To: mark561 and RW-1
First of all, I was trying to solicit responses from mechanics that work on Robinson helicopters as to what they were taught about the rigging of the two helicopters and what they were taught about flight theory. I was not looking for any criticism. Paul Cantrell writes the two web sites I often refer to and Robinson dealers and flight schools sponsor both. Mr. Cantrell addresses the function of various aspects of both the Robinson and Bell dynamic systems and then addresses gyroscopic precession indicating that it is 90-degrees (phase angle) for both the Bell and the Robinson. When he demonstrates the principles of gyroscopic precession he uses a diagram of the Bell control input and response which showed where the input and ultimate responses of the disc tilt were. On the RW-1 website you indicated that you got the information from a US Army flight instruction manual. Well the illustration used by Mr.Cantrell is the same as that used on your website so I can only assume that gyroscopic precession is addressed in your website as being 90-degrees.
In regards to this aspect of the control input Vs response, the Robinson is completely different in that during the rigging procedure the position of the blades during pitch setting are offset by eighteen degrees as opposed to where the Bell Blades are positioned for the same setting.
If the Robinson blades are offset by 18-degrees during rigging then the maximum pitch input on advancing blade is decreased to the maximum and the retreating blade which is also offset by 18-degrees and it is at its’ maximum pitch change then please explain to me the following. How in hell will the Robinson rotor system defy the laws of physics governing gyroscopic precession and tilt down over the nose and up over the tail. If you refer to what Frank Robinson said in his reply I will tell you both that you are full of S**t and so is he.
Listen to what I am about to say and then go out and look at the Robinson rotorhead. Frank Robinson stated that they evaluated the benefits of a 90-degree pitch horn Vs a 72-degree pitch horn and determined that the 72-degree pitch horn would solve a problem relating to transverse flow effect. He implied that the 72-degree pitch horn would eliminate this problem that effected the Bell with its’ 90-degree pitch horn. That is pure bull crap. RW-1 what happens to your R22 when you speed up from a hover to say around 20-30 Knots. Do you encounter transverse flow effect? If you do, then what Mr. Robinson stated about his choice of a 72-degree pitch horn and why it was selected is wrong.
Another point I have made regarding the rotorhead design is that from the very beginning, Frank Robinson incorporated cone hinges on his rotorhead. This was not done to counter the effects of transverse flow it was done to minimize the bending moments of the blade and to minimize the transmission of flapping (coning) moments so the design could never incorporate a 90-degree pitch horn.
He also stated that the delta 3 effect would make up for the 18-degree offset and result in a 72-degree phase angle and allow the blade disc to tilt down over the nose when the cyclic was pushed forward. This too is bull crap. The delta 3-effect causes pitch to be removed or added to the blade when it flaps due to external aerodynamic forces. If the blade flaps up pitch is removed and if it flaps down pitch is added. Just like on a tail rotor. However this can only happen if the pitch horn / pitch link attachment is above or below the cone hinge. If the two points are coincident then there is no pitch coupling. Explain this, if the points are coincident when forward cyclic is pushed then which way will the disc tilt? Will it tilt down over the nose or, will it tilt down left of the longitudinal centerline. You can’t have it both ways and state that it will tilt in one way or the other if you use the explanation used by Frank Robinson.
RW-1 here is something you can demonstrate since you like flying on the edge. Lift off with your cyclic in the rigged neutral position. Do not move it laterally. Push it forward and fly through the transverse flow effect. The helicopter should roll to the right but don’t move the cyclic. When you are through the transverse flow effect, let me know which direction the helicopter is flying.
This is for mark561.
According to your Bio, you are most likely working at the Lazy B but then again there are a lot of places in your area that employ engineers. Your Bio also indicates that you fly model helicopters.
I don’t know what kind of engineering training you have (ME, AE or, EE) but I assume that you learned the theory of gyroscopic precession and that barring any mechanical or, friction problems the gyroscopic phase angle is always 90-degrees. If you downloaded my diagrams especially the one that Helidrvr put on this thread you can see the difference between a Robinson blade and a Bell blade during the rigging process. The relative positions of the blade sets are the point that they have the maximum perturbing force and according to the laws of physics the blade disc will react 90-degrees later in the direction of rotation. It is my contention that there will be a left roll component added when the reaction takes place. Regarding the demonstration I asked RW-1 to perform, two pilots on this thread performed the test and their conclusions were that I was correct.
When the Robinson accelerates forward the pilot will counter the transverse flow effect by adding left cyclic. This is in addition to the left roll caused by the 18-degree offset. When he passes through the transverse flow effect he moves his cyclic to the right. In doing this he is reestablishing the helicopter in forward flight as opposed to rolling left. Is there a possibility that in the process of moving the cyclic to the right he is not only recovering from the transverse flow effect he is also countering the effect of the left roll induced by the offset? This is why I asked if in the certification process they used a stick plotting board, then they would have noted this problem.
This is also for mark561. You seem to have taken a stand based solely on what Frank Robinson said in regards to my postings and not from a detailed understanding of the mechanics of the Robinson Helicopters. If this is an incorrect assumption then I stand corrected. I stated this in a previous post, if Frank Robinson makes a counter statement to my postings it doesn’t mean it is true. He is not Jesus making his Sermon on the Mount and he is not God in the form of a burning bush giving the Ten Commandments to Moses. He is an engineer and businessman that will say anything to protect his interests and if you are a pilot that buys the farm in a Robinson Helicopter then he will be your survivors’ worst enemy.
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The Cat