Oleg Golovidov, I have read your note in RCSE about RDS. I have not actually built an RDS setup, but I have done some considerable thinking about it. Also, I have been back and forth with Harley a few times and in the end I understood what he is doing. I also think that I have some idea what is troubling you. Let's say there are three elements to the system. 1. The surface hingeline. 2. The shaft from the servo. 3. The bent piece that fits in the pocket. The ideal RDS setup would be to have the axes of all three elements intersecting. You might also have a little roller bearing at the tip of the bent piece to reduce friction and to make sure that the moment is taken out with the least force (longest moment arm). Lastly, the shaft would be well and fully supported near the hingeline. This setup would have no slop, minimum forces, and no binding. You could use this system in an airliner and it would work well and last forever. This is not how Harley does it. Harley's way works just fine all the same. What Harley does is to use a vertically slotted bearing at the rear spar for the shaft. Instead of taking the moment out between the shaft bearing and the tip of the bent piece, Harley takes all of the moment out in the bent piece by contact with the parallel plates. The front of the bent piece presses on the parallel plates one way, and the tip of the bent piece presses the other way. This gives a shorter moment arm and greater forces (and friction) but it still works. The slot in the shaft bearing restricts spanwise motion but permits vertical motion. This permits a vertical misalignment between the hinge axis and the shaft/bent piece axes. As to the pulling in/out (chordwise direction) I thought that Rob Crockett's contribution was good - set the shaft length with the flap down - that ought to get things pretty close since the bent piece can slide chordwise within the parallel plates at smaller deflections. !! Note also that by slotting the shaft bearing that the vertical motion of the shaft also accommodates (makes up for) in-out disagreements!! The fact that skilled and discriminating modelers are happy using RDS is concrete evidence that the kinematics work. It has been my experience in modeling that when my theoretical model and reliable experimental data disagree that my theoretical model needs some work! Or that I am missing something. You might want to check out my website. I offer an inexpensive spreadsheet that works out servo linkage geometry and torques for several setups, including RDS. I also have comments about RDS in the website that do not incorporate these more recent insights - I have not updated it yet... That's all for now. Blaine Beron-Rawdon Envision Design San Pedro, California http://memebers.home.net/evdesign/ RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
