John Knudsen Northrop, aka “Jack” Northrop, doesn’t need an introduction, and I have fond memories of the first time seeing his XB-35 flying wing on the cover of an old magazine that my father had been reading the night before. I must have been five or six at the time, and that single image still has lasting impressions for me to this day. I’ve always know Northrop’s involvement with military aircraft, but never seemed interested or paid much attention to his past or previous designs. Because I found the XB-35 so fascinating, I never gave it much thought about the career path that this legendary man had taken in creating an array of distinguishing aircraft.
In the above news clipping dated January 1933 by my father, a Northrop Delta illustrates the future sixteen-hour coast-to-coast schedules for TWA’s passenger transport with a delivery date of March 1 of fifteen aircraft. The Delta can carry eight passengers and 1,000 pounds of freight at 187 mph, as stated above and powered by a 700 hp Wright engine. These details seem vague to me, and I thought a thorough investigation of the Northrop Delta is necessary.
The Northrop Delta came about from the partnership of Jack Northrop and his good friend Donald Douglas of the Douglas Aircraft Corporation. Douglas hired Northrop in 1923 to design the fuel tanks for the Douglas World Cruiser. Their relationship was complicated, and Northrop decided to part ways in 1926 to further expand his career. Northrop left on good terms when he accepted a position as chief engineer with Lockheed Aircraft Company. Shortly after being hired, Northrop began to work on a new project, the Lockheed Vega. On July 4, 1927, the Vega test flight was such a massive success that it created an instant backlog of orders. Every pilot wanted a Vega, and many set new records that Lockheed advertised the slogan “It Takes a Lockheed to Beat a Lockheed.”
Even though Northrop was ecstatic with the Vega’s performance and worldwide acceptance, he knows the future of aviation lies within all-metal construction, making the wooden airframes obsolete. Northrop decides to leave Lockheed on June 28, 1928, to form the Avion Corporation, where he can work on new commercial aircraft designs using his new all-metal stressed-skin construction. He developed and built his first flying wing, the Avion Experimental No. 1, unveiling it in 1929. Northrop’s new “multi-spar” wing construction is revolutionary to future aircraft construction where multiple full-length span-wise stiffeners, or shear webs, replaced the traditional wing spars attached directly to the fuselage for structural support. I’ll cover a bit more on his multi-cellular wing construction in a few paragraphs, but let’s continue with the timeline.
On January 1, 1930, Northrop sold his Avion Corporation to William Boeing’s company, the United Aircraft & Transport Corporation, establishing the Northrop Aircraft Corporation. Northrop then turned his attention to designing and building a new commercial aircraft, the low wing Alpha featuring his metal stressed skin technique. The highly polished aluminum skin gleamed in the sunlight, and Northrop was proud of his newly designed aircraft! He always felt that his most significant contribution to aviation technology was his new structural innovation, the stressed skin construction. Northrop often quoted, “As far as the structure is concerned, that which was developed into the Alpha was really the pioneer for every airplane in the sky today.“
The Northrop Alpha is an all-metal six-passenger cabin low wing monoplane powered by a Pratt & Whitney Wasp radial engine rated at 425 hp. The pilot is seated slightly above the passenger cabin in an open cockpit located towards the aircraft’s aft section. The Alpha is the first commercial aircraft to use deicer boots on the leading edges, allowing day or night operations in all weather conditions combined with the state of the art radio navigation equipment. On April 20, 1931, TWA started their coast to coast service with the Alpha on a flight from San Francisco, California, to New York, New York, in just over 23 hours with 13 stops. The Alpha was a great success, and a total of 17 were built, with TWA operating 14 planes.
In September 1931, the Northrop Aircraft Corporation merged with Stearman Aircraft in Wichita, Kansas, due to the Great Depression’s collapsed economy to economize the company. Northrop isn’t happy with the merger and decides to form a new company, vowing not to leave California. He has three people agreeing to stay with him, Walter J. Cerny, Kenneth Jay, and Don Berlin, but he still requires the financial support of his good friend Donald Douglas.
Douglas thought very highly of Northrop’s designs, especially his new “stressed skin construction,” which he thought would be perfect for the D.C. airliners. As a result of their conversations, the two men formed the Northrop Corporation based in Inglewood, California, as a Douglas subsidiary on January 1, 1932.
To help me better understand Northrop’s multi-cellular wing construction, I found a quote in the document 3-22(a-b) 3-22-b: Engineering Department, Douglas Aircraft Co. “Development of the Douglas Transport,” Technical Data Report SW-157A, ca. 1933-34, Folder AD-761184-05, Aircraft Technical Files, National Air & Space Museum, Washington, D.C., as stated;
“In determining the wing construction of the early Douglas machines single, two, three and multi spar designs were considered as well as shell type and multi-cellular designs. After a thorough investigation of all types the Northrop multi-cellular wing construction was finally decided upon. This type of structure consists of a flat skin reinforced by numerous longitudinals and ribs. The bending is taken by the combination of flat skin and full length [longitudinal] stringers. Three main flat [vertical] sheets or ‘webs’ carry the shear loads. Torsion and indirect stress are carried by the skin with frequent ribs preserving the contour and dividing the structure up into a number of small rigid boxes or cells. Since the major loads are carried in the outer surface of the wing as well as in the in the internal structure, an inspection of the exterior gives a ready indication of the structural condition. The unit stresses in the material are low and therefore the deflections are at a minimum giving a maximum in rigidity. This construction has proven to be a happy medium of those considered since it combines practically all of the advantages of each; namely, very small unsupported areas, extreme lightness for its strength and rigidity; also ease of construction, inspection, maintenance and repair.“
Initially, the Northrop Corporation’s main focus was to serve as an experimental and research department for Douglas but soon began to produce aircraft when output capacities exceeded Douglas’s production limitations. Looking to fill the request of a fast cargo mail plane over long distances for the airlines and an aircraft capable of experimental over-weather or high altitude flights with deicing technology, Northrop designed and built the Gamma, an upgraded version of his successful Alpha aircraft. A 710 hp nine-cylinder Wright “Cyclone” radial engine, SR-1820-F3, provides the power for a cruising speed of 215 mph at 7000 ft with a service ceiling 20,000 ft. The pilot’s cockpit retains the original location, aft of the wing’s trailing edge, but features an enclosed sliding canopy that offers an unobstructed view of the 47′ 10″ cantilever wingspan. The front of the large round fuselage has two cargo bays with a total capacity of 1300 lbs, placing the entire payload weight over the center section of the wing. Gross weight is 7350 lbs with a range up to 1700 miles at 40 gallons per hour supplied by the 334-gallon fuel system. The fuselage has an overall length of 31′ 2″ and is 9′ in height.
Production started in 1932, and the first Gamma off the assemble line, the Northrop Gamma 2B Polar Star, went to Lincoln Ellsworth on November 29, 1932, to be shipped to the Ross Sea for the start of his 1934 Antarctica expedition. Northrop produces a total of 61 Gammas through 1937, with 49 sold to the Chinese.
Frank Hawks of the Texas Oil Company purchased the second Gamma, a Northrop Gamma 2A Texaco Sky Chief, and set a record flight on June 2, 1933, from Los Angeles, California to New York, New York in 13 hours, 26 minutes, and 15 seconds.
TWA received their Gamma 2-D for the transport of mail and cargo, and on May 13, 1934, Jack Frye set a new cross-country record for transport planes leaving Los Angeles, California, and arriving in Newark, New Jersey in 11 hours and 31 minutes.
While in the middle of the Gammas production, Northrop added the newly designed Delta passenger transport to the assembly line to start production in 1933 at the new plant in El Segundo, California. The prototype, Type 1A, successfully flew in May of the same year, and Northrop received an order from TWA for 15 planes. Taken from the proven and popular Gamma design, the Delta retains the same airframe and powerplant but relocates the cockpit to the airplane’s front. The widened semi-monocoque fuselage can accommodate up to eight passengers, plus the pilot seated slightly above the passenger level in an enclosed cockpit. An optional configuration of two pilots with six passengers and cargo arrangements are also available. The Delta Type 1A receives certification to carry six passengers after a few months of testing. On a lease, TWA receives delivery on August 4, 1933, for preliminary trails to transport mail between Los Angeles, California, and Kansas City, Missouri. Unfortunately, on November 10, 1933, the plane develops an engine fire in flight near Albuquerque, New Mexico causing the pilot Harlan Hull to eject from the aircraft. He survives by parachuting safely to the ground, but the airplane is a total loss. TWA decides to cancel its order due to the recent flight problems and a rumored amendment to the Air Commerce Act of 1926 taking effect in October 1934, banning the Delta from being operated by U.S. airlines. More on that later.
The second Delta, Type 1B, is purchased by the Mexican subsidiary Aerovias of Pan American Airways in August 1933 for the Los Angeles-Mexico City flight route. In May 1934, another engine fire destroyed this second Delta, but fortunately, no one is injured. I looked into the possibility of a common issue with the engine, but the Type 1B used a different powerplant, a 660 hp Pratt & Whitney Hornet T2D-1 engine, so that doesn’t seem to be a common cause. Unless there was some defect in the fuel delivery system, I’m not an A&P mechanic, and your guess is as good as mine. Some articles state that the aircraft crashed due to an engine fire while in service on a flight to Mexico City, but I cannot confirm this statement. Most accident reports say there was an engine fire without any injuries, but it’s unclear if it was on the ground or in flight.
The last Delta to be sold to an airline is the Type 1C and was purchased by AB Aerotransport in Sweden in April 1934, and given the name “Halland.” Only one of the Type 1C model is built and featured the optional Pratt & Whitney T1D-1 engine rated at 700 hp. This aircraft had a long service life without mechanical issues, as the previous models, operating on the Gothenburg-Copenhagen-Malmo and Malmo-Copenhagen-Hanover flight routes. “Halland” ceased its airline service in May 1937 and was later purchased by a private citizen.
These first three Delta models had a single-seat cockpit with a sliding canopy and operated with a two-bladed propeller. Later, the new Delta models switched to a three-bladed propeller and reconfigured the cockpit to allow room for a pilot and co-pilot. Northrop produces 32 Deltas, but the majority are sold outside the U.S. or to the private market.
The initial plan to sell the Deltas as single-engine airliners capable of carrying medium loads on the U.S. trunk airline routes came to an abrupt halt when an amendment to the Air Commerce Act of 1926 regarding airline safety requirements take effect on October 1, 1934. The revision requires all airlines operating on the trunk routes to use multi-engine aircraft at night or over rough terrain, instantly banning the Delta from any airline.
“The new provisions included the requirement for airline pilots to use multi-engine aircraft capable of operating with one engine not functioning when flying at night or over terrain not readily permitting emergency landings. Instrument or blind flying was permitted only for multi-engine airliners equipped with two-way radio.“
Northrop, discouraged with the new amendment, turns his attention to the mounting military aircraft contracts and finds the short-lived Delta project a much-needed break from the nuisance that the Delta was creating. He did continue to produce the Delta 1-D, already in the assembly line before the new amendment, but reconfigured the cabin for the limited private sector sales and selling the remaining inventory to other countries unaffected by the amendment. In August 1936, Canadian Vickers Ltd purchased the last Delta produced by Northrop as part of assembled patterns and built 19 additional aircraft under license in their factory until October 1940. Canada initially selected the Delta as a photographic survey aircraft. Still, in August 1939, with the approaching Second World War, the Deltas are converted to coastal patrol planes fitted with floats to carry out long anti-submarine missions. After only two months of use, the ocean environment proved to be too damaging to the Deltas from the large ocean swells and corrosion caused by the salty water, the military quickly returned them to land use.
Now on to the private market. Northrop offered the optional “Executive Model” for the Delta 1-D, which included custom seating for 5 to 7 people and focused the advertising towards professional sports athletes and businessmen. A Wright “Cyclone” radial engine, SR-1820-F2, produced 735 hp at 2100 rpm at 4000 ft giving the Delta 1-D similar performance as the Gamma perfect for long country flights. The maximum speed is 219 mph at 6300 ft with a cruising speed of 200 mph at 8000 ft at 3/4 throttle. Six fuel tanks located in the center section of the wing carry a total fuel capacity of 328 gallons providing a range between 1100 and 1500 nautical miles at 3/4 throttle depending on the headwind or tailwind. The climb rate is 1200 ft/min at sea level with a service ceiling of 20,000 ft. Northrop offered a Wright SR-1820-F52 engine as an option rated at 775 hp at 2100 rpm at 5800 ft for those interested in a little more performance. Now that should get your blood pumping!
A spacious cabin measuring 58 inches wide is heavily sound-proof with a left side entry door and customizable in either the “Club” or “Executive” packages. Both versions are incredibly lavish, featuring overstuffed chairs, a divan with storage underneath, a bathroom, and a 25 cubic foot baggage compartment behind the tail section’s cabin. The “Club” upgrade reduced the seating for 4 or 5 people. It included a refined interior, some upholstered in red and tan leather, a complete lavatory, a Sperry autopilot, and extra instruments. Standard equipment for either package includes; a Hamilton-Standard controllable propeller, an electric starter, a generator, an Exide battery, an oil-cooling radiator, navigational lights, landing lights, parachute flares, a fire extinguisher, a Western Electric radio, window curtains, and a full set of airline-type instruments. The base price started at USD 37,500 with standard equipment in 1934, which roughly equates to USD 727,500 in this writing, 2020.
Some of the “Delta Executive” owners include; Powell Crosley Jr., Hal Roach, Richfield Oil, Stewart Pulitzer, Earl P. Haliburton, and Wilbur May, to name a few. I recognize Powell Crosley Jr. for his invention and manufacturing of the 1921 Crosley Harko tubless crystal radio and Hal Roach, Laurel and Hardy’s comedy producer. These are extraordinary men, including Jack Northrop, and these talented individuals’ success always inspires me.