In an airplane, it it slides forward and backward to control the thrust of the engines. The problem is, I am not sure how to go about adding more friction to the sliding motion. If I were to just design a sliding handle, If you let go of it, it wouldn't be held in place, and it would slide back down. I need something sort of "reverse bearing" that will add friction to the rotation of the handle, so that when you let go of the handle, it wont slide around-- it will just stay in the same position until it is moved again.
In Piper Cherokee airplane, the power throttle assembly is just a bushing and shaft with an adjustable pressure handle to increase the grip. It has worked on my airplane for 41 years, no problems.
It is a really simple mechanism. Here are some photos from Ebay. they sell it for $85. Cherokee quadrant throttle
I assume your looking for that smooth, expensive feel, just like with volume buttons on higher-segment audio installations. Their resistance and damping allow you to easily make very precise adjustments, since the knob gradually gives in when you try to rotate it. I assume plane controls also give you this feeling, since they also need to be controlled precisely.
One way used to achieve this effect is using a spring loaded arm or friction plate, against another friction plate, all submerged in high-viscosity grease in a sealed container. The friction plate gives the resistance to rotating, the grease gives damping, to prevent the knob from abruptly rotating once enough force is applied. The grease also makes for lubrication, elemininating the abrupt effect. You could use other methods of damping, but this one's very easy to make yourself.
For optimal effect, create a friction plate not too small; a larger plate will decrease any abrupt reaction. Use a heavy grease, like faucet grease or something. Thicker grease will give more damping, and will increase that smooth, expensive feel. (only to a certain point, but it's hard to find a grease to go beyond that.)
Additionally, you could attach a rubber band or spring to gently bring back the lever to its neutral position. Obviously, you don't want that for your throttle, but other controls like rudder pedals might benefit from this behaviour. Last, make a rubber bump stop at the end for the lever to hit, so the lever will silently and smoothly stop at the end of its reach. Otherwise it will hit e.g. the end of the plastic cover, causing an unpleasant sound and feel.