hello everyone,
well i have a black horse models speed air 40 plane ARF that has a 10.5 in wing cord. the recommended CG is 100mm from the leading edge

well thats just shy of 4 inches thats almost half the wing cord and i know thats not right, when i do the math 25 to 30% of the wing cord is 3 inches to 3.25 inches.

the kit is made overseas and i am unsure if the translation was right. any ideas on where i should start to balance this plane now that i have a new engine in it ?

thanks in advance for the help

bassman

what is wrong with the recommemded location???? the CG on my duraplane is almost in the middle of the wing cord, it flies great

well at the recommended CG it will need a ton of weight in the tail to get it to balance properly. so i dont think the CG is correct . thanks for the reply

bassman

my duraplane takes about 2 oz in the tail to balance properly, so maybe it is correct???

For a trainer i'd start at 25% - 30% MAC (should be the thickest part of the wing)and see how it goes, if you start at 4" and its too tail heavy your plane may not survive for a second try

i should have put this in first but it is a low wing plane, my second plane. i have put the CG at the 30% mark and had to add 2 ozs to the tail.

when i had it at the recommended CG i would have had to add about 10 to 12 ozs to it so i guess i will try it at the this and see how it flies i will be going out on thursday night. i will keep you posted as to what happens keep your fingers crossed. here is a link to a site that has my plane . again thanks for the help

bassman


http://www.brucknerhobbies.com/black_horse_models.htm http://www.brucknerhobbies.com/image...e/speedair.gif

Try balancing at the point on the wing that is in line with the main spar. See if that's close to balance to some of the other suggestions you've had (eg. 25-30%,etc.) If you start at the main spar you won't be a large amount off. Then you can make minor adjustments (nose or tail) from there.

If it is a conventional aircraft: monoplane with an aft horizontal stabilizer that is not a lifting stab as in some vintage types Then the 25 to 30% figure is indeed the way to go for any sport airplane. Yes some extreme aerobatic types as well as some pylon craft will exceed this somewhat but not much. The only other exception to this is flying wings which need a more forward cg around 15% or thereabouts as well as tandem wing/canard craft.
Going to anything beyond around 33 is looking for trouble.

John

also does this plane have to be balanced inverted.

That is the usual method with a low wing. Doing it upright would be be very difficult with the CG 'above' the balance points.

John