Hello,

I have been thinking of designing an eurofighter or rafale. I know that I can get the general shape from a 3 view plan. I was wondering how one does select the airfoil, compute the CG and make sure that his design is feasible ? Does anybody can recommend a good textbook or web site ?

Thanks,

Le fou

Carefully.....

CG {if the foreplane (Rafael is a canard fighter if I remember) is over 5 inch average chord} will be at a point determined by "balancing" the area of the foreplane wiht the area of the mainplane, using 27% MAC as the locations of the "weights"

You will find ths discussed many times....

If the average chord of the forplane is smaller... you essentially ignore its presence and then balance at appx 15% to 17% MAC of the mainplane. (just a bit ahead of normal for a flying wing)

Airfoil selection is a matter of determining:
A) how close to scale do you want it to appear
B) how do you want it to perform
C) which is more important... A or B?

A scale airfoil will be thin and at model scale... essentially a streamlined flat plate. (inefficient at making lift... its partly a matter of never getting near sonic speeds...)
The thicker airfoil that works better at R/C model airspeeds may just plain look wrong.

You'll probably end up using a symetrical airfoil that is a compromise between effciency and scale-like appearance (a thinned variation on one that is commonly used in Pattern aerobatics models for example)

Make a mock-up of your final design from blue styro insulation... weight it to ballance and see how it glides. You can learn a lot very cheaply that way. When it glides well... add 3 channel electric prop drive... (why waste the model?)

For basic model airplane design, you can use "R/C Model Aircraft Design" by Andy Lennon... Amazon.com has it.
You should get a grounding in the basics of flight and aerodynamics in order to accomplish your end goal with the least amount of trial and error.
The delta is a special form of airplane, and needs more care in how it is designed..
A more advanced reference would be Martin Simons' "Model Aircraft Aerodynamics", also available from Amazon. There's more of the theory than Lennon has, but Lennon's book will get you there.

Do the numbers for sure but in the case of something like this with the canards and all you cannot do better than to test it with a small all sheet balsa glider. Something in the 12 inch span range with a simple 1/16 surfaces and 1/8 fuselage. Test glide it and trim the elevons on the main wing to flatten the glide with the CG at various test points. Start forward and keep working it back until when you toss it the nose does not come up with the extra airspeed. That will be pretty close to neutral. Move it back a bit more and you should find that it can't be trimmed for a simple glide any more. The last spot ahead was very close to the neutral point. You don't want the larger model to have a balance point behind that and preferably a 1/2 inch to an inch in front of it would be best.

After the CG testing you hang it up over your workbench as inspiration. Felt pen decoration is optional but highly recomended. [8D]

One note... TINY canard designs are special cases... as the foreplane gets smaller it suddenly becomes insignificant for producing lift. (thus the 5 inch chord note above) But its still fairly effective at controlling pitch IF you don't mess up its initial incdence.

Some designers goof and in overzealously tring to gan some lift from the foreplane when ts to small... set the foreplane at an obnoxiously high incidence. the thing starts to fly with the CG set by the balance calculation... but the plane NEVER performs well.

Keep the incidence of the foreplane within a degree or two of the incidence of the mainplane. Adjust the CG. and the CG will be VERY critical if the foreplane is small... contrary to normal for a canard. Normally a Canard would have a wider CG range than a conventional design, or a flying wing or just plane anythng but another canard. But tiny canards have a CG range of 3 to 5 milimeters.