To: Chips
Up until now the NTSB and the FAA have attributed almost all failures of the Robinson design that resulted in death to pilot error and therefore, my theory about the rotor design as the main contributor remains as a theory. I didn’t state that airplane wings or tails don’t come off as it is proven that they do. This type of failure is normally attributed to overstress which is pilot error or the onset of corrosion that leads to structural failure which can be attributed to poor maintenance. Very few if none of these failures are attributed to faulty design. Coupling all three types of failures that result in separation of a wing or tail and the frequency of occurrence per 100,000 flight hours would most likely be less than that of the Robinsons’ loss of the main rotor or fuselage incursion.
It is my theory that the design of the Robinson rotorhead can lead to mast bumping even in the hands of a high time pilot. This is evidenced by the rotor loss incident in Watsonville, California. This pilot had in excess of 20,000 hours much of it in helicopters and he was an airshow demo pilot flying in an R22. I believe it may have been the same aircraft used in the airshow that was involved in the crash.
I tried to prove my theory about the 18-degree offset by asking pilots on the forum to perform a test and you know where that led. Well, I doubt if I could ever get the test performed even if I bought an hour of flight time on an R22 however there is an agency that will have the test performed and that is the NTSB. In reopening the investigation of the rotor loss/incursion accidents their entire focus is on the rotorhead.
After the investigation by Georgia Tech at the behest of the FAA it was determined that sideslip and flying out of trim resulted in progressively increasing flapping loads which were dependent upon the degree of sideslip and the degree of out of trim flight. It was determined that these flapping loads could result in mast bumping and subsequent rotor loss or fuselage incursion. As a result, the Robinson R22 and R44 were restricted from performing these maneuvers. It was these restrictions and the increase in pilot training and awareness that resulted in no mast bumping or rotor incursions from 1995 until last year when the Robinsons' incurred four rotor separations / rotor incursion accidents. Was this due to relaxed flying standards by the involved pilots or, did the rotor design place them in jeopardy when the countered a zero G condition. All of this will come out in the NTSBs investigation.
------------------
The Cat