Flight, January 1927
AN AMERICAN TWIN-ENGINED LIGHT 'PLANE
The "Johnson Twin 60," with Two Bristol "Cherubs"
THE multi-engine idea seems to be spreading. From single-engined aeroplanes we went to twin-engined, and from twin-engined to three-engined. Nor has
this evolution been confined entirely to very large, powerful machines, although, naturally enough, these were the first to be produced. Thus, in this country, we had last year the Handley Page "Hamlet," a small three-engined commercial passenger machine with three Bristol "Lucifer" engines. We ourselves have suggested in FLIGHT that the small machine of this type, with even lower total power than that of the "Hamlet," might be a useful type for certain localities and conditions. In the seaplane class we have had the little Short "Cockle," fitted with two Blackburne motor-cycle engines, which flies very well and is now, we believe, about to be equipped with two Bristol "Cherubs." Thus there is nothing particularly startling in the general design of the two-seater light 'plane recently produced by the Johnson Airplane and Supply Company, of Dayton, Ohio, U.S.A., a machine fitted with two Bristol "Cherub" series III engines.
The accompanying photographs show this machine to be a twin-engined pusher, looking in its general lay-out like a small edition of a large twin-engined machine. Whether such a machine is really worth while is, perhaps, open to debate. To begin with, the twin-engined aeroplane, unless capable of flying on one of its engines, is illogical. In the case of the Short "Cockle" this was not the case, and there was very excellent reason for using the twin-engined arrangement, because with a monoplane flying-boat no other arrangement was possible, or, at any rate, practicable. In the case of the Johnson "Twin 60," however, it is less obvious what was in the mind of the designer. Good view and absence of slipstream, probably, although the extra complication of the twin-engined principle would appear to be rather a high price to pay. It might have been thought that if these two desiderata were the raisons d'etre of the "Twin 60," a simple way of obtaining them would have been to follow rather the lay-out of the little "Albatros L.72," described and illustrated in FLIGHT of January 28, 1926. That machine was "a flying-boat on wheels," with the Siemens engines mounted behind the top plane and driving a pusher airscrew. That this arrangement necessitated the usual difference between centre of resistance and centre of thrust associated with the flying-boat type was probably of small moment in a machine of such small size and power.
It is, of course, possible that the Johnson "Twin 60" will fly on either of its two "Cherub" engines, in which case the criticisms fall away automatically. Pending the arrival in this country of more detailed information, one cannot say. In the meantime it is worth recording its production as an interesting experiment.
For the time being all that is known concerning the “Twin 60" is that it is reported to weigh 860 lbs., and that with pilot, one passenger and 22 gallons of fuel it gets off the ground from standing start in 3 seconds (!), while the climb to 3,000 ft. is accomplished at the rate of 500 ft./min. The machine is credited with a top speed of 85 m.p.h., and the landing speed is given as about 22-5 m.p.h. The latter figure, at any rate, seems open to doubt. We have no figures for wing loading, but, even allowing for a high-lift section (that used appears from the photographs to be one of the Gottingen “tadpole" sections), a landing speed as low as 22 m.p.h. would seem to infer a maximum lift coefficient rather higher than appears likely to be attained. However, even if the landing speed is 32 m.p.h., instead of 22, it should be low enough to ensure a very considerable degree of safety.
It is reported that the machine has been thoroughly tested out for taking off and alighting under particularly difficult conditions, and has been found to behave very well indeed. One of the accompanying photographs shows the machine taking off alongside what appears to be a road or railway embankment, presumably in a cross-wind with the wind coming over the embankment and causing a down-draught, and the cinematograph operators give the appearance of being rather nervous and very possibly experiencing a considerable up-draught!
Features such as the two petrol tanks on the top plane and the Reed Duralumin airscrews, as well as the twin rudders, can be seen in the photographs. The undercarriage is of the type using rubber rings in compression. The front legs are telescopic, while the lateral bracing is in the plane of the rear chassis struts. Some kind of wheel brake appears to be incorporated in the undercarriage.
After their many successes at home and abroad, no surprise need be expressed at the choice of the Bristol "Cherub" engines, which may certainly be relied upon to do their share towards making the Johnson "Twin 60" a success.