Editing Rolls-Royce Thrust Measuring Rig (section)

== Development ==
The man largely responsible for the development of the TMR was Dr [[Alan Arnold Griffith]], who had worked on [[gas turbine]] design at the [[Royal Aircraft Establishment]] (RAE), in the 1920s and was a pioneer of jet lift technology. In 1939, Griffith had been employed by Rolls-Royce.<ref>{{Cite book |date=April 1985 |title=Flying the Bedstead – Part 2 |publisher=Aeroplane Monthly}}</ref> During the 1940s, he conceived of using [[jet propulsion]] as a method of directly providing vertical lift to produce an aircraft that could take off vertically. The construction of such an aircraft for research purposes was suggested by Griffith.<ref name = "ill 2" />

Being suitably impressed by Griffith's concept, while also being keen to explore and harness the capabilities of its newly developed range of jet engines, Rolls-Royce commenced construction of the aircraft at the company's facility at [[Hucknall Aerodrome]], [[Nottinghamshire]], England.<ref name = "ill 2" /> The crucial auto-stabiliser for the aircraft was designed and produced by the Instrument and Air Photography Department of the [[Royal Aircraft Establishment]] (RAE). The aircraft was designated as the ''Thrust Measuring Rig'' (TMR), two were constructed for the test program.<ref name = "ill 2" /><ref name = "fricker 25">Fricker 1962, p. 25.</ref>

On 19 August 1953, the first TMR conducted its [[maiden flight]] at Hucknall Aerodrome.<ref name = "ill 2" /> In order to perform these flights, a purpose-built gantry-like arrangement had been devised and assembled at Hucknall which, while not restricting the aircraft's movement within a defined space, prevented it from exceeding that boundary; it also prevented excessive descent rates, allowing for a maximum descent rate of {{convert|10|ft/s|0}}, from occurring in order to avoid sustaining damage and allowed struggling pilots to readily close the throttles without a resulting accident.<ref name = "ill 2 17">Illingworth 1961, pp. 2, 17.</ref> During the first year of flights, the aircraft remained tethered within the gantry system for flight testing. On 3 August 1954, the TMR conducted its first ''free'' flight, piloted by [[Ronald Thomas Shepherd]], Rolls-Royce's chief test pilot.<ref name = "ill 2" />

In late 1954, the TMR was transferred to the RAE's research facilities, firstly being assigned to [[Farnborough Airport|RAE Farnborough]].<ref name = "ill 3" /> In June 1956, it was relocated to [[RAE Bedford]], [[Bedfordshire]], for the purposes of conducting further flight tests. While the practicalities surrounding controllability had been addressed during its time at Hucknall, the RAE were more interested in using the TMR to determine if artificial stabilisation would be necessary for such aircraft, both during the hover and the low-speed stages of flight, and to investigate desirable characteristics towards achieving stable vertical flight.<ref name = "ill 3">Illingworth 1961, p. 3.</ref>

Information from typical flights was primarily acquired through the reported experiences of the pilots.<ref name = "ill 6">Illingworth 1961, p. 6.</ref> During stability trials, more quantifiable data was gained by instructing multiple pilots to follow the same sequence of manoeuvres, many of which were intended to be representative of VTOL aircraft transitioning into hovering flight; multiple observers were also employed as well. Test flights had several safety restrictions placed upon them: the TMR was not typically flown if the wind speed was 10 knots or greater, it would only fly under weather conditions in which the aircraft could be controlled in the event of a fault.<ref name = "ill 6 7">Illingworth 1961, pp. 6-7.</ref> Pilots were able to perform take-offs and controlled landings, but found both feats to be more difficult if wind was present, particularly if the TMR was required to tilt in order to counteract the wind's effects.<ref name = "ill 8">Illingworth 1961, p. 8.</ref>

Reportedly, pilots found that the main initial difficulty in flying the TMR was the regulation of the aircraft's height; this was partially due to the slow response of the engine to throttle movements being commanded by the pilot.<ref name = "ill 7">Illingworth 1961, p. 7.</ref> The delay interval between the throttle and the engine response was often around the one-to-two second mark; pilots would typically adapt to this peculiarity of the aircraft and become adept at mastering height control. Two attempts were made to improve the height control, the addition of a simplistic trimmer on the throttle to restrict its possible speed of movement, and the installation of 'throttle-anticipators' that failed to operate as intended.<ref name = "ill 7 8" /> The TMR effectively demonstrated that delay in the height control response would be a major difficulty of VTOL aircraft, and the engines of later VTOL aircraft did typically feature faster response times.<ref name = "ill 7 8" /><ref name = "fricker 60 61">Fricker 1962, pp. 60-61.</ref>

The aircraft survived a failure of its [[Reaction control system|thrust-vectored control system]] on 16 September 1957 whilst being piloted by Wing Commander Stan Hubbard of the RAE.<ref>{{Cite news |url = https://www.telegraph.co.uk/news/obituaries/11320471/Wing-Commander-Stan-Hubbard-obituary.html |title = Wing Commander Stan Hubbard&nbsp;— obituary |work=Daily Telegraph |date = 1 January 2015}}</ref> On 28 November 1957, the second TMR, [[United Kingdom military aircraft serial numbers|Serial]] ''XK426'', was destroyed during a test flight, resulting in the death of Wing Commander H. G. F. Larsen, who had been piloting the aircraft for the first time.<ref>{{Cite news |url = https://www.nytimes.com/1957/11/29/archives/vertical-jet-crashes-britains-flying-bedstead-fails-in-trialpilot.html |work = [[The New York Times]] |title = VERTICAL JET CRASHES; Britain's 'Flying Bedstead' Fails in Trial--Pilot Killed |date = 29 November 1957 |at = Page 6, column 5 |access-date = 23 May 2023}}</ref><ref>{{Cite newspaper The Times |title = On This Day November 29, 1957 |department = |date = 29 November 2007 |page = |issue = |column = |url = https://www.thetimes.com/business-money/companies/article/on-this-day-november-29-1957-l6pxl62k2px |access-date = 23 May 2023}}</ref>

The research from the TMR's test programme were of considerable value to future VTOL aircraft, as least in some areas: an official report published by the Ministry of Aviation summarised that "the main conclusion to be drawn from this experience is that any practical jet-lift aircraft must have some artificial stabilisation while hovering if it is to operate in other than very favourable weather conditions...the main difficulty in learning to fly the aircraft was the height control; any reduction in the time constant of the engine response would make the problem of learning to fly a jet-lift aircraft easier".<ref name = "ill 13">Illingworth 1961, pp. 13.</ref> Following the relatively successful trials of the TMR, Rolls-Royce decided to proceed with the development of the [[Rolls-Royce RB108]] direct-lift turbojet; five of these engines were used to power the first true British VTOL aircraft, the [[Short SC.1]].<ref name = "fricker 60">Fricker 1962, p. 60.</ref>