The Olympus engines, located in pairs near the wing-roots, were further reminders of the Comet with its Rolls Royce Avon engines located similarly, at the wing-root, and in pairs. Placing engines so close to the fuselage, and to each other, makes it easier to control the yaw should an engine fail, and can be useful in minimizing drag but it concentrates the weight inboard – rather than spreading the load across the wing. Given the nature of the slender delta wing however it usefully enables their considerable weight to be placed near the centreline of the centre of lift, a moveable feast for supersonic aircraft, limiting shifts in longitudinal trim. The down side being the lateral weight distribution and the fact that blade containment becomes a major issue. A broken blade, be it in the turbine or the compressor stages, has to be prevented from either damaging the paired engine, or structurally damaging the wing and integral fuel tanks. To that end the wall between the engines was carefully reinforced, as was the steel panel between engines and wing. It added more, unevenly distributed, weight and, despite working as intended, it wasn’t enough. Later I was to learn, first hand, that it wasn’t enough.
The ramps and doors housed in the huge intake assemblies on the front of the engines were there to reduce the airspeed from a screaming Mach 2.0 at the entrance to something more modest at the engine face.
Two large ramps were fitted in the ceiling, a spill door fitted in the floor, and an auxiliary intake section, within the spill door, to increase the flow at low speed. The object of all this rather sophisticated equipment was to balance a series of shock waves in the entrance in order to limit the speed of the air entering the engine to half the speed of sound: the ideal speed for engine operation.
Engine airflow through the intakes and exhaust
So important were these ramps and doors to the safe operation of the aircraft that all three of the hydraulic systems were routed there to take care of failure conditions, and an array of position monitoring and manual controls were presented on the systems panel.
Ramp and spill door position indicators and manual control selectorsR
This arrangement worked well for the pressure control at the engine face but still left a vast range of temperatures at the inlet that had to compensated within the engine. To this end a variable primary-nozzle was fitted just aft of the low-pressure turbine to control the relationship between the high and low pressure assemblies. It sounds complicated, and it was, enormously complicated as were the petals of the nozzle itself which operated in temperatures up to two thousand degrees. The open area of these nozzles was displayed on the centre engine panel along with the fuel flows, temperatures, and rpm gauges to tell us how the engine were operating.
A mode selector and indicators for the primary nozzle schedules were located on the engine secondary instrument section of the systems panel where we also found oil and fuel pressure and temperature gauges and, of course, lots and lots of warning lights. There were also selectors for the engine control amplifiers, the take-off, climb, and cruise rating selectors on the overhead panel, and the switches for the reheats, or afterburners, just behind the throttle levers. Over and above all that were the Autothrottles, located on the Automatic Flight Control System panel, designed to integrate, and to optimize, the power settings for the various phases of flight.
It all seemed a little intimidating. Manual control of ramps and doors to balance a live, critical, shock wave in supersonic flight was an entirely new experience, as was the Low, Mid, High, and Flyover engine mode selections. Add to that the amplifier selectors for engine and intake controls, the thirteen fuel tanks and thirty-two pumps to not only feed the engines, but also to control the aircraft centre of gravity to match the shifting centre of lift, and I was beginning to understand the purpose of that initial phone call.
Before we leave the engine controls a word about the starting procedure. The Olympus is a long engine, with a particularly long low-pressure assembly that, when subjected to uneven cooling, tended to bow. The uneven cooling, that is the temperature difference between the upper and lower parts of the shafts due to convection, balanced out overtime, over five hours we were told, but routine transits are much shorter than that. To run the engine at speed in this, bowed, condition would be to damage the bearing assemblies so a procedure was adopted in which the engine is held at sub-idle speed for a few minutes during start up in order that the rotating assemblies could even out the temperatures gently, allowing the bow to dissipate without damage. We called this procedure the De-bow cycle. It raised many questions but, as the British Aerospace instructors nipped over the questions popping into the heads of the other engineers I found myself wondering if Elijah would have coped with the De-bow cycles given all his other duties. Of course he would – he grew higher and higher among his peers as he did more and more of the transit jobs out there on the Mombasa tarmac. “Hello cockpeet,” he would call up the intercom. Are you ready to de-bow the engines now?” He would have risen to the occasion.
The engine start controls were located low on the systems panel next to the knee hole, or, actually, right where the engineer’s right knee would rest in the forty-five degree position, which was necessary because the high pressure fuel inlet valves were on the overhead panel, the rpm and temperature gauges were on the forward, centre, panel, and the low pressure inlet valves and feed lines were on the systems panel. I have no problem with this architecture: it encompasses many solutions. The complaint remains with the engineer’s seat position and its inherent lack of leg room. Moving on . . .