The B747 is known as the “Queen of the Skies” by many all around the world, but did you know there was a proposed tri-jet version of the 747?
A 747 with three engines and looking much like a DC-10, the 747-300 was actually on the drawing board and was seriously being considered by Boeing as a type.
In the 1960s and 1970s, Boeing considered creating this three-engine version of the plane in competition to the big tri-jets at the time. It can be argued that the Boeing 747 is the most successful aircraft in history of commercial aviation, so why did the tri-jet version fail to materialize?
The proposed 747 Tri-Jet would have been a fraction of the length of the standard 747, and that it would rival commercial aircraft such as the DC-10 and the Lockheed L 1011 Tri-Star.
Unfortunately, due to some major concerns, it seemed as if the proposal was doomed from the start.
The new aircraft would have required a whole new wing to be designed for it to be structurally sound.
A standard 747 wing hangs four engines, and eliminating the outer two engines just does not make good engineering sense. Fuel tanks, wiring and hydraulics cannot just be removed.
Due to the new fuselage being shorter, the standard wing would be too large. It would be cheaper and more cost effective to design a wing for the new aircraft.
Additional engineering problems would be the required strengthening of the rear part of the fuselage to accommodate the third rear engine.
Other problems such as aerodynamic flow to the rear engine would be a problem due to the 747’s famous ‘hump’ housing the cockpit and extra passengers. This would be especially true in high angles of attack during the taking off and landing phases of flight.
Another reason for the project’s failure was the pilot training requirements. The third engine produced a new thrust line that would affect the pitch handling of the aircraft that would require completely new training.
Because Boeing was striving to deliver a product that was nearly identical to its usual 747 offerings, and aimed to maintain the existing handling characteristics throughout the conversion to the three-engine configuration, the minimum type rating idea was more and more out of reach.
Rather than continuing development with three engines, the manufacturer constructed a special 747 with four engines, the 747SP. The suffix stands for ‘Special Performance’.
Boeing manufactured 45 747SP aircraft, the first of which was delivered to Pan Am in 1976. Today, six of these aircraft are still flying, according to Planespotters.net.
South African Airways operated a total of six 747SP’s. The long range of the 747SP instantly transformed SAA’s offerings, with direct non-stop flights being made available to London for the first time, as well as other long range flights to Sydney, Brussels, Madrid, and New York City. Through the balance of the 1970’s and into the 80’s, the 747SPs were a workhorse of the long haul fleet.
SOFIA, which stands for “Stratospheric Observatory For Infrared Astronomy”, is arguably the most intriguing 747SP still in service. This 747 holds a flying telescope, which is accessible through a large door on the back of the aircraft that opens during flight. This aircraft was built in 1977 and is now registered as N747NA. ‘Clipper Lindbergh’ previously served Pan Am and United Airlines before being acquired by NASA in 1997.
Boeing did in fact manufacture the 747-300, but stayed with their traditional offer of four engines.
The launch of the first flying 747-300 was on June 11, 1980. The 300 series resulted from Boeing studies to increase the seating capacity of the 747, during which modifications such as fuselage plugs and extending the upper deck over the entire length of the fuselage were rejected. The first 747-300, completed in 1983, included a stretched upper deck, increased cruise speed, and increased seating capacity. The -300 variant was previously designated 747SUD for ‘stretched upper deck’, then 747-200 SUD, followed by 747EUD, before the 747-300 final designation was used. Passenger, short range and combination freighter-passenger versions of the 300 series were produced
Modern aircraft of today have two engines that offer increased fuel efficiency and reliability due to the change of ETOPS (Extended-range Twin-engine Operational Performance Standards) regulations, so the days of large quad engine and tri-jet aircraft are rapidly coming to an end.
However the Boeing 747 will forever be the ‘Queen Of The Skies’ no matter what.
For Boeing, the 747 Tri-Jet has become an example of what not to do.