1/2 VW and a shrouded/ducted propeller?

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

Dan, U.S. Air Force, retired

(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

From: (Ralph DuBose)

snip

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.

http://www89.pair.com/techinfo/MassFlow/ductbook.htm

http://www.cds.caltech.edu/~murray/projects/dfan/

http://www.bridgingworlds.com/DUCKT.HTM


Dan, U.S. Air Force retired

(B2431) wrote in message ...
From: (Ralph DuBose)

snip

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.

http://www89.pair.com/techinfo/MassFlow/ductbook.htm

http://www.cds.caltech.edu/~murray/projects/dfan/

http://www.bridgingworlds.com/DUCKT.HTM



Thanks for the links. The kind of ducted fan he is working with
seems quite different than what I am familiar with. Hovercraft want
better static thrust and much lower tip speeds for noise suppression..
My hovercraft has a 36 in duct, tip speeds around 500ft per sec, 65
hp, and around 250 lb. thrust.
Dan, U.S. Air Force retired

On 04 May 2004 07:30:44 GMT, (B2431) wrote:

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

Dan, U.S. Air Force, retired

Didn't McD-D test one on a Super 80? I think the tests were slightly
positive, but the costs prohibitive. I remember this from an old Av
Leak.
--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

From: Dillon Pyron


Didn't McD-D test one on a Super 80? I think the tests were slightly
positive, but the costs prohibitive. I remember this from an old Av
Leak.
--
dillon


I remeber seeing a video of an open fan on the starboard engine of one. I have
no idea of the status.

Dan, U.S. Air Force, retired

B2431 wrote...

Didn't McD-D test one on a Super 80? I think the tests were slightly
positive, but the costs prohibitive. I remember this from an old Av
Leak.

I remeber seeing a video of an open fan on the starboard engine of one. I
have
no idea of the status.


I've got a couple of pictures of it in the Long Beach haze.
It was noisy as all get-out - one of the reasons it was
abandoned, IIRC

Dave 'WHAT?!' Hyde