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P-63 (?) Airacobra/Kingcobra power question



 
 
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  #1  
Old November 3rd 09, 03:13 PM posted to rec.aviation.piloting
Ricky
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Posts: 259
Default P-63 (?) Airacobra/Kingcobra power question

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
  #2  
Old November 3rd 09, 04:09 PM posted to rec.aviation.piloting
vaughn[_2_]
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Posts: 92
Default P-63 (?) Airacobra/Kingcobra power question


"Ricky" wrote in message
...
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?


As its name "rec.aviation.piloting" implies, this group is more for airplane
drivers than for aircraft designers or aviation historians. You will get better
answers at rec.aviation.military, and perhaps some very interesting answers at
rec.aviation.homebuilt.

Regards
Vaughn



  #3  
Old November 3rd 09, 04:24 PM posted to rec.aviation.piloting
a[_3_]
external usenet poster
 
Posts: 562
Default P-63 (?) Airacobra/Kingcobra power question

On Nov 3, 9:13*am, 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


Ricky, the question you'd have to ask is, if the energy is put into
the shaft at the engine end, where could it go? One answer is heat,
the the other sound energy, but really most of it is delivered to the
prop. Long shafts do cause vibration problems, but those can be
overcome.

As it happens, there are other reasons for putting engines close to
the front of a single engine airplane. The middle is a good place to
park passengers, you avoid the weight/space issues with the shaft.

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 fact one of the things that made the Mooney 201 better
than the Executive is the windscreen and cowling were redesigned to
more effectively deflect the wind. In the case of the Mooney, the wind
against the airplane is airspeed plus that contributed by the prop,
and losses go up like something of the square of wind velocity.

This could be a long thread, and some posters may actually contribute
to the discussion.
  #4  
Old November 3rd 09, 04:33 PM posted to rec.aviation.piloting
Ron Wanttaja[_2_]
external usenet poster
 
Posts: 108
Default 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.


The shaft itself won't eat up power, but the various gearboxes and shaft
supports required will. Every bearing has a bit of friction; every
gearbox has a bit of drag. A long drive shaft, and the gearbox required
to let the cannon shoot through the hub, would cost more power than the
straight installation.

Whether it was enough to matter, in the case of the P-39, is another
thing. ISTR the P-39's problem was the lack of a turbocharger rather
than overall low power... the Airacobra started losing oommmmph above
12,000 feet, and it turned out that most of the combat was higher than that.

Remember, Tex Johnston won the Thompson Trophy in a P-39, and set a
speed record, besides.

Ron Wanttaja
  #5  
Old November 3rd 09, 04:55 PM posted to rec.aviation.piloting
Ron Wanttaja[_2_]
external usenet poster
 
Posts: 108
Default P-63 (?) Airacobra/Kingcobra power question

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
  #6  
Old November 3rd 09, 05:10 PM posted to rec.aviation.piloting
Ricky
external usenet poster
 
Posts: 259
Default P-63 (?) Airacobra/Kingcobra power question

On Nov 3, 9:09*am, "vaughn"
wrote:

As its name "rec.aviation.piloting" implies, this group is more for airplane
drivers than for aircraft designers or aviation historians...(rest snipped) *


Regards
Vaughn


Hey, thanks for your suggestion. I've been in Usenet since the early
90s and am very careful (generally) about on-topic discussion. This is
totally on topic and useful, interesting & beneficial to this
particular community. I am an "airplane driver," and, I'm sure you
know or will learn, drivers run the gamut of interest in airplanes in
every aspect.
I submit this topic with absolutely NO reservation that this is
violating the traditions of an "airplane driver's" group.

Thanks anyway,

Ricky

  #7  
Old November 3rd 09, 05:16 PM posted to rec.aviation.piloting
Mike[_30_]
external usenet poster
 
Posts: 1
Default P-63 (?) Airacobra/Kingcobra power question

On Tue, 3 Nov 2009 08:10:54 -0800 (PST), Ricky wrote:

On Nov 3, 9:09*am, "vaughn"
wrote:

As its name "rec.aviation.piloting" implies, this group is more for airplane
drivers than for aircraft designers or aviation historians...(rest snipped) *


Regards
Vaughn


Hey, thanks for your suggestion. I've been in Usenet since the early
90s and am very careful (generally) about on-topic discussion. This is
totally on topic and useful, interesting & beneficial to this
particular community. I am an "airplane driver," and, I'm sure you
know or will learn, drivers run the gamut of interest in airplanes in
every aspect.
I submit this topic with absolutely NO reservation that this is
violating the traditions of an "airplane driver's" group.

Thanks anyway,

Ricky


This article should answer that for you. Good Luck!

http://tinyurl.com/5gt7
  #8  
Old November 3rd 09, 05:21 PM posted to rec.aviation.piloting
a[_3_]
external usenet poster
 
Posts: 562
Default 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.
  #9  
Old November 3rd 09, 06:23 PM posted to rec.aviation.piloting
Steve Hix[_2_]
external usenet poster
 
Posts: 50
Default P-63 (?) Airacobra/Kingcobra power question

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.
  #10  
Old November 3rd 09, 06:32 PM posted to rec.aviation.piloting
Steve Hix[_2_]
external usenet poster
 
Posts: 50
Default P-63 (?) Airacobra/Kingcobra power question

In article ,
Ron Wanttaja 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.


[snip]

Whether it was enough to matter, in the case of the P-39, is another
thing. ISTR the P-39's problem was the lack of a turbocharger rather
than overall low power... the Airacobra started losing oommmmph above
12,000 feet, and it turned out that most of the combat was higher than that.


Combat in the ETO tended to be higher than other theaters, which, since
the USAAC pulled the turbocharger from the P-39, hamstrung it in that
arena. The Airacobra was also a small aircraft, with limited fuel, as it
was designed as a point defense fighter, and lack of range hurt it, too.

That said, the Russians liked it pretty well, since air combat on the
eastern front tended to remain below 15,000', and it performed well down
there against the Luftwaffe. (In spite of the 37mm cannon, the P-39 was
used much more in the anti-air role, and not against German armor; the
Il-2 was much better down in the mud.)

The P-39/P-400 didn't exactly shine, not that it embarrassed itself, in
the Pacific, partly due to the long distances that were common there.
 




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