you need to open it up just enough for the fuselage to fit between the uprights, with the balancing pads on the wings right next to the fuselage.

Ken

thank you sir

thanks for everybody for the great replys

as i thought , fingers are fine and i will start a little nose heavy then SLOWLY move the rx battery rearwards untill i have the c of g that i like.

thanks again
foxypike