I'm going to have to side with the physicists who have been working on human-powered for nearly a decade and say this is doomed to failure.
The amount of data that they have seemingly overlooked is enormous. It's like someone trying to reinvent the wheel and starting out with a square. The "discoveries" they've made could have been learned through a simple Google search and saved them money to be used on a more efficient design.
Well, of course this design runs contrary to currently accepted aerodynamic principals! Very few 'innovative' designs don't.
Rob, you answered your own question. The co-axial driven rotor eliminate the need for a tail rotor by counteracting the inherent torque rotation of the entire vehicle.
Dennis, you are assuming that this design team hasn't 'Googled' the concept. The nature of the competition limits the scope of information a team will admit to have in its possession.
This reminds me of those crazy days when men dreamed of flying through the air, over 100 years ago.
At $19,700 short of their goal with seven days to go, I think it's a pretty safe bet they won't get the money. About as safe a bet that they'll never get off the ground.
So what would the effect of coaxial counter balance rotors be? I was waiting to see that on the vid. looks pretty cool tho.
Snicker, polite snort SMH
When Bell Helicopter modified the 212 model into the 412 the important change was that the replaced the two bladed main rotor with a four bladed main rotor, this gives about a 20 knot speed advantage to the 412. However the four bladed rotor's diameter is only two feet less than the two bladed rotor on the 212. Obviously most of the lift is generated at the blade tips. Therefor it appears to me that the rotor should be designed to minimize drag and weight near the center and maximize lift at the outer few feet of rotor blade.
A conceptual improvement is possible. The tip vortices spiral inward towards the shaft, to some extent. Those from the top rotor will therefore interfere with the flow at the tips of the bottom rotor thus increasing the drag and decreasing the lift. To prevent this reduce the diameter of the bottom rotor and, to keep the same torque at the same tip speed, increase the number of blades in the bottom rotor to three of four.
@Noel Frothingham- Silly me, of course you're right. There're just pretending to not know about basic concepts of aerodynamics to throw the other competitors off! When no one expects it they'll show up with the real design and win the contest! I should have known they couldn't be that uninformed.
Noel, what I meant was 2 single blades counter balanced running co axial .
Human powered helicopters are urgently needed by humanity. Most urban cycleways are becoming dangerously clogged with speeding lycra-clad commuters.
They refer to possible recreational uses like hang gliding ... I for one would prefer the risks of hang gliding to pulling a hamstring at a few hundred feet in one of these! If you lay still in a hang glider without chasing thermal updrafts, you just slowly sink along your glide path, if you stop pedalling in a helicopter, your reaching the ground, at the very least, is going to be a fair bit faster and probably of a more vertical nature.
Launch it off a cliff, and you'll fly alongside that hang-glider, without even touching the pedals - same as any other gyrocopter can.
My paramotor produces 90lbs of static thrust, and it launches me no problem off flat ground. These guys are producing almost that same amount of thrust, without having to carry that extra motor and fuel.
The only thing between them and the prize, is getting the aerodynamics right. If a 160-square-foot paraglider and 120cm prop pushing 90lbs flies, all they need to do is figure out the correct shape of their lifting surfaces, and so can they.
Adjustments are nothing more than dividing up the power. Without enough power - it will never work. Even the strongest of men have never had enough power. Sorry guys!
Not off the ground in 2 years? Maybe tubercles would help.
Bruce H. Anderson
Why is no one considering the power source? The seated position is very efficient in bicycles, however not when the intent is solely power production. A more vertical position would allow use of the cyclists weight in producing power and the angle of the leg during the power stroke is most efficient with less knee bend.
Compressed air jets at the the tips of the rotors. what would be needed is a efficient Air compressor and light storage tank.
this would allow pilot to rest during flight without the nasty side effects.
Pretty basic stuff. If they tried to make the blades more efficient, like a whale's fin, then it'd work better. A whale's fin isn't just straight like the blade shown, but with points on the leading edge that help it cut through water better to reduce drag. This feature can work in air applications as well.
Sikorsky correctly calculated that no human powered vertical take-off and landing vehicle could overcome the lift burden unless materials and muscle mass weighed much less than they do.
It seems that the only way to achieve this somewhat silly goal is to achieve relatively high RPM and feather the otherwise thin air-slicing lift surfaces. If there were also balanced & weighted tips, the flywheel effect might help delay the inevitable descent...
Great. That's all we need now. Some people pedaling along, high above our cities. I see trouble in the making ... What about leg cramps!
These two seem to have this stuff covered UNLIIKE EVERY OTHER UNIVERSITY TEAM.
Jack Norris book
Betz Goldstein Theodorsen BGT
I understand only a small amount of the idea.
My takeaway from Norris (may be wrong) - end of blade goes to a point for drag reduction.
Charles Morgan Olmsted (Jan. 19, 1881 – 1948 ) was an American aeronautical engineer.
... Charles Olmsted then formed the CMO Physical Laboratory and continued to manufacture and sell the
ultra-efficient propellers on his own for another seven years.
Article link On C.M. Olmsted Patent number 1019078 of March 5, 1912:
click view or download PDF upper right of page.
My takeaway from Olmsted - equal thrust from all sections along the blade.
See the lovely propellers on the Horten Ho 5. (5a~5c)
I can't recall the google hit that disclosed who designed the propeller, it was an interview of one of the Horten living in Argentina, The prop was not attributed to Olmsted & and it was not the Horten's idea, I did
find this:"The propeller manufacturer Peter Kempel produced the propellers from Lignofol (beech wood impregnated with synthetic resin)." and "Peter Kumpel, who also made the "Habicht" propeller"
I too would like to see some whale turbicles on a prop, looks sexy.
http://en.wikipedia.org/wiki/Tubercle_(anatomy) "... they are also found on the leading edge of Humpback Whale's flippers, improving fluid flow over the flipper's surface."
Maybe some winglets at the end, (winglets idea came about by investigation of the spread feathers at the end of soaring birds wings, the end result in drag reduction is the same as if the wing were longer, but it's not.
Oops, per wiki they already do winglets on propellers - on existing aircraft.
A propeller is a rotating wing, how about a propeller with leading edge slats,
Maybe some vortex generators. to keep the flow stuck to the wing.
Maybe some golfball dimples?
Ok, so dimples too tough to do, use burlap for the covering fabric.
Maybe a biplane propeller like on this powered submarine built by some Italian guy in Barcellona Spain the Ictenio II of around 1860 or so.
Well water is 1000 times thiker than air, so Reynolds number factor would need to be applied.
It can be worse. The nautical crowd, may be way the ahead of the aeronautical crowd, maybe they got more time, since they have a lesser burden by two whole syllables:
Translate some of the jibber-jabber through that Reynolds Number magic
My personal dumb-down of the Reynolds Number is that air to tiny things is de-facto a lot thicker than the same thickness air is to large things, and attibutes to the fact that bumblebee flight does not defy the laws of physics.
Copy paste portion of my post Gamerea 1 - Things to consider:
Ergonomics & drive - Add arm & back muscles to leg muscles
Which brings to mind something about helicopters, forward flight dynamics are different, and require far less energy than hovering helicopter flight dynamics, the rotor "disk" functions as one giant wing in forward flight.
http://en.wikipedia.org/wiki/Vortex_ring (hovering flight realy sucks)
And while I'm on a roll, how about some holes or fipples in the wing so it will "whistle" opposite in motion to the vortices that would otherwise be shedded, so thier is no turbulence.
It could then be called the hovering Ocarina.
Or maybe design to excite flutter, then you could have a ornithopter-helicopter, might sound like a giant kazoo, too bad if it works.
Gotta go, white coats coming, not lab coat white coats either, it's the attendants, again.
Whew, I think they should have structured their pledge amounts differently:
4 Decals $25, naw, one decal & paper (not brass) airfoil - $10.
48 page book -$100, nope. How about $50 post paid, $80.autographed, $25. ebook on amazon
$500 ~ $1000 - Video of you peddling their existing version for 10 ~ 20 minutes.
$10,000 or more - One of them marries your X-wife, and you pay them 5% of the alimony you were paying her.
I love thier project, I'd like to see them win.
Doh, I had'nt read:
"Direction of the current model will be controlled by shifting the weight of pilot, but plans are afoot for a cyclic control system that should offer more precision."
You all need to take a long hard look at how the existing helicopters with counter rotating rotors are controlled, tip spoilers for yaw is the big item you need to address, If you go with something like the Snek bicycle instead of regular peddle power, maybe have some twisted elastic with a clutch that locks things up so it can be loaded by some rowing (or peddling, also not so even), then keep winding one end while the other end unwinds to power the rotors. Hopefully the rules don't disallow some small battery powered widgets to manage stability, or lessen control difficulty. The russians were way bigger on counter rotating rotors than the west, as you'll find googling.
From the video it is apparent that the pedals are not far enough out for the rider - his knees have significant bend in them throughout. This greatly decreases efficiency (try riding your bike with the seat too low).
Hey my friends,
Your results were misleading because the test with high angle of attack was conducted with only a fraction of the power used in the second "zero-angle" test. Horse power (and human power) is a result of torque times RPM. You have to change the gear ratios and redo the bench-mark.
Another idea came to mind from 1987 TV news article on America's Cup Yacht race, or Chicken McRiblets, not sure which:
Drag Reductions in Fluid Flows - Techniques for friction control
"... The use of streamwise microgrooves, or riblets, for turbulent skin friction reduction originated at NASA Langley for aerodynamic applications. ... providing a decrease in skin friction of about 8% ... " (... 6.8% max for marine...)
The fact that despite their extreme aspect ratio helicopter blades manage to support the weight of the whole craft at the rotor's center is due to the centrifugal pulling force generated at typically high rotor speeds.
So the problem with Kenneth's design (like with all other competitors') is one of too low rotational speed with consequent cantilever construction, i.e. weight penalty, i.e. insufficient blade aspect ratio, i.e. poor aerodynamic yield.
Hence, without increasing rotor diameter, blades with much higher aspect ratio would allow for substantially higher tip speed yielding in turn substantially higher lift -- though along with a collateral problem arising from the higher loss factor of a multiplication gear needed to spin the blades.
However, blade tip speed would thus come way closer to the air speed of modern gliders at their best sinking rate -- which might turn out a distinct advantage over state-of-the-art human powered fixed and rotary-wing aircraft bound to fly at very low speeds because of their huge and relatively low aspect-ratio cantilever airfoils.
What I don't understand is why all projects heading for the Sikorsky prize are managed by students -- as if the best of inventions had always come from students, and not from experienced self-taught senior experts...
IMHO, the most promising perspective is to be seen in the cycloidal rotor concept (no cantilever blades, no wing-tip vortices, evenly distributed air speed along the blades) -- which leads me to just another wondering*: why are so many student teams working on reduced scale cycloidal rotors, and no one on a human powered one?
Old-age pensioner's wondering...
"What I don't understand is why all projects heading for the Sikorsky prize are managed by students -- as if the best of inventions had always come from students, and not from experienced self-taught senior experts..."
euroflycars, you have a point.
"...designer of the human-powered aircraft that won the first Kremer prize ...'
There may not be a lot of ability to make money (other than the prize) from a human powered helicopter.
Senior Experts, need to eat, pay alimony , and so work on stuff that comes with a paycheck.
Or at least the possibility of a paycheck:
For students - one huge problem solving / learning exercise , almost incidental if they achieve their goal, and they can get grant money.
The below started out as a joke, became a routine assignment for students, then a Soviet State secret, then decades of routine frustration for those attempting to bring it to market, Got Money?
One of the ultimate self-taught senior experts:
@Dave B13: ultra-light aircraft are a highly sensible political and strategic issue, e.g. being even totally prohibited in both Switzerland and North Korea (as the only countries in the world to ban these aircraft of the future) -- and please note that according to Swiss rule, Piccard's Solar Impulse, with less than half of the required 20kg per square meter of wing area should be prohibited in his own country!
Instead, it has federal backing through engineering services provided by Swiss high schools -- because the Swiss government's message is the following: "As you can see, ladies and gentlemen, solar flight needs a monster with a 60-meter wing-span, so forget about your ultra-light personal solar aircraft...". That's probably why, a few years ago, Piccard claimed boldly (and wrongly) in the Swiss magazine AeroRevue that he was going to build the first man-carrying solar aircraft, thus ignoring (or rather dismissing), McCready's 163-mile flight from Paris to Manston Royal Air Force Base in the UK performed 20 years ago with his sturdy Solar Challenger taking off and flying on solar cells alone without batteries and with less than 15m wing span -- but now you may also know why it was a one-off headed straight for the Smithsonian...
For the same reason (i.e. because it has tremendous potential as an ultra-light electric VERTOL personal aircraft) the DARPA refused funding of Sikorsky's X2 -- so it might be interesting to take a closer look at the rules of the student challenge to see if there are any symptomatic conditions or restrictions set to prevent a civil break-through in ultra-light rotary-wing technology.
After all, if any one of the teams came up with a genuinely practical concept in the vein of the Solar Challenger, nobody would object to electrical assistance for mass-use -- as witnessed by the booming electric bicycle market!
Another project that would be fun,would be to try to make a short flight by using some type of wind up mechanism,using large rubber bands or spring and flywheel.You pedal the mechanism real tight and release it,making a short flight.How about a small multirotor using /jobi motors 4 of them,like E volo but with a pod below the rotors,keeping it cheap and simple.Good luck,I'm sure you have you hands full.
Since the surface swept by the inner two thirds of the blades doesn't contribute significantly to total lift, rotor lift has to be optimized for the high-speed area defined by the surface swept by the blades' outer third. Hence, in order to compensate for the inner area's low yield, the upper rotor should be scaled down to two thirds of the lower rotor and made to spin so much faster as needed for torque compensation at the driving shaft of its multiplier gear.
This configuration would not only increase the high-yield area of the rotor's swept surface, but also reduce the necessary volume of a streamlined central body as recommended to accelerate airflow trough the innermost swept area -- whereby the overall effect of a smaller and faster upper rotor in conjunction with a streamlined central body ought to grant almost evenly distributed air speed over the entire length of the rotor blades.
If I had the necessary resources to build a human powered helicopter of the above described type, I would of course rather not disclose my concept...
I'm somewhat frustrated that no one (including, evidently, the team itself) has stepped back and actually put bounds on how much power they're going to need. Here are the back of the envelope calculations they should have done in prior to any other design work.
Suppose the vehicle is hovering with zero airspeed away from the ground such that there is no ground effect. Now consider a stream tube enclosing the steady flow processed by the propellers and assume that:
- the thrust is distributed uniformly over the disc
- no rotation is imparted to the flow
- the pressure far ahead and far behind the prop matches the ambient value.
Upstream of the propellers, the inlet velocity V0 is approximately zero while downstream, there's a jet of fluid exiting the CV with a velocity of Ve. Neglecting pressure on the side of the stream tube as it decreases in cross sectional area, the thrust will approximately be given by
T = mdot dV = rho A V1 (Ve - V0)
...where V1 is the velocity at the propeller and A is the prop area. In general, V1 < Ve, but for the sake of argument, suppose they are getting more thrust than they actually are and let V1 = Ve such that
T = rho A Ve^2
Power will roughly be given by
P = 0.5 mdot (Ve^2 - V0^2) = 0.5 rho A V1 Ve^2 ~ 0.5 rho A Ve^3
Rearranging and substituting,
P = 0.5*sqrt(T^3 / (rho A))
This is a highly simplified equation. It assumes perfect power transfer efficiencies and no drag, but it should give a ball park estimate of the minimum power that could conceivable make this thing work.
Let assume that they have a fairly light 70 kg person such that the total mass is about 120 kg. The required thrust then becomes 1.18 kN.
Using a sea level density of rho = 1.225 kg/m^3, an area of A = pi (3.6)^2 = 40.7 m^2, the required power is 2.86 kW.
Now some reference:
- A typical, reasonably fit person, is able to do between about 180 and 250 W on a bike (with the proper seat height)
- Lance Armstrong, at his training peak (not his doping peak mind you) was able to push about 350 W for extended periods of time (http://www.physics.fsu.edu/courses/Fall08/phy2048c%20Studio/CalendarSC/W12D3/LanceArmstrong.html).
- Mark Cavendish can apparently hit 1700 W in all out sprints (http://wattbike.com/uk/blog/post/sprinting_at_the_tour_de_france)
In short, this will NEVER work. A Tour de France sprinter would not even be able to make this thing hop, and it gets worse. Also accounting for the contraction of the stream tube, a slightly more detailed analysis (Sforza 2012, Gessow 1985) gives:
P = sqrt(T^3 / (2 rho A))
which means the minimum power is actually above 4 kW. Again, this will NEVER work, even before you add real world losses. I don't care how efficient you make your propellers.
One last widget:
Which Gurney was next to last to know about.
29th May 2014
Good evening Gamera II Team , would it not be possible to change the propeller design , so that it does not have to be subject to high revolutions per minute , but rather obtain a low revolution count with a lower Aspect Ratio and a more pronounced Camber line to increase the lift .
I salute you for your innovation and do not give up . Best regards , Charles H .