OK, I guess this is a top post thread.

It ain't horsepower, it's the PROP. To improve the 0 - 20 acceleration,
improve the propeller. Have you ever tried to figure out how much power
actually gets to the tow hook on the glider from a 260 HP Pawnee? Maybe 20
HP?

At low speeds, as at the beginning of the TO roll, the tug's prop is mostly
stalled and converting little of the engines HP to thrust. As it
accelerates, more of the prop disc becomes unstalled and the prop picks up
efficiency and therefore more acceleration. A headwind helps a lot here.

So, what to do?

1. A constant speed prop reduces the blade AOA and lets the engine rev to
its redline RPM. (Noisy)
2. Big, slow turning props make much more thrust at low speeds than small,
high RPM props. (Quieter but require PRSU gearbox)
3. Ducted fans work really well at low speeds but lose out to a standard
prop at 100 MPH +. (A LOT quieter)

The ducted fan looks very good in that it can turn at crankshaft RPM while
producing several times the thrust of an unshrouded prop at zero airspeed.

So, why don't you folks living in a country blessed with friendly regulators
design and build a certified ducted fan tug using the minimum engine
necessary - say a 140 HP LOM M132CE. (Less fuel, less noise).
See: http://www.moraviation.com/

I imagine an airframe that looks somewhat like an Ogar. A cute trick would
be to make the fan and duct as one rotating unit constructed of carbon
fiber - this eliminates the problem of fan tip-duct clearance.

Bill Daniels


"Jim Phoenix" wrote in message
...
Back in the REAL old days, we had alcohol tanks in the DC-4's, but not for
water meth, for the props. Lessee - those REAL old days were back in
1985 -
the last millennium.

But back to the subject at hand - shooting nitrous into a Lycoming
presents
its engineering challenges, I suppose there are other methods of
increasing
acceleration at takeoff. At Sugarbush they do a modified angle takeoff
roll,
the geometry of that seemes to increase the initial tow speed, very
slightly. (The towplane is on the main runway - the glider in the grass to
the right , aft of the towplane. The glider is angled towards the runway
anf
rolls up onto the runway during the takeoff roll.

Jim

"Joseph L. Hyde" wrote in message
.. .
"BACK IN THE OLD DAYS" Hey I've flown planes recently using water
meth.....rolls dart and garretts.....oh wait that has been over 20
years
ago....never mind.....






"Jim Phoenix" wrote in message
...
Back in the old days water-meth worked pretty well, same basic effect.
I
think Metros still use it, at least they did 10 years ago. Handy in
the
Convair 580's as well - like, they needed more horsepower?

You just needed to be careful not to run out of water-meth at the
wrong
time.

Jim

"Jason Payne" wrote in message
...
Just a thought. Wanted to see what you guys thought. I know that
FAA
aproval would never happen, but seems like a good idea to me.

You could easily and safely run a 100hp shot of NO2 for the first
10-15
seconds of a takeoff roll in an 0-470 or similar motor, and get to
100
feet
and 65 knots a lot quicker than without, increasing safety margins.

NO2 is especially nice in a heat soaked motor because the shot cools
the
intake air a good 30-50 degrees...

From being in a ASH-25 at a full 750 kilos on a hot Uvalde day that
another
100 hp would really help getting off the ground if you are not
behind
a
big
motor like Scratch.