I'm building a Hirobo Cap 232/15 Nitro, The book says to balance the aircarft so the CG is 30-40mm from the leading edge, so far in building i have not used the manual. The placement of my equipment is based solely on my previous knowledge of building. I don't want to find out i have an airplane with a CG out of limits the first time i fly it. I hear the CAp is a very snappy airplane. How can i ensure my self that i have a forward CG, but not too far forward for the first few times i fly it. Anybody have any techniques or calculations to figure this. Is it necessary to buy a CG machine for balancing.

I've got one of the Great Planes CG machines, it works like a champ, NEVER had a problem with a plane that was set up with it. I feel it was well woth the cost.

The CG location for an airplane is basically an aerodynamic thing. The shapes and sizes "decide" where the weight should be. So you figure out from the measurements of the airplane where the CG range would be and how long it'll be.

About the easiest way to go about this is to go to this online application and plug in the measurements. It's very easy to do. Measure what they want measured, plug in those numbers and it gives you the answer.

http://www.geistware.com/rcmodeling/cg_super_calc.htm

There is nothing magic about CG "machines". They're all basically two sticks. Well, most are. They are one of the most "luxury" of the luxury tools. You can get the most accurate CG location with two long strings, so anything that costs more than that is luxury expense. And you can beat the cost of string by using your fingers.

There are threads all over these forums that go into minute detail about CG locating.

I have sent you a spread sheet all set up for your problem. If you can open Excell spreadsheets then this will be all you need. Just don't change anything except the valuse in the cells that pertain to inches,millmeters, etc and the weight values as they pertain to your aircrafte in other words if you use metric values then use all metric, you can change the cells from metric to inches just by typing over the metric values in the cells. But make sure you do all the cells.
Steve

Dude,

Read the manual. I have been building Kits, ARF's for over 25 years no matter what your experience is, you should read the manual. There is always something to learn about or a technique needed to be done for that specific airplane. The manufactuer gives radio andand CG. advice because they have built, flown and tested the prototype and found the best set-up so you don't have these kinds of questionsor have to experiment. Sure it is OK to deviate and we all do, but you should still at least review the instructions.

CG.= 25-30% of the wing chord.

Ya think??????

CAPs -are- snappy!
Proceed with caution on the c.g.
Put it where the manual says for the first flight.
Any further aft, and the first and last flights might be the same.
And watch your elevator travel.
You do not need the maximum available from the servo for the first flight.

Trust me, i have read the manual, really it is useless, worst i have ever seen. But that is what has made building this so much fun. Steve i got your email excel spreadsheet, thank you.

Your welcome. It should get you in the air safley. After that you can adjust CG a needed and all you have to do is plug in the new CG data and it will calculate the tail wheel weight to achieve that desiredd CG.

By the way, this is how they do it on full scale as well.

Uhh, for the record, mine was won as a door prize, well worth the $1.00

cg machine that is.

Caps - heavy ones ar snappy-light ones are docile -excellent flyers - best CG for all but the hang-on-the-prop-stuff is 25%-on CAPS
- that's 25%of the average chord- no calculations or tools required - a yardstick is plenty of tooling.
The crappy about snappy all came from a series of absolutely wretchedly overweight CAPS sold by Great Planes in the mid 1980's -many modelers bought these and the rep quickly grew .
A scale CAP has a quite small (relatively) stab and is close coupled - built correctly is still one of the best aerobatic setups .

I think your full of Cap.........

LOL

I just could'nt resist, only joking. I have the Matt Chapman 580.