Designing control force loading

[WJH308]

I believe I discovered how to do this. I am going to connect the flight controls to linear actuators, and they will be connected to the linear actuators with load cells inbetween. My L1011 yoke has 4 load cells in it, 2 for pitch, 2 for roll, one for each autopilot. Light control loading, the linear actuator moves with the pilots movements as sensed on the load cells. To increase control loading, you simply require the pilot to excert more force on the controls to make the linear actuators move with the pilots inputs. For pitch trim, as we all know, trim feels neutral at a certain airspeed, as trim is for airspeed. As the airplane picks up airspeed, more than what is trimmed, the linear actuator will move the yoke in the direction of pitch that the airplane is trimmed for. Pilot resists this, and the larger the airspeed spread to trim speed, the more force that is required to fight against the linear actuator. Simply move the trim wheels to relieve control pressure, which will also trim the airplane for the new airspeed, as it does in real life. I just ordered a microcontroller developement board and a 25lb load cell to experiment with this. Will probably make a mosfett powered H bridge motor controller that runs off the MCU to control the linear actuator. More to come when I find time between my flight instructor job that takes 6 out of the 7 days in the week...
I am pretty sure this is how the professional sims do it, and well, how the L1011 did it with the autopilots and the trim wheel. The trim wheel on the yoke of the L1011 didn't do anything when in CWS mode unless the pilot excerted 4lbs or more of force. I am going to rename the L1011 the "Enterprise" Freaking airplane was way ahead of its time.

[Jackpilot]

I do not want to be rude ..but in plain English ..how does it work?

[WJH308]

Blood, sweat, and tears

[Michael Carter]

I believe I discovered how to do this. I am going to connect the flight controls to linear actuators, and they will be connected to the linear actuators with load cells inbetween. My L1011 yoke has 4 load cells in it, 2 for pitch, 2 for roll, one for each autopilot. Light control loading, the linear actuator moves with the pilots movements as sensed on the load cells. To increase control loading, you simply require the pilot to excert more force on the controls to make the linear actuators move with the pilots inputs. For pitch trim, as we all know, trim feels neutral at a certain airspeed, as trim is for airspeed. As the airplane picks up airspeed, more than what is trimmed, the linear actuator will move the yoke in the direction of pitch that the airplane is trimmed for. Pilot resists this, and the larger the airspeed spread to trim speed, the more force that is required to fight against the linear actuator. Simply move the trim wheels to relieve control pressure, which will also trim the airplane for the new airspeed, as it does in real life. I just ordered a microcontroller developement board and a 25lb load cell to experiment with this. Will probably make a mosfett powered H bridge motor controller that runs off the MCU to control the linear actuator. More to come when I find time between my flight instructor job that takes 6 out of the 7 days in the week...
I am pretty sure this is how the professional sims do it, and well, how the L1011 did it with the autopilots and the trim wheel. The trim wheel on the yoke of the L1011 didn't do anything when in CWS mode unless the pilot excerted 4lbs or more of force. I am going to rename the L1011 the "Enterprise" Freaking airplane was way ahead of its time.

Sounds like an interesting project.
Pictures, as always, are welcome when you start your project. I'd really like to see this.

[Mike.Powell]

WJH308,

That's pretty much the way it works. One item you didn't mention was the position sensor. Your control electronics will need the control position as a parameter when calculating the force required of the actuator.

[Roland]

Indeed a very professional approach. You may want to contact Ian Hopper (buggies build for fun). He also experimented with control loading and toyed with the load cells idea.

This approach is a bit over my head, I'll stick with the servo-gain-offset system.

[AndyT]

Mike beat me to it.

You will need the position sensors. You should also have a strain guage connected to your sensors so that you can keep track of how much force you are actually imposing. I don't have the numbers, but I know that Pro sims have them all calculated and can dial up different control forces depending on the plane being flown.

For those of you that are wondering:
A load cell is like your bicep muscle. The more electricity you give it, the more it contracts. It's an analog system that can be controlled digitally. The less juice you give it, the more it can stretch out. While the newer type of load cells are electromagnetic in design, it's my understanding that the older electromechanical ones are the ones to use because of the magnetic interference created by the newer ones.

[warvet]

WHAT THE **** ARE YOU GUYS TALKING ABOUT??? *someone pass the nachos*
Tim

[AndyT]

Tim,

We are talking about making the yoke actually shimmy and shake with the air pressure hitting the control surfaces of the plane as you fly. Control loading will make it harder to fly unless you trim the plane correctly just like if you were really flying.

Ever hit a serious bump in your car? It makes the steering wheel jump wildly. Same kind of thing.

[WJH308]

WJH308,

That's pretty much the way it works. One item you didn't mention was the position sensor. Your control electronics will need the control position as a parameter when calculating the force required of the actuator.

I'll use the pots connected to the controls as the servo sensors

Mike beat me to it.

You will need the position sensors. You should also have a strain guage connected to your sensors so that you can keep track of how much force you are actually imposing. I don't have the numbers, but I know that Pro sims have them all calculated and can dial up different control forces depending on the plane being flown.

For those of you that are wondering:
A load cell is like your bicep muscle. The more electricity you give it, the more it contracts. It's an analog system that can be controlled digitally. The less juice you give it, the more it can stretch out. While the newer type of load cells are electromagnetic in design, it's my understanding that the older electromechanical ones are the ones to use because of the magnetic interference created by the newer ones.

I need to figure out how to interface to the load cells in my l1011 yoke, I'd rather not alter the yoke.

Indeed a very professional approach. You may want to contact Ian Hopper (buggies build for fun). He also experimented with control loading and toyed with the load cells idea.

This approach is a bit over my head, I'll stick with the servo-gain-offset system.

That is a method I will do some research on. Is it like the frascas where the elevator trim simply moves the centering spring back and fourth, and on the rudders to move the center position as to simulate an engine out on a multi engine aircraft?