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Minimum Rotor RPM

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Minimum Rotor RPM

Old 28th Sep 2011, 12:08
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Exactly - calculate how much power it'll take for get the desired rotor rpm at flat pitch & you'll find it far higher than 1 or 2 humans can generate.
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Old 28th Sep 2011, 12:10
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HPH Hop

I would agree. It definately feels that way when you are trying to turn it. Those calculations I did not know. So you estimate at 3X the power I presently have, would yield about 75 to 95 ish RPM. There is just too much weight there. Good to know.
We will give it a boyscout try, then go to plan B.

Thanks for the input.
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Old 29th Sep 2011, 07:06
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Froude theory

Froude theory tells that with a 10m diameter rotor you need at least 7.5kW to hover 500lb and more than 12kW for 700lb. The burden is less on the second crew member but still challenging !
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Old 29th Sep 2011, 07:54
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I don't think that this contraption will manage any more than a hop of a second or two, and that's assuming sufficient Rrpm and a rapid application of collective - I'd guess that the Rrpm will decay with a conventional smooth and gentle raising of the lever even with the inertia of a heavy main rotor. IMHO of course.

Keen to see the test though. Good luck.
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Old 29th Sep 2011, 13:45
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Looking at the picture, the solution hangs in the background.
Add some 'boyancy' like helium, to counter a portion of the weight,
paddle hard, and off you go...
Maintaining control seems quite difficult, while paddling like a madman.
Also you need some way of anti-torque and anti-torque control (pedals?)
Thus, you would need two sets of feet.

FTF

Last edited by FullTravelFree; 29th Sep 2011 at 18:20. Reason: spelling
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Old 29th Sep 2011, 13:56
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HPH Hop

7.5 KW is about 10HP. Somebody already stated the strongest, most fit human can only generate .7 HP.
I am curios, can anyone tell me, how much HP does it take to turn a 10M heli rotor weighing 220lbs at 80 RPM? (transmission losses aside)

I realize the science, as we understand it is stacked against us, to lift, or even hoping to hop 500+lbs on thin air. That is like lifting a car V8 engine in weight, and for one person, to pick it up onto nothing? Huge Challenge.
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Old 29th Sep 2011, 14:01
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HPH Hop

I like the helium idea but it is a DQ for the Sikorsky Prize.
The second seat is for a second counter rotating rotor. It is coaxial. If the first test proves to lift the pilot plus the frame, the second pilot and rotor should be a success. (providing I survive)
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Old 29th Sep 2011, 16:57
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Consider the following very approximate figures: At flight idle in a 206B it takes about 30 shp to turn the rotor at 100%Nr. Reducing that by 10 shp for friction in the transmission and power being absorbed by the T/R drive etc. still leaves a power requirement far in excess of 1,2 or even 3 humans on steroids could produce. Yes you are light but 206 or even B47 blades are too heavy and will have much more drag then you could cope with. Have you thought of building very light weight high lift fabric blades (think glider wings as a design guide). For human powered anything weight is critical.
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Old 29th Sep 2011, 19:08
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Froude theory (cont)

220 lb asks for 2.2kW. It is only the minimum power required to produce the momentum and lift that weight (assuming 100% efficiency). The drag of the blades and the antitorque are additional power.
The power increases with power 3/2 of the weight and directly decreases with the diameter. With a 30m diameter, you would be close to a 0.7kW (1sHp) level.
These figures apply to HOGE. In HIGE, very close to the ground, you can gain 20-25%.
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Old 30th Sep 2011, 01:36
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HPH Hop

That would explain why the other teams have put the Rotors on the ground. They need that advantage.
I see your equations and estimations, and they are in line with the engineers I have talked to... Still,
Energy is neither created or destroyed.

Other lighter versions include the large rotors that engineers are requiring (in the 100' diameter range.) I will go there if I have to, but this Saturday afternoon, I am doing a spinnup test.
Human Powered Helicopters - Thunderbird
Human Powered Helicopters - Da Vnci III
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Old 30th Sep 2011, 22:51
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Why not try a R22-main rotor?

...and what about anti-torque?
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Old 3rd Oct 2011, 03:32
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HPH Hop

There are a couple of ways to solve this problem, one is, the craft is a coaxial craft with opposing rotors. So when completed, it should be entirely stable, however, the horsepower is already depleted due to the fact that at peak torque, I should be under 1HP. So if torque is null at lift off due to the depletion of energy, so should the anti-torque.
I have some other ideas to counter the torque that do not require HP. I am going to experiment with those also.
Thanks for participating.
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Old 3rd Oct 2011, 07:45
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The extension wobbling about above the head seems to suggest that you need to balance that main rotor.

How did you ensure proper alignment of the blades to prevent any forward sweep?

Why did you test at anything other than flat pitch? I appreciate that the blades are twisted but there is effectively a null point.

I will hopefully be constructing a cyclical disk controller to employ 3 axis control..
Which part of the pilot's anatomy will operate this control? He seems too busy 'rowing'...
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Old 4th Oct 2011, 01:02
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HPH Hop Questions

1. Wobbling: that was unexpected. The rotors were balanced as well as I could. I believe what is occuring is a main torque tube is flexing in the center. The tube spans about 9 feet and has a thin schedule wall. There is no center hub. I am working to provide 2 or 3 spaced teflon guides for the main tube. In addition, I will check the balance on the rotors, this time with some assistance. (they are much to manage for one person.)

2. Forward sweep: I made an assumption, centrifugal force would align them. Thoughts or Suggestions? It is limited, but may have negative ramifications. The Rotors are not showing any signs of strain from this movement. I am also trying to figure how to lighten these blades, perhaps cut out, perhaps, laminate some thin composite or wood to make the surface area larger in addition to providing more strength.

3. Pitch: curiosity. We wanted to see how much drag was induced if we began to apply collective. It was minimal, and the degree was estimated.
What appeared to be a null pitch at first, after closer examination (three opinions) we agreed it appeared to actually be slightly negative (at the tip). So we corrected it after the first spin-ups.

4.Controls: It is entirely doable with the arms and wrists (providing Mechanical advantage can be within operable limits). I will post the videos when I have this complete. I understand the concerns and they are definately affecting the ergonomic design of the controls. It is an uneducated guess at this point (as is the rest of the craft)

Sorry, those are the best answers I have for you.
Thanks for interest.
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Old 4th Oct 2011, 20:04
  #35 (permalink)  
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The rotors were balanced as well as I could
You must static balance the main rotor before you do any more ground runs. The torque tube (M/R mast?) flexing is thoroughly undesirable. Caused by rotor inbalance, or lack of sufficient strength - probably both.
It's a straightforward but time-consuming process to align and statically balance a two-blade rotor. Align first, using the rigging nails at the tip of each blade and - assuming you're using standard 206 blade retention bolts - the correct chamfer within the hollow shank of the bolt. You'll need to get hold of the relevant pages from a 206 M&O manual to align using the standard parts, and to understand why you need FOUR datum points for alignment.

Once aligned, with both blades pitch angles 0 relative to the hub you can balance the assembly - both spanwise AND chordwise. The Bell MM shows very well how to use the special tooling (not rocket science to reproduce if you can get your hands on a set to copy) to achieve spanwise and chordwise balance.

I made an assumption, centrifugal force would align them. Thoughts or Suggestions?
Once aligned you should lock the position of each blade to the hub. The 206 uses latch bolts clamping the blade root tangs to the grip, the 47 uses drag braces. Do not rely on centrifugal force as you would with a model, the balance will probably be lost if the blades are allowed to wander about on their own. In any case, I can't see it working full size and at low Nr.
Pitch: What appeared to be a null pitch at first, after closer examination (three opinions) we agreed it appeared to actually be slightly negative
The blades are twisted along their length to equalise lift along the span. If the tip is at 0 degrees, the root will have an appreciable angle of attack. So if the root is at zero the tip will be at a negative pitch angle.

Much has been said on here about the horsepower needed to turn a 206 main rotor at 100% (394rpm). I really don't think you need anything like this rpm to 'hop' - and I mean hop - your 500lb machine.

As for lightening the blades, the mass of the blades as they are - if you can get enough Nr - will give you a good flywheel effect.

Get the rotating bit sorted out before you go any further. I wouldn't want a 206 blade falling on me, let alone one with significant rotational energy.

Last edited by TRC; 4th Oct 2011 at 21:30.
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Old 9th Oct 2011, 05:02
  #36 (permalink)  
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HPH Hop

Thank you for the info. I did a static balance on the rotor and hub assembly. That should take care of the basic balance issue you suggested. However, as far as the rigging pins, and alignment, I am very curious about the datum points and what the tolerance limits are.

Last night I was considering a new M/R mast or torque tube, This design was never built for such a heavy rotor, but I couldn't beat the price (I am working with what I can). And I do not want it falling or striking anyone either. During the last test there was a group of people standing beside at about 30 feet out. I suggested that if they did not want to possibly get sliced in two, (in case of mishap) they should move to a safer distance. They moved.

As for blade wander or sweep, there of course is a stop for rearward sweep movement, and vertical movement. You feel I need a stop for forward sweep is critical? I also noticed some flapping during the last test.
Not sure why.

Your explaination of the twist and pitch is what I had come to understand and design around.

How much pitch can be applied before a blade stalls or is no longer proportioanally lifting? Is there a curve or a chart for effective pitch?

I want to apply the most effective pitch I can, as fast as I can, for obvious reasons.

Thanks again for the input and support, it is appreciated.
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Old 10th Oct 2011, 21:16
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However, as far as the rigging pins, and alignment, I am very curious about the datum points and what the tolerance limits are.... This design was never built for such a heavy rotor, but I couldn't beat the price (I am working with what I can)....You feel I need a stop for forward sweep is critical?... I also noticed some flapping during the last test.... Not sure why.
Somehow, I don't think you have a sufficient grasp of the enormity - and the likely consequences - of what you are attempting.

I suggest that you think long and hard before you proceed any further.
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Old 10th Oct 2011, 22:21
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Never sweep forward in an attempt to balance chord wise from. Forward sweep is dangerous! However I don't think you will ever get enough rpm or torque to suffer the consequences.

Heed TRC's advice.
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Old 13th Oct 2011, 03:25
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HPH Hope

Copy.

This was never just about a contest. The contest was to try to get resources for other inventions like conceptual engines, flying cars, motors, safety devices, tools. There is more at stake than my welfare. I have a modification that, if successful, can change the face of Rotor and Fixed wing craft alike. I have to try. This is not as dangerous as my Counter-Rotating-Axial-Turbine-Engine or CRATE design, but I do not take this lightly. The heavy blade must fail so that the modification can prove it's value.

If this goes like many things throughout my life, many problems lie ahead; I can remember as a child, regularly digging vegetables out of a grocery store dumpster for our table. This is my life. Take what you get and do your best with it.
I am trying, but without sincere professional interest, somebody with real finances who actually wants to make a difference, true facilities not a garage, driveway, and unplowed field, or maybe even an answer to an email or letter from the big folks who could easily make this test more feasible and "safer".... to most, I am just an stupid crazy guy doing a dare devil stunt for nothing. I have better things to do with my time. There are much more satisfying things to be loony about. No, I am forced to proceed more dangerous and risky route like the Wright Brothers. Do I want to? Not on my life!
This is why I am on this blog. I want to know the risks, design advancements, things I can and cannot overcome. I wanted to hear from you, the pros who know what is at stake. The guys who can tell me how ignorant I am, how foolish, an maybe perhaps I won't be as much.

This sort of blog is not even really supposed to be on here, and I shouldn't be talking to you Professionals, and my craft isn't supposed to fly.
I am close to failing or succeeding, I have to finish.

Safety, Strength, Balance, in that order. Check. These are my goals.

What I do understand now is that only I can be the one to test it, because of the risk.

I end the blog with this,
Thanks to those of you who sincerely took interest and answered me, for your help and information. It is more than I have received from anybody outside of the team. Who knows, perhaps we will meet one day, and I can thank you personally.

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Old 13th Oct 2011, 08:49
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Bumblebee

I admire your perseverance.
...but I must agree with above comments, think it through carefully.

You have to think about the "what if-s", and there are many of them.
Mostly, think about your safety and the bystanders while experimenting.
Look at a few helicopter crash video's on youtube and you'll see.

My suggestion is this: go to your local helicopter flying school,
take a few lessons in hovering. Ask the instructor about the things
that can go wrong.

Goodluck,
FTF
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