Minimum Rotor RPM
 

The application is a human powered helicopter. Yes, human powered.
I cannot generate the 470HP as supplied for the 1500 Ft/Sec ascent a factory Bell 206B is equipped with, but pehaps I can get my craft to hop. Any thoughts on a minimum Rotation RPM at zero pitch, the applying a 7 to 10 degree collective pitch using a Bell 206 Rotor? Vehicle gross weight is just over 500lbs. I am not looking for an engineered response, (unless you have one), merely an experiential case in point when a Bell 206B copter had hopped due to a __________. Any thoughts from you, the professionals, and your experiences would be a great value to me.

470 HP?
 

I would have thought 470 HP is somewhat more than the main Xmsn is rated for? ( But someone correct me if I am wrong ! :ugh: - VFR

Can I just get a few things straight here...

You are:

Intending to human-power a 206 main rotor?

... with 7 - 10 degrees of pitch?

Expecting to get this 500lbs of machine off the ground - even to hop?

Well, thinking about it - if you can get a decent rpm (Yes, I know that was your question) and have some sort of mechanism that snaps pitch on the blades very quickly - like a jump-start autogyro - the high inertia in the rotor system might give sufficient lift for a hop. Using the rotors as a flywheel really.

How will you control it if it gets off the ground?

In my day, the 206 xmsn was rated at 317hp, which equated to 100% Tq. regardless of engine installed. Originally the max rated output of a 250-C18. - I think.

How many humans are you planning to use? The 206B transmission is 317shp the 206L4 is a little over 450 shp.

HPH Hop
 

Thanks for the clarification on the HP, I appreciate the assistance. I am employing a cable enacted, hand operated, variable collective pitch control, (not sure how much effort that will take) , and then, providing I get positive test results on my spinnup test, I will hopefully be constructing a cyclical disk controller to employ 3 axis control. But, yes, I should be in Auto-rotation, given the input HP, as soon as it is off the ground. Given the airspeed will be next to zero, it could be an interesting ride.

HPH Hop
 

I can employ up to 2 humans, but that may bring the craft weight up to 700lbs. 510lbs + second human

The University of Maryland have build a prototype human powered rotorcraft with very lightweight material (approx 220lbs including the pilot) which they just managed to get off the ground for a few seconds.


Not sure how easy it's going to be to get over twice that much off the ground.

Best of luck though!

OH

HPH Hop
 

Yes, the weight is definately the most difficult hurdle, given the Bell Rotor weighs in at 184LBS plus the Hub to hold it together and provide pitch. The advantage is that it is inertia energy once it is airborne. Thanks for the support.
DB

Think you`d be better off with a B-47 rotor...

Interested to hear why you suggest that. A 47 M/R hub is more complicated (not talking stab bar here) and wouldn't 206 blades with their extra weight be an advantage?

HPH Hop
 

I used what was available. May have to go back to the DB. Design is for a coaxial craft. but I can modify all energy to single rotor.
I had hoped the weight would be an advantage to a point. I realize the Gamera, Yuri, and Da Vinci Crafts all were under 150lbs plus pilot, but they had no pitch control. The operated at full pitch from the start. No inertia, no storage.

Really? I'd like to see that - please post a video on Youtube asap.

It already is on Youtube.
 

If you view the rotor spinnup video, you can see I was able to get to almost 50 RPM, but the sprocket was too high ratio. I have just installed a lower ratio for more torque (3X), which I anticipate to increase RPM to 100+. Test is this Sat.
I was hoping to get some tips if this thing hops, recommended pitch settings to not stall the rotor, to safely lift, and if it does, Any pointers on how to survive...

Flat Pitch Power Required
 

If memory serves me correctly, it takes approximately 17%-20% to turn the B-206 rotor at 100%. That would be somewhere between 50 and 60 ESHP. This would get you to your starting point. Your system would have no accessories (i.e. hydraulic pumps generators or tail rotor take off) so the number would be somewhat reduced from the 50 to 60 ESHP.

Assuming it does 'hop', you won't be in autorotation as the term properly applies to helicopters, as significant rate-of-descent airflow and minimum pitch is required for that.

I imagine this is an attempt to win the Sikorsky prize? I guess it lets you store some energy without using flywheels or other storage devices (I just had a quick look at the rules on the web), which is fair enough, but in all honesty the weight of the setup compared to the power you can put in is going to be too much, I think, (not to mention control issues) to be airborne for more than a second or two, let alone a minute.

Best of luck though.

HPH hop
 

I see your point on the auto-rotation and the weight.
I will give it a shot and see what we can do.

I appreciate this blog and all of you that took the time to contribute, and had patience with me considering I am not a professional pilot.

Thanks again.

Can't wait until the day you tell us that your name is also a reincarnated,
Johnny Weismuller.

Tarzan swings,
Tarzan faaaaalls,
Tarzan hannnnnnngs,
by the hair of his balllllllllllls;

Banjo strumming in the background.

After reading all the pros and cons above. Whats the chance of getting a set of Skeeter main rotor blades, head and transmission? No it won't have high inertia, but will be considerably lighter than the weights you are discussing. To carry this statement to an extreme; make your own plywood and doped fabric blades, and utilize simple belt drive reduction. The head flap system would not be hard to make as its got a short usage life. Last thought is wear a good crash helmet.

HPH Hop
 

The Latter is my only option given the budget. That is the next step.
For now this is where I have progressed to (if you are interested)...
https://sites.google.com/site/hphbumblebee/

https://sites.google.com/site/hphbum...FBP1290378.JPG


You can see the rotor hub that I have created, and the size of the main torque tube, Frame, and some of the drive components. This is what I have to work with. I can build a rotor, and will probably need to, but much to learn in that realm and $$$.

What I have is at least worth a try. I will know this Sat. if this current config. is feasible at all.

A quick bit of google'idge reveals that a REALLY strong person can muster approx 0.7hp. Remember the power required to turn the rotor (rotor profile power), increases exponetially as a factor of the RPM ie to double it takes 4x power, to quadruple it takes 16x power etc.

I am intrigued by your plan and wish you best of luck, but mister physics says that you do not have a chance. Sorry.

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.

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.

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 !

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.

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

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.

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)

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.

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%.

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

Why not try a R22-main rotor?

...and what about anti-torque?

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.

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.

Which part of the pilot's anatomy will operate this control? He seems too busy 'rowing'...

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.

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.

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.
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.

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.

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.

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.

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.

:ok:

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