British Airships, Past, Present, and Future

by George Whale

The theoretical endurance at full speed as regards petrol consumption is a little over 8 hours, but in practice it is probable that the oil would run short before this time had been reached. At cruising speed, running the engine at 1,250 revolutions, the consumption is at the rate of 3.6 gallons per hour, which corresponds to an endurance of 16 1/2 hours.

With the engine running at 1,800 revolutions, a speed of 50.6 miles per hour has been reached by one of these ships, but actually very few attained a greater speed than 40 miles per hour.

The envelopes of S.S. airships are composed of rubber-proofed fabric, two fabrics being used with rubber interposed between and also on the inner or gas surface. To render them completely gastight and as impervious to the action of the weather, sun, etc., as possible, five coats of dope are applied externally, two coats of Delta dope, two of aluminium dope and one of aluminium varnish applied in that order.

One ripping panel is fitted, which is situated on the top of the envelope towards the nose. It has a length of 14 feet 5 inches and a breadth of about 8 inches. The actual fabric which has to be torn away overlaps the edge of the opening on each side. This overlap is sewn and taped on to the envelope and forms a seam as strong and gastight as any other portion of the envelope. Stuck on this fabric is a length of biased fabric 8 1/4 inches wide. These two strips overlap the opening at the forward end by about three feet. At this end the two strips are loose and have a toggle inserted at the end to which the ripping cord is tied. The ripping cord is operated from the car. It is led aft from the ripping panel to a pulley fixed centrally over the centre of the car, from the pulley the cord passes round the side of the envelope and through a gland immediately below the pulley.

The nose of the envelope is stiffened to prevent it blowing in. For this purpose 24 canes are fitted in fabric pockets around the nose and meet at a point 2 1/4 inches in front of the nose. An aluminium conical cap is fitted over the canes and a fabric nose cap over the whole.

Two ballonets are provided, one forward and one aft, the capacity of each being 6,375 cubic feet. The supply of air for filling these is taken from the propeller draught by a slanting aluminium tube to the underside of the envelope, where it meets a longitudinal fabric hose which connects the two ballonet air inlets. Non-return fabric valves known as crab-pots are fitted in this fabric hose on either side of their junction with the air scoop. Two automatic air valves are fitted to the underside of the envelope, one for each ballonet. The air pressure tends to open the valve instead of keeping it shut and to counteract this the spring of the valve is inside the envelope. The springs are set to open at a pressure of 25 to 28 mm.

Two gas valves are also fitted, one on the top of the envelope, the other at the bottom. The bottom gas valve spring is set to open at 30 to 35 mm. pressure, the top valve is hand controlled only.

These valves are all very similar in design. They consist of two wooden rings, between which the envelope is gripped, and which are secured to each other by studs and butterfly nuts. The valve disc, or moving portion of the valve, is made of aluminium and takes a seating on a thin india rubber ring stretched between a metal rod bent into a circle of smaller diameter than the valve opening and the wooden ring of the valve. When it passes over the wooden ring it is in contact with the envelope fabric and makes the junction gastight. The disc is held against the rubber by a compressed spring.

The valve cords are led to the pilot's seat through eyes attached to the envelope.

The system of rigging or car suspension is simplicity itself and is tangential to the envelope. On either side there are six main suspensions of 25 cwt. stranded steel cable known as "C" suspensions. Each "C" cable branches into two halves known as the "B" bridles, which in turn are supported at each end by the bridles known as "A." The ends of the "A" bridles are attached to the envelope by means of Eta patches. These consist of a metal D-shaped fitting round which the rigging is spliced and through which a number of webbing bands are passed which are spread out fanwise and solutioned to the envelope. It will thus be seen that the total load on each main suspension is proportionally taken up by each of the four "A" bridles, and that the whole weight of the car is equally distributed over the greater part of the length of the envelope. Four handling guys for manoeuvering the ship on the ground are provided under the bow and under the stem. A group of four Eta patches are placed close together, which form the point of attachment for two guys in each case. The forward of these groups of Eta patches forms the anchoring point. The bridle, consisting of 25 cwt. steel cable, is attached here and connected to the forepart of the skids of the car. The junction of this bridle with the two cables from the skids forms the mooring point and there the main trail rope is attached. This is 120 feet long and composed of 2-inch manilla. This is attached, properly coiled, to the side of the car and is dropped by a release gear. It is so designed that when the airship is held in a wind by the trail rope the strain is evenly divided between the envelope and the car. The grapnel carried is fitted to a short length of rope. The other end of the rope has an eye, and is fitted to slide down the main trail rope and catch on a knot at the end.