I crashed my Edge 540 into a tree a while back and got it fixed. I'm struggling to get the exact cg position. The manual calls for a 94mm from the leading edge. The person that fixed it for me balanced it and told me it is slightly nose heavy. I flew the plane a couple of times with no hassles - it doesn't feel that much nose heavy, it comes in a tad hot, but nothing extreme. Now I decided that my Edge looks so dull and boring without a pilot in it - so I want to put one in. Can't find a nice pilot anywhere, so the crazy person I sometimes am found a old teddy of mine with a football helmet on its head and decided he is perfect! I put the teddy (from now on pilot) in the canopy to test the weight. I do not have a long enough ruler to get the cg at fuse and then determining the the position/point at the wing tip. I'm also not sure whether the wing tappers a bit (it doesn't seem to, but I can be wrong). It's just that if I calculate 94mm from the leading edge at the wing tip backwards it seems to just be to far back.

So I taped two rulers together and tried to get a straight line to the wing tip that way (using the tube where the wings slide in as a reference). Lets say that I determined the cg correctly when doingthis (without the pilot it balances slightly nose heavy here) - with the pilot it goes tail heavy. When I glued the pilot in I mounted it in the middle of the "cockpit" (it cant go further forward anyway). Now the pilot weights around 2 ounches. Now to compensate (I'm hecked scared of a tail heavy plane) for this a bit, I mounted a sinker (got it from my fishing gear) just behind the fuel tank in the nose (its about the same weight as the pilot), but because it's not right at the front of the nose (can't get into there and get it down properly) it doesn't balance out all the weight. Now I'm still about 1 ounch tail heavy - The tail drops slightly, I shall say about 30mm when I hold it at the wing tips in the air. The tail doesn't touch the ground, it just drops and then hangs there. I attached a photo (an old one which I used to asked another question a couple of months ago) - indictating where I balance it on the wing tip (not 100% to the mm)

Do you think this is going to be a struggle in the air or not? I have never flown a tail heavy nitro plane before. Only an electric, but it was waaayyy tail heavy and I know it almost didn't end good.

The plane is aGreen Models Edge 540 with a 60 ASP engine up front. If I calculated the CG to far infront of the plane then it will be fine - because then its going to be nose heavy I think - then I can correct it from there. I'm one of those people who works on the worst case scenario, that's why I'm rather working on the cg which has more the tendency to make it tail heavy.

If this is too difficult to answer, then I totally understand. I know I'm not giving a lot of info regarding this. It's just something which is bothering me a bit and thought while I'm doing nothing at work I'll ask .

<span style="font-size: larger;"><span style="font-family: Comic Sans MS;">I don't get why you need to measure it at the wing tip and then take it to the root of the wing to find there is a difference? The Edge 540 has a straight leading edge, so it should be the same. What does manul say to measure it from? For small planes its always at the root, only on the big planes is it sometimes measured at the wing tip. I hope I am reading you right ...</span></span>

Check your CG without the pilot, and mark the point.  Then put the pilot back in.  If your CG is within a cm of the previous CG, you'll be fine.  If its at all tail heavy, you'll be able to manage it.  If it feels too sensitive, you can always add some noseweight later.

The recommended CG is just that - recommended - primarily for the initial flight.  After that its normal to make adjustments for your flying style and capabilities.

I had a student that came to the field with an older design Goldberg Falcon.  He had added about 4 ounces of weight to the nose to get it to balance in the middle of the recommended range.  The plane was so nose heavy it couldn't rotate for takeoff.  He removed the weight, but then moved the battery forward to keep the CG where it was.  Same problem, but we did get it in the air after a very long takeoff run.  I told him to move the battery back to its original position.  The plane now balances about 1/4" (about 8mm) behind the recommended range.  Now the plane flies beautifully!

Small adjustments in CG won't make huge changes in flight behavior.  Just make the changes slowly and methodically.

Brad

That is not entirely correct. The balance point can be anywhere the manufacturer says it is. Yes, most are measured at the wing root, but my Seagull Extra 300s specifies that the balance point is measured at the wingtip.

If you ever see the manual you will laugh yourself silly. It's really a pathetic excuse for a manual. The manual only states : "CG : 94mm". Thats it. No pictures nothing else - just that. I always measured my other planes next to the fuse - but then the more experienced people I know told me I should balance at wing tip. If I balance by the fuse the plane drops it's nose the moment it leaves the floor.

Bkdavy
Off my head now I think the plane balances at around 1 cm from the previous cg.

I spoke to a buddy of mine a couple of minutes ago and he is heading to the LHS on Saturday. I'm working Saturday morning so it's out for me to go. I think I'm going to ask him if he could take my plane with and let them balance it for me / just second my balancing. I think this might be the best option at the moment. There they have three heads which can argue with where to balance etc. The last two times they balanced it, it came perfect so I think they better have a look at it.

Thanks for the advice though.Like I said I'm not too familiar with cg's and balancing. But yes, I am going to be playing with the cg after a couple more flights when I want to start trying 3D stuff. Now I atleast now where the boundaries are about. Thanx