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What are the problems on human powered aircraft?

  1. Aug 6, 2015 #1
    i have planned to make a human powered aircraft.For that i want to know about the problems on making that.
     
  2. jcsd
  3. Aug 6, 2015 #2
    You want to read up on the Gossamer Condor.

    Flight of the Gossamer Condor
     
  4. Aug 6, 2015 #3

    SteamKing

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    For one thing, assuming you can build a craft capable of flight, it's exhausting work keeping the thing aloft. ?:)

    I'm sure if the airlines could find a way to do so, they would make their passengers do all the work of keeping the plane in the air and flying it from point A to point B, rather than purchase all that expensive fuel and all those even more expensive engines. :biggrin:

    It's much more comfortable to relax with a nice drink in First Class, than huffing and puffing trying to stay in the sky. :wink:
     
  5. Aug 6, 2015 #4

    russ_watters

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    The main problem is low power to weight ratio.
     
  6. Aug 11, 2015 #5
    That's easy to overcome. Simply use lighter than air.

    Unfortunately the best candidates spend too much time in Washington. The rest of us can't seem to generate the needed hot air.
     
  7. Aug 12, 2015 #6
    Humans are weak. Imagine lifting 550 pounds a foot every second, that is 1 horsepower. A person could sustain lifting ~30 pounds a foot every second for a sustained period. That is ~1/20 of a horsepower.

    You can't do much with 1/20 of a horsepower.
     
  8. Aug 16, 2015 #7

    Baluncore

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    The air is not thick enough.
    The human needs to be an athlete.
    The craft must be stable and fly itself as the rider will be exhausted most of the time.
    The lifting surfaces must be efficient which requires long wings to reduce drag.
    Long wings do not help directionally stability which is essential to maintain lift.
    The craft must be low weight but also strong enough to survive atmospheric disturbances and hail stones.
    There is no economic imperative.

    Birds have hollow bones as structure with feathers as an addaptive aerofoil surface.
    The heaviest bird flying reliably today is the Kori Bustard, males weigh about 18kg.
     
  9. Aug 21, 2015 #8

    cjl

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    That's a fairly pessimistic estimate of human power output - most reasonably in-shape people can maintain 150 watts for a period of an hour or more (which is about 1/5 of a horsepower), and professional athletes might be able to do more like 350-400 watts (1/2 horsepower or so). Of course, even with half a horsepower available, the power to weight ratio is still a hugely limiting factor for a human powered aircraft.
     
  10. Aug 26, 2015 #9
    Your numbers are optimistically unrealistic and you can't back it up with data. You are stating that an "in shape" person can maintain a consistent exertion of lifting 110 pounds per foot per second for hours on end (no rest, consistent energy output like a motor can do). Say a 110 pound person ascended stairs at the rate of 1 foot per second (1/5 of a horsepower or 110 pound⋅ft per second). In one hour that person would have climbed 3600 feet. Simply stated - in eight hours that person could be at the top of Everest.

    I challenge you to produce 1/10th of a horsepower for 15 minutes (consistent power output, no breaks). Think of it in imperial units.
     
  11. Aug 26, 2015 #10

    cjl

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    I produce more than that all the time riding my bike. I don't have a power meter on my road bike, but based both on comparisons to stationary bikes with power meters and based on calculations estimating rolling resistance and aerodynamic drag, combined with my knowledge of my cycling speed (I have GPS logs for my rides), I definitely output 150+ watts regularly. As for data, will this do? It isn't for me, but I think it shows my point...

    http://www.cyclingpowerlab.com/CyclingPowerOutput.aspx
    http://users.frii.com/katana/biketext.html
    http://toonecycling.com/2012/03/26/tour-de-tuscaloosa-power-data/ (this guy is in significantly better shape than I am - note that he has a 1 minute power output of almost 600W, a 25 minute power output of 307W, and a 2.5 hour output of 272W)
    http://www.cyclingmusings.com/2011/02/golden-cheetah-quick-start-guide.html [Broken]

    (I'd really love to have a power meter on my bike, since I'd be very curious to see the data, but it's $1k+, and sadly I can't justify that right now)
     
    Last edited by a moderator: May 7, 2017
  12. Aug 26, 2015 #11

    russ_watters

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    I agree with CJl's numbers and this is easily googlable, but you should also try looking at it another way (comparing it to real exertion) to make it lot easier to see.

    For biking, max efficiency is at somewhere around 100 rpm. Assuming each foot pushes down a foot, that's only 33 lb of force per pedal stroke. Not much for a strong leg.
    When I wrestled in high school at 120 lb, we would run stairs or stadium steps for 45 min at a time. At a 120 step/min pace, that's about 240 ft-lb/sec on the up-steps.
    There's a big, big difference between "an hour or more" and 8 hours. Not to mention the cold, snow and gear. Not a realistic comparison.

    People do race up skyscrapers though: http://www.startribune.com/with-skyscraper-stair-climbs-fitness-races-to-new-heights/198494531/

    And maybe someone will pop-in and provide stairmaster results.
    You're really really far off base here. 1/10th horsepower is a pretty light bike ride -- I'd barely even consider it exercise. If you want a photo of my exercise bike's screen I can provide one for you.

    Also, the first in the "Gossamer" series planes (like the video in post #2) required about 300W to stay airborne:
    https://en.wikipedia.org/wiki/Gossamer_Albatross
     
  13. Aug 26, 2015 #12
    Let's ignore the uncalibrated bike screens and look at the physics of it.

    Say a pro bike rider weighs 137.5 pounds. That rider would have to lift an additional 137.5 pounds (that is three plates of 45 pounds and a 2 1/2 if you ever lifted weights) one foot vertically every second and sustain that to create 1/2 horsepower. I don't see a bike rider being able to do that, they are too scrawny. So the other extreme would be for the bike rider to lift himself 2 feet vertically every second. That is 7200 feet in an hour and I don't see that happening either.

    Anyway we are arguing over a fraction of a horsepower. I submit to cjl - go to Home Depot and move 10 eighty-pound bags of concrete about 50 feet, then move 'em back to where you found them. I am sure that is no more than 1/10th of a horsepower.
     
  14. Aug 26, 2015 #13

    russ_watters

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    How far off do you really think being uncalibrated means? 10%? 20%?
    You've upped the horsepower from what we were discussing before. Since you aren't a pro it makes it harder for you to use your intuition to see it.
    In any case, as said before you can easily verify this stuff via a quick google:
    http://www.bicycling.com/training/2015-tour-de-france/you-versus-tour-de-france-pro
    Not sure what else can be said here other than now that you've seen others provide sources, it is your turn to start doing some of your own research. Your intuition/imagination is not providing you the right answer.
    That is a useless test because moving an object horizontally doesn't require applying any power to it.
     
  15. Aug 27, 2015 #14
    I would add that there's a huge difference between lifting with arms and efficient use of leg muscles.

    I don't know what the problem is here. The answer is what the answer is. The data is there. It's been collected. It's not a matter of opinion. Personally I thought a human body could produce about 5W continuously. But I'm willing to admit I was wrong. The data is clear.
     
  16. Aug 27, 2015 #15

    russ_watters

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    Yes. Lifting an object up, carrying it, then putting it back down is a zero output, zero efficiency process. There is basically nothing calculate about it. And even if it is useful to know the input energy, it's impossible to calculate with any accuracy.

    For biking or rowing or any other human-powered output process, measuring the output is pretty easy and accurate because a quality exercise machine actually regulates the load by generating electricity. This can be accurately indexed or measured. The input energy (calories burned) is the inaccurate one.
     
  17. Aug 27, 2015 #16

    Baluncore

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    But aircraft still consume fuel when flying horizontally.
     
  18. Aug 27, 2015 #17

    cjl

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    Let's ignore the "uncalibrated" bike screens, sure. Yesterday, after work, I went on a bike ride. With my bike, my backpack, and myself, I weigh about 215 pounds (~190lb for me, 5lb for my backpack, 20lb for the bike). On a hill during the ride, I climbed 550 vertical feet in about 23 minutes (measured by GPS). This means the power used for climbing alone was about 115 watts. Based on some rough estimates online, I'd guess that the drag and rolling resistance adds another 50 watts or so, so my total power output was around 165 watts. This is around 1/5 horsepower, and I'm definitely not an athlete of any kind.

    As for pros, let's look at a famous Tour de France climb. The Alpe d'Huez climbs 1071 meters in 13.2 km. The record fastest climb was by Marco Pantani, in 1997, who ascended it in 37 minutes 35 seconds. He weighed 57kg, and Tour de France bikes weigh 6.8kg, for a total weight of 63.8kg. To lift 63.8kg 1071 meters in 37:35, the average climbing power was just under 300 watts (about 0.4 horsepower). In addition, to travel 13.2 km in 37:35, he had to average about 13mph (21kph). This requires another 50-80 watts to overcome aerodynamic drag and rolling resistance, for a total average power output of 350-380 watts (0.47-0.51 horsepower). Interestingly, this is a climb of over 3000 feet in a bit more than half an hour, which isn't far from your "7200 feet in an hour" calculation.

    Just because you don't find this level of power output credible doesn't mean it doesn't exist.
     
  19. Aug 27, 2015 #18

    CWatters

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    I recall a quote by one of the teams that built an HPA. It went something like... It's easier to teach a racing cyclist to fly than teach a pilot to produce the required power.
     
  20. Aug 27, 2015 #19
    technically a blimp is aircraft.

    Here's your human powered aircraft


    notice its speed even in a hangar with no wind.
     
  21. Sep 11, 2015 #20
    The basic problem with humans' sustaining flight- is physics. Gravity of the earth, density of the atmosphere, hence buoyancy; strength and endurance of our muscles... sustained human flight isn't happening.
     
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