Flight, October 1938

British Commercial Aircraft

DE HAVILLAND

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   The D.H.91, or Albatross, which is undoubtedly the most efficient aero­plane of comparable size in existence to-day, is being produced in two forms. One of these is for long-range mail-carrying work across the Atlantic, and two examples have been ordered by the Air Ministry; the other is a twenty-six-seater passenger-carrying machine, of which five have been ordered by Imperial Airways. Examples of each are now ready for delivery and the rest of the order will be completed shortly.
   The structure of the Albatross is a particularly interesting application of new ideas in the use of wood, and to some extent follows that of the well known Comet, on which type the design may be said to have been based. The thin-section cantilever wing is built up of two spars with spruce-strip covering; the fuselage is a particularly ingenious monocoque structure in which a balsa wood sandwich is used to support the plywood. The four engines are Gipsy Twelves, which each give a maximum of 525 h.p. for take-off, and the airscrews are of the constant-speed type.
   The mail-carrier version is designed for an all-up weight of 32,498 lb. and the passenger type at 29,500 lb. Minor differences, apart from those involved in tankage arrangement, are to be found in the two types; the former, for instance, has normal split flaps with Dunlop anti-icing equipment along the leading edges, while the latter has slotted flaps. Both, of course, have electrically retractable undercarriages.
   Provisional D.H. Albatross data (mail-carrier version).- Span, 105ft.; length, 71ft. 6in.; all-up weight, 32,498 lb.; weight empty, 20,860 lb.; disposable load, 11,638 lb.; payload, 1,000 lb.; wing area, 1,078 sq. ft.; wing loading, 30.20 lb./sq. ft.; power loading, 15.50 lb./h.p.; maximum speed, 231 m.p.h. at 8,750ft.; cruising speed, 212 m.p.h. at 62 per cent power; cruising range, 2,500 miles against 40 m.p.h. head wind, and maximum range, 3,300 miles.
   D.H. Albatross data (passenger version).- Span, 105ft.; length, 71ft. 6in.; all-up weight, 29,500 lb.; weight empty, 21,230 lb.; disposable load, 8,270 lb.; payload, 4,188 lb.; wing area, 1,078 sq. ft.; wing loading. 21.5 sq. ft.; power loading, 12.4 lb./h.p.; maximum speed, 234 m.p.h. at 8,750ft.; cruising speed, 210 m.p.h. at 11,000ft. on 62 per cent power, and cruising range, 1,100 miles.
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Flight, November 1938

THE ALBATROSS in DETAIL
De Havilland's Big Transports Described : Mail and Passenger Versions : Lobster-claw Fuselage Construction : Low-drag Four-engine Installation : Lessons from the Comet

   Ninety-first in the distinguished line of De Havilland aircraft is the Albatross four-engined transport monoplane. Equipped for day travel over typical main-line routes, the machine accommodates twenty-two or twenty-three passengers in three compartments with a vestibule and main entrance at the rear. Thus arranged, the machine disposes (aft) a toilet room and a wardrobe for outdoor clothing and (forward) a kitchen, a mail or luggage compartment and a radio cabin. There is a separate front entrance for the crew, which would normally comprise the captain and the first officer, a radio operator and a steward. Behind the passenger quarters is a large baggage and freight hold with a capacity 158 cu. ft.
   Fully equipped, the Albatross has a block-to-block range of 1,000 miles, carrying twenty-two passengers and baggage.
   The seats are disposed in pairs on each side of a central aisle 21 inches wide. There are large tables for meals and the usual racks for light articles, in addition to the wardrobe previously-mentioned. Lighting at night is by a system of diffused upward illumination supplemented by individual reading lamps. Ventilation is by conditioned air, there being a system of steam heaters and filters. The air volume in the passenger and crew quarters is changed thirty times an hour. The minimum standing height is 6ft. 3m.
   It is claimed that conversion to a sleeper may be effected in a few minutes. Fitted with berths, the machine is known as the Albatross Nightrider. Sleeping accommodation takes the form of twelve wide berths 7ft. long and arranged longitudinally, there being three upper and three lower berths on each side of a wide aisle with a bedside armchair for each passenger. The four lower berths of the forward and midships compartments are designed to provide spring mattress beds of single or double width at will.
   The first two examples of the Albatross to be built were arranged as long-range mail carriers for transatlantic work. The name Albatross Intercontinental Mail has been conferred by the company on this version Under the contract terms of the British Air Ministry, to whose order the first two machines were constructed, a 1,000-lb. mail load was to be carried for 2,500 miles against a 40 m.p.h. headwind.
   It is claimed that should one engine - even an outboard unit - fail just after take-off, the Albatross, at 32,500 lb., could attain a height of 11,900ft. on its normal climb output of only 390 h.p. from each of the remaining three engines. The Albatross Mail has fine take-off characteristics even though it carries a load 3,000 lb. greater than that of the passenger version. Actually, the screen height is 175ft. at 1,200 yd. from the start of the run; the stipulated figure is 66ft.
   With its engines delivering 1,300 h.p. (62 per cent. take­off power) the Albatross will cruise at 210 m.p.h.
   According to estimates made by the manufacturers, if the machine were perfectly streamlined (for example, if its weight and its 4,000 sq. ft. of wetted surface were represented as a pane of glass of negligible thickness towed edgewise through the air by the same power) it would travel only 49 m.p.h. faster. Translating the efficiency of the Albatross into commercial terms, it will carry a crew of four and enough fuel for a normal range of 600 miles and 2.4 tons of pay load, 210 miles in an hour for a fuel expenditure of 83 gal., thus giving, it is claimed, a power-economy factor hitherto unequalled by any machine of comparable speed and payload - 6.07 ton-miles of payload per gallon.
   Unique in several respects, the cantilever wing (R.A.F.34 modified section) is built in one piece, the covering being continuous throughout the span. Attachment to the fuselage is by bolts through a tubular structure, sufficient clearance being left to allow a straight run for the controls.
   In effect, the wing is built round a central stressed-skin box formed of the two main box spars and the top and bottom spruce laid over the stringers. The nose ribs are of conventional formation, the diagonal bracing being glued and bradded through ply gussets to the spruce booms. Though Elektron fairings are to be found at certain points on the leading edge, the covering of this portion is mainly of ply. In essentials the trailing edge is of similar construction, though the lower surface is, of course, recessed for the flaps. As at present in production the Albatross has ply-covered wing tips with spruce ribs, but any future machines will have detachable tips.
   At the root the front box spar is 23in. deep, the corresponding measurement for the rear spar being 15 7/8 in. The widths of the front spar at the root and tip are 1 1/4 and 7in. respectively; the rear spar tapers from 5 1/2 in. to 1 1/4 in. Tego-cemented birchwood ply is used for the vertical webs and the flanges are of spruce. In all there are 101 ribs in the wing. They serve as formers to stabilise the top and bottom planking. Square spruce diagonals (15/16in.) join the top and bottom formers. There are eleven spanwise spruce stringers over the greater part of the wing, the number being reduced to io at a point 3.75ft. from the tip.
   The spruce slatting or planking is applied diagonally in two layers at 30 degrees to the spar and is bound with casein glue. At the root the skin is 7/8 in. thick, tapering to about 1/5 in. at the tip. The inner layer is 0.65in. thick and 3in. wide at the root and is laid on in lengths of 12ft.; at about semi-span the thickness is 0.4m. and the width 2 1/2 in. A thin layer of Tego-cemented cedar three-ply forms the final covering. On the top surface the slatting covers one more wing tip bay than on the lower surface.
   A point that should interest operators of over-water services is that the wing is practically sealed, though there are eleven small drain holes for condensation, and inspection holes sealed with plates. Seals are also fitted over the eight lightening holes in the front spar of the centre section.
   To simplify the alignment of bearings the Frise ailerons, which extend for 33 per cent. of the chord, are made in two parts and are sealed by fabric. They are built up of welded steel tube and are mounted on tubular outriggers bolted to the rear spar. The aileron spar itself is com­posed of two tubular booms with vertical and diagonal bracing, and carries no torsion. Bracing ribs are arranged diagonally and are welded to the spar. Balsa wood, shaped to contour, forms the leading edge; the covering of this section is ply.
   Mass balances are provided for the two portions of each aileron, the bob weights working in slots in the underside of the wing and protruding only when the aileron is raised to an extreme angle. A small trimming tab is inserted in the port aileron. De Havilland differential control is specified.
   Stretching, it is claimed, is avoided through the use of duplicated swaged rods over pulleys instead of long lengths of cable; these rods terminate in short cables attached to the pulley of the differential gear inboard of the aileron. Tubular push-pull rods run from the differential to two bell-crank levers, one opposite the centre part of each aileron.
   On the Air Ministry machines split flaps run from beneath the fuselage to the ailerons; the series for Imperial Airways have slotted flaps of the Handley Page type. Balsa wood sandwich construction is used for the first-mentioned, with ply covering and spruce members at front and rear, the trailing edge being faired with a stiff anodised duralumin section, but the H.P. variety have a ply "D"’-section nose, built-up spruce ribs and fabric covering.
   Flap operation is effected by an electric motor installed centrally and driving a screw jack through gearing. The jacks operate a lever from which swaged tie-rods run through the trailing edge of the wing to a number of other operating units. A second lever is bolted at right angles to the levers on the units, these latter being connected by push-pull tubes to the operating arms on the flaps.
   Any setting between fully up and fully down can be selected by the pilot; a small angle is used for take-off. On the inner set of operating levers are two cams which operate electrical switches to cut out the motor when the desired angle has been reached.
   In view of the novelty of the fuselage this component deserves a particularly detailed inspection. The section is circular, offering possibilities for “supercharged” cabins. Briefly, the “lobster claw” shell is composed of a sandwich of balsa (acting as a stabiliser) between two layers of Stress-bearing, double-camber plywood. Construction varies throughout the length of the fuselage.
   According to data supplied by the manufacturers, from the cockpit to the end of the passenger accommodation the outer layer is 2 mm. Port Oxford cedar; then comes 7/8 in. of balsa and the inner cedar ply, 1 1/2 mm. thick. Cedar shows a considerable saving in weight in comparison with birch ply.
   Aft of this section is a four-foot portion with 2 mm. birch outer ply, 7/16 in. balsa, and an inner ply of 1 1/2 mm. Port Oxford cedar. From a point 5ft. before the end of the tail to the extreme end of the fuselage the materials are 3 mm. birch outer ply, 7/16 in. of balsa, and an inner ply of 1 1/2 mm. cedar.
   Balsa, 7/8 in. thick, sandwiched between two layers of cedar, forms the floor, which is about an inch thick and is attached to the main structure by duralumin angle plates.
   An interesting point is that the doors are made integrally with the fuselage shell on the jig, and are subsequently cut out.
   Bulkheads divide the fuselage into a number of sections. The entrance door is on the port side of the machine, opening into a vestibule, to the rear of which is the mail compartment, accessible through a door on the starboard side. A second mail hold is located aft of the cockpit, likewise on the starboard side. The arrangement of the fuselage fuel tanks will be described later.
   Access to the controls, which run beneath the floor, is gained through removable hinged panels in the bottom fairing. Forward of the wheel wells is a watertight compartment through which the controls pass in a duct. Controls in the rear part of the fuselage are inspected through a manhole in the rear bulkhead of the aft mail compartment.
   There are twelve cabin windows in the standard passenger-carrying version of the Albatross and four emergency exits in the roof. These are made of Perspex, and are attached by a process developed by Imperial Chemical Industries, Ltd., and the Wilkinson Rubber Co.; so that in an emergency they may be pushed outward, the roof exits being pulled inward. In the mail carrier version there is a special hatch in the roof for taking bearings or for use as an emergency exit.
   Though of the modern twin rudder layout, the tail, with its shapely surfaces, bears the traditional De Havilland stamp. The fins and rudders are mounted at the extreme ends of the tail plane. All hinges are fitted with sealed, dustproof ball races, and trimming tabs are mounted on the rudders and elevators.
   The tail plane structure is in two halves, and consists of two box spars with spruce stiffeners screwed and glued on. The spruce and ply ribs are attached to the stiffeners, and the covering is of ply. Ply covering is also used for the fins, which are of similar construction, with spindled laminated spruce leading edge. Alclad is employed for the rudder hinge fitting. This material is used also for the elevators, which have a spar of “D” section to which are attached the Alclad ribs. Forward of the "D" section are lightened Alclad diaphragms over which a skin of thin Alclad is wrapped. Mass balancing is incorporated, and fabric covering is employed over the entire surface. Similar construction is used for the rudders, the mass balances of which take the form of lead-filled tubes lying vertically down the length of the leading edge. Wooden trimming tabs with a 20-degree movement in each direction are fitted.
   The wheels of the retractable undercarriage move inwards and forwards into wells forward of the front spar. Fairings with movable flaps operated by flexible drives close the wells when the wheels are up.
   An electric motor of 24 volts and 5.3 average h.p. is used for the retracting operation and there is a detachable handle which may be operated through a hole in the floor in case of electrical failure.
   Welded steel forks, attached to the compression legs, carry Dunlop wheels. A portion of the cabin heating air is sidetracked to avoid freezing up of the undercarriage. The Dowty tail wheel does not retract.
   The electrical system is divided into two 24-volt supplies with no wire connection between the two. Each is fed by two Dagenite 12-volt batteries in series, and charged from a 500-watt engine-driven generator in the two outboard nacelles. In one case the unit is of 45 a.h. capacity and in the other of 70 a.h. This arrangement affords greater safety to the fuel supply, since the four electrically driven diaphragm-type fuel pumps draw their energy in two pairs from each supply and are so connected that failure of one half of the system leaves two pumps to supply all four engines at cruising speed.
   In addition to the fuel pumps the electrical services are divided between the two halves of the supply as follows: Supply 1: Undercarriage retracting motor, with control and indicating circuits; flap operating motor with control and indicator circuits; cabin and cockpit lights; fuel con­tents gauges. Supply 2: Engine starter motors; radio installation; electrically heated pitot head; oil and air temperature indicators; air fuel ratio indicators; landing, navigation and signal lights.

De-Icing

   Dunlop anti-icing equipment is optional and is, in fact, fitted to the two Air Ministry mail carriers. Slinger rings are provided for the airscrews. There is a flask of Ethylene-glycol in the pilot’s cockpit together with a Dowty hand pump. The liquid is delivered to a hydraulic accumulator and thence to the leading edge of the main planes, the fins, tail plane and airscrew slinger rings. A separate glycol spray is provided for the windscreen.
   The Air Ministry mail carriers have four fuel tanks, each with a capacity of 330 gallons, mounted in the cabin, two on each side of the gangway. These are filled from outside the fuselage and are fitted with Smith’s electrical fuel gauges registering in the cockpit. Welded aluminium construction is used and cable-operated jettison valves are incorporated, allowing the fuel to be dumped by way of large aluminium pipes through the belly of the rear fuselage.
   A different arrangement is specified for the passenger-carrying version. Here there are two tanks beneath the floor, the one forward of the wing holding 270 gallons, while the rear one holds a hundred gallons less. Between the tanks and fuel pumps there are Amal filters. Four pipes, each controlled from the cockpit by Teleflex-operated cocks, run from the pumps to the individual nacelles where the petrol again passes through filters attached to the fire-proof bulkheads. From these filters the petrol runs through a Superflexit pipe to the carburetters.
   Both versions of the Albatross incorporate a gallery type of fuel system whereby one tank will supply sufficient fuel for all four engines. A separately ventilated compartment behind the rear spar prevents the spread of petrol fumes in the passenger-carrying type.
   On the mail carrier the oil tanks are installed in each nacelle, two interconnected tanks being fitted for each engine. Oil is drawn from the tank sump by the engine pump, passing through a thermometer pocket and returning to the tanks through Gallay coolers.
   A particularly interesting feature about the oil system is that something like four gallons is isolated by a baffle in the front tank and is circulated initially for quick warming-up. In each case the tank vent is connected to the oil sump on the engine to prevent oil being thrown out and fouling the exterior of the aircraft.
   The passenger-carrying Albatross has only one oil tank (9 gallons) per engine.
   The power plant consists of four Gipsy Twelve air-cooled geared and supercharged inverted-vee engines operating on 87-octane fuel and driving two-bladed De Havilland constant-speed airscrews (10ft. 6in. diameter) at 0.66 times engine speed. These units are installed in Elektron cowlings and are cooled by a specially developed system described in some detail in Flight of March 31. Briefly, the cooling air enters orifices in the leading edge of the wing, whence it is conducted to the outside of the cylinder banks. After passing between the cylinders the air is exhausted on the underside of the needle. At the mouth of the exit is a flap operated by a self-contained hydraulic unit controlled from the cockpit. This is kept fully down for take-off and climb but is closed under normal cruising conditions, leaving a small gap for exhausting the air.
   Hot and cold air intakes, adjustable from the cockpit, are provided for the carburetters, which incorporate oil-heated butterfly valves.
   On each outboard engine is a 24-volt, 500-watt generator running at double engine speed and cooled by an air duct. Each outboard unit also carries an Eclipse vacuum pump for operating the automatic pilot and blind-flying instruments. The starboard inner engine has a B.T.H. air compressor for the brakes and a Northern oil pump supply­ing high-pressure oil for the automatic pilot and engine cooling flaps. No accessories are fitted on the inner port engine.
   Data for the Gipsy Twelve are: Take-off power 530 h.p. at 2,600 r.p.m. and + 3 1/2 Ib./sq. in. boost at sea level; max. power for level flight 432 h.p. at 2,450 r.p.m. and 8,100ft.; max. power for climb 425 h.p. at 2,400 r.p.m. and 6,750ft.; max. cruising power 550 h.p. at - 3/4 Ib./sq. in. boost and 8,200ft.; economical cruising power 320 h.p. at 2,200 r.p.m. and -2 Ib./sq. in. boost at 11,200ft.
   Tests were made in the early design stages of the Albatross to provide good alighting qualities on the water with undercarriage retracted. The mailplane, of course, benefits from the buoyancy of its big tanks.

The Operational Side

   Year by year, as the standard of service efficiency improves, the operational equipment of transport aeroplanes becomes steadily more interesting. Since it is the latest of the fast large-size transport machines to be produced in this country, the Albatross might be expected to incorporate navigational equipment which may be considered as the last word as far as ideas over here are concerned.
   As already explained, two types are being produced, one to the order of the Air Ministry for Atlantic experiments, and the other for use on the European services of Imperial Airways; or, perhaps (and eventually), of British Airways. The equipment in the two types is, however, very similar, and many of the slight differences to be seen in the first of the machines for Imperial Airways are those which have been made as a result of test-flying experience with the first Atlantic model. Additionally, the control cabin incorporates certain minor modifications which the operating staff of Imperial Airways have demanded.
   Naturally enough, there is nowadays a tendency, at least in a general way, towards the standardisation of essential controls. In the Albatross the major engine and incidental flying controls are arranged in a central bank. Virtually, this control bank may be considered as extending from the dashboard proper, with the Sperry automatic pilot as the central theme, to the floor of the control cabin. Below the dash, and on the tray which carries such items as switch gear, are the undercarriage and flap switches with their appropriate indicators. The indicator for the former consists of a red and green warning light device covering a sufficiently large area and being bright enough to defy forgetfulness. The flap indicator is of the simple mechanical type which shows the actual position of the flaps as they are being raised or lowered.
   The simple two-way switch governing the flap motor may be moved to the “off” position at any time while the flaps are being raised or lowered and the position of these flaps thereafter remains unaltered. Consequently, it is an easy matter to adjust their positions on the indicator either for take-off, in which approximately fifteen degrees are used, or during an approach in a strong wind when the flaps would naturally not be lowered to their fullest extent. Actually, the D.H. test pilots have found that in almost all conditions an angle of 45-60 deg. is most suitable for approach purposes.
   These figures apply, of course, to the split flaps which are fitted to the Air Ministry machines. Those for Imperial Airways have Handley Page slotted flaps, and the tests, in the case of the Albatross, have been satisfactory. The idea behind the use of these slotted flaps is simply that of improving the take-off - more lift and less drag.
   Below these controls is the throttle gate, with the four throttle levers on the left, the constant-speed airscrew controls matching them on the right, and the lever for adjusting the angle of the landing lights in the centre; this last lever is, of course, longer than the others and could not in any case be used in error. On either side of the throttle gate are the two pairs of mixture controls. In the case of the machines for Imperial Airways this engine control arrangement is slightly different. Here the four throttles are on the left and the airscrew controls are on the right as before, but the mixture controls are immediately behind and below the throttles and are arranged, as usual, so that the closing of the throttles automatically pulls them back to the full rich position. Outside the gate are the landing light and automatic pilot cut-out controls.
   At the base of the control bank is a panel carrying the two cranks for operating the rudder and aileron bias gears, as well as the fore-and-aft trim indicator, which is also of the simple mechanical type. The trimming crank itself is on the right-hand side of the first pilot’s seat in the case of the Atlantic machine, but the more normal wheel, arranged on the port side of the control bank, is used in the Imperial Airways type.
   The main fuel cocks are immediately behind the second pilot's seat and on his right are the engine-cooling controls. In the case of the Atlantic machine, which is fitted with Dunlop Anticers on the leading edges of the wing, the tailplane and the fins, as well as controllable slinger ring arrangements for the airscrews, the second pilot must also look after the controls and the hand pump for this equipment, which includes pressure gauges for each of the items.

Control Incidentals

   From the pilot’s point of view the Bendix braking system is extremely simple. In the centre of the control spectacle is a long lever which, when moved over to the right, frees the entire braking system and, when moved to the left, is "at the ready." In this position the differential arrangement is in action through the rudder pedals, and braking is then effected merely by light pressure with the left thumb. For parking purposes the lever is pressed down to its fullest extent and locked in that position by means of a little pin at the head of the column.
   Above the screen are the ignition and starter switches for the engine, the necessary temperature and pressure gauges, the homing indicator, and the Graviner automatic fire-extinguisher controls and indicators.
   The pilot's compass is mounted in the shallow tray below the dashboard proper, and on this tray also is the vacuum switch for the choice of gyro instrument drive, as well as the lighting switch panel and pitot-head heater switch. In front of the first pilot is a typical blind-flying instrument group with the A.S.I. and sensitive altimeter on the left, the artificial horizon and directional gyro in the centre, and the rate-of-climb indicator and turn indicator on the right. To the left of this group is the Telefunken blind-approach indicator. On the right of the Sperry automatic pilot panel - that is, facing the second pilot - are the boost gauges, with an additional A.S.I. and sensitive altimeter, while the fuel gauges are below on the tray and the vertical reading r.p.m. indicators in a box between the second pilot’s legs. It is interesting to see on the Albatross that the fullest possible information concerning take-off, climbing and cruising boost pressures, revolutions and optimum cylinder-head temperatures are clearly given on a panel at the side of the control cabin.
   Following its use on the Empire boat series, the appearance of the now well-know Sperry automatic pilot equipment on the Albatross is not surprising. As is customary, the control panel is mounted in the centre of the dashboard so that it can be reached and seen from either seat, and it is worth remembering that in case of emergency, and quite apart from the cut-out control, this pilot can be over-ridden on the normal flying controls.
   The Atlantic Albatross carries self-contained Marconi radio equipment which is in every way similar to that fitted as standard on the Empire boats. This equipment comprises both long- and short-wave transmitters and receivers, with a D/F loop which can be used on either waveband and can be fixed athwartships for homing purposes. This equipment, with the operator's seat and table, is arranged immediately behind the first pilot’s seat, while farther aft, behind the next bulkhead, is the auxiliary engine and dyna-motor. The latter, it may be remembered, is used first to start the engine and then as a generator; in cases of real emergency, when the batteries are so drained that the engines cannot be started by this means, a handle can be used. Still farther aft on the portside is the navigator’s table. A hatch has been arranged in the roof for sextant work, but at a cruising speed of more than 200 miles an hour it is probable that the navigator will prefer to take his sights through the specially designed windows at the rear of the fuselage. These windows may be opened, and a special draught deflector is mounted for use with each. The machine also has the new Marconi ultra-short-wave beacon receiver.
   Two of the Imperial Airways machines will have normal two-way radio and D/F equipment manufactured by Radio Transmission Equipment, as well as an ultra-short wave receiver and indicator from the same firm.
   From the conversation of those who have handled the Albatross it would seem that this machine flies very nicely indeed and is so completely stable in all axes that the technical people who carried out the tests with the automatic pilot when this was first installed experienced some difficulty in doing their job. Naturally enough, such stability must necessarily be paid for in the slightly greater effort needed to turn the machine from its natural course. Correctly trimmed, the machine flies itself off the ground at any loading, and it seems that there is little or no tendency to swing even in the early stages of the take-off. We are accustomed nowadays to machines which turn correctly on ailerons alone, but there is a tendency for the present-day type to be over-stable directionally; the Albatross (with, of course, due trimming) will turn on either the ailerons or the rudder.


DE HAVILLAND ALBATROSS
Four-engined Civil Transport

Dimensions and Areas.
   Span 105ft.
   Root chord 15ft. 7.1 in.
   Tip chord 6ft. 7.9in.
   Length (tail up) 71ft. 6in.
   Height ... 22ft 3in.
   Wing area 1.078 sq. ft.
   Track 17ft.
Loadings (on 29,500 lb.)
   Power loading (take-off) 13.9 Ib./h.p.
   Wing loading 27.4 Ib./sq. ft.
Weights.
Passenger Carrier. Mail Carrier.
   Tare weight 21,230 lbs. 20,800 lbs.
   Gross weight 29,500 lbs. 32,500 lbs.
Performance.
   Top speed at 8,750ft. 225 m-p.h. 222 m.p.h.
   Max. economical cruising speed at 11,000ft. 210 m.p.h. 204 m.p.h.
   Range 1,041 miles 3,300 miles
   Take-off ran (5 m.p.h. wind) 385yd. 548yd.
   Rate of climb at sea level (climb power) 710ft./min. 550ft./min.
   Climb to 10,000ft 15min. 19min.
   Service ceiling (climb power) 17,900ft 15,100ft
   Absolute ceiling with one outboard engine stopped (climb power) 14,100ft. 11,900ft.