I finally got a few minutes to respond in the long form. Here are a bunch of points in no particular order:

* For a human factors class towards my psych minor, my semester project was comparing a sliding side stick with a pivoting center stick for a simple tracking task. The results suggested that tracking was improved when it involved angular displacement of the wrist. Tracking was also improved with greater linear and angular travel.

* Because of their size and general characteristics, sailplanes tend to have long control system paths and also a lot of roll and yaw inertia. Flying a sailplane is definitely work in the technical sense of a force applied over a distance (control stick travel). The shorter the travel, the greater the force required to do the necessary work of defecting a control surface. But when you crowd the control stick up against the cockpit rail, you tend to run out of travel.

* From a practical perspective, if you're going to have a side stick, you improve its chances of working well if you:
-Maximize control stick travel
-Reduce control system friction
-Reduce control system slop and lost motion
-Increase control system stiffness (reduce "springiness")
-Reduce control system and surface inertia

To this end, some of the side stick implementations we've seen in the soaring world have been disappointing. In the HP-18, you get 4.3" of horizontal travel between full nose up and nose down. In that travel, you move two relatively large ruddervators that are sized and counterweighted more for their effect as rudders than as elevators. To move them, you slide 24 feet (!) of 5/8" aluminum tubing through a dozen raw nylon guides. The ailerons aren't much better, again using simple plastic guides. In both dimensions there tends to be a lot of slop and friction that effectively masks what little stability the ship has.

In the Zuni, the side stick is connected to an all-flying tailplane, which regardless of its demand for fine touch has a lot of inertia of its own.

* I flew an HP-18 once with the side stick, and converted it to center stick before I flew it again.

* I anticipate that we might see a resurgence in side stick adoption once fly by wire becomes more common. I figure we'll see a hybrid approach in which the control stick has a limited direct mechanical connection, say to the outboard flaperons and half of the elevator. That will be supplemented by electronic connections to inboard flaperons, spanwise camber control, and the other elevator half. Such a system would offer advanced control features including auto flaps, auto speed-to-fly, and perhaps even auto thermal centering, but still have enough control for a safe landing if the electronic stuff fails.

Thanks, Bob Kuykendall
https://www.facebook.com/HP-24-Sailp...t-200931354951
www.hpaircraft.com