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.