Leading and trailing edges, blunt or sharp??
 

I' building a 35% Cap and was wondering which would be better for slow stable flight. Blunt or sharp leading and trailing edges.

Kent

RE: Leading and trailing edges, blunt or sharp??
 

this is good for a few beers and as many hours .
Having been thru this a number of times -here is my take on it.
in the size stuf we fly and having done that size and 40% and 33% and 27% etc., ----
what really counts is simply good solid but very light structure
Then make that as thin as practical
then just make a nicely rounded leading edge and keep the trailing edge a bit thick -to keep it stiff.
As far as making it snap better or causing problems
no problem with kinda sharp or blunt but thinner airfoils are more efficient for this type model.
The wing loading and correct balance and throws make far more difference.
Th old bit about snappin Caps stemmed from the ungodly heavy Caps mostly 20L types kitted by various mfgrs
Keep you wing loading for the 35% at under 35 oz ft -but preferably lower (as close to 30-32 as you can get) and you can drag it in .
the pics are a 40% I designed for some local friends - these weighed 36 lbs -with tuned full length pipes ZDZ160 and DA150 with in cowl mufflers- absolute rockets.
The wings are clipped 9% from scale the rest of the model is scale.

RE: Leading and trailing edges, blunt or sharp??
 

Blunt for leading edge. Someone with more technical knowledge will have to provide the why.

Trailing edge sharp, within reason. It's sharp to reduce turbulance in the air flow when it leaves the wing. But don't make it sharp like a knife, because that's just too fragile. At the speeds we fly, a bit of bluntness on the trailing edge won't matter much and helps greatly to make the trailing edge less fragile.

RE: Leading and trailing edges, blunt or sharp??
 

Kent,

For stable flight, place your CG so that you have a decent
margin of stability. If the dihedral angle is something you're
willing to adjust, increasing the dihedral will give a bit more
stability in the roll axis, but that would not be very consistent
with the type of flight the Cap is intended for, I would think.
For slow flight, make sure that you have a low wing loading.
Within reason, the shape of the leading and trailing edges don't
have much effect on speed or stability.

banktoturn

RE: Leading and trailing edges, blunt or sharp??
 

Ok no more worring about the edges, time to cut some weight. I was able to remove 4 oz by coreing the turtle deck. It is still 3/4 in. thick . Also sanded out .5 oz in the fus near the tail.


Thanks for the info guys Kent