Flight, February 16, 1939

THE DE HAVILLAND 95A
Medium-sized Transport with Wide Applications : The First All-metal Machine from the Hatfield Factory Described : A Design to the Newest Formula

   WHEN a commercial machine is introduced to airline operators and prospective purchasers they ask two questions. In the first place they want to know what the machine will do, and in the second why a particular form of construction or a certain aerodynamic and general layout was decided upon.
   In the case of the D.H.95 or Flamingo, the first question is easily answered. It has been laid out as a medium-sized civil type with applications which are as universal as design considerations allow. It is not a special-duty type, and can be operated with accommodation varying from twelve to twenty seats. While the performance in the matter of speed and range is intended to equal or to better that of any contemporary transport type, very considerable attention has been paid to safety considerations.
   In the present state of aerodynamic knowledge a high cruising speed now inevitably means a comparatively high landing speed, but designers still have it in their power to ensure that the flying characteristics at speeds near the stall are as safe and normal as possible. The need for safe low-speed qualities is all the more noticeable nowadays when airline flying is so often carried out in weather conditions which involve long periods of blind flying followed sometimes by a virtually blind approach to the terminal aerodrome.
   The reason for the fact that the 95 is of all-metal construction - actually the first of such construction to be produced by De Havillands - might simply, but not too accurately, be explained as the result of demand. Operators expect all-metal construction and, therefore, it must be offered to them. This, however, is obviously not the whole story. There are no very intrinsic advantages in all-metal construction as such. In fact, for many purposes, the older methods have distinct advantages. Only when quantity orders may be expected is the all-metal machine an economically reasonable proposition, while in such circumstances it is, for production reasons, the only possible means of construction.
   Changing ideas in the world of air transport on the subject of financial assistance have made the 95 possible. Without the expectation of a fair series of orders for such a type it would not be possible to go to the expense of laying down jigs for large-scale manufacture. With a very reasonable hope of direct and indirect support and assistance from our own Air Ministry the 95 prototype has been built and preparations made for the production of a series at a cost which should make it an attractive proposition both at home and abroad.
   The particular size was chosen by the designers as being that most suitable for general use, while a twin-engined power plant was preferred for its simplicity, particularly as it was possible in the circumstances to provide a really adequate power reserve. This reserve is necessary to ensure a good take-off from high altitude or tropical aerodromes, and from those which are small or with somewhat obstructed surroundings.
   The power reserve gives an adequate single-engined performance. The Flamingo is designed to cruise at only 56 per cent, of its maximum power at a speed of 204 m.p.h. At this speed the machine carries 3,505 lb. of payload for 600 miles at a fuel consumption of 64 gal. per hour.
   The use of large-diameter airscrews, geared to run at half engine speed, means that the full available power for take-off may be efficiently converted into thrust, while the use of constant-speed airscrews - later to be full-feathering Hydromatics - means that this thrust efficiency is available during the initial climb as well as at the take-off. Large airscrews mean also that the engine diameter is small in relation to the airscrew disc, so that little power is wasted through slipstream interference.
   A high-wing arrangement was chosen for a number of reasons. Those normally considered by the operator are fairly straightforward: the passengers obtain a better view, while the fuselage may be both deeper and so near the ground that there are few personal or freight-loading problems. Aerodynamically, the high-wing type has the benefit of an unbroken upper wing surface between the two engines.
   In this particular machine the latter are carried well below the chord line, so that there is little disturbance of airflow. This unbroken surface shows its advantages at low speeds and high angles of incidence, when the even distribution of lift over the span reduces the likelihood of vicious tendencies at or near the stall. During the take off and the approach the characteristics are further improved by the use of Handley Page slotted flaps which increase the lift quite considerably even when they are in the fully-down (53 deg.) position. For the take-off, when they are lowered to the 25-degree position, extra lift is available with little of the usually attendant drag.
   it is worth noting here that with a full load the 95 can take off in 250 yd., and be at a height of 170ft. after a “run” of 650 yards. Within two miles of the start of the take-off (at a climbing speed of 100 m.p.h.), the machine can be at 1,800ft. if full take-off power is used for the period.
   While on the subject of safety, two other little points should be mentioned. Either one of the two engine pumps is capable of supplying sufficient fuel to both engines for maximum power. Even if both the pumps fail, the position of the tanks means that gravity would still be available to provide the necessary flow. The retractable undercarriage, too, has three alternative methods of operation. If the hydraulic pumps fail there is an emergency supply of compressed air with, separate pipe-lines, while there is a stand-by hand-pump system which is independent of either.
   Very briefly, the structure of the Flamingo - might be described as an interesting example of the translation of wood into metal. The designers have used many of the best features of normal wood construction - at least where the fuselage is concerned - and have obviously not felt themselves bound to follow previous ideas in metal stressed-skin layout.
   The details are described later, but it should be said, by way of an introduction, that one of the most important features in the design is the way in which accessibility and interchangeability have been considered. For instance, the two halves of the tailplane may be reversed, while the wing, excluding the continuation of the main spar across the fuselage, is in four pieces, so that, when necessary for packing purposes, the machine’s width can be reduced to a matter of 9 feet when the engine-carrying stub wings and the outer sections have been removed.
   The fuselage is built in two separate parts largely for reasons of ease of production, though the fact would reduce rebuilding time in the event of a minor ground mishap. The wing tips, too, are detachable, and these are undoubtedly the most vulnerable parts of an aircraft.
   Operators who are endeavouring to make a small fleet do the maximum amount of work will be interested in the way in which the two Perseus engines are not only quickly removable but interchangeable. When one is taken out the various leads are merely detached at the bulkhead, while the accessory gear box remains mounted on the spar. An engine can, in fact, be changed in rather less than an hour.
   In the works the necessary jigs have been split up so that the maximum amount of work can be done on each section of the machine without the hold-ups caused by the fact that only a certain number of men can work together in one place. This splitting-up also economises floor space. At the moment several 95’s are in course of construction, and the production plans are well advanced for the quantity manufacture of the type.

Passenger Accommodation
   There are four different cabin arrangements for the 95. Those for twelve, fourteen or seventeen passengers may be had without extensive alterations, though the twenty-passenger arrangement involves certain structural modifications, which must be incorporated at an early stage in the manufacture of the machine.
   Figures by themselves do not convey any real idea of cabin size, but for what they are worth here are the main cabin dimensions of the Flamingo: Maximum width, 7ft. 6in. (2.29 m.); height, 6ft. 7in. (2 m.); width of seats inside armrests, 19in. (0.48 m.); and width of gangway, 14in. (0.356 m.). The length of the cabin varies with the seating arrangements, that for the twelve-seater being 15ft. 11in. (4.85 m.); for the fourteen-seventeen seater 19ft. (5.8 m.); and for the twenty-seater 21ft. 8in. (6.6 m.). In addition to the normal windows there are four which may be used as emergency exits, while there are two exits in the roof, one in the passenger’s compartment and one in the control cabin. The windows are of the doublepane type, which provide insulation against sound and cold. The air in the cabin is steam-heated and the temperature is controlled, while each passenger has, as usual, an individual supply of dry cold air.
   Structurally, the most interesting feature of the Flamingo is the wing, which is made up in four sections, consisting of a pair of stub wings and a pair of outer wings. The former carry the engine and undercarriage assemblies, the fuel tanks, and the inner section of the flaps.
   The centre section has one main spar (a lattice girder of extruded aluminium alloy) and the two auxiliary spars, which are Wagner beams with alloy extruded flanges. The undercarriages and the engine mountings are carried on rigid bulkhead ribs lying transversely between the spars. The four fuel tanks, two on each side of the main spar, are carried outboard of these bulkheads, while tank inspection covers are integral with the under surface of the wings. The main spar is continued through the fuselage, while the auxiliary spars are attached to two strengthened hoops in the fuselage structure.
   The outer wings, which are quickly detachable, are made up of a stressed skin ”D” section spar in which the web and the booms form a Wagner beam, while the nose of the spar itself forms the leading edge. The covering is of Alclad sheet, and the extruded sections are of light aluminium alloy. The ribs and formers, also of alloy, are riveted to the spar stiffeners, and the aileron hinge brackets and the outer sections of each flap are carried on the stronger ribs. Aft of the spar the wing is fabric-covered, though there are all-metal wing tips, these being detachable for ease of replacement in the event of damage. In the stub wings are hinged panels giving access to the engine controls, hydraulic pipelines, electrical leads, and fuel pipes, while jacking points are provided under each wing slightly outboard of the engines.
   The ailerons are carried on three hinges and located by the central one only. An Alclad web beam forms the main spar of each aileron with a “D” section torsion nose-piece: aft of this spar are pressed Alclad ribs, fabric-covered. Differential control is used as on all D.H. machines, for the operation of the ailerons, to give a larger upward than downward movement and thus reduce drag.
   The actual wing section employed in the Flamingo is a modified R.A.F. 34.
   Retractable landing lights are fitted to each outer wing, these being flush with the surface when not in use. They have been specially designed by Rotax and their retraction movement is controlled by a small electric motor through a reduction gearing, a clutch being used to avoid any possibility of overload. The same firm is responsible for the navigation lights (with Osram lamps, which are used throughout for exterior and interior lighting), the engine starter, the cooling-gill motor, the vacuum pumps and for the undercarriage warning equipment.
   The good take-off and landing characteristics of the Flamingo are partly the result of fitting Handley Page trailing-edge slotted flaps. These extend from the sides of the fuselage to the ailerons, each main section being in two parts. Rapid dismantling is possible because of the special hinge design, and these hinges are provided with appropriate inspection doors. For optimum take-off a small flap angle is normally used, the flaps being fully depressed for landing. Any desired intermediate setting can be selected by the pilot through a lever under the centrally placed control box. This operates, through Exactor hydraulic controls, a pre-selector valve situated in the wing, close to the ram.
   The operation of the flaps is hydraulic, through a ram acting directly on a parallel-motion hinge linkage system housed just inboard of the joint between the stub wings and the outer panels. This hinge linkage picks up at the central end of each part of the flaps, the other hinges at the outboard and inboard extremities being provided with a similar linkage system. No part of the hinge system protrudes outside the boundaries of the aerofoil.
   The structure of the flaps comprises, in the first place, a stressed skin nose of ”D” section, made up of a channel-section beam and Alclad sheet conforming to the profile of the leading edge and stiffened with formers. Aft of this are ribbed pressings of Alclad riveted to the channel beam and nose skin. Recessed into the ribs is a tube of oval section which forms the trailing edge. The flaps are fabric-covered.
   A notable feature of the fuselage design is its division into two sections, the front portion being detachable for replacement in the event of damage. All pipes and controls, of course, have joints at the junction of the two portions.
   The first section extends from the nose to the bulkhead behind the pilot’s cabin, and is built of channel-section Alclad formers covered with Alclad sheet, but having no longitudinal stringers This nose section includes the whole of the control cabin and its controls, with the seats for two pilots and a radio operator, the instrument panels, accumulators, wireless crates, mail compartment, and front luggage hold. Above the floor level, ahead of the cabin, the nose is hinged to give access to the two accumulators, the controls, and the rear of the instrument panels. Even in flight it is possible, through the provision of detachable panels in the cabin roof, to obtain access to controls and piping. On the starboard side of the nose are large doors for the mail and luggage compartments, these being arranged at a convenient height for loading on the ground.
   The second section of the fuselage, which contains the passenger cabin, toilet room, and luggage hold, extends aft from the pilot’s bulkhead to the rear end of the fuselage, and is constructed of Alclad formers of channel section, extruded stringers of light aluminium alloy, and Alclad sheeting. Under the floor are special keel members and strengthened rings to protect the machine in the event of an emergency landing with undercarriage retracted. In the rear bulkhead of the luggage compartment is a hatch giving access to a walkway for the inspection and maintenance of the controls, fittings, and structure in the rear portion of the fuselage.
   The fuselage itself terminates in a completely detachable “tent” fairing, the removal of which gives access to the tailwheel mounting, tailplane, elevator attachments, and controls for the elevators and rudders.
   The stressed skin tailplane is fully cantilever with three stressed-skin fins, all-metal fabric-covered elevators, and two all-metal fabric-covered rudders. Trimming tabs are fitted to the elevator and rudders. The most interesting feature of this unit lies in its port and starboard interchangeability. The outboard fin and rudder can be used on either side, while, each half of the tailplane itself is similarly reversible.
   Structurally, the tailplane is essentially a two-web stressed skin box beam with the nose and rear portions detachable - the latter being secured by five bolts. The elevator is carried on light alloy outriggers and consists of an Alclad ”D” nose with internal diaphragms and pressed Alclad ribs. Elliptical steel tubing is used for the trailing edge. The fins are similar in construction to the tail plane and the rudders to the elevators.

The Undercarriage
   To provide aerodynamic balance, the hinges of both the rudder and the elevator are set back. The two halves of the elevator are statically balanced, each with an external weight on its under side. These balance weights may easily be reversed if the elevator halves are interchanged.
   While the trimming tabs are operated by a screw jack driven by a chain and sprocket from a flexible shaft, the rudder and elevator are operated through a push-rod system connected to cables. Needless to say, inspection doors are provided at all points where the control system must be reached.
   A single Lockheed cantilever compression leg, retracting rearwards into the engine nacelle, is the ”core” of each half of the undercarriage, the unit on each side of the fuselage being interchangeable. On each leg and wheel fork are fixed fairings which follow the contour of the rear cowling and leave a small portion of each wheel protruding. Retraction of the undercarriage takes eight seconds and is affected by a Dowty high pressure hydraulic jack working on a cut-off pressure of 1,100 Ib./sq. in. from an accumulator charged by either or both engine pumps. Actually, a pressure of 450 Ib./sq. in. is sufficient to operate the gear under maximum load.
   The wheels (10in. x 16in.) are of Dunlop manufacture, with tyres which give high braking efficiency. The wheels are carried in forks constructed of riveted Alclad sheet and attached to the compression leg by bolts, shear bushes and screwed rods.
   The removal of four Simmonds nuts and bolts, which hold the axle caps to the forks, and the Avery coupling on the brake pipe-line, permits the complete assembly (wheel, axle, and Bendix two-leading-shoe hydraulic brake) to drop free. A special casting is supplied to facilitate wheel removal. This fits on each side of the fork, enabling the machine to be lifted by an ordinary portable jack.
   At the top of the compression leg is a flange which is bolted to the top hinge fitting. This embodies a steel-phosphor bronze bearing which is lubricated by grease gun. At the lower end of the fixed portion of the compression leg is a forked lug picking up the radius rod, the other end of which pivots about a pair of lugs attached to the main spar in the stub wing. The retracting jack picks up at the centre of the radius rod slightly above the knuckle where the radius rod folds. To meet Air Ministry safety requirements a latch is provided to prevent accidental retraction, due to drag or landing loads, in the event of pressure failure in the jacks. The gear is not locked in the up position, oil trapped below the piston of the undercarriage jack providing the necessary support.
   In the pilot's cabin is an electric indicator which show’s two green lights when the undercarriage is down and the latch is locked; two red lights when the wheels are being drawn up; and no lights at all when they’ are fully raised. Also incorporated in the circuit is the usual warning horn. This warning also sounds if the engines are throttled back with the undercarriage lock unfastened. To ensure that mud is not thrown up on the lock a special mudguard and wheel scraper is incorporated; the scraper also prevents mud jamming the wheel fork. Towing points are attached to the undercarriage axle caps. The tail wheel is of the Dowty non-retractable type embodying a caster-locking device operated by the pilot through a control in the roof.
   The hydraulic system provides a common supply for undercarriage retraction, flaps, brakes, De Havilland Hydromatic airscrews (if fitted) and Sperry automatic pilot. Power is provided by two Pesco gear pumps, one on each engine box. Either one of these pumps can be selected to feed a large hydraulic accumulator, storing 1.75 gallons of special fluid at a pressure of 1,100 Ib./sq in., which is sufficient to enable the undercarriage to be fully retracted in ten seconds and to operate all the services except the automatic pilot. When the hydraulic accumulator becomes fully charged an automatic cut-out comes into operation and allows the pump to idle at zero pressure.
   When the pressure in the system drops, the pump is brought into action to restore the supply. In addition to the duplicated engine pump there is an emergency supply of compressed air in the hydraulic accumulator. This has separate pipe-lines and is available for lowering the undercarriage. Additionally there is a stand-by hand pump for use on the ground or in an emergency. This takes its supply through a system which is independent of either engine pump.
   The electrical power is provided from two 12 volt 45 ampere-hour batteries in series and charged by two 500 watt generators, one in each engine. Should either generator fail a red light shows on the control panel. The electrical services are: - engine cooling-gill operating motors; electrically retractable landing lights; navigation lights; cabin, lavatory and luggage compartment lights; a number of electrical indicating instruments in the control cabin; engine starting gear; windscreen wiper; heated pitot-heads; and four sockets (at nose, tail and undercarriage) for use with a plugged-in inspection lamp. The lights in the luggage compartment, incidentally, switch on automatically when the door is opened.
   Should the starter motor fail, the engine may be turned manually to a point just over top dead centre in any cylinder, when by pressing a button on either undercarriage leg the booster coil is actuated, supplying a spark and thereby starting the engine.
   The power plant of the 95 consists of two Bristol Perseus XIIc nine-cylinder medium-supercharged, geared sleeve-valve radials. This type of Perseus has a capacity of 24.8 litres; is 52 inches in diameter and is rated at 680-710 h.p. at 2,250 r.p.m. and 4,000ft. The maximum power (available for 5 mins.) is 815 h.p. at 6,000ft. For take-off, 890 h.p. is available at 2.700 r.p.m. The airscrews are normally of the De Havilland three-bladed constant speed type, 12ft. 9in. in diameter, though the new Hydromatics will eventually be specified and will considerably improve the already good one-engine performance.

The Power Units
   The engine mounting, which embodies Bristol rubber-in-shear mountings, is of welded steel tube construction and is attached to the wings by quickly removable expanding steel bushes. Each engine unit (including the complete engine on its mounting, with exhaust system and tail pipe, the entire oil system, fireproof bulkhead, and Exactor engine controls) is completely interchangeable with the other. Each engine has a remote gear box upon which is mounted a 500-watt generator, hydraulic pump and vacuum pump. Engine removal is simplified by a special derrick for use in places where overhead tackle is not available. This apparatus fits on top of the wing and can be adjusted for the “tail up” or “tail down” positions of the machine.
   The cowling of the Perseus is rather different from standard. The de Havilland Company, in order to improve the performance, take-off and “single-engine ceiling conditions,” has departed from the normal type with a ring of gills, and instead of allowing the cooling air to escape around the complete circumference of the engine, has led it down by means of a sloping fireproof bulkhead behind the cylinders to the surface of the wing; here it passes through ducts on each side of the undercarriage, the outlets being situated approximately at mid-chord. The outlet area of these ducts is controllable by gills operated by a Rotax motor. Three positions are provided - open, half open, fully closed. A great advantage, of course, is that as the flow of air over the top surface of the wing is undisturbed, and the lift, therefore, is practically unimpaired.
   The wrapper cowl which encircles the cylinder head is in two portions which fix on to the exhaust pipe at the top, and, by means of dead-centre fasteners, are drawn together at the bottom permitting access to the sparking plugs. The other cowlings are quickly removable and held by Dzus fasteners.
   Four welded aluminium fuel tanks are mounted in the inboard sections of the wings - two on each side of the fuselage; one, of 89-gal. capacity, is placed in front of the main spar and the second, of 112-gal., is behind the spar. Detachable panels are provided in the top skin of the wing for inspection or removal. There is a selector valve for each engine; this is mounted on the front spar and has four positions:- “off,” “supply from front tank,” "supply from rear tank,” or a cross feed from which each tank is connected to the opposite engine. The fuel passes from this valve to a unit of D.H. design mounted behind each engine on the fireproof bulkhead. This comprises a filter, a non-return valve and a pressure reducing valve, with connection for the gauge and a low- pressure warning device. The fuel is drawn from the filter by a Bristol duplex pump and returned at 10lb./sq. in. to the pressure-reducing valve, which delivers it at 2 1/2 lb./sq. in. The non-return valve is located between the suction and return connections from the pump, and gives a gravity feed to the carburettor when the pump is not running, closing again after the generation of pressure.
   On the top rails of each engine mounting is an oil tank of 10 1/2-gal. capacity. Within the tank is the main suction filter, the thermo-pocket and the quick warming oil chamber, consisting of a cylindrical device in the centre of the tanks into which the cold engine oil percolates as soon as the warm oil is used. The oil cooler is mounted on the starboard member of the engine mounting. Cold air is directed from the front of the engine to the oil cooler and is controlled at the exit. A yellow light shows in the. cockpit when the oil pressure falls below the minimum limit. The controls and instruments are described and illustrated on pp. 168-169.


THE NINETY-FIVE IN THE AIR
Details of the Control and Instrument Layout : Some Remarks on the Flying Characteristics

   WHEN flying in the control cabin of the 95, two points are particularly striking. The first is concerned with the obviously good flying characteristics, which are especially noticeable and important at low speeds - during and after the take-off and during the last phase of the approach. The second is the simplicity of the control layout. One has become accustomed in modern transport, and, for that matter, in military aeroplanes, to the need for dealing with a very vast number of items which are disposed more or less irregularly all over the control cabin. In the Flamingo every essential item is conveniently placed, and no operation, whether lowering the undercarriage and flaps, or resetting the trim, requires any sort of exertion or thought.
   Two of the more important features which go to make one feel thoroughly at home in the cockpit are the good view, both while flying level and while taxying in the tail-down position, and one’s comparative nearness to the ground. The latter effect, which is characteristically the result of the high-wing layout, should make the hold-off and landing exceptionally straightforward, while there is no very marked change of attitude when the control column is brought fully back for the landing.

Crew Comforts
   The dual controls, incidentally, have a direct fore and aft movement through the dashboard, so that there is no inconvenient column in the cabin itself, and each is more or less instantaneously adjustable for length. At the same time, the seats have the usual means of adjustment both in the fore and aft and the vertical directions, so that it should be possible to tailor the 95 to suit a pilot of any possible stature.
   At all speeds it seems that the machine is fully stable fore and aft, and the incorporation of an additional central fin has removed all traces of the directional instability which was apparent when the prototype was first flown. Certainly, in a level attitude and at cruising speed the machine flies by itself, and any mass demonstrations by the occupants of the main cabin can be felt and corrected at once by a movement of not more than an inch or two of the large trimming wheel which is placed on the left of the central control bank.
   The less-used rudder bias gear is arranged in the form of a crank in the roof. With the latter are the master fuel taps, the tail-wheel lock, the oil cooler control, the slow-running cut-out, and the carburetter heater control. Since the floor of the control cabin is a good deal higher than that of the passenger compartment (with the freight and mail compartment underneath), the roof is comparatively low, and the various controls can easily be reached.
   Below the throttle and constant-speed airscrew control quadrants in the central bank are somewhat similar controls for the undercarriage, flaps and automatic pilot. The use of the first two is simple and quick in the extreme, and this rapidity is repeated in the action of the hydraulic operating gear itself. The undercarriage legs, after the lever has been pulled up to the top of its quadrant, come up smoothly and are fully retracted in something like ten seconds. Once they are up (or locked in the down position) the lever is moved to “neutral.” A safety locking device, in the form of a pinned stop, is incorporated in the quadrant so that the undercarriage cannot be retracted by accident while the machine is on the ground. Any flap angle may be selected by leaving the control in the required position. Ordinarily, an angle of 25 degrees is used for take-off, and this position is clearly marked.
   Normally, the 95 is brought in over the last part of the approach at an airspeed of about 85 m.p.h., and at this speed the machine is stable in all axes and with adequate remaining control. In bumpy weather, or with a full load, 90 m.p.h. would probably be the figure. Needless to say, the engine-off flaps-and-undercarriage-down attitude is quite steep, and height is lost with extraordinary rapidity. In fact, one’s impressions during a first approach are that the machine must be over-shooting the landing ground.
   The instrument group, apart from the centrally disposed Sperry panel, is in two main units, which may be remove completely or hinged open while in flight. Each of these units consist of two parts - the main panel, which is mounted on special shock-absorbers, and the rigidly mounted sub-panels. As explained elsewhere, the backs of these instruments may be reached for test or examination simply by hinging open the nose of the machine.
   The left-hand panel on the dashboard carries all the essential flying instruments, while the right-hand panel is devoted mainly to engine speed, boost and temperature gauges, though for the benefit of the second pilot, there js an airspeed indicator and a sensitive altimeter. The separate panels carry the usual operating switches and subsidiary indicators, and the entire wiring of the dashboard incorporates plug and socket connections which permits the boards to be quickly and easily detached.
   Very little can be said by the ordinary interested copilot about the handling characteristics except that these are as normal and straightforward as they should be. The ailerons, even at a cruising speed of 205 m.p.h., are quite light for the size of the machine, though a good deal of pressure is required on the rudder pedals to instigate a turn.
   Cursory impressions suggest that the control reactions are likely to be more suitable for blind-approach conditions than those to which one has become accustomed in modern transport aeroplanes. Usually, the short, sharp turns, which must be made while holding the equi-signal track, can only be done on the ailerons, but with the 95 it seems that it will be possible to make such corrections on the rudders - a fact which simplifies both directional gyro and beam flying. The fast machine of to-day is much too stable directionally, and the application of rudder (with great difficulty) induces nothing more than a yaw, with little or no deviation from course.
   This, of course, is purely an impression, and only in actual service will it be possible to see whether the machine is more than usually suited to blind-approach work.
   The official speed figures for different heights and powers are given elsewhere, and, without any knowledge of possible position error, A.S.I. readings are not of any great value. While flying level for a matter of ten minutes or a quarter of an hour at 10,000ft., however, the reading was round about 180 m.p.h., which, corrected for altitude, gives a true speed of some 210 m.p.h. The revolutions were about 2,200, and the boost pressure -2 lb./sq. in., figures which suggest an average output from each engine of approximately 500 h.p., or 60 per cent, of the maximum available power.

H. A. T.

Flight, November 1939

Britain's Civil Aircraft

DE HAVILLAND

   BEFORE the war the De Havilland Company was in production with the attractive and highly promising Moth Minor light tandem two-seater. "Civil" interest, however, now centres on the Flamingo transport, which promises to be just as successful as the smaller Rapide and 86 series of biplanes.
   The Flamingo is a high-wing twin-engined monoplane and may be regarded as the country's first all-metal medium-capacity transport. The two Bristol Perseus XIIC give a sufficient reserve of take-off power for the machine to fly and climb on one engine up to 8,000ft. with full load.
   The span is 70ft.; the length 51ft. 10in, and the wing area 651 sq. ft. A continuous cruising speed of 210 m.p.h. can be maintained and the top speed is 234 m.p.h. The climb to 10,000ft. takes only 10.1 min.

The De Havilland Aircraft Co., Ltd.. Hatfield Aerodrome, Herts.

Flight, March 1940

THE 1940 FLAMINGO
Hydromatic Airscrews : Perseus XVI Engines : Increased Pay Load

  FROM the remarks made during Mr. A. S. Butler's speech at the annual general meeting recently, it was obvious that the De Havilland Aircraft Co., Ltd., does not intend to let its commercial business die during the war. Already the firm has translated its chairman's words into action by announcing an improved version of the Flamingo. It was always a very good aeroplane, and the new features will help it to keep its place in commercial aviation during the coming years. In spite of insistent calls upon their production in other directions, the works will make time to keep the D.H. flag flying in the commercial world. The importance of maintaining our exports has already been stated in Flight, and we need not stress it here.
  The 1940 model of the De Havilland Flamingo (DH 95) passenger liner has a later type Bristol sleeve-valve engine, the Perseus XVI, which has a greater power rating at altitude than the Perseus XIIc fitted to earlier models. Maximum power in level flight for 5 minutes is 905 h.p. at 6,500ft. for the XVI, compared with 815 h.p. at 6,000ft. for the earlier XIIc. This gives an improved performance in rate of climb, higher two-engine and single-engine ceilings, and quicker take-off at altitude.
  The new Flamingo has De Havilland Hydromatic feathering airscrews, and though this involves an increase in airscrew weight of 100 lb., the better performance due to increased engine power has allowed the loaded weight to be increased by 600 lb., so giving an increase in disposable load of 500 lb. The loaded weight is now 17,600 lb. (7,990 kg.). Wing loading becomes 27.0 lb./sq. ft. (131,8 kg./sq. m.) and power loading 10.05 lb./h.p. (4,5kg./Cv.) on take-off power.
  The increase in disposable load allows the provision of more comprehensive equipment, such as automatic pilot and de-icing apparatus, without reduction of passenger accommodation. This increase is not at once evident in the new tare weight of 12,020 lb. (5,452 kg.) because of the inclusion of these and furnishing and equipment items additional to those given in the article on the Flamingo in our issue of February 16, 1939. The tare weight now includes the following: -
  Full dual control, complete twelve-passenger cabin and toilet room furnishing, cabin ventilation, heating and lighting systems, Lux type engine fire extinguisher and hand extinguishers in cabin, 200 lb. (91 kg.), allowance for radio equipment with full D.F. apparatus, complete set of instruments, and Sperry automatic pilot, 100 lb. (45 kg.), provision for fitting blind approach radio receiver, forced landing flares, 50 lb. (23 kg.), complete hydraulic and electrical systems (including landing lights), Goodrich airscrew and airframe de-icing, 95 lb. (43 kg.), control locking gear, signal pistol, and cartridges, 9.5 lb. (4,3 kg.), engine and airscrew covers, 15 lb. (6,8 kg.), glycol windscreen spray and Hydromatic airscrews.
  Single-engine performance gives an absolute ceiling on continuous emergency power of 9,300ft. (2,836 m.) and 8,200ft. (2,499 m) for starboard and port engines respectively, the performance on each being slightly different. Rates of climb at sea level on take-off power are 230 and 210ft. /min. (1,17 and 1,07 m./sec.) respectively.
  The rate of climb at sea level on two engines at takeoff power is impressive, being 1,470ft./min. (7,47 m./sec.); on climbing power it is 1,010ft./min. (5,13 m./sec). Absolute ceiling on continuous emergency power is 22,200ft. (6,771 m.) and service ceiling 20,900ft. (6,374 m.).
  Fuel tanks for 402 gals. (1,827 litres) are provided and an oil capacity of 24 gals. (109 litres). This gives a still air range of 1,210 miles at 65 per cent., and 1,345 at 50 per cent, of continuous emergency power.
  Other technical data relating to the Flamingo are given below :-

Weights
With 500 miles range against a 40 m.p.h. head wind, cruising at 65% Continuous emergency power
  Tare weight 12,020 lb. 5,452 kg.
  Crew, 2 at 170 lb., plus 1 at 140 lb. 480 lb. 222 kg.
  Fuel, 212 gals 1,590 1b. 722 kg.
  Oil, 24 gals. 216 lb. 98 kg.
  Buffet equipment 50 lb. 23 kg.
  Payload 3,244 lb. 1,472 kg.
  Total loaded weight 17,600 lb. 7,990 kg.

Engine Ratings (per engine)
H.P. Altitude Cv.
  Take-off power at S.L. 875 S.L. 887
  Max. take-off power 930 5.750 ft. 943
  Climbing power 745 6,500 755
  Continuous emergency power (30 mins.) 805 6,000 816

Performance
  Max. speed at max. power 239 M.p.h. 384 Km./hr. Altitude 6,500 ft.
  Cruising speed at 65% continuous emergency power (523 h.p., 66.5 g.p.h. consumption) 200 M.p.h. 322 Km./hr. Altitude 10,000 ft.
  Take-off run with flaps at sea level in 5 m.p.h. wind 312 yds. 285 m.
  Height at 656 yds. from rest with flaps in 5 m.p.h. wind 145 ft. 44 m.
  Landing run with flaps in 5 m.p.h. wind 325 yds. 297 m.
  Takeoff fun at 5,000 ft. with flaps in 5 m.p.h. wind 340 yds. 311 m.