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rough sketch of the aircraft's cross-section

I'm thinking of constructing a flying machine in the comic story I'm working on. Since I'm not an aviation expert, I'll try my best to describe this aircraft and you guys can tell me if this machine is plausible.

The aircraft looks somewhat like a glider made out of lightweight wood (akin to the wooden hull of a boat), where the wings meet at the center, and there are two adjacent cockpits, one within each wing. Beside the cockpits, on the underside of the wings, there are propellers.

The idea is the pilots can get in the cockpits and constantly drive an internal lever that sets the propellers in motion. I'm assuming the wingspan will have to be long, but I'm not sure how long. I'm also assuming that the lever mechanism amplifies the work put in to pumping it, so it doesn't take too much energy to make the propellers whir. Furthermore, this aircraft would probably be pushed off a high altitude location, like a cliff, in order for it to take flight.

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    $\begingroup$ You're essentially describing a two cockpit version of the Daedalus aircraft. I see no reason why it wouldn't work. $\endgroup$ – Samuel Apr 30 '18 at 20:39
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    $\begingroup$ Those propellers are far too small to make any difference in how that thing flies, at any reasonable rotation speed. You'd probably need to make them something like 3-4 times that size for them to have any appreciable impact. You might want to do an image search for "touring motor glider", and then consider that those typically use internal combustion engines which pack a lot more punch than any human can hope to achieve for more than a very brief moment. On real-life aircraft, propellers are typically sized such that the tips are driven at just below (~80-90% or so of) the speed of sound. $\endgroup$ – a CVn Apr 30 '18 at 21:04
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    $\begingroup$ "I also assuming that the lever mechanism amplifies the work put in to pumping it, so it doesn't take too much energy to make the propellers whir." TANSTAAFL. Whether it's a "few" hard pushes, or lots of easy pushes, you're still going to expend the same amount of energy. $\endgroup$ – RonJohn Apr 30 '18 at 21:05
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    $\begingroup$ To @RonJohn's comment, your wording of "amplifying work" would make it so that your vehicle can stay aloft without overexerting the person's physical endurance. However, no known device can amplify work without an exernal power source (it would violate the conservation of energy). If you are using the informal concept of "work," which is more akin to the idea of "effort," then RonJohn's TANSTAAFL issue applies. $\endgroup$ – Cort Ammon Apr 30 '18 at 23:28
  • $\begingroup$ @RonJohn what is TANSTAAFL $\endgroup$ – bendl May 1 '18 at 0:16
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Human Powered Aircraft have been a thing for a while. Using a lever to provide the power is maybe not the best solution, just because putting out that kind of power for an extended period is a job better left to the legs, and it leaves no free hands for, say, piloting the aircraft.

Assuming that your pilots are strong enough to keep this in the air with their arms, then they're going to need a way to steer. Maybe they can do this with their legs? In any case - human powered aircraft are definitely possible, and without any extra information you can say that this design could work. It doesn't sound like the best possible solution though.

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  • $\begingroup$ what if they can use the lever to get the propeller going, but they can also rotate the propellers with this same lever, hence enabling the aircraft to turn? $\endgroup$ – ani ben Apr 30 '18 at 20:45
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    $\begingroup$ Rotating the propellers seems like a very bad method of controlling an aircraft. Instead of doing what you expect, you'll probably end up losing lift and stalling (HPAs already run on the minimum possible flight speed, as humans aren't that good at pedaling). In any case, if you try to put the controls on a lever that needs to be constantly cranked, you'll probably end up crashing. I'd stick to controlling with the feet if you have to crank this lever. $\endgroup$ – bendl Apr 30 '18 at 20:49
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    $\begingroup$ Worth noting: the human powered aircraft I have heard of all pushed the limits of endurance. It was truly difficult for an athlete to keep them in the air for long periods of time. $\endgroup$ – Cort Ammon Apr 30 '18 at 23:29
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Your biggest issue is the mechanism to convert the mechanical energy of pulling the lever into the rotational motion of the propeller. This isn't impossible, but it is rather inefficient.

At the beginning of the pedal stroke, the foot is stopped but the output shaft is moving at full speed. It takes a portion of the pedal stroke for the pedals to catch up to the output shaft and during this catch-up phase no force is being produce and, as a result, no power is produced. Both the Dragonfly and the Harris Vertical incorporated cams to gear up the pedal stroke in the beginning to allow the pedal speed to more quickly match the speed of the output shaft. However the cam must be designed for a specific gear ratio. So on the Harris Vertical, the cam will only be effective for around one gear selection.

http://lefthandedcyclist.blogspot.ca/2014/07/graeme-obrees-beastie-lure-of-linear.html

enter image description here

The Alenax Trans-bar bicycle was commercially produced in the 1980’s.

There is an entire blog article here outlining all kinds of variations of linear to rotary drives, one constant when looking at the descriptions and illustrations is how complex most of them are.

enter image description here

Try working out the mechanical system on this bike....

This brings up the second issue, mechanical advantage. Your pulling on levers (or even peddling on a conventional bicycle setup) is unlikely to produce the proper torque and rotational velocity for the propellers directly. You will need a gear train or something more exotic to translate the movement you make into the proper rotation for the propellers. This is generally done with a gear train or transmission, and it too will add weight to your airplane, making it more difficult for the human power plants to actually propel it through the air.

Looking at real human powered aircraft, you will see the two common factors are extreme lightness and fairly extreme wingspans. This is to maximize the rather tiny amount of power a human being can actually produce, and allow for control flight (underpowered aircraft are generally good at uncontrolled flight, and usually straight into the ground).

enter image description here

A typical human powered aircraft

So the short answer is, your design is rather implausible, and would need considerable rethinking to become an actual, flyable airplane.

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You have to rethink some of your assumptions.

If you wish to have an aircraft powered by a person moving levers, it has been done before. Some examples I can think of right now:

  • In Kiki's delivery service, there is a boy who builds a flying bike.
  • In Warcraft II (and III as well, if I remember right) gnomes pilot flying bikes.
  • One of the villains in the old Care Bears cartoon also had a flying bike.

This is very unrealistic in real life, but it works quite well for comic books realism.

The problem with pedaling for flight is that the amount of energy required to give you lift cannot be reduced by any gearing system - and humans cannot reallistically output enough to power any flying craft on Earth. This does not stop us from jumping from high places strapped to hang gliders, parasails, or even towing gliding planes and then releasing them midair. These have limited autonomy compared to powered planes, and you need to start in high altitudes... But they can go really far once they're on their own.

As for the minimum wing area, materials and other thoughts for inspiration, you may be interested in this question:

Minimum tech level needed for a flying vehicle

P.s.: After your edit, I couldn't help but think of Nausicaa's glider:

Nausicaa of the Valley of the Wind

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  • $\begingroup$ reality-check has been added, but that doesn't really change anything because OP specifically states that this is about a "comic story". Note the first sentence in the reality-check tag wiki excerpt; Asks if a given concept is realistic in a given context. (my emphasis) $\endgroup$ – a CVn Apr 30 '18 at 20:50
  • $\begingroup$ This comic story is going to be science fiction, so I do want the machine it to be practical. Note that in kiki's delivery service, there was only one propeller and the wingspan wasn't that big - that's why I was wondering if my aircraft would operate any better. $\endgroup$ – ani ben Apr 30 '18 at 20:52
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    $\begingroup$ Yup, Nausicaa's glider has inspired the design somewhat. $\endgroup$ – ani ben Apr 30 '18 at 21:05
  • $\begingroup$ @MichaelKjörling thanks, I had forgot about that. I edited the part about realism. $\endgroup$ – Renan Apr 30 '18 at 21:43

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