A theoretical what if question

Discussion in 'Aviation' started by engguy, Nov 16, 2012.

  1. engguy

    engguy Member

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    What if...... there was a recip engine that would run at full power for an hour putting out 5000 hp using 5 gallons of fuel, would all the jet planes and airlines go back to recip?
    Its just a fun thing to consider. :lol:
     
  2. cimmex

    cimmex Member

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    AFAIK this a WWII forum. please go to the modern section
     
  3. Shortround6

    Shortround6 Well-Known Member

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    Or the science fiction/fantasy section. Right after perpetual motion and anti-gravity paint.
     
  4. Readie

    Readie Well-Known Member

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    and the Eurozone
     
  5. engguy

    engguy Member

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    Its a what if, no sci fi etc. I bet they would be more than happy to go back to the super effcient new recips.
     
  6. Shortround6

    Shortround6 Well-Known Member

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    5 gallons an hour barely covers the friction in an Allison engine IF you can get a fuel burn of .30lbs/HP/HR.

    One web site claims that 1 hp is equal to 42.41 BTUS per minute. If we assume a very generous 120,000Btus per gallon of gasoline, 5 gallons gives us 600,000BTUs per hour or 10,000Btus per minute. IF the 42.41 Btu's/min per HP is correct then 10,000 Btu's per minute is good for about 236hp IF the engine is 100% efficient. NO friction, NO heat loss, NO exhaust loss.

    236HP from a 100% perfect engine is a far cry from 5000 hp. It is right up there with the anti-gravity paint.
     
  7. fubar57

    fubar57 Well-Known Member

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    And where might I purchase some of this anti-gravity paint.

    Geo
     
  8. meatloaf109

    meatloaf109 Well-Known Member

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    I had a stock of it, but it got away somehow...
     
  9. tyrodtom

    tyrodtom Well-Known Member

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    A 65 hp Continental in a J3 Cub uses 3.5 to 4 gals a hr. at cruise.
    Don't you realize that 5 gals a hr. for a 5000 hp engine is too far out there in lala land to be considered " theoretical" ?
     
  10. N4521U

    N4521U Well-Known Member

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    Paul, I think I saw a couple of cans of the stuff over the Harbour Bridge a while back..... was it OD?
     
  11. engguy

    engguy Member

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    I don't remember mentioning gasoline. I'm suprized anything ever gets invented when hardly anyone wants to think out of the box. And the question is not can it be done. But what would happen if it could be? All manufactures would rush back to the recip's. I think the regression back would be very cool.
     
  12. cimmex

    cimmex Member

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    put pure water in the gas tank of your car and add a magical pill.... can you stop this nonsense, please!
     
  13. Shortround6

    Shortround6 Well-Known Member

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    I see, a Fuel that is not gasoline. A fuel that has over 3 million Btus per gallon. A fuel that cannot be used in a turbine engine.

    Excuse me, but I need to go finish up some work an a batch of Flubber :)
     
  14. krieghund

    krieghund Member

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    Be careful, this story is from the late forties from US Army R&D quickly nabbed by the oil companies.....or so the story goes....
     
  15. meatloaf109

    meatloaf109 Well-Known Member

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    Hard to say, it was invisible also.
     
  16. gumbyk

    gumbyk Well-Known Member

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    OK, I'll bite, and reply to the question...

    The answer is - it depends.
    How much does this hypothetical fuel cost?
    What are the maintenance costs? If the maintenance costs more than fuel for a current series turbine, what is the gain?
    How heavy is this hypothetical engine? Would you lose so much payload, that the flight is not profitable?
    Even if all these were favourable, it would only be looking at the turbo-prop market. The limitation for anything flying at jet speeds is the propeller.
    Then you start creating issues such as having to have multiple fuelling systems at airports, etc.

    There would have to be some serious financial benefits for any manufacturer to look at it.
     
  17. Jabberwocky

    Jabberwocky Active Member

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    What if we went back to recip powered aircraft? Well, my flight back from Dubai last week would probably have taken an extra 2-3 hours, for a start.

    As gumbyk alluded to, there is a major problem here: prop powered aircraft have a sweet spot under about 450 mph. After than, you start to run into major drag problems and you’re just adding more horsepower for very little gain.

    Most turboprops do under 350 mph, although there are exceptions: the new Q400 turboprop with 5100 hp per engine cruises at about 410 mph, a Saab 2000 at about 4150 per engine cruises at 420 mph. And yes, I know about the Tu-95, which was very quick, but even it only cruised at about 440-450 mph.

    Apart from cargo and maybe a low/slow strike aircraft, I’m not sure that there is a military around that would accept that sort of limitation. Airlines have already made it clear they wont, at least on anything that operates flights longer than about 1000 miles / 2 ½ hour flight time.

    Faster prop powered aircraft are maybe on the way though. Rolls-Royce and GE tested unducted rotor concepts of the late 1990s offering up to 35% improvement over in service engines. The main engineering problems were noise and increased maintenance costs and engine control.

    Rolls estimates that a modern propfan engines offers a 20-30% fuel saving over the next generation of commercial aircraft turbofans, which due to enter service in 2015-2018. These offer 11-13% improvements over current generation engines.

    The latest research using a par of 10-11,000 hp propfans gets a theoretical 200 seat commercial aircraft up to about 470-480 mph (maybe a little more). Existing single-aisles cruise at about 510-530 mph, large jets cruise at about 540-565 mph.

    The global airline industry is going to spend a minimum of 200 billion (yes, billion) on fuel this year. If you can’t convince them to go with a propfan yet – saving themselves about 60 billion dollars per year in the process – then even this hypothetical ‘wunderengine’ probably isn’t going to fly until the speed problem is solved.
     
  18. cimmex

    cimmex Member

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    there are really people who reply to such a nonsense, never thought...
     
  19. engguy

    engguy Member

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    There is not much speed with the Jets anymore because as soon as the climbout is done, they back way off the throttle, and slow way down. I've watched some of the high flying contrail makin planes and figured they were barely at 300 mph, and yes that is estimating the distance they moved in a certain amount of time.
    So I don't think speed is a factor nowdays with the cost of fuel. As far as maintenance, how often does the average car engine need fixin?
     
  20. Shortround6

    Shortround6 Well-Known Member

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    Instead of trying to estimate speed from the ground when you have little or no idea of how high they are or how far away try looking at a schedule. How many hours for a coast to coast flight or NY to Florida. East west flights always take longer than west to east flights due to jet stream.
     
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