(B2431) wrote in message ...
From: Richard Lamb

snip

The problem with ducted fans is the increased weight and increased
drag really don't help that much. Also, there are efficiency issues.

I have thought some about a novel fan arrangement though.

This is for a high speed twin engined airplane with the engines mounted
on plyons back near the tail. Similar to jet engines on airliners.

The set up uses a 50 to 60 HP Rotax 2 stroke turning an unducted
multiblade fan - direct drive. The fan pitch would be electrically
controlled - virtual constant speed - single power lever per engine.

That means the fan would spin 5 to 6 thousand RPM, have short fat
blades,
have horrible effeciency at low speeds, but the idea is to go like stink
at cruise.

Oh well, daydreaming doesn't cost much...


Richard

I have been looking into a similar set up for years. The only successful set up
I have ever personally seen is on a gyro.

I have considered a constant RPM system as well as inflight adjustable pitch.
Both are too complicated, heavy and expensive for a system where the prop
efficiency is down to the lower 60s.

Things are stranger than you realize g

http://www.visionpacific.com/humming...DuctMyths.html


The problem with multi-wing fans is that the blades have a lot of
camber/concavity. THey are better at generating pressure than at
moving air. Serious hovercraft enthusiasts have been to make composite
replacements for better performance. Not very certified.
The new 4 stroke snow-machine motors look great except 1. Still
available only 90 hp and above. 2. I cannot afford one.
Dan, U.S. Air Force, retired