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Old 02-20-2007, 10:27 PM   #1
rede2fly
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Default BALANCING GIANT AIRPLANES

hey guys dont want to sound like a idoit here but, what balancer are you using to balance airplanes that are say around or over 20 lbs?? all i have is the great planes balancer and i dont trust it to cary that much weight. plus it isnt very user friendley when trying to balance bigger planes. whats out there??
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Old 02-20-2007, 10:30 PM   #2
Pale Rider
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Default Re: BALANCING GIANT AIRPLANES

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Last edited by Pale Rider; 02-21-2007 at 10:24 PM. Reason: because
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Old 02-20-2007, 10:44 PM   #3
Wayne
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Default Re: BALANCING GIANT AIRPLANES

I posted this a long time ago on RCU..
It works!

This method is how I go about checking CG on a plane that weighs too much to put on a CG machine. This is generally the same way full scale planes are balanced. You can’t go lifting a 747 by your fingers!


First, have the plane assembled as
RTF, but minus fuel. Find a place where you can put the nose of the plane up against a wall. Take a level and prop up the tail wheel until the fuselage is sitting level. You will probably have to take the hatch off in most cases to find a suitable area to set the level on.

Once the plane is sitting level, place masking tape under the area where the main wheels are touching the surface and draw a line where the wheels contact the tape. Make an index mark where the center of the tailwheel falls in the same manner. This mark will be on whatever you propped the tail up with. (I use magazines). It’s also a good time to measure from the wall, to the point where the recommended CG is. Save that number for later.

What you are looking for at this point is the distance to each wheel from the tip of the spinner. (which should be touching the wall at this point) I use a long straightedge to get the distances

As an example, let’s say you come up with theses numbers:
LH main – 22”
RH main – 22”
Tailwheel – 70”

Now, place a scale under each wheel individually. You will have to re-adjust the height of the other wheels each time to keep the plane sitting level. Add more magazines as necessary. (If you have three scales you can get the weights at the same time but make sure the plane is level)
Don’t forget to re-install the hatch before you weigh each wheel. You will wind up with three weights, one for each wheel.

Let’s say you come up with these numbers
LH main – 9 lbs
RH main – 9 lbs
Tailwheel – 5 lbs

Now its just a simple math problem to find where the CG sits right now on the plane.

Weight x ARM (distance) = Moment
22x9=198 in-lbs
22x9=198 in-lbs
70x5=350 in-lbs

Now add the total of all the moments and the total of all the weights.
Weights 9+9+5 = 23lbs
moments 198+198+350 = 746

Then divide the total moments by the total weights.
746 divided by 23 = 32.43

That number 32.43 is "in inches" how far back from the tip of the spinner to where the plane balances right now.
Compare that to the distance that you measured earlier to the recommended CG location.
If you are off one way or another adjust items then recalculate the weights. The distances (or ARM's) arent going to change so you already have those numbers.


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Old 02-21-2007, 10:21 PM   #4
rede2fly
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Default Re: BALANCING GIANT AIRPLANES

thanks wayne. i knew i was saving my 15 year old mags for something. thats a lot to take in, after only reading once. think ill have to print this out
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Old 02-21-2007, 10:24 PM   #5
Wayne
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Default Re: BALANCING GIANT AIRPLANES

It looks worse than it is.
Pretty simple to do.
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Old 02-21-2007, 11:21 PM   #6
rede2fly
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Default Re: BALANCING GIANT AIRPLANES

Quote: Originally Posted by Pale Rider
View Post
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hey pale rider why did you pull your post?? i didnt have a chance to go look at it.
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Old 02-24-2007, 05:43 AM   #7
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Default Re: BALANCING GIANT AIRPLANES

I downloaded this spreaadsheet from some where but for the life of me I can't remember. Havn't tried it yet but it is basically the same method that Wayne described above except total weight of the model is needed. At the time I found this, those that used it said it worked well. Any way, it might be worth a shot. I will be attempting this myself in a week or so.
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Old 02-25-2007, 08:11 PM   #8
rede2fly
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Default Re: BALANCING GIANT AIRPLANES

thanks digger ill take a look at it
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Old 04-14-2008, 08:21 PM   #9
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Default Re: BALANCING GIANT AIRPLANES

WAYNE...... That is great. I took my A&P (Airframe & Power Plant) a lot of years ago. That really takes me back. You are spot on.... Thanks Jay P.
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Old 04-14-2008, 08:23 PM   #10
Wayne
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Default Re: BALANCING GIANT AIRPLANES

Jay,

As you know, I didnt make it up.
Just passing it along.
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Old 04-14-2008, 08:59 PM   #11
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Default Re: BALANCING GIANT AIRPLANES

Most of the larger planes will tell you to start out with the plane balanced on the wing tube, so just take the canopy off, grab the tube (lightly) and lift.

Some obviously won't have wing tubes (warbirds) or will balance at different points... the above weighting method works great.
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Old 04-23-2008, 01:15 PM   #12
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Default Re: BALANCING GIANT AIRPLANES

If the balance point is the wing tube. I take a string and make a loop on both end. Put the loops over both sides of the wing tube (with tube thru plane) put the wings on and all other parts (canopy, cowling, etc). Lift the plane off of the ground by the string, should be pretty easy to see if it is balanced.
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Old 04-23-2008, 01:41 PM   #13
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Default Re: BALANCING GIANT AIRPLANES

I made a simple balancing jig so I can do it by myself with some accuracy. There are also after market ones available but they are expensive. I bought an after market one to share with friends but they are easy enough to make. http://www.ezbalancer.com/index.html I got the version 1 for large planes and have used it for many planes at the club. It is more easily adjustable than the wood one I made. I see they have a new version that looks very nice too.

If you want to make one...
Basically you make some "cradles" out of ply(1/2") (padded with some pipe insulation foam) that the wings sit on near the root. Those are bolted through a bushing onto some ply supports (3/4".) You make a line that runs throught the pivot point of the bolt and use this to "sight" the CG mark. You should also add some stops to the side rails so that the cradles cannot tip so far that the plane would fall. The supports are bolted to a frame of some type. I used some aluminum brackets on a 3x4 ply sheet so I can move the cradles in and out to support the plane near the fuse.

I set the jig up on some sawhorses and then lift the airplane onto the cradles. It is very accurate and you can move batteries around and play with weights while it is up there.

As has been mentioned almost all giant monoplanes balance on the wing tube - but not all. Biplanes are also different. Thats another reason why I like the jig.
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Old 04-23-2008, 04:50 PM   #14
hawk21
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Default Re: BALANCING GIANT AIRPLANES

the gp cg machine works, can handle up to 40 pounds
I have use it, but it is dificult to put the plane
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Old 05-24-2008, 08:11 PM   #15
Dennis 9412
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Default Re: BALANCING GIANT AIRPLANES

You might want to try the Vanessa rig. You can make one of these for about $2.00 and it will work with any size plane. I didn't believe it would work, so I figured, "what do I have to lose but a couple bucks?"

I built one to balance my 28% WH Edge 540 and it works slicker than can be!!

Have a look here, and give it a try.

http://www.rcuniverse.com/forum/m_708060/tm.htm
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