Birth of a Breed: The Development of the Douglas DC-1

The Douglas DC-1 at its 1933 handover to TWA
(San Diego Air and Space Museum Archives)

The crash of a TWA (Transcontinental & Western Air) Flight 599 on 31 March 1931 served as a major catalyst in the airline industry for adoption of all-metal aircraft. The Fokker F.10 was on a scheduled flight from Kansas City to Los Angeles when it encountered turbulence on its first leg between Kansas City and Wichita. As the Fokker F.10 airline had wings of wood laminate, accumulated moisture had caused a weakening of the glue used which led to delamination and structural failure. Aboard Flight 599 was the famed Notre Dame head football coach Knute Rockne, who along with five other passengers and two crew, were lost in the crash when the aircraft went down between the rural Kansas towns of Bazaar and Matfield Green. As a result of the crash, the Bureau of Air Commerce required operators of aircraft with wood wing structures to undergo frequent inspections- as this was economically unfeasible for most operators, all-metal designs were procured as soon as possible. TWA nearly shut down for good while its Fokker fleet was grounded for  inspections. Most of the types that were procured were interim types- but in 8 February 1933, a new airliner made its first flight that was a quantum leap over anything that had proceeded it, and that was the Boeing 247 which entered service with United Air Lines just fifty days later. All metal with a retractable undercarriage, the Boeing 247 was sleek and much faster than anything that had flown passenger services up to that point. Even the most current designs were instantly obsolete- for example, the Curtiss Condor biplane airliner had entered service with Eastern Air Lines and American Airlines just five weeks before United put its Boeing 247s into service. 

United's main rival on the transcontinental market was TWA- the Boeing 247 could now make the east to west transcontinental run in only 21 hours 30 minutes including technical stops. By comparison, TWA's Fokkers took 28 hours 43 minutes to fly from New York to Los Angeles. When TWA learned of United's order for the Boeing 247, he contacted Boeing about ordering the aircraft for TWA, but at the time, United and Boeing were part of the same holding company, United Aircraft and Transport Corporation and Boeing was contractually bound to deliver 60 Boeing 247s to United before it could supply airframes to other customers. TWA's vice president for operations, Jack Frye, wasted little time in sending a letter to other aircraft manufacturers soliciting interest in building at least 60 three-engined airliners for the airline. That letter went to Consolidated Aircraft, Curtiss-Wright, Douglas Aircraft, General Aviation Manufacturing, Stout (Ford) Aircraft, and Glenn Martin Aircraft. The letter included general performance specifications that any design had to meet: 

Jack Frye of TWA
(FindAGrave.com)

1. All metal, trimotor preferred, combination structures and biplane would be considered, but the internal structure had to be metal. 

2. Thee engines of 500-550 hp. 

3. Maximum gross weight of 14,200 lbs. 

4. Weight allowance for radio and mail carriage of 350 lbs. 

5. Weight allowance for full instrumentation, including night flying, fuel to fly 1,080 miles at 150 mph, crew of two, at least 12 passengers in comfort. Payload had to be at least 2,500 lbs with full equipment and fuel for maximum range. 

6. Minimum top speed of 185 mph, cruising speed at least 146 mph. Landing speed not to exceed 65 mph, rate of climb at least 1,200 feet/min, minimum service ceiling of 21,000 feet and a minimum service ceiling with one engine out of 10,000 feet. 

The specifications page also emphasized that any design, fully loaded, "must make satisfactory take-offs under good control at any TWA airport on any combination of two engines." This landmark letter from Jack Frye is considered the "birth certificate" of the DC-1. When Donald Douglas received the letter in Santa Monica, he immediately convened a meeting with his top heads- James "Dutch" Kindelberger (of P-51 Mustang fame) who was his chief engineer, Arthur Raymond who was the deputy to Kindelberger, and Harry Wetzel, the Douglas Santa Monica plant director. With the United States in the midst of the Great Depression, it didn't take long for them to decide this was a tremendous business opportunity for the company. Just ten days after Jack Frye sent his letter of proposal, Douglas dispatched Arthur Raymond and Harry Wetzel with a ten-person team by transcontinental train to New York to meet with TWA. The Douglas team by this point had moved quickly and concluded that even though TWA was leaning towards a three engined design, they would offer a twin engined design that would be equal if not superior to TWA's specifications. The design would be an all-metal monoplane with a retractable undercarriage that would have passenger comfort as a priority. With Kindelberger supervising the design work in California and telephoning design details to Raymond and Wetzel as they were enroute to New York, the design was refined as the team prepared for its presentation to the TWA evaluation team which consisted of Jack Frye, Richard Robbins, president of TWA, and Charles Lindbergh, the airline's technical consultant. Also present were the teams from four other aircraft manufacturers, all of whom tendered three-engined designs. 

Having prior flying experience with other Douglas designs, Frye was favorable to the Douglas proposal, but Lindbergh had his doubts that a twin engined design could meet the airline's stringent specifications. Lindbergh in particular was concerned about single-engined performance at TWA's hot and high airports in the southwestern United States. The Douglas team in consultation with the engineerings staff in California rechecked their calculations repeatedly to be sure that their design could take off with a single engine from any of TWA's airports. With considerable trepidation, Douglas instructed his team meeting with TWA that he would agree to a contract provision guaranteeing this particular specification to satisfy Lindbergh's concerns. On 20 September 1932, TWA signed a contract for the first Douglas DC-1 for $125,000 (about $2 million of today's dollars) with options for 60 more aircraft based on the flight tests and performance of the DC-1. As an insurance policy against a possible failure of the DC-1, General Motors, which owned TWA, had its General Aviation Manufacturing subsidiary work on the GA-38X which was a three-engined larger derivative of the smaller single engined GA-43 airliner. Construction had started on the prototype, but work ceased early on when it became clear the DC-1 would be successful. 

Arthur E. Raymond, chief designer for the Douglas DC-1
(General Aviation News)

With a signed contract in hand, Donald Douglas assigned Arthur Raymond as the DC-1 project manager. Assisting him would be the legendary Jack Northrop, who was at the time managing the Douglas El Segundo division and would be managing the structural design of the DC-1. Other able Douglas engineers were put in charge of various systems and components for the DC-1. In addition and a first for a transport aircraft, extensive wind tunnel testing at Cal Tech's facilities in Pasadena, California, would be an integral part of the design and development process. Cal Tech's aeronautical faculty would head this effort to uncover as many issues as possible before any metal got cut for the prototype- it was wind tunnel testing that found the planned wing design was unstable and further wind tunnel testing at Cal Tech showed that sweeping the wing leading edge back addressed the stability issue. This was how the DC-1 and later DC-2 and DC-3 got their unique wing shape. 

With passenger comfort a priority, it was decided that the benchmark would be the interior noise of a Pullman rail car. The DC-1 cabin had to have the same level of noise or less. As the design effort proceeded, the early specifications for the Boeing 247 were published in Popular Mechanics and Arthur Raymond had copies of the article posted everywhere with the admonition "Do Better than Boeing!" It was vital at every step of the design process that the DC-1 be more comfortable than the Boeing 247 and an important design step was Northrop's wing design that would fit at the bottom of the fuselage without intruding into the cabin as was the case with the Boeing 247. Northrop's wing center section was relatively flat with the engine nacelles at the ends, outboard of which the outer wing panels were attached with the needed dihedral for stability. In a unique feature of the day, the passenger seats could also be reclined. Heating, ventilation, and the aforementioned soundproofing efforts were as considerable as any aircraft system to meet Douglas's desire for the DC-1 to be comfortable. The aisle width was a then-generous 16 inches (Americans in those days were nowhere near as obese as they are now) with a cabin height of 6 feet 4 inches. This would lay down the reputation of Douglas aircraft for years to come to be considered passenger-friendly.

Note the faired struts ahead of the wings on the DC-1
(San Diego Air and Space Museum Archives)

Both the Pratt and Whitney 9-cylinder R-1690 Hornet radial engine and the Wright 9-cylinder R-1820 Cyclone radial engine were evaluated with the Douglas team selecting the Hornet as the DC-1's power plant. Fixed pitch metal propellers were to be used for the prototype. Developments of both engines would figure prominently in American aircraft of the Second World War- the Cyclone would be progressively developed into larger versions that would power the B-17 Flying Fortress, the TBF Avenger, the B-25 Mitchell and in its ultimate development, the B-29 Superfortress and Lockheed Constellation. The Pratt and Whitney Hornet radial engine was a modest success but was developed into a twin row radial as the Twin Wasp which would be used on the DC-3 which in turn was developed into the outstanding Double Wasp and Wasp Major engines. The engine development is of course a future topic here at Tails Through Time! The engines of the DC-1 were one of the first transport aircraft to use the NACA cowling which streamlined radial engines by as much as 60%. When the prototype was rolled out in the summer of 1933, there were also faired struts that connected the forward fuselage with the engine nacelles ahead of the wings- in the prototype these carried sensor cables from the engines for test instrumentation but were later removed. 

On 9 April 1934, Dutch Kingleberger and Arthur Raymond filed for Patent No. 94,427 "Design for an Airplane" which described the layout and configuration of the DC-1 and later DC-2 development. Despite the patent's rather sparse documentation, it was issued by the US Patent Office in the following year. 

On 1 July 1933, the DC-1 would make its first flight as the birth of the Douglas breed of airliners. The story of the flight test program and service history of the DC-1 will be the subject of a subsequent article here, but it should be noted that in 1918, a very young Donald Douglas was working for Glenn L. Martin where he designed bombers for Martin but it was a transport derivative of his bomber designs that fascinated Douglas- the GMT or Glenn Martin Transport was a 15 seat aircraft that had a fully enclosed cockpit. Only one was built and it was destroyed in an accident in March 1920. The GMT was the first Douglas-designed transport and it was where Donald Douglas resolved that his dream was to design and build an aircraft that whose sole purpose was to carry passengers in comfort. That was in 1919-1920, the DC-1 when it made its maiden flight in 1933 was just the start of Donald Douglas's dreams coming true. 

Source: Douglas Propliners: Skyleaders, DC-1 to DC-7 by Rene J. Francillon. Haynes Publishing, 2011, pp 9-11, 46-53. 

The Rise of Coach Class Airfares

Prior to the Second World War, several small airlines tried to break into the market by offering low fares, but none of them survived as at the time, passenger operations were only sustainable at charging fares that were roughly 10 cents a mile. The first serious attempt at low fares on a sustained basis came from United Air Lines which started what it called "Sky Coach" service on 10 April 1940 between San Francisco and Los Angeles with intermediate stops with a fare over the whole route coming out to $13.90 (approximately 3.5 cents per mile). The reasoning for the Sky Coach service's low fares were that it would only use 10-passenger Boeing 247s that were already old and paid off, therefore cheaper to operate and would offer a less extravagant level of service than on United's primary services between the two cities. The "Sky Coach" ended on 23 April 1942 with the mobilization of the US airline fleet to support the war effort. 

In the immediate postwar period, the boom in air travel meant there were more passengers than seats and the airlines were in no rush to cut prices. In those days, fares were governed by the US Civil Aeronautics Board (CAB) and any rate cut had to pass their review as not being detrimental to the general interest of the industry and the route in question. If an airline wished to offer low fares, they had to provide rationale to the CAB to approve those fares in the days before deregulation. A growing number of charter and non-scheduled airlines, however, began to slowly nip away at the passenger market that was long the exclusive domain on the established trunk and local service carriers. These airlines offered low-frills services at cut rate prices that eventually forced the established airlines to act. The first out of the block with the first scheduled coach class service in the United States on 4 November 1948 was Capital Airlines on the lucrative Chicago-New York route. Capital charted only 4 cents per mile instead of the standard 6 cents per mile on the route established by the CAB. It justified the coach class fares to the CAB by using older Douglas DC-4s with high-density seating for 60 passengers. Only the minimum of inflight services was provided and the flights were scheduled at off peak hours and late at night so not to detract from Capital's own premium services. After approving Capital's coach class services, other airlines raced to establish their own coach class services and the CAB was so flooded with applications for approval that it was forced to issue a policy statement, apprehensive that the airlines would end up offering services that was out of balance with their operating costs:

"We would caution the carriers that the burden of proof for additional coach class service is clearly on them. We do not propose to allow the indiscriminate extension of coach fares, no do we intend to permit a general debasement of the existing passenger fare level."

Regardless, on a case-by-case basis, the CAB approved numerous other coach class services and within a year of Capital's ground breaking services, coach fares could be found on most major routes. On 27 December 1949, both American Airlines and TWA offered the first transcontinental coach class services on high-density seating DC-4s with several stops. The fares were around $110, and due to the success of the services, in less than a year both airlines replaced the elderly DC-4s with better equipment- American put DC-6s on the routes and TWA put Lockheed Constellations on the coach routes. Curiously, though, United refused to start its own coach services despite its own experiments in 1940 with the Sky Coach. William "Pat" Patterson, United's paternalistic president, warned that expansion of coach fares would lead to chaos in the market and ruin the fare structure of the industry. After holding out, United finally introduced its own coach services on 14 May 1950 with 60-seat DC-4s between Los Angeles and San Francisco at 3 cents per mile. United's services ran at night and at off peak hours until later than summer when Western Air Lines added its own daytime coach services. For the remainder of the year, United and Western fought a small fare war on coach services in California.

To get CAB approval for these services, the airlines had voluntarily imposed all sorts of restrictions on the fares from off-peak schedules, no discounts, no refunds, less on-board amenities, and reduced seat pitch. Most of this was done freely by the industry to protect their own premium services. In 1950 the CAB issued another policy statement that the objective of fares should be to balance the ratio of fares to seating standards so that the net revenue per flight should be the same, irrespective of the ticket prices. This had the effect of eroding many of the previous restrictions on coach fares due to competition- since an airline merely had to demonstrate to the CAB that the net revenue on a given route didn't change much, airlines began to incorporate coach class cabins on their regular flights. Coach fares were now available for daytime flights and peak times. As a result, United set its coach fares on all flights on the West Coast at 4.5 cents per mile and for flights within California, coach fares were set at 3.5 cents per mile. Much to United's surprise (and undoubtedly to that of Pat Patterson), United's coach fares were a huge success and the airline aggressively introduced coach class cabins on its transcontinental services between San Francisco and New York at only $110 on 25 September 1951. 

But the expansion of United's coach class cabins got the attention of the United States Senate's Select Committee on Small Business. The committee investigated the CAB decisions regarding coach class services and found that the Board had unfairly been favoring the established airlines and criticized the CAB's strict policies on charter airlines and non-scheduled airlines that had shown a market for low airfares. So in November 1951 the CAB reversed direction but instead of taking a more favorable approach to the charter and non-scheduled carriers, the CAB denied transcontinental applications of several carriers and instead directed the established airlines to expand coach class fares on their network. Many of the smaller airlines cried foul, but the political influence of the established airlines maintained the CAB's change in policy. The airlines now began to aggressively push coach class fares, particularly on the transcontinental routes by by 1952 the coach class fare between New York and Los Angeles had fallen to $99 and New York to Chicago fell to only $32. By 1955, coach class fares had grown exponentially to the point that on some routes, the coach class cabin took up more space than the first class cabins that once made up the entire cabin of airliners of the day. As traffic soared into the 1960s, the majority of airline passengers in the United States would travel via coach class fares, laying down the foundation for the beginnings of deregulation in the 1970s.

Source: Airlines of the United States Since 1914 by R.E.G. Davies. Smithsonian Institution Press, 1998, p336-338.

The Boeing 247 Flying Laboratory of United Air Lines

United Air Lines' legendary president William "Pat" Patterson listed his corporate goals in what he called his "Rule of Five"- safety, passenger comfort, dependability, honesty, and sincerity. To Pat Patterson, the goal of safety was the most important that he asked each and everyone one of his employees to strive for above all else. Despite the rapid advances in aviation technology in the 1920s and 1930s, airline flying was nowhere near the routine that we today take for granted. Patterson believed that the industry as a whole would benefit from investing in technology that increased aircraft safety. His first tangible commitment to that goal came in 1929 when the United Communications Laboratory based on the second floor of a hangar at Chicago Midway was established as the airline industry's only communications laboratory. One of the first developments from United Air Lines engineers assigned to the Communications Lab was a practical two-way radio for aviation use. 

In 1937, one of United Air Lines' Boeing 247Ds, NC13365, was pulled off the line and assigned to the airline's laboratory at Chicago Midway. This particular aircraft also happened to be the last Boeing 247 built. Re-registered as NX13365, the interior was fitted with test benches to hold equipment and the ceiling hat racks were modified to carry wire bundles to and from the various test equipment being used. Nicknamed the "Flying Lab", the Boeing 247D made its first flights for what became the United Flight Research Lab (as its efforts moved beyond communications and into general flight safety) the standard all-over gray color used on United's 247 fleet at the time. Before long, however, NX13365 was repainted in an attractive white and red scheme with "Flight Research" titles on the fuselage. 

The first assignment flown by NX13365 was the problem of static electricity build-up on the airframe. Particularly during bad weather, the static build-up on the airframe could reach levels sufficient to interfere with the communications and navigation equipment. Several Boeing 247s were lost due to accidents directly attributable to static build up on the airframe during flight. Working together with the Bendix Radio Corporation, NX13365 would log over 25,000 miles of flying developing a practical static "suppressor". A long wire extended from the tail that drew the static charge away from the airframe and dissipated it harmlessly. A resistor was part of the wire and a small waxed cup at the end of the wire kept it deployed in flight. Today we know these wires as the static wick dischargers on the wings and tail of modern aircraft. The first static dischargers were five foot long wires and true to his word, Pat Patterson had them fitted on every aircraft in the United fleet and shared the his lab's findings with the industry. 

NX13365 was also used for the development of what the lab called a "terrain clearance indicator". With many crashes at the time due to CFIT in poor weather (controlled flight into terrain), United's engineers worked with Western Electric and Bell Telephone to create the first radio altimeter which provided the pilots constant updates of the relative height above the ground. If the aircraft descended too low, a red light on the radio altimeter came on, alerting the flight crew. The first public demonstration of the radio altimeter was conducted on a flight above New York City that continued north over the Hudson River and over the Palisades. Following the completion of tests of the radio altimeter, again and true to his word, Pat Patterson had radio altimeters installed on everyone of United's aircraft and as he did with the static discharger, shared the findings with the rest of the industry. 

Before NX13365 was retired, United's engineers also developed an instrument landing system as well as a terrain-viewing television system in cooperation with the US Army Air Corps and also trialled different antenna configurations. In October 1945, United modified the aircraft back to passenger configuration and sold it to LAMSA (Lineas Aereas Mineras S.A.), a Mexican airline that United had invested in back in 1942. After flying with LAMSA for two years as XA-FIH "Estado de Sinaloa", it passed through several Mexican owners before ending up with an air taxi service that crashed the aircraft in Mexico City in 1952. 

Source: The Boeing 247: The First Modern Airliner by F. Robert Van Der Linden. University of Washington Press, 1991, p155-158.