MOBILE MAST USED AT LAKEHURST, NEW JERSEY, USA, for mooring airships. The mast can be used also for towing airships directly into or out of the airship shed. It may be used in a comparatively strong wind and has the great advantage that it requires considerably fewer men than the hundreds who are needed when an airship is guided into a shed by means of man power.
ALTHOUGH rigid and non-rigid airships were introduced by France and Germany respectively, Great Britain inaugurated the practice of mooring airships in the open instead of returning them to their sheds after each flight. Airship mooring may be divided into three classes; mooring on the surface of land or water, mooring to a mast and mooring in the air by means of one or more anchoring wires.
Between 1907 and 1914, British Army airships were regularly moored in the open in the shelter of high trees. No damage was experienced in a single instance, and during the manoeuvres of 1913 the Delta and Eta, thus moored, rode out fifty-miles-an-hour gales.
In the war of 1914-18 the submarine blockade necessitated the accommodation of small non-rigid airships at different points near the coast of Great Britain. At many of these points it was impossible to build sheds for housing the airships. Fields or clearings of sufficient size for an airship to land, and bordered by woods, were therefore selected. Circular cuttings connecting with the fields were made in the woods, and in each cutting pits were dug at regular intervals. These pits were large enough to take the airship’s car. The circular cutting enabled the airship to be moored in the shelter of the trees and head-on to the direction of the wind, to avoid the danger of side gusts that might come through the trees. The guy wires used for handling the aircraft were secured to trees or pickets. The placing of the airship’s car in one of the pits lessened the effect of vertical currents of air.
By August 1918 there were eleven of these mooring sites in commission. More were required, and sites with thick trees and adjacent open ground could not always be found where desired. Experiments were therefore carried out at Pulliam (Norfolk) with the S.S.14.A. The object of these experiments was to enable an airship to be moored on the lee side of an ordinary wood. The S.S.14.A was fitted with quick-release slips both in the main rigging wires and in the control wires. To reduce the possibility of error when re-rigging, each slip was painted a different colour. The rudder, with its vertical fin, was placed on top of the airship’s envelope and the control wires were carried on tripods round the outside of the envelope. The airship’s car was thus made detachable from the envelope, and was wheeled away on a special chassis. This left the envelope to be “bagged” down with its underside close on the ground. Inflated “bumping bags” were laced to the envelope to prevent the fabric from chafing on the ground and to hold the envelope valves clear of the ground.
As soon as the airship was brought down to the ground, sandbags were attached to ropes on its envelope. These sandbags caused the wires suspending the car to become slack, enabling it to be released and wheeled away on the special chassis. The time taken to bag down the airship was five minutes; from six to eight minutes were taken to re-rig it. The Armistice followed soon after these experiments had been completed and the method was never adopted at the coastal bases. To improve this scheme further, fabric gas holders and gas compressors were proposed to provide quick inflation and deflation of the envelope.
THE R 100 AT A MOORING TOWER IN MONTREAL CANADA. This mast, now dismantled, was somewhat similar to that at Cardington, Bedfordshire, the culmination of experiments in Great Britain on high mooring masts. The advantages claimed for the high mast were that it could be used for mooring in almost any weather, and that the car was unlikely to be damaged through being brought into contact with the ground by the wind.
The first airship to be moored to a mast on the water was Great Britain’s first, rigid dirigible - the naval airship No. 1, which was taken out of her shed for the first time at 1 a.m. on May 22, 1911. The shed in which she had been built had one side resting on the side of Cavendish Dock at Barrow-in-Furness, Lancashire. The airship floated on her gondolas in the shed. She was towed out stern first and moored to a short mast.
The mooring arrangement was as follows: A reinforced concrete pillar was sunk into the bottom of the dock, which at this spot was about 8 feet deep. The remainder of the mooring device was free to swing round this post and consisted of a free pontoon secured to the concrete pillar by ties of wood and steel. On the pontoon stood a latticework steel mast which served the purpose of taking the mooring wire up to the height of the airship’s nose above water.
The airship carried a 4-in mooring wire 43 ft 6-in long secured to her bow. The mooring wire on the mast was also a 4-in wire; it was 111 feet long. When the airship had been hauled nearly to the mast the ends of the wires were shackled together, and the airship was pulled close up to the mast. The nose of the ship was brought as near as possible to the mast, so that there should be a minimum of play. The main object in having the mast on a pontoon was to give a certain amount of elasticity to the mooring. If a heavy horizontal pull were to be suddenly applied, such as might happen if the airship jerked at her mooring, the first effect would be to submerge the pontoon a little more; as the strain eased up the pontoon would gradually rise again to its normal level. The difficulty experienced in such an event was to prevent the pontoon from touching the bottom, the normal draught of the pontoon being 6 feet and the depth of water only 8 feet.
THE OSBORNE METHOD OF MOORING which requires little gear. The three forces of A, the wind; B, the buoyancy of the airship; and D, the lift of the elevators, are arranged always to balance Ballast is hung from the car by lines, and just clears the ground.
A windscreen made of wooden strips and canvas was arranged to lessen the force of the wind on the airship’s bow.
The chief difficulty encountered was a tendency of the mast to yaw about when the airship was secured to it. The wind screen was removed and rafts were added to the pontoon in an endeavour to check the tendency. This expedient was to some extent successful, though the yawing could not be entirely eliminated.
THE U.S. AIRSHIP MACON being moored to the mobile mast at Lakehurst, New Jersey. The Macon was built in 1933 and had an overall length of 785 feet. Her diameter was 132.9 feet and capacity 6,500,000 cubic feet. Powered by eight Maybach engines having a total horse-power of 4,480, she had a complement of eighty-three and carried six fast fighting aeroplanes. The Macon was lost off the California coast in February 1935.
The ship safely rode at the mooring mast in a steady wind of 36 miles an hour, with squalls reaching 42 to 45 miles an hour.
Having spent nearly four days on the mast, the ship was taken back to her shed. On being taken out for the second time she broke her back, and naval airship development was thereafter discontinued.
After this abandonment, airship mooring development was continued by the Army. A lattice girder mast was built with a cone, free to move in any direction, at the top. This cone was reminiscent of an umbrella, and the nose of the airship, while facing into wind, was drawn to the cone by means of a hawser running on to a hand winch.
The first experiment with this mast was conducted at Farnborough, Hampshire, on February 13, 1912. An old skin envelope of 17,000 cubic feet, known as Koppa, was used. The Koppa withstood heavy rainstorms and winds of 26 miles an hour while moored to the mast. It was therefore considered safe to experiment with one of the existing airships.
On February 19, 1912, the airship Beta came down to 200 feet about 50 yards to the leeward side of the mast. A landing party then brought her down to 80 feet and guided her nose into the cone. The Beta remained thus moored for nearly twenty-four hours without incident.
A TEMPORARY AIRSHIP MOORING can be provided by a sea anchor lowered from the airship. An inverted cone is attached to the mooring line about 80 feet from the sea anchor. This cone stabilizes variation in lift and keeps the sea anchor submerged the whole time. When it is desired to withdraw the anchor, atrip weight is run down the anchor wire and turns the cone round, spilling the water from it.
After this success with the Beta, experiments were continued with other airships. Sometimes a high mast was used, with the airship floating in the air. At other times a low mast was adopted, with the airship on the ground but able to turn with the wind. This method required a number of men constantly in attendance to deal with the side handling guys as the ship swung with changes of wind. To obviate this need a new scheme was introduced.
A cradle, fitted with shock absorbers, was attached to the centre of the airship’s car. This cradle was mounted on ball-bearing wheels running on circular monorails, with the mooring mast at the centre. The airship was thus able to swing freely into any direction and only two men were required to be in attendance. This scheme was the foundation of the mooring method used today in America and Germany.
In Great Britain the high mooring mast was preferred, and experiments culminated in the mooring tower built at Cardington, Bedfordshire. The advantages claimed for the high mast were that it could be used for landing and taking off in almost any weather, and that possible damage to the airship, through vertical air currents or side gusts bringing the car into sudden contact with the ground, was eliminated.
The procedure adopted in mooring an airship to a high or low mast is the same. The airship approaches the leeward side of the mast at a height of about 200 feet. An order is given to men stationed on the winch platform up in the nose of the airship to pay out so many hundred feet of the main wire. This is done, and the next order from the control car is: “Pay out main to stopper and stand by to pay out port yaw guy”. The stopper fits into a cone at the extreme point of the bow of the airship, and care has to be taken in easing the stopper into place after it has left the winch. By this time the port yaw guy has been run out, and also the star-
board yaw guy, care having been taken in the process to prevent them from becoming entangled with the main wire. A 25-tons wire led out from the top of the mooring mast is joined to the main wire from the airship. The airship is then trimmed bow light so that the slack on the wire is taken up.
THE AFTER ENGINE CAR OF THE GRAF ZEPPELIN photographed when the airship was moored to a low mast at Recife (Pernambuco), Brazil. The car is fastened to a mobile truck running on circular rails so that the airship may swing at the mooring mast if the direction of the wind changes. A quick-release lever is provided to free the engine car from the truck in an emergency. Auxiliary latticework struts are used between the airship and the truck while the airship is moored.
The main winch on the mooring mast now begins to wind in the wire. When the airship is sufficiently near the mast, the main winch is stopped and the yaw guys are coupled up to their winches. All three wires are now used to haul down the airship. The winches for the yaw guys are set well back to prevent the nose of the airship from overriding the mast.
When the airship’s cone is fifty feet from the cup at the top of the mast the yaw guy winches are stopped. Hauling in for the last fifty feet is carried out entirely by the main wire. As the cone comes up to the cup the yaw guys are released, allowing the cone to ride over the lip of the cup and down into it. On its way into the cup, the cone presses out three spring stops in the cup and these spring back into grooves in the cone. The telescopic arm which carries the cup is now retracted inside the masthead and securely locked in a central position. The mooring of the airship is thus completed.
A consideration which arose early in the development of airships was that of reducing the large number of men required to bring the craft in and out of the hangar. In Great Britain in 1920 a short lattice mast was fixed to an army tank, and the airship was towed in and out of her hangar attached to the mast. This device was the forerunner of the short, mobile, telescopic mast used today in America and Germany.
This modern towing mast is known as the “iron horse”. It consists of a pyramidal framework of steel members mounted on widely spaced railway tracks. The height of the mast is 75 feet, but it can be extended to a height of 160 feet. The total weight is 300 tons. In the extended position the mast is designed for a side pull of 40,000 lb, and in its lowered position for a pull of 58,000 lb.
FIRST AIRSHIP TO BE MOORED TO A MAST ON WATER. On May 22, 1911, Great Britain’s first rigid dirigible, the R 1, was floated out of her shed on her gondolas and attached to a floating mast in Cavendish Dock, Barrow-in-Furness, Lancashire. The lattice work frame of wood and canvas which was designed to protect the nose of the airship from the wind, was later discarded. The floating mast was fixed to a concrete block, and was able to turn in any direction as the wind varied.
Electric power is used for operating the mast, and this power is supplied by generators driven by an eight-cylinder 565 horse-power petrol engine. The power thus generated not only drives the mast along its rails, but also operates the main mooring winch and the telescoping gear of the mast. A pull of 25,000 lb at a speed of 400 feet a minute can be exerted on the main mooring wire.
The telescopic mast enables an airship when taking off to be lifted through a temperature inversion. This may save several hundreds of pounds of ballast and fuel that might otherwise have to be jettisoned. When the mast is pulling the airship into her shed, side gusts of wind are counteracted by side handling guys fixed to trolley cars running on rails. The use of this mast
enables the airship to be moored out in the best conditions. Moreover, if the airship is towed in and out of her hangar, this method considerably reduces the number of men required.
The mooring of airships to masts has today passed from its experimental stage, and mooring masts are found wherever airships fly. The United States Navy has six mooring masts. One of these has been built in the navy tanker Patoka and has proved successful. There is also a mooring mast for commercial airships on top of the 1,250-feet Empire State Building, New York City. This mast is equipped with passenger lifts.
Occasions may arise, however, when an airship has to be moored on land or water at short notice, and where no mooring masts are available. One system for mooring an airship in the air over land was evolved by the late Commander Osborne, R.N. Its chief advantage is the small amount of gear required - a mooring block and a few screw pickets.
Two wires are attached to the airship, one at a point near the nose and the other to the forward end of the car. These two wires are made fast to a single mooring block. Fore guys are led aft on either side of the airship at an angle of about thirty degrees, and made fast to screw pickets. These guys are moved to different pickets if the direction of the wind changes.
ILLUSTRATING THE PRINCIPLE of the three-wirer system of mooring. The guys running up from the ground are attached to the junction point of three short wires fixed to different parts of the airship. The points of attachment of the wires to the airship are comparatively close together.
The elevators of the airship are put down so that they tend to cause the tail to rise. Also, the airship’s ballast is arranged so that the airship is buoyant. Spare ballast is hung on lines attached to the car and clears the ground by a small distance.
This system is so arranged that the stresses produced by any wind velocity are equalled by the combined effects of the buoyancy of the airship and the pull of the guy wires.
When a strong wind forces the airship down towards the ground, the spare ballast rests on the ground. Its weight is thus removed from the airship, whose buoyancy therefore increases and counteracts the downward force of the wind.
Another method of mooring an airship over land is that which was used when the British airship R 34 arrived at Mineola, Long Island, USA, in July 1919, after her historic Atlantic flight. Under the command of Squadron Leader Scott, she had crossed from East Fortune, Scotland, in 103 hours 12 minutes. The R 34 remained on the mooring for a few days before returning across the Atlantic. During this period the airship suffered no harm from the gusty weather. The method is a three-wire system, and the airship is moored far enough from the ground to reduce the effects of irregularities in surface wind.
Three wires are joined to points near the nose of the airship. These three wires are joined at a distance from the ground. From their junction point three more wires run to anchors arranged to form a triangle on the ground.
Static and Dynamic Forces Balanced
The airship is given a static lift to keep a strain on the mooring wires. This lift is kept forward so that the tail tends to drop and the force of the wind on it produces a dynamic lift.
The junction point of the wires is so adjusted that static and dynamic forces are balanced, and all three wires are kept taut, no matter how the strength of the wind varies.
To moor an airship to a permanent anchorage a single wire is used which is attached to a buoy. The airship is brought down to within 400 feet of the water on the windward side of the buoy. A sea anchor is then lowered and the airship' is allowed to drift astern past the buoy.
The line to which the sea anchor is attached is picked up from a motor boat and attached to the buoy. This line is 600 feet long, and the ship rides at a height of about 500 feet. Side swaying is damped out by the dragging of the sea anchor through the water. The sea anchor, which is too heavy for the airship to lift, contains two tons of water and moves in the arc of a circle with a radius of about 500 feet and with the buoy at its centre.
A sea anchor is used also to provide an emergency mooring on water. The airship is first brought down to within 500 feet of the water and trimmed to equilibrium. The sea anchor is then lowered and, about 80 feet from it, an inverted cone is attached to the line. This cone holds 1,000 lb. of water, stabilizes variations in lift caused by aerodynamic disturbances and keeps the sea anchor submerged in all conditions. Thus the drag-load is constant and wave shock is eliminated.
The sea anchor can be pulled on board again after a trip weight, which runs down the anchor wire, has turned the cone round and spilled the water from it. This emergency anchor is valuable in the event of engine trouble. It keeps the drift of the airship down to a quarter of the wind speed while repairs are being carried out.
ONE OF THE THREE TRACTORS at the corners of the movable mooring mast at Lakehurst, New Jersey. These tractors are driven from a central engine and enable the mast to be manoeuvred into any desired position. The great weight of the mast, and the considerable distance apart of the three corners, give the mast the necessary stability.