Ben Dixey South west UK

skyguynca

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If it were a single rotor, yes it would be impossible to tilt or move.

the counter rotation will counter the hooks force.

Your drive shaft to rotors should not have that much torque.
 

btd1982

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If it were a single rotor, yes it would be impossible to tilt or move.

the counter rotation will counter the hooks force.

Your drive shaft to rotors should not have that much torque.
Thanks. When I applied 55lbs/ft of torque to the primary drive pulley I checked that the mast hinges still had the freedom of movement I desire in all directions although I would like to reduce the play in the hinges. I should have gone for taper rollers instead of needle rollers in the hinges I think. Any estimation on how much the mast will need to tilt for a controlled hover? Full mast tilt at the moment is about 5 degrees from vertical.
 

Martin W.

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Interesting (clever) design for reversing rotation on the lower drive sprocket
Question ... is the lower drive belt toothed on both sides ??
I have never seen a belt like that before.... that is why I ask . thanks.

Next question .... you say you are using a tilting mast for control
I see the pivots below the belt-sprocket assembly
That must mean the whole drive-sprocket assembly tilts as well
Engine is fixed to main frame
So drive shaft must have a slip-joint and universals to allow drive assembly and mast to move as a unit (tilt)

Do I have that right ?

Love your project and machining.

ps: ... At this point I don't think engine torque would be an issue.
 

btd1982

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Interesting (clever) design for reversing rotation on the lower drive sprocket
Question ... is the lower drive belt toothed on both sides ??
I have never seen a belt like that before.... that is why I ask . thanks.

Next question .... you say you are using a tilting mast for control
I see the pivots below the belt-sprocket assembly
That must mean the whole drive-sprocket assembly tilts as well
Engine is fixed to main frame
So drive shaft must have a slip-joint and universals to allow drive assembly and mast to move as a unit (tilt)

Do I have that right ?

Love your project and machining.

ps: ... At Interesting (clever) design for reversing rotation on the lower drive sprocket
Question ... is the lower drive belt toothed on both sides ??
I have never seen a belt like that before.... that is why I ask . thanks.

Next question .... you say you are using a tilting mast for control
I see the pivots below the belt-sprocket assembly
That must mean the whole drive-sprocket assembly tilts as well
Engine is fixed to main frame
So drive shaft must have a slip-joint and universals to allow drive assembly and mast to move as a unit (tilt)

Do I have that right ?

Love your project and machining.

ps: ... At this point I don't think engine torque would
Interesting (clever) design for reversing rotation on the lower drive sprocket
Question ... is the lower drive belt toothed on both sides ??
I have never seen a belt like that before.... that is why I ask . thanks.

Next question .... you say you are using a tilting mast for control
I see the pivots below the belt-sprocket assembly
That must mean the whole drive-sprocket assembly tilts as well
Engine is fixed to main frame
So drive shaft must have a slip-joint and universals to allow drive assembly and mast to move as a unit (tilt)

Do I have that right ?

Love your project and machining.

ps: ... At this point I don't think engine torque would be an issue.
Hello thanks for the comments!

Yes the lower belt is double sided and wraps around the backside of the large pulley to reverse the direction. It's the same gates gt2 poly chain as used on the top. When I started this project I also didn't realise you could get a double sided synchronous belt like that. They aren't off the shelf items and have to be made to order but are available.

Yes the whole drive assembly tilts and so it was necessary for the primary drive shaft to extend and tilt to accommodate this. I've used Audi A4 tripod plunging constant velocity joints, these plunge by using 3 roller bearings meaning there's little to no resistance while plunging under torque. If I used the more typical spline type plunging cv joint there is a lot more friction under load and wouldn't work on my machine.

The cv joints aren't designed to rotate at engine rpm so there is a question mark there. When I first tested the joints to around 5000 rpm the lower boot burst throwing cv grease all over my tool box which was about 5m away. Luckily it was a nice narrow band of projectile grease and only really got the tool box and more importantly missed me. 😀
 

Martin W.

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Thanks for the answers .

I can only see one monster under the bed (maybe)

Your spinning rotors will act like a giant flywheel (gyroscope) and to tilt the whole assembly may require armstrong forces ... on the other hand when you move the controls the suspended fuselage itself may move instead ... which would act like a weight shift machine ... and accomplish the desired results anyway.

On further thought , your blades are on teeter hinges , so the gyroscopic resistance may be eliminated from the mast itself ... I don't know for sure .... my knowledge does not extend that far.

ps: the Audi axle is excellent and bulletproof and they last forever if boots are good and no dirt gets inside ... flat out on the Autobahn they spin at 2000 rpm so they can handle some rpm fairly well
 

btd1982

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Thanks for the answers .

I can only see one monster under the bed (maybe)

Your spinning rotors will act like a giant flywheel (gyroscope) and to tilt the whole assembly may require armstrong forces ... on the other hand when you move the controls the suspended fuselage itself may move instead ... which would act like a weight shift machine ... and accomplish the desired results anyway.

On further thought , your blades are on teeter hinges , so the gyroscopic resistance may be eliminated from the mast itself ... I don't know for sure .... my knowledge does not extend that far.

ps: the Audi axle is excellent and bulletproof and they last forever if boots are good and no dirt gets inside ... flat out on the Autobahn they spin at 2000 rpm so they can handle some rpm fairly well
Good to hear 👍
You have asked a question I've wondered myself when I'm articulating the rotor mast in the air, am I moving the rotor discs or am I moving the fuselage or both ? As you say gyroscopes want to continue in the same plane so I'm thinking it's more weight shift. The Nolan brothers of a similar design marketed their machine as a pendulum helicopter. Maybe that's a clue, I know they used hydraulic cylinders for control but I don't think it was pump assisted in anyway, so normal mechanical advantage would apply through piston sizes.
I doubt I've got the ratios right for the inclination of the mast to the movement of the cyclic stick.
Ben
 

skyguynca

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On mine since the weight is only 248lbs with rotor almost at flight rpm it makes the whole helicopter easy to lift, and it is controlled through total weight shift, just like a hang glider. Plus I have a tail rotor. One hand on the flight bar has pitch for the main rotor and the other has tail rotor control. Hopefully not too much of a load to handle.
 

btd1982

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Opposite rotation cancels gyroscopic force if the rotating bodies are equal. Each rotating body still generates gyroscopic force against its suspension.
Thanks for the input Chuck, I've read many of your posts.
I understood that the gyroscopic precession would be cancelled in a counter rotating system but I didn't know the gyroscopic force will be cancelled. So the force required to tilt the mast will be minimal?

Here are some figures for the machine any thoughts on whether it will fly?
Engine Johnson Outboard 60hp 2 stroke 55lbs/ft torque
Rotor gear reduction 5.6:1
Rotor Diameter 4.3m/14.1ft
Rotor RPM 900
rotor tip speed 453mph
Airfoil section 0012
Blade chord 4.75"
Blade Centripetal force 2757kg/6078 lbs
Blade COM from axis 1169.5mm/46"
Blade Weight 2.6kg/5.73lbs
Solidity Ratio 0.07:1
Disc Loading 1.625lbs/ft2
Empty weight 130kg/286lbs
AUW 240kg/529lbs
Teeter undersling 25.5mm
cone angle 1.25 degrees

thanks Ben
 

btd1982

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On mine since the weight is only 248lbs with rotor almost at flight rpm it makes the whole helicopter easy to lift, and it is controlled through total weight shift, just like a hang glider. Plus I have a tail rotor. One hand on the flight bar has pitch for the main rotor and the other has tail rotor control. Hopefully not too much of a load to handle.
wow, sounds amazing. you have done extremely well to achieve that weight. Using weight shift is there a time lag in control inputs compared with a swash plate type control?
 

btd1982

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Thanks David Just read it again. Excellent thread !
 

btd1982

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I expect you have seen the helitrike on youtube. Apart from being really tall and top heavy I was wondering why didn't they have the control to fly it more than a few inches above the ground? It looked a decent attempt.
 

skyguynca

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I expect you have seen the helitrike on youtube. Apart from being really tall and top heavy I was wondering why didn't they have the control to fly it more than a few inches above the ground? It looked a decent attempt.
Yes I have seen it. Even though it does not look like the B9, its principle of operation and your rendition of the B9 are similar and will have the same problems. If you look you will see a swash plate and PC control rods. This is hooked only to the rudder pedals for yaw control.

Still it is on a gimbal like your rotor system except theirs is not an offset design. The offset design of Bensen's heads on both the B9 and the Gyros helps in stabilization in flight. Now even though both use a pivot to control cyclic movements, the most dangerous time is when the airframe is on the ground and you move to hover. Yes you can compensate for wind and unlevel terrain, transition to hover would need to be quick. That is how they had the accident that destroyed two prototypes. Skid drag then followed by dynamic roll over. It is unstoppable once it starts.

That is why I chose to go with a single rotor and tail rotor. Keep mechanics simple, the aircraft can be lifted clear of the ground then transition into hover. I also don't use a lower airframe attached to the rotor system by a gimbal. Just a rigid seat harness that allows me to shift my weight separate of the airframe for cyclic control.

While the B9 flew, a few observers said it was an handful in transition to hover. Still it was big and heavy. The rotorblades very inefficient requiring to much power. The pamplet on the B9 said it weighed 450 lbs empty and needed 70 hp to fly. Just for an comparison a KA-10 with full cyclic and collective controls, and two 3 bladed rotor systems had an empty weight of 516 lbs (only 66 lbs heavier) and needed only 54hp......

The B9 is a great starting point but with a bit more work and better chosen materials you could not only make it lighter, but with full controls and still do it on less hp when you use the KA10 as example.

I believe you could still keep it weight shift but with collective and yaw control (just one cam assy for differential collective) and make it lighter using less hp.

Another thing you have to remember is that even though it is a coaxial and probably arguably more stable than a single rotor, it is still unstable.

If you look at the HZ-1 Aerocycle you see that the early flying platforms of the 1950's were much more stable, again after you got it into hover. Oh and a later version of this one had skids installed, much better than the airbag landing gear. Sort of what the PAM copied but a smaller rotor system requiring much more power.

Specifications (HZ-1 Aerocycle)​

Data from [5][8]

General characteristics

  • Crew: 1 (pilot)
  • Height: 7 ft (2.1 m) from air bags to handle bars
  • Empty weight: 172 lb (78 kg)
  • Gross weight: 454 lb (206 kg)
  • Fuel capacity: 1 US gallon (3.8 l; 0.83 imp gal)
  • Powerplant: 1 × Mercury Marine 20H outboard motor, 40 hp (30 kW)
  • Main rotor diameter: 2× 15 ft (4.6 m)

Performance


  • Maximum speed: 75 mph (121 km/h, 65 kn)
  • Cruise speed: 55 mph (89 km/h, 48 kn)
  • Range: 15 mi (24 km, 13 nmi)
  • Endurance: 45 minutes
  • Service ceiling: 5,000 ft (1,500 m)
1614461095963.png 1614461158736.png



At least that is my take on it.
 
Last edited:

skyguynca

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I have to admit I have toyed around with doing a flying platform too........you could buzz around at tree tops and more if brave enough.
Theoretically you could auto-rotate if you built the rotor system to do so.

Hazard is the low rotor system, no more of a hazard to the pilot, whether the rotor is on top or on bottom you still have to clear the rotor system when hovering and movement on the ground. However HUGE hazard to people not paying attention and getting too close.

But in all my research I have never found a single instance of a coaxial rotor system below the pilot that was ever designed to or even try to auto-rotate.
 

skyguynca

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Also when researching my coaxial drive units for projects I came up with using a planetary gear set from an automatic transmission. Mounted in a housing with the housing connected to one rotor drive and the output shaft connected to the other you would still get shaft rpm reduction but also drive both rotors in different directions. Always torque balanced.
 

C. Beaty

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Equal and opposite rotation cancels external gyroscopic force. I once made up a demonstrator using a pair of small DC motors to illustrate this effect. Many people were amazed to learn that external force was zero.
 

btd1982

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Yes I have seen it. Even though it does not look like the B9, its principle of operation and your rendition of the B9 are similar and will have the same problems. If you look you will see a swash plate and PC control rods. This is hooked only to the rudder pedals for yaw control.

Still it is on a gimbal like your rotor system except theirs is not an offset design. The offset design of Bensen's heads on both the B9 and the Gyros helps in stabilization in flight. Now even though both use a pivot to control cyclic movements, the most dangerous time is when the airframe is on the ground and you move to hover. Yes you can compensate for wind and unlevel terrain, transition to hover would need to be quick. That is how they had the accident that destroyed two prototypes. Skid drag then followed by dynamic roll over. It is unstoppable once it starts.

That is why I chose to go with a single rotor and tail rotor. Keep mechanics simple, the aircraft can be lifted clear of the ground then transition into hover. I also don't use a lower airframe attached to the rotor system by a gimbal. Just a rigid seat harness that allows me to shift my weight separate of the airframe for cyclic control.

While the B9 flew, a few observers said it was an handful in transition to hover. Still it was big and heavy. The rotorblades very inefficient requiring to much power. The pamplet on the B9 said it weighed 450 lbs empty and needed 70 hp to fly. Just for an comparison a KA-10 with full cyclic and collective controls, and two 3 bladed rotor systems had an empty weight of 516 lbs (only 66 lbs heavier) and needed only 54hp......

The B9 is a great starting point but with a bit more work and better chosen materials you could not only make it lighter, but with full controls and still do it on less hp when you use the KA10 as example.

I believe you could still keep it weight shift but with collective and yaw control (just one cam assy for differential collective) and make it lighter using less hp.

Another thing you have to remember is that even though it is a coaxial and probably arguably more stable than a single rotor, it is still unstable.

If you look at the HZ-1 Aerocycle you see that the early flying platforms of the 1950's were much more stable, again after you got it into hover. Oh and a later version of this one had skids installed, much better than the airbag landing gear. Sort of what the PAM copied but a smaller rotor system requiring much more power.

Specifications (HZ-1 Aerocycle)​

Data from [5][8]

General characteristics

  • Crew: 1 (pilot)
  • Height: 7 ft (2.1 m) from air bags to handle bars
  • Empty weight: 172 lb (78 kg)
  • Gross weight: 454 lb (206 kg)
  • Fuel capacity: 1 US gallon (3.8 l; 0.83 imp gal)
  • Powerplant: 1 × Mercury Marine 20H outboard motor, 40 hp (30 kW)
  • Main rotor diameter: 2× 15 ft (4.6 m)

Performance


  • Maximum speed: 75 mph (121 km/h, 65 kn)
  • Cruise speed: 55 mph (89 km/h, 48 kn)
  • Range: 15 mi (24 km, 13 nmi)
  • Endurance: 45 minutes
  • Service ceiling: 5,000 ft (1,500 m)
View attachment 1151861 View attachment 1151862



At least that is my take on it.
Thanks so much for sharing your research. Questions are being answered that I haven't been able to find answers to, its brilliant!

So it seems I can expect high instability going from ground to hover but once in hover things might get easier. Thinking about it I have experienced this to some degree in a rc model, the transition from ground to hover is always a bit sketchy, then it stabilizes further away from the ground.

I reckon a dynamic roll over with the helitrike would be a major problem with so much weight so high.

Interesting thought on the offset hinge I don't know much about this but looking at the air scooter and Nolan designs I can't work out if they had offset hinges.

on your weight shift machine, is the pilot seat suspended from a single chord like a hanglider?

I need to decide how best to tether the craft to try and make testing as safe as possible. If I ever experienced a dynamic roll over and walked away I think it would be the last time I went near the machine. Its tether versus long poles bolted to the skids or I make some sort of telescopic platform?
 

btd1982

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Equal and opposite rotation cancels external gyroscopic force. I once made up a demonstrator using a pair of small DC motors to illustrate this effect. Many people were amazed to learn that external force was zero.
I'm amazed but also really pleased that this is the case! super bit of info!
 
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