Flight, July 1933

THE LOCKHEED "ELECTRA”

   A SHORT while back the Lockheed factory decided to discontinue building a large, single-motored, all-metal monoplane then in hand, and concentrate on a small, twin-engined machine. The result is the "Electra." This is a low-wing monoplane designed to combine speed and comfort with low cost and maintenance. It is all metal, the wings being of semi-stress skin type construction, readily accessible and repairable. For the structural parts 24 ST is used throughout, the covering being 24 ST Alclad. Detachable wing panels facilitating inspection and maintenance.
   The cabin measures 4 ft. 10 in. wide, 5 ft. high, and 15 ft. long; it is well ventilated, comfortable, and soundproof. Excellent vision is possible from the pilot's cockpit, which is situated forward. Conventional wheel controls are used, and complete instrument equipment, including Sperry Directional Gyro and Sperry Artificial Horizon, are fitted. The engines, in streamlined nacelles, are built into the wings close to the fuselage. The fuel tanks, of 100 gallons capacity each, are built into the entering edge of the wing stub between the engines and the fuselage.
   Simple wing flaps are incorporated which reduce take-off and landing speed. Horizontal and directional balance is accomplished with adjustable flaps at the trailing edge of the rudder and elevator. A retractable landing gear is operated electrically and has an auxiliary emergency hand-operated system. The wheels swing directly back into the rear of the nacelle and arc completely faired in when in the retracted position. The retraction system used permits a variable fore and aft location of the wheels in extended position, so that the machine may more suitably be balanced on the ground with variable loading conditions. Goodyear air wheels are used with Goodyear hydraulic brakes controlled by a hand lever conveniently located and differentially connected to the rudder pedals.
   It is claimed that this machine will cruise at 180 m.p.h. with 2,200 lb. of payload. The two engines develop together 840 h.p.

Flight, January 1934

The Lockheed "Electra"
The latest Lockheed product which cruises at 180 m.p.h. with a 2,200 lb. pay load

   THE Lockheed "Electra" is an all-metal low-wing monoplane of comparatively small overall dimensions and low power, but possessing a remarkable performance as the result of clean aerodynamic design.
   The all-metal wings are of full cantilever construction, the centre section being built integral with the fuselage. To facilitate the replacement of damaged wings, the outer sections are detachable from a point just outside of the nacelles. The surface is smooth skin throughout, and rivets are made flush over part of the upper surface where they would offer resistance. The construction is of the "stressed skin" type, with heavy corrugations under the skin, making it possible for a person to walk down the centre portion of the wing without causing damage. The skin over the centre section and part of the outer wings is of heavy-gauge duralumin of the latest type manufactured by the Aluminium Company, namely, 24 S.T. All outer skin is Alclad 24 S.T., which has remarkable corrosion-resisting properties. The interior of the wings and centre section are carefully cleaned and coated with Lionoil. The centre section, which contains the nacelles, fuel tanks and cargo compartments, is cut away at the fuselage, which is placed partly within the wing, giving the aircraft a very small frontal area. The ailerons are in the conventional positions at the trailing edge and tip. Inboard of the ailerons are the wing flaps, which extend through under the fuselage. These flaps give an increase in lift of approximately 25 per cent, and a large increase in drag. Although a reduction in the load factors for multi-engined transports has been allowed by the Department of Commerce, this has not been used in the wings of the "Electra." In fact, the whole machine has been designed to single-engine factors.
   The monocoque fuselage is constructed entirely of 24 S.T. duralumin. A smooth skin of Alclad 24 S.T. is used throughout. This skin is reinforced and held in place at frequent intervals by channel bulkheads and longitudinal stringers. The skin over the passenger cabin is 0.032 in. thick. Special attention has been given to the tail of the fuselage to give rigid support to the cantilever empennage and tail wheel. Seating accommodation is provided for ten passengers, but fewer passengers and a correspondingly larger baggage or mail load may be carried. A lavatory is situated at the rear of the cabin.
   The tail plane and elevator rest on top of the fuselage in which position the maximum protection is afforded from flying stones. Forward of the pilot's cabin is a baggage compartment of 40 cu. ft. capacity, reinforced so that the baggage will not injure the outer skin of the fuselage. A removable tail fairing forms the end of the fuselage and houses the tail wheel. Easy access is given to all moving parts of the empennage.
   The engine nacelles are located directly ahead of the leading edge of the wing. According to tests conducted by the N.A.C.A., this arrangement gives the lowest drag and the maximum lift. Wind tunnel tests with the "Electra," with and without nacelles, proved that the lift was the same in each case. The nacelle structure and engine mountings are of steel tubes. Numerous large holes are provided for inspection. The nacelle not only supports the engines but also the landing gear and retracting mechanism.
   The tail surfaces are cantilever metal structures with smooth skin covering. Fin and tail plane are not adjustable but are bolted direct to the fuselage. The rudder and elevator, both of which are adjustable from the cockpit, are fitted with "tabs." The word "tab" has been approved by the Department of Commerce as the name for auxiliary control flaps. In place of the usual type aerodynamic balance for ease of control, the rudder and elevator loads are lightened by making the tab act not only as a Servo but as a trimming device. The control surfaces have removable tips which may be replaced in case of damage. To eliminate any possibility of flutter the elevators are statically balanced.
   The wheels of the retractable landing gear are located directly under the engine nacelles into which they retract by swinging back and up. When the wheels are retracted a small portion of the tyre is left exposed in case of a forced landing. The landing gear is electrically operated by means of gears and torque shafts. One motor operates both wheels. The operation is automatic in that when the switch in the cockpit is operated for retracting the gear, the gear rises, and when up, the motor stops without further action by the pilot. Auxiliary hand mechanism is provided to raise and lower the gear in case of failure in the electrical system. The Goodyear air wheels are fitted with hydraulically-operated brakes, which may be applied with the landing gear either up or down. The Aerol shock-absorber struts have a stroke of 6 in. An Aerol strut, also with a 6-in. stroke, is provided for the tail wheel.
   Soundproofing of the cabin has been carried out under the direction of the Western Electric Company, and 1 3/4 in. of space has been allowed all the way round the cabin. The doors are heavily soundproofed and are of the same thickness as the cabin walls. Special latches hold the doors tightly shut at all times, allowing almost no sound leakage. An efficient ventilating system combined with a thermostatic heat control maintains correct cabin temperature and assures proper fresh-air conditions.
   Complete dual controls are fitted and are so designed that the set on the right-hand side may be disconnected if desired. The control columns are not in the centre of the seat, but to the side as far as possible. This arrangement permits the pilots to leave and return to their seats while in flight with little inconvenience. The rudder bar is adjustable to suit pilots of various heights. All control surfaces are operated by steel cables at points of adjustment to the control column and control surfaces. The cranks are made as arcs of circles, thereby eliminating the possibility of tension or slackness eliminating possible source of surface flutter. The differential ailerons have a down movement of only 4 deg., while the upward movement is 25 deg.
   Complete two-way Western Electric radio is installed in the passenger cabin under the two front seats. These seats are located just at the head of the spar and are hinged to it. The hinges allow the seats to be raised up and laid back, permitting easy access to the radio for inspection or repair. Controls for the radio are mounted on a separate instrument board located below the main board. All wiring throughout the machine is placed in aluminium conduits with metal junction boxes entirely eliminating the possibility of fire from the electrical wiring system.
   Two fuel tanks are carried, located one in the leading edge of each wing between the engine nacelle and the fuselage. For rapid filling the tanks are furnished with large filler necks 3 in. in diameter, which are surrounded by gastight metal cylinders permitting no fuel to spill into the wing when the tanks are overflowing. The tank compartment in the wing is drained and ventilated to prevent any accumulation of fuel or fumes in case of fuel leakage, and both tanks may be withdrawn from the aircraft with little inconvenience. There are two oil tanks, one for each engine, located in each nacelle just ahead of the fireproof bulkhead.
   The two "Wasp Junior" engines (420 h.p. at 2,200 r.p.m. at 5,000 ft.) are bolted to welded steel tube mountings which are fitted with shock-absorber units of the Lord type. A Pratt & Whitney oil regulator and heater assembly eliminates the usual type oil radiator. The engine controls from the pilot's cockpit are of the Arens push-pull type. N.A.C.A. cowlings and small inner cowls are provided for the engines. The leading edge of the outer cowl is in one piece and is not readily removable, making a rigid support for the entire outer cowling. All the cowling aft of this nose piece is quickly removable. The nose piece has been placed far enough ahead of the rocker boxes to permit inspection and adjustment of valves and rocker arms. Both fuel and oil pumps are made from the Aluminium Company's latest type 4 S.O aluminium with Parker duralumin fittings.

Flight, April 1937

SIMPLEXITY ITSELF
Some Cockpit Impressions of the Lockheed Electra: Special Equipment for British Airways: Complexity Simplified
By H. A. TAYLOR

   TWO general impressions are current at the present time in the matter of the modern transport aeroplane and the trend of its development. The first is that we are rapidly arriving at the stage when two pilots will have more on their hands than they can possibly cope with; the greater the operational efficiency to be demanded, the greater is the mass of equipment to be carried. The second is that high speeds leave a very small margin for possible error in such things as E.T.A. estimations with a low ceiling and in navigational calculations generally. Parenthetically, it is also suggested that the high-speed machine is a "handful" - requiring constant and undivided attention.
   Such impressions, either mine or other people's, were at the back of my mind when British Airways provided the chance of making a reasonably extended flight in the control cabin of one of their new Lockheed Electras. Mr. Lynch-Blosse, the commodore of the company, was there to show me how everything worked, and Mr. Roode, who was getting his hand in with the new equipment, was there to show - incidentally, and without intention - how the experienced newcomer reacted to the new and extensive gadgetry to be found in these machines.
   After a period of forty minutes in the second pilot's seat I felt that I could remember the whereabouts and purposes of all the controls, dials and indicators, and that any normally experienced transport pilot would be able to go through the various movements with subconscious ease after an hour or two of practice, leaving his thinking mind free to deal with the various D/F and D/R problems which are met in the ordinary course of all-weather transport flying. So much for the "complications."
   Twenty minutes of personal experience and demonstration convinced me that this high-speed aeroplane was a good deal easier to fly and more foolproof - as a flying machine - than the average light aeroplane. There are simply more things to look after. Once the Electra has settled down to cruise she flies by herself and will turn accurately on the ailerons alone. These are pleasantly light and smooth at all speeds - and they continue to work at or near the stall. Normal trimming requires only a turn or so of a handle mounted in the roof.
   With the flaps down and the engines throttled back the glide is as steep as anyone could wish - so steep, in fact, that it is preferable to motor right down to the ground if the feelings of the passengers are to be spared. Furthermore, the normal approach is carried out at a speed very little in excess of an indicated 100 km./hr. (62 m.p.h.), and the machine is comfortably under control at speeds very much lower than this. The stall itself appears to be so innocuous that a slow approach is more than safe, it is normal.
   All the operations necessary in preparation for the approach require the minimum of effort. Both the flap and undercarriage gear are electrically operated and each completes its work in a few seconds The flaps can be left in any position at will, and, in addition to the warning light on the dash, a hooter goes off in no uncertain manner if the engines are throttled back with the undercarriage still up.
   Leaving Southampton Airport in fairly poor visibility, we flew along the south coast in a gradual climb, until, by the time we had reached Brighton, we were at full operating height - a matter of 9,500 ft. Thence the machine was put into a power glide towards Gatwick, which was reached at a height of 2,000 ft. or so. Consequently it was possible to make a study of engine-handling technique with constant-speed airscrews and so forth.
   The throttle bank on the Electra carries, in addition to the two throttles, the c.s. airscrew governor regulators on the left and the mixture controls on the right. Below are gated levers for the carburettor heater controls, the undercarriage control (in bright scarlet) and the flap control. Very briefly, the engine revolutions are set by means of the pitch regulators, the manifold pressures are kept within reasonable limits by means of the throttles, and the mixture controls are moved in accordance with the readings shown on the Cambridge exhaust gas analyser. This, by registering the electrical resistance changes in a platinum wire stretched across the exhaust outlet, indicates the amount of carbon monoxide in the gases, and, consequently the efficiency of combustion - or the state of the mixture itself. In this country the Hobson automatic mixture control has been developed to save the pilot the trouble of regulating his mixture, and is being extensively used. In any case, however, a mixture indicator provides a useful guide for accurate setting when operations are being carried out at heights varying between zero and 15,000 ft.
   For those who are not familiar with the operation of the Hamilton or D.H. constant-speed airscrew - which necessitates the use of such a control or indicator - it should be explained that, once the revolutions have been set by the pitch regulators, the airscrew governors automatically change the pitch within certain limits, keeping the revolutions constant. In other words, the c.s. airscrew permits an engine to operate quite automatically, and all the time, at its most efficient speed for different heights and conditions. A dangerously lean or expensively rich mixture will not therefore be shown by any falling-off in the indicated revolutions, such as is normally the case with c.p. or two-position v.p. airscrews. A slight loss of speed, or, more likely, of height, would provide the only indication of trouble, and by the time such a change had been noticed the pistons might be irrevocably damaged.
   Only in the maximum “high” position of the regulators, when the airscrews are locked in coarse pitch for optimum altitude cruising, will the revolution counters tell their tale of any impending woe. In this case, the counters and the analyser are used together to obtain the most economical setting of the throttles and mixture controls for any speed which it is necessary to maintain in order to fly to schedule on a regular service. At 2,000 r.p.m. and 9,600 ft. the Electra cruises at 195 m.p.h., and at this speed the engines are giving about 300 b.h.p. each. Incidentally, it is perhaps a good moment to remind those who look upon the Electra as an uneconomic proposition that it carries ten passengers, a crew of two and the usual baggage for 700 miles at this speed - and the maximum total horse-power is not excessive at 900
   During the take-off the pitch regulators are, of course, placed fully forward in the fine-pitch position, the mixture levers are in the full-rich position and the throttles are opened just far enough to maintain the reading of the manifold pressure gauges below the danger sector - which starts at a figure equal to 90 cm. of mercury, or about + 3 lb. /sq. in. at ground level. Full throttle at ground level can be used for a few seconds in case of emergency.
   Two other instruments and the appropriate controls must also be watched when operations are being carried out over a wide range of throttle positions and outside temperatures. These are the carburettor temperature gauges and heater controls. During a prolonged descent on small throttle openings, such as is normal nowadays, the carburettors might get so cold that either ice would be formed or the engines would not give their maximum power just when it was most needed.

Special Instruments

   It would be impossible to describe all the instruments and controls which are to be found on the Electra, but a few of the more important and interesting ones may be dealt with. Needless to say, the navigational equipment is just about as complete as could be imagined. Apart from the radio equipment, which will be dealt with later, there are two compasses, one of the direct-reading bowl type and the other of the verge-ring type, Sperry horizon and gyro, a turn indicator, a Kollsman sensitive altimeter and a rate-of-climb indicator. Engine-driven vacuum pumps provide the power for the gyros, and the pitot head is electrically heated. A tray in front of the chief pilot carries all the essential electrical switches and fuses, and spares can be fitted in a moment when necessary. This tray also carries the Goodrich de-icer "volume" control, though the main control for this lies below the starboard seat. This de-icer works on the pneumatic pulsation principle, breaking away the accretions. Beside the first pilot's seat are the emergency hand control for the undercarriage, the fuel dump valves (in scarlet) and a master switch for the entire electrical equipment of the machine.
   One of the most interesting features of the Electras, as they are being fitted out for British Airways, concerns the radio equipment, which consists of Marconi transmitters, receivers and D/F or homing equipment, and a Lorenz ultra-short-wave approach system installed by Standard Radio.

Radio Equipment

   Each machine has a Marconi remote control panel placed on a tray in front of the second pilot, with a tapping key on his right, while the main equipment, with controls and key, is on the starboard side of the passenger cabin behind. The result is that any one of the fleet may be placed, without alteration and consequent delay, either on an easy daylight service where the second pilot's seat is taken by the radio operator, or on more difficult services when two pilots are carried in addition to a radio operator, who will then carry out his work in the passenger cabin.
   Furthermore, the D/F loop aerial receiver also has a remote control both for operation and tuning, so that it may be used either by the radio operator, wherever he may be placed, or by the pilots. The loop itself is mounted below the fuselage, and the control cabin panel is so placed in the roof that it may be reached from either seat. The bearing dial for this is coloured in red and green sectors so that the operator may, if required, read the bearings straight off to the pilot as so many degrees “to port” or "to starboard." For homing purposes the loop can also be fixed and the appropriate indicator is, of course, on the first pilot's dashboard. Power for the entire equipment is obtained from a rotary transformer driven by the battery - which certainly has a good deal to do on this machine; the "All-Electric Electra" would be a good name for it.
   With such equipment the Electra should be almost entirely self-contained from the navigational point of view, and only routine messages need be transmitted when the air is congested. For some time it has been the practice on several Continental routes for the crew of the machines to obtain both bearings and fixes for themselves. Only so can the present radio troubles be satisfactorily solved and the air left free for messages of real urgency.