To: Kyrillian
“I still have the feeling that he wasn't familiar with the head and assumed it to be like that on the 206 (link-horn connection in-line with teetering hinge). Some of your descriptions make it seem like the swashplate input links are phased wrong, and that this is the sole cause of all the problems”.
Regarding Ray Proutys’ understanding of the Robinson head he wrote an article on it in the AHS technical forum. I also believe he had some involvement in the early design.
Regarding the swashplate input links I have no problem as they cause the swashplate to operate just like on a two blade Bell. Push the cyclic forward and the front end goes down over the nose and the back end goes up over the tail. The similarities between the Robinson and the Bell stop at that point.
On the Bell when the blade is disposed over the lateral axis and cyclic is pushed forward the pitch horn which is 90-degrees ahead of the blade causes the blade angle to be at its’ lowest point. Conversely the other blade is at the highest pitch. Precession causes the blades to flap down over the nose and up over the tail.
On the Robinson with the blades disposed in the same manner and forward cyclic is pushed the front of the swashplate will move down just like the Bell. The Robinson blade will not be at its’ lowest pitch like the Bell. The blade will have to travel another 18-degrees until it is at its’ lowest pitch. The Bell is rigged for forward cyclic with the blades disposed as above over the lateral axis. The Robinson blade is advance 18-degrees from that position in order to establish forward cyclic settings but I’m sure you were well aware of that fact. I’m also sure that Ray Prouty is also aware of it as well.
On the infamous Robinson (Cantrell) web site they show a Robinson head and address gyroscopic precession. When you get to the explanation they have an illustration addressing precession on the Robinson but the illustration is for a Bell swashplate. Now if you look above at the positioning of the blades on both helicopters the inputs are wrong for the Robinson because it implys that the Robinson has a 90-degree phase angle. If it does the blade will dip down and to the left with forward cyclic. However Nick sez that pitch flap coupling will cause the blade to respond in 72-degrees as opposed to 90-degrees.
Now I think If I am correct about the offset the test will prove it, contrary to what you might think.
You have access to a 206 and a Robinson. Perform this test. On both helicopters place the blade over the longitudinal axis. Move the cyclic forward from the rigged neutral position. The Bell blades will not move but the Robinson blades will. Now advance the Robinson blades until the pitch horns are directly above the lateral axis. Move the stick forward and backward from the rigged neutral position and the blades will not move.
Now I don’t have your educational background but I have always been told that with maximum change in cyclic pitch the blades will respond 90-degrees later. If what Nick said and Frank Robinson alluded to by saying it was too technical to explain to non engineers and pilots then I am wrong and all of my instructors and engineers that I have worked with are also wrong.