Algis Budrys - Michaelmas

“Give me some detail.”

“The most efficient engine working fluid is, unfortunately, also extremely hygroscopic. It’s practically impossible to store or handle it for any length of time without its becoming contaminated with water absorbed from the air.

The usual methods, however, ensure that this contamination will stay at tolerable levels, and engines are designed to cope with a certain amount of steam mixed into the other vapours at the high-pressure stages. Clear so far? All right; this particular series of helicopter utilizes an engine originally designed for automobiles produced by the same manufacturing combine. The helicopter cabins have the same basic frame as the passenger pod and engine mount of the automobile, the same doors and seats, and share quite a bit of incidental hardware. This series of helicopter can therefore be sold for markedly less than equally capable competing machines, and is thus extremely popular worldwide among corporate fleet buyers. The safety record of the model Watson was flying is good, and indicates no persistent characteristic defect. However, this is not true of an earlier model, which showed something of a tendency to blockage in its condenser coils. They froze now and then, usually at high altitudes, causing a stoppage of working fluid circulation, and consequent pressure drop followed by an emergency landing or a crash due to power loss.”

“Power loss,” Michaelmas said. “Like Watson.”

“But not quite for the same reason. This is a more recent model, remember. In the earlier ones, it had been found that the downdraft from the helicopter rotors, under certain conditions of temperature and humidity, was creating cold spots in the coils, and causing plugs of ice. This was not a defect in the engine as an automobile engine. So, since it was economically impractical to redesign or to relocate the engine, the choice was between thermostatically heating the coils to one degree Celsius, or in making sure there was never any water in the working fluid passing through the coils.”

“Option One resulted in performance losses, and was therefore not acceptable; one reason the helicopter application worked so well was the steep temperature gradient across the coil. So they went to the other choice; they installed a desiccator. This is essentially a high-speed precipitator; exhausted vapour from the high-pressure stages passes through it en route to the coil. The water vapour component is picked off and diverted below one hundred degrees Celsius into a separate reservoir, where it is electrically superheated back to about one hundred twenty degrees and vented into the atmosphere as chemically pure steam. The electrical load is small, the vent is parallel to the helicopter’s long axis so that some of the energy is recovered as an increment of forward motion, and the whole thing has the sort of simplicity that appeals.”

“But the unit failed in this case,” Michaelmas said.

“It has happened only twice before, and never over Alpine terrain in gusty wind conditions. These were its first two fatalities. What happens if the electrical heating fails is that the extracted moisture vents as water rather than steam, gradually forming a cap of ice, which then creates a backup in the desiccator. The physics of it all then interact with the engineering to rupture the final stage of the desiccator, and this creates a large hole in the plumbing. All the high-pressure vapour vents out through it, in preference to entering the condenser, and half a cycle later the turbine has nothing to work with. Result, power loss; furthermore, the percentage of water required to have it happen is much less than is needed to create condenser freeze-up. You can be almost sure that any change of working fluid, even a fresh one right out of a sealed flask, will have picked up enough.”

“A very dangerous design,”

“Most add-on new parts have to compromise-fit the basic hardware, and have to add as little as possible to total unit cost, since they inevitably skew the original profit projections. But as it happens this is a rather good design. The electricity comes from a magneto, gear-driven by the output shaft. The wiring, which you would expect to be the weak spot, is vibration-proofed, and uses astronautics-grade insulation and fasteners. It is also located so that no other part can rub through it, and is routed away from all routine service hatches so that fuel-loaders, fluid-handlers, and other non-mechanics servicing the vehicle cannot accidentally damage the unit. The desiccator has its own inspection hatch, and only certified mechanics are shown how to operate the type of latch used.”

They were clearly targeted on Control Tower now; staring forward with his eyes half-focused, Michaelmas could see the structure larger than any of the others, dead ahead and apparently widening out to either side of the tapering white thread of highway. He glanced back through the rear window; they were being followed by a short caravan of trucks. The lead unit, a white, ground-hugging Oskar with shooting platforms collapsed against its sides like extra accumulators, carried the sunburst insignia of Mr Samir’s crew.

“Then what happened?”

“The European Authority found one wire hanging.”

Michaelmas nodded to himself, then grinned humourlessly and looked around for a moment. Everyone was busy doing something or nothing. “What did they think of that?”

“They’re not sure. The connection is made with a device called a Pozipfastner it snaps on, never opens of itself, and nominally requires a special tool for removal.”

“Nominally?”

“The fastener sells because it’s obviously tamperproof; any purchasing agent can demonstrate to his supervisor that the connection can’t break, can’t shake loose, and can’t be taken apart with a screwdriver or a knife blade. The special removal tool has two opposed spring-loaded fingerlets that apply a precise amount of pressure to two specific points. It’s an aerospace development. But any mechanic with any experience at all can open any Pozipfastner by flicking it with his index fingernails. It’s a trick that takes almost no practice, and most of them do it; it’s much quicker than using the tool.”

“And I presume anyone on any aircraft service crew knows how to work the special latches that only certified mechanics understand.”

“Of course. How could anything get done on time if the nearest man couldn’t lend a hand?”

Michaelmas pursed his lips. “What do you make of that wire?”

“Sabotage. The AEV really thinks so too, but they can’t bring themselves to accept the idea. Nevertheless, the unit flew without incident early this morning from a charter service to meet Watson. It was parked while Watson held a meeting with his network’s local people, but it certainly wasn’t serviced during that time. While Watson was talking, someone deliberately opened that hatch and then either used the factory tool or did the fingernail trick. I suppose it might have been someone demonstrating knowledgeability to an acquaintance. I suppose that someone might have forgotten to resnap the connection before remembering to close the hatch all nice and tidy. There might be some reason why such a person chose to demonstrate on a Pozipfastner that could only be reached by opening an inconveniently located hatch, bypassing scores of others more accessible. The AEV has already drafted an order; henceforth, the desiccator circuit must be wired to an instrument-panel-failure telltale light, or the model’s airworthiness certificate will be cancelled; all existing members of the type are grounded immediately for inspection of quote potential spontaneous failure endquote and installation of the warning light, and so forth. The manufacturer has already filed an objection, citing unreasonable imposition of added cost, since there are several hours' labour involved, but that’s pro forma so they can file a compensation claim against the Common Market authority. Und so weiter.”