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Part Four - Results!
By Gene BuckleControl and Movement
This is the connecting fork for the pitch control. This originally connected via pushrod to a large pendulum and then from there on back to some kind of actuator. Here's a picture of the pendulum:
As near as I can figure, the pushrod from the pitch moment fork connected to the right side of this pendulum, and the pushrod back to the actuator connected to the left side. The pendulum itself moves like it's quite heavy. [Update 10/09/00] I've found through reading of an article on the control system in Eagle Talk (a MCAIR published "magazine" on the F-15) that the pendulum is actually used to limit G induced pitch movement of the stick. For the "upgrade" to simulator use, I'm going to connect a new pushrod from the pitch moment fork back to the right side of the pendulum as I think it was originally. From the left side of the pendulum, another pushrod will be connected to a bidirectional, scratch built spring damper that will return the flight stick to its neutral position when you let go of it. [Update 10/15/00] The primary pushrod for the pitch axis has been installed.
I've also got the spring damper built for it and it's ready to install. The roll axis pushrod has been built now as well. It's 59" long and the rear portion is where the spring damper will be built. Because of the pendulum I had to use two pushrods for the pitch axis, but I only needed one for the roll system. After some serious thought on the trim system, I've decided to accurately replicate the "feel" of it. The trim system in the F-15 actually deflects the control stick when trim is applied. This is true for the rudder pedals as well. In my version, only the stick will deflect as the rudder trim system is much more complex to replicate, especially considering the space I have available to me. It won't be installed in the "first" version of the control system however.
I'll be utilizing reversable DC motors with screw drives to move the center mounting point that the spring dampers attach to. This will allow the trim hat on the stick to move the center of the stick to trim out the aircraft. The other half of the pitch moment fork will have a segment of NyRod connecting it to a 100k linear potentiometer. I was originally considering a fancy rack & pinion system so I could translate the small movement the pitch moment fork has into something usable with a rotary pot. Then I remembered that they do indeed make nice little linear pots. I felt sheepish to say the least. :)
You'll notice that there is another fork to the upper left of the pendulum picture. This is actually the lower half of a pushrod passthrough. The roll moment fork connects to this and this drives a lateral pushrod that translates the movement to the aft avionics bay on the right side of the airplane. I don't think I'll end up using that in the final version of the control connections, but we'll see. Here is a picture of the roll moment fork:
As you can see, it's got three "prongs" to it. It will be connected up almost indentically to the method I'll be using for the rudder and pitch controls.
