The human-powered helicopter challenge | Hacker News Reader

The human-powered helicopter challenge

humansinvent.com

105 pointsleonardRenter50 comments

Without any disrespect to the pilot, if they're close, why don't they get a slightly faster person to pilot it?

Their elite racing cyclist (according to the bio page) is this guy: https://www.usacycling.org/results/?compid=286471

Not bad at all: it takes a lot of time and dedication to race at that level and also having a life outside racing. However, you could probably improve on his strength to weight ratio by getting a professional cyclist. For instance, in this hill climb time-trial, he came in over a half a minute down from the guy who won his category, in a race of under 5 minutes:

https://www.usacycling.org/results/?permit=2012-2687

That kind of event is fairly similar to the kind of effort getting the helicopter off the ground entails: a short effort where, due to the climbing, weight is against you.

These guys, for instance, got a cyclist who had been in the olympics:

http://en.wikipedia.org/wiki/MIT_Daedalus

The team is likely made up of humans who may have formed emotional attachment to the project and wish to complete it alongside their long-time teammates.

Could be. But it's primarily an engineering challenge: I'd see that as the big success, not whether they have one guy who's a bit faster than another, who happens to take it over the line.

There is plenty of engineering left to do once the $250k is in pocket.

50 people, efforts applied over 18 months, carbon-fiber construction costs, other costs.... they're not in it for the money.

Not to mention the assumption that this is not the best cyclist who:

* will work for free

* is local

* is reliable and not an asshole

* would rather do this than actually cycling

This is a long-term challenge, where they have been getting progressively better for months and years. It's not like they just built the machine and then need a pilot for a day.

My guess is that the "limiting factor" is finding someone associated with the engineering program at that university. They could probably find a local racer that met the above qualifications without too much trouble.

The helicopter requires pedalling with both hands and feet. Upper body strength is not something that goes hand-in-hand with cycling, due to the extra weight.

Well, they do seem to have picked cyclists as test pilots.

It may be, too, that the hand pedals are more of a distraction. It's something that has been tried with bicycles, and in general doesn't work out very well. Granted, in part this may be because you also have to steer a bike, whereas for a short effort like this, that's not so important. There's something to be said in any case for an otherwise rigid frame that you can hold onto with your hands, and really just sink all the leg power you can into it, kind of like standing up on a bicycle as you go uphill: you actually do pull on the bars.

They did a little bit of testing:

http://www.agrc.umd.edu/gamera/gamera2/gamera2-human-power.h...

Page also mentions that their pilots weigh less than 145 pounds. I bet it matters a lot and wonder where the pros you are citing come in.

Great link; it's interesting to see that indeed, they do get a lot more out of the hand cranks.

> I bet it matters a lot and wonder where the pros you are citing come in.

Where they come in is that a small climber has an excellent power to weight ratio. This guy weighs 48 kg, for instance: http://en.wikipedia.org/wiki/Jos%C3%A9_Rujano

Power to weight ratio varies over time as well. Smaller guys are great at climbing long distances, because they can maintain a higher power-to-weight ratio for an hour or longer. Bigger guys tend to be sprinters (Chris Hoy is 205lbs) because their peak power can be much, much higher and compensate for the extra weight. For a one-minute effort, I'd suspect that a somewhat heavier sprinter profile would be an advantage over a lightweight climber profile.

Even moreso because the weight of the craft will be a smaller percentage of their overall weight. A 150lb cyclist capable of outputting 10W/kg for a minute will have an effective 6.6W/kg on a 75lb craft. A 180lb cyclist capable of the same 10W/kg would have an effective 7.0W/kg on the same craft. And a 180lb cyclist capable of 11W/kg would manage an effective 7.7W/kg.

The Pros tend to be pretty light. Guideline for weight of a cyclist is (Height in Inches) x2 = (Weight in Pounds).

> It's something that has been tried with bicycles, and in general doesn't work out very well. Granted, in part this may be because you also have to steer a bike, whereas for a short effort like this, that's not so important.

I would expect pedaling with your hands to be a huge stability problem on a bike, and once again, not so much of an issue with a helicopter.

This is a 90 second anaerobic sprint where cycling is an aerobic activity. Thus building up lactic acid in the upper body lets you extract more energy where the lungs can't support the extra load in aerobic cycling.

There are plenty of anaerobic efforts during most road races. Sure, it's primarily an aerobic activity, but you need to be able to 'go anaerobic' too.

Exhibit A would be the finish of the Fleche Wallone. This video (at about 8:00 ) shows it: http://www.youtube.com/watch?v=DU-kNDQuiIo - just about 90 seconds.

Perhaps a more even distribution of lactic acid lets you generate more power overall... I don't know.

Engineers would rather improve their tech than improve the human.

Wrong. I'd love to improve the human, but the tech will have to be improved.

From the link maxericson provided[1], we can get numbers for their pilot with and without hand cranks, and from Andy Coggan's power profiling spreadsheet[2], we can compare those to documented numbers for competitive cyclists:

  UMD pilot, no hand cranks: ~6.5 w/kg for 60 seconds
  UMD pilot, with hand cranks: ~8 w/kg
  "Untrained" cyclist: ~6 w/kg
  "Good" cyclist (average amateur racer): ~8.2 w/kg
  "Exceptional" cyclist (domestic pro): ~10.35 w/kg
  "World class" cyclist: 11.5 w/kg

Of course, this isn't quite apples-to-apples, given the different seating posture. I would suspect that the prone position loses them some power (from experience, there's a lot of body emglish that goes on in an all out 1' effort on a bicycle), some of which (and maybe more, hard to say) may be brought back by the hand cranks.

I suspect that their reason for not hiring the cycling talent is that, for UMD, this is ultimately an educational endevour. The point isn't just to claim the prize, but to have students do it.

1 - http://www.agrc.umd.edu/gamera/gamera2/gamera2-human-power.h...

2 - http://home.trainingpeaks.com/media/69406/powerprofiling_v4.... . This is the standard reference for bike racers, and comes from Coggan's records of hundreds of cyclists.

edit: formatting

> Flying the aircraft requires a lot of energy. Gore says, “If we’re going all out, I’m pretty much drained by the end of a minute and a half

Seems like this isn't a helicopter, more a human-powered-helicopter-challenge-winning-machine.

I mean, if it can't fly for more than 90 seconds it might technically pass the requirements but is it in the spirit of the prize?

Did we add to the corpus of human knowledge from people trying to win the challenge? I'm guessing we got something for the $250,000 prize money. There are larger Kickstarter projects.

Someone should start another prize for 3 minutes.

You can probably get to 3 minutes by improving the human.

Ok, I was simply throwing out the idea of putting up the next challenge. Consider my suggestion the "straw man proposal."

http://en.wikipedia.org/wiki/Straw_man_proposal

A straw man would work well if he was strong enough.

I'd say yes. Obviously it's not a challenge easily solved and thus requires custom engineering and creative solutions. It's probably not a breakthrough of epic proportions, but it certainly educated multiple teams of young engineers to explore novel solutions, something they'll maybe have good use for later. That's how it is with challenges - they may or may not have major impact on the body of knowledge, but they all add a little at least, pushing the envelope further (think: X-Price)

I think the main issue limiting flight time is that the propulsion system uses pedaling to unwind a cord around the main shaft. When the cord is fully unwound, more pedaling does nothing. I think they do this because its lighter than using a gear transfer system.

If you are trying to win a challenge, it makes sense to optimize your solution for it. And fundamentally, it's just never going to be possible to make a human powered helicopter that is compact and can run for a whole. Hovering just requires too many RPM.

As far as I understand it, the spirit of the challenge was to demonstrate that a human powered craft could take off vertically. Sustained human powered hovering is somewhat past that.

90 seconds should be enough :-)

http://en.wikipedia.org/wiki/Wright_brothers

"On September 20, 1904, Wilbur flew the first complete circle in history by a manned heavier-than-air powered machine, covering 4,080 feet (1,244 m) in about a minute and a half."

Yes. The challenge is exactly what it purports to be, a call to build a feat of aeronautical engineering, not to build something for practical use (which is impossible short of a breakthrough in lightweight materials). This should be seen as comparable to programming challenges for programs in 64k or x number of lines.

-former HPH participant (not at U Maryland)

If they wanted something practical, they would have specified practical requirements (and then had nobody enter, because it would clearly be impossible).

If practicality were the point, lifting gasses wouldn't be prohibited.

The last time something about this was posted on HN there were a lot of comments about them taking advantage of the ground effect: http://en.wikipedia.org/wiki/Ground_effect_(aircraft)

Apparently a lot of the aircrafts flying capability has to do with its proximity to the ground. I'm sure part (if not all) of the reason why the rotars almost touch the ground.

It seems that you're certainly right, they're not creating a fully functioning flying machine, they're building a challenge winner, and that's what they set out to do.

So what? Burt Rutan didn't build a spaceship, he built a X-prize-winning-machine. Is that a reason to deride his words?

In both cases, the people who set up the competition where perfectly aware of what they would get. Also, they were smart enough to make their challenge hard, but not impossible (some would argue Sikorsky set the target too high, as it took 30+ years to see a worthy challenger, but it is impossible to foresee how hard a problem is, and Gossamer Albatross had flown the channel in 1980. Also, Hilbert surely set some harder problems)

So how useful is pedaling a wheel with your upper arms? It seems like such an awkward and weak motion. Would a push/pull action lose too much energy trying to convert it into rotational power?

I'm still surprised that they use only legs and arms.

Intuitively I'd expect some form of curling up into a squat and extending back out to be able to capture the most energy from a human body.

True, but if they managed to work this out, I don't think you want to be flying through the air using an anaerobic exercise to keep you aloft. What happens when you are exhausted after 15 squats? Making it aerobic allows for longer flight

I never considered that. So essentially once you go fully aerobic which / how many muscles you use isn't that relevant anymore.

I think they want as little variation in energy output as possible (the normal solution, a flywheel, would not be useful here. You would want to keep it light, so you would have to spin it up to insane speed, and that during flight, as doing it before would qualify as an energy storage device).

Looking at the photos, I get the impression they try to accomplish that by having the arm stroke 180 degrees out of phase with the leg stroke. I don't think that would be easy to accomplish with added back bending and stretching.

Also, I doubt they would get much more power out of extra muscles for 90 seconds. Looking at http://www.agrc.umd.edu/gamera/gamera2/gamera2-human-power.h..., you see that adding arms barely gives extra power after two minutes, presumably because their pilot does not have the anaerobic capacity.

Finally and maybe most importantly, this may not be a matter of getting maximal pilot power output. It may be a matter of minimizing jerk at a goven power output instead. The smoother the ride that the pilot manages to make, the lighter they can make the machine.

You mean like rowing? If so, then I think you'd be surprised. Most athletes who compete in both rowing and cycling report that they see higher wattage numbers on the bike than the rowing ergometer. Biomechanics can be funny.

Wow. I've never enjoyed being proven wrong this much. Never expected that! The higher wattage numbers that is ...

Why don't they add another pilot? 2x the power for less than double the weight.

Or the logical conclusion: 20 pilots, forming the world's first flying galley!

The free rider problem would probably come in to play and make that impractical. But with two, both pilots must pedal or the craft would experience a gentle decent to the ground.

Given the span of the rotors and distance from the ground, it looks as if they have designed it specifically to fly in ground effect, which puts a pretty low ceiling on it.

It also means they have more of a ground effect craft than a helicopter. We'll call it a RIG (Rotor in Ground-effect) as opposed to WIG craft as we did for the fixed wing Russian varriant. http://www.youtube.com/watch?v=rUTWWsh6iGA

A story about the team's efforts from back in Oct last year:

http://www.npr.org/2012/10/14/160670295/flight-club-human-po...

The problem they had then was keeping the helicopter from drifting outside the 10 meter box. I don't see what they've done since then to help with that problem.

Hmm. Looking at the cyclist, his legs aren't fully extended on each down-stroke (akin to having the seat too low on your bicycle). They could get a lot more power out of each stroke if the cyclist could extend her or his legs fully.

Holy bejesus the <strike>lined diagonal background</strike>yellow sidebar contrast makes the text pulsate when I read... poor design decision. Going to have to tell someone about that.

Ignorant here, handle with care.

Is it possible to use pedaling force in a turbine? I'd like to try different approaches just for curiosity.

Technically the definition of a turbine means something powered by a working fluid or gas. So it's akin to asking 'could we have a human powered windmill?' By definition you can't.

Assuming you mean something along the lines of a small shrouded propeller. There are aerodynamics at work here that involve trade-offs. Generally larger slower props are more efficient at low speeds.

Flywheel? It could be a flywheel you spend all week pedaling up to speed with human power.

Reply on news.ycombinator.com