Forty-Seven Years in Aviation: A Memoir; Chapter 10: Strategic Air Command, Part 2
The engineer sat sideways, behind and between the pilots, facing to the right side of the airplane. He had a panel full of instruments, switches and knobs in front of him, a panel to his left and overhead (circuit breakers and engine controls), and another sub-panel for managing the aerial refueling systems; all told, the engineer was responsible for 200-odd indicators, valve positions, switches and the like. The small, round, analog, engine instruments critical to takeoff were placed in groups of four in the engineer's direct line of sight (left center in the photograph at right) and were installed so that when full power was being generated all the needles pointed straight ahead, i.e., to the engineer's left; the FE could tell at a glance if any of the four engines was not pulling its weight.
Another unique component of the engineer's panel took the guesswork out of managing the KC-97's fuel system (there were two independent fuel systems, one to deliver avgas to the tanker's engines, the other for offloading fuel to a receiver airplane). At the extreme lower left of the FE's panel are the four fuel-valve selector switches that controlled fuel flow from the airplane tanks to the engines; by rotating the knob until the red lines on the switch indicated the desired routing through the valve, the engineer had a clear picture of where the fuel was coming from and where it was going. The KC-97 was powered by four Pratt & Whitney R-4360 engines, the largest air-cooled radial engines ever put into production. (One R-6000 was built as an experimental engine, but the power-to-weight ratio was so unfavorable the project was abandoned ... goodbye, big radials; hello, lighter and much more powerful gas turbine engines).
Truth be told, the R-4360 was four 7-cylinder radial engines bolted together in a spiral pattern around a common crankshaft -- no wonder it was nicknamed "the corn cob." It may have looked rough on the outside, but when this engine was properly set up and managed it ran smooth as silk ... 28 cylinders on a common crankshaft provided a lot of power impulses. It was not uncommon for the engineer to pull the props back to 1100-1200 RPM in a long-range cruise configuration; at that rotational speed, you could see the nuts on the prop domes turning. If there had been a prize for the airplane engine with the largest number of moving parts, the R-4360 would have won, hands down. At 2700 RPM and 60" manifold pressure (normal takeoff power settings), the R-4360s developed 3500 hp each, but the supercharging that almost doubled sea-level atmospheric pressure would have caused detonation, very high cylinder-head temperatures and eventual engine failure; the problem was solved by injecting a water-alcohol mixture into the cylinders to cool the engines when they were operating at full power. (See sidebar above-right about the B-47's water-alcohol injection system.) Its virtues were many, but the KC-97 had two weak points, both of them involving the propellers. The original blades were steel with hollow cores filled with neoprene, but over time centrifugal force compacted the neoprene in the outer extremities of the blades. The resulting imbalance and heavy vibration occasionally caused a blade tip to separate, sometimes resulting in the entire prop assembly breaking loose and taking an adjacent engine or propeller with it ... disaster guaranteed. The problem was exacerbated by the long, slow, climb profiles that required abnormally high power settings for extended periods of time. Applying an abundance of caution, SAC dictated that each and every KC-97 prop blade must undergo a dye-penetrant inspection for cracks at the conclusion of every flight and a visual inspection by the flight crew using magnifying glasses as part of each preflight inspection procedure. The problem was eventually resolved by refitting all the tankers with solid metal blades. The second serious problem showed up in the propeller pitch-control system, which was prone to a malfunction that would permit the blades to go -- without warning -- to flat pitch in a matter of seconds ... the dreaded "runaway prop." This was a double whammy; not only did the affected propeller stop producing thrust, it was now generating roughly the same amount of drag as a solid disc 17 feet in diameter. There was precious little a crew could do except fly as slowly as possible to reduce drag and hope the engine held together until they could get the airplane on the ground. The eventual fix for this problem was the installation of a pitch-lock system that recognized the onset of an overspeed condition and slammed the door, so to speak, on any further increase in RPM ... and KC-97 crews breathed a bit easier. The Stratotanker (a rather euphemistic name for an airplane that seldom flew higher than 15,000 feet) was designed to operate at a maximum takeoff weight of 155,000 pounds, but on occasion we loaded the airplanes to the SAC-decreed maximum of 175,000 pounds. These missions called for large offloads to the bombers, even if we had to dip into our onboard supply of avgas. The J-47 jet engines on the bombers didn't care much which type of fuel they were fed; they probably could have burned olive oil if push came to shove. (However, the R-4360 certainly did care; see sidebar at above-right.) It was easy to identify a taxiing KC-97, even when it was out of sight: The brakes had a distinctive, high-pitched squeal that simply couldn't be mistaken for any other airplane. And when a taxiing tanker was visible, the trail of light-blue oil smoke gave it away. The R-4360s were great engines, but they were known to leak a bit of oil now and then; my AC, Jimmy Stewart, would chide me (tongue in cheek) now and then if he couldn't find a fresh oil stain on my cap, a clear indication that I hadn't ventured into the main wheel wells during my preflight inspection. An anonymous mechanic once said, "The R-4360 didn't leak oil; what you saw was nothing more than the normal functioning of its outstanding external lubrication system." In any event, our engines consumed a lot of lubricant; we seldom changed the oil, we just kept refilling the tanks. Each engine had a built-in 40-gallon oil tank (that's not a typo; big engines require big oil tanks) and with great foresight, Boeing had equipped the KC-97s with a 100-gallon reserve tank from which the engineer could pump oil to any of the engines in flight. If that weren't enough, when we flew across the pond we carried an additional 55 gallons of oil in a steel drum strapped down on the upper deck ... and at the end of the flight most of it had been used. [Continued with Chapter 11.]