Balancing the large planes - RCCanada - Canada Radio Controlled Hobby Forum
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Old 09-30-2003, 08:14 PM   #1
Don H
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Balancing the large planes

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Can anyone shed some light on any pictures of jigs or fixtures that they use to balance large giant scale airplanes? I have two large biplanes that I need to check the C of G on, and am curious just what some of you are using to do this.

I would like to use this same setup for both biplanes and momoplanes as I have some large mono's to balance as well.

Thanks guys
Don H.
MAAC# - 47196

Burlington, ON
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Old 09-30-2003, 10:31 PM   #2
Kevin McGrath
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Funny you should ask . .I have spent the evening building a jig that will handle up to 50# planes including twins and bipes. It was featured in RCM two or three issues ago and may be available on the web.If not ill photo mine and post it here soon......this jig will balance both fore and aft and side to side......and is cheap and easy to make.........
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Old 10-01-2003, 05:12 PM   #3
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Looking forward to that, Kevin! I'm in need of something to balance my big ones as well.

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Old 10-01-2003, 08:36 PM   #4
Don H
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Kevin...that would be excellent if you could do that. I will wait and hold off buying any supplies to try and piece together something on my own.

Sounds like it is a handy piece of kit then if it will handle up to 50# and balance for and aft, just what I'm looking for.

Thanks for teh replies gents...

Don H.
MAAC# - 47196

Burlington, ON
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Old 10-05-2003, 11:43 AM   #5
Don H
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Well I have come up with a design for balancing large biplanes that I think will be useful. I will post pics of this as I make the jig.

Looks like a second piece can be adapted for use in balancing monoplanes as well. Someone answered my request in another forum from the US that suggested using Pro-Balance legs from a manufacturer, this would have been fine except that it was only good for monoplanes and could not be used for bipes.

I will also mention about using laser levels for getting exact levelness in my posts once I get it all together. I use two of them, one for the horizontal and one for the vertical strapped to a tripod. It works really well.

Thanks gents, talk soon....Don
Don H.
MAAC# - 47196

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Old 10-05-2003, 08:45 PM   #6
Frank Klenk
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Here is a simple method for balancing your airplane without any fancy equipment:
1. Either on the top, or bottom of the wing, near the fuse, take a scale and measure from a convenient point on the leading edge to the preferred C.G., e.g., 3�. Then mark, in 1/8� increments on both sides of the mark, i.e., 2 �, 2 7/8, 3.0, 3 1/8, 3 �, �.. These will be just dots on the wing. Mark both sides of the wing in exactly the same way.
2. Get two wide blade screwdrivers, or bladed pencil erasers, etc. I just use two large , long bladed screwdrivers.
3. Lay the wing across the arms of two armchairs, garbage cans, etc. that are high enough to crawl under. I use two lawn chairs.
4. Lying between the chairs, and under the airplane, place the blades of the screwdrivers on your mark. (the blades run along the span, not from front to back) Gently lift up. If the airplane rotates tailheavy, move to the next mark back and pick up again. Do this until the airplane rotates tailheavy on one mark and noseheavy on the next one. You now know that the balance is between these two points.
5. Generally this is close enough. If you want it closer, then move the blades between the two marks until the airplane balances.
6. If you are out at the field, someone can hold the airplane for you while you move the blades back and forth. (out of the wind!!) If they gently turn the airplane loose and it rotates so quickly that the spinner stabs you in the chest, then the airplane is too nose heavy. File a claim with MAAC and move your battery back.
The beauty of this technique is that you never really have to balance the airplane. Just move it back and forth until it changes direction. It works like a beam balance and it�s fast and very accurate. Almost everyone who has seen this for the first time has laughed�then they start doing it.
One last thing: Make sure you balance the same way every time. Use a propeller, empty the tank and make sure you have everything installed in the airplane. Keep notes so that you can make your next airplane the same.

Frank Klenk
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Old 10-05-2003, 08:53 PM   #7
Peter Gordon
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CG machine

Bob Hudson has a fantastic jig to balance the biggies

...then go to "Part 16, Centre of Gravity Jig"

Basically, you make a fake rib to fit over the wing tube and one (or both) anti-rotation pins. Then you drill the fake rib at the specified CG, and insert a blind nut. Assemble the plane and sandwich the fake rib inbetween the fuse and the wing. My description doesn't do it justice. Just check out Bobs site...

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Old 03-18-2004, 09:41 PM   #8
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bad link

the url is not found....
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Old 03-18-2004, 10:01 PM   #9
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Balancing the big birds

Try this link instead
Part 20 .......Centre of Gravity Jig
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Old 03-19-2004, 05:49 PM   #10
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If you send me a fax number, I'll fax you some simple plans that were copied on 8.5X11. It was published years ago in one of the mags. It consists of either blind cord or light rope, a couple pulleys and a plumb line. You actually suspend your plane from the ceiling and put it in a level attitude ( or whatever attitude you want it balanced) and the plumb will point to the existing CG.

From that point you either add weight to the nose or the tail and the CG will move accordingly.

I have balanced 10 oz electric park flyers, high and low wing sport planes from 4.5 lbs up to 14 lbs and the planes have always been perfect off the mark. I just finished my first Bipe and balanced it the same way.

A guy in my club turned me on to this a few years ago. He has never had it fail either.
John Kovats

aka Johnny Versatile

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Hespeler Model Aviators Inc.
Cambridge Float Flyers

I don't have the answers, but I have a personal relationship with the Guy that does.
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