A REMARKABLE LIGHT PLANE ENGINE The 75-85 h.p. Pobjoy which weighs only 1301bs.
VISITORS to Hooton aerodrome on occasion of the meeting there some little time ago were treated to a really striking demonstration of the flying qualities of the single-seater Comper “Swift,” when in the hands of Mr. Snaith, this little craft performed all manner of aerobatics (including inverted flying for a considerable length of time), loops, rolls and so forth. Mr. Snaith’s machine was powered with an A.B.C. “Scorpion,” but more recently the Comper Co. -have been experimenting with other motors, and in particular, the Pobjoy.
This engine was first produced in 1926, the designer being Mr. D. R. Pobjoy, and it was to have made its first public appearance at Lympne in the light ‘plane competitions of that year, installed in a machine with Flight-Lieut. Comper as the pilot. Unfortunately, it could not be got ready in time.
The first engine was known as the” P “type and after its preliminary ” teething ” troubles had been overcome it passed its Air Ministry type tests with great success.
The latest type is known as the” R” engine, and like its predecessor it is a seven cylinder radial. There is nothing actually revolutionary in its design, and all the main principles incorporated are already standard on -engines of larger size. As a light ‘plane engine, however, it is unusual in having a geared propeller, while the r.p.m. is higher than that of other units of the same power. The Pobjoy has been designed to run at a cruising speed of 3,000 r.p.m., while the air screw speed is 1,500 r.p.m. With the wonderful standard of reliability which is met with in the modern engine, this tendency towards higher revs, is finding favour not only because of the improvement gained in the weight-per-horse-power ratio, but also because a higher speed tends to make for smoothness in running. These two qualities are salient features of the Pobjoy, especially in regard to the weight-perhorse-power figures, for while giving an output of 75-85
h.p., the weight in only 130 lbs. .
Another striking feature of this little engine is that its overall diameter is but 25i inches. Thus, one of the main disadvantages of the radial type—excessive frontal area—has been virtually overcome. Its fuel and oil consumption is also on the economical side, and, aided by the geared propeller, it is an easy starter. . Although the Pobjoy has never been made as a production job, several examples are to be found both in -Europe and America, and these experimental models
have given, and are still giving extremely good service. Some idea may be gained of what a light aeroplane like the ” Swift ” can do when fitted with this engine, when it is mentioned that Lieut. Comper, a short time ago, climbed one of these machines to 1,000 feet in 47i seconds, a performance worthy of a modern fighter.
Having passed through a most thorough and searching experimental stage, the Pobjoy is now to be built on a production basis, and for this purpose a company has been formed with the title of Pobjoy Airmotors, Ltd. The works and headquarters of this concern are at Hooton Park, Wirral, Cheshire, and the directors are :Messrs. I. C. Maxwell, D. R. Pobjoy, T. Barton, A. Comper and G. M. Edge.
The price of the Pobjoy ” R ” has been provisionally fixed at the quite reasonable figure of 2195, inclusive of hand starter and integral mounting, and the production engines will appear at the end of this year.