View Full Version : Did Anyone Ever Use Hydraulics for Rotor Control?
02-05-2009, 01:45 PM
I figure that with something as light as gyro controls, that hydraulics is probably overkill and over-complication. But, in thinking about it, I had to ask. Anyone ever tried it? Did it work? Was it a terrible idea or a great idea?
02-05-2009, 02:35 PM
Iíve seen one gyro that used hydraulic cylinders instead of pushrods to tilt the rotorhead.
Large helicopters use the equivalent of power steering to control the swashplate.
02-05-2009, 03:31 PM
How about push pull cables/rods?
02-05-2009, 03:46 PM
The Littlewing, among others, uses push-pull cables.
02-05-2009, 05:42 PM
The push-pull cables can be controlled with a "Morse mixer" arrangement as shown here.
02-05-2009, 05:59 PM
Do you have more/better photos and sketches for this device?
02-05-2009, 06:00 PM
The UFO helithruster has push pull cables that control the rotorhead.
02-05-2009, 06:02 PM
What in the World is that apparatus, Al?
Could it be a device by the late BJ Schramm? He seemed to be very fond of Morse cables, using one for collective in the very first Scorpion.
Someone once told me a story about the Morse cable on his Scorpion developing a whipping motion that made it feel like a rattletrap car going down a washboard road. I have no idea of the storyís veracity.
02-05-2009, 06:56 PM
Ben, that's the only picture I've got, sorry to say.
Chuck, I can't recall where the picture came from. Its been a few years since it was first posted on one of the forums. Pretty sure its not one of BJ's devices.
02-05-2009, 07:29 PM
I could use more info on the type of push pull cables. where to get them. and any thing elts that would help
02-05-2009, 07:42 PM
John, the push pull cables on the UFO were the same that boats use for the steering. May check boat part suppliers
02-05-2009, 08:45 PM
I just found a company that will build them right here in town.
02-05-2009, 11:52 PM
In the Czech Sky Walker are also cables.
02-06-2009, 12:49 AM
Any more views of the sky walker ?
Whats the big cable for ?
My guess is its got a big parachute at the other end of it.
02-06-2009, 01:19 AM
The big cable is to get tangled around the rotorhead so that the blades stop in-flight. for very quick unplanned landings !!!!!!!!
Can't they add some more stuff up there ?????
02-06-2009, 09:46 AM
Link to manufacturer ( sory , english: Under contruction)
Unfortunately, the Proair company probably does not work.
02-06-2009, 01:51 PM
Nice looking gyro, I hope it handles as good as its looks.
02-06-2009, 11:28 PM
I have no more information.
02-12-2009, 03:50 PM
I keep thinking that hydraulics could be made to work if properly designed but is there any real advantage? And if so, do the advantages outweigh the disadvantages?
The one advantage I see is that the routing of the hydraulic lines can be wherever without any compromises that I can see other than adding weight for every turn made. And the weight could be minimized with small diameter tubing. We are not talking about high hydraulic pressure here. There might be a weight penalty once the final actuating mechanism is included. I would think that the cyclic input end would be simpler than the cyclic system now used.
A person would want to make sure the fluid was clean when adding it to the system and then inspectable filters used to make sure that clean fluid to the cylinders is maintained.
I've heard pilots comment on sloppy controls (from wear, I assume) and hydraulics should eliminate that although there would be other types of maintenance.
I suspect designing the controlling apparatus at the rotor head or rudder would be the difficult part. And then I would want some redundancy which in the case of the rudder, at least, could be satisfied by double acting hydraulic cylinders. Someone that is capable of making their own cylinders could probably incorporate a rack and pinion, to help reduce and weight and component count, for final actuation but don't know if that is feasible or practical.
The cylinders themselves would not need to be large in diameter but the length might be something else. And then there is the ratio between the actuating cylinder diameter and the actuated one that would have to be determined. If the mechanical force required to move the rudder or rotor head were known and then what force the pilot would normally input then any one of our engineers here could determine this ratio. Heck, if I had that info I could probably do it! Then there is the actual rotor head movement to cyclic movement ratio to consider.
I wonder if the operating friction in the cylinder(s) would cause a problem for the pilot. Could dampening be incorporated in the cylinder, using a floating piston of sorts, so that rotor shake felt at the cyclic would be minimized or eliminated? All in all there would have to be some diligent design work in order to put together a well functioning system.
I find this intriguing (the subject activated my Da Vinci gene!) and I'm surprised that someone hasn't done more investigation. But then what has been used all these years works and is simple even though I understand there are maintenance issues.
One thing for sure, there wouldn't be any bolts coming loose to jam controls, cables to fail or control rod issues. And redundancy should solve any cylinder malfunctions. How often do we see auto hydraulic brake or master cylinder failures that can't be survived? I've only had one hydraulic brake problem in 50+ years of driving and it was a hose failure. That was an experience!
02-12-2009, 04:44 PM
I have worked with some industrial hyd applications. I think to use hyd to dampen stick shake, you would have to use a accumilator. I also belive this could make your input's feel mushy unless your pressure was set perfect. You would also have just as many joints that could get worn and loose if not maintained. 2 on each slave and 2 on each master.
02-13-2009, 06:36 AM
I have worked with some industrial hyd applications. I think to use hyd to dampen stick shake, you would have to use a accumilator. I also belive this could make your input's feel mushy unless your pressure was set perfect. You would also have just as many joints that could get worn and loose if not maintained. 2 on each slave and 2 on each master.It has been a while (retired since '99!) since I had to think about these types of projects and even then I was a concept guy and not the engineers who had to work out the details. So, what I'm doing here is just throwing out ideas as food for thought. However, your mentioning 'having to use' an accumulator started me thinkin'.
The accumulator can come in several forms and actually is just a mechanical capacitance device.
I suspect that the bourdon tube in a small pressure guage would serve the purpose since I don't think we are talking about much capacitance. The problem with a pressure guage in this service would be the pulse frequency from any rotor blade shake. The mechanical mechinism inside a pressure guage doesn't like pulses. But since reading the pressure isn't the reason for using one then who cares if the needle falls off! The problem would be with the fatigue life of the Bourdon tube.
There are other types of pressure guages that just use a several turn coil directly hooked to the needle without any mechanical movement. But, I don't recall any small enough to be practical in this application. A small bellows would also probably serve the purpose and even a loop in the hydraulic line might do it. But, like the Bourdon tube, fatigue life is a consideration.
Normally all air should be removed from a hydraulic system but I wonder if a means of maintaining a very small fixed size 'air bubble' were incorporated wouldn't serve the purpose. I say maintained when in fact it probably wouldn't need any maintenance once the system was charged. I think the 'mushiness' in this case would be negligible and since what ever there was would be consistant it shouldn't be a problem for control. I suppose smoothing out rotor shake could seem like mushiness but as long as the control is crisp and precise I think that a pilot could adapt.
I mentioned the rotor head control rods in my previous post and forgot about the fact that the scissors that are required on some control rods could be eliminated by using hydraulics. I can see the possibility of the parts count in the control system(s) going down by using hydraulics but still not sure there wouldn't be a net weight penalty.
02-13-2009, 06:56 AM
Wow...cables...it makes so much sense to me. Eliminate slop at 3 or 4 connecting points, each connecting point eliminated is a point of failure eliminated, it looks so easy to build. And so much more aerodynamic than all that tubing. Why haven't there been more designs using this? Please explain any drawbacks to me, before I get all fired up and build a cable system on my 2 projects. I'm betting I could reduce weight as well.
02-13-2009, 08:15 AM
I have decided that push-pull cables are the answer to my problem. Having changed the yoke position from under the rear seat to under the front seat, I was going to have to build a fairly complicated series of bell cranks and push rods to get the job done, or reverse the yoke and lengthen the torque bar forward the rotor and do something different with the rotor brake.
Neither option seemed appealing. The bell crank/push rod route, because it was tedious and potentially heavy and the yoke rebuild, thought it might be a popular idea, because the yoke controls are already complete and I don't want to mess with the torque bar.
Push-pull cables solve another problem I was looking at. If a passenger gets freaky in flight and grabs the push rods, it is going to be a bad day. Push-pull cables take that problem off the table.
I see redundancy as an issue. Some designs using push-pull cables seem to favor dual light-weight cable pairs. I believe I'm going to err on the side of one fairly heavy (3/8) cable per side. No redundancy...but then, neither is there redundancy in push rods.
Cables are heavy and expensive. I think that is what keeps them off single-place gyros. They might makes sense in the weight area on a larger gyro that has to have pretty hefty controls on a bigger rotor. I think it is the expense that keeps them off most machines.
I still think hydraulics might make sense in a really large machine...say, a 4 place. But, I don't see that in my future.
02-15-2009, 08:29 AM
So, what I'm doing here is just throwing out ideas as food for thought. However, your mentioning 'having to use' an accumulator started me thinkin'. Me too!
One thing that I just thought of..... It might be very bad to use a slave and master set up. If you had a seal that started to leak, you would end up with the slave and master that wasn't centered. You could even end up running out of stroke.
The other thing I just thought of is: You might have issues with using one slave for push and pull movements. The push movement would work good. The pull movement you would be pulling a vacume. The issue with this is anything over a -14.7 psi would just be pulling a gas. (I realize there is no such thing as -14.7 psi, but if there was, it would be the same as 29.92 inches of mercury or HG)
I might be wrong, but you would almost have to use a hyd pump and a valve block to eliminate these problems. This would be alot of extra weight and would add alot more to go wrong.
Any feedback on this?
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