Vance and Emily Jaqua wrote:
Vance and Emily Jaqua wrote:
On Sat, 26 Jun 1999 08:52:18 Paul wrote:
I still consider Kuchemann & Webers's book the Aerodynamics
of Propulsion to be the last word on ducted fans but
Martin Hollmann's book on Modern Propeller and Duct
Design is not bad. I got my copy at Spruce and Speciality
but I think Martin advertizes in the back of EAA's Sport Aviation
mag.
Here is a pertinent excerpt from page 98 and 99.
holmduct.jpg
Paul Lamar
Marty's statement on no high speed airplanes use
ducts is pretty frivolous- TurboFans are ducted fans
just using a turbine instead of some other engine
and I don't consider Mach .85 to be slow nor Mach
2 in the case of afterburning fans (they are really
approaching ram jet operation at that point) -Vance
Did I say it was perfect?
I think he was talking ducted props rather than fans.
Anything over three blades is a fan :-)
Paul Lamar
Boy! you were quick on that one Paul!! Quick turn around
- Prop or fan?
I believe the air thinks they are the same except
in the cases of high solidity the interferences
and interactions become more complex, particularly
with multi stages - They are all pumps or
compressors to various degrees and the basic physics
remain very much the same - I made an over
simplified response to what was propbably in his
case an over simplified statement.
In actual case
the pure jet can be treated as a fan or propeller
with the heat engine included in the air flow. It
is a very high disk loaded system adding energy to
accelerate a relatively small mass of air to a very
high velocity - thrust remains mass flow times the
increase in velocity. The exit can also be equated
to horsepower (usually lots of it ) by using mass
flow times velocity squared divided by 2 times
the 550 ft lbs a sec that is one of Watt's tiny
English ponies - Vance
Maybe horses were smaller in those days amd breeding made them
bigger :-)
Paul Lamar
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