I only know of two methods to balance an RC airplane.

The first method is the finger method. This method is cheap but inaccurate. This is the only method I've ever used.

The second method is to buy the Top Flite contraption. Is this tool worth the money if I want to accurately measure the CG? I've also read a few articles about cheap home-built variations of this tool. My half-hearted attempt didn't work out well.

I've heard there is a trapeze method, but I don't know any details about it. Can anyone explain this method? I couldn't find anything about it when doing a search on RCU and Google.

Are there other methods to find the CG?

Thanks in advance,
Juice

The Great Planes C.G. Machine does a very good job for me. I use it to balance all my warbirds, and all of them fly great.

Here is my WM Spit on the C.G. Machine:



Here is my Kyosho Corsair on the C.G. Machine:



This tool is a great investment.

In the June '03 Radio Control Modeler Magazine there is an article on how to build a very good balancing stand. I built one in about 20 minutes out of scrap wood I had hanging out in my garage and it works great. Just a suggestion.

Don't know if its called like that but look hereor here.

Good luck,
Edgar

I use my fingers, It's close enough to get the CG close enough to fly. Once I fly a plane, I always wind up changing the CG anyway because I may want the plane a little more or less sensitive. I'll add a little weight, or shift batteries around, but after the initial balance, I never really check it again. Once the plane is flying the way I want it to, I don't care if it's an inch or two outside the recommendation.

Yeah, try to fly a warbird with the C.G. an inch or two outside the recommendation, especially with the C.G. an inch or two aft of the specified location.

Richard, I am not saying that.

What I am saying is that once I have flown a plane, I may or may not decide that I want to change the CG to change the performance. Let's say that I want to add weight to the tail, I will add small amounts between flights until the plane either flies the way I want it to.

Once the plane flies the way I want it to, I'm a happy camper (flier?).

But the bottom line is, once I have done the initial balance, I never check it again (unless of course if I change an engine, or swap equipment etc).

I have balanced it, flown it, added weight, and it flies great. I have no idea where the CG is, and I don't care.

If someone walked up to it and balanced it and said, "Hey! This thig balances 2" forward of where the plans say it should!", I would reply. "It does? Well waddyaknow. It flies great like that though!"

MinnFlyer:

This is the exact tecnique I use and it seems to work well for me.

Miloh.

definitely go with the great planes balancer or build on similar to it out of wood. The finger method leaves too much to chance, you will find yourself balancing the plane on your fingers instead of being objective.

I have a Multiplex stand which works well ! You will be surprised how much difference 1 mm makes. So if you have a hotliner which only has a cg range of about 5mm you could be way off using finger tips.

It is much easier (and more accurate) to adjust the the cg with the aircraft on a stand.

1 mm? So how far does a full tank of gas move this C.G.?

I just use the finger tip method, or use two pencils with the eraser tips ground to a point. put each pencil on your C.G target marks, then fly it, get it trimmed and adjust accordingly. depending on how sensitive I want it to fly.

Nose heavy for stability. (Just don't dive or loop it) tail heavy for Radical, touchy and or almost impossible to fly. LOL.

Anyway after the finger tip balance and initial flight, I adjust the Weight in increments until I am satisfied with the Balance.

these things cost Enough money without having to buy all the tools to fill a shop! LOL.
Just my 2 cents.

Smoky.

How far does a full battery pack move the cg ??

Many fliers try to position their fuel tanks on the cg. My point was really, that if you move the cg by a small amount it takes a surprising amount of weight to re-balance the plane AND it is a lot easier using a stand (of any kind) than fingertips.

I have seen more than one aircraft go into the bin bag on its maiden flight because the cg was too tail heavy !

I suppose it is down to time & money - the stands are relatively cheap and I don't have the time to spend it making tools.

What is Center of Gravity? How would it affect the plane?

I am no expert but as I understand the correct cg (center of gravity) gives the aircraft pitch stability.

There is a saying that goes "A nose heavy aircraft won't fly well but a tail heavy aircraft won't fly for long" the right cg is inbetween these two extremes and depends on flying style and the aircraft!

Every object has a center of gravity. It is the point where all the weight of the object can be considered to be concentrated. An arrow has the C.G. near its tip. So when you drop or throw an arrow, the tip will always go first. What will happen if you place the C.G. on the plane near its tail? The C.G. affects longitudinal stability in an airplane. On a 3D plane or a fun fly type plane, the location of the C.G. does not have to be precise. However, on a jet or a warbird, the location of the C.G. is very crucial. The Center of Gravity is covered in high school physics. You get a lot more of it in college physics and even more of it in aeronautical engineering courses.

Can someone clarify when to balance the plane upside down? Is this what you do for low-wing planes? Also, the 2 planes pictured above "appear" to be nose-heavy, or is that the way they "should" look when balanced?

Neo

how do i find out where the CG of my plane is?

Balance low wing planes upside down. Balance high wing and mid wing planes right side up. I like to balance my warbirds slightly nose heavy as they fly better that way. Like many have said "numerous" times before, it's better to balance a plane slightly nose heavy than tail heavy.

The CG for your plane can be found in the instruction manual that came with the plane. If you no longer have the manual, then try to get the CG info from the manufacturer website.

As a General Rule of thumb. the CG. is ussually on the Main wing spar. Or the front edge of the thickest part of the wing.
And yes the two planes shown, Slighly nose heavy. is the best attitude to balance a plane. Strive for a similar angle while balancing yours. Nose slighly down like that.
Much easier to fly.

This is just a starting point. tho and you will adjust according to your preferences (likes,dislikes) after your first flight or so.

Do some GENTLE flights with it. and then adjust weight according to your preferences. start with level flight, go 3 mistakes high! then some shallow climbs and very shallow dives, then if your happy with it so far. Gradually increase your angles. if it is sluggish coming out of a dive? then increase your weight in the tail slightly.

AFTER! and Only after! your completely satified with the way it handles. then you can try a loop. or whatever.

Experience talking here. I been flying for about 12 years and went extremes both ways. Not good! LOL

You can take a very stable trainer, and be able to do some awesome stunts! just by adjusting the C.G.

If you go TOO heavy on the nose, It will seem to fly OK. but will not pull out of a Dive very well, if at all!
BUT if tail heavy you probably will stall it on take off, and or over control it and have a wreck almost imediately (sp?). as the back end will try to pass the front end, on anything but straight and level flight.

Of the two, it is better or err slightly on the nose heavy side.

Smoky.

SPADs dont come with manuals. I want to know how to get the CG with my fingers!!!

Good info though!

csisfun:

We have about 50 spads at our field and they come in at all sizes and shapes.
Most of the guys build with the yard stick main spar and balance at this point. Of course we do have a few that like to prop hang and these guys go just a little tail heavy. But like in the previous post I would recommend balance as close to the main spar and then adjust to your liking from there.

Miloh.

Been meaning to get back with you guys, I finally scanned in the article that I was talking about earlier on and put it up on my web page. Get it while you can, because I'm only going to leave it up for a couple of weeks so I don't get into too much trouble by the magazine.

http://home.comcast.net/~k.kimberlin...e/balance.html

Beardking...

Thanks for those pictures. It's looks like a much better and sturdier design than the one I devised.

Juice

Juice, may be sturdier, but I wouldn't necessarily say better. I love the one I built, but I've seen TONS of people suggest doing it like yours. I just like something that is a little heftier than that or the GP CG Machine, ya know.

I just thinking about having my “penny worth” of advice here in response to Neo’s post. As it is said before – you balance high wing plane normally, and low wing plane – upside down, as it is perfectly shown on Richard’s pictures (by the way – very nice warbirds).

Nose heavy or tail heavy? Here I am immediately thinking about final approach. This is the point where you like your plane to be slightly nose heavy, because in this case it helps you to maintain correct glide path and airspeed. Tail heavy will try to “fight you” by attempting to flare, thus it might cause premature stall… and we all know what this means… [sm=crying.gif]

Have a good flying!