mikeh251

I have a Sig Fazer and a Somethin Extra. The wing seems to be almost exactly the same in all geometrical aspects. The tail surfaces are very similar in size and also in location (with respect to the wing ie heighth of tails compared to heighth of wing) However, the tail is 4 or 5 inches closer to the wing on the fazer. I personally like the flight characteristics of the SE better.My question #1 is: are 3d planes shorter and sport planes longer? I'm not very goodat 3d and fly these types in "sport mode". Q# 2:Can I extend the tail of a second unbuilt fazer to make it more like the SE? I suppose I would compare recommended cg for both kits and decide where to set cg. Q#3: The nose is also longer on the Se what effect does this have? BTWI did shorten nose on Fazer per recommendation to achieve cg on first build. I assume this relationship to be less critical than longer tail. Thanks in advance for assistance.

da Rock

A lot of your re-design considerations can be worked out with the help of the geistware.com application.

Moving any tail back improves the leverage it has for controlling the pitch and yaw (if you move the vertical stab and rudder with the horizontal surfaces) control. Precision flyers moved the empennage back in the days when smooth was what scored in their pattern and moved it forward when snaps were important.

3D mostly depends on larger than usual surfaces but a longer tail moment would let you reduce them somewhat. Bottom line is that for 3D, too small won't do well. Extending the tail as you think will do what you expect.

The CG won't be a problem for your new plane. Use geistware and you'll get absolutely reliable and exact location for whatever you wind up with. No need to debate the issue, find out exactly based on your exact measurements.

da Rock

The nose measurement is like you assumed, it's all about balance. The engines are significantly heavy. Where the prop is doesn't do much compared to where the weight is.

mikeh251

I thank you for the reply and will check out the link you provided. I have not done that yet, but will soon. I like the way the Se tracks a straight groove and can handle like a trainer when desired. The Fazer is a mild plane on lo rates also, just not as good as the other. I didn't mention in post, but I had to really weigh the fazer aft to get balance as I mounted servos in the rear and moved motor rearward. Anyhow, if I do extend the fuse on next Fazer kit, that should assist in c/g situation also. I will soon be investigating the link provided with more detailed measurements and should be able to get a second kit better than the first.For my personal intended use that is. Thanks again.

da Rock

mike,
The geistware application uses the formulas that've been in use by the aircraft industry forever. The one most of us use for models is usually employed to find a safe reliable CG range, but can be of use for modifying an existing design like you're doing. In any case, whatever you decide to create, it'll be the best tool for getting a starting CG location for your first flight on the new bird.

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