I had another thought for a force feedback yoke....Wrap wire around the shaft of the yoke, to make an electromagnet. Slide it into a tube, around which you wrap more wire to make that an electromagnet too. Connect them in series in such a way that their polarities are opposite. When both coils are energized the magnetism will center the inner coil inside the outer one. Drive the voltage to the coils from the output to the ASI, in such a manner that at at 0 knots there is nothing, and the yoke can flop around with no force at all, while at 200 knots or whatever the voltage is at maximum and you really need to pull hard to move the yoke more than just a little bit. A bell crank and a push rod could drive a similar arrangement for aileron force, while the cable between the rudder pedals could push/pull a magnet in a tube for rudder force.Elevater trim would be easy to make realistic in this manner too - a physical connection such as a chain and gear between the trim wheel and the outer tube could move the outer tube magnet along the shaft of the yoke so as to remove any centering force in the position you desire.Richard

Richard,The physics is basically correct, but the magnitudes are too low to be effective.It is surprising how strong the magnetic fields must be and how much current is needed to produce even a few pounds of force. If you have a magnetic field of 10,000 gauss, a wire at right angles to the field 1 meter long carrying 1 amp of current, there will be 0.22 pounds-force imparted to the length of the wire.The design of magnetic systems is not at all intuitive. The pull a small neodymium magnet can exert on a refrigerator door is amazing, but does so over only a very small distance. When trying to extend this force over distances of several inches, one gets outrageous numbers.There are commercial products called linear magnetic actuators that do this. Typically they make use of a track with embedded permanent magnets and a set of air-core coils that extend into a gap in the track. Essentially it's a three phase, electroncially commutated motor. Mikewww.mikeslfightdeck.com

Is the physics really correct? For example... if you take a transformer with dual primary windings for 110/220 input and connect them in series out of phase, you will get NO output on the secondary as ther is no net change in flux. The fields will cancel each other, so you would need to be able to control the current through each coil/solenoid independently so that one could "win" over the other.Gus

Gus,Coaxial solenoids will exert a magnetically mediated force on each other regardless of the relative phase of the two coils. The direction of the force will flip if the phase is reversed, but the magnitude will be the same. I understand what you're saying about transformer flux, but it doesn't really apply to this. The magnetic fields are not uniformly distributed or directed in these coaxial solenoids. The forces on each solenoid is the summation of the force exerted on each turn. Most turns see a force that is directed outward (or inward) orthogonally from the solenoid axis. It's only those few turns that are in the field at the end of the other solenoid that experience a force with a component in alignment with the axis. It's hard to explain in words. It's really a vector field problem that begs for a lot of drawings.You might think of this arrangement of two solenoids as an extended voice coil (ala, audio driver or speaker) with the permanent magnet assembly replaced by a second coil.Mikewww.mikesflightdeck.com

Hi,I would just agree with Mike. My tests here are not that encouraging.Theoretically it works, but getting it working on a flight control is not that simple. The tests I made with 12200 Gauss Neodynium magnets are funny, but a simple spring is doing a better job. I did get in contact with a engineering company called www.movingmagnet.com. and which are not to far from Strasbourg/FranceThey are making such magnetic actuators Mike is talking about. I explained to them what I wanted to achieve. They were ready to help me but it would have cost at least 10.000 Euros. As Mike said, theoretically, it seems very seducing, and I was seduced. Looking at some examples, one believe it will easy to do by itself. That's the error. There are so much mechanical precise items to build in order to match your pitch column or roll axis that either you have all the specific equipement or then you have to pay a lot.The principle is known since decades but applications in automotives, aerospace and more are just coming yet. I did talk to a Flight engineer school in France and they were even not aware about all possibilities offered by electro-magnetics devices It will one time as it is doing now, changing a lot of thing. The hydraulic circuits of the Boeing Dreamliner will be cut by two due to the intensive use of electro-magnets. Steering wheel, Flight controls AFU, even landing gear and much more, will be made using electro-magnets. The french company Messier ( just close to my city) is producing the landing gear for the 7E7 and I heard about that challenge. I am convinced that a company like -Movingmagnet- would be able after a certain time of R&D to produce such device especially conceived for us, I would say, a force feedback plug and play stuff. But myself, just armed with my Dremel, and some basics electric tools wont be able to do the job. But I would follow with great interest every attempt in that area from any of you guys.RegardsRoger

Coming from the (clearing of throat sound) mechanical engineering side, a hydraulic system would be a whole lot easier and inexpensive to meet your requirements. It would also offer the advantage of being adjustable. You could easy adjust the feel. John

MikeStill not convinced the "theory" holds. I still see it as coupled coils, why would it make a difference if they are air core? The same "rules" still apply. The only difference is the permeability (for air, 4*pi*10^-7, which "stinks" for generating higher flux densities unless the coil diameter is very small and you have a very high number of turns). Is it some sort of fringe effect? We use this flux "canceling thing" routinely for integrated planar magnetics in power converters.Gus

Gus,For want of a better term, it is very much a "fringe effect". If you have two coaxial solenoids, the flux density inside will indeed add/cancel depending on the relative direction of the currents in each. But it's not the center of the solenoids that act on each other. It's the flux passing through the windings of the solenoids, and the flux densities vary in direction and magnitude along the length of the solenoids.The trick to determining magnetically mediated forces is to look at the flux densities on the wires that make up each solenoid. The only flux that will generate a force parallel to the solenoid axis is flux that is at right angles to both the axis and to the wire. This condition exists at the ends of each solenoid where it "exits" the solenoid and loops back to the other end. There is no net force if the two solenoids are centered on each other. However, if one is moved partially off the other, the asymmetry creates an imbalance and there is a net force.The reason some magnetic linear actuators use air core windings is to prevent the permanent magnets in the armature tracks from grabbing the moveable windings and causing it to stick to one of the track's pole faces. I believe there are some units that have magnetic cores in the windings, but they have a more complex mechanical support to prevent this problem.