digsy

I have a question about a fuselage I am designing for a EPP slope glider (a trainer).


I know you get asked a lot how long a fuselage should be but I have another question.

The answer to the question is usually - 70-80% of the wingspan.

But I've also been told that the tail moment arm (the distance 25% back from the wing LE to the position 25% back from the tailplane LE) should be about 3 times the wing root chord.

And that the nose moment should be about 1.25 x wing root chord (measured from the wing LE).

So if I have a wingspan of 60", then the 70-80% rule says the fuselage should be 42-48"


But the for a wingspan of 60" and a wing root chord of 6", that gives a tail moment of 18" and a nose moment of 7.5".

This gives a length of about 27" from the nose to a position 25% back from the tailplane LE. (so maybe about 30" for the total length). This is only 45% of the wingspan.

Which means I have either:

a) misunderstood a lot
b) calculated it wrong
c) am missing something


Can someone help ? (and explain it in small words as my brain is now throbbing)


Thanks,
Nathan

scalebldr

My Feedback: (7)

the 75 percent rule for fuselage applies to powered aircraft.gliders have larger wingspans to make up for no engine;if you use the wing chord meaurements that you already have done you should be ok.hope this helps.john

digsy

Thats great - the difference between glider and powered planes fuses never even occured to me.

Thanks,
Nathan