In article , Bill Daniels
writes
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

Something like that was developed here in the UK a few years ago.
It was a place STOL with a ducted fan and it could fly very slowly.
It was called the Optima and it was designed by a Mr Edgerly, who also
designed a sailplane, using unconventional materials.

Several examples were completed, more were under construction, but were
destroyed in a fire.

And isn't nitrous oxide N2O, not NO2 which is nitrogen dioxide?



--
Mike Lindsay