RJWS

What would the technical problems be in having contra-rotating gyro rotors? They could be a smaller span, presumably, and therefore more rigid, thereby getting around the likelyhood of blade clashing and the problems of ground bunts done away with because the gyroscopic forces would be cancelled out. I'm definitely no authority on gyros, but it works for helicopters, doesn't it?
Secondly, why not dual rotors like a Chinook on a gyro? I know the chinook has some unique flying problems but they are due mainly to the fact that it has powered rotors. It would not be difficult to synchronise the two rotors, albeit at the expense of some weight gain. Can anyone set me straight on these questions?
Ron

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RJWS

BeefBear

Ron, just another thought for you to consider. Normally as a rotor begins its circuit there are a number of phases the the rotors go through. By this I mean as a rotor comes into the wind it will generate more lift than it does when heading downwind. If you have counter rotating blades one will be wanting to climb where as the other as it goes down wind will be wanting to sink. What ever the rotor behaviour is, it will mean that the height between the two sets of rotors may be critical.

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Another day, another chance to ask why it is so?

RJWS

I thought as much. But how do helicopters get away with it? Do they have super-rigid blades, or some such? Perhaps they don't! There are not too many double rotor craft about, from what I have seen. But, hey! I'm stuck over here in the place the technology comes to last (W.A.).
Ron

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RJWS

JOE NELSON

RON,

ITS MY GUESS THAT A CONTRA-ROTATING GYRO WOULD HAVE PROBLEMS WITH TIP VORTICES. THE UPPER BLADES WOULD PASS THROUGH THE TIP VORTEX OF THE LOWER ROTOR. THIS WOULD BE A PROBLEM SINCE THEY WOULD BE PASSING THROUGH THE DRIVEN PART OF YOUR UPPER ROTOR BLADES CAUSING YOUR UPPER ROTOR TO BE INEFFECT IN LIFT AND REDUCING YOUR UPPER RRPM.

YOUR CHINOOK IDEA MAY WORK! THE ROTORS WOULD HAVE TO BE COUNTER-ROTATING AND CO-PLANAR. THE BLADE OVERLAP WOULD NEED TO BE APPROX 30 PERCENTAND A POT FULL OF HORSEPOWER.

ITS BEEN ALMOST 40 YEARS SINCE I HAD ANY FORMAL TRAINING SO PLEASE CHECK MY INFORMATION!!! BESIDES, BACK THEN I WAS MORE INTERESTED IN FAST CARS AND FASTER LADIES. NOT TO FORGET MANY BRAIN CELLS KILLED BY FOSTER'S AND FLYING AT HIGH ALTITUDES WITHOUT O2.

Echo 2

Hey Ted ,
where you bin hiding ?
Contra-rotating blades & dual rotors - seems like taking a simple design & making it complicated ( & probably less efficient ) .

Contra-rotating would have the problem of the top blades not getting clean air ( as Joe pointed out ).To get enough teeter the blades would have to be a fair distance apart , plus how would you spin them up?
Not by hand ! A mechanical pre rotator would be complicated , meaning more things to go wrong plus the extra weight .

Dual rotors for one thing would make the whole machine too long to be practicable , plus the cost of an extra set of blades/rotor head/controls . I don't know what the dynamics of it would be inflight , with the counter rotating blades , but again you would have prblems with teeter & the rear blades not getting clean air.
Side by side dual intermeshing blades may work . They are both out in clean air ( sort of ) , the advancing blade on , say , the left hand might not pass far enough over the retreating blade on the right to get clean air . I wonder what size blades you would need ? If you normally fly on 27'ers , would two sets of 13's or 14's be enough ?
I think I will stay with KISS . Don't get me wrong , it's always good to have some discussion ( even though the idea is not new ).

Echo

niquenaque

Ron,

From memory I think that Cierva did try this in his very early and 'failed' designs, so it may have been done before and discarded. It may pay for you to go trawling through the archives

The torque that you refer to on take off is a product of the operation of the propeller, the air frame and rotor thrust vector have to offset the twisiting forces caused in reaction to the torque of the propeller when the wheels leave the ground. So the solution there is to have contra rotating propellers as opposed to rotors, that would neutralise the torque roll on take off.

Here's a link to google for co-axial gyrocopters - http://www.google.com.au/search?hl=e...G=Search&meta=

As a co-axial design the chance of blade clash would be much greater than for a helicopter I believe, not forgetting that a helicopter draws air *down* into the rotor system, whereas a gyro flys on the *rising* air entering the rotor system, though I'm quite sure that a co-axial heli must be able to autorotate, otherwise no smart pilot would be caught dead in one... on skimming back through the history of co axial helis there seem to have been a few fatal failures relating to blade clash, I wonder if that was when an auto was attempted?

Here is an interesting site: http://www.hyperdynamics.net/ though what they say is regurgitated from the usual sources.

As to the intermeshing rotor system, isn't that the Focke-Wolfe FW-61? I'm pretty certain it is [answer - no - I'm wrong, it is a helicopter and is not intermeshing see: http://en.wikipedia.org/wiki/Focke-Wulf_Fw_61]. I've thought of such a beast with the advancing blades set to the outside and the retreating blades going over the fueslage, it would need a gear box or similar to lock the blades into synchronised position. They must have got it right with the FW-61 in terms of control of the heads, etc as they did fly - you could investigate that design.

Here's a good read on how the gyro works - at a radio control model level:

http://www.rcgroups.com/forums/showthread.php?t=614030

Hope this helps,

Cheers,

Nick.

Bell430

Another good question,

There is no reason why a dual rotor gyro couldn't work. As already pointed out, ALL counter rotating helicopter designs have the ability to auto.

The hardest design to make work would be the co-axial design for a couple of reasons....

1. Cyclic control of the rotor system must be through a swash plate or similar (weight, feathering hinge, bearings etc) or you would need to pivot the entire mast (CoG changes, large moment arm at top rotor, control travel is reduced and weight of design.

2. The rotor blades would need to have 'washout' or taper to increase the tip clearance as each blade 'flaps to equality' or the mast would need to be alot higher than what you would find in a comparable helicopter.

Just to mention a few....

The intermeshing desing is the one that I favour ( I am actually building an intermeshing design as we speak) The heads are in the same plane so direct control can be used with some success, tip clearence is not an issue in a two bladed system especially when the advancing side is over the fueselage, and you can use a pre-rotator to spin up the blades to effect a jump takeoff without the probs of torque. The only real technical issue is the synchronisation, but as mentioned can be accomodated reasonably easily, especially concidering that there is minimal torque being transmitted through the synchros.....

My design is primarily as a true helicopter but I may adapt it to a gyro design if/when I get the 5hits with the drive system.....

My main interest for adapting it to a gyro is for the ability to make jump take offs and to reduce ground roll... I also like the challenge, so even though it won't be the fastest or most practical design, I am having fun building it.

Paul

Fencing Wire

G'day Ron,
I'm not a rocket scientist or aero engineer. In fact, I have a little trouble spelling my name the same way twice. But I did train as a motor mechanic about 40 years ago. While I've been out of the game for 35 odd years, I still understand basic principles. Tim is probably the man to explain it more fully (once he gets back from Lameroo). But I'll give you my laymans understanding.

The way I understand it is that it has to do with lead/lag (you'll know far more about that than I will). The gyro mast is limber to absorb some of the impulse from the rotor. When you have 2 rotors (no pun intended, Geoff) operating on the same mast, the impulses from one set of rotors will interfere with the mast flex that is designed to absorb the impulses from the other set of rotors. That means that the impulses get absorbed by the hub bar, rather than the mast. I might have the bull by the balls with respect to the terminology etc, but you might get the drift of where it is going. That is my understanding of what killed off 2 rotor systems that were being experimented with by Boyette, Henley-Smith, Goodwin et al (even though they weren't contra-rotating), I can't see why the same circumstances shouldn't occur.

Greater minds can probably give you a far better explanation.

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FW

I can't remember what I did for brains before shit became popular.

JOE NELSON

RON,

I WAS LOOKING AT SOME RUSSIAN KAMOVS AND IT APPEARS THEY HAVE RIGID ROTOR SYSTEMS. THE TEETERING ROTOR MAY NOT WORK IN YOUR APPLICATION AFTER SEEING MY VIDEOS.

ALSO, THE ROTORS APPEARS TO BE INTERCONNECTED SO THEY ALWAYS HAVE BLADES ADVANCING (INTO THE WIND) EITHER ON THE UPPER OR LOWER ROTOR. ANOTHER OBERVATION IS THEY ALL HAVE 3 BLADED ROTORS AND TWIN ENGINES MAKING OUR APPLICATION PROBLEMATIC.

I DON'T KNOW IF TWO ENGINES SAYS SOMETHING ABOUT THE KAMOVS ABILITY TO AUTOROTATE (WHERE WE FLY ALL THE TIME) OR IS IT A PERFORMANCE IMPROVEMENT ISSUE. BELIEVE ME, BAD AUTOROTATION TECHIQUES "HURTS."

RON, IF YOU GET A CHANCE TO LOOK AT SOME CONTRA-ROTATING AIRCRAFT CHECK OUT THE KA-50 AND KA-52....BEAUTIFUL MACHINES!! I'M A TERMINAL GEARHEAD...SORRY.

JOE

Bell430

Joe

Some terminology probs here.... The rotor heads that the Kamovs use are concidered 'fully articulated' in that they have physical hinges that allow lead/lag, flap and pitch. A true 'rigid' design, as yet, has not been commercially produced, we have instead the class of 'hingeless' rotors that incorporate flexures whether through elastomerics or blade composites... I may have mentioned this before. The aerodynamic conciderations for a truly rigid design are huge and the forces associated are even bigger. I believe we will see very rigid designs in the near future but as yet they are not viable.

Ok, now we have covered that I should just check one of you observations...."THE ROTORS APPEARS TO BE INTERCONNECTED SO THEY ALWAYS HAVE BLADES ADVANCING (INTO THE WIND) EITHER ON THE UPPER OR LOWER ROTOR." Yep, all counter rotating systems will have a leading side and a retreating side, no matter from which angle or side you look at.

Teetering systems or 'semi rigid' designs are possible in co-axial designs but the gap between blades will have to take into account the phenominon refered to as 'flapping to equality' which is the dissimetry of lift produced with any forward speed. There have been several designs in the past that use teetering heads.

Now we should talk a little more about lead and lag. For those that arn't familiar with the term etc I will give a quick generic (read... basic) explanation. Lead and lag is a by product of the 'flapping to equality' mentioned above. On a gyro/heli traveling with any forward speed there will be a difference in the 'relative airflow' (RAF) over the blades. The advancing blade will have its rotational speed PLUS any forward speed of the aircraft. The retreating side has the rotational speed MINUS the forward speed of the aircraft. As a result of the the difference in airflows the advancing blade will produce more lift and the retreating side less. The advancing side will fly (flap) up and the retreating side will decend. As the advancing side flys up its centre of mass moves inboard in reference to the 'tip path plane' (TPP) this is called the coriolis effect (the usual analogy is the spinning ice skater bringing her arms closer to her body to increase rpm) the result is that the advancing blade tries to lead (go faster) in reference to the retreating blade which is trying to lag equal and opposite. To compensate for this reaction designers (cierva) came up with the 'underslung' head. As the centre of mass of each blade moves the total mass of the rotor system is allowed to shift lateraly (toward the retreating side), this balances out the rotor system and effectively cancels out the urge to lead and lag....... clear as mud.

The flex in our gyro masts is a nice feature as it allows small inbalances associated with the rigging or manufacturing of our rotor heads/blades to be absorbed giving us a relatively nice stick feel. Believe it or not, if the rotor head etc is well balanced from the start we would not need a flexible mast...... as long as we undersling our teetering hinge. I'm sure I will get some flack for the last bit, but hey, it's true. I guess I can mention the fact that there will always be some stick shake due to the different pressure changes throughout the rotor cycle etc.... a flexy mast will alleviate some of these shakes from getting to the stick.

Underslinging of the rotor head is the key to reducing lead and lag forces and ALL teetering semi rigid designs incorporate undersling.

Another point mentioned was the airflow interaction between the upper and lower rotors. This dosn't have alot of bearing on dual rotor design. there has been some developement in the use of different rotor diameters (between upper and lower) to reduce noise but was not for airflow interaction per sei, but for tip vorticy interaction. The 'solidity ratio' of gyro's/helis with two bladed systems is very small so the intereaction of airflows is not great. Start putting more blades on and things change.

So there we have it.... sorry Joe if it seems that I was targeting you in particular, I just thought it was a good idea to clear up a few points.

Multi rotor gyro's are not impossible by any means, so if you want something that will turn heads (but not really achieve anything) I say, go for it !!

Cheers

Paul