Sunday, March 6, 2016
Tilting at the sky
After my article on Friday about DARPA's X-Plane contest, a few people asked how many tiltrotor and tiltwing aircraft had been developed. I thought I'd answer their questions in this blog post. It was an interesting investigation.
The concept was first discussed by George Lehberger in a US patent application in 1929. His proposal looked like this, although as far as I know it was never built.
The first serious attempt to design a tiltrotor aircraft was Germany's Focke-Achgelis Fa 269, conceived during World War II. A full-size mock-up was built, and wind-tunnel tests were conducted, but the war ended before a prototype could be constructed. Here's a photograph of a model of the proposed aircraft, courtesy of Wikipedia.
The first tiltrotor aircraft to actually fly was the Transcendental Model 1-G (shown below) in 1954. Two prototypes were built, but the aircraft didn't enter production.
A much more successful experimental tiltrotor design was the Bell XV-3 (shown below), which first flew in 1955. Two examples were tested over the next decade, helping to uncover many of the problems and issues that would plague later tiltrotor programs, and giving engineers and designers a head start on solving them.
While the XV-3 was testing the tiltrotor concept, two other programs tried tilting the entire wing instead. The Canadair CL-84 "Dynavert" (shown below) was successfully tested, but only four examples were built, and no production orders were received.
The Ling-Temco-Vought (LTV) XC-142 (shown below) was a much larger tiltwing design tested in the USA during the 1960's. Five were built, but numerous problems emerged during evaluation, so that no production orders were placed.
Also during the 1960's, Westland in the UK proposed two tiltrotor projects: the six-seat We 01C and the much larger 68-seat We 02B. Models of each were displayed at the 1968 Farnborough air show (shown below - We 02B in the background, We 01C in the foreground), but neither was built.
In the early 1970's the Soviet Union studied the Mil Mi-30 project (an artist's impression is shown below). A scale model was built, but no full-size aircraft resulted.
After its experience with the XV-3, Bell decided to try a new approach. Instead of mounting the engines in the fuselage and using drive shafts to convey power to the rotors, it would mount the engines themselves in rotating pods at the end of the wings. The result was the very successful Bell XV-15 demonstrator project (shown below). Two were built, and flown until 2003.
Lessons learned in the XV-15 program were applied to the design and development of the Bell Boeing V-22 Osprey (shown below), currently in production for the US armed forces. Over 400 are to be built under current plans.
The AgustaWestland AW609 (shown below) began as a joint project between AgustaWestland of Italy and Bell in the USA, although it was later transferred to AgustaWestland exclusively. It's a six-passenger aircraft designed for the civil market. Production is expected to begin in 2017.
The Bell Eagle Eye (shown below) was an unmanned aerial vehicle project that began in the early 1990's and continued testing until 2006, when the prototype crashed. It did not enter production.
There are a number of tiltrotor projects currently under development, including the AgustaWestland Project Zero and the Bell V-280 Valor. An artist's impression of the latter is shown below. All are in the design stages at present, and none have flown.