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



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

On Wed, 28 Mar 2007 23:11:29 -0500, "Montblack"
wrote:

("john smith" wrote)
On the new aiplanes, there are HUGE fillets fore and aft of the wing. This
really became a design consideration in the mid-1980's.


Wheel pants, gap seals, ....and HUGE new fiberglass fillets (fore and aft).
Are they part of everyday speed-mod packages?

If so, what is the "anecdotal" gain, after installing (just) them?

I've read reports on wheel pants, on gap seals, and on Power Flow exhaust
systems, but not on aftermarket fillets for the GA fleet.

http://www.powerflowsystems.com/

Knots2U sells a wing/fuselage fairing.

http://knots2u.com/28WR.htm

I have it on my Cherokee, but cannot discern the exact performance
gain as it was added in conjunction with a number of other mods.

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.

The composite construction makes a big difference in making
possible the use of supercritical airfoils. These airfoils need a
slick surface, so much so that flying in rain degrades their
performance to the point that they can become dangerous. You'd never
build a wing like that using sheet metal and rivets. Just the lap
joints or any waviness in the aluminum would cause trouble.
Composite looks nice, but I became allergic to some of that
stuff way back in the '70s. And in the cold winters here I've seen it
crack and delaminate. My preference is for something more resistant to
everyday life. Kinda like my old truck.

Dan

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

Philippe Vessaire wrote:

Nathan Young wrote:



So my question: How much drag does a wing on a Hersey Bar Cherokee
generate, and and hypothetically speaking, how much faster could the
plane go if it was retooled with a sleek, composite wing?


You may take the other side of your question.

You choose a composite plane (ie Lancair) with the same engine.
You take the 75% cruising speed of the lancair (V-lancair)
You take the Cherokee 75% cruising speed (V-cher)

If you want the same speed for your plane, you need more HP

The formula is HP=180 * (V-lancair/ V-cher)³

You may do the reverse: how many HP the lancair need for the Cherokee
speed....

You know the cost of drag....

But don't think all drag is from wing, part of drag is from fuselage and
a roomy fuselage will generate more drag.
But the comfort is in roomy fuselage


By

And a LOT of the drag is from cooling the engine!
There is an ideal place for big gains.

Richard

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

"cavelamb himself" wrote ...
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.


Richard,

That's not really true for a light airplane. The only place weight shows up
in the drag equation, and thus the power equation, is in the induced drag
term.
But,because the wing on a light airplane is relatively large, the induced
drag at cruise is small. Cruise induced drag is lift coeffients squared
divided Pi e Aspect Ratio. Light airplanes cruise at small lift coeffients
of around 0.1 to 0.2. It can be shown that they will fly the farthest on a
pound of fuel at L/D max. Lift coeffients around 0.6 to 0.8. So, an
increase in airframe weight doesn't increase the cruise power requirements
very much.

Of course, an light airplane could be designed to fly at L/D max but the
wing would be tiny and you'd pay for it on the slow speed end. With a
single engine and relatively inexperienced pilots, it would be a handful at
slow speeds. Both the BD-5 and the Questar venture are examples of under
winged airplanes that have poor engine out safety records.

Where weight does show up is in climb performance. One of the things that
make an airplane "fun" is how well it climbs. You don't spend much time
there in a cross country flight, but a large high aspect ratio wing with
lots of power will give the pilot the feeling that the airplane is a good
flying airplane.

One of the problems I've had in the past is how much should a designer try
to protect a future user of a product? I've decided that a minimalist wing
is a bad design in the light plane market.

Rich

And a LOT of the drag is from cooling the engine!
There is an ideal place for big gains.

Yes, look at the difference in performance of the J model Mooneys vs.
the pre-J models.