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#11
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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 |
#12
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P-63 (?) Airacobra/Kingcobra power question
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. |
#13
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P-63 (?) Airacobra/Kingcobra power question
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?). |
#14
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P-63 (?) Airacobra/Kingcobra power question
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 |
#15
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P-63 (?) Airacobra/Kingcobra power question
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. |
#16
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P-63 (?) Airacobra/Kingcobra power question
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 |
#17
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P-63 (?) Airacobra/Kingcobra power question
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. |
#18
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P-63 (?) Airacobra/Kingcobra power question
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 |
#19
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Jeffrey Bloss (was Airacobra/Kingcobra.. )
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. |
#20
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Jeffrey Bloss (was Airacobra/Kingcobra.. )
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. |
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