To: Nick Lappos
I do take the forum seriously and I have learned a lot from the participants on the forum. However I will continue to believe the theory of loss of lift until I am set straight by Bell Helicopters. I am also awaiting a copy of a paper delivered to the American Helicopter Society dealing with Fuselage Nodalization. I believe that the answer lies in that paper.
As a test pilot, an engineering graduate and a former Army Snake driver I would like to ask a couple of questions.
1) As a Snake driver did you ever ask yourself or anybody else what causes the 2-per rev bounce and why the frequency of the bounce was two time the rotor speed and not three or four times?
2) As an engineer can you explain in layman’s terms how the energy is developed that would lift and drop a 1000 pound dynamics system by 2+/- inches at a frequency of about 500 times per minute.
I quote,” What exactly will it take to get you to stop saying "I was once told by a Bell engineer..." as some kind of proof for this simply absurd premise?
An open mind is a wonderful thing!
I would like to paraphrase you question. What will it take me to stop saying “I was once told by a Sikorsky engineer…” as some kind of proof that my premise was absurd?
Here is a story about a Sikorsky engineer and his limited understanding of how a helicopter works. I was once involved in a comprehensive 14 month technical training program at Sikorsky. Aside from extensive classroom work I worked in every department of the company from engineering to flight-test. If a part or an assembly was made in an assigned department I built it, I tested it and I flew in it.
On one assignment I was working in the hydraulics test lab. While there I witnessed a hydraulics engineer cobble together a system that was supposed to drop the collective when engine oil pressure was lost. In order to work the collective was raised by a hydraulic piston until a spring was cocked and then the collective dropped. I asked him how the collective was raised and he stated that as hydraulic pressure built up the piston would lift the collective.
I told him that the system would not only not work it could cause serious damage to the airframe. He became extremely belligerent saying that I didn’t understand his device and that it would not damage the helicopter. It seems that his involvement with design was limited to hydraulics and he had no knowledge of theory of flight.
I told him that the hydraulic pump was on the transmission and as the transmission was brought up to speed the blades could not support lift. I further told him that at a slow rotational speed the blades would rise up and stall out falling and hitting the tail cone. The next day the device was gone and two days later, the engineer was gone.
I don’t know what bearing this story has our discussion other than that it takes a lot to change someone’s feelings about something that they hold dear.
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The Cat