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You the village Idiot Peter, definately not. But I am sure that you (like me and every one else) knows someone who is. There is generally one in every village.
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Tim, to me there are people who are gaining knowlege, people who have knowlege and people that add to knowlege. At this time I am both gaining knowlege and if I can I would like to add to knowlage. For this your answers to my questions, or comments on my statements are important to me. I feel that there is something missing from conventional theory on gyro rotor systems. If I am correct I will have nothing to gain other than making life a bit better for somebody else flying over the scrub all day.
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In the real world except at rare moments there will be no symmetry of lift. The underslung rotor system minimises but does not eliminate lead lag. If this lead lag is transmitted to the mast the hub and mast will be moving as one and there is very little blade pitch change. If there is not enough friction in the gimbal, the hub pivots on the mast changing the pitch on the blades. It is dependent on weight distribution above and below the teeter point as to which direction the hub moves. If the teeter point height is low the hub movement will pitch the blades to counter dissymmetry of lift and is self limiting. It is this stick shake that is less noticeable with play in the controls. If the teeter point is high the hub movement will pitch the blades to increase dissymmetry of lift. This one is self energising and is only governed by the controls. This is the stick shake that is less noticeable with no play in the controls. If the controls break it will quickly increase in magnitude and in just a few revolutions the rotors will be hitting the teeter stops.
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mmmm bu--er the bush theorys bu--er the experts. if you have the same problems Ive had, check the next gyro news. Bones wants me to do an article.
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Undersling ~ Posting by CA Beaty ~ December 22, 1999 Trying to eliminate 2/rev shake is often like wrestling an octopus. Get one tentacle (I once had a young lady in my employ who always confused tentacle with testicle; she now has a Ph.D. in education) pinned down and another pops loose. As a first cut, the teeter bolt ought to be located on the CG of the coned rotor. Take a length of welding rod and put an abrupt bend in the center so as to create a shallow "V" to simulate a coned rotor. Lay a straight welding rod on a level surface, place the bent welding rod on top and slide things around until the bent rod balances. Assuming each leg of the bent welding rod touches the straight rod at the same span wise point, the CG of the coned rod is at the center of the straight rod. This is where the teeter bolt ought to go. But life with teetering rotors is seldom that simple. If the undersling is too little, the rotor CG rotates in a 2/rev circle with cyclic flapping in forward flight. The spatial visualization of combined rotation and flapping is very difficult for left handed people and nearly impossible for right handed people. Too little or too much undersling produces a 2/rev fore and aft shake in forward flight The shake from too little undersling is out of phase with the aerodynamic input to the rotor and produces some cancellation. Most rotors, depending to a very large extent on mast stiffness, are smoother with undersling a bit less that a consideration of CG alone would indicate. This is a subject not covered in any text book I"ve been able to locate and involves a bit of speculation on my part. I"ll now wait to be shot down. I"ve put together some very simple programs on Excel to calculate undersling, tail volume as a percentage of rotor volume, disc loading, blade loading and HP Vs torque. It"s very easy to use and might appeal to those people who don"t agree that pie are square. Email me for a copy. _Undersling ~ Posting by CA Beaty ~ April, 21, 2004 In actual practice, a rotor is usually smoother if undersling is a bit less than calculated. I suppose 2/rev shake from mass force is out of phase with 2/rev aerodynamic input. I suspect optimum undersling is also affected by mast compliance, ie., the resonant frequency of the mast/rotor system. Rotorhead: Vibration, Stability & Controllability
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As the deadline for gyro news is not until the 15th February, I missed getting my article in this month"s gyro news because I didn’t email it to the editor until the 12th of February. Peter
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My rotors are 29HS with no shake at all in any direction. I know nothing of all the theories but instead went on trial and error. Balancing blades is the most important and zero movement(slop) in all control joints is a must. The undersling in the perfect world would be flight adjustable like trim, but this is impossible. Mine is perfect up to about 480 kg all up but a slight shake diagonally for and aft develops above this weight. Taller towers would be the answer, but its easier just not to carry the weight. I think a piece on how we all balance our rotors and the different methods of doing so may help a few. Ken
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I put this thread starter up to help people, not to appear as an ex-spurt. I reckon it will help somebody
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