P-63 (?) Airacobra/Kingcobra power question

Ricky wrote:
A question for the physics-minded among us, or for anyone who just has
the answer.

I have heard the Airacobra was underpowered and that got me to
thinking;
Does having an engine at the middle of the fuselage (in any plane for
that matter, like the XP-58) and connected by a long shaft contribute
to a loss of power delivered to the propeller? In other words; would
there be more power delivered the closer the engine is to the prop?
Does the shaft "eat up" power in any way? I am a mechanic and pilot
and fairly knowlegable about a/c physics & aerodynamics but this has
me stumped.

Thanks in advance for your ponderings and/or solution!

Ricky

It's a question often asked in connection with long shafts.
The elastic angular compliance can be a positive help with vibrations,
which are absorbed by a quill shaft. But a shaft drive train that's
curved takes pillow blocks to support the curve, and these bearings take
some (small) power on their own account. Otherwise, air drag, and
bearing drag apart, there's no loss in a long quill shaft.

Brian W

On Nov 3, 8:51*pm, brian whatcott wrote:
Ricky wrote:
A question for the physics-minded among us, or for anyone who just has
the answer.

I have heard the Airacobra was underpowered and that got me to
thinking;
Does having an engine at the middle of the fuselage (in any plane for
that matter, like the XP-58) and connected by a long shaft contribute
to a loss of power delivered to the propeller? In other words; would
there be more power delivered the closer the engine is to the prop?
Does the shaft "eat up" power in any way? I am a mechanic and pilot
and fairly knowlegable about a/c physics & aerodynamics but this has
me stumped.

Thanks in advance for your ponderings and/or solution!

Ricky

It's a question often asked in connection with long shafts.
The elastic angular compliance can be a positive help with vibrations,
which are absorbed by a quill shaft. But a shaft drive train that's
curved takes pillow blocks to support the curve, and these bearings take
some (small) power on their own account. Otherwise, air drag, and
bearing drag apart, there's no loss in a long quill shaft.

Brian W

I had a ME design a centrifuge application with the shaft running well
above its critical speed a bunch of years ago, but don't remember the
tradeoffs that led me to accept that embodiment. It was not an
aviation application in any event. I did find the observation about
wind profiles around a pusher imposing design constraints -- I'd have
thought that far aft winds in the disk would be fairly uniform except
at high angles of attack.

Have you a sense of the improvement of thrust, if any, a given engine
might have wing mounted vs nose mounted? There's less to blow against
but the wind does extend to well past the prop disk so some of that
air near the outside diameter is compromised by the wing. I'm thinking
of an application where one wants the maximum endurance at fairly low
speeds. That around the world airplane that came out of Scaled
Composites might hold the answer.

On Nov 3, 9:52*pm, a wrote:
On Nov 3, 8:51*pm, brian whatcott wrote:



Ricky wrote:
A question for the physics-minded among us, or for anyone who just has
the answer.

I have heard the Airacobra was underpowered and that got me to
thinking;
Does having an engine at the middle of the fuselage (in any plane for
that matter, like the XP-58) and connected by a long shaft contribute
to a loss of power delivered to the propeller? In other words; would
there be more power delivered the closer the engine is to the prop?
Does the shaft "eat up" power in any way? I am a mechanic and pilot
and fairly knowlegable about a/c physics & aerodynamics but this has
me stumped.

Thanks in advance for your ponderings and/or solution!

Ricky

It's a question often asked in connection with long shafts.
The elastic angular compliance can be a positive help with vibrations,
which are absorbed by a quill shaft. But a shaft drive train that's
curved takes pillow blocks to support the curve, and these bearings take
some (small) power on their own account. Otherwise, air drag, and
bearing drag apart, there's no loss in a long quill shaft.

Brian W

I had a ME design a centrifuge application with the shaft running well
above its critical speed a bunch of years ago, but don't remember the
tradeoffs that led me to accept that embodiment. *It was not an
aviation application in any event. I did find the observation about
wind profiles around a pusher imposing design constraints -- I'd have
thought that far aft winds in the disk would be fairly uniform except
at high angles of attack.

Have you a sense of the improvement of thrust, if any, *a given engine
might have wing mounted vs nose mounted? There's less to blow against
but the wind does extend to well past the prop disk so some of that
air near the outside diameter is compromised by the wing. I'm thinking
of an application where one wants the maximum endurance at fairly low
speeds. That around the world airplane that came out of Scaled
Composites might hold the answer.

Opps, not built by scaled composites after all. Interesting that the
rear engine was the one that ran all of the time, so that was the more
efficient location (but what does Rutan know?).

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

Jeffrey Bloss wrote:
/snip/

Did anyone hear a noise? Sounded like an empty head rattling.

To elaborate, my suggestion is that before posting you should give your
head a shake to determine if there is anything inside and to consider
whether you really wished to make the fact public.

/snip/
Clown, I never said that a canard can't be well-cooled only in answering
your fourth grade level question as to why "there has always been fewer
pusher props.".

duh.

They are much harder to cool for one and several other reasons none of
which you will be able to wrap your tiny, stunted clown mind around.

Jeffrey, I have largely skipped your posts til now.

But I just noticed how derogatory, abusive and nasty sounding
they are. Is this what you intended?
It's human nature to carry on an individual vendetta at times - but
you are broadcasting.

I imagine if someone whines to Google they will pull your mail.
That's just a minor inconvenience I know, but why don't you instead just
lighten up? Be abusive in private emails and we will never know.

Sincerely

Brian Whatcott.

It's sad that such a few unhappy individuals in their desire to impress
others with their infallible aviation knowledge have turned this ng into the
almost completely worthless cesspool that it has become with their
sophomoric sexual name calling and insults.

It's hard for me to believe that they are actually pilots considering the
personalities involved. I would certainly be ashamed to be associated with
any of them.


"brian whatcott" wrote

Jeffrey, I have largely skipped your posts til now.
But I just noticed how derogatory, abusive and nasty sounding
they are. Is this what you intended?
It's human nature to carry on an individual vendetta at times - but
you are broadcasting.

I imagine if someone whines to Google they will pull your mail.
That's just a minor inconvenience I know, but why don't you instead just
lighten up? Be abusive in private emails and we will never know.

Sincerely

Brian Whatcott.