1. Design Origins:
Transition periods sometimes prompt transition solutions. During the 1950s, the piston airliner, in the form of the Douglas DC-6 and DC-7 and the Lockheed L-649/749 and -1040 Constellations, were moving toward their technological peaks, yet the pure-jet engine, other than that powering the ill-fated de Havilland DH.106 Comet I and emerging military aircraft, had yet to reach commercial aviation maturity. The compromise, at least in terms of speed, seemed to be the turboprop engine, which combined elements of both and had already been introduced by the Vickers Viscount in the UK.
It was during this period-specifically 1954-that American Airlines, supported by interest from Eastern, submitted design specifications for what it considered a new class of airliner. Those included a greater than 400-mph cruise speed, profitable operations on sectors ranging from 100 to 2,700 miles, a passenger capacity of at least 65, and the type of short-field performance that would enable it to serve all of the country’s 100 major airports.
In short, it sought greater speed, comfort, and economy than that offered by the current generation of quad-engine piston transports, but that could operate multi-sector flights without requiring enroute refueling and attain profitability with load factors as low as 50 percent.
“American and Eastern had demanded a plane equally adept at short- and long-haul operations,” according to Robert J. Serling in “The Electra Story: Aviation’s Greatest Mystery” (Bantam Books, 1963, p. 15). “This was mostly achieved by the thirteen-and-a-half-foot props, which swept their mighty air stream over all but nine feet of the wing area.”
Toward that end, Lockheed elected to employ the same C-130 Hercules design team and Allison T-56 engines that powered the type, creating the US’s first turboprop-powered airliner, the L-188.
“Lockheed opened America’s commercial jet era by hanging a propeller on the jet engine,” according to Jim Upton in “Lockheed L-188 Electra” (Specialty Press Publishers and Wholesalers, 1999, p. 7). “Research left Lockheed convinced that, while jets without propellers (would be) excellent on long-range fights, airlines would be better served by having an effective vehicle for segments which historically showed little or no profit-(that is), short to medium routes.”
The aircraft was almost the product of an equation which read: “Jet power + propeller efficiency = proper performance and economy.”
Aside from its design team and powerplant, it also shared another aspect of the manufacturer’s lineage: its name. Ensuring that its products would bear the designation of a star, as had occurred during the 1920s and 1930s with names such as “Orion,” “Vega,” “Sirius,” and “Altair,” it would borrow the nomenclature of its twin piston engine L-10 Electra, L-12 Electra Junior, and L-14 Super Electra.
Eastern and American respectively placed orders for 40 and 35 L-188 second generation Electras in 1955.
2. Design Features:
“(The Lockheed L-188 Electra) has a purposeful and powerful profile,” according to veteran American Airlines Captain Arthur Weidman, who had flown DC-3s, Convairliners, DC-6s, and DC-7s. “The nose slopes downward sharply to provide good forward visibility on the ground and in the air. Then, her lines go straight back along a perfectly cylindrical fuselage to give her a wider cross section than the DC-7… There is a graceful upsweep to its dorsal fin and rudder, effecting a sleek, trim, streamlined look. Slender nacelles jut forward like giant probes, offering a minimum of frontal resistance.”
With a 104.6-foot-long and 11.4-foot-diameter fuselage, the Electra featured large, square passenger windows.
One of the keys to its design was its wing. Appearing proportionately too short in span for the aircraft it supported, mounted with considerable dihedral, and sporting square tips, it was only 5.5 feet shorter than the fuselage itself, at 99 feet in length, and offered both a low-drag and -aspect ratio. Its trailing edge flaps ran from the fuselage root to the ailerons, or just beyond the outer engines’ exhaust nozzles, and almost 80 percent of its span was subjected to lift-generating prop wash, facilitating low-speed handling.
Power was provided by four 3,750-eshp (equivalent shaft horse power) Allison 501-D13 turboprops, which turned 13.6-foot-diameter, single-rotation, hydraulically-controlled, constant-speed, reversible pitch, four-bladed propellers. Compared to the pure-jet engine, the prop jet featured reduction gear that drove both the propeller and additional gas turbine section stages, resulting in a 90:10 thrust production ratio, or 90 percent created by the propeller and ten percent by the exhaust gases.
The ailerons, elevator, and rudder were operated by push-pull, tube-linked hydraulic booster units, while engine compressor bleed air provided anti-icing of all control surfaces.
The aircraft’s 5,520-US gallon fuel capacity was stored in four wing integral tanks, divided into the two, 1,100-gallon inboard and two 1,660-gallon outboard ones. In-flight fuel cross-feeding was only necessary on long-range sectors exceeding 1,800 miles.
The L-188 rested on a twin-wheeled, hydraulically actuated, forward-retracting tricycle undercarriage, which had the provision for gravity free-fall extension in the event of either hydraulic or electrical system failures.
Integral, fuselage extendable air stairs, along with other self-contained features and its low-to-ground, support san po kong coworking space equipment-independent position, facilitated turn-arounds at transit stations where fueling was not required in as little as 12 minutes.
The Electra was standardly flown by a three-person cockpit crew, with a duplicate throttle quadrant on the captain’s and first officer’s sides and the flight engineer’s station behind both in the center on domestic routes, while a fourth crew member, the navigator, was employed on international ones and positioned on the aft, left side, occupying the location of the otherwise observer’s eat.
Although passenger cabin configurations and densities varied according to the operator, Lockheed initially offered several options, facilitated by the installation of seat tracks. Either 66 four-abreast, 20-inch-wide seats at a 38-inch pitch with a 26-inch aisle or 85 five-abreast, 18-inch-wide ones with a 17-inch aisle could be installed, both of which also featured a six-place, tail-located lounge arranged in a semi-circular configuration. Installation of aft, as well as the standard mid, lavatory reduced the capacity to 83, while the maximum was 99 five-abreast in 20 rows. Alternatively, 127 passengers in a six-abreast, 32-inch pitch configuration was available, but required structural modifications and additional exits to meet evacuation criteria.
A maximum, 6.55-psi differential, achieved by two engine-driven superchargers, provided cabin pressurization and temperature was maintained by radiant heating.
Baggage, cargo, and mail were carried in two underfloor, starboard door-accessed holds.
Featuring a 113,000-pound maximum takeoff weight, the initial, domestic L-188A version had a 2,200-mile range and attained a 373-mph cruise and 448-mph maximum speed.
“There were… two basic versions, the L-188A for US domestic operation, with a fuel capacity of 5,520 US gallons, and the L-188C with 900 US gallons more fuel and a higher gross weight of 116,000 pounds… ,” according to Michael Hardy in World Civil Aircraft since 1945 (Charles Scribner’s Sons 1979, p. 93).
Its range was 3,500 miles.
3. Test Flights:
Piloted by Captain Herman “Fish” Salmon, First Officer Roy Wimmer, Flight Engineer Laurie Hallard, and Flight Test Engineer Bill Spreurer, the L-188 Electra made its inaugural flight from the Lockheed Air Terminal in Burbank, California, on December 6, 1957, after which Spreurer commented, “The smoothness and quietness of the aircraft (were immediately apparent). The vibration level was very low and the engines were so quiet that you could hear the chase aircraft.”
After a four-airplane, 655-hour flight test program, the type was certified on August 12, 1958, five weeks ahead of schedule, permitting first delivery of aircraft 1007 to launch customer Eastern Airlines two months later, on October 8.