Extreme fuel mileage

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by BBerson, Mar 9, 2008.

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  1. Mar 11, 2008 #21

    BBerson

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    Yep, thats cheating.
    Maximum miles per gallon would be in zero lift conditions.
    I agree the aircraft would look like a motorglider but I think the wingspan could be much less and the weight much lower than most motorgliders. With smaller wing area the speed could be higher where induced drag is lower. Since there is no requirement to design for thermalling like a sailplane.
    BB
     
  2. Mar 11, 2008 #22

    orion

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    Mileage will be a function of a number of variables, ranging from the specifics of the airplane to atmospheric conditions. The Experimental arena tends to do well in this endeavor, primarily due to the quality of the build (especially that of the pre-molded structures) and the fact that most homebuilts are dramatically smaller and lighter than their certified counterparts.

    There is a fine balance between a highly efficient airplane and one that is sufficiently durable for its extended life. If we look at a basic comparison of a certified airplane and one of the most "efficient" (Mike Arnold's AR-5), we see a dramatic contrast in values and capabilities. I'll use my Cherokee Pathfinder as an example: With the 235 hp O-540, the Cherokee has a very "economical" cruise at about 130 mph (indicated at 1,000 ft. on a standard day), a normal cruise of about 145 mph and a fuel sucking cruise of about 165 mph, for the same conditions. The economical cruise is able to deliver somewhere between 11 and 12 mpg, the normal cruise is then between 9 and 10 mpg, and the top cruise is down to about 8 mpg. These numbers do increase with altitude but the rise is relatively moderate.

    One of the most efficient fixed gear production airplanes used to be the Grumman Tiger, which was able to deliver about 16 mpg for normal cruise. A Glasair III on the other hand can give you a range between about 13 and 15 mpg, although I've seen numbers above and below this range.

    The AR-5 on the other hand calculates out to about 53 mpg.

    And therein lies the trade. Are you going for all out efficiency, or do you want to carry something. A glider, modified with shorter wings and a very efficient engine (or two engines, one on each wing) will do a good job but you can't carry anything. The KR-1 mentioned above is unlikely to do much better than an efficient certified airframe - I'd be surprised if in normal cruise it can do much better than about 15 mpg. If the build was really optimized for efficiency, I could foresee that it might start encroaching into the upper teens but again, you can't carry anything and if you're taller than about 5'10" you'd have to do a lot of modification to be comfortable.

    So I guess the bottom line in all this is that you have to determine your goals first, and then see how well you can do in wrapping something around that basis.
     
  3. Mar 11, 2008 #23

    Suprememayo

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    What about waste heat recovery to improve efficiency? Run a turbo impellor off the the exhaust such as you would any turbo set up, but connect the output shaft to an alternator, which in turn is attatched to an electric motor geared into the flywheel. Similar in concept to the turbo compounding being done pryor to the jet age.
     
  4. Mar 11, 2008 #24

    RacerCFIIDave

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    Having run a bunch of numbers for a project that is currently in a holding pattern for $$$... an ultra-efficiency land vehicle...

    I agree fully with the thought that the diesel-electric or better yet turbine-electric series hybrid fueled by algae oil is the answer to max efficiency and min environmental impact...

    The current methods of producing biofuels are silly... using agricultural products that can be used for food for fuel...economically unsatisfactory and environmentally foolish...but algae oil is a whole 'nother world...:ban:

    Having the instant "throttle response" of electric propulsion coupled with the efficiencies of the modern turbine sized to provide the power needed only for cruise..and use either batteries or a small fuel cell to store excess energy for use as short term takeoff/climb power... yummy...

    In Liberty,

    Dave
     
  5. Mar 11, 2008 #25

    Dana

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    That's why a better measure is "passenger-miles per gallon". An airliner gets abysmally low miles per gallon but the passenger-miles per gallon must be pretty good (I have no idea what the actual figures are) since a round trip ticket to Florida is far cheaper than the gas I put in my truck (16 mpg) for the same trip last week.

    -Dana

    1. Programmers are expensive.
    2. Press releases are cheap.
    3. Therefore, it's cheaper to explain the bug than to fix it.
     
  6. Mar 11, 2008 #26

    PTAirco

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    A late model 747 can get an amazing 50 mpg/per passenger, according to Boeing's own figures.
     
  7. Mar 11, 2008 #27

    needswings

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    That still leaves the ar-5 on top - just.... 53mpg/passenger (single seater). Maybe the kg cargo weight miles per gallon would be a better measure - pretty sure the boeing would come out on top then.

    Like Orion said, its a compromise - if you want to hoot around having an absolute ball in your homemade fighter (okay i might be a little envious) the AR-5 is for you. If you want to go on holidays with your family then you'll need something else.

    Looks like the main things you can do to improve effeciency are:

    a) reduce weight
    b) reduce drag
    c) reduce wing loading
    d) improve engine effeciency

    or am I missing a few points?

    anyway, if your designing from scratch a), b) and c) seem like the most likely area for big rewards to me. But then I don't really know anything..
     
  8. Mar 11, 2008 #28

    Georden

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    e) reduce speed. in Orions example going 35 mph slower increases mileage by 50%.
     
  9. Mar 14, 2008 #29

    mikemill757

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    If the Gossamer Condor could climb(?), and cruise on 1/2 H.P. imagine what a similar design could do on 2-3 H.P.! IIRC, the Mitchell U-2 did around 100 MHP on a 10 H.P. chainsaw engine... there are 4-stroke weedeater engines around 32 c.c that should be good for about 2-1/2 - 3 H.P. Just depends on how fast, far and how safely you're willing to fly - in some aircraft, you're cautioned not to fly any higher than you're willing to fall (ouch!)
    Mike
     
  10. Mar 19, 2008 #30

    JerryFlyGuy

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    In "Speed with Economy" Kent Paser increased his speeds by ~60mph while cutting his fuel burn in half.. I think the end result was something like 35mpg or so..? [memory] for a two seat a/c and some baggage.. that's not tooo shabby really.. it'd cost less for the average person to fly a trip vs drive .. if fuel was dollar for dollar [or you burned Mogas]

    Fwiw..

    Jerry
     
  11. Mar 19, 2008 #31

    Midniteoyl

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    http://speedwitheconomy.com/
     
  12. Mar 22, 2008 #32

    z7eightball

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  13. Mar 23, 2008 #33

    JerryFlyGuy

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    In theory, however I would be very suprised if this indeed was the result.
     
  14. Jun 11, 2008 #34

    bmcj

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    My first thought (concern ) is that this system may be heavier, and aircraft usually suffer more than cars when pounds are added.

    On the plus side, part of a hybrid car's strength is regenerative braking, and a plane might be able to use that to great effect by recovering energy with the windmilling prop during descent.

    Bruce :)
     
  15. Jun 11, 2008 #35

    bmcj

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    Sorry for being a little out of sequence with my last post guys... I guess I landed on page one instead of page three.

    Bruce :emb:
     
  16. Jun 11, 2008 #36

    Rom

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    Apart from the the internal combustion engine or turbine. The only way to achieve efficiency in the conversion of fuel into usable energy for propulsion is going to be an electric motor powered by the hydrogen fuel cell.
    Instead of MPG we we'll have to start thinking in miles per kilowatt-hour or kilograms of hyrogen per hour.
     
  17. Jun 11, 2008 #37

    rtfm

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    Hi,
    And speaking of electric-powered aircraft, what are your thoughts on the Electric Sonex under development?

    Duncan
     
  18. Jun 15, 2008 #38

    Wittmandriver

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    Duncan,

    The electric Sonex was more PR than anything. The battery comartment was empty...I think the motor might have been real. There have been no articles on it since the originals that I could find, or based on them anyway. It might be in the works, but I doubt it. I think it's on a back-burner...but maybe with the fuel crisis, there is a re-emergence. They were nowhere near the achievement of sustained flight the public believes. I think they were surprised to see the Electraflyer actually flying at Oshkosh last year. I have correspondence with the Electraflyer designer-he is working on a motorglider now.

    Jerry
     
  19. Jun 16, 2008 #39

    bmcj

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    Not sure if I'm talking about the same thing here, but an electric powered Monerai has reportedly made its first flight and is supposed to be demonstrated at Oshkosh this year. You can find the story on the front page of the EAA website (www.eaa.org) or go directly there with this link: http://www.airventure.org/2008/news/080612_electraflyer.html.

    Bruce :)
     
  20. Jun 16, 2008 #40

    BBerson

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    The aircraft in that EAA photo is a Moni, a John Monnett motorglider design from a few decades ago. The Monerai was another John Monnett design, a glider.

    The electric Sonex is a project of the current Monnett company and is not related to the Moni project as far as I know.
    I can see how this history is rather confusing.
     

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