COG

[fireguzzi]

Ok, so what is the technique for finding the center of gravity on a plane? I kow how to on a heli but i have no idea about planes.

[Tony]

That is a tough one because there is not really a simple answer.

Are we talking about a store bought "kit" plane or something built from plans where the manufacturer/designer gives you a recommended CoG, or a scratch build where you need to figure it out on you own.

[dubehigh]

hey fire, it should be from the center of the wing tip, thats were it is on the super cub. what plane are you referring to?

[fireguzzi]

It's a RTF cub. An ultra micro. If it mentions it in the manual I have missed it.
I ask because it likes to climb. I have trimmed the tx all the way and it still does it. I have moved the batt forward and it's helped some but not much. Just want to find the proper way to do it before I get too drastic and start adding more weight which is something I don't want to do if I can help it.

[BTCat]

Cog should be around the thickest part (cord) of the wing on something like a cub. In the case of the Super Cub, it is between 2.25 and 2.5, depending on who you ask (2.25, if you ask me . If the manual doesn't give specifics on your ultra, the thickest part of the wing is your best bet, I believe. You can set to this and then play around with it to get it to handle like you want.

I made a simple jig to check mine. Its just a board with two pieces of even length key stock (dowels work fine). I drilled two holes and put the rods in. I just set my cub on the tips of the rods and eyeball it. I put mine just a slight bit nose heavy.

Hope it helps.

Here's a pic of my F22 on the CoG jig:

[19000rpm]

High wings are, like BT said, normally locate the CG through the thickest part of the wing cord. Since you don't have that type of wing, I'd look at roughly 1/3rd of the width of the wing.

You should always want to err toward a heavy nosed plane for stabilities sake. A heavy tail never works out well.

If it's climbing that may not be a CG issue at all. That generally means that there is a slight "up" elevator situation or the wing is at an angle. Check your elvevator control rod and "pinch" it down a little and try that.

[BTCat]

That's just an illustration of my jig, BTW. I don't have a pic of my cub on it.

[akent]

Nice jig, BT!
I just use my fingers, but a jig would sure be nice.

[BTCat]

Mar 24, 2010 19:29:47 GMT -6 akent said:

Nice jig, BT!
I just use my fingers, but a jig would sure be nice.

Took a whole 5 minutes to make. Took me longer to try to get a hanger bent. ;D

[fireguzzi]

Good info. I like that jig BT, and thanks everyone.
I checked it out using my fingers. I put them about 1/3 from the front edge of the wing and i was a smidgen tail heavy. I cut a little more foam so i could move the battery forward more. Got it where it was just a hair nose heavy. I got her flying around to test fly it and started messing with the trims. What happens while you fly around a bunch of trees and start paying attention to the tx? Yup. Finally got it down from the tree after having to throw a small trash can at it about 200 times. (It was stuck too good for rocks or sticks) Cracked the elevator fin? Don't know the proper name for it. Also lost one of the dummy engine sides. It got lost in the leaves. Soooooo I'll be gluing today instead of flying.

Oh yeah, this is the third time it has been stuck in this same tree. I'm really beginning to feel the need for more firewood.

[dubehigh]

cut the tree, cut the tree, cut the tree ;D you can always plant seeding in its place, so its easer to get the plane out ;D

[fireguzzi]

I think I'll give it one more chance. I'll let the leaves grow back and see if it helps me see it in my peripheral vision. I think that is the main problem, it blends in with the background to easy while it's bare. It may live another season yet.

[19000rpm]

The first couple of years I flew all my planes were "Tree Magnets". I even flew a heli or two into trees.

That got better once I learned to keep one eye on the plane and the other eye on where it was actually going. Not so easy for a new pilot to do. ;D

I swear I did 10 times more damage getting the planes down from a tree than I ever had in any other crash; including the ones when I flew it straight into the ground. ;D

[fireguzzi]

Mar 25, 2010 15:38:59 GMT -6 19000rpm said:

I swear I did 10 times more damage getting the planes down from a tree than I ever had in any other crash; including the ones when I flew it straight into the ground. ;D

Exactly what is happening. 90% of the damage is from getting it out of tree's. Almost always the tail too, it's beginning to look like a puzzle instead of a tail.

[19000rpm]

Mar 25, 2010 19:57:49 GMT -6 fireguzzi said:

Mar 25, 2010 15:38:59 GMT -6 19000rpm said:

I swear I did 10 times more damage getting the planes down from a tree than I ever had in any other crash; including the ones when I flew it straight into the ground. ;D

Exactly what is happening. 90% of the damage is from getting it out of tree's. Almost always the tail too, it's beginning to look like a puzzle instead of a tail.

The tails on these ultra minis take a beating. I'd buy at least one extra set and reiforce them with strips of packing tape, one running the length of each stab, and then across the width where they meet the fuse. That really helps.