Hershey bar wing vs composite wing - how much drag?

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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On Mar 29, 2:10 am, DR wrote:
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

------------ And now a word from our sponsor ---------------------
For a secure high performance FTP using SSL/TLS encryption
upgrade to SurgeFTP
---- Seehttp://netwinsite.com/sponsor/sponsor_surgeftp.htm ----- Hide quoted text -

- Show quoted text -

From wha I have read in the past, the major reason for lack of weight
reduction in composite structures results from differences in the
design standards. The design standard for metal wings is based on a
1.5 times specification. Thus, a wing rated for 3g's is designed for
4.5 g's. The standard used for composite wings has been set at 2
times specification. The composite wing rated for 3g's is designed
for 6g's and as a result any weight savings is lost to the extra
strength. The difference in the standards was ment to compensate for
perceived quality variations in composite contstruction techniques.

BobR wrote:


From wha I have read in the past, the major reason for lack of weight
reduction in composite structures results from differences in the
design standards. The design standard for metal wings is based on a
1.5 times specification. Thus, a wing rated for 3g's is designed for
4.5 g's. The standard used for composite wings has been set at 2
times specification. The composite wing rated for 3g's is designed
for 6g's and as a result any weight savings is lost to the extra
strength. The difference in the standards was ment to compensate for
perceived quality variations in composite contstruction techniques.


The main reason for the 2x standard has to do with the fiber alignment
(or rather misalignment) of the laminations in the spar. Since this is
the single heaviest, and most important component of the wing, its
construction is critical. Unfortunately, with traditional wet layup
techniques, perfect alignment of the fibers in the spar is not possible,
thus decreasing its strength. The obvious solution recommended in the
books is to increase the design over design to compensate.

Not too long ago, I saw that someone had solved this problem by using
small diameter, precured carbon-fiber rods as the core material for the
spar. This solves the disadvantages of the traditional techniques.

"Evan Carew" wrote in message
t...
BobR wrote:


From wha I have read in the past, the major reason for lack of weight
reduction in composite structures results from differences in the
design standards. The design standard for metal wings is based on a
1.5 times specification. Thus, a wing rated for 3g's is designed for
4.5 g's. The standard used for composite wings has been set at 2
times specification. The composite wing rated for 3g's is designed
for 6g's and as a result any weight savings is lost to the extra
strength. The difference in the standards was ment to compensate for
perceived quality variations in composite contstruction techniques.


The main reason for the 2x standard has to do with the fiber alignment
(or rather misalignment) of the laminations in the spar. Since this is
the single heaviest, and most important component of the wing, its
construction is critical. Unfortunately, with traditional wet layup
techniques, perfect alignment of the fibers in the spar is not possible,
thus decreasing its strength. The obvious solution recommended in the
books is to increase the design over design to compensate.

Not too long ago, I saw that someone had solved this problem by using
small diameter, precured carbon-fiber rods as the core material for the
spar. This solves the disadvantages of the traditional techniques.

Jim Marske has been involved in sailplane construction for many years. I
believe he was one of the first to use carbon rods in the spar caps. Check
out his website for more information: http://marskeaircraft.com/

Aluminum wings can be "profiled" with performance results close to a
composite wing. (http://tinyurl.com/2r8b7d) The time involved is such a
project is normally 400+ hours.

Wayne
HP-14 N990 with profiled aluminum wings
http://www.soaridaho.com/Schreder/N990_Near_Arco.jpg

DR wrote:
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


If strength were the only issue, you'd be right on.

But there is also the question of stiffness.

Composite structures tend to get strong enough long before they
get stiff enough.

Then there is the "margin of safety".
Metal and wood wings are designed to a 50% MS.
Composites tend to go to 100% extra.
That alone means more weight.

Richard

DR wrote:
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...

Last I knew, Young's modulus was a measure of stiffness, not strength.

Matt