I am buying an Avistar and putting a TT Pro .46 engine in it and I was told I will have to move the battery farther back in the plane to compensate for the engine weight in the front. how do I check the center of gravity to make sure the battery is back far enough?
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Flyn' High, Real High[&:]

Look at the plans, figure out where the cg should be, usually about at the spar, and put your fingers on that spot on both sides of the fuse and pick it up. It should ballance level

An easy and fast method: (I'm sure you gonna get plenty of tips, but this is easy!)

Check the manual, it should say where the CG should be.
Then measure the stated distance from the leading edge of the wing and mark the point of CG with a magic marker.
Move the battery around until you can balance the plane on your fingertips by the CG point you marked.

how do u make the battery stay in the same place? I have not bought the plane yet but I am going to this comming week. So I dunno if u tape it or it just stays there or what.
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Flyn' High, Real High

Hi!
In a highwinged trainer you just wrap a lot of soft rubber foam around the RX and the batteries...you just fill the space inside fuselage with it ...that way the RX and batteries stay put.
Holding my fingers under the wing is what I do on all airplanes to find the C of G.
Regards!
Jan K
Sweden

I had same problem with my Avistar when I upgraded to ST .40. I wound up moving the battery behind the radio compartment. I secured it with some double sided tape and a small piece of balsa, it was basically held under the control rod housings. I guess I should have cut a hatch and secured it with velcro, but it never moved and I'm lazy.


Andy

That is Cool..So I stick my fingers underneath the belly of the plane and but in the middle of the wing length?

Yes
1. Make a fist with both hands
2. Extend your index finger, on both hands
3. Place your index fingers, one under each wing...
4 Lift the plane up, only supported by your two index fingers, on the by the manual suggested CG point...balance...
5. Shift existing weight, such as the battery around until you find the CG, if needed add additional weight


Methods to fasten battery:
-Wrap in foam and clamp it tight in the fuselage
-Glue velcro on the battery and another piece in the plane
-Drill two small holes in the fuse and zip-tie the battery

...Remember to keep the battery and reciver padded and keep in mind that the battery is heavy and WILL shift forward in a nose-down crash, possibly crushing things (like an expencive reciver) in it's way!

Godspeed StoneDeaf

Thanks alot Test..i am going to need all the Godspeed I can get!
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Flyn' High, Real High

No worries StoneDeaf, welcome to the hobby, you'll enjoy it.
Asking questions here at RCuniverse is a good start and here you'll find lot's of useful information and friendly people.

Unless I missed it, when you pick up the plane using your index fingers, get as close to the fuselage without touching it as you can. and you do it facing the front of the plane, placing your fingers under the wings

In your one post you mentioned the belly and that had me concerned.

I guess I misunderstood it. I am still alittle confused. but I am sure I can figure it out from the instructions I hope
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Flyn' High, Real High

Stonedeaf,

Actually here are 2 links to the Avistar's manuals.

On page 8 of the first link which is the Avistar Select, is an excellent description of how to balance the model

http://www.hobbico.com/manuals/hcaa16-manual.pdf

On page 19 of the second link is another way to do it using the Great Planes CG machine

http://www.hobbico.com/manuals/hcaa2016-manual.pdf

You really do not need the machine, Use the description in the first link to balance either of the models.

The Avistar Select (first link) is balanced anywhere between 2.5 and 3.5 inches back from the leading edge

The Avistar Monokote (second link) is at 3.25 inches

As far as the battery is concerned, just wrap it in at least 1/2 inches of foam and either tape or use rubber bands and wrap them around the foam that you just wrapped around the battery. You also do the same thing to the receiver.

Now place the battery and the receiver (wrapped in foam and battery on the bottom) in between the servo tray (where the servos are mounted) and the fuel tank (there is a spot there for it) Now put the wing on and check the CG. If it balances right where it should then take the wing back off and pack the area where you put the reeiver and battery with foam and stuff it under the tank and the servo tray (where the servos are) bit do not let the foam interfere with any linkage.

Put the wing back on and recheck the CG

The plane should sit level or very slightly nose down when it is sitting on your finger tips and balanced

Oh, by the way, this is all done with the fuel tank empty and the engine, prop, servos and everything else installed. This is what as known as ready to fly condition, short of having fuel in the tank the plane is essentially ready to go.

Hope this helps...

Yeah it all does help..There are a bunch of great guys in this forum..Thanks again

or you can get a fancy-shmancy C.G. machine from your local hobby shop. They take all the guess work out of the problem. IF you know wher the C.G. is located on the plane. Now. How do I FIND the proper C.G. point on a 1/4 scale Sopwith Pup? 80 inch span, 15 inch cord bi-plane? Any suggestions?

A good start is 25 to 33 percent of the cord. Most likely it will be right around the spar and in the case of the bipe, I would do it inverted on the lower wing.

But I could be wrong as to the exact way for that plane. Who makes the Pup? I'll see if I can find it.

Bubblegates, I am sorry but I have not idea what u are talking about(cord,spar, bipe) I have not gotton my plane in the mail yet, so I have not been able to see what all the parts are.
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Flyn' High, Real High

Cord is the width of the wing

Bipe stands for Biplane

Spar is a structural part of the wing. Some wings have only one near the front of the wing, some have two, both at the front and rear of the wing.

I do not mean to sound rude. If you are that new to the hobby then a biplane is not want you want at this point in time. Some are great handlers (Ultimate, Stearman, Hog Bipe, and a few others) The Pup is kinda twitchy and can be hard to control on the ground.

Again, I am not trying to be rude here. Just pointing out some facts.

To find a starting place for CG on a biplane (straight non-tapered wing like the Pup), do the following:

Level the plane on it's main wheels and block it up (wings attached)

Using a large carpenter's square, mark the position of the front of the top wing on the work surface

Take the square and mark the position of the trailing edge of the bottom wing on the work surface.

Measure the distance between these 2 points.

Multiply this dimension by 25% and 30%.

These new numbers are the CG range.

On the underside of the top wing, measure back from the leading edge and mark each side at these dimensions.

This is the starting CG range. Use findertips, CG Machine, whatever, to check balance.

The range may be near the training edge of the top wing.

I was not wanting a Biplane at all. I have not even got my trainer plane I ordered in the mail yet. I have to put that together and learn to fly that for a long time before I even think about buying another plane.
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Flyn' High, Real High

We have a guy at our field and i am sure he checks his cg by taking the plane to the field winding up the engine, take off and them crack first and last flight. I check mine over and over to make sure it's right and then i will get someone else to check it. better nose heavy than tail heavy, you can fly a plane thats nose heavy but if it's tail heavy it will only fly once

Sorry Stone Deaf.

After going back through the posts I answered the wrong one, I was supposed to be answering jeffEE and was thinking of you when I did it. Confusion and not enough coffee, someday I'll learn not to do much in the AM until I'm completely awake.

I have not read about the leading edge/trailing edge table top method. All other ways to find C.G. on a bipe have the C.G. at 6 inches from the leading edge of the top wing. I will try your method. and let you know what I find out. Thanks to all. JEFF.

rrr

What surface needs to be "level" to consider a plane balanced? Is it the stab? And is level defined as parrallel to the ground?

I tried balancing my PT40 today for the first time (she's almost ready to fly!) the nose sat slightly lower than the tail, but didnt tip off the balancer. If anything, the nose was maybe 1" lower than the stab. Is my PT40 "balanced"?

Thanks guys