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In article ,
says...
mark, the transision for sub-sonic to super-sonic is in no way related in any
way to a discussion of "hull speed" in sailboats.

Except that both power/speed curves show inflection points, I suppose.
The change in curvature is even more pronounced as a sailboat goes
from hull speed to planing speed, though.

duh.

Sounds like the observation of someone who has lost an argument! ;-)

Mark Borgerson

From: Mark Borgerson
Date: 9/3/2004 11:36 AM Eastern Daylight Time
Message-id:

In article ,
says...
Until you get past Mach 1, at least! ;-) after that point,
there are some inflection points in the power/speed curve, IIRC.

no, you don't remember any such thing. unless of course you were stoned
out of
your gourd in your fourth sophomore year in college.

Whoa! You must have me mixed up with someone who went to UC Berkely in
the 60's. My sophomore year was at UC Davis in '65 and we weren't
smoking much grass at all! (although there were probaby a lot of
students figuring out how to optimize the yield---Davis being a
world-class agricultural school) ;-)

As for inflection points, consult the definition at

http://www.math.com/tables/derivatives/extrema.htm

and look at the following crude graphic

*
*
*
*
P *
*
O *
*
W *
*
E
*
R *
*

************************************************* *******************
0 0.5 1.0 1.5 2.0

MACH NUMBER

There is an inflection point at about Mach 1. However there is no point
on the graph where you get an increase in speed without an increase in
power.

If you look at the engine data at
http://www.voodoo.cz/hornet/info.html

you will find that the F-18 engines develop about 14,000 pounds thrust
at full military power and 21,000 pounds at full afterburner. Yet
it takes full military power to get to mach 1, but with 50%
more power, you can end up at mach 1.8. Thus the inflection
point just past mach 1. (Like most modern military jets prior to
the F-22, the F-18 cannot sustain supersonic speeds in level flight
without afterburners.)

If you have more detailed power/speed curves for the transonic region,
feel free to post some links to enlighten us.

Mark Borgerson

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