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Royal Aircraft Factory Eta
The "Eta" which in a progressive series of small experimental airships built at the Royal Aircraft Factory. The small airships that have been built there were quite inadequate from the standpoint of national requirements.
The capacity of the 1913 "Eta" is 100,000 cubic ft, carried 160 hp in two radial stationary Canton-Unne engines, set on opposite sides of the car with their axes placed transversely. Oblique shafts transmit the power to gearing, supported by an overhead framework, which also carries the swivelling propellers. As the airship ascends, these propellers are swivelled round, so that ultimately their axes are horizontal for full speed ahead. In order to stop the airship they can be turned completely round so as to thrust backwards, and they can similarly be used for lowering the airship for the purposes of descent.

Launched in August 1913, the Eta was a non-rigid of 118,000 cu.ft incorporating twin ballonets and capable of 46 mph. The Eta introduced the ‘Eta patch’ in its design as an improved anchorage system for car suspension that greatly reduced drag. The Eta patch allowed the car to be made smaller and attached nearer to the envelope, providing a better streamlined form and reducing drag. The patch consisted of a steel ring through which several layera of overlapping material were rove, forming a fan-shaped patch with the ring positioned at the lower apex. The overlapping layers of fabric were glued and stitched to each other and to the envelope, forming a strong attachment position allowing for better distribution of load.

On August 19, 1913, “Naval Airship No.2” (the re-constructed “Willows No.4” – under the command of Lieut. Neville Usborne, R.N.) experienced engine failure due to a broken crankshaft near Odiham in Hampshire. In order to save the hydrogen in the disabled airship, it was decided to try and tow it home employing the airship “Eta” – newly-constructed by the Royal Aircraft Factory and currently undergoing its acceptance trials. Accordingly, a tow-line was attached and the two airships ascended, the “Eta” keeping about 600 feet above the towed ship so as to avoid all chances of fouling the rudder gear. The approximate 8-mile trip back to the airfield at Farnborough was made at a groundspeed of 25 mph against a 5 mph headwind. The “Eta” was in all probability skippered by Army Capt. Waterlow at the time.

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