Rag and tube construction and computer models?

I have never seen the plans for the Nesmith Cougar, but I pulled out my old
set of plans for the Wittman Tailwind to check tube sizes. BTW, in talking
with Mr. Wittman, I quickly learned that you don't even mention the Cougar.
He was very sensitive about someone who wasted a lot of his time asking
questions, then stole his design, and then ruined it with bad modifications.

Anyway, there were 22 different sizes and/or wall thickness of tubing listed
in the Tailwind plans. That is a lot more than I remember seeing in the
plans for the others I mentioned. The did step down the further back they
got. I doubt that anyone ever did a stress analysis for the Tailwind (at
least before it was built) and it was done by "eyeball". However, I have a
lot more faith in Mr. Wittmans eyeball than the numbers from some structural
engineers I know.

Another off-topic comment about the Tailwind. I talked to Steve Wittman
several times. One time was about the engine. I bought a Lycoming
0-290-D2. He looked down on that. He used an "85hp" Continental at the
time. Much lighter and delivered as much power (?). I asked about the
pitch of the propeller and the speeds he was getting. They did not match.
I talked to him again. I found out that he was running the little engine at
about 3,200rpm. Way, way over the manufacturers "redline". The propeller
pitch and speeds he was getting matched at the higher rpm. He did say that
he only got about 400 hours from the engine between rebuilds, though. Since
he did them himself, he did not think that was much of a problem. No doubt
he balanced and blueprinted the engines, too.


"Stealth Pilot" wrote in message
...
On Wed, 7 Apr 2004 18:29:03 -0500, "Harry O" wrote:

Anyway, to get back to your question, it depends. I have run some tube
and
fabric designs through finite element analysis. If you were to check the
Tailwind design, you will not find ANY reductions in tube size or
thickness.
You will undoubtedly find some suggested tube increases. I checked the
design on one of the later programs and also built a Tailwind airframe.
I
believe that he probably used every tube size and wall thickness there is
available in that design. There are little itty-bitty tubes branching
all

It is interesting to look at the airframe of the nesmith cougar and
the w8 tailwind together. as you say the wittman uses the one tube for
each longeron. the nesmith steps down in diameter at every cluster.
the tailwind looks to be about half the fiddle factor of the nesmith.

Stealth Pilot
Australia

Steve did more than just "eyeball" engineering. He had some contacts at the
University of Wisconsin that he sent his drawings and parts down to have
them analyzed.
"Harry O" wrote in message
...
I have never seen the plans for the Nesmith Cougar, but I pulled out my
old
set of plans for the Wittman Tailwind to check tube sizes. BTW, in
talking
with Mr. Wittman, I quickly learned that you don't even mention the
Cougar.
He was very sensitive about someone who wasted a lot of his time asking
questions, then stole his design, and then ruined it with bad
modifications.

Anyway, there were 22 different sizes and/or wall thickness of tubing
listed
in the Tailwind plans. That is a lot more than I remember seeing in the
plans for the others I mentioned. The did step down the further back they
got. I doubt that anyone ever did a stress analysis for the Tailwind (at
least before it was built) and it was done by "eyeball". However, I have
a
lot more faith in Mr. Wittmans eyeball than the numbers from some
structural
engineers I know.

Another off-topic comment about the Tailwind. I talked to Steve Wittman
several times. One time was about the engine. I bought a Lycoming
0-290-D2. He looked down on that. He used an "85hp" Continental at the
time. Much lighter and delivered as much power (?). I asked about the
pitch of the propeller and the speeds he was getting. They did not match.
I talked to him again. I found out that he was running the little engine
at
about 3,200rpm. Way, way over the manufacturers "redline". The propeller
pitch and speeds he was getting matched at the higher rpm. He did say
that
he only got about 400 hours from the engine between rebuilds, though.
Since
he did them himself, he did not think that was much of a problem. No
doubt
he balanced and blueprinted the engines, too.


"Stealth Pilot" wrote in message
...
On Wed, 7 Apr 2004 18:29:03 -0500, "Harry O" wrote:

Anyway, to get back to your question, it depends. I have run some tube
and
fabric designs through finite element analysis. If you were to check
the
Tailwind design, you will not find ANY reductions in tube size or
thickness.
You will undoubtedly find some suggested tube increases. I checked the
design on one of the later programs and also built a Tailwind airframe.
I
believe that he probably used every tube size and wall thickness there
is
available in that design. There are little itty-bitty tubes branching
all

It is interesting to look at the airframe of the nesmith cougar and
the w8 tailwind together. as you say the wittman uses the one tube for
each longeron. the nesmith steps down in diameter at every cluster.
the tailwind looks to be about half the fiddle factor of the nesmith.

Stealth Pilot
Australia

Steve said that. However, he also said that it was done many years after
the plans were first offered for sale. I believe it was about the time he
changed it from the W-8 to the W-10. There were a few tube sizes that were
increased in size then, particularly at the top, front of the cabin to carry
the spar loads. Of course, it was because of the heavier Lycoming engines
being used rather than from failures.

"Cy Galley" wrote in message
news:1uJdc.117$xn4.5040@attbi_s51...
Steve did more than just "eyeball" engineering. He had some contacts at
the
University of Wisconsin that he sent his drawings and parts down to have
them analyzed.