To: Nick Lappos
“You wax on so much you get all muddied. The entire point of your first post was about how much you knew about the (mythological) precession and how it made water operations a bad idea. You start in again at the end of your last post. This is not a factor, and (parden the pun) you are all wet here”.
“Furthermore, if you felt that I "have no standing" in matters like water operations because you RODE as a PASSENGER in a water landing, that makes you all hot air, as you have never flown anything, let alone an amphibious helicopter”.
Response:
Once again you have taken my statements out of context and twisted the meaning. I stated that boat hulled helicopters are very stable in the water because of the large wetted area of the fuselage and the fact that they have sponsons. I also stated that the HTL-1 was very stable on the water and that you could shut down and start up on the water and by inference the boat hulled helicopters including the CH-47 could do the same. However I stated that the HO3-S was unstable on the water because of it’s landing gear configuration and as a result was susceptible to movement of the fuselage because of a very high CG. Because it was a three bladed helicopter you would not want to shut it down and then restart for the reasons quoted in another thread dealing with the possibility of resonance. Using the term resonance I am implying that the helicopter would move all over the place during start up due to temporary imbalance of the rotor system until it came up to speed. When I made the statement about you having no standing I specifically stated that you had never flown an S-51 off the back of a pitching and rolling flight deck.
Oh by the way, I have several hundred hours of stick time in S-51s, S-55s, HO5-Ss and the HTL-1.
“It is a shame that you can't separate the great number of things you do know from the even greater number of wrong things you THINK you know! Please don't ask any questions on precession, you will only hurt yourself trying to screw it all up”.
Response:
Nick did you ever hear of the word imagery or maybe they never used the word at Georgia Tech. Imagery among other things is defined as creating images or pictures in your mind. I have to use this process every day as a RMS Engineer. Here is an example.
Picture a spinning articulated rotor disc. The disc as a whole has rigidity in space ala a gyroscope. The blades can respond individually to gusting or some other external force and flap up in response to the gust load. When the blade flaps up the pitch coupling will extract pitch from the blade and it will return to its’ in track position. If the external aerodynamic forces are continuous the entire disc will respond and you can get flap back / blowback and the pilot must take corrective action by application of a countering cyclic input. If we are addressing Bell or Robinson helicopters the swashplate and disc are parallel to each other and on any other helicopter depending upon phase angle the swash plate will deflect in a different direction than the disc. However this is the normal state for the swashplate in relation to the disc. If the blade moves in relation to the swashplate there will be pitch flap coupling.
Now lets’ reverse the situation. On the water the blades are rotating through a fixed tip path and they exhibit rigidity in space. If the fuselage is displaced sufficiently it will move in relation to the spinning disc. If the fuselage moves then the swashplate and pitch rods will move with it as a single unit. With the blades rigid in space the pitch rods will move in relation to the blades causing a pitch change. Because of the wave action and the frequency and amplitude of the wave action as well as the directions of the waves in relation to the fuselage the pitch input can vary in both amplitude and direction causing the rotor system nutate. The amount of nutation and the frequency of change can cause the rotor to be unstable. If the offset interlock is sufficiently strong the disc movement can be reflected in the movement of the fuselage. The S-51 due to the nature of its’ rotor design had minimal offset interlock. If the helicopter is stable in the water this action will be minimal however if the helicopter is not stable then this movement will be quite noticeable. This is why I likened it to ground resonance. To my knowledge the only helicopter with an articulated rotor system that was mounted on floats was the US Air Force H-19 and having never worked on or flown in it I can’t say how stable it was and how it responded to being started up on the water. There may be others but but I have no knowledge of these helicopters.
We can take the argument one step further. Let’s assume that the offset interlock is strong enough to allow the disc to reflect fuselage movement. The constant movement of the disc will result in the onset of gyroscopic precession causing the disc to respond 90-degrees after the input of the upsetting force. As the wave direction and intensity varies the disc will end up chasing itself like a dog chases its’ tail.
Over
[ 10 November 2001: Message edited by: Lu Zuckerman ]
[ 10 November 2001: Message edited by: Lu Zuckerman ]