Flight, April 1932

The Airspeed "Ferry"
3 DE HAVILLAND "GIPSY" ENGINES

   WHEN work on the rigid airship R.100 ceased, the technical staff had to look around for positions elsewhere. Fortunately, the majority were able to secure work with various aircraft firms, while at least two, Mr. N. S. Norway, who had been chief designer to the Airship Guarantee Company for a time, and his chief assistant, Mr. A. H. Tiltman (some years ago connected with the de Havilland Aircraft Co.), decided to establish their own aircraft company, as it was felt that there was still room for a firm to produce aircraft of a type not hitherto introduced on the aircraft market. Norway and Tiltman succeeded in interesting Lord Grimthorpe in their undertaking, and the company was established under the title Airspeed, Limited, with works and offices at Piccadilly, York. Sir Alan Cobham also joined the board of directors.
   Since their establishment the firm has been working away quietly on a machine of novel design. The first machine has now been completed and flown, and is at present at Martlesham undergoing official tests. It is known as the "Ferry," and it is believed that many of its unusual features owe their origin to the wishes of Sir Alan Cobham, who wanted some machines specially suitable for his forthcoming tour of the country. High performance and long range were not a necessity, but a large number of passengers for a limited horse-power was. Consequently Messrs. Norway and Tiltman designed a machine which has, as they express it, “a large cabin and a small petrol tank." When we say that this machine is designed to carry 10 paying passengers on a total of 360 h.p., or 36 h.p. per paying passenger, it will be realised that here should be a machine very economical to operate, while the three-engined power plant, with such reliable units as the Gipsy II and III, should rule out entirely the risk of a forced landing. From Sir Alan Cobham's point of view, the use of the "Ferry" will also have the advantage that it will show its passengers something of a three-engined passenger aeroplane on a slightly reduced scale, and thus give them an idea of what the air line machines are like to fly in. The multi-engine idea has already become deeply-rooted, and many will go up quite gladly in a three-engined aircraft who would hesitate to entrust themselves to a single-engined type. For joy-riding, three engines are, perhaps, not strictly speaking necessary, but considerations of the outlook of potential passengers are well worth studying.
   The functions of the "Ferry" are not, of course, confined to joyriding. For air routes on which the traffic is not great, such a machine might be usefully employed, the carrying capacity being good and the cruising speed enough for many purposes.
   In the table of data most of the relevant characteristics of the "Ferry" are set out in a form convenient for reference. It will be seen that the machine is not a particularly small one, the wing span being 55 ft. and the wing area, including that enclosing the undercarriage axles and radius rods, being 641 sq. ft. The normal gross weight is 5,400 lb., of which something like 2,100 lb. is disposable load. This corresponds to a disposable load of over 5.8 lb./h.p. When the machine is used for flights of short duration, a very large percentage of this load can, of course, be in the form of pay load.
   The constructors of the "Ferry" realise that when the machine is to be used outside England, the potential purchaser will quite naturally wish to know something of the sorts of pay load he will be able to carry, assuming one of the three engines to break down. On the assumption that normally fuel for 5 hours at cruising speed will be carried, and that in case of an engine failure petrol may be jettisoned to reduce the quantity to enough for two hours with two engines running, two examples have been worked out by the designers, one for continuing the flight at 5,000 it. altitude and the other for 8,000 ft. altitude. In both cases the estimated figures were, of course, based on these altitudes over England.
   The calculations indicate that the "Ferry" will maintain a height of 5,000 ft. on two engines when the gross weight is 5,060 lb. At this weight the rate of climb at 5,000 ft. is 50 ft./min. As the bare weight is 3,300 lb., and pilot, fuel and oil for 2 hours account for 460 lb., there is left a pay load of 1,300 lb., which could, for instance, be allocated to seven passengers of 165 lb. average weight, and would leave 145 lb. for luggage.
   For the machine to be able to fly level on two engines at 8,000 ft. it is estimated that the gross weight should not exceed 4,670 lb. This means that the number of passengers should not be more than five, and there would then be a reserve of 85 lb. for luggage.
   If one of these two contingencies is stipulated by the user of the "Ferry," the figures for normal flight with all three engines running become :-
   For the 5,000-ft. case: Seven passengers, 5 hours' cruising, and a gross weight of 5,602 lb. This is in excess of the normal C. of A. gross weight of 5,400 lb., and represents an overload of 200 lb. However, it is claimed that no difficulty would be experienced in taking the machine off at this weight, but modifications to the structural C. of A. would be necessary.
   For the 8,000-ft. case, the figures would become: Five passengers, 5 hours' cruising, and a gross weight of 5,212 lb. This figure is well within the gross weight of the machine.
   It is pointed out that if the altitude for the two engines' case were in the tropics, the five passengers at 5 hours' cruising range would probably be the load normally carried. These figures are estimated, and actual flight tests are still required before they can be definitely confirmed.
   In the table of data estimated performance figures are given. These are based upon the normal gross weight of 5,400 lb. If the machine is flown with half-load only, so that the gross weight becomes 4,550 lb., it is estimated that the stalling speed would be reduced to 45 m.p.h., while the initial rate of climb would become 970 ft./min. and the service ceiling 17,500 ft.
   The above figures, while still requiring experimental verification, do give an idea of the probable capabilities of the "Ferry." If the machine is used in Great Britain or Northern Europe, and a duration of less than 5 hours is sufficient, there should be no need to worry unduly about its ability to find a suitable landing ground on two engines and at low altitude, even when carrying the full complement of 10 passengers.
   In design the "Ferry" is mainly unusual on account of its engine arrangement All three engines are tractors, but one, instead of being placed in the nose of the fuselage, as is usually the case, is mounted in the centre of the upper wing. The other two engines are placed in the orthodox positions on the lower wing. Another innovation is to be found in the small triangular wing which, on each side, encloses the wheel axle and radius rod. These two small surfaces have a total area of 30 sq. ft., and it is expected that they will contribute sensibly to the lift, especially when the machine is landing, when it is thought that these two winglets should give quite a considerable "cushioning" effect. A practical advantage of the placing of the engine in the top plane is that the pilot's view is particularly good, a point of great importance in a machine t be used for joy-riding, when take-offs and landings are numerous.
   Structurally the "Ferry" is a very simple straightforward machine mainly of wood construction. The fuselage is a flat-sided monocoque consisting of a spruce skeleton covered with three-ply birch. The wings have box spars with spruce flanges and three-ply walls, while the ribs are also of wood. The compression struts of the internal drag bracing are steel tubes.
   The engine installation, apart from the placing of one engine in the top plane, is unusual in that the three engines are not of one type. The outboard engines are "Gipsy II's," while the top engine is a "Gipsy III" inverted. This choice was made because the inverted engine "worked into" the design better in the top plane, while in the case of the wing engines the upright type suited the arrangement best. In any case, many of the spares for the two engines are identical, so that the operator of a "Ferry" will not be called upon to increase his stock of spares to any serious extent.
   The petrol tank is of streamline form and mounted above and behind the central engine. In this position it affords gravity feed to all three engines, even when the machine is climbing steeply with the tank nearly empty. For rapid filling such as is essential in a machine with relatively small petrol capacity and used for joy-riding, a 1 1/4-in. diameter pipe line has been installed, which connects to a union on the side of the fuselage, the upper end of the pipe passing through a flange in the sump of the tank and discharging into the highest point of the tank. A sight gauge of the glass tube boiler type is fitted into the rear end of the petrol tank, and shows at a glance the amount of fuel in the tank. This gauge is for use by the ground engineer only. A Smith's petrol gauge (remote electric type) is provided for the pilot.
   The undercarriage is of the "split" type, and, as already mentioned, the axles and their radius rods are enclosed in winglets hinged to the fuselage. The shock absorber legs contain coil springs giving a travel of 4 in., while the special oil damping gear gives a further travel of 6 in. The spring and the oil work in series, and the degree of oil damping is adjustable. The wheels are Dunlops (35 in. by 8 in.), and Palmer hydraulic brakes are fitted. The wheels are partly enclosed in "spats."
   All control surfaces are of orthodox design, and the ailerons (fitted on both upper and lower planes) have "Frise" balances. All bearings are fitted with ball races.
   The cabin measures 12 ft. 7 in. in length, 3 ft. 9 1/2 in. in width, and 5 ft. 9 in. in height. There are two doors, one on each side, and in the forward wall another door communicates with the pilot's cockpit. In the roof towards the rear there is an emergency exit, while the pilot's cockpit is provided with an emergency exit on the starboard side. The cabin floor is only a little more than 1 ft. above the ground, so that passengers find it particularly easy to step in and out. Owing to the fact that the lower wing roots are sloped up to the top longerons, the view from the cabin outward and downward is good.
   Seating accommodation will depend upon the requirements of the particular operator. For a full complement of ten passengers, eight of the seats are placed along the sides of the cabin, with a gangway between. Against the back wall there is a sofa seat for two.
   Particular attention has been given to the view obtainable from the pilot's cockpit. Owing to the absence of a nose engine, the view forward is good, as also outwards and downwards. The wing engines are so far behind the pilot that, although he can see his airscrews, the engines themselves do not cut off any useful arc of view.

Flight, November 1932

British Aircraft

Airspeed, Limited
Piccadilly, York

   AMONG the younger British aircraft firms is that established a couple of years ago by Mr. N. S. Norway and Mr. A. H. Tiltman, under the title "Airspeed Limited." As their first aeroplane these two young men produced the small "Ferry" commercial three-engined 10-passenger biplane (p. 1079). Sir Alan J. Cobham, who is on the board of directors, wanted a machine of this class for his "National Aviation Tour" of Great Britain, and during the past summer the "Ferry" has taken up thousands of passengers.
   Cheap construction, high pay load, and economical operation were the things aimed at by the designers in producing the "Ferry," which is a biplane mainly of wood construction, powered by three de Havilland engines, an inverted Gipsy III in the top wing and two Gipsy II engines outboard on the lower wings.
   For Sir Alan Cobham's work a good view from the pilot's cockpit was important, and this was provided by placing the third engine in the top wing instead of in the nose of the fuselage, leaving the latter free to accommodate the pilot in the extreme front, where the view in all important directions is very good. It seems likely that the engine placing chosen also helps materially in reducing noise in the cabin.
   The equipment of the "Ferry" cabin can, of course, be arranged to suit operators' requirements. For the purpose of Sir Alan Cobham's tour it was desired to carry as many "joy-ride" passengers as possible, while large petrol capacity was not essential, and the cabin was arranged to carry ten passengers. As the total horse-power of the three de Havilland engines is only 360 h.p., the power expenditure per paying passenger is only 36 b.h.p., which must represent extremely economical operation. In spite of the large pay load, the "Ferry" had no difficulty in taking off, and went through the flying season without any mishap.
   The main data relating to the Airspeed ''Ferry'' are:
   Length o.a. 39 ft. 8 in. (12,1 m.)
   Wing span 55 ft. 0 in. (16,8 m.)
   Wing area 641 sq. ft. (59,5 m")
   Tare weight 3,445 lb. (1 563 kg.)
   Disposable load 2,150 lb. (975 kg.)
   Permissible gross weight 5,600 lb. (2 540 kg.)
   Maximum speed 108 m.p.h. (173,8 km/h)
   Cruising speed 85-90 m.p.h, (136-144 km/h)
   Rate of climb 520 ft./min. (2,65 m/sec.)
   Absolute ceiling 13,000 ft. (3 962 m.)