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Help Design a Human-Powered Helicopter

by jzvonek
Tags: design, helicopter, humanpowered
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mheslep
#55
Nov29-09, 05:47 PM
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Quote Quote by FredGarvin View Post
I'll absolutely dismiss it. The power that can be provided by a good cyclist is somewhere in the area of 300 W. Not only will you be hard pressed to find a very light person that can put out that kind of continuous power, ...
It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.
Cyrus
#56
Nov29-09, 10:22 PM
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Quote Quote by mheslep View Post
It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.
Damn, if they can do 600W for 6 mins thats extremely impressive.
mheslep
#57
Nov30-09, 03:19 PM
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Quote Quote by Cyrus View Post
Damn, if they can do 600W for 6 mins thats extremely impressive.
To my mind, olympic rowers in these time frames (6 minutes), out perform any other athlete type.
The athletes are frequently tested on ergometers (flywheel machines). The world record a few years ago was 5 min 36 s. over 2000 meters. That's a continuous power output of 590W, i.e. work done on the machine. Over 500M (1m 16s) these guys can exceed 1HP. I've tested at the 2k distance a hundred times in competition and came in, ehem, somewhat lower. The typical top 10 school college rower (male) will rate at about 430W.

BTW, the do-it-yourself helo would have to hold that record holder's 97kg, 2m to get that power:
FredGarvin
#58
Nov30-09, 03:33 PM
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Quote Quote by mheslep View Post
It's not very continuous, but olympic calibre athletes can do work at 600W for 6 minutes. Such an athlete might helo across a hefty lake then, never the channel.
Yeah. I wouldn't use that as a data point. Those are definitely outliers from the norm.
mheslep
#59
Nov30-09, 03:51 PM
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Quote Quote by FredGarvin View Post
Those are definitely outliers from the norm.
So is this idea of a human powered helo.
Mech_Engineer
#60
Nov30-09, 06:09 PM
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The point is that a helicopter like is being proposed needs at least 1hp (745W) to fly (I'm still convinced it would be more, but flying within the ground effect does help). The problem is, every pound kills you, and "successful" designs like the Davinci III only had an available payload of 59kg (130lb) for the pilot. Even powerful professional athletes which are significatly heavier cannot sustain that kind of output for very long.
Cyrus
#61
Nov30-09, 06:55 PM
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Quote Quote by Mech_Engineer View Post
The point is that a helicopter like is being proposed needs at least 1hp (745W) to fly (I'm still convinced it would be more, but flying within the ground effect does help).
I just showed you a calculation concerning the power.


The problem is, every pound kills you, and "successful" designs like the Davinci III only had an available payload of 59kg (130lb) for the pilot. Even powerful professional athletes which are significatly heavier cannot sustain that kind of output for very long.
That's right exactly right, and the power goes with the weight^(3/2).
Phrak
#62
Nov30-09, 10:26 PM
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Does anyone know how high Allen flew crossing the English channel?

My second question would be, what is ground effect as a function of wingspan?

Edit: I've been searching for Bryan Allen's estimated power output and weight while crossing the channel and haven't found them.
FredGarvin
#63
Dec1-09, 06:47 AM
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Ground effect is essentially any height below one rotor diameter.

The aircraft was powered using pedals to drive a large two-bladed propeller. Piloted by amateur cyclist Bryan Allen, it completed the 35.8 km (22.2 mi) crossing in 2 hours and 49 minutes, achieving a top speed of 29 km/h (18 mph) and an average altitude of 1.5 metres (5 feet).

The empty mass of the structure was only 32 kg (71 lb), although the gross mass for the Channel flight was almost 100 kg (220 lb). To maintain the craft in the air it was designed with very long tapering wings (high aspect ratio), like those of a glider, allowing the flight to be undertaken with a minimum of power. In still air the required power was of the order of 0.4 horsepower (300 W), though even mild turbulence made this figure rise rapidly.
Phrak
#64
Dec1-09, 10:36 PM
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That's nearly full ground effect. The root of the wing was maybe 10 feet and the tips another 10 feet or so. This compares to a span of 100 feet.

I would expect that ground effect is exponential decaying with height.

I think I should discover the difference in total ground effect to none. That is "What is the maximum percent gain in lift due to ground effect?"
Phrak
#65
Dec2-09, 09:48 PM
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Didn't you like my last post Fred? This thread is about a contest with no practical application, isn't it?
Phrak
#66
Dec2-09, 09:54 PM
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Fred, on a more serious note, the contents of prize state nothing limiting supporting equipment. Ground effect could be sustained throughout the required excursion to 10 feet by ducting the blades with a circular fence.

How are you at hovercraft ducted fans?
Mech_Engineer
#67
Dec2-09, 11:39 PM
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Quote Quote by Phrak View Post
Fred, on a more serious note, the contents of prize state nothing limiting supporting equipment. Ground effect could be sustained throughout the required excursion to 10 feet by ducting the blades with a circular fence.

How are you at hovercraft ducted fans?
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.
dr dodge
#68
Dec3-09, 10:42 AM
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"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
Cyrus
#69
Dec3-09, 03:21 PM
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Quote Quote by dr dodge View Post
"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.
Phrak
#70
Dec3-09, 06:49 PM
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Quote Quote by Mech_Engineer View Post
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.
Cyrus
#71
Dec3-09, 07:15 PM
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Quote Quote by Phrak View Post
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.
FredGarvin
#72
Dec3-09, 09:51 PM
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Quote Quote by Phrak View Post
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:

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

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.


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