props: tractor v pusher, q tip, ducted?

If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling. The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects. Finally, does anyone know of any work on small airplanes
using a ducted prop (shrouding it rather than using the q tip bent
end? I'm not worried about ease of flying (the problem with pusher
props are pretty obvious) but rather with converting the horsepower
delivered to the prop into usable thrust, that is, getting the
greatest efficiency (miles per gallon is a crude way of expressing it)
for a small single.

opps, should have said Cessna 337.

On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

Kingfish wrote:
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?


I believe the performance is better flying on the rear engine alone vs.
the front alone.

Matt

"Kingfish" wrote in message
oups.com...
On Aug 5, 8:27 pm, Tony wrote:
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.

It is? How do you figure, seeing as the 337 has a tractor AND a pusher
prop?

The single engine climb performance is pitiful regardless of which engine is
caged, but the aircraft has more performance on the back engine than the
front. That may or may not be due to prop efficiency. It could also be due
to reduced fuselage drag. The tractor prop blows a high speed stream of air
across the fuselage, creating its own source of drag. This isn't as much of
a factor with the pusher.

KB

"Tony" wrote in message
oups.com...
If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling. The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects. Finally, does anyone know of any work on small airplanes
using a ducted prop (shrouding it rather than using the q tip bent
end? I'm not worried about ease of flying (the problem with pusher
props are pretty obvious) but rather with converting the horsepower
delivered to the prop into usable thrust, that is, getting the
greatest efficiency (miles per gallon is a crude way of expressing it)
for a small single.


On the subject of shrouded props, yes studies have been done, but I did not
link to them, so do not know where to find them.

There are very few flying examples of shrouded light plane props. A shroud
is tough to justify, because of a couple reasons. Prop to shroud clearance
has to be VERY small, generally under 1/16", for any great improvement of
efficiency. Therein lies the rub.

Maintaining the close clearance is tough, because the shroud would have to
be very stiff, and strong, to not flex and hit the prop. That means weight.
That means it will have to increase efficiency a good deal, to justify
carrying the extra weight around.

Also, the shroud would have to be mounted to the engine mount, (more
complexity, more weight) or else the engine would have to be hard mounted.
That is because the soft mounts of the engine would allow the engine (and
prop disc) to move around (and most of them move around a LOT), and if the
shroud were mounted to the fuselage, you can imagine that there would not be
close prop clearance for very long. g

Also, there is also the subject of the shroud and that dreaded drag. Of
course, we don't want to add anything to our airplanes that stick out in the
wind that does not need to be there. A shroud and mounts is something, and
a pretty big something at that. So more drag means it will have to produce
even more efficiency.

Humm, it seems like we have now said that it has to increase efficiency a
couple times, and we have now used up all of the possible efficiency gains
just to balance the disadvantages.

What does it mean in the long run? We have a more complex, heavier
airplane, for no noticeable improvement in performance.

That's why you don't see many shrouded airplanes running around out there.
--
Jim in NC

Tony wrote in news:1186363629.396826.234140
@k79g2000hse.googlegroups.com:

If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling.


No, it isn#t actually. After Cessna sorted out the cooling drag on the
front engine, the performance was identical on either engine. The legend
lives on though!


The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects.


I flew a few q tip mooneys as well as standard equipped airplanes. The q-
tip airplanes all performed worse.


Bertie

In article .com,
Tony wrote:

If one uses the Cessna 377 Skymaster as an example, it's pretty clear
a pusher prop is more efficient than one pulling. The data seems mixed
though on q tip props -- any leads as to where there may be quantative
data? What I found suggested the extra length of the prop might just
as well go to increasing its radius as in decreasing end vortix
effects. Finally, does anyone know of any work on small airplanes
using a ducted prop (shrouding it rather than using the q tip bent
end? I'm not worried about ease of flying (the problem with pusher
props are pretty obvious) but rather with converting the horsepower
delivered to the prop into usable thrust, that is, getting the
greatest efficiency (miles per gallon is a crude way of expressing it)
for a small single.

Have you looked at the Edgley Optica?

"Morgans" wrote in message
news

snip

There are very few flying examples of shrouded light plane props. A
shroud is tough to justify, because of a couple reasons. Prop to shroud
clearance has to be VERY small, generally under 1/16", for any great
improvement of efficiency. Therein lies the rub.

Nice pun. I am proud of you :-)

Danny Deger

P.S. I liked the rest of you write-up.

The data I saw showed the 337 single engine pusher doing better, maybe
it is old data. The tractor prop is wasting energy blowing on the
windscreen and cowling, problems the pusher doesn't have. I know the
biggest gains the Mooney Exec had in going to the 201 had was because
of the cowling and windscreen redesign.

I never heard that q tips did worse than straight bladed props, that
was an interesting observation.

Aren't Lakers configured as pushers? That is an interesting example.
because the engine is just hanging out there, you could put the prop
on either end.