C.G.

[rruhter]

I am new to the giants. Have flown for many years and glad to be back flying. I was having a problem checking the C.G. on my giant by myself as it is a handful. Anyone got suggestions on an easy way to balance without help. Stand, jig, ect.
This may not seem like much of a problem but with one person it is a pain.

[rede2fly]

hello there rruhter. there are some great threads about doing this on giant planes do a thread search in the upper left corner and you will find them. also welcome to the giants. good to have ya here lots of great information here. i asked this very same question long time ago but you will find it doing a thread search icant remember the answere in it entirement or i would gladly post it.

[Mithrandir]

are you good at algebra? you can get it with a scale under each wheel and a little math.

[FireFighterFSFD]

there are several different giant scale balance contraptions you can buy the best way for me to balance a giant by my self is just balance it on the wing tube. you can use some string around the wing tube on each side and put the wings on and just pick it up by the string. if you balance it on the tube it is close enough to fly and figure it out the rest of the way by the way it acts in the air. I dont know your knowledge with the big planes but the cg is not like setting it in a small glow plane. those things give you a garenteed crash if they are tail heavy with the big planes you can usually get them back to the ground no problems. good luck finding out what works the best for you

[Downhumpty]

I know this is on here somewhere. Here try this. Good luck.

Kent Porter

You wont even have to lift the plane with this method.
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.

It may sound confusing and a lot of work but it really only takes about ten minutes to do it.

Try it......

[Al Lewis]

I got a J&L building stand for my birthday. Took out the top two plastic plugs and put in two swivel jacks screwed onto .500-13 UNC set screws that I wrapped a couple times in duct tape. Then I took the scales off of the GP CG checker and mounted them onto the uprights of the stand. Those uprights move in and out to adjust for the width of the fuse. Now I just put on the wings and set the plane on the pads like a regular CG machine and check it. I stow the scales in the foam padding when not in use. http://www.jlproducts.net/