To: 3top
“ About the droop stops Lu is complaining on the Robbie. Well they are fixed, so what, so are the ones on any other helicopter once the machine is running. I understand that most models use moveable stops (personally I know only the systems on B-47 and 206) to limit movement on the stopped or very slow rotor on run-up or shutdown. Maybe it slipped Lu that the Robbies use FRICTION in their heads and quite a bit (AND it works beautifully!), so when the rotor is slow or stopped the blades hardly flap at all. Once very slow or stopped they seat on stops to avoid too much droop in the CONING HINGES. So you would have to move the rotor by hand to move the head all the way to the flap stops”.
What you say about the Bell and Robinson droop stops is correct with one exception. The last two words in your paragraph above should read "teeter stops" as opposed to "flap stops". The point I was making was that with the fixed droop stops on the Robinson the blades could contact the stops during high flapping excursions. And, in doing so, the kinetic energy will turn the rotor system into a first class lever with the fulcrum at the teeter hinge and force the entire head down making contact with the mast. This flapping is very intense and occurs at a high frequency, which literally beats the head into the mast at a high rate causing mast separation. This in effect would turn that part of the Robinson head into one half of a Bell blade and head.
On other helicopters that are equipped with flapping capability they employ centrifugally operated or other devices such as used on the Hughes design that maintains the static droop angle but permits the blades to flap lower than the static angle during flight. Many of these helicopters also have limiting stops, which limit the maximum up and down flap of the blades. When the blades hit either of these stops during maneuvering the pilot will feel a heavy beat and then he will limit his cyclic input. The Robinson can not flap below the static droop limit of the blade.
Regarding the strength of the components on the crashed R-44 as demonstrated by what bent and what broke as the result of the crash the loads are distributed in a different manner in a crash. In the case of a mast separation the loads are repetitive and they are applied in a very concentrated area. Although the mast and head were not visibly or overly damaged as a result of the crash mast bumping would have been a different story.
[ 15 December 2001: Message edited by: Lu Zuckerman ]