I am in the process of balancing my plane. Can someone explain exactly what I should do. I have the plane upside down, Its nose heavy I know. I place weight at the tail & cant seem to make it balance. The manual says 100 mm back from leading edge, done that.....then I'll try again with weight in a different spot on the tail & it will take more or less weight & want to balance somewhere else, either more forward or back, I,m confused........thanks, Dave

Could you post a pic of your set up?

Check these articles out:

http://www.rcuniverse.com/magazine/a...?article_id=84

http://www.rcuniverse.com/magazine/a...article_id=601

Remember that the CG point given to you in the manual is the point from the leading edge back towards the trailing edge measuring along the sides of the fuselage. This is also know as the "root of the wing". As a general rule the CG is 25-30% of the wing chord measured from the leading edge.

If you can't get the plane to "balance" - that is, to stay on the balancer without teetering to one side or the other, it's no big deal.

If you place it on the balancer and hold it level and it will drop to one side consistantly (Nose or tail) add weight to the other side until it will drop to either side equally.

In other words, let's say you place it on the balancer, level it and it drops to the tail, now level it again, but tip it slightly nose-down and it tips toward the nose, you are close enough.

Remember that the balance point is not necessarily an EXACT point. Adding fuel will change it, getting dirt and oil on the plane will change it, etc. So getting it close is close enough.

This is why we usually tell people to err on the nose-heavy side. This way, if there are any minor changes, you have a built-in safety margin.

If it is a high wing model, balance it right side up. Balance it upside down if it is a low wing model. The motion you describe indicates that the actual CG (which is a single point) is above the CG machine's point of contact with the wing and therefore the model is unstable on the stand.

Bruce

thanks guys!!!!!

Hi everyone, I'm not a big poster would rather talk in person. I also have a C.G. Question I don't mean to butt in someonelse's conversation.but this seamed like the right place. I picked up a Lanier Razor 3-D at a meet recently beautiful plane beyond my flying but couldn't pass it up. It has a swept wing I have read on straight wings but whats the rule for swept wings is it the same ? i.e. 25-30% also anyone know what the best prop for this app. would be I am running an eagle 46 2 stroke. Any help would be appreciated thank you, Bill

Bill,
We all know the CG affects your model's pitch stability. So does the horizontal tail. Matter of fact, thats what controls your model's pitch stability AND it's pitch. So to ignore it doesn't make any sense, does it. The easiest way to consider all the things that affect the stability and therefore the CG location is to not consider them at all. Let this program work it all out for you. http://www.geistware.com/rcmodeling/cg_super_calc.htm

It takes me 2 minutes to make 9 measurements with a yardstick or tape measure. I don't have to know a thing other than how to measure. Plug those into that application and it'll give you the CG range for your exact model.

You do have to give it a Static Margin value, but don't worry about what that is right now. After you've plugged in the 9 measurements, just plug in 5 for a 5% Static Margin and click the button.

The application will instantly fill in the rest of the boxes with computed info. It's so fast you won't even see it blink. Write down the CG location that's filled in down the page a bit. Now change the 5 to 15 and click again. The CG location has changed as you see. The two you now have are the CG range for your exact model

and you didn't have to know squat....... or draw scale planform views on graph paper.......... and it takes less time than it takes to type a post here...... and it used the formulas that the aircraft industry and the airline industry and airforces and ........... etc etc

Bill, you can always start your own thread. Name it something like "A couple of questions about my model" or "CG and prop question"