Pervertiplanes: A Forgotten Argot Of Aeronautical Engineering?

Even though the term dates back to the Cold War era 1960s American aeronautical engineering boom, does anyone still use the term “pervertiplane” these days? 

By: Ringo Bones

Any group of specialists has its own private lexicon and aeronautical engineers are surely no exception. The word “pervertiplane” could be defined as a corruption of the term “convertiplane” – which is a contraction of the term “convertible aircraft” – pertaining to aircraft constructed in such a way that their lifting and propulsion systems may be converted to permit efficient operation either for vertical take-off and hovering or for high-speed forward flight. Such craft are now more commonly termed as VTOL or vertical take-off and landing aircraft. 

Convertiplanes – at least their experimental prototypes – began life back in the beginning of the 1960s. Examples of which are the X-19 broad-bladed tilting rotor turboprop VTOL plane, the X-22 tilting ducted fan VTOL plane, which is probably the great-granddaddy  of the V-22 Osprey that got fielded back in 2007 and some jet-engine high-performance experimental VTOL fighter planes like the British-built Hawker P1127 cascade vane-nozzle turbojet VTOL that later became the USMC’s Hawker Siddeley Harrier / Harrier Jump Jet and the then West German EWR VJ-101C tilting engine turbojet VTOL interceptor. 

Convertible aircraft are sometimes called “convertiplanes”; however, one prominent aeronautical engineer – legend has it that it was Igor Sikorsky – has suggested the name “pervertiplanes” because so many of the machines, in his view, combine the worst features of the helicopter and the fixed-wing aircraft. The necessary provision of such structurally difficult features as tilting wings, tilting rotors, cascade-vane assemblies and the like which may be subjected to high gas temperatures and periodically fluctuating air loads, all at minimum structural weight, leads to the development of very complicated mechanical devices that in turn leads to a high probability of mechanical failure. 

By far, the most serious problem with convertible aircraft lies in its characteristics following engine failure at low altitude. Unlike fixed-wing aircraft, which can fly as a glider following engine failure or the helicopter, which can descend at a safe – but rapid – rate with its rotor being spun by the flow of air past it (a process called autorotation), the convertible aircraft commonly lacks wings large enough to descend slowly as a glider, or a rotor large enough to permit a safe autorotation descent. Worse yet, if power failure occurs during transition, it may not be possible to achieve either type of descent and the vehicle will fall like a rock. Looks like a convertible aircraft or convertiplane’s reputation as a “pervertiplane” seems apt.