Editing Rolls-Royce Thrust Measuring Rig

{{Short description|1950s British experimental VTOL aircraft}}
{{Redirect|Flying bedstead|the NASA lunar landing training simulator|Lunar Landing Research Vehicle}}
{{Use dmy dates|date=August 2017}}
{{Use British English|date=August 2017}}
{{Infobox aircraft
| name=Thrust Measuring Rig
| image=File:Rolls-Royce Thrust Measuring Rig science museum.jpg
| caption=On display in the [[Science Museum, London]]
| type=Experimental vertical take-off
| national_origin=United Kingdom
| manufacturer=[[Rolls-Royce Limited|Rolls-Royce]]
| designer=
| first_flight=3 August 1954 (free)
| introduction=
| retired=
| status=
| primary_user=
| number_built=2
| developed_from=
| variants=
}}

The '''Rolls-Royce Thrust Measuring Rig''' (TMR) was a pioneering vertical take-off and landing ([[VTOL]]) aircraft developed by [[Rolls-Royce Limited|Rolls-Royce]] in the 1950s. It has the distinction of being "the first jet-lift aircraft to fly anywhere in the world".<ref name = "ill 2" />

The design of the TMR is unique. It was powered by a pair of [[Rolls-Royce Nene|Nene]] [[turbojet]] engines, which were mounted back-to-back horizontally within a steel framework; in turn, this framework was raised upon four legs fitted with castors for wheels. The TMR lacked any lifting surfaces, such as [[wing]]s; instead, lift was generated purely by the thrust being directed downwards. Due to its unconventional appearance, it was [[nickname]]d the '''Flying Bedstead'''.<ref name = "ill 2">Illingworth 1961, p. 2.</ref>

The TMR had been envisioned specifically for conducting research, specifically to explore the potential applications of then-newly developed [[jet propulsion]] towards carrying out vertical flights. First flying in August 1954, extensive studies were conducted during a series of test flights into how stabilisation could be performed during the aircraft's hover. It contributed to a greater understanding of the level of power and appropriate manners of stabilisation involved in a VTOL aircraft, as well as proving the feasibility of the concept in general.<ref name = "ill 2 3">Illingworth 1961, pp. 2-3.</ref>

== 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>

== Design ==
The Rolls-Royce Thrust Measuring Rig (TMR) was a VTOL aircraft developed to explore the practicality, characteristics, and requirements of such an aircraft.<ref name = "ill 2 3" /> It was widely known by its nickname of the ''Flying Bedstead'' due to its radically unconventional appearance for an aircraft, basically consisting of a rectangular tubular framework that was built around the engines, a platform being placed on top of which to accommodate a single pilot. It did not have any [[Aerodynamics|aerodynamic]] shape, lacking either wings or a tail; it instead generated all of its lift by directing the thrust of its engines directly downwards.<ref name = "ill 3 13">Illingworth 1961, pp. 3, 13.</ref> Due its small size, the TMR had a maximum flight endurance of only six minutes.<ref name = "fricker 25" />

It was powered by a pair of [[Rolls-Royce Nene|Nene]] [[turbojet]] engines, which were installed in a back-to-back configuration.<ref name = "ill 3" /> The output of the [[Jet engine|jets]] was directed towards the [[Center of mass#Center of gravity|centre of gravity]] of the rig; one jetpipe discharging downwards through a central nozzle while the other jet discharged downwards through two smaller nozzles on either side; this was so that, in the event of a single engine failing during flight, there would not be any sharp adverse movement as a result. Considerable precautions were taken to safely sustain such an engine failure; the four-leg [[landing gear|undercarriage]] was designed to support a vertical velocity of {{convert|34|ft/s}}, and to withstand a single-engine landing from any height below {{convert|50|ft|round=5}}.<ref name = "ill 3" /> The TMR possessed only marginal excess power, which complicated the act of flying the aircraft; this was further compounded by the slow response time of the engines to throttle changes. Accordingly, there was a considerable degree of anticipation in the use of engine power required to prevent overshooting of desired altitude, and to ensure a gentle touchdown when landing.<ref name = "ill 7 8">Illingworth 1961, pp. 7-8.</ref>

A total of four outrigger arms extended out from the rig, one on either side and one each at the front and rear, through which [[compressed air]] was released for control in [[Flight dynamics|roll]], [[Flight dynamics|pitch]] and [[Flight dynamics|yaw]] when in flight.<ref name = "ill 3 4">Illingworth 1961, pp. 3-4.</ref> While the controls for yaw and height were mechanically based, the pitch and roll controls were electrically signalled, without any provision for reverting to mechanical operation. Initially, key components for the electrical control system components were duplicated; however, in order to make the detection of faults infallible, a safer partial-triplex arrangement was adopted for the RAE's free flight testing phase.<ref name = "ill 4">Illingworth 1961, p. 4.</ref> As the TMR possessed no inherent [[Flight dynamics|stability]], it incorporated an experimental automatic stabiliser system.<ref name = "ill 12">Illingworth 1961, p. 12.</ref> During its numerous test flights, varying degrees of intervention by the stabiliser were performed, including a few in which no stabilisation was active at all.<ref name = "ill 9 10">Illingworth 1961, pp. 9-10.</ref>

== Aircraft on display ==
The first machine (Serial ''XJ314'') is preserved and on public display at the [[Science Museum, London|Science Museum]] in London, England.<ref>[http://www.makingthemodernworld.org.uk/icons_of_invention/technology/1939-1968/IC.063/ "The Rolls-Royce Flying Bedstead, 1954."] ''makingthemodernworld.org.uk'', Retrieved: 7 January 2016.</ref><ref>[http://collection.sciencemuseum.org.uk/objects/co29091 "The Rolls-Royce vertical take-off-thrust measuring rig, 1954."] ''Science Museum'', Retrieved: 7 January 2016.</ref>

== Specifications (Thrust Measuring Rig) ==

{{Aircraft specs
|ref=<!-- reference -->
|prime units?=imp
<!--
        General characteristics
-->
|crew=
|capacity=
|length ft=28
|length in=0
|length note=
|width ft=14
|width in=0
|width note=
|height ft=12
|height in=8
|height note=excluding pylon
|empty weight lb=6000
|empty weight note=
|gross weight lb=7500
|gross weight note=
|max takeoff weight lb=
|max takeoff weight note=
|fuel capacity=
|more general=
<!--
        Powerplant
-->
|eng1 number=2
|eng1 name=[[Rolls-Royce Nene]]
|eng1 type=[[centrifugal-flow turbojet]] engines
|eng1 lbf=4050
|eng1 note=
<!--
        Performance
-->
|max speed mph=
|max speed note=
|cruise speed mph=
|cruise speed note=
|never exceed speed mph=
|never exceed speed note=
|range miles=
|range note=
|ferry range miles=
|ferry range note=
|endurance=<!-- if range unknown -->
|ceiling ft=
|ceiling note=
|climb rate ftmin=
|climb rate note=
|time to altitude=
|thrust/weight=1.08

|more performance=
|avionics=
:*Automatic stabilisation 
}}

== See also ==
;Comparable aircraft
*[[Aérospatiale Ludion]]
*[[SNECMA Atar Volant]]
*[[Lunar Landing Research Vehicle]]
*[[VFW SG 1262 Schwebegestell]]

== References ==

{{Reflist|colwidth=26em}}

=== Sources ===

* Buttler, Tony and Jean-Louis Delezenne. ''X-Planes of Europe: Secret Research Aircraft from the Golden Age 1946-1974''. Manchester, UK: Hikoki Publications, 2012. {{ISBN|978-1-902-10921-3}}
* Fricker, Jon. [https://books.google.com/books?id=bHZ-ngYi4zUC&pg=PA24 "Jet Lift: The Rolls-Royce Concept."] ''Flying Magazine'', July 1962. Vol. 71, No. 1. pp.&nbsp;24–25, 60–64.
* Illingworth, J. K. B. [http://naca.central.cranfield.ac.uk/reports/arc/rm/3336.pdf "Flight Tests of a Hovering Jet-Lift Aircraft (Rolls-Royce Flying Bedstead)."] ''[[Ministry of Aviation]]'', May 1961.

== External links ==
{{Commons category}}
* [https://web.archive.org/web/20070223235719/http://vtol.boom.ru/vtol/TMR/index.html Pictures of the Thrust Measuring Rig (with text in Russian)]
* [http://www.scienceandsociety.co.uk/results.asp?image=10437314&wwwflag=&imagepos=1 A Science Museum picture of ''XJ314'']
* [http://www.scienceandsociety.co.uk/results.asp?txtkeys1=Flying+Bedstead Flying Bedstead' after its (Low Fuel) accident, Hucknall, Nottinghamshire, 1957. With Air Commodore Larsen]
* [https://www.youtube.com/watch?v=f8W2SI4c93s Pathe News – ''Flying Bedstead'']
* [https://soundcloud.com/zazie-dans-le-metro/flying-bedstead-from-transcription-disc BBC transcription disc Interview – ''Flying Bedstead'']

[[Category:Ashfield District]]
[[Category:1950s British experimental aircraft]]
[[Category:British inventions]]
[[Category:Rolls-Royce aircraft|TMR]]
[[Category:Science and technology in Nottinghamshire]]
[[Category:VTOL aircraft]]