I'm calling it The Little Mermaid

On Mon, 14 Mar 2005 19:45:09 -0600, "Montblack"
wrote in
::

("Larry Dighera" wrote)
It's an interesting design. Is it a home built?


I didn't get the feeling from their web page it was being offered for the
homebuilt market.

Then, why'd you crosspost to rec.aviation.homebuilt?

You are missing the point. Take a small engine, divide the output in
half, and the prop is going to be small.

Why?

Because I can. Because that would divide the HP into two, so a smaller size
bike belt would be reliable. Pay attention.

I am paying attention. I'm trying to learn something, no need to be rude.

Seems to me that dividing the HP in two does not mean a smaller prop.
The same HP can turn a large prop slowly or a small prop quickly. The
same power goes into each prop no matter what. However, with a large
prop turning slowly, the =force= on the prop would be smaller (so force
times distance remains constant). But the force on the belt should be
the same, since the belt is turning at engine speed around the engine
shaft, (and at prop speed around the bigger prop shaft).

What I have read indicates that props are more efficient turning slower
(than 2500 RPM) and (gas) engines are more efficient turning faster than
that. Aside from the issue of the large prop pully at the pylon, what
am I missing?

Jose
r.a.homebuilt trimmed, as I don't follow that group
--
Math is a game. The object of the game is to figure out the rules.
for Email, make the obvious change in the address.

I'm calling it "dead in the water" :-)

MJC

"Montblack" wrote in message
...
High Performance Aircraft out of Germany - HPA TT62
http://www.hp-aircraft.de/edoc/tech.html


I'm calling it The Little Mermaid.

Montblack

("Larry Dighera" wrote)
I didn't get the feeling from their web page it was being offered for the
homebuilt market.

Then, why'd you crosspost to rec.aviation.homebuilt?


A: It's an interesting idea ...with pictures.

B: It's spawned some "what if" ideas based on HPA's design.
http://www.hp-aircraft.de/edoc/tech.html

C: It's gennerating an interesting belt-drive propeller discussion. Very
1903. g

D: It's not like I cross-posted The Little Mermaid to
rec.shipping.propulsion.


May I please have my hall pass back?


Montblack

"Jose" wrote i What I have read indicates that
props are more efficient turning slower
(than 2500 RPM) and (gas) engines are more efficient turning faster than
that. Aside from the issue of the large prop pully at the pylon, what
am I missing?

Jose

OK, I'll be nice, since you asked so nice. ;-)

Homebuilt group is really where this discussion belongs, but whatever. It
is an interesting group, if you like discussions like this.

Yes, big props are turning slowly are more efficient, and more efficient,
especially at climb. Smaller faster props work better for speed in cruise.

The big pulley out on the pylon is a big drawback, due to drag where you
don't want it. The other problem of trying to get it to turn slower, is
that it would need to done by using gearing, and the gearing I was talking
about was a motorcycle gearbox They have been shown to have durability
problems, when running a low gear at high power for extended periods of
time.

The whole issue of a smaller prop turning fast is not that big of a deal, as
long as it is not too fast. Yes, the tips definitely have to stay out of
the supersonic flow, where big losses occur. There are many very successful
designs running around on engines like Volkswagen engines, or Subaru direct
drives, or even the small Continentals trying to make more HP.
--
Jim in NC

:Yes, that is all true. The real problem is the rapid decline in the
efficiency of conversion from power to thrust as the propellor rpm
increases. The pounds of thrust per horsepower declines like a capacitor
discharge curve as the rpm increases and you have lost two thirds by the
time the prop rpm gets to 2000!

A ducted fan helps a little, but they are much less efficient than a big old
lazy unshrouded propellor chugging away.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( KPJY )

PS: Pinckneyville rec.aviation flyin is coming up May 20, 21, and 22. See
the article in AOPA Online.
"Morgans" You are missing the point. Take a
small engine, divide the output in half,
and the prop is going to be small. Small props do not mind turning fast.
Also, if you use the belts for the RPM reduction, you have to put the big
pulley out on the pylon, where you want a small one.
--
Jim in NC