P-63 (?) Airacobra/Kingcobra power question

On Nov 3, 10:55*am, Ron Wanttaja wrote:
a wrote:
My aerodynamic question had always been why there are fewer pusher
props. In a puller some of the wind energy is used up against the
airplane.

In a pusher, the prop has to operate in turbulent air stirred up by the
structure in front. *Depending on the design of the airplane, the prop
also has to be stronger (e.g., heavier) to withstand the cycling loads
if there's a wing or something blocking part of the prop disk from the
slipstream (think Long-EZ).

Ron Wanttaja

Thanks! I seem to remember the pusher in the C310 was less effective
too.

In article
,
a wrote:

On Nov 3, 10:55*am, Ron Wanttaja wrote:
a wrote:
My aerodynamic question had always been why there are fewer pusher
props. In a puller some of the wind energy is used up against the
airplane.

In a pusher, the prop has to operate in turbulent air stirred up by the
structure in front. *Depending on the design of the airplane, the prop
also has to be stronger (e.g., heavier) to withstand the cycling loads
if there's a wing or something blocking part of the prop disk from the
slipstream (think Long-EZ).

Ron Wanttaja

Thanks! I seem to remember the pusher in the C310 was less effective
too.

Cessna?

The C-336/337 turns out to perform slightly better in single-engine
flight on the rear engine than the front.

a wrote:
On Nov 3, 10:55 am, Ron Wanttaja wrote:
a wrote:
My aerodynamic question had always been why there are fewer pusher
props. In a puller some of the wind energy is used up against the
airplane.
In a pusher, the prop has to operate in turbulent air stirred up by the
structure in front. Depending on the design of the airplane, the prop
also has to be stronger (e.g., heavier) to withstand the cycling loads
if there's a wing or something blocking part of the prop disk from the
slipstream (think Long-EZ).

Ron Wanttaja

Thanks! I seem to remember the pusher in the C310 was less effective
too.

As Steve pointed out, you were thinking of the C336/337 Skymaster. It
*did* have a better rate of climb on the rear engine. One theory I read
was that it was due to the aerodynamics of the rather blunt back end
being better when there was an engine to help suck the air past....

There's no real pat answer; you can find efficient pusher aircraft, just
like you can find efficient tractor planes.

For an example, see:

http://www.ar-5.com/

Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: They built two identical ships, with identical engines,
one with paddles and one with a prop. They tied a rope between the
sterns, and had the captains go to full power to see which had more thrust.

Pity you can't do this with a couple of airplanes....

Ron Wanttaja

Ron Wanttaja wrote:
Years ago, when there was a controversy as to whether paddles or
propellers were most efficient for ships, the British came up with a
simple test: They built two identical ships, with identical engines,
one with paddles and one with a prop. They tied a rope between the
sterns, and had the captains go to full power to see which had more
thrust.

Wikipedia says that "In 1848 the British Admiralty held a tug of war
contest between a propeller driven ship, Rattler, and a paddle wheel ship,
Alecto. Rattler won, towing Alecto astern at 2.5 knots (4.6 km/h)...."

http://en.wikipedia.org/wiki/Propeller

However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

Jim Logajan wrote:

However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

Jim, Jim, Jim.... HOW can you set us up with a straight line like that?

1. "It's not the size of the wheels, it's how you use them."

2. "If they would have set up the wheels in a canard configuration, it
would have been more efficient."

:-)

Ron Wanttaja

On Nov 4, 1:19*am, Ron Wanttaja wrote:
Jim Logajan wrote:
However, it is probable that the paddle wheel ship simply didn't have the
right size paddles. Paddle wheels should be capable of efficiencies similar
to propellers - but it takes very large wheels.

Jim, Jim, Jim.... HOW can you set us up with a straight line like that?

1. *"It's not the size of the wheels, it's how you use them."

2. *"If they would have set up the wheels in a canard configuration, it
would have been more efficient."

:-)

Ron Wanttaja

Paddle wheels got screwed. It's just another demonstration that the
spinning thing belongs on the back of the hull.

a wrote:

Paddle wheels got screwed. It's just another demonstration that the
spinning thing belongs on the back of the hull.


Except when it belongs in the front.

"At full load the Mackinaw displaced 5,252.4 tons and drew 19' 2.25" of
water. Her innovative features included a 12 foot diameter bow propeller
which draws water from beneath the ice ahead, both weakening the ice and
sending water along the sides of the hull and reducing ice friction. The
Mackinaw also has a heeling system which can shift nearly 112,000 gallons of
ballast water from side to side in 90 seconds, allowing a rocking motion
which assists the Mackinaw in freeing itself from ice."

http://www.mightymac.org/cgcmackinaw.htm