Help Design a Human-Powered Helicopter

jeff kimathi

when you talk of all this does it end up to energy storing devices which are illegal by the rules.....according to me if the fixed wing was easily achieved why don't we just make these rotors just like a wing but not fixed i.e by incorporating an extended flap like trailing edge n with a built in pitch angle n make them coaxial blade settings this saves on weight n with efficient driving mechanism then we are definitely airborne rather than complicated mechanisms with more weight

Cyrus

First and foremost, the fixed wing flight was not "easily achieved" by any stretch. But to your second comment, I fail to see the point of incorporating trailing edge flaps. You will have to justify this design, because doesn't make sense for this application. Moving on to a coaxial design, this will indeed save structural weight; however, and more importantly, it will be unstable (if you don't believe me, google the coaxial designs to see the common problem that plagued all of them). "then we are definitely airborne" ......sure, whatever you say . Honestly though, stability of a coaxial is a poor, and the actuation lag time constants are high. In short, you save weight but gain significant stability and control problems.

dr dodge

if the design of the component does nothing but store energy, and nothing more, then it does IMHO violate the rules. I am not saying that, what I am saying is the flight has specific time goals, but if it takes 2 men (or women) 4 hours to bring the whole machine up to speed, then it is not an energy storage device. the idea is that you can only apply x amount of work/time so if you can not change the power you (as a person) can put out, then the only way to get the power you need is more time. because the counter rotating rotors are critical to the aircraft, and do the lifting once proper rotational speed is reached, they are not storing the energy, it is being used. The counter rotating rotors will add a natural "gyro stability" by not needing to offset the rotation with a tail rotor. You control the amount of lift by the amount of power you split between the two, but both are doing the work. simpler example: 2 dc electric motors connected together by their leads together. if you spin one, the other will turn. no energy storage. add a battery in between, charge it with one motor, and run the other. energy storage

dr

Cyrus

I think you should reconsider this statement in light of the extremely low rotor rpm. There is no such stability, as I stated previously.

dr dodge

????
a little less cryptic response would sure help
action-reaction works the same regardless of rpm

dr

Cyrus

The pole-zero structure of the open loop A stability matrix of the coaxial human powered helicopter at low RPM has right half plane poles. It is unstable, as was found out by the CalPoly HPH team, and the associated NASA TN.

dr dodge

my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's

dr

mheslep

Several modern aircraft frames are inherently unstable, but made stable with computer controlled fly-by-wire in the loop. Is that a possibility here?

Cyrus

Because they spin much, much faster. When your HPH rotors are spinning 12-15 rpm, good luck getting gyroscopic anything.

Cyrus

They tried it, but to no avail. The problem is that things happen so slow by the time you move your control surface, the blade has already rotated significantly before the blades move in response. So you are always 'behind the power curve' - so to speak.

Coaxials are the best in terms of reduced structural weight, but they are like trying to balance an upside down broom by its handle. If you can figure out stability, you will have a significantly lighter vehicle. Or you can go the quad rotor route as the Japanese did, but now you have huge structural weights. There is no easy answer. Do you want to try to make really light weight structures (that's not easy), or can you come up with a clever control scheme (that's not easy either)? Either choice has significant challenges.

Cyrus

So I got back home and found that NASA-TN. It's not on a coaxial rotor, but a single reaction drive rotor. However, stability of a coaxial rotor will still be a problem due to the excessively low rotor RPMs.


References
[1]NASA TM-101029

IcedEcliptic

I am impressed by the feat of engineering, but god, what of the fail-safe? You get off the ground, and presumably your "out" is a parachute, but there is a large range in which it will not deploy in time. This seems... odd.

I suppose you could spend a few hours spinning up a flywheel, but that is dangerous too if you're sitting near it. I would much rather consider dirigibles for human powered flight.

Cyrus

It's not legal to have flywheels, or to spin up rotors before hand, as per the rules. As for a parachute, why would you need one at 10 feet (if you run the numbers, you'll find that a person can't fly any higher than that)? There is no danger in those spinning rotors, because they max at around 20-25 rpm.

IcedEcliptic

Falling from 10 feet can be unpleasant, or lethal depending on your landing. My point is that a parachute requires a couple thousand feet to fully deploy, but you can shatter wrists, ankles, or your neck from 10 feet. The rotors I understand play no role in the danger. I did not remember the flywheel portion.

I'm not saying that this is some terrible risk, but falling 10 feet and not being hurt requires luck, or preparation and control in the fall. I just don't see the point of removing energy storage in some form, even though I know the rules are the rules.

Cyrus

Sure, falling from 10 feet would not be pleasant: but no risk no reward . As for the energy storage, that's because the rules are so that one designs a good vehicle. Storing energy would be a cop-out.

IcedEcliptic

True, people take greater risks for lesser ends. Thanks for clarifying things!

jeff kimathi

that exactly my question to the guy who dismissed my idea of coaxial rotors...but looking at stability part and the weight saved plus the efficiency of having two sets of blades which increases the solidity i think coaxial would save tha day since by the rules there is provision for not more than two guys who would help support the machine...