Recreational slow, draggy, solar ever-flying bi-plane: Is it possible ?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by dtrip, Apr 6, 2013.

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  1. Apr 6, 2013 #1

    dtrip

    dtrip

    dtrip

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    Hello people!

    This is Dimitris from Greece. The device described in the title, annoys me as a recurring dream for a couple weeks now.
    Therefore I turn to you for a cure! [​IMG]

    What power would a very slow biplane require to sustain level flight ? (single seat)



    CALCULATIONS:
    The glider + pilot = 120 kg weight ( = 264 lbs)
    Wing area of 20 m2 ( = 215 sq feet)
    Wing loading = 6 kg / m2 (similar than a hang-glider)

    Now if we lay this area with PV (photovoltaic cells), we can get power of about 150 Watt * 20 m2 = 3000 Watts.

    Also, with the addition of a small battery, we could utilize a more powerful motor (say 5000 Watts) for limited time.
    (e.g. for takeoff needs). But we can not count on such power on the long run. The average must be 3000 Watts.

    Are 3000 Watts enough ? Or some other suggestion ? I am interested in a relaxing slow flyer, not the sailplane low-drag
    type, which has already been done years ago.

    Thanks for reading, waiting for your reply, thanks
     
  2. Apr 6, 2013 #2

    Jay Kempf

    Jay Kempf

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    You can't plan on getting the max rating out of your solar panels. That is only in perfect conditions on a tracker assembly at a perfect temp. The concept will work with enough area and off the shelf motors and props. You take off and climb as an electric and recharge while you cruise on almost no power. There are a couple teams working on this with very large, very slow airplanes with large solar panel area and lots of motors and batteries.
     
  3. Apr 6, 2013 #3

    dtrip

    dtrip

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    Hello!
    Thanks for your reply!

    Yeah perhaps you are right, continuous flight maybe harder to achieve. But letting in charge, then fly around, would be more than possible.

    What Im talking about is attaching a slow-fly propeller to something like this:

    [​IMG]



    Do you think that 2000 Watts would be enough to sustain level flight ?
     
    Last edited: Apr 6, 2013
  4. Apr 6, 2013 #4

    highspeed

    highspeed

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    Not likely. 2000 watts is only 2.6 horsepower. Drag is your enemy here.
     
  5. Apr 7, 2013 #5

    ultralajt

    ultralajt

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    Draggy and solar powered dont go hand by hand.... they are rather divorced. :D
    Adding a battery pack for increased power for take off just add to the awerall weight, and that will lower the plane efficiency when flying just on solar...

    You need low drag and low wing loading. Thats mean sleak smooth design and large wing with large aspect ratio.
    When solar powered, you need every square inch of surfaces for installing the solar cells, so biplane is out of option here as lower wing is unusable for accepting the cells.

    Need a proof?

    article-1386759-0C09B00400000578-260_964x583.jpg sunseeker_solar3.jpg 800px-Helios_in_flight.jpg solarchallenger.jpg

    Sorry mate... solar biplane will be unpractical for recreational use.

    A Sunseeker sailplane (also second photo above) seems to me the best option so far as it can be practical for everyday use. It is a "hybrid" like your desire.. solar power for cruzing, and battery help for take off.

    newssunseeker.jpg

    Mitja
     
    Last edited: Apr 7, 2013
  6. Apr 7, 2013 #6

    dtrip

    dtrip

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    Yeah I guess so.

    I know about the Sunseeker.
    The Helios and Solar Impulse are huge and are trying (succeeded ?) to fly 24/7 (via battery storage)

    I was wondering wether the concept could be transferred to something slower (because slow = large wings = a lot of power).

    But I did not take drag as much into consideration as I should.

    Thanks guys, you 've been really helpful
     
  7. Apr 7, 2013 #7

    henryk

    henryk

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  8. Apr 7, 2013 #8

    BBerson

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  9. Apr 7, 2013 #9

    addaon

    addaon

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    One thing I don't see discussed (for obvious reasons) is battery-assisted launch, achieving altitude, and dropping the battery (presumedly under 'chute or on its own set of autonomous wings -- doing this with a twin cantilever biplane and becoming a solar monoplane is left as an exercise to the reader). Cruise power is way lower than takeoff/climb power, especially at half the weight.

    Haven't really thought it through for solar, but I've been non-seriously half-mulling an RC version of the idea to try to autonomously dynamically soar the bottom shear layer of the jet stream.
     
  10. Apr 7, 2013 #10

    dtrip

    dtrip

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    For an ultralight plane (like the black/white photo above, or similar), the battery for assisted launch will not be a burden.
    Assuming a 10kW motor and a battery that you want to run it for 6 minutes, this means battery capacity = 1 kWh (10 kWh motor x 1/10th of the hour capacity)
    In LiPOFe (modern lithium battery terminology), this means 6-7 of those cells:
    Battery - Synopoly LiFePO4 - 40AH, 3.2 V cell
    (each of those is 40 Ah x 3,2 Volts = 128 Watt hours = 0,128 kWh)

    ...at 1,6 kg (4 pounds) each, we get a total weight of = 11,2 kg

    In practice it might be more because 7 of those cells make up 3,2 x 7 = 22,4 Volts and a 10 kW motor does not run on such low Voltage.
    If we use a 48 Volts motor (6-7-8 kW) we will need 15 of those = 24 kg.

    Here is an example of successful application:
    https://www.youtube.com/watch?v=6br6DJ1Dis4
     
  11. Apr 7, 2013 #11

    addaon

    addaon

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    And for a design that draggy, you're probably targeting a power loading of at least 25 lbs/hp for takeoff... so your MTOW is around 335 lbs if you're targeting 10 kW/13.4 hp; so your LiFePO4 batteries at 11.2 kg (if you go to more, lower capacity cells you'll get roughly the same weight at higher voltage) is 7.3% of your weight budget. Less than I expected, but certainly not negligible even in the most optimistic case. The bigger issue is that your climb rate is going to be miserable with this sort of power loading... assuming motor weight scales well with 5-minute power (which it will, since you're in the time range where you can just sink heat locally), going to 13 lbs/hp will make you much happier/safer at take-off, at the cost of needing at least 2x the battery (probably a bit more, since you really want to have your motor get peak efficiency of ~90% at cruise, not climb).
     
  12. Apr 7, 2013 #12

    dtrip

    dtrip

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    Hey guys!

    Yep the Condor is closest to what I thought but its too big!

    The RC model is wonderful, thats the speed I was hoping to achieve :) but, as the Condor, it will be huge.

    addaon this is very useful pratical information, thanks!

    Hmm then a 15-20 kW engine is needed... that changes things, it can not be done ultralight anymore. Just the additions to the frame
    to support the power system, will change the frame significantly. I mean there are frames that weight 15 - 20 kg. Which (17 kg) is only
    the weight of a brushless 10 kW motor. Crap :)

    A "sailplane-type" can be done (SunSeeker). But this is lightyears beyond my manufacturing abilities. Not to mention that I would
    never dare to fly it, even if I had made it LOL ! :) (they go too fast for me to have fun)

    Hmm there goes my dream of "flying forever" :)

    Oh by the way, small capacity battery cells are not a solution to save weight, because they can not tolerate the same current as
    higher capacity cells. In general the rule is "you cant run a big motor on small cells" and it is due to the Amperes involved. The Voltage
    is not a problem.

    Thanks again folks, you are very knowledgable and have helped me a great deal
     
    Last edited: Apr 7, 2013
  13. Apr 7, 2013 #13

    henryk

    henryk

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    -see PREDATOR30=10 kW, 1.5 kg !
     
  14. Apr 16, 2013 #14

    Starflight

    Starflight

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    Here is a way you can use two wings of almost equal size and reduce the aspect ratio requirement: "Flying Flea" :eek:) Both wings are exposed to the sun; just increase the span slightly. There was a legal (103) ultralight version w/ 10hp Moto engine that had empty weight of 243 pounds, I think.
     
    Jon Ferguson likes this.
  15. Apr 16, 2013 #15

    Starflight

    Starflight

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    Just found the reference: Croses Eac-03 "Pouplume". Empty 238# Area 172 sq. ft. max speed w/ 12hp= 43.5 mph cruise=31mph stall???= God only knows...probably same as "Lazair" LOL (circa 1967)
     
  16. Nov 23, 2014 #16

    b7gwap

    b7gwap

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    What about a flying flea type tandem wing with higher aspect ratio wings?
     
  17. Nov 23, 2014 #17

    WonderousMountain

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    You can fly slow, but drag is a real enemy to low power applications.
    Could maybe stagger a biplane to get full sun, that's a new approach as far as I know.

    There are a few things you can do to get low drag out of simple or cost effective build techniques.
    Really think your goal is feasible if you make good compromises the whole way through.

    There's enough sun power, and technology advance to work through it.

    Do you have a good test field? RC could be very useful if you can get off the ground with a proper scale model you might be able to learn a lot.

    LuPi
     
  18. Nov 28, 2014 #18

    Jon Ferguson

    Jon Ferguson

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    A solar flying flea, that sounds very cool.
     
  19. Nov 28, 2014 #19

    cluttonfred

    cluttonfred

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    The Croses EC-3 Pouplume (Feather Flea) was originally flown with a tiny 8 hp engine, I believe for a contest, but then re-engined with something more powerful to be practical. Successive variants had bigger engines, most you'll see today have VW engines.

    774749344.jpg

    I believe that the two-seat, microlight Croses Criquet L (for Leger or light) pictured above is, despite it's name, a development of the PouPlume series not the much heaver Croses Criquet with a LyCon engine. It would be a great candidate to adapt as a battery-electric single-seater able to easily carry more than 200 lbs of batteries for decent range. In fact, I would recommend that approach for anyone seeking to build an electric plane without starting completely from scratch: find an efficient, low-powered two-seat microlight or motorglider, leave one seat empty and carry batteries instead.

    Notice that I didn't talk about solar-powered cruising. It's a beautiful concept I don't think the technology is there yet for a practical rugged aircraft for frequent use. Plus, it really only works if you live where there are very few clouds and/or you can get up to very, very high altitudes. Personally, I'd leave the solar cells on the ground on the roof of a farm strip hangar and plug into them for a trickle charge between local flights, which would be much cheaper and much less weight for the airplane to carry. With a little advance planning you should be able to arrange "fuel stops" where you could plug in along the way for an occasional cross country.
     

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