Hi ive got a black horse models chipmunk and im having problems balancing the plane. I have got an os 70 ultimate four stroke engine in the plane. The balance point by the manual is 100mm from the leading edge of the wing. when i tried this the plane was so tail heavy i couldent get the tail off even with the battery and all my gear as far forward as i can get. i tried 8 oz of lead and still cant get the weight forward. Any sugestions would be gratefull

Hi speedy you don't say what the wingspan is.For a 70 four stroke i guess it's about 70".If that is about right put a 125 saito in it and smile all day

sorry to be obvious but you must have too much weight at the back.
are there any rear mounted servos?
are they metal geared? that could make a huge difference.
putting a bigger engine in to correct the C of G is not the answer, unless it is designed for one.
can you change the metal push rods for carbon?
can you remove the tail wheel and replace with a carbon skid?

I don't know this model at all so anything I suggest is "generic".
One thing you could do that would be helpful is measure the chord at the wing root and the chord at the wing tip. Where does the manual say to measure the CG position? At the fuselage?

Check that the engine is far enough forward. You should fit the engine to suit the cowl on a scale model, not the other way round.
Make sure the wheels are in the correct position.
Bring any tail servos forward into the fuselage.
Review the tailwheel weight and consider a non-scale skid.
Remove any pilot figure in the rear seat.
Add a pilot figure to the front seat.
Use carbon rods in the wing servos.
Fit an alloy spinner.
use a spinner weight (Harry Higley?)
Use an in-cowl silencer.
Add doublers to the fuselage skin in the forward section (if you need forwards weight, you might as well make the thing stronger)
Bring the battery forwards into the engine bay, and use thicker leads.
Invest in an on-board glow system and fit it forwards.
Visit the fishing tackle shop and buy some lead!

That's about exhausted my to-do list.
'Hope some of it was helpful.
Carole Sherrington

Hi i havent got any servoes in the tail. The model is artf so the servo plate has already been done. all the manual says is the c/g should be 100mm from the leading edge of the wing and doesent mention anything about the fusalage. The only other thing i could thinck of was getting lead on the rocker cover and straping it to the engine. I was just wondering if this would work

if it is a reputable ARTF kit then there must be something that has gone wrong in the building.
is it designed for the size of engine that you have fitted?

too much epoxy on the tail feathers?

If I were having this problem, I would take the wing chord, multiply by 25%-28%, and check that 100mm measurement to make sure it is correct. The 25%-28% is conservative, move back later if needed.

"a nose heavy plane flies badly but a tail heavy plane flies once!"

Do as RCShadow said and then, if you need to, add as much lead as it takes to balance it.

There is no sin to adding lead to an airplane. What IS a sin is trying to fly an airplane that is not properly balanced.

I have one plane that has a 22oz hunk-o-lead in the nose. That's what it needed and it flies great!

Thanks the engine is in the recomended range but its on the lower side of the recomended engine size. ill try adding more lead and look at how the c/g is then

try doing the balance with your plane upside down

Thanks for all your help im going to try to fly tomorrow and ill proberbly let you know how the flight goes

I should have this plane coming in the mail tomorrow. I'd be interested in knowing how your experience turned out.

Tnx
Zipperneck

Let me see if I got this right. You have a BH Chipmunk with a .70 four stroke engine. .70 being equivelent to roughly a .45 to.50 two stroke. I could be wrong but the only BH Chipmunk that I can find is their 85 in 40 to 50 cc model. If this is the case, your about two lbs and two horse power off on the nose as the balance is designed to have a much larger engine up front. If this is the same airplane. Im surprised the .70 was able to even taxi it around!!

Check here
http://www.sussex-model-centre.co.uk...d.asp?id=22505

My bad!! Didnt know they had a smaller one. Im stymied now except I agree with RCShadow. Do that and it should fly. I do it that way for all my models and never trust the book CG. Most, not always, they are way off!!