To: Nick Lappos
“I hate to yet again be the gadfly to put pins in Lu's credibility, but on water operations in helicopters is very normal, very natural and very safe. Rotor starts, takeoffs and landings are normal water operations for many helicopters, and gyroscopic precession problems are a mythological problem, like glowing helicopters and 18 degree rigging problems. I have many water landings in boat-hulled helos, and know of lots of normal water-borne operations in many types”.
I was operating on a float equipped helicopter (HTL-1) most likely before you took your first airplane ride. That helicopter was very stable on the water and it was able to shut down and start up and then take off with no problems. The HO3-S on the other hand was highly unstable because of a high CG and the fact that the pop out floats were mounted on tricycle landing gear. As I indicated previously we had problems in operations off of the back end of an icebreaker. Under the stated conditions and with this helicopter you have no standing because you were never exposed to this type of operation with this type of helicopter.
Regarding your experience with boat hulled helicopters; these aircraft were made for water operations. While at Sikorsky I watched the first tests of the S-52. They had a small model and they shot it into a child’s wading pool while taking high-speed motion pictures of the models behavior when it hit the water. The model was equipped with a weight that could be raised on a shaft to simulate changes in vertical CG. I asked why they had to perform the tests under various CG conditions. The engineers replied that they had to get CG right in order to maximize the stability of the helicopter when it was in the water. The HH3 has a much lower vertical CG by comparison to the S-51 and the lateral stability is much greater than the S-51. I would think that the S-51, which was susceptible to going into ground resonance on the flight deck, would also be subject to rotor perturbation due to the movement of the helicopter as a result of wave action. Your boat-hulled helicopters are immersed along their waterline and this provides the major buoyant support while the sponsons provide lateral stability while helicopters on floats ride much higher on the water. Many other helicopters that have pop out floats are partially immersed in the water and can’t recover or take off as the tail rotor is in the water. The S-61s at least those that were made by Agusta had sponsons that were much bigger than the standard S-61 to improve lateral stability and add additional buoyancy. These helicopters were used in offshore work.
Regarding gyroscopic precession please tell me what would happen if you move the fuselage in relation to the spinning rotor disc. It seems to me that when the fuselage is displaced it changes the swashplate angle in relation to the rotor disc causing a pitch input that would result in a change in the disc attitude. If the wave action is erratic the disc could be moving all over the place. If the helicopter were on land this would be ground resonnance.
Over