We recently competed in the Class B flight competition. I was coaching, and the kids decided that they wanted to design and build a plane from scratch. Well, we managed to get a plane built, but unfortunately it didn't fly real well, too many calculation errors... but we leaned a ton for the next competition
! I think I now have a pretty good understanding of the different parts that go into designing these planes, and most things I can relate to some mathematical relationship. There are two things, however, that I was not able to determine 100%. The first was the CG marking on most plane drawings, and the second was the length of the motor stick.1) I assume that when the drawing says 70% CG, they are just indicating a starting point on the fuselage for where the calculate neutral point (NP) would go? I can calculate the distance needed between the LE of the wing to the LE of the stab to determine the NP. Then one would used a moment arm calculation to find the actual CG?
2 )The only thing I could think of to determine the length of the Motor Stick, was the incident angle of the stab would drive the boom length. Then subtracting the length calculated from 1 above would give the the length from the prop to LE of the wing and from there one can determine the length of the Motor Stick. But is that correct?? It seems that many planes I've looked at use the root span of the wing to estimate the Motor Stick. Is there really a mathematical relationship here? What if the incident angle of the boom is 0?
Thanks for any help you can provide... looking forward to our next plane design!
david