props: tractor v pusher, q tip, ducted?

Tina wrote in news:1186370891.595213.170320
@w3g2000hsg.googlegroups.com:

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.


That's for the early airplanes regarding the Skymasters. the loss was in
cooling drag, which Cessna improved. After that the SE ceiling cruise
and climb were virtually identical, but the reputation the rear engine
had for better SE performance never went away..

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


Actaully, it was more than an observation. the Q tips were installed as
a noise requirement for Swiss registered airplanes. These airplanes had
a supplememt to the POH with degraded performance. Having said that they
also had "Swiss Mufflers" but they're supposed to have no effect on
performance.
Also flew a couple of Arrows similarly equipped as well as a Cessna 182
RG. Same deal for all of them IIRC. Some were German and I seem to
remember they had a different muffler assembly in Germany which deliverd
worse performance and made more noise.


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.


Well, you're getting down to comparing apples with oranges. You'd have
to take two essentially identical aircraft and try both configurations
with it for a satisfacory answer based solely on observed performance,
but in reality, a real world airplane is going to throw so many other
variables, such as cooliing requirements, planform due to CG
considerations, disc availability due to fuselage cross section, whoch,
of course is down to cabin space, mission requirements yadda yadda
yadda. At the end of the day, when you look at similarly powered
aircraft with similar missions, or even better, if you look at the Cafe
racers, the evidence says it's al down to how clever the designer is,
and there's not a lot in any configuration, pusher, tractor tandem wing,
canard or conventional...



Bertie

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

On Aug 5, 11:46 pm, Bertie the Bunyip wrote:

That's for the early airplanes regarding the Skymasters. the loss was in
cooling drag, which Cessna improved. After that the SE ceiling cruise
and climb were virtually identical, but the reputation the rear engine
had for better SE performance never went away..


How can that be? The engine cowling has the same openings wether the
engine is turning or not. In other words, whatever the drag of the
front engine cowling, it should be the same whether the engine is
turning or not.

I'm assuming that the propeller does not effect airflow tooooo much
near the root, where it spins slowly and has a less aerodynamic shape
than near the tip, where most thrust is generated.

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


Yup! g

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

The event is now called (B)laine (A)viation (W)eekend


Paul-Mont
(2007) B.A.W. Event Chair for:
Parking / People (Our Volunteers) / Pop

Charles Talleyrand wrote in
ups.com:

On Aug 5, 11:46 pm, Bertie the Bunyip wrote:

That's for the early airplanes regarding the Skymasters. the loss was
in
cooling drag, which Cessna improved. After that the SE ceiling cruise
and climb were virtually identical, but the reputation the rear
engine
had for better SE performance never went away..


How can that be? The engine cowling has the same openings wether the
engine is turning or not.

It doesn't
Same openings, different drag profile with the engines running.

In any case, it's a fact that the later Skymasters had virtually the
same performance with either engine out.


In other words, whatever the drag of the
front engine cowling, it should be the same whether the engine is
turning or not.


It isn't.


I'm assuming that the propeller does not effect airflow tooooo much
near the root, where it spins slowly and has a less aerodynamic shape
than near the tip, where most thrust is generated.

The drag is induced by the cooling itself.


Bertie.

On Aug 7, 7:34 am, Bertie the Bunyip wrote:


The drag is induced by the cooling itself.

How can the drag be induced by the cooling itself? If I understand
you, the same cowling with the same air flow shows significantly
different drag depending on whether the engine inside is hot or cold.

I honestly don't understand that.

"Charles Talleyrand" wrote in message
oups.com...
On Aug 7, 7:34 am, Bertie the Bunyip wrote:


The drag is induced by the cooling itself.

How can the drag be induced by the cooling itself? If I understand
you, the same cowling with the same air flow shows significantly
different drag depending on whether the engine inside is hot or cold.

I honestly don't understand that.

The air entering the engine compartment, and flowing past the running
engine's hot cooling fins expands at LEAST double.

That is why the exit opening is much larger than the intake.

That is why there have been claims that the P-51 has a positive cooling
drag, that is the heated air exiting actually gives more thrust than the
drag of air entering the radiator passage and going past the radiator.
--
Jim in NC

"Morgans" wrote in message
...

"Charles Talleyrand" wrote in message
oups.com...
On Aug 7, 7:34 am, Bertie the Bunyip wrote:


The drag is induced by the cooling itself.

How can the drag be induced by the cooling itself? If I understand
you, the same cowling with the same air flow shows significantly
different drag depending on whether the engine inside is hot or cold.

I honestly don't understand that.

The air entering the engine compartment, and flowing past the running
engine's hot cooling fins expands at LEAST double.

That is why the exit opening is much larger than the intake.

That is why there have been claims that the P-51 has a positive cooling
drag, that is the heated air exiting actually gives more thrust than the
drag of air entering the radiator passage and going past the radiator.
--
Jim in NC

Double? Naah. It expands, but doesn't double. Boyle's law (PV=NRT) is
based on absolute temperature, which is measured in kelvin. Kelvin is
Celsius plus 273 degrees. Guessing now, if the air temp went from 300k to
350k (or about 80F/27C to about 160F/70C) you'd see volume increase by
(350/300 -1) = 1/6th = about 17%...

KB

Charles Talleyrand wrote in
oups.com:

On Aug 7, 7:34 am, Bertie the Bunyip wrote:


The drag is induced by the cooling itself.

How can the drag be induced by the cooling itself?


If I understand
you, the same cowling with the same air flow shows significantly
different drag depending on whether the engine inside is hot or cold.

I honestly don't understand that.

Not what I mean. the flow inside is quite different with the prop
turning or not, though.

I'm away at the moment, but I'll look in my library when I get home for
a better definition than I can provide off the top of my head..K?

In any case, It's Cessna's claim nd not mine that cooling drag was
sorted on the airplane.

I also recently read an aricle in a very old Sport aviation about the
pros and cons of pusher/tractor arrangements. I can't remember if the
author came up with a definitive answer as to which was better or more
efficient, but I don#'t see how he could, really.



Bertie

"Kyle Boatright" wrote in
:


"Morgans" wrote in message
...

"Charles Talleyrand" wrote in message
oups.com...
On Aug 7, 7:34 am, Bertie the Bunyip wrote:


The drag is induced by the cooling itself.

How can the drag be induced by the cooling itself? If I understand
you, the same cowling with the same air flow shows significantly
different drag depending on whether the engine inside is hot or
cold.

I honestly don't understand that.

The air entering the engine compartment, and flowing past the running
engine's hot cooling fins expands at LEAST double.

That is why the exit opening is much larger than the intake.

That is why there have been claims that the P-51 has a positive
cooling drag, that is the heated air exiting actually gives more
thrust than the drag of air entering the radiator passage and going
past the radiator. --
Jim in NC

Double? Naah. It expands, but doesn't double. Boyle's law (PV=NRT)
is based on absolute temperature, which is measured in kelvin. Kelvin
is Celsius plus 273 degrees. Guessing now, if the air temp went from
300k to 350k (or about 80F/27C to about 160F/70C) you'd see volume
increase by (350/300 -1) = 1/6th = about 17%...

KB


It's certainly standard practice, at least on airplanes where min
cooling drag is desired, that the outlet be conderably larger than the
inlet...


Bertie