You perhaps remember that sometime in the dim past, at the Naval Academy or elsewhere, you made the acquaintance of PVT Prime. Except as a convenient formula for working some simple problems in physics, you gained no lasting acquaintance, and have forgotten PVT' unless you have been engaged in certain branches of engineering. However, anyone engaged in aerostation soon discovers that PVT' is piloting him at all times; unless he knows PVT' intimately, and all his relations, some unforeseen circumstances may develop which are later found to be the standard behavior of PVT' and should not have been in any way unexpected.
Some months ago it was suggested at Lakehurst that training flights of the U.S.S. Los Angeles should be extended somewhat. The short experimental and training flights were getting too commonplace, and more extensive experience would be gained from an occasional longer flight. It was decided to fly to Panama, which is U. S. territory, a suitable and safe distance, and which could provide an adequate Navy ground crew. As soon as this flight was suggested we began as usual in planning a flight, to consult PVT'. What were the pressures (barometric) to be expected at Panama and Lakehurst at the time of the flight? What volume of gas was required to carry the necessary fuel? What would be the change in this volume as pressure and temperature changed?
After making all calculations, and loading the ship accordingly, we decided to start during the early morning of February 26, 1928, expecting to take about thirty-six hours for a non-stop flight to Panama. We would use PVT' to help us get off with a heavy load, by taking the ship out of the warm hangar into the cold air. With a temperature several degrees higher than the surrounding air, called superheat, the gas would have greater volume and hence greater lift. Of course we would soon lose this false lift when the gas cooled, but by that time we would be in the air, and could maintain the extra load dynamically until some of the fuel had been consumed. But we went farther than this! In order to get a little more T in the gas, we started hot air blowers in the hangar, and soon had 3,000 pounds extra lift.
At 6:20 a.m., the big hangar doors rolled open, and the ground crew commenced walking the ship out. Stationed around the ship in groups, each group with a line to the ship, the ground crew functioned just as tugs do in warping a big liner out of a dock. The shore pilot called for more speedy movements. Why? PVT' told him that T would decrease quickly, particularly as an eleven- to twelve-mile wind was ventilating the ship; if we wanted to use the extra lift he must get the ship away quickly. Only one man of the crew for each station had embarked on the hangar. As the ship emerged into the colder air, she became so light that all the crew of forty-one were rushed aboard, and even then it was necessary to take more men temporarily from the ground crew as ballast until some of the false lift was lost.
Soon the extra handling lines were detached, and at 6:55 a.m. the order was given to “Up ship.” The engines started immediately. As we climbed, PVT' again got to work, for we ascended rapidly into colder air. However, superheat began to decline sharply as soon as the flying level was reached and the air rushed by as speed was gained. As the air grew less dense with altitude the gas cells gained in volume; this made no change in lift as the weight of air displaced remained the same.
We reached lower New York Bay at 8:00 a.m. and set the course on a direct line for Colon, Canal Zone. The course led over New Jersey, leaving its coast at Atlantic City, bringing us just in sight of Cape Hatteras, and then over water again until the Bahamas were reached. Several snow squalls were encountered, but as more southerly latitudes were reached the temperature rose. By sunset most of the crew had abandoned the heavy fur lined suits in which they had frozen at six degrees Fahrenheit at the start. It became possible in the early afternoon to operate the water recovery condensers, which would have frozen if started at less than twenty- three degrees Fahrenheit. There was as yet no need for the water recovery, as the ship was flying heavy, due to the false lift with which she had taken off.
The water recovery installation is an American invention which was originated in the development of the technique of helium operation of airships. Formerly, with hydrogen inflated airships, it became necessary to valve off some of the lifting medium as soon as the ship became light from the consumption of fuel, in order to maintain static equilibrium. The cost of helium made it mandatory to avoid this loss. This was done by designing a light air-cooled condenser suspended above the engine car, into which the engine exhaust gases are circulated, and the moisture content liquefied and returned to the ballast system. The efficiency of this system (from ninety to 115 per cent in practice) makes ft unnecessary to valve out a large amount of lifting medium when two or three tons of fuel have been consumed, as an equal amount of water ballast has replaced it, and the load remains constant.
Shortly after leaving Cape Hatteras, heavy rain clouds were observed, and we knew we were over the Gulf Stream. From the air the water appeared steaming hot. Long feathers of vapor rose from it and traveled with the wind. Several steamers were sighted making very heavy weather, and we congratulated ourselves that we were being transported comfortably, rapidly and safely by more modern means. As soon as darkness fell the navigating officers began to drop flares upon the water to provide a point from which to determine the drift of the airship from the course.
At 10:40 P.M., an island of the Bahamas was sighted, but almost immediately a fog or cloud closed in and all sight of the surface was lost before any identification of the position could be made. We soon learned that whenever we were over shallow water, which was probably warmer than deep water, we were surrounded by low clouds. We asked the radio operator at Nassau for his conditions and he reported weather clear. By using our radio compass, we obtained his approximate bearing and soon sighted the lights of Nassau, only to have them disappear as another cloud intervened between us. In two or three minutes we were over the island; sure enough it was clear over land. After slowing the engines to look over the island, we continued on our line, and at dawn started across Cuba.
As the rising sun illuminated the surface of Media Luna Cay, we saw the U.S.S. Patoka, which had been diverted from carrying oil to the fleet, waiting to service us. There being no reason for stopping, we continued for Panama, having covered nearly two-thirds of the distance and having used only about two-fifths of our fuel. We expected to pick up the northeast trade winds as soon as we got offshore, which would add materially to our ground speed. However, before we got twenty-five miles offshore we encountered some ominous looking clouds which resembled violent thunderstorm clouds of our usual latitudes. Upon approaching them we found them to have no turbulence whatever, and except for causing us to fly low for visibility reasons, they afforded us no inconveniences.
At 10:00 a.m. we passed about three miles to seaward of the western point of Jamaica. We had not yet encountered the northeast trades! The wind was easterly and gave no help although it did not impede us. The clouds were magnificent in extent and most fantastic in shape. They extended from about 1,000 feet above the water to 4,000 or 5,000 feet. Since we had been in the air for thirty hours, time began to hang heavy on our hands, and we amused ourselves by pointing out figures of men, animals and other objects formed by the clouds. Officers off watch abandoned their bridge game to compete in pointing out the unusual formations. Every small island or shoal had its stationary cloud hanging over it. Later in the afternoon as the atmosphere began to cool, the clouds began to drop their water; often we would be within a hundred feet of a downpour and still be able to avoid it, although we did not try if more than a minor temporary change of course was necessary.
Colon reported a north wind and we watched our drift and ground speed closely to determine when we would be in it. As we neared Panama, a sight was taken of a star in the Southern Cross to check our latitude and a radio compass bearing was utilized to determine if we were off our line. We had predicted earlier in the day that we would arrive about 10:00 p.m. At 9:15 p.m. we sighted the breakwater lights at the Atlantic end of the canal about twenty miles away, and soon we were over the Naval Air Station at Coco Solo, and France Field, where we were to land.
The engines were idled and the controls put in neutral in order to “weigh off” the ship. No change in inclination was noticed; the ship was in trim. Neither did the very sensitive instruments showing vertical movement indicate any marked rise or fall, hence it was determined that the ship was also in equilibrium, and ready for landing. PVT' did not have so much to do with this; his part was seen in the air density, which the humidity had reduced, so that the ship was relatively heavier in the humid atmosphere. Water recovery had been about ninety-five per cent efficient, the other five per cent loss of weight having been made up from change of lift from humidity and by the addition of moisture soaked up by the fabric of the outer cover and gas cells. If the water recovery apparatus had not been available, it would have been necessary to valve a considerable amount of lifting gas to compensate for the fuel burned. With helium at current prices the water recovery installation had more than paid for itself on this one flight, and also it had been demonstrated that this gear would be an economical adjunct for a hydrogen inflated ship. Of course the air cooled condensers retard the speed of the ship, but not in proportion to the economy in fuel or lifting gas afforded by their use. Undoubtedly commercial operation of even hydrogen inflated airships will demand water recovery apparatus, or a fuel gas of about the density of air.
An officer from Lakehurst had preceded the ship to Panama to supervise the landing and to erect an experimental stub mast to which the ship was to be moored during her stay. This mast was about sixty feet high and consisted of a wood spar topped by a “flower pot” or cup into which the mooring cone of the airship could be locked. With the mooring cone in this cup the forward car of the airship would be about ten feet from the ground, with a quickly detachable pneumatic wheel placed under the after car. This arrangement left the ship free to swing in azimuth to keep into the wind, while the heavy wheel aft kept the stern down if the ship became light. With the ship so close to the ground, vertical air currents were impossible, and gusts were much reduced below those encountered at the altitude of a high mast.
By the time the field had been circled twice a blinker message was received reporting the readiness of the ground crew, and at 10:20 p.m. the Los Angeles reached the ground. During the approach and landing it was noted that PVT' had influenced the altimeter, for it read 600 feet when we were on the ground, and the ground was only six feet above sea level. The barometric pressure had been much higher at the time of beginning the voyage, and the altimeter, an aneroid barometer calibrated in feet, requires the application of a correction whenever the surface barometric pressure differs from that at the time of takeoff. Extra handling lines were attached and manned and the ship was “walked” over to the stub mast and secured. The water and fuel hoses were coupled and the ballasting and fueling begun. As fuel was obtained, the water which had been recovered on the flight was dropped. No supply of helium was necessary, as none had been valved, and the only servicing necessary was to exchange water for fuel. Newspapers were delivered in thirty-eight hours, the first New York newspapers received in the Zone less than five days old.
The routine of riding at the mast was very simple. An instrument in the control car told the officer of the watch the exact pressure or tension between the ship’s bow and the mast. The pneumatic wheel under the after car could be observed for downward pressure at the stern. The ship was thus constantly weighed, and the officer of the deck adjusted ballast as necessary to take care of changes of lift or load, at all times keeping the airship slightly heavy.
After receipt of the weather map the next morning, it was decided to begin the return flight. The morning sun again heated the gas so that temporary extra lift was obtained, and also increased the volume of the gas cells so that the ceiling would not be very high unless helium were valved. Two extra passengers were embarked, making a total of forty-three on board. The officials of the Zone had requested that the Los Angeles fly over the canal before departure. By 10:00 a.m. the flight crew was all aboard, the after wheel was detached, and at 10:12 a.m., the ship being weighed off slightly light, the commanding officer ordered the mast to “Let go.” The ship commenced to rise steadily, but as an additional precaution an emergency ballast bag was emptied at the bow. The engines were cut in, and the flight began. We had left Lakehurst in a temperature of six degrees Fahrenheit and now had an air temperature of eighty-six degrees, with the gas somewhat above this, so that the gas cells were much fuller than at the start. But PVT' had told us just what to expect and everything turned out as calculated. The barometer also was lower and the gas expanded somewhat under the reduced pressure. We left the mast with rather less water ballast than is habitually carried. This was made possible by the installation of fuel dump tanks, which are regular fuel tanks with valves controlled by wires leading to the control car. This extra ballast is required only at the take-off provided that the trip is to be long enough for acquiring sufficient water ballast from the water recovery, to use in landing or in heavy rain, etc.
Since the air over the Zone was bound to be turbulent due to the uneven contour, the two oceans, water, and trees, it was desired to obtain a high altitude. At first a long turn was taken over water to give the gas time to cool and to decrease in volume. In a few minutes the ship was back over the breakwater, and transited the isthmus in forty minutes. After circling Balboa and Panama, and viewing the placid Pacific, we returned, and departed at 12:19 a.m. for the Gulf of Guacanayabo, Cuba.
As forecasted, head winds of about eighteen knots were encountered, but no effort was made to speed up, as the flying was comfortable and there was no necessity for high speed. Only four of the five engines were run, and these at economical speed. The low clouds were again present in unending procession, and in the fantastic shapes before observed. The flying altitude was from 800 to 1,100 feet to keep under the clouds and to avoid winds which were probably of higher velocity at higher altitudes. After a few hours, routine again began to pall. After dark, sextant altitudes of Polaris, which was nearly dead ahead, were taken hourly to check the latitude. The drift was relied upon as sufficiently accurate to keep upon the line laid down on the chart, but ground speed is not so easy to determine at night, unless time is taken to change and obtain the drift on another course, thence working out the ground speed, wind force and direction, etc.
At dawn, as expected, the outlines of Jamaica Island appeared a little on the starboard bow and at 10:58 a.m. the U.S.S. Patoka was sighted at her anchorage near Media Luna Cay. PVT' now began to work against us; the drier atmosphere and bright sunshine gave us extra lift which we did not desire if we wished to moor with the airship in equilibrium. Also as we slowed down for the approach for mooring, the lessened ventilation of the gas cells permitted them to absorb more heat. We could then wait until late afternoon to moor or we could valve a little helium. Our morning weather map was of such composition that there could be quite a variety of forecasts, with good reasons for each. However, it seemed practicable to us to moor at once, refuel, and take off again before sundown for Lakehurst. Hence the maneuvering valves were opened until we had lost about 1,500 pounds lift, and the mooring was completed at 1:00 p.m. Fueling was begun. PVT' immediately got busy and sent the gas temperature more than twenty degrees Fahrenheit above the air temperature. Soon the Weather Bureau forecast was received by radio, and its diagnosis differed somewhat from our own. Since conditions in the Gulf were perfect, and there was no hurry to return, it was decided to remain at the Patoka and perhaps make some local flights to Guantanamo or Havana. Our mission was training and we could obtain this as well by operating in the Caribbean as elsewhere.
The next morning, March 1, the weather map seemed to have borne out our prognostication and we decided to start for Lakehurst. In any flight of 1,400 miles or more it is always difficult to forecast accurately the conditions along the entire route, and it would be procrastinating to await until the whole line of flight would have perfect conditions. After superheat had given us extra lift, more fuel was taken aboard and at 10:40 a.m. the Los Angeles was unmoored. At this time the superheat was twenty-three degrees and as the gas cooled off the ship became very heavy. A direct route to Miami would probably give less head winds at the start, but would cause the winds encountered north of Miami to be well forward of the beam. If we went further west at first, the westerly winds to be expected from Florida on to the north would be more abaft the beam and probably help instead of retard us. But due to heating of the air over land, the atmosphere was very turbulent over Cuba, and is was not desirable, although not dangerous, to carry a heavy ship through the one hundred miles or so of turbulent air. Therefore the course was set along the southern coast of Cuba. By the time Havana was reached enough fuel had been burned to put the ship near equilibrium.
Over Morro Castle we took departure for Tampa, and at once plunged into the clouds and mist of the Gulf Stream. Although we passed only a little more than thirty miles to the westward of Key West we were able to make out the light at that place. Tampa was not reached until 2:00 a.m.
After we left Tampa, ground fog began to form and soon the surface was totally obscured. Overhead, however, the stars were bright, and we knew that if the fog lasted for a long time, we could obtain our position from celestial observations. The fog gradually rose in height, and finally we had to fly at 2,500 feet to remain above it. The course led to the vicinity of Jacksonville. As the sun rose the fog dissipated and Jacksonville was in sight. We now intended to head for Lakehurst, but as Charleston, South Carolina, was only a few miles off the course, it was made the immediate destination and was passed over at 12:30 p.m. Up to this time the winds had been so far forward of the beam that we were not making much speed, but now they began to get more astern, and the ground speed gradually increased. At 7 45 p.m. we were over Norfolk, Virginia, and a little later we were logging as high as seventy knots over the ground, our engine speed never having varied from the economical four-engine speed. The reliability of these engines was remarkable. For six days none failed to respond, although some had run 800 hours without overhaul. At 11:35 p.m. we arrived over the home station at Lakehurst. We signaled our desire to moor to the mast, as the surface wind prevented our entering the hangar, and a fifty-two knot wind at 1,800 feet made it desirable to moor rather than use fuel to heave to over the station. However, we had from eighteen to thirty hours’ fuel remaining so that there was no necessity for mooring.
While mooring the ship to the mast, a sudden veering of the gusty wind caused one of the mooring wires to break. We cast off to await better conditions and the assembly of the ground crew for a landing on the ground. The landing was made at 4:00 a.m. and the ship “walked” nearly to the lee of the hangar, when a sudden snow squall whipped out of the north. Old PVT' worked with a vengeance; the almost instantaneous temperature drop of ten degrees made the ship light. Gust of wind up to thirty-miles per hour caused the ground crew some difficulty in holding the ship, so that the word was passed to “Let go 1” The engines started and the ship rose into the snow storm, disappearing at about two hundred feet altitude. Four men had not gotten the word to let go and were seen dangling from the car rail. They were quickly pulled into the car and shortly afterward a report was made to the station that the men were all safe. The ship heaved to over the coast about twenty miles from Lakehurst for about an hour, when a message was received from the station stating that the squall had passed, and that the ground crew was being assembled again. As we approached this time the landing field was seen to be covered with a blanket of snow over an inch deep. The landing was made without incident, and the ship was half way into the hangar before another squall hit which caused no inconvenience. PVT' was not through however, for as we entered the warm hangar, the relatively colder gas caused the ship to become very heavy, and it was necessary to valve some ballast to keep her from bearing down too heavy and slowing the movement into the hangar.
From start to finish, on the ground or in the air, for the whole six days and 5,500 miles, PVT' rode with the pilot.