Hershey bar wing vs composite wing - how much drag?

On Mar 28, 4:35 pm, Alphonse Le Creur wrote:
"BobR" wrote roups.com:





On Mar 28, 12:40 pm, Alphonse Le Creur wrote:
"BobR" wrote in
news:1175092590.355514.234030 @y80g2000hsf.googlegroups.com:

On Mar 28, 8:51 am, Nathan Young
wrote:
I have a Cherokee 180, with the short hershey bar wing. While I
love the plane, I always wish it could go a bit faster, or use a
bit less fuel to get to my destination.

I have followed the composite homebuilding movement for many
years, and am amazed at the sleekness of a composite wing. The
wings on
most
composites tend to be the complete opposite of a Hersey bar wing:
high aspect ratio, low thickness, no rivets, no screws for fuel
tanks,smooth curves faired into airframe, and streamlined landing
gear
structure.

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?

I can't remember if it was Kitplanes or SportAviation that had a
recent article on a Piper knockoff being produced as a kitplane in
South Africa. That might be a good starting point for the
difference in performance between the different planes as well as a
discussion of the differences in design and construction. Much of
the difference has to do with better airfoil designs being used but
also weight differences.

Well, that airplane is "inspired" by the Commanche and it's really
just comparing apples and oranges since there are so many other
differences in the two airplanes, but having said that, it's better
than comparing a cherokee to a Cozy, for instance..

In any case, the Ravin Commanche is
herehttp://www.saravin.com/review.htm

ALC- Hide quoted text -

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It's about as close a comparison as can be made. I am building the
KIS Cruiser which uses a hershey bar style wing as well but the
airfoil is different. The comparison from a performance standpoint is
much faster than the Commanche for the same power (180 hp). The
difference must be attributed to several differences beyond just the
wing, weight being the most obvious.

Well, the Ravin is actually a couple hundred pounds heavier than the
original Commanche empty and has a higher gross. It also has a much
smaller fuselage cross section.
I'm certainly not saying that the Ravin is not a better airplane. It is.
I'd sure like to have one! I'm just saying that while it is probably one
of the better comparisons, no absolute conclusion may be made from it.
There's too many other things going on there. The Commanche uses what
was a then state of the art NACA 6 series laminar flow airfoil. It was
streets ahead of what was on any lightplane of the time, but it's use
was most probably not dictated by the material of which it was made. I
have no idea what the Ravin is using for an airfoil.
If Piper were to set out to make the same airplane again today using
aluminum for the wing, they could still build a more efficient wing than
they did in the fifties by simple virtue of the fact that fifty years
later there's been quite a lot of innovation in airfoils, structures and
what not. Again, I'm not saying that the Ravin isn't a better airplane,
nor am I denying that composites might be a better way to build an
airplane, just saying (at the risk of flogging the proverbial dead
horse) that the comparison , while it is as good as you're going to get,
is still flawed.

ALC- Hide quoted text -

- Show quoted text -

Agreed, you will always be dealing with differences that can skew the
comparison including differing prop combinations. Another good
comparison might be VANS RV-10 which does use a metal wing. The
performance numbers on that plane are also better than the
Commanchee. The RV-10 is probably a good comparison to the Ravin
since both would probably be about the same weight, size, and use the
same engine. The RV-10 with the O-360 combination might be a good
comparison to the commanchee.