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