- #176
airport
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Nice post...Thank you very much!...[PLAIN]http://parkservice-flieger.de/Icons/smileycool.ico
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Help Design a Human-Powered Helicopter
- Thread starter jzvonek
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- Design Helicopter
In summary: I don't know if ground effect would be significant with the slow-moving rotors of a human-powered helicopter. I've seen experiment results that show the effect dropping off quickly as the rotors move away from the ground (< 3m).Stability and control will be major issues, and I believe electronics are not allowed by the rules.And the problem is not impossible. We have better engineering tools than at any time in the past. We just have to take advantage of them.When they say 'human powered' - do they count 'human fuelled'?A gas turbine will run on bio-diesel !Looks like you are going to need Leonardo on this one.He's
- #177
mugaliens
- 197
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Cyrus said:
Instead of using coaxial rotors, how about using counter-rotating rotors offset at opposite ends of a support boom? Would that be more stable? I would think it would have the same degree of stability/instability, but it actually make it more larger than is required, as well as more unwieldly, resulting in additional handling problems.
I know a good deal about airplane flight stability, but little about helo stability, even though I've flown two of 'em (not licensed - just fun rides). I'm having a difficult time picturing the instability part. Yes, technically counter-rotating rotors, whether coaxial or offset tend to counter gyroscopic forces. I get that part. But zero stability doesn't equate with negative stability i.e. it's not like flipping itself over is a more stable position than remaining in one position. Broomsticks balanced upside down on one's hand are dynamically unstable, yet kids manage to do it all the time, and the response rate required to stabilize that small of an object is much more rapid than for a human-powered helo with 30 feet of blade.
My thought towards what might be the best way to control the rotors is to use spoilers, not ailerons. Obviously, using a centralized blade-angling approach (http://en.wikipedia.org/wiki/Swashplate_(helicopter)" ) for such large, slow-moving rotors is probably a poorer approach than controlling the lift of the blades more directly, through ailerons.
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- #178
jeff kimathi
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is there any simple approach on to getting the leading edge radius of an airfoil model of say chord of 45cm and maximum thickness of 8cm with the point of max thickness being 1/4 of chord:confused :
- #179
mugaliens
- 197
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jeff kimathi said:
I'm sorry, but you're going to have to specify which of the many thousands of fully-wind-tunnel-tested airfoils you're talking about.
If you're proposing your own, then you're on your own.
- #180
Cyrus
- 3,238
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FYI: the cat is now out of the bag so enjoy
I was on briefly on the team early on but had to stop to finish my research and graduate: in any event, these guys and gals are working hard at it, so keep your fingers crossed for them.
I was on briefly on the team early on but had to stop to finish my research and graduate: in any event, these guys and gals are working hard at it, so keep your fingers crossed for them.
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- #181
jeff kimathi
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Cyrus said:
congratulations on your graduation...so what's new in you 4 us
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- #182
helisphere
- 22
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The stability issue is an aerodynamic one. As the NASA-TM states the basic reason for the instability in the human powered helicopter is the high lock number of the blades. For those unfamiliar with this term and without getting unnecessarily technical, the lock number is basically the ratio of aerodynamic forces acting on the blade compared to the inertial forces acting on the blade.
Lock number = Aerodynamic Forces/Inertial forces
So it make sense that the low rotational speed, light weight blade and large blade area combination make for a very high lock number.
The inertial forces acting on a blade are stabilizing, just like a gyro, as per Newton's first law. The Aerodynamic forces are a little more complicated, but basically they make the helicopter and rotor unstable. The aerodynamics actually cause a combination of both positive and negative stability at different times but overall the result is undesireable and unstable. So with a high lock number the aerodynamic forces have a larger impact on the stability which means a less stable rotor.
Watch the following video starting at 4:30 to see some good examples of the stability issues of a helicopter rotor. I would suggest that the stability issue is just as solvable today in a human powered helicoper as it was in the 1940s in this model that eventually became the Bell 47, whether coaxial or not.
Also the little coaxial models that are very stable in a hover are not stable just because they have a higher RPM and lower blade lock numbers. They are stable because they have a weighted stabilizer bar that acts as a gyro and generates aerodynamic control inputs to a rotor that would other wise be unstable just like the model in the video below.
fast forward to 4:30
https://www.youtube.com/watch?v=uir9Engj4v4
Lock number = Aerodynamic Forces/Inertial forces
So it make sense that the low rotational speed, light weight blade and large blade area combination make for a very high lock number.
The inertial forces acting on a blade are stabilizing, just like a gyro, as per Newton's first law. The Aerodynamic forces are a little more complicated, but basically they make the helicopter and rotor unstable. The aerodynamics actually cause a combination of both positive and negative stability at different times but overall the result is undesireable and unstable. So with a high lock number the aerodynamic forces have a larger impact on the stability which means a less stable rotor.
Watch the following video starting at 4:30 to see some good examples of the stability issues of a helicopter rotor. I would suggest that the stability issue is just as solvable today in a human powered helicoper as it was in the 1940s in this model that eventually became the Bell 47, whether coaxial or not.
Also the little coaxial models that are very stable in a hover are not stable just because they have a higher RPM and lower blade lock numbers. They are stable because they have a weighted stabilizer bar that acts as a gyro and generates aerodynamic control inputs to a rotor that would other wise be unstable just like the model in the video below.
fast forward to 4:30
https://www.youtube.com/watch?v=uir9Engj4v4
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- #183
Phrak
- 4,267
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Cyrus said:
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- #184
helisphere
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Phrak,
I think he meant that for an airplane you only need to create a thrust of about 1/15 of the weight of the aircraft in order to achieve flight but with a helicopter you have to create a thrust equal to the weight of the aircraft. That would be 15 times more thrust to hover a helicopter than to fly an airplane.
- #185
Phrak
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helisphere said:
Good thinking. That might be it, assuming a nominal L/D of about 6 to 1.
but I'd still give you ten to one odds UMD fails if the video is any indication of their design paradigm.
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- #186
mheslep
Gold Member
- 364
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Is it? Lowering the lock number likely means adding mass to the blades - something the human powered helo can ill afford.helisphere said:
Thanks for the video. The demand by the executive suit to pilot the prototype leading to predictable disaster shows that the suits weren't any different back then. It's amazing the suit only suffered a broken arm.
- #187
Phrak
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This, http://vtol.org/awards/HPHCBooklet.pdf" .
I draw your attention to the sketches pages 44 and 48 of http://vtol.org/awards/HPHCBooklet.pdf" as counted in .pdf pages.
Is this not a viable design method?
I draw your attention to the sketches pages 44 and 48 of http://vtol.org/awards/HPHCBooklet.pdf" as counted in .pdf pages.
Is this not a viable design method?
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- #188
helisphere
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mheslep,
My point was that the model in the video was also unstable but they made it stable and they didn't do it by lowering the lock number. They took a stable reference and made the blades fly to it.
Phrak,
Yes I think that is probably the best way to go. The problem with big slow rotors is little centrifugal force to keep the coning and bending moments down. Those designs distribute weight more evenly.
My point was that the model in the video was also unstable but they made it stable and they didn't do it by lowering the lock number. They took a stable reference and made the blades fly to it.
Phrak,
Yes I think that is probably the best way to go. The problem with big slow rotors is little centrifugal force to keep the coning and bending moments down. Those designs distribute weight more evenly.
- #189
PedalPower
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IcedEcliptic said:
Fly off a dock on a calm day...get it as high as possible, when tired...let off a little...then descend with a little auto rotation and dump in the lake. Fish it out with a boat and find the tag line, attached before lift off, with a tennis ball.
But don't make the frame out of balsa wood, need aluminum for the frame and plastic or carbon fiber for the props...
- #190
PedalPower
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mgb_phys said:
Eat only beans for three days before, hook up a gas powered rocket engine under the seat, get the rotors going as a distraction, then ...ignition!...if only they had smileys here!
- #191
JaredJames
- 2,818
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PedalPower said:
They do:
...- #192
Phrak
- 4,267
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helisphere said:
We see these hopeful engineering teams taking the same dead end road. I'm perplexed as to why this seemingly obvious solution hasn't been tried.
A ten meter square target is not easy to hover over with a large machine, say 100 to 200 meter diameter, but this should be easily solved with software sending information from the pilot to those providing the peddle power and adjusting control surfaces.
- #193
PedalPower
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Thank you for your reassurance...my experience is generally restricted with structural and mechanical engineering skills and the advanced calculus was never mastered by me as far as aerodynamics are concerned.
Eventually we can run a test on the foil shape and the props surface areas/angle of attack to find the optimal rotation speed required to hover for 45 seconds, then lift to the height required...we honestly see the potential, but with so many attempts, the school based design teams were left with advancing the previous vehicles and trying to make their "hovercraft" sustain flight...we have had success reinventing the Pedicab, the modern rickshaw, and are now moving onto the entry for the vehicle design summit this summer at MIT. With this engineering as a background we are able to achieve a greater advantage over other riders and gain the momentum to get going on this project.
We are hoping that the rotor speed will be accelerated from the internal hub gear we are including in the drive train, allowing us to get it up to speed on a gradient scale through gears 1-4, by fifth we hope to be at a 1-1 ratio with the internal hub, and will have generated 8.94 full rotations for every rotation of the main pedal powered wheel, if one rotation per second (definitely possible) is maintained, then we will have created a rotor with 40 sq ft of surface area traveling at 535 RPM's, far more than is needed to attain lift of a regular sized helicopter that usually runs at 400-460 RPM's and weighs a ton.
Although the rotors on a regular heli are also able to produce lift from adjusting the angle, we have a fixed angle of 2% that we feel will be enough to allow for the slipstream effect to be more fluid with less drag and still create lift, and direct the trailing edges' airflow directly into the main lift producing area of the next blade, after the vacuum has collapsed upon itself and returned to it's original density...by generating more momentum, and creating the final rotor rpm to sustain, with at least three gears left to get off to a higher altitude, there is no way we can lose.
Would you be interested in handling the advanced calculations as a co-conspirator/awardee? We are merely looking for scientific calculations to back up our design, so we can obtain sponsorship with endorsements, to make the process go smoother.
Eventually we can run a test on the foil shape and the props surface areas/angle of attack to find the optimal rotation speed required to hover for 45 seconds, then lift to the height required...we honestly see the potential, but with so many attempts, the school based design teams were left with advancing the previous vehicles and trying to make their "hovercraft" sustain flight...we have had success reinventing the Pedicab, the modern rickshaw, and are now moving onto the entry for the vehicle design summit this summer at MIT. With this engineering as a background we are able to achieve a greater advantage over other riders and gain the momentum to get going on this project.
We are hoping that the rotor speed will be accelerated from the internal hub gear we are including in the drive train, allowing us to get it up to speed on a gradient scale through gears 1-4, by fifth we hope to be at a 1-1 ratio with the internal hub, and will have generated 8.94 full rotations for every rotation of the main pedal powered wheel, if one rotation per second (definitely possible) is maintained, then we will have created a rotor with 40 sq ft of surface area traveling at 535 RPM's, far more than is needed to attain lift of a regular sized helicopter that usually runs at 400-460 RPM's and weighs a ton.
Although the rotors on a regular heli are also able to produce lift from adjusting the angle, we have a fixed angle of 2% that we feel will be enough to allow for the slipstream effect to be more fluid with less drag and still create lift, and direct the trailing edges' airflow directly into the main lift producing area of the next blade, after the vacuum has collapsed upon itself and returned to it's original density...by generating more momentum, and creating the final rotor rpm to sustain, with at least three gears left to get off to a higher altitude, there is no way we can lose.
Would you be interested in handling the advanced calculations as a co-conspirator/awardee? We are merely looking for scientific calculations to back up our design, so we can obtain sponsorship with endorsements, to make the process go smoother.
- #194
JaredJames
- 2,818
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PedalPower said:
All the calculations and explanations regarding power are shown previously.
If you read back, you will see that a human being cannot, for a long enough period of time, provide enough power to generate the required lift. Making everything you wrote above irrelevant.
I'd also note that no one here will do the work for you - as previously, the calcs are a few pages back showing the power issues.
- #195
helisphere
- 22
- 0
535 rotor RPM? You don't say what your rotor diameter is but let's say that it's only 25 ft in diameter. That would give you a tip velocity of 535*2*pi*12.5/60 = 700 feet/sec. Typical helicopters don't use tip speeds any faster than this because of sonic compressibility effects and if your rotor were any bigger in diameter it would have a faster tip speed at that RPM. Let's say 40ft dia: 535*2*pi*20/60 = 1120 feet/sec This is Mach one!
In order for a 25 foot rotor to lift 200lbs: horsepower = sqrt(T^3/2*rho*A)/550 = 3.36 hp and this momentum theory calculation is for an IDEAL rotor which is not even possible to make.
And a 40 ft dia rotor: 2.10 hp
Testing shows a strong athlete can only make 0.7 to 0.8 hp
In order for a 25 foot rotor to lift 200lbs: horsepower = sqrt(T^3/2*rho*A)/550 = 3.36 hp and this momentum theory calculation is for an IDEAL rotor which is not even possible to make.
And a 40 ft dia rotor: 2.10 hp
Testing shows a strong athlete can only make 0.7 to 0.8 hp
- #196
helisphere
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PedalPower,
Don't let me or anyone else discourage you. If this is something you really want to do then do your homework, find the answers and go for it! I'm not trying to smash anyone's dream, reality has a way of doing that on its own. I'm not your enemy, Love us, hate us, learn from us, I wish you the best, but it does seem there are a few things you don't understand about helicopters, especially the human powered type, but that doesn't have to be anything but temporary...
Don't let me or anyone else discourage you. If this is something you really want to do then do your homework, find the answers and go for it! I'm not trying to smash anyone's dream, reality has a way of doing that on its own. I'm not your enemy, Love us, hate us, learn from us, I wish you the best, but it does seem there are a few things you don't understand about helicopters, especially the human powered type, but that doesn't have to be anything but temporary...
- #197
PedalPower
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helisphere said:
Maybe we should design it like this ... http://www.clydecaldwell.com/photos/sandiego01/time_machine2.html
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- #198
JaredJames
- 2,818
- 22
EDIT: Link correction noted.
What does that design have to do with the human powered helicopter? That's a time machine.
What does that design have to do with the human powered helicopter? That's a time machine.
- #199
PedalPower
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jarednjames said:
That's funny you say that cause there are numerous pictures of guys "doing it" and also videos, as well as a couple of really heavy looking ones created by the engineers of other helicopter companies, they ended up facing tragic endings before they tried to take off...these were placed on display in the many aerospace museums, and I have even seen a couple as a student on field trips to DC.
Try speaking for yourself...others have interest, and you don't.
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- #200
JaredJames
- 2,818
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PedalPower said:
Please do show us these pictures and videos - especially those that fall within the rules of this challenge. The davinci III is the only one of note so far and it's not even close to within the challenge rules.
They faced tragic endings before taking off? As in they were destroyed trying to take off? That means they didn't work.
Again, as per the posts above, they show you HP required and HP possible.
- #201
PedalPower
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jarednjames said:
So does your every reply come in the form of cynical metanoia, or can you take a joke?
- #202
Phrak
- 4,267
- 6
"cynical metanoia" has a certain ring to it, jarednjames. Maybe Greg will let me change my screen name. Cynical_metanoid, perhaps. Of course you get first dibs, all things being fair.
- #203
JaredJames
- 2,818
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Phrak said:
I want to say 'oxymoron' but I can't work out what "metanoia" is. Only some sketchy definitions floating around.
- #204
Phrak
- 4,267
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jarednjames said:
I dunno. but it's got to good if PeddlePower came up with it.
- #205
jeff kimathi
- 8
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pedalpower av read thru your comment n all i can tell you is that sometimes it takes one own effort without any much consultations to succeed in something especially these science related projects...i prefer you work it out practically n rely on the outcomes of your project to reason out the next move or your next modifications simply because critics will always out shine the kudos in real life situations....i to am in the race to trying this task i decided to do my own design n try it to make the next move from my results simply because there are those who think they are more learned thus tend to look down to others which is a great threat to your success...av done my design with my colleagues n made the necessary parts n we are awaiting the assembly n then the trial of the machine...i mean no offense at all to anyone of you registered in this forum...so go for what you think is right n let the outcomes determine your rights n wrongs
- #206
Sum1
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Yesterday student engineers from Maryland University were testing for the first time their quad-rotor human powered helicopter "Gamera" -after nearly 3 years of development. They will continue their tests today too and there will be a live stream.
promo:
http://www.youtube.com/watch?v=uT4y4xb2UYI&playnext=1&list=PL342EC9DE5332F42F
preparation:
yesterday's attempt:
a)short:
http://www.youtube.com/watch?v=A_bLNHr6qPU&feature=related
b)long: The whole 3h video capture from yesterday's live stream (needs Silverlight):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=dae7b8b7686a4639a0faa0f58ebd08651d
Website:
http://www.newsdesk.umd.edu/bigissues/release.cfm?ArticleID=2424"
EDIT: Today's live link (it has started a while ago):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=25e3de8c875444169b873aecaa9f04731d
promo:
http://www.youtube.com/watch?v=uT4y4xb2UYI&playnext=1&list=PL342EC9DE5332F42F
preparation:
yesterday's attempt:
a)short:
http://www.youtube.com/watch?v=A_bLNHr6qPU&feature=related
b)long: The whole 3h video capture from yesterday's live stream (needs Silverlight):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=dae7b8b7686a4639a0faa0f58ebd08651d
Website:
http://www.newsdesk.umd.edu/bigissues/release.cfm?ArticleID=2424"
EDIT: Today's live link (it has started a while ago):
http://lecture.umd.edu/detsmediasite/SilverlightPlayer/Default.aspx?peid=25e3de8c875444169b873aecaa9f04731d
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- #207
whynottry
- 2
- 0
I believe that rpms overcome weight. All of the "successful" designs have focused on very low weight materials but they cannot produce high rpm of the rotor. If the rotor is a smooth disc that can deform into a lift producing rotor then a much-higher-than-needed rpm can be achieved before it starts moving air.
- #208
HowlerMonkey
- 368
- 17
They need to change the powerplant's (awesome blonde chick) indexing between the pedals and the hand crank as well as change how her posture is aligned with the force she is exerting.
They could also make far more use of her power if they added as large a diameter flywheel to the pedal crank assembly.
It could be very light with most of it's mass concentrated on the outer diameter.
As it is now, much of the energy is being used up by flex.
They could also make far more use of her power if they added as large a diameter flywheel to the pedal crank assembly.
It could be very light with most of it's mass concentrated on the outer diameter.
As it is now, much of the energy is being used up by flex.
- #209
whynottry
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flywheel equals weight. not going to happen.
- #210
HowlerMonkey
- 368
- 17
When you watch the video, it is easy to see how jerky the application of power is and the fact that the rapid acceleration and deceleration of the cranking motion is being absorbed by the structure rather than being applied to the props.
It only takes a couple of pounds to make a flywheel which has mass concentrated on outside diameter that would smooth out her pedaling and recover the lost energy.
Since the average human varys 1 or 2 (maybe more) pounds from day to day and the fact that this girl not fully shreaded, I think it would benefit far more than detract.
It only takes a couple of pounds to make a flywheel which has mass concentrated on outside diameter that would smooth out her pedaling and recover the lost energy.
Since the average human varys 1 or 2 (maybe more) pounds from day to day and the fact that this girl not fully shreaded, I think it would benefit far more than detract.