Flight, July 1920

The Olympia Aero Show 1920

The machines

Blackburn Aeroplane and Motor Co., Ltd. (STAND 64) Olympia, Leeds.

   THE machine exhibited by this firm will be one of the latest torpedo-carrying ships' aeroplanes. Official permission to exhibit has been granted on condition that certain special equipment is not shown. As exhibited the machine will therefore be minus the torpedo and its gear, but the special arrangement of the undercarriage is evidence of the purpose for which the machine is ultimately intended.
   The pilot's view, always an important consideration, is even more important in a machine intended for use from a ship where the space available is restricted. In the Blackburn "Swift" this feature has been especially studied, the high position, the lines of the fuselage, and the forward stagger of the wings all tending towards that object. Incidentally it may be mentioned that the problem of providing folding wings is complicated by a stagger, and the manner in which this difficulty has been overcome in the Blackburn "Swift" will no doubt attract a good deal of attention.
   Concerning the detail design and construction of the ''Swift'' we hope to have more to say in next week's issue. Suffice it here to point out that the question of ease of upkeep has received attention, and that the whole of the central unit, comprising the engine mounting, the centre part of the fuselage, the undercarriage, and the centre section of the wings is a steel framework which, it is anticipated, will need practically no trueing up in actual use.
   The question of fire on board is an ever-present danger which, in the "Swift," has been guarded against by separating the entire engine installation from the rest of the machine by a fireproof bulkhead. The main petrol tank is of the self-sealing type, so that even in a crash there is little likelihood of the tank catching fire. The petrol is pumped positively from this main tank to a small gravity tank placed in the upper plane. The engine installation is arranged to give good accessibility for small engine adjustments, and also permits of easy removal of the engine unit for full overhaul.
   As a ship's aeroplane the "Swift" is fitted with airbags for flotation in the case of a forced landing on the sea, and the wheels are automatically removable in the air to render safer the alighting on the sea. Needless to say, slings are provided for hoisting the machine on board ship.
   It may be pointed out that the Blackburn Co. have had some three years' experience with machines for bomb-dropping, and that the "Swift" represents the practical results of this experience.


The Blackburn "Swift"

   As pointed out in our issue of last week, the Blackburn "Swift" has been designed to an Air Ministry specification, and consequently many of the most interesting points in the design cannot be referred to in detail. This applies particularly to the torpedo gear and its various accessories. The "Swift" is designed to start from and alight on the platform of a warship and carries a standard torpedo. As exhibited this torpedo is not shown in place, as some of the gear for slinging and dropping it, etc., is of such a nature that the authorities do not wish details published.
   One special feature of the machine is the construction of the central unit, comprising the middle portion of the fuselage. The under-carriage, the top centre section, and lower wing roots, etc., are all built up in one unit of strong steel tubing. The machine, as already mentioned, is designed to alight on a ship's platform, but for cases where this is not possible, a special arrangement (not shown) is provided whereby the wheels can be dropped before the machine touches the sea, as the presence of the wheels in place would have a tendency to cause the machine to nose over on striking the water.
   For use on ship-board it is essential that the machine should stow into as small a space as possible, and this is accomplished by arranging the wings to fold back as in the ordinary vertical biplane. The fact that the Blackburn "Swift" has staggered planes has rendered the problem of folding more difficult, but it would appear to have been solved in a very efficient manner, and the only difference in actual use is that as the pivoting points of upper and lower rear spars are not vertically above one another the wing tips point upward slightly when the wings are folded back. Slings are provided for hoisting the machine, and this can be accomplished either with the wings folded or spread, the only effect of hoisting the machine with folded wings being to cause it to be slightly down by the tail.

Flight, July 1923

Gothenburg International Aero Exhibition 1923

THE MACHINES

Blackburn Aeroplane and Motor Company, Ltd., Olympia, Leeds

   THE Blackburn "Swift" torpedo-plane, for fleet use, which is being shown by this firm, is a machine of unusual and extremely interesting design, although it is not an entirely new type - having been originally designed in 1921. In the "Swift" the somewhat exacting requirements of this class of work have been carefully considered.
   Perhaps the most serious problem in the design of machines for fleet work is to produce one capable of being safely operated from the deck of a carrier, and this has received first consideration in the "Swift," even at the expense of performance in other respects. The essentials for deck work may be said to consist of: Complete control, especially at low speeds; manoeuvrability; best possible view for pilot; rapid acceleration; low minimum flying speed; and rapid deceleration on landing.
   The consideration of manoeuvrability calls for concentration of loads and minimum moments of inertia about all axes. For quickly turning and banking, as may be necessary in landing on a deck, the yawing and lateral moments of inertia are all-important, and these two depend almost entirely on the size of the wings, which, therefore, have to be kept as small as possible. For minimum flying speed the use of a highly-cambered aerofoil suggests itself, but this is ruled out on the score of the first consideration - i.e., control at low speeds.
   It is consequently necessary to find the best possible compromise between the conflicting requirements of small planes and low minimum speed. Aerofoil No. 64 has consequently been chosen as being much the most efficient aerofoil having a medium lift coefficient, whilst the area has been fixed as low as possible - sufficient for getting off the deck in the distance available.
   In order to keep the moments of inertia down the span is made as small as possible, and the chord being the largest that will fit into the required folding dimensions after allowing for putting the torpedo in place with the wings folded.
   The planes are staggered, partly to gain a little on lift coefficient and efficiency, but chiefly to improve the pilot's view downward and forward. The pilot is placed high up, his eyes being in line with the top plane, and the forward part of the fuselage fairing falls away at a steep angle giving him a clear view horizontally forward over the engine, even when climbing or when flying throttled at a low speed. At top speed the pilot has a clear view forward for some 12° below the horizontal, and on either side of the fuselage for 50° below the horizontal. Rapid exceleration is aimed at by providing a propeller which will give good thrust at low speeds, and the minimum flying speed is reduced by arranging the propeller, as regards position and angle, so that the main planes get the full benefit of the slipstream. Careful calculations, including the slipstream effect, show that the machine should be capable of flying with full load at 39 knots, whereas the stalling speed in a glide is 43 knots. For landing on deck without the torpedo the stalling speed is 37-5 knots.
   Rapid deceleration is provided for by arranging that the wings reach an angle beyond that of the maximum lift coefficient when the tail skid touches the deck. On getting the tail down the lift consequently falls off, and the risk of bouncing is reduced while the drag is greatly increased.
   The centre section has been designed entirely in steel tube with fittings machined from the solid, and the engine mounting, chassis, main spars, and fuselage longerons all joint directly on to these solid fittings with their centre lines meeting correctly at a point in each case. It is considered that this form of structure is free from any of the strains incidental to structures in which heavy loads are carried through timber by lugs and bolts, and it must be free from warping due to climatic variations. In the chassis all bent tubes are avoided, and bending moments are provided for by a patented triangulated system. The springing is of the compression rubber type which has been found very satisfactory in service and to need only very rare renewal. In the tail skid a similar form of springing has been adopted.
   The sternpost of the fuselage, which is of steel tube, is used as the cylinder for these rubbers, and is carried up as a cantilever support for the fin and rudder, thus eliminating all bracing above tail plane. The tail plane adjusting gear is also carried on this tube.
   Channel section spindled spars of spruce are used for the main planes and tail plane, and solid spruce for the longerons. Interplane struts are of steel tube.
   The engine is a Napier "Lion," carried on a mounting of steel tubes, and is very accessible, the cowling being made so as to be quickly removable. A radiator of ample proportions, fitted with shutters, is mounted in the nose.
   The main petrol tank (66 galls.) is carried in the fuselage, at the e.g., and supplies petrol to a Vickers pump placed below the tank. The supply is carried up to a three-way cock, leading (a) to the carburettors, (b) to the gravity tank (16 galls.) in the top plane; a separate pipe runs from the hand pump to the gravity tank.
   A fire-proof bulkhead is fitted in front of the main petrol tank, only one petrol pipe being led through it.
   For alighting on the water floatation gear is fitted, and provision is made for throwing off the wheels in flight.
   The "Swift" is designed to carry an 18-in. torpedo and the necessary dropping and adjusting gear. The full load carried, including pilot, torpedo and gear, instruments, fuel, oil, etc., is 2,876 lbs. The following is the approximate performance :- Top speed, 95 knots; rate of climb at sea level, 650 ft./min.; ceiling, 15,000 ft.; run to get off in a 20-knot relative wind, 150 ft.

Flight, May 1925

THE BLACKBURN TWIN-FLOAT SEAPLANE
Napier "Lion" Engine

   IN our issue of April 16, 1925, we published a number of photographs of the new Blackburn twin-float seaplane used at the Blackburn flying school at Brough. This machine is a development of the Blackburn "Dart" torpedo-plane, to which it has a strong family resemblance, and it is thought that a slightly more detailed description may be of interest to our readers.
   The Blackburn "Dart" seaplane has been designed as a dual-control school machine for more advanced pupils, and the fact that it is almost identical with the service machines which pilots will be called upon to fly should make it a very valuable part of the Brough equipment. At the same time, the machine can, of course, be used for other than school work, as its high-power engine naturally enables it to carry quite a considerable load.
   In general design the "Dart" seaplane is a tractor biplane with two floats of boat-built construction extending aft sufficiently far to do away with the need for a tail float. The recent demonstrations at Brough showed that the machine gets on to its step very easily and that it is particularly "clean" in running, while showing no tendency to "porpoise." In fact, it is claimed that the machine is so well trimmed at taking-off speed that the pilot can take his hands off the controls. The float volume is ample for the weight of the machine, so that not only would one float be sufficient for keeping the machine from sinking in case of puncture of the other, but the seaworthiness is, naturally, greatly increased. As regards general design, perhaps the only slightly unusual feature is the back-swept wings, which, although very popular in the early days of flying as a means of obtaining stability, are not so frequently seen on modern machines, and when they are, the object is usually connected with questions of fore-and-aft trim for a given disposition of main loads rather than with aerodynamic stability. The somewhat unusual lines of the fuselage are, of course, connected with the object of good visibility for deck-landing purposes in the ordinary "Dart," and they have been retained in the seaplane.
   Although not shown in the general arrangement drawings, the "Dart" seaplane is equipped, for school work, with landing wheels which form a permanent part of the equipment, in that they are not dropped on taking the water. These wheels are not, however, intended as an amphibian gear in the ordinary sense of the word, and the machine is not designed to alight on land, the wheels merely being a form of trolley on which the machine is transported down the slipway into the sea, and back again on its return from a flight. It would appear that with very little modification, and not a great increase in weight, the trolley gear might be elaborated and extended to turn the "Dart" seaplane into an amphibian.
   The fairly small wings, the use of a medium-lift section (T.64), and the general concentration of all heavy weights were, of course, results of considerations connected with the original machine, but are found no less useful for school work, the more so as the general behaviour of the seaplane is more or less identical with that of the torpedo-plane.
   Constructionally the "Dart" seaplane follows standard Blackburn lines in that it has wood wing structure and partly wood and partly metal fuselage. The latter is built in three sections: the engine mounting with cowling, etc., shown in a set of photographs; the fuselage centre portion, taking the cockpits, undercarriage attachments, etc., and the tail portion. The first two sections are of steel-tube construction, while the rear part of the fuselage is the usual wood-girder structure braced with tie-rods.
   Some of the accompanying photographs show the steel-tube centre section of the fuselage and some of its details. The fittings, it should be pointed out, are machined from the solid, and have been so designed that all struts and wires meet on the centre lines, or neutral axes, thus avoiding off-set moments. The Blackburn designers consider this arrangement superior to the older method of transmitting heavy concentrated loads through timber members with lugs, plates, and bolts. This centre section of the fuselage forms, in fact, a sort of rigid backbone of perfectly triangulated construction, to which all other members are attached, and to which all the heavier stresses are transmitted.
   The wings, as already pointed out, are of wood construction, with spars spindled out from the solid to form an I-section. The ribs are also of wood, but the wing covering is the usual doped fabric. The interplane struts, however, are in the form of steel tubes with wood fairings. The wings are designed to fold, and the hinges for this (on the rear spars), as well as the Stacking devices on the front spars, are shown in our photographs.
   The engine mounting is tubular, as regards the main supporting structure, with subsidiary channel-section frames carrying the cowling, etc. The three photographs give a good idea of the structure, as well as of the cowling and general arrangement. The petrol tank is mounted inside the fuselage, aft of the fireproof bulkhead, and is situated approximately on the centre of gravity of the machine, so that the trim is not altered as the fuel is consumed. The main tank supplies petrol to a Vickers pump placed below the tank to ensure constant flooding. The supply is carried up to a three-way cock, one branch of which supplies the carburettors, the other being connected to the gravity tank, and a separate pipe being run from the hand petrol pump to the gravity tank. The gravity or service tank is placed in the top centre section, in which position it gives a "head" of at least 24 ins. when the tail is on the ground.
   The two floats are built of two skins of mahogany, placed at an angle to one another, and are of the single-step type. They have Vee bottoms both ahead and aft of the step, and the heel of each float terminates in a sprung skid, which takes the place of the usual fuselage tail skid in the land machines. The two floats are placed a considerable distance apart, so that the machine is very stable on the water, the strut attachments being partly direct to the fuselage and partly to the lower plane at the point of attachment of the sloping outrigger struts. The hinges for folding the wings, incidentally, occur at this point also.
   The main dimensions are as shown on the page of general arrangement drawings. No detailed performance figures are available, but we understand that the top speed of the "Dart" seaplane is about 87 knots (100 m.p.h.), and the rate of climb at sea level is approximately 600 ft./min. The general design and workmanship is, as in all Blackburn products, of a very high order.