I hope not. I have to bleed the brakes on my mountain bikes on a regular basis, get even a little of that mineral oil on the pads and they squeal like banshees, and they're almost impossible to repair in the field. Between hydraulic brakes and 1X drive-trains bicycles have been going backwards recently. I like my airplanes foolproof and functional, and besides the mechanical linkages exercise those flabby arm and leg muscles.Now that hydraulic brake systems are commonplace in bicycles, I wonder if you could adapt such components to aircraft use? If not the primary flight controls then maybe flaps or spoilers.
Lol FLY for YOUR HEALTH!I like my airplanes foolproof and functional, and besides the mechanical linkages exercise those flabby arm and leg muscles.
Oh I see where you’re going now.There is bunch of seal friction and fluid friction in moving two pistons 3 inches. That's why it isn't done on a one seater. Also, I hate hydraulic maintenance like the hydraulic clutch on my Toyota pickup. Much prefer cables.
Depends on what you call significant.There’s also no reason for any significant amount of fluid friction for the same reason.
Easy. In any system, you have to put in all of the energy to make the force on the control through its travel plus the friction forces through its travel. The control surface energy is fixed. Drag on a few pulleys or bellcrank bearings and spherical joints can be quite small and thus the energy nearly negligible. Go to hydraulics and the seal drag on both ends times the travel of both cylinders is significant. You have to supply that extra energy with your muscles. That is for big control movements.I do not see how your first two statements would relate in anyway to the third.
Could you explain what you mean?
Bill ski you say that those forces make an aircraft unpleasant to operate .Easy. In any system, you have to put in all of the energy to make the force on the control through its travel plus the friction forces through its travel. The control surface energy is fixed. Drag on a few pulleys or bellcrank bearings and spherical joints can be quite small and thus the energy nearly negligible. Go to hydraulics and the seal drag on both ends times the travel of both cylinders is significant. You have to supply that extra energy with your muscles. That is for big control movements.
When we consider that much of our flying is at small movements and small forces on the controls, you find another disavantage to them. The friction drag of seals on cylinders and rods is about the same no matter how hard you are using them. This significant threshold force to move the cylinders at all is something you have to go through for every little correction. and then you can feel what the airplane is telling you until the forces being made at the control surfaces exceeds the seal drag... It can be flown, but it makes it more difficult and distinctly removes the fine feel many of us prefer. It makes the airplane harder to fly well and unpleasant to operate. Who needs THAT crap?
Why do the work well on bikes and motorcycles and cars. The piston movement is tiny between rest and applied positions. The seal mostly deforms to allow this movement - If you imagine the seal cross section as a rectangle, with one side in a seal groove and the other running on the piston or bore, travel to apply the brake just deforms the seal elastically into a bit of a parallelogram. Release the brake, and the seal rebounds back to a rectangle, pulling the piston back a tiny distance, but enough to relive pressure on the pads. The only time the seal slides significantly in disc brakes is when you have pushed the pistons back to do service work - you cycle the lever a couple times to push the piston back in contact, and then the seals slide only microscopically on each brake apply - the amount of pad wear.
Unboosted Hydraulics = OK for brakes, Unboosted Hydraulics = Bad for control surfaces.
You sound like you have quite a bit of experience in hydraulic systems.I've worked with hydraulic flight controls in various setups for almost my whole career. I'd never consider using such a system in a light aircraft. Too complicated, too heavy, too many things to break, and no real need. Cables and/or pushrods are sufficient.
Large aircraft with mechanical (non-FBW) hydraulic controls generally run cables/pushrods to the actuator, where they control a servovalve which ports high-pressure (~3000psi usually) fluid to the piston. Even FBW aircraft have servovalves at or next to the actuator; they just control those electronically.
What you don't see is valves at the stick porting fluid down long runs to the flight controls; that would be lots of extra tubing and have very poor control response. We experimented with locating the valves well away from the actuator on a ground test article and performance was marginal going to hilariously awful as we cooled the system down (to represent fluid characteristics at altitude).
Valves located remotely and porting fluid over long runs works fine for things like landing gear deployment or thrust reverser actuation, or even brakes (since as Billski notes, they don't move far). Not a good idea for things that need fast response.
Not answering for wsimpso1 but:Bill ski you say that those forces make an aircraft unpleasant to operate .
Have you ever operated one?
Every system I have worked with uses a high-pressure supply (powered by an engine-driven or electrically-driven pump). Crack the valve and you get movement. A system like this will tolerate some small level of internal leakage, and even a small level of external leakage over a finite time, without affecting functionality. And with a pressurized source you need valves, and a pump, and if you want real control feedback (usually considered a good thing on light airplanes) you need cables and/or pushrods to the control surface anyway. By that point on a light airplane, there's no reason to have an actuator, pump, tubing, valves, and so on.You sound like you have quite a bit of experience in hydraulic systems.
Do you think a small plane system would need any valves at all?
Well, we were testing at -40F/-40C (they're the same!) and below. Probably not dealing with those temperatures in a small airplane. But still, it's really not worth the effort.Do you know if there are hydraulic fluid’s with very thin viscosity?
I don’t think my small planes would have significant temperature differences between the ground and flight levels that they use do you think a very thin fluid could be used perhaps in the winter time when temperatures might get quite cold?
On a different note that might illustrate a problem with controls that have no feedback, I once had the chance at work to fly a simple PC sim setup with a center stick that had no centering springs (long story there that I can't talk about)--it just flopped about all over the place. It was horrible--with no force feedback of any kind you just porpoised all over the place. I had better luck flying the statically-unstable aircraft sim in my controls class.It is a problem in any kind of equipment where the operator expects linear response. Move a control X% of the throw and you should expect X% of movement. For example if all you want is 3% of movement but there is 2% of stiction in the system from rest then you have to move the control 3% before you get any response at all and then the system is likely to overshoot to maybe 5% movement. Works the same in reverse when you try to correct the overshoot.
The problem is even more pronounced on a system with light control forces where we tend to think in terms of pressure rather than actual movement.