It seems that I did not think the implications all the way through before I
pressed the "send" button.

Running the C85 at 3200 RPM should result in around 125% power, so that a
cruise setting of 85% power would be around 65% of the "available" power.
Therefore, a clean little airplane like the Tailwind would actually have
a greater (rather than less) surplus thrust for take off and initial climb.

The note of caution would be that full throttle would be take off only,
and not maximum continuous; so the pilot would have to understand the
limitations and treat it like a high performance engine rather than like
a trainer engine.

Peter


Peter Dohm wrote:

I only met Steve Wittman once, when he had brought his inverted V8 tailwind
to Sun-n-Fun, and didn't talk that long; and then only about the V8.

I was not aware that he turned his C85 at 3200 RPM, although it makes good
sense given his orientation. Steve was reputed to have long advocated that
homebuilt aircraft with small certified engines like the C85 cruise at 85%.

The rationale was that most homebuilt aircraft are operated less than 80
hours per year and that rust is the true enemy, rather than wear; so that a
conservatively operated engine will never reach its certified TBO. Thus,
since most homebuilt aircraft also operate at lower altitudes where higher
cruising power can be attained, the hypothesis suggests that it is really
more conservative to operate the lighter and less expensive engine at the
higher power setting.

I do not entirely agree with the concept, mainly because it does not give
a lot of extra thrust for takeoff and initial climb on a really slick and
fast modern aircraft with a fixed pitch propeller. However, I must admit
that it makes a lot of sense for most designs from the 50's 60's and 70's.

Peter

Harry O wrote:

From memory, the differences were slight. The wing airfoil was different.
The W-10 has a curve on the bottom where the W-8 was flat. I understand
that there were 2 or 3 inches of extra width in the fuselage. Also, the
W-10 was stressed for larger (Lycoming) engines. I built the airframe for a
W-10 and talked with Mr. Wittman about it a couple of times. I also saw him
at Oshkosh several times and talked with him in person once. He was a VERY
thin man and medium height. I can easily understand the change in the
fuselage.

He did not think much of people who put in Lycoming 0-290's or 0-320's (like
I was going to do). He much preferred the 85hp Continental. When I talked
to him, I found out that he was turning his little engine at about 3,200
rpm -- way, WAY over readline. It was putting out as much HP as the larger
(and heavier) Lycomings. He did say that he had to overhaul it about every
400 hours. Since he did it himself (rather than hiring an A&E), he did not
think that it was a problem at all.

"Daniel Lapointe" wrote in message
...
Can somebody tell me where to find the difference between a W-8 and a W-10
?