Hi,

I don't see why a composite should be heavier:

For carbon composite, the Young's modulus is ~70GPa for a density of 1.3
g/cm3. Al has the same Young's modulus but twice the density (2.7
g/cm3). For glass the strength is about half but again the weight is
halved too -so it's not a gain over Al. I think the composites excel in
their lack of rivets and joining pieces tho...

Cheers MC


Composites are indeed heavier than metal but if carbon fiber is used, not
that much heavier. The real payoff is in the extremely smooth surfaces that
promote natural laminar flow. The payoff is huge across the entire speed
spectrum but highest at the low speed end where the flow is less stable and
more likely to separate if the wing surfaces are rough..

Bill Daniels


"Wayne Paul" wrote in message
...
I have helped rig many sailplanes, both composite and conventional aluminum
construction. In almost every case the metal wing are lighter then the
composite. (1-35 and HP-18 aluminum wings are lighter then ASW-20, ASW-27,
and LS-6 composite wings.)

It is much easier to build a laminar flow airfoil and complex shaped
wing to fuselage transition using composite construction. These wing have
a better lift to drag ratio. The decrease in drag aerodynamic drag of
the wing and static drag decrease associated with the wing/fuselage
transition allow faster speeds.

Wayne
http://www.soaridaho.com/



"cavelamb himself" wrote in message
news
At these speeds I suspect surface condition is a small part of the
overall drag.

However!

If the new wing were a couple hundred pounds lighter, then you'd
see some inprovement in speed.

It takes power to stay aloft.

The heavier the plane, the more power is required just to stay up.


Lighter is mo' betta!


Richard



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