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Everybody thinks of the B747 as the queen of the skies with 4 engines, however, once upon a time Boeing was working on a shortened B747 with 3 engines.

The Boeing 747

The Boeing 747 is one of the company’s most successful aircraft. February will mark 50 years since the first flight of the original test aircraft, with many different iterations of the aircraft being released over time. As of July, 1,548 B747 aircraft had been built, very roughly equating to around 30 per year.

The latest model currently being built and delivered by Boeing is the B748 and the B748F. In a three class configuration the aircraft is designed to hold 467 passengers. In fact, the B747-800 is the worlds longest airliner, succeeding the A340-600 by 5 feet. Additionally Boeing is currently working on two new Air Force One B747s for the US Government.

The B747 Trijet

Believe it or not, in the 1960s and 1970s Boeing was considering constructing a three engine B747. This trijet aircraft would have had one engine on either wing, with an additional engine mounted in the tail, similar to a B727. The Boeing 747 Trijet would have been significantly shorter than the base 747. It was designed to compete with both the Lockheed L1011, and the McDonnell Douglas DC-10. The aircraft would have had a greater passenger capacity, payload, and range than both of these competitors.

Why Did The Project Fail?

Ultimately the project failed because of two things. The engineering required for this new aircraft was the first. Pilot training requirements was the second. In order for this new aircraft to have been structurally sound the aircraft would have required a brand new wing to be designed. This is because the current wing at the time was very much designed with two engines clinging on to either side. Boeing eventually decided against developing this new wing that was suitable for two engines.

In addition, Boeing were aiming to create a product that was almost identical to its regular B747 product as far as pilots could tell. Wanting to require minimal training for the conversion to the 3 engine variant, Boeing was aiming to maintain the existing handling characteristics. This was proving hard for the company to achieve with two main engines, and a third mounted in the tail.

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What Became Of The B747 Trijet?

Boeing didn’t completely abandon the B747 Trijet. Instead of continuing development with 3 engines, the manufacturer created the shorter B747 with 4 engines. This would go on to be named the B747-SP. Entering service in 1976 with Pan Am, Boeing went on to build a total of 45 B747SP aircraft. 13 of these aircraft are still in operation today.

Arguably the most interesting B747SP still in operation is called SOFIA. SOFIA stands for Stratospheric Observatory for Infrared Astronomy. With a huge door on the back of the aircraft that opens during flight, this aircraft is housing a flying telescope. This aircraft was previously in operation by United Airlines before it was acquired by NASA.