Flight, February 1922
A GLOUCESTERSHIRE GOODS TYPE COMMERCIAL AEROPLANE
Rolls-Royce "Eagle” Engine
WHEN civil aviation was first attempted in 1919, the machines used were, without exception, War types which had been variously modified to meet, in some measure,
the altered requirements. This they did to a limited extent only, and it is now becoming more and more evident as experience is gained that the "general utility" machine is not the solution of the problem, and that from now onwards the tendency will be more and more towards specialised aircraft. For a certain route, and a certain type of cargo, there will always be types which possess certain features that make them particularly suitable, although these features may, and probably will, hare been attained at the expense of others which are not, however, so necessary for the particular purpose. Thus we shall see certain types developed for mail-carrying, others especially suitable for passenger work, and, let there be no mistake about it, certain types designed specially for carrying goods. At first the division into types may not be very marked, but it is already beginning to be noticeable, and will become more and more so as time goes on, and it will be the designer who is best able to anticipate the requirements of future types who will be in the most favourable position for meeting them.
It might have been thought that the day for the goods-carrying aeroplane is not yet, but we have the word of no less an authority on the subject than Sir Samuel Instone for it that goods machines specially designed for the work are required. That being the case, it is extremely interesting to learn that that progressive firm, the Gloucestershire Aircraft Co., Ltd., of Cheltenham, has actually completed the design for a machine of the goods-carrying type, which has several novel features, and which has been designed with commercial conditions in view the whole way through.
As the accompanying drawings will show, the new Gloucestershire machine is a tractor biplane, fitted with Rolls-Royce "Eagle" engine. The wings, it will be observed, are of unequal area, and an interesting innovation is found in the employment of different wing sections for top and bottom planes. The section of the top plane is that known as airscrew 4, which has a maximum lift coefficient of about 0,77 absolute, and a maximum top camber of 12-18 per cent of the chord. Although of relatively high lift, this section has a good L/D ratio (nearly 18), and its thickness is such as to give ample room for spars of light construction. The lower plane will be of ordinary medium-lift section, and is of smaller area than the top one. The reasons for adopting this arrangement are various. The cantilever monoplane, with thick, high-lift wing, is necessarily of considerable span, so that, for the same landing speed, a biplane structure will be more compact. If both wings are of the high-lift type, the gap between them has to be fairly large to avoid too great biplane interference. Also, the L/D of high-lift sections is usually inferior to that of the medium-lift aerofoils, and by employing one plane of ordinary section and one of high-lift section, the overall L/D of the biplane is increased. It appears possible that such an arrangement might also be used for obtaining a certain amount of longitudinal stability, although in the Gloucestershire machine no attempt has, we understand, been made to attain stability in this way, the usual tail plane arrangement being relied upon for this purpose. Although a fairly large machine, there is to be only one set of struts on each side. No doubt, this reduction in bracing has been rendered possible largely as a result of the employment of a thick top plane. Another advantage of the biplane bracing over the cantilever monoplane is, Mr. Folland, the designer of the machine, points out, that the incidence bracing provides a duplication of bracing in case of fracture of one of the lift wires, whereas in the cantilever monoplane no such duplication exists.
Apart from the unusual wing arrangement, the new Gloucestershire machine is of interest on account of the provision made for easy loading and unloading of bulky goods. The fuselage, which is of rectangular section, is built in three separate units: the front unit is the engine housing, the middle unit forms the cabin, and the rear unit is the aft portion of the fuselage, carrying the tail and tail skid. At the rear end of the cabin, a hinged attachment is provided for the rear portion of the fuselage, so that this can be swung out laterally, thus giving access to the cabin through an opening of approximately the full size of the cross section of the fuselage. A partition hinged at the bottom, folds down to form a gangway up to the floor of the cabin, along which trolleys, with the goods to be loaded or unloaded, can be wheeled. Jacks under the rear corners of the cabin prevent the machine from tilting over backwards.
Although ample space for loading and unloading is thus provided by this rear door, the machine might be used for less bulky packages, which would not necessitate such a large opening. Ordinary doors have consequently been provided in the sides of the cabin, one in each side aft, and a third in one of the sides, forward of the wings. Through these smaller packages can be loaded, avoiding the necessity of "breaking" the fuselage. The cabin space available is large, 11 ft. 8 ins. long, by 5 ft. 6 ins. high, by 4 ft. 2 ins. wide.
Constructionally, the fuselage will be of the composite type. That is to say, the front portion (engine unit) will be largely of steel tubing, with aluminium covering. The cabin will have spruce longerons, and three-ply covering, no other bracing being employed, so as to leave a clear space inside the cabin. The rear portion of the fuselage will be of the ordinary brace girder type, but with steel tube longerons and struts.
Apart from other advantages, the employment of a thick top plane is useful in providing ample space for mounting of tanks inside the wings, thus obtaining the benefit of direct gravity feed to the engine without unsightly tanks projecting above the top surface of the wing. In the present machine, there are two tanks, one on each side, each containing 43 galls, of petrol.
The undercarriage is to be of the simple V-type, with the front struts (steel) cross-braced, with streamline wire, and the rear ones telescopic, to give the necessary springing. The latter will be by rubber cord, and a pneumatic damper gear is to be fitted.
The engine, a Rolls-Royce "Eagle" of 360 h.p., will, as already stated, be mounted in front as a detachable unit, four lugs being provided, for securing it to the cabin. By suitably designing the engine controls and petrol leads, the whole engine unit, with its nose radiator, can be changed for a new one in a very short time. For inspection, and minor adjustments, the engine is made accessible by designing the engine cowling somewhat after the fashion of the bonnet of a motor-car, quick-release safety catches being used for fastening the cowl in place.
As regards the controls, these are to be of standard type, with joy-stick for elevators and ailerons, and a foot bar for the rudder. No cables will, however, be used in the controls, all movements being transmitted by rigid control rods, or tie rods, running in suitable guides. In this manner, the wear and tear and the amount of attention usually associated with control cables will be avoided. Ball-bearings will be used extensively so as to render the controls easy to operate, and to lessen the physical fatigue of the pilot on long journeys.
The tail plane will be of the trimming type, with hinges on the front spar, and a worm gear, similar to that used on the Nieuport "Nighthawks," will be incorporated, in the support of the rear spar so as to allow of trimming the tail during flight.
Following are the main characteristics of the Gloucestershire "Goods 'Plane": Length o.a., 36 ft.; span (upper), 45 ft.; chord (upper), 6 ft. 2 ins.; span (lower), 34 ft. 8 ins.; chord (lower), 5 ft. 2 ins.; area (upper), 261 sq. ft.; area (lower), 154 sq. ft.; total wing area, 415 sq. ft.; structure weight, 1,936 lbs.; weight of engine, radiator, water, piping, accessories, and propeller, 1,175 lbs.; petrol, 628 lbs.; oil, 70 lbs; pilot, 180 lbs.; goods load, 1,600 lbs.; total loaded weight, 5,589 lbs.; wing loading, 13-5 lbs./sq. ft.; power loading, 15-5 lbs./h.p.; useful load per h.p., 4.45 lbs. at 104 m.p.h.; 5-7 lbs. at 92 m.p.h., maximum speed, 104 m.p.h.; speed at three-quarter throttle, 92 m.p.h.; climb to 10,000 ft. in 30 mins.; ceiling, 14,000 ft.; air endurance, 4 3/4 hrs. at cruising speed of 92 m.p.h.