## Help Design a Human-Powered Helicopter

 Quote by dr dodge "4.1.4 No devices for storing energy either for takeoff or for use in flight shall be permitted. Rotating aerodynamic components, such as rotor blades, used for lift and/or control are exempt from consideration as energy storing devices" couldn't you use multiple staged rotors with a gearing so it took maybe an hour to get everything rotating in a "no lift mode" then after critical rotation is reached, pull on the stick to get the pitch needed. during "run up" with a rotor not fighting for lift, I would think rotational velocity could be brought up high enough that inertia would then help keep it rotating with less immediate power needed? just a little sprinkle to add to the current brainstorm dr
Why on earth would you do such a thing? Think of it this way, what do you think will happen to the stresses at the hub when you suddenly dump the collective? The change in AoA will give a large impulsive pitching moment - bye bye blades.

 Quote by Mech_Engineer You couldn't have a giant duct, because the rules state the lowest part of the "helicopter" has to attain the maximum height. The bottom portion of the "ducts" would therefore have to reach the height. I doubt you could justify such a system weight-wise anyway.
The fence or duct is attached to the ground, not the helicopter.

 Quote by Phrak The fence or duct is attached to the ground, not the helicopter.
This is outside the spirit of the rules, and would not be allowed, for obvious reasons.

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 Quote by Phrak Didn't you like my last post Fred? This thread is about a contest with no practical application, isn't it?
I can't really comment on it basically because I'm not sure where you are going with it. The reason ground effect exists is because of the blockage of reingested vortices at the rotor tips. It's either blocking that reingestion or it's not. I doubt there is any exponential decay of ground effect, or however you want to put it.

[EDIT] OK. So I did some looking after writing that, and found some references that disprove what I wrote. Seddon shows a theoretical expression (making a few major assumptions) that seems to work well in most cases:

$$\left[\frac{T}{T_\inf}\right] = \frac{1}{1-\frac{R}{4Z}^2}$$

This is supported by Figure 7 from Knight and Hefner:

http://naca.central.cranfield.ac.uk/...aca-tn-835.pdf

I also found this graphic which I am kicking myself because I have seen this before (a longggggg time ago)

So it's not exponential, but it does decrease with increasing Z/R ratio. I stand humbly corrected.

 Quote by Cyrus This is outside the spirit of the rules, and would not be allowed, for obvious reasons.
So it's within the rules, but outside some unstated rules?

To continue with this unspirited concept, it occurs to me that it might be equally beneficial to have 'ceiling' effect to double things up. I'm not sure if this makes sense.

Edit: I've re-read the rules, and the spirit erules to eliminate hovercraft and other stuff outside the intended box). But to be fair, all these attempts would have exploited ground effect.

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 Quote by Phrak But to be fair, all these attempts would have exploited ground effect.
The only way one of these things can get off the ground is to exploit the ground effect. Too much power will be required to fly outside the ground effect, that's why these things barely make it a foot or two off the ground with 100ft rotor diameters.

 Quote by Mech_Engineer The only way one of these things can get off the ground is to exploit the ground effect. Too much power will be required to fly outside the ground effect, that's why these things barely make it a foot or two off the ground with 100ft rotor diameters.
Additionally, the DaVinci III (with 100ft rotors) did not hover for very long because of stability. So you cannot say it was due to power issues. The Yuri had to stop its flight because it ran out of space due to drift. Again, a stability issue, not power. So sweeping statements about the power being too high are not strictly valid.

 "Why on earth would you do such a thing? Think of it this way, what do you think will happen to the stresses at the hub when you suddenly dump the collective?" the main reason is that the total accumulated work over time is "banked" in an hour or two of "run up" in order to have momentum help to keep the rotors going with the available power from the pilot. Isn't the changing angle of attack what causes a conventional "rotor'd craft" to fly? If so, why in this application it assembly would self destruct? dr

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 Quote by Cyrus Additionally, the DaVinci III (with 100ft rotors) did not hover for very long because of stability. So you cannot say it was due to power issues. The Yuri had to stop its flight because it ran out of space due to drift. Again, a stability issue, not power. So sweeping statements about the power being too high are not strictly valid.
Stability or no, the guy is pedaling like a maniac and barely made it a foot off the ground. If power were not a major issue, the craft would have been able to take off and consistently gain altitude with time. Instead, it seems to be they lift off and stabilize in altitude at a very low height.

 Quote by Mech_Engineer Stability or no, the guy is pedaling like a maniac and barely made it a foot off the ground. If power were not a major issue, the craft would have been able to take off and consistently gain altitude with time. Instead, it seems to be they lift off and stabilize in altitude at a very low height.
But they don't stabilize at a low height. The blades were so long that any small angular deflection results in a tip strike. My point is that they did not have the stability to try and get to any significant height.

 Quote by dr dodge the main reason is that the total accumulated work over time is "banked" in an hour or two of "run up" in order to have momentum help to keep the rotors going with the available power from the pilot.
This is fundamentally wrong if you look at the power output curve of a person and the power demands of the aircraft. You simply do not want to use such a method.

 Isn't the changing angle of attack what causes a conventional "rotor'd craft" to fly? If so, why in this application it assembly would self destruct? dr
My understanding of what you have described is to spin up the rotors for an hour (and waste the pilots energy for no reason with a bunch of gearing that adds unnecessary weight) and suddenly change the collective on the blades. You would have to change the AoA of the blades quickly, otherwise they will slow back down. So you now need a larger, heavier blade hub to absorb the large transient stresses. This is idea gets worse and worse any way you slice it.

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 Quote by Cyrus My understanding of what you have described is to spin up the rotors for an hour (and waste the pilots energy for no reason with a bunch of gearing that adds unnecessary weight) and suddenly change the collective on the blades. You would have to change the AoA of the blades quickly, otherwise they will slow back down. So you now need a larger, heavier blade hub to absorb the large transient stresses. This is idea gets worse and worse any way you slice it.
Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules.

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 Quote by Phrak So it's within the rules, but outside some unstated rules?
Phrak, please drop this line of discussion, as it is distracting from the purpose of the thread. You're not the one who gets to interpret the rules of the contest, the people running it are. So it isn't useful to try an weasel around them for the purpose of discussing it in this forum, when it is obvious that such weaseling wouldn't fly with the organizers of the contest.

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 Quote by mheslep Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules.
On that point, I'm not so sure the judges would agree. Yes, he's essentially saying to use the rotors as flywheels, but the judges may consider that acceptible. The rules certainly imply it where they give a specific exemption from that rule for rotors.

 Quote by mheslep Not only that, but Dodge is essentially suggesting an energy storage scheme, in this case storing energy in the blades angular momentum, which is against the rules.
What he said is OK, it's not energy storage because the pilot put in his own energy to spin up the rotors and then went on with the flight. However, it's a useless endeavour.

What you could not do, is spin them up, and have someone else jump in and then take off. Or, store energy in a spring, and then come back an hour later and try to fly after you are refreshed, along with the help of the spring.

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 Quote by Cyrus What he said is OK, it's not energy storage because the pilot put in his own energy to spin up the rotors and then went on with the flight. However, it's a useless endeavour. What you could not do, is spin them up, and have someone else jump in and then take off. Or, store energy in a spring, and then come back an hour later and try to fly after you are refreshed, along with the help of the spring.
You need not switch out the human. If they allow energy storage as long as it is 'the same continuous operator', then someone could leisurely store up 100 watt-hours in an hour of work/pedalling and then release it all via some mechanism (e.g. electric motor) at the rate of 6kw (8HP) for one minute of flight, collect \$20k, thank you. But this is moot, storing energy is not the goal of this exercise.

 Quote by FredGarvin I can't really comment on it basically because I'm not sure where you are going with it. The reason ground effect exists is because of the blockage of reingested vortices at the rotor tips. It's either blocking that reingestion or it's not. I doubt there is any exponential decay of ground effect, or however you want to put it. [EDIT] OK. So I did some looking after writing that, and found some references that disprove what I wrote. Seddon shows a theoretical expression (making a few major assumptions) that seems to work well in most cases: $$\left[\frac{T}{T_\inf}\right] = \frac{1}{1-\frac{R}{4Z}^2}$$ This is supported by Figure 7 from Knight and Hefner: http://naca.central.cranfield.ac.uk/...aca-tn-835.pdf I also found this graphic which I am kicking myself because I have seen this before (a longggggg time ago) So it's not exponential, but it does decrease with increasing Z/R ratio. I stand humbly corrected.
Thanks Fred, that would help a great deal, but I'm afraid I can't figure out the variables.