props: tractor v pusher, q tip, ducted?

Tina

I can only tell you what Air Force ground school said when checking us
out in 0-2. Know from experience that SE rear was better than SE front
engine. Not much, but better.

Big John
*********************************************

On Thu, 09 Aug 2007 16:36:56 -0700, Tina
wrote:

I would have thought the gain for the rear engine was because the air
stream was not hitting the windscreen and losing energy that way. The
air coming into the prop comes from all directions (just flowing into
a low pressure area) but the stream leaving is directed.

But if in the newer Skymasters both engines give the same single
engine performance my idea has to be wrong






On Aug 9, 2:28 pm, Big John wrote:
I flew the 0-2 in VN. Single engine performance, either front or rear,
was not very good. That being said, the rear engine gave better SE
performance. We were told in ground school that the rear prop sucked
air over the wing center section at a higher velocity and gave more
lift than the front engine could push it up and over the center of
wing.

No matter the reason, the bird flew better SE on rear engine. SE on
either engine, the machine turned into a donut making device or worse
if you were not careful.

Big John
****************************************888

On Sun, 5 Aug 2007 22:15:55 -0400, "Kyle Boatright"



wrote:

"Kingfish" wrote in message
roups.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- Hide quoted text -

- Show quoted text -

"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

"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.

improvement of efficiency. Therein lies the rub.

Nice pun. I am proud of you :-)

------------------------------------------------------------------------

As a point of interest the 4-place shrouded pusher developed by Ryan
after WWII had the tips in contact with a compliant gasket embedded in
the shroud.

The plane was an all-composite design, by the way. Interesting in the
engineering sense but over-weight and too expensive. They did the
test flights
at Holtville and there's still a few films of it.

-R.S.Hoover

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?

("john smith" wrote)
Have you looked at the Edgley Optica?


Yup! g

http://www.midwaysailor2.com/blaine/optica.html
Discover Aviation Days (2003)

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