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January 6

When BAC went in search of an international partner their first stop was the USA where five major manufacturers were engaged in building large jet propelled aircraft that seemed a reasonable match to the BAC design for a medium long range supersonic airliner. Douglas had the DC-8 introduced in 1958, Boeing the 707 its direct competitor also introduced in 1958, Lockheed had the Electra which was introduced in December 1957 powered with turbo-prop engines while North American Aviation was busy developing the Mach 3 prototype XB-70 long range supersonic bomber. Last but certainly not least was the Convair corporation which had just begun delivering large numbers of B-58 bombers to the USAF which also used a delta wing and flew at Mach 2, however Convair, Lockheed and Boeing all declined to form a joint project because they were very busy with their own business at this crucial time supplying both military and civilian aircraft, and didn't want to get tangled up with a foreign contract. Douglas was interested because going supersonic would allow them to leapfrog the Boeing 707 which was already cutting into their sales of jet passenger aircraft and North American Aviation expressed an interest to hedge their bets suspecting their XB-70 project would be axed as soon as the votes were counted in the November election despite the fact that both candidates had firmly promised to build hundreds of the new Mach 3 bomber design.

Accord 1960The key to success was when Douglass, which wanted to enter the supersonic realm, partnered with North American Aviation and BAC and Pan Am Airlines for a new medium range 200 passenger Mach 2.0 supersonic commercial aircraft. Douglas would supply the passenger design aspects, North American Aviation and BAC would combine their studies and practical experience to design the wings and engine combination and Pan Am would buy the first ten units. The USA would kick in a grant for 300 Million as compensation for the cancellation of the YB-70 development aircraft and the project would be named the Accord, or agreement, because the work was international in scope. Douglas and Pan Am quickly convinced the other two partners that a 2.0 Mach maximum with a 1.7 Mach cruising speed was more than enough to satisfy the airline markets as this was slightly more than twice as fast as the Boeing 707 or Douglas DC-8, which was the market they were after.

Because of the expertise brought to bear the development went relatively quickly for such a large system. The basic shape was an enlarged copy of the XB-70 designed around the passenger compartment which seated 12 first class in four abreast and 192 coach in six abreast for a total of 204. By starting with the passenger cabin and designing the wing and engines to fit the passenger requirement, which was the crucial factor for any commercial airline, the aircraft would have a long career. While swing wings were suggested at one point they were quickly set aside because the weight penalty of the hinge and framework to support it were far greater than the weight of simply increasing the length of the delta wing surface. The outer section of the wing tip however did retain the droop feature because the hinge and droop setting was much lighter than the very robust swing wing system that would have to extent the wing surfaces forward into the onrushing wind in preparation for landing. By drooping the outer wing sections at a 45 degree angle the Accord would create an air cushion effect at cruising speed which would cut fuel consumption by almost one third compared to a standard delta design. The Canard surfaces just behind the cockpit encouraged vortex formation on the upper delta wing surface and provided fine control of the aircraft pitch and at first glance many passengers thought the Accord was put together backwards with the wing at the tail and the horizontal tail surfaces just behind the cockpit. However for supersonic flight the arrangement was a major improvement because at and above the speed of sound the center of pressure on the aircraft moved closer to the back, meaning for lift to remain effective the wings needed to extent further aft as well. It was also important to keep wing span as narrow as possible for high speed flight and the only way to get enough wing surface area on a narrow span was to have the wing extent longer front to back as in the F-102 Delta Dart Fighter and B-58 Hustler Bomber aircraft used by the USAF.

Because of the very long wing front to back the passengers in coach had tiny porthole shaped windows set at eye level for a seated passenger which would allow them to look out across the large wing to the distant horizon. looking down towards the ground was only possible in the first class section which had more typical airline windows and the option of looking out and up or down instead of just out or up.

The first flight of the Accord aka the (Douglass/North American Aviation) DN-109 was in September 1963 and received high praise from President Kennedy who had put off buying a new Air Force One in favor of the existing 1958 model Boeing 707-120's the Air force already owned in hopes that he could have a supersonic model in the near future. Once the Accord flew that first time JFK ordered the USAF to prepare plans for a modified executive version of the SST to be ordered as the new Air Force One model as soon as the Pan Am first generation order had been filled. Sadly President Kennedy was assassinated just two months later while visiting Dallas, but his successor LBJ would receive those new Executive Aircraft as units 11, 12 and 13 off of the assembly line in California where they were under construction at the North American Aviation plant.

As soon as the prototype Accord was flying in late 1963 the new President, LBJ, put pressure on the FAA to come up with flight rules to ease transition into the new era of supersonic passenger travel. As an interim measure the FAA ruled that all supersonic flight must be above 40,000 feet and to the greatest extent possible pass between population centers instead of near them unless they were the destination center. For Pan Am airways which received its first aircraft September 1, 1965 these rules were easy to follow because almost all of their routes were already over water. Simply placing a few turns in the existing overland routes to avoid large cities between destinations like Miami and Chicago or Detroit was not a major handicap as there was far more rural land in North America than Urban or Suburban.

The DN-109 Accord had retained the 'six pack' of side by side centrally located engines of the B-70 design and they had afterburners for liftoff to get up the speed necessary for flight as quickly as possible. However as soon as the aircraft was high enough to retract the landing gear the afterburners were shut down to conserve fuel. The higher thrust to weight ratio of six powerful GE-YJ93 engines compared to just four in the BAC proposal compensated for the increased size of the aircraft for mating to the larger Douglas passenger cabin with enough extra power left over to safely disengage the afterburners as soon as the aircraft was moving at flight speed. Once beyond local air traffic control operating the arrival and departure traffic at the airport the DN-109 Accord would get permission from regional air traffic control for rapid climb to 40,000 feet. Once the aircraft was at altitude the rate of ascent would be sharpy reduced from a 20 degree climb to 10 degrees while accelerating to Mach 1. At just below the sound barrier the afterburners would be briefly ignited to ensure a rapid and complete transition from 0.95 to 1.05 Mach speed, and then the afterburners would be cut again to reduce fuel consumption. Once the aircraft had broken the sound barrier and the bow wave formed the wing tips would be drooped 30 to 45 degrees depending on exact speed to shape the sonic wake into a cushion effect This reduced fuel demand a full 30% at cruise velocity of 1,300 mph, Mach 1.7! If necessary the aircraft could turn the afterburners back on and accelerate to hold mach 2.0 but doing so greatly increased fuel consumption even with the sonic wake ride effect in place. Theoretically they could even exceed this speed from pure engine power, however the decision to cruise at Mach 1.7 had been made to allow much cheaper aluminum alloy materials to be used in construction instead of the stainless steel honeycomb structure used in the prototype XB-70 Valkyrie design which had been intended to fly at up to Mach 3.0 with much greater heating and wind shear stresses. By limiting the overall speed to twice the rate of the existing commercial aircraft a huge investment in expensive high tech alloys and weight was saved in the DN-109.