Jobu

Hi,
I am making an F15 and the size and length will be somewhat to scale. The airfoil will be pretty tame with a somewhat flat bottom. Does anyone know roughly the Center of Gravity for an F15? I am just looking to get it close for the build and then will probably adust during test flights.
Thanks
Joe

Bax

My Feedback: (11)

You can get a starting point by making yourself a small profile glider of the airplane. I once made a profile-fuselage F-4 Phantom out of 1/16" sheet. The wing and stabilizer were also 1/16" sheet. With a bit of clay on the nose and playing with the tail, I got it so the glide was nice. The balance point came amazingly-close, in relative terms, to the location on a much larger R/C model.

This is quick, inexpensive, and a lot of fun. You can make such gliders from the 3-views you find in the model magazines from time-to-time. I did one that had an overall length of 6" with a 5" span. It took a bit of trimming, but I did get it to glide. A bit of work with a ball pen, and the canopy, panel lines, and major markings were on it for a "scale" look.

You can learn a lot from small models like this. If they're very hard to balance and trim for a nice glide, the R/C version you're going to build may have terrible handling characteristics. You can mess with moments and areas to get a better-performing glider, and you'll find out what you'll have to do to make the R/C model fly well.

Jobu

Thanks Bill. Good Idea, I will try it out with some left over depron 2mil. I am assuming that the airfoil plays a big part but the CoG IS the Cog.
Thanks again,
Joe

Bax

My Feedback: (11)

Sure, the airfoil will have some effect on balance point because different airfoils have different pitching moments, but the small model made of flat sheet balsa, depron, or whatever, will get you close enough that your prototype will fly. Even with a flying-wing design, or tailless delta, you'll learn the location of a basic balance point as well as some idea of the amount of reflex the wing will need.

It's not an exact process, but you can get a model that will fly and, more important, be contollable.

Jobu

Thanks Again!

DanSavage

My Feedback: (5)

Here you go. Try this. It shoud get you airborne. CG shown is 23% MAC.

Dan

Jobu

Hehe, That oughta work. Narrows it down too. Do you have any other tech. data?
Thanks alot Dan,
Joe

DanSavage

My Feedback: (5)

Hi Joe,

Nope. I've never built an F-15. This is all the data for an F-15 I have.

Happy landings!

Dan

Jobu

thanks Dan

Mike_Engle

What scale is your Eagle going to be? I'm just starting a 1/6 scale F-15C twin turbine project( still doing all the cad drawings and using various plastic model's for reference...). Did you buy plans somewhere or is it from scratch? Good luck with it!

Jobu

I am not really sure on scale. I am going by actual dimensions and breaking down to about 30" ws or so. It will be a pusher prop with a kontronics fun 400-23 brushless. Off the top of my head the ws on an F15 is about 46' and I am going to be 100% from scratch. To be double laminated 6 mill depron wing with semi airfoil and all depron fuse. Full 4 channel functional with depron and 1/32" gear. I am shooting for a complete flying wieght of 18oz. I have used this motor on a Greatplanes Slinger @ 27oz and got 70-80 mph.

A twin turbine is quite an endevour from scratch Mike, I wish you good luck as well.

Mike_Engle

Thanks Jobu!!! It is quite the undertaking to say the least!!!!!. It's my second scratch build. I'm in no rush to complete it right now but once I get all the formers cut and some plans drawn up I will start a build thread here, maybe in a few months or so. Still alot to accomplish between now and then the research I've done has taken 6 months.