Above & Beyond: Milk Run
How a milk run from an aircraft carrier nearly killed me.
- By Chris McKenna
- Air & Space magazine, May 2007
(Page 3 of 4)
Ground effect—the cushion of air that provides extra lift for a helicopter operating within one rotor diameter of the surface—can be a blessing or a curse. With a long hovering run, a pilot can accelerate in the ground effect cushion until reaching flying speed, thereby lifting far more than would be possible from a standard climbing transition. The carrier, however, presented the opposite situation. From our position adjacent to the deck edge, I would take off into a ground-effect hover, then transition over the edge of the flight deck, 90 feet above the water, to an immediate loss of ground effect. The voice in my head warned me as I raised the collective to increase rotor pitch and add engine torque, but the big voice in my headset drowned it out: “I need my deck, Knightrider!”
Normally I would have taken my time to evaluate a takeoff this critical. But this was the air boss’ deck, and he wanted it back. “Get that damn helo off my deck, now!”
Without the stabilized torque reading that would tell whether the aircraft would fly at this weight, and against my better judgment, I eased the cyclic stick forward and the aircraft lumbered across the deck edge.
Immediately we were in trouble. The aircraft settled, and I instinctively countered by raising the collective. But instead of slowing its descent, the helicopter settled faster. The steady hum of the rotors changed to a distinct whump whump whump, and the familiar blur of the rotors slowed until I could see each individual blade. A quick glance at the instruments confirmed that both engines were operating normally. I was simply demanding more power than they could produce, and the strain was making the rotor speed decay.
I should have predicted what would happen next. With a jolt, both generators kicked off and we lost everything electrical. Powered by the rotor system, the generators had been designed to “shed,” or drop offline, at 88 percent of optimum rotor speed to preserve torque for lift. The jolt was the loss of the flight control stability system. The helicopter was still controllable, but controlling it took far more work without the stability system. Things were starting to go very badly.
As the rotor speed continued to decay, I realized the only chance we had was to get back into ground effect. If I continued wallowing, the helicopter would “run out of turns”—lose lifting rotor speed—and crash, or settle into the ocean and sink. I had to try what the old salts called “scooping it out.”
Faced with an undesirable sink rate, it is counterintuitive to decrease either power or pitch, but scooping it out required both. To dive back into ground effect, I lowered the nose, and the windscreen filled with the sight of blue water and white foam. To preserve rapidly deteriorating rotor speed, I lowered the collective. The bottom dropped out and the ocean rushed upward. I blurted “Brace for impact!” Dave immediately understood what I was attempting and began calling altitude and rotor speed.
“Fifteen feet, 84 percent.”
I needed airspeed. I had to trade more altitude to get it, so I eased the cyclic forward a little more.
“Five feet, 84 percent.”
I checked the descent and stabilized in the ground effect run.
“Three feet, 83 percent.”
We were flying, and the rotor speed had stabilized, but I couldn’t seem to coax any acceleration out of it. This low, even a rogue wave could bring us down. Milk, I thought. Evil stuff.
With only the speed I had bought with the dive and no sign of acceleration, I despaired. Then the old salts spoke to me again. If you ever need a little something extra, try a 15-degree right yaw. The drag is negligible, but your aft rotors get undisturbed air.