With very few exceptions, commercial aircraft designers have followed a similar rule book for design for more than half a century. Key.Aero explains why this is and reveals the military aircraft that kicked it all off
It’s often said that plane spotting is less interesting nowadays compared to when the likes of the 747, TriStar and Concorde routinely graced the skies around airports.
But even before a decline in the variation of aircraft designs in recent decades – which involved a shift towards the stereotypical twin-engine silhouette that some have derided – the typical jet-powered airliner still followed a basic design philosophy.
The position of the engines, the shape and design of the wings, the position of the tail and horizontal stabiliser etc are all similar amongst most turbine-powered airliners. Of course, there are notable exceptions. One that springs to mind immediately is Concorde which broke all the unwritten rules to become a masterpiece of design and engineering.
But how did it all start?
The first aircraft to be manufactured in a way that would be recognisable today as conforming to some of the key design rules for airliners was the Boeing B-47 Stratojet. The long-range turbojet-powered strategic bomber is credited with contributing to the development of modern-day airliner design.
The key innovations Boeing pioneered on the bomber included the position of the engines and the shape and design of the wing.
While the first-ever jet-powered commercial airliner – the de Havilland Comet – had its powerplants mounted in the wing root, the B-47 boasted underslung nacelles. This meant access to the engines was easier whilst also reducing structural weight.
Another advancement came with the wing design which incorporated a 35-degree sweep and a much thinner profile from root to tip. This was achieved because the engines were not located within the root.
The shoulder-mounted position of the wings would later change to a lower wing design, but the general shape and size have stayed the same.
The jet flew for the first time on December 17, 1947, and examples were used in service with the United States Air Force between 1951 and 1977. More than 2,000 were built.
Dash 80 dreams
By the late 1940s, the success of the B-47 Stratojet and the de Havilland Comet, encouraged Boeing to begin considering developing a passenger jet. The manufacturer felt it had mastered the swept-wing podded engine design and saw it as an important way to improve upon and differentiate from the British-built rival.
The Boeing 367-80, or more commonly known as the Dash 80, was built by the then Seattle-based manufacturer to convince airlines of the benefits of jet-powered airframes.
The Dash 80 took around two years from project launch to its roll-out in 1954. Powered by Pratt & Whitney JT3C turbojets, the prototype was a proof-of-concept aircraft for both military and civilian use. The US Air Force was the first customer, using it as the basis for its KC-135 Stratotanker.
The type’s wings are swept back at 35° and like all swept-wing aircraft, produce an undesirable “Dutch Roll” flying characteristic that manifests itself as an alternating combined yawing and rolling oscillation. Already having experience with this on the B-47 and B-52, Boeing had developed a yaw damper system which is used on the 707.
The 707 went on to be a hit and has since been credited for truly getting the Jet Age going following the troubles that faced British rival de Havilland at the time.
Not only this, but the aircraft continued design trends in engine placement and wing design that we still see in today’s airliners. A true trendsetter if ever there was one.