SoCalSal

My Feedback: (16)

Hi , Can I get some ideas on how to balance a 33%waco. In other words what is the best way to do it. I know the C.G. position but I'm trying to figure out how to balance a 40+lbs plane.
Thanks for any help

RK-Aircraft

My Feedback: (81)

I'm told you can use a KollerCraft balancer. Don't know where to get one.

wgeffon

My Feedback: (4)

This method is how I go about checking CG on a plane that weighs too much to put on a CG machine or lift.

Have the plane all assembled RTF 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 till the fuse is sitting level. Your gonna have to take the hatch off in most cases to set the level on.

Once the plane is sitting level, mark on the ground the two points where the main wheels are with masking tape and draw a line right where the wheels contact the tape. Then make a mark where the center of the tailwheel sits in the same manner. Its gonna be on whatever you propped the tail up with. (I use magazines)
Its also a good time to measure from the wall, how far back the reccomened 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

Lets say you come up with theses numbers:
LH main - 22 inches
RH main - 22 inches
Tailwheel - 70 inches

Now get a scale and place it under each wheel individually. You will have to re-adjust the other wheels to keep the plane sitting level. Add more magazines.
(If you have three scales you can get the weights at the same time but make sure the plane is level)
Remember to put the hatch on after you level the plane before you weigh each wheel. You gonna wind up with three weights. One for each wheel.

Lets say you come up with these numbers
LH main - 9lbs
RH main - 9lbs
tailwheel - 5lbs

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
22x9=198
70x5=350

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 reccomended 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.

This is generally how full scale planes are balanced. You cant go lift one of them by your fingers or stick it on a CG machine.

Try it......

RK-Aircraft

My Feedback: (81)

I got a cradle from ArcayAircraft.com that works and is easy. Just get the fittings for balancing. Easy.

tonyc

My Feedback: (4)

I use the trapeze method for all my airplanes. I just finished a 1/3 scale Cap and the CG was located this way.

Only 3 steps.

1) I run a line from the propeller up to an eyebolt in the ceiling and back down to the rudder. Pull the airplane off the ground and let it hang level.
2) From the eye bolt drop a plum line down to almost touch the airplane, this plum line is pointing at the current CG.
3) Add weight or move things around until CG is where you want it. I will also balance the wing tips if one side is heavy.

That’s it. Good luck

tonyc

RK-Aircraft

My Feedback: (81)

Tony,
That really is the best way I used!! [sm=thumbup.gif]

PS: But I use a pulley at the eyebolt too. There is too much friction coefficient on the cord directly bearing on the eyebolt surface. It would not be very precise otherwise. [&:]

tonyc

My Feedback: (4)

I never thought of using a pulley. Your right this would make it better.

thanks

tonyc

SoCalSal

My Feedback: (16)

I don't understand. If you hang the plane from the pully till it is level. Then hang a plumb line down to the plane, does that line point to the current center of garvity? At this point do I shift the plane forward or aft to the indicated CG on the plans and if it is nose heavy add weight to rear or visa versa? Is this what you are trying to tell me?

Thanks
Steve

RK-Aircraft

My Feedback: (81)

Sort of. With a pulley, the plane will level itself out to be either nose heavy or tail heavy. The plumb bob just points straight down. You need to know where the manufacturer tells you the CG should be. Some of you may have noticed a little bullseye or crosshairs on your decal sheets enclosed in the box the plane came in. They never tell you what thats for. ITS A GC MARKER. You put it on your wing or fuse where the CG is supposed to be measured. So, put it or a dot where that should be. Now, put a ribbon of masking tape across the fuse from GC dot to GC dot. Use a marker to connect the dots with a line (use a straight edge if you can). This is not possible with a mid-wing, so "eyeball" it. You balance a low-wing upside down. Next start moving things around like the battery, servos, rx, smoke pump, etc. ( or heaven forbid, lead) until the plane levels itself with the plumbob pointing right to the line you just drew. Thats it !! You can do the same thing laterally.

SoCalSal

My Feedback: (16)

Thanks, I know what you mean now. I'm trying to balance a 33% Waco YMF 5 I do know where the cg is supposed to be, it is marked on the plans, actually to different spots depending on how you want the plane to perform.
Thanks again
Steve