by Hal Clement
“True,” replied the artificial intelligence. “The scale height on Habranha, particularly in the Cataract area, is large, though there are no exact figures. In view of the high surface oxygen partial pressure, you can probably breathe unaided at heights well above seven kilometers, and at such altitudes the main circulation is toward Dark-side. You need not make a high-speed craft; low wing loading, such as you would use on a planet of Erthuma-comfortable gravity, will be adequate—indeed, highly advisable, since there is no reliable information on how far you would have to travel between updrafts. Launch in the way you suggest should be quite possible.”
“It’s still silly!” Hugh was almost snarling. “We’ve flown in calm atmospheres, with nice, steady thermals a few kilometers apart, marked with cumulus clouds at the top. You know it’s not like that here! You—”
“What else can you think of?”
The only answer Hugh could have given to this grossly unfair question would have been to point out its unfairness. He didn’t bother; Janice knew that as well as he did. He was silent.
The woman refrained from triumphant remarks, which would have been even more unfair, and even blanked her facial expression now. She did love her Hugh. She also knew that he might be right; not even The Box could have considered everything. She was, however, a determined person, and greatly preferred doing something even when not sure that it was right. After all, as any scientist knew, there was never any way to be completely certain. Not objectively, and faith was inappropriate to the present problem.
The submarine’s frame served as basis for the glider. To the long hull, now a fuselage, were added wings of twelve-meter span and one-meter chord at the root, far more area than was really needed in Habranha’s gravity. They were designed carefully with the aid of The Box and assembled even more meticulously. It was embarrassing to Erthuma and Cephallonian alike to find that they needed to make their own measuring devices before doing any cutting; construction of this sort had not been planned for the study. Work was not really delayed by the resulting philosophical debate about fundamental equipment, but the debate served as background.
The hull had to be covered carefully with sheeting from the raft, and only the upper surfaces of the wings could be treated similarly before supplies ran short. Hugh would have liked well-shaped airfoils, but a fuselage that would float and not collect weed on its frame members while being launched, as the submarine had done even on its brief trip, seemed still more necessary. Also, there was no easy way to find the center of gravity unless the object were floating, though this could of course be shifted somewhat in flight by having the crew shift. The cockpit was open, longer than necessary merely to contain the Erthumoi; the crude seats were easily movable to permit this.
Seats, plural. Hugh was for once firm. His wife was not going alone this time. She made little argument and the Cephallonians none. It made no difference to the swimmers, and she was glad enough to have him along.
The other possibility, that he might make the flight without her, never crossed her mind, and if he thought of it he had the sense to keep quiet.
The Cephallonians were ready to make another rescue trip themselves, but courteously said nothing about it. They would have more difficulty this time, of course, since The Box had no sense of what went on above the ocean surface and could present no image of the atmosphere. If the glider had trouble, no one below would know until it reached the ocean, and then only if the accident occurred within the radius of the current sea image. It was quite possible, everyone including The Box realized, that even within that range a splash might be misinterpreted and go unnoticed; once in the water, the crew would have to use their transducers and signal as loudly as possible for help.
Splasher remarked to her husband, translator off, that she didn’t think the Erthumoi would get half a kilometer vertically or horizontally; if the Habras themselves didn’t fly in this region it seemed pretty silly for walkers to try it. Thrasher gave the equivalent of a nod.
Hugh had not repeated his essentially identical opinion since the initial argument, but it remained unchanged. He made sure that their environment suits were still adjusted for positive buoyancy, and was somewhat relieved when he saw his wife unobtrusively making the same check. This might, of course, have been mere routine, not pessimism or even realism, but at least it was being done.
They checked their suit filters with even greater care, and loaded a few oxygen tanks for possible need—only a few, since they did not expect the glider to be able to take much weight, and the swimmers might have a hard time with the launch no matter how light the machine was kept.
The real uncertainty was in wing symmetry. Even a slight warp, too minute to spot by eye alone, would mean a built-in tendency to bank and turn, and eyes were all they had—no precision assembly jigs or anything else “precision.” With someone at the controls, of course, such a warp could be countered, but that would mean a constantly alert pilot. Hugh had planned and started to build the wings so that they could be rotated around a lateral axis in flight, the axis represented by a single main spar, before his wife convinced him that any significant motion of that sort would mean gross overcontrolling. As an experienced recreation sailplane pilot himself he had known this perfectly well but had been highly pessimistic about their ability to build a really symmetrical pair of wings. He still was, and was not looking forward to the launch with any great confidence. Naturally, he wanted to be at the controls himself during the process. For similar reasons, so did Janice.
To minimize any temporary warping the wings were rigged with cord provided by the Cephallonians, though as little of this was used as possible. Even if weed could be picked up only during launch, any would be too much; there was no way such a load could possibly turn out to be balanced, either as weight or drag.
There was little doubt by the time it was assembled that the glider would fly kitewise, as long as its launching lines were held from below and someone was controlling its roll; there was always enough wind for that. The question was what would happen when those lines were cast off. It would then be necessary for the Erthumoi to find, or better to have found already, a wind with at least some upward component within gliding distance. There were plenty of spouts where ammonia was leaving the ocean violently, and these should have velocity enough to offset their lower density and lift; but whether the glider would hold together inside their violent structures was decidedly doubtful. On more Erthuma-normal worlds sailplane pilots stayed out of thermals that were growing thunderheads at the top; on this part of Habranha one could not see high enough to tell when this was the case. Free ammonia met water vapor, or much more rarely even hydrogen cyanide, in concentrations high enough to form clouds sometimes quite close to the ocean surface, though the adiabatic lapse rate was small. Thunder was nearly constant in The Cataract, the flicker of lightning sometimes detectable even in the constant daylight, but their sources could seldom be located. It was obvious only that they were high. The thunderheads were out of sight.
Janice was in the cockpit, and the Cephallonians a hundred meters away holding what all hoped would serve as launching lines. Hugh was casting off the numerous cords they had found necessary to keep the glider from blowing away as it neared completion. He trusted his wife to hold it firmly down until he could get on board, but made a point of leaving until last the tiedowns at the forward end—after all, neither of them knew just how effective the control surfaces would be in air, though they had worked well enough when the craft was a submarine. The specific question was whether they could hold the tail high enough to keep the wings from lifting at any time on a pitching deck. Several times during the unmooring the man leaped gliderward as the raft tilted the nose up, wind caught under the wings, and for a moment the fuselage rose and strained upward against the remaining ropes. It promised well for the flight, but made the casting off a nervous procedure.
“Box, have them take up the slack in the launch lines,” Hugh called as he approached t
he last two moorings. This order obeyed, he reached for the nearer of the two; then an idea struck him, and he went back to the cockpit, knotted another cord to an exposed longeron by his own seat, and with the other end of this clipped to his suit went forward again. The moorings clear, he ran and handover-handed back to his cockpit, wondering simultaneously whether his wife could hold the craft down for five seconds and why they hadn’t thought to improvise some means of releasing all the moorings at once from on board. He reached his goal without being lifted off the deck, slid over the side as quickly as his suit allowed without risking the fuselage fabric, settled onto his lurching seat, and tied the multiply-braided cord intended for a safety belt across his legs. Looking up from that precaution, he saw that they were already eight or ten meters above the raft—straight above; the swimmers hadn’t yet started to pull.
Whether they were flying, as opposed to blowing around, was debatable. Janice was certainly using her controls. These consisted of a horizontal foot bar on a vertical axis with lines from its ends directing the rudder, and two vertical rods: one for ailerons manipulated by her left hand, and one for vertical control at her right. Each set of lines had another bar within Hugh’s reach as he sat behind his wife, though he had to lean forward rather awkwardly for the aileron one. This was from his seat’s present position; it might turn out, they knew, that his would have to be moved so far back or hers so far forward to balance the glider properly that only one could reach controls at all.
The craft was far from steady so far, dipping, soaring, and yawing. The wind was doing all the lifting; the swimmers were holding position a hundred meters from the raft, and the Erthumoi were oscillating above it. Janice was still overcontrolling but learning quickly, and their crewed kite began to settle into a steadier pattern—not perfectly motionless, of course, in Habranha’s chaotic air currents, but something far more comfortable than it had been at the start. Hugh wondered briefly how his wife’s motion-sensitive stomach had been able to take the first few minutes, and then recalled what a difference it made when the owner of the stomach was doing the piloting. She had been right to insist.
She had almost completely stopped the roll and yaw wandering now, and was managing, on the average, a gentle climb. The tow lines were taking on a remarkably steep slant, and Hugh almost automatically began estimating the lift and drag vectors involved. The weight was small enough, but it wasn’t zero even on Habranha. Was there an updraft anywhere near that could support them?
A spout showed half a kilometer to the left, reaching up into the haze beyond human vision; another was behind them, presumably being carried away by the wind now holding up the glider. If they cast loose from the Cephallonians, what would be their glide angle? Could he compute it from the present slant of the rope? Not without knowing the wind speed, of course.
Their trackers would let them calculate the last only after they were free. Then they could get glide angle from the recent rope slant, assuming wind was reasonably constant, which was asking a lot. Then they would know if they could get close enough to the spout to use its vertical air currents. If they couldn’t—if the glide were too steep—well, they could land on the sea and the Cephallonians could tow them back for another try.
Or they could wait as they were until a spout came so close that there would be no doubt about their reaching it.
Or maybe they shouldn’t use a spout. A whirlpool should have a less violent lifter above it. Less likely to tear wings off. The endlessly varying howl of The Cataract’s wind didn’t completely drown out the occasional mutter of thunder that reminded Hugh of what real thermals could do to aircraft—even professionally built ones. Neither he nor his wife had any illusions about the rugged-ness of the gimcrack device they were riding.
Hugh saw a whirlpool a few hundred meters to their right, and pointed. Janice nodded silently. The launch cables, unlike the tie-downs, had been arranged to be released from the cockpit; she dropped them at once and swung right in a slightly overcontrolled but fairly graceful turn. She was trying to find the narrow line between maximum glide range and stall attitude as she headed for the possible source of lift. They had no airspeed instrument; their inertial trackers were useless for any such problem, of course, without independent wind information. Almost useless; they did show local vertical, since Habranha’s radius, rotation, and even its orbital parameters had been set into them.
The glider recovered easily from stalls, it turned out, and the pilot lost control only twice. Fortunately, wings stalled before control surfaces. This was rather surprising, considering the history of the latter as hydrofoils, but neither of the crew thought of that.
They still had reserve altitude when they felt an upward surge. Janice glanced over her shoulder, and each could see a grin of triumph through the partner’s face protector. The woman concentrated on a gentle turn that kept them in the updraft, using her trackers after the raft faded from view in haze below them. At four kilometers’ altitude they ceased to climb; the current was just able to support them. She straightened out in the planned direction—headings were not quite all equivalent. All points on The Iris’s near edge were about equidistant from the substellar pole, but the raft was much closer to one side of The Cataract than the other. There was, however, no way to tell where another updraft might be found, and this was the more immediate problem. Janice was pretty certain now of the ideal glide attitude, and maintained it with the aid of the vertical-component tracker since no horizon was visible.
The other component readings suggested for some time that wind was helping them on their way, as The Box had predicted. Below about two and a half kilometers added turbulence heralded the end of this status and their true descent angle steepened, though the glider’s ideal attitude did not of course change. Just below one kilometer the ocean surface became visible once more, and both Erthumoi began to search it earnestly for signs of another rising current.
Several spouts showed up almost at once, clustered rather closely together for reasons known only to chaos; no others could be seen within the ten- or fifteen-kilometer range that the slight haze permitted to Erthumoi vision.
Whirlpools would be smaller and harder to see, of course. The flyers had the obvious choice of a straight-line glide that would cover more ocean, get them farther on their way, and in theory give them a better chance of finding whatever lifters there might be, or circling to remain within gliding distance of the spouts in case no whirlpools could be found and the more dangerous alternative had to be used. Hugh said nothing when his wife banked the glider into a gentle turn that kept them circling the spouts. He would have made the same choice. They seemed risky, but at least they were definitely there.
Two-hundred meters above the raging surface Janice glanced back at her husband once more. He shrugged. She nodded, and started another slow turn in toward the nearest column of ammonia-rich spray.
The glider was already shuddering in turbulence, and maintaining a steady descent was not really possible. She did not, of course, head straight into the misty pillar but a few dozen meters to its left. They should still be nearly a hundred meters above the waves when they came level with it, and ought to be feeling lift before then.
They did, but under the right wing only. The glider went into a nearly vertical bank to the left and started a steep diving turn in that direction. Hugh’s training normally kept him from being a control-grabber, but this time he helped; between them they leveled out at thirty or forty meters. The man released his bars with a major effort of self-control, and Janice promptly and deliberately nosed down again to gain speed and banked back toward the spout—straight toward it. This time the nose felt the lift first, but she forced it down firmly. Hugh nodded silently, not looking at the chop ten meters below. Only when Janice felt strong general lift did she turn once more to bring them side-on to the spout.
Now the difference between the two sides was not so great and she was able to maintain control, and even to hold the inner wing—the left
one this time—down so they remained in a slow turn and stayed inside the lift region. They were climbing again, far faster than before; Hugh felt uneasy as he saw the wings bending visibly.
Not bending, flapping. A little yield was normal for any structural material and the woody stems they had used for the frame were extremely springy, but this shouldn’t be happening. A steady updraft might have bent them during the initial acceleration, but once they were lifting steadily—
They weren’t lifting steadily, of course. Habranha’s chaos was manifesting itself again. The glider was jerking and twisting, pitching and banking and yawing in gaseous eddies quite undetectable until one was in them and, Hugh guessed, quite beyond the power of even The Box to resolve into a predictable pattern had it been with them.
“Cut out of this!” he cried to Janice.
“We need more altitude. We have less than a kilo so far. We’ve got to get higher!”
“We need wings and tail more. We’ve got enough to give us some gliding range. We can look for a safer updraft.”
“But at this height the main wind is still toward The Cataract.”
“We can live with that. We were expecting lots of climb-and-glide cycles before we got anywhere near where we wanted.”
“But that first one—”
“Don’t let one piece of luck spoil you. Get out while we have wings!” Tense as he was, Hugh made no attempt to seize the controls; he was a recreational flyer, not a professional, but too good a pilot for that. A vehicle—any vehicle, land, ocean, air, or space—must be controlled either by a single entity or by a completely cooperative and informed team.
If there are two or more experts aboard, the one actually taking a turn at the controls is responsible.