1/2 VW and a shrouded/ducted propeller?

Hi all...

was sketching out a plane this weekend (just for kicks, nutin serious, just
playing with numbers for the fun of it)...

And no matter how I sliced it, I kept coming up with needing 35 to 40 hp and a
4 cycle at that....well, the only thing I know of that fits that bill without a
lot of money is the old 1/2 VW....and besides that I get the impression the 1/2
VW might actually be more reliable than the more expensive commerically
available equivalents (IF its built and treated RIGHT)....

And everything I've seen/recall pretty much says you can swing a 52 inch prop
at 3500 rpm and get 35 hp from a 1/2 VW...give or take...so the engine
alllllmost reaches the requirements...and it would IFF you could swing a
decently larger prop...

Now, first off....anybody here know how much continous HP you can get from a
1/2 VW? And lets assume you are careful to do the cooling pretty effectively
rather than just letting stuff stick out in the wind.....and yes I know for the
full VWs the continous rating is 40 hp or so....but Ive gotten the impression
that the 1/2 VW cools significantly better than a full one, so thats why the
answer isnt .5 times 40 something.....

Second, people increase the bore and stroke....and I understand those
implications (I think)....but I dont recall this being mentioned much
......can't you play with the valves and have a custom camshaft so that you
could get the same HP out at a significantly lower and useful RPM? Yes, I
realize your still gonna be limited to a maximum given HP due to cooling
considerations....the suggestion seems obvious, so have people done it and/or a
custom cam/valve tinkering doesnt help much or am I missing something here...

Then if THAT doesnt work....and we cant get the rpms down....

What about a shroud/duct to make that small prop more efficient?

Okay, the shroud will kill ya thrust wise when its outside of its design
range...and that design range is rather narrow....and making one just right
aint trivial...

But, is THIS possible/reasonable....can the duct be designed so that it
maximises the performance at say 50 mph airspeed and the performance is no
worse than than the 52 inch prop at 70 mph? Or the reverse
perhaps....performance is maximized at 70mph and is no worse than a plain 52
inch prop at at 50 mph? Or perhaps we split the difference and maximize at 60
mph with no penalty above 50 and less than 70?

Assuming the answer to the above is yes, or close to yes with minor
variations/gotchas.....roughly how much bigger a prop (assuming you COULD spin
it lower and at the same hp) would that duct/shroud be equivalent to at its
optimized speed?

And.....would you still want to run a 52 inch prop in the duct/shroud? Or when
your doing the duct/shroud thing are there other significant considerations
that make smaller props preferable? (assuming the size, location, and weight of
the shroud isnt an issue)....or once you go shrouded can you go with a much
smaller propeller and not loose any performance but yet gain value from have a
smaller, lighter shroud?

Now a shroud prop seems perfect for a pusher application.....but has anyone
seen one a tractor configuration? That would be one weird looking setup....and
I am NOT talking where there is a big intake in the front, some internal
passageways, and air gets blasted outa the back...like a "fake" jet
aircraft.....Im talking take a normal tractor airplane, maybe or maybe not
change the size of the prop, and put a shroud around the prop....and boy would
you have some visibility issues (I'd think).....

take care

Blll

Has anybody ever looked at a 1 lung bike motor for this application??
Honda XL650 or Suzuki DR650??

This bike uses a Honda engine thats been pro reworked to
provide about 70 peak HP.
http://www.allamericanracers.com/all...ator_tech.html

The cool thing is that it would be reasonably trivial to get dual
ignition (Double stack the ignition coils and use two plugs.) The motors
are designed to be light and strong. the ride characteristics of both
the XL650 and Suzuki are low rpm grunt motors, But they don't mind
pulling hard for extended periods. They also don't shake much for
being thumpers, A stock XL650 motor makes about 35HP.

Another source would be the new 4 stroke snowmobile engines.

Dave

BllFs6 wrote:

Hi all...

was sketching out a plane this weekend (just for kicks, nutin serious, just
playing with numbers for the fun of it)...

And no matter how I sliced it, I kept coming up with needing 35 to 40 hp and a
4 cycle at that....well, the only thing I know of that fits that bill without a
lot of money is the old 1/2 VW....and besides that I get the impression the 1/2
VW might actually be more reliable than the more expensive commerically
available equivalents (IF its built and treated RIGHT)....

And everything I've seen/recall pretty much says you can swing a 52 inch prop
at 3500 rpm and get 35 hp from a 1/2 VW...give or take...so the engine
alllllmost reaches the requirements...and it would IFF you could swing a
decently larger prop...

Now, first off....anybody here know how much continous HP you can get from a
1/2 VW? And lets assume you are careful to do the cooling pretty effectively
rather than just letting stuff stick out in the wind.....and yes I know for the
full VWs the continous rating is 40 hp or so....but Ive gotten the impression
that the 1/2 VW cools significantly better than a full one, so thats why the
answer isnt .5 times 40 something.....

Second, people increase the bore and stroke....and I understand those
implications (I think)....but I dont recall this being mentioned much
.....can't you play with the valves and have a custom camshaft so that you
could get the same HP out at a significantly lower and useful RPM? Yes, I
realize your still gonna be limited to a maximum given HP due to cooling
considerations....the suggestion seems obvious, so have people done it and/or a
custom cam/valve tinkering doesnt help much or am I missing something here...

Then if THAT doesnt work....and we cant get the rpms down....

What about a shroud/duct to make that small prop more efficient?

Okay, the shroud will kill ya thrust wise when its outside of its design
range...and that design range is rather narrow....and making one just right
aint trivial...

But, is THIS possible/reasonable....can the duct be designed so that it
maximises the performance at say 50 mph airspeed and the performance is no
worse than than the 52 inch prop at 70 mph? Or the reverse
perhaps....performance is maximized at 70mph and is no worse than a plain 52
inch prop at at 50 mph? Or perhaps we split the difference and maximize at 60
mph with no penalty above 50 and less than 70?

Assuming the answer to the above is yes, or close to yes with minor
variations/gotchas.....roughly how much bigger a prop (assuming you COULD spin
it lower and at the same hp) would that duct/shroud be equivalent to at its
optimized speed?

And.....would you still want to run a 52 inch prop in the duct/shroud? Or when
your doing the duct/shroud thing are there other significant considerations
that make smaller props preferable? (assuming the size, location, and weight of
the shroud isnt an issue)....or once you go shrouded can you go with a much
smaller propeller and not loose any performance but yet gain value from have a
smaller, lighter shroud?

Now a shroud prop seems perfect for a pusher application.....but has anyone
seen one a tractor configuration? That would be one weird looking setup....and
I am NOT talking where there is a big intake in the front, some internal
passageways, and air gets blasted outa the back...like a "fake" jet
aircraft.....Im talking take a normal tractor airplane, maybe or maybe not
change the size of the prop, and put a shroud around the prop....and boy would
you have some visibility issues (I'd think).....

take care

Blll

"D.W. Taylor" wrote:

Has anybody ever looked at a 1 lung bike motor for this application??
Honda XL650 or Suzuki DR650??

This bike uses a Honda engine thats been pro reworked to
provide about 70 peak HP.
http://www.allamericanracers.com/all...ator_tech.html

The cool thing is that it would be reasonably trivial to get dual
ignition (Double stack the ignition coils and use two plugs.) The motors
are designed to be light and strong. the ride characteristics of both
the XL650 and Suzuki are low rpm grunt motors, But they don't mind
pulling hard for extended periods. They also don't shake much for
being thumpers, A stock XL650 motor makes about 35HP.

Another source would be the new 4 stroke snowmobile engines.

Dave

BllFs6 wrote:

Hi all...

was sketching out a plane this weekend (just for kicks, nutin serious, just
playing with numbers for the fun of it)...

And no matter how I sliced it, I kept coming up with needing 35 to 40 hp and a
4 cycle at that....well, the only thing I know of that fits that bill without a
lot of money is the old 1/2 VW....and besides that I get the impression the 1/2
VW might actually be more reliable than the more expensive commerically
available equivalents (IF its built and treated RIGHT)....

And everything I've seen/recall pretty much says you can swing a 52 inch prop
at 3500 rpm and get 35 hp from a 1/2 VW...give or take...so the engine
alllllmost reaches the requirements...and it would IFF you could swing a
decently larger prop...

Now, first off....anybody here know how much continous HP you can get from a
1/2 VW? And lets assume you are careful to do the cooling pretty effectively
rather than just letting stuff stick out in the wind.....and yes I know for the
full VWs the continous rating is 40 hp or so....but Ive gotten the impression
that the 1/2 VW cools significantly better than a full one, so thats why the
answer isnt .5 times 40 something.....

Second, people increase the bore and stroke....and I understand those
implications (I think)....but I dont recall this being mentioned much
.....can't you play with the valves and have a custom camshaft so that you
could get the same HP out at a significantly lower and useful RPM? Yes, I
realize your still gonna be limited to a maximum given HP due to cooling
considerations....the suggestion seems obvious, so have people done it and/or a
custom cam/valve tinkering doesnt help much or am I missing something here...

Then if THAT doesnt work....and we cant get the rpms down....

What about a shroud/duct to make that small prop more efficient?

Okay, the shroud will kill ya thrust wise when its outside of its design
range...and that design range is rather narrow....and making one just right
aint trivial...

But, is THIS possible/reasonable....can the duct be designed so that it
maximises the performance at say 50 mph airspeed and the performance is no
worse than than the 52 inch prop at 70 mph? Or the reverse
perhaps....performance is maximized at 70mph and is no worse than a plain 52
inch prop at at 50 mph? Or perhaps we split the difference and maximize at 60
mph with no penalty above 50 and less than 70?

Assuming the answer to the above is yes, or close to yes with minor
variations/gotchas.....roughly how much bigger a prop (assuming you COULD spin
it lower and at the same hp) would that duct/shroud be equivalent to at its
optimized speed?

And.....would you still want to run a 52 inch prop in the duct/shroud? Or when
your doing the duct/shroud thing are there other significant considerations
that make smaller props preferable? (assuming the size, location, and weight of
the shroud isnt an issue)....or once you go shrouded can you go with a much
smaller propeller and not loose any performance but yet gain value from have a
smaller, lighter shroud?

Now a shroud prop seems perfect for a pusher application.....but has anyone
seen one a tractor configuration? That would be one weird looking setup....and
I am NOT talking where there is a big intake in the front, some internal
passageways, and air gets blasted outa the back...like a "fake" jet
aircraft.....Im talking take a normal tractor airplane, maybe or maybe not
change the size of the prop, and put a shroud around the prop....and boy would
you have some visibility issues (I'd think).....

take care

Blll


No, can't say flying a one lung engine ever seemed attractive to me.
And other than 2 strokes, I've not seen many flying 2 bangers either.

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

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

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

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