Return from Nagasaki to Okinawa by B-29 “Bockcar.”
In his book, “War’s End,” the aircraft commander Major Sweeney writes:
“Paul Tibbets taught me a technique that caused a lot of controversy among pilots, some vehemently denying it existed and others vocal apostles that a skilled pilot could use it. It was called “flying on the step." In theory, it was very simple. You kept the power steady and took the aircraft into a gradual descent, the airplane would pick ups fraction more airspeed without using more power and fuel. The pilot would then level off. To retain the increased speed and perhaps even supplement it a bit more, you would start down another step and then another step, and so on.
You could milk only a little bit more speed and fly a little farther without consuming more fuel, but that was all I needed—a little bit more. I had the advantage of being at 30,000 feet, so I started my way down the staircase.
I also decided to add some insurance by throttling back the propellers to 1,800 rpm from the recommended setting of 2,000 rpm. Turning the numbers over in my mind, I knew this wasn’t going to be enough. So I throttled back to 1,600 rpm, well below the engine specifications for any circumstance. This could damage the engines, but balancing the risks against the benefits, I concluded that I’d rather replace the engines and get my crew safely tucked away for the evening than be bobbing in the Pacific aboard a life raft hoping that we’d be picked up.”
Lt. Olivi, the copilot in his book “Decision at Nagasaki,” writes:
“Sweeney throttled back and put Bockscar on the step— the maneuver we had practiced so many times before at Wendover——…”
The interesting thing to me is that Sweeney describes a dynamic maneuver to extend the range. The Boeing POH describes ‘Flying on the step' as just over-climbing and diving slightly into your cruise condition. I think that is the common definition. Using the altitude dynamically, and repeatedly, for extra airspeed seems to be a key issue. Is it more fuel efficient that just setting a shallow dive, considering the extra altitude and distance to go, and flying the best speed for that descent angle? I have used quasi-steady aerodynamics and cannot find that Sweeney’s technique, compared to a steady 0.012 radian descent angle gives any better fuel consumption. I use the approximation that fuel usage is proportional to the horsepower multiplied by time.
I’ll be interested if anyone can find an improvement in fuel consumption using a flight simulator.
