X-Mozilla-Keys:
Jeff Spitzer wrote:
At 02:39 PM 7/1/99 -0700, you wrote:
I have this SAE paper from Moller 900037 wherein it states
the static thrust from the 50 HP at 6500 RPM (or so) engine used
at the time was 70Kg or 154 pounds.
If the engine was 50 HP or 27500 pound feet/second that would
make the duct 5.6% efficient at 10 feet per second assuming
the thrust was the same as it was at static conditions.
At 100 FPS assuming the thrust stayed constant (unlikely) the eff.
would be 56%. Usually the thrust is dropping off at this
point and the eff. is getting better but perhaps not this
much better.
All this jibes with convential wisdom of course :-)
Small diameter high RPM ducted fans just plain don't
become eff. until you get to 400 MPH or so.
Jeff knows a lot about this engine as he was project engineer
on it. According to the paper it was 32.3 cubic inch
engine. Here is a picture of the final engine design.
Jeffs-Moller2.jpg
Quite a leap in time in your statement. I was project engineer to redesign
the single rotor, air-cooled engine into a twin rotor, liquid cooled
screamer making 150 hp. Also designed all the duct systems. The duct
shown was using two twin rotor engines. It was capable of about 800 lb
static thrust.
Oh good another data point. Let's see 300 HP with 800 pounds of thrust.
4.8% efficient at 10 feet per second. Do you have a curve
showing the thrust as a function of aircraft velocity or
did Paul Moller consider that amount of thrust constant with speed?
Ironically, although the engine exists and is offered by
Moller's subsidiary Freedom-motors, he chose to abandon all the great stuff
that you see in that picture in favor of a quick and dirty attempt to hover
the M400 (well after I left). The Q&D returns to single rotor, air cooled
engines and has been featured in a press release recently. He is ready to
fly!! Maybe.
As you pointed out his single rotor engines will make about
150 lb static thrust each. In counter-rotating pairs maybe 400 lb with
unrealistic optimism. If he gets anywhere near the claimed 95% turning
efficiency (never) then that leaves 380 lb per nacelle. With 4 nacelles
thats 1520 lb thrust with all engines full. We had a rule of thumb at
Moller of minimum 20% power margin for stability which leaves 1216 lb
usable thrust. The airframe pictured in the glossies had like 100 lb of
bondo on it bringing it to a (measured) hefty 350++ lb. Assuming the
nacelles systems now weigh about 150 lb each (they were 300 lb as shown)
and he's got about 100 lb of airframe systems thats an empty weight of
about 1050 lb. That means that on the best cool day, if his diet works,
with zero fuel and all engines running good he MIGHT just lumber that thing
into the air. What a brilliant move to not use the twin rotor engines.
That'll show 'em.
Jeff Spitzer
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