Rare civil aviation instrument designed to record an aircraft's flying time and engine hours. It dates from the 1930s, was manufactured by the Air Log Co. Ltd, Elgin Terrace, London W9 and was retailed by S. Smith and Sons.

This high quality instrument, containing a mechanical clock movement, enables an aircraft's total flying hours and engine's running time to be recorded. The front of the instrument has a large knob, which when rotated anti-clockwise both resets the timer back to zero and winds clock's spring. The back of the Air Log has a brass nozzle which is designed to be connected to a venturi behind the propeller, enabling the instrument to record the engine running time, and a pitot tube in order to record the flying time. The black dial has an outer scale which is divided into minutes (and further into 25 second increments) and the time elapsed is registered by a white indicator, rotating 360 degrees each hour. The flying hours are recorded by a green counter at the 12 o'clock position (designed to record up to 9 hours in a single trip). Below the knob is another counter which records the total flying time the aircraft has made. The dial is signed, "Air Log" and also with the maker's name, "The Air Log Co. Ltd, London W.9", the patent numbers, "32158, 361663" and the labels, "Total Flying Time" and "Max 9 Hrs". The instrument has a brass bezel and is fitted with its original glass.

Overall diameter (including bezel): 85mm. Overall length (including nozzle and setting/winding knob): 115mm. Very good condition. Recently serviced. Good working order. This Air Log has been adjusted so that it runs without the use of a pitot or venturi, however if required, it can be easily reinstated to its original operation.
 

The following extracts have been taken from period issues of "Flight" magazine:

"Flight" November 24, 1932

Air Log Co., Ltd. 193, Elgin Terrace, London

Instruments being produced by this company may be worked either by a pitot head or by a venturi tube. The Air Log itself is usually worked by the former and records both the time of trip and the total flying time. It is fitted with dual pointer indicating the time of trip, moving in a clockwise direction round the circumferential scale. This scale is divided into hours and a peculiar feature of the instrument is that when this trip pointer is returned to 0, the spring motor is automatically re-energised, thus obviating the necessity of having to do more than cancel the trip reading when finished. This form of air log does not start to function until the machine is in the air, and it therefore greatly assists accurate cross-country navigation. The engine log type is operated by a venturi tube placed directly behind the airscrew, and it therefore records the total time during which the engine is running, thus eliminating the necessity for guessing the time of taxiing or running up and ensuring overhauls at regular intervals. Such instruments are also valuable for time checking on machines used by flying schools and joy-riding concerns.

"Flight" March 21, 1935

Both trip time and total flying time are recorded by the Automatic Air Log, produced by the Air Log Co., Ltd. The instrument is usually worked from a pitot head, but a venturi tube may be employed if desired, and in the former case a " T " joint is inserted in the main lead from the pitot head to the A.S.I. The instrument consists of a cup-shaped casing, to the rear portion of which is secured a metal capsule which is provided with a nipple connected to the " T " joint. Within the casing is a clockwork mechanism with the inner end of the main spring attached to a winding spindle provided with a winding and resetting knob. The capsule is connected, by means of a spring lever, with a wire, which is normally disposed between two teeth of the escapement wheel. When the aircraft to which the Air Log is fitted has taken off, and when sufficient air pressure is applied to the capsule, the wire is lifted away from the escapement wheel, thus starting the clockwork mechanism. In order to indicate trip time a hand is carried by a sleeve rotatable upon the winding spindle, and is driven at the rate of one revolution per hour. A "trip hour" integrating device is provided for recording the number of complete revolutions made by this hand during the flight. The instrument also embodies a "total time" indicator comprising a series of four discs driven by star wheels so as to indicate decimals, units, tens and hundreds of hours' flight. The hand co-operates with a '' minute '' scale, each minute being divided into quarters for the purpose of enabling accurate time indications to be made. The address of the Air Log Co. is 193, Elgin Terrace, London, W.9, and the sole agents are S. Smith and Sons.