Moving the CG

Wherever the plane is balanced, whether good or bad is currently its center of gravity. When you are trimming the plane for proper flight, you move the CG forward or backward. To shift the balance point-the CG, forward you add weight to the nose. To shift the CG rearward, you add weight to the tail.

When we've been building from kits, we're spoiled because they always say where the CG should be. But when you are building an unknown entity, you have to shift it around until you find where it flies just on the edge of stable for a stunter. For a trainer, you'll shift it more forward to make it more stable.

EDIT: Okay Ken beat me to it with a better answer.

Remember, with the new ringmaster "noseheavy is good, noseheavy is good" keep saying it. It will be more stable and less twitchy. I found out the hard way. I just went and looked, I have 1.5 oz's of lead in th tail for a fox engine. And a half oz. of lead in the outboard weight box. My front leadout is right on the CG for the airplane. My Bellcrank pivot hole is 3/8" from the center hole on a standard 3" SIG bellcrank, My controlhorn is the 3 hole off of the plan's with the pushrod in the furthest hole. Ringmasters have a relatively narrow foil and like to fly fast and stall easy. Very lite up on take off or it will stall. Fun as heck to fly once it is up, overhead for me is still scary, I've managed to start doing some inside loops and wingover's. I'm just starting to work on getting into position and diving into a outside loop, but haven't pulled the trigger yet. I alway's seem to chicken out. I'll get there. We will have to get together and fly some time. I just bought the wood to cut another Ringmaster out for my winter build.

Jim Hayes
AMA 988835

Ok guys,

I got it now. It's what I thought all along. When I hear things like shifting the CG I thought maybe there was some sort of genious calculus going on and folks were coming up with a new balance point. In reality the balance point stays the same and all you do is add weight either side of it to shift the balance of the plane.

Jim, no worries I always balance on the slight edge of nose heavy that way I know I am safe. The only plane that sits level when balanced is my Baby Clown which is probably why it flys the way it does. All my other planes are slightly nose down.

Probably stated already but the CG is the point along the length of the body where the plane is balanced level when 'teetered' there. If you move the CG forward by adding weight to the nose, then the point along the body at where you have to hold it to keep it again balanced flat is the new CG. Plans will tell you to put the CG at a certain point so that the plane has just the right amount of control, from experiment. Of course full-size aircraft builders will model the drag of the plane and lift forces to figure out where the CG should be to keep it stable in flight, same with simple finned rockets since they're related.

Nose heavy is good to a point. Too nose heavy and it is a powered lawn dart. RC and freeflight airplanes usually want to balance at the thickest part of the wing. Because control line airplanes are attached and dragging the lines along they tend to want balance a little more forward.

Control line airplanes can balance as far forward as the leading edge and not be "maverick." The controls will still respond without power, but they sure won't glide for squat like that. This makes for hard landings that more closely resemble crashes. The airplane will also be sluggish to respond to control input.

Balance too far back and the response is twitchy. Control flutter will overpower control input and the airplane will become uncontrollable.

balance = the current location of the CG

Phil

Yo Ron
As you can see my tyre man Chris now has 5 gram self adhesive weights in stock for wheel balancing.

You all know my views on adding weight but sometimes..........
You could even trim them with tin snips for small gains.
I'd keep adding a little to the nose till it feels 'orrible then try going the other way, you'll find the sweet spot
fairly easily.

Remember the old maxim,- too nose heavy fly's bad, too tail heavy fly's once.

IMHO the two most important trims are,- engine thrust and cog, cog is without doubt the MOST
important and when wrong will be the cause of almost ALL flying problems assuming the wing
and tail are square.



In my world (RC) I've seen guys countless times programming mixes into their radio's to 'dial out' say a plane that
pulls to canopy when in knife edge. It's all too easy to overlook the obvious especially if you have a sexy JR radio .
Most of you won't know to whom I'm referring but if he see's this he'll know/Hello Paul......
I don't know if there's something similar in CL but in RC we take the plane up high put it in a vertical dive and watch what it does.