Tethered flight test

A tethered flight test is a type of flight testing where a machine is connected by a tether to the ground. Tethered testing may be used when motion through the atmosphere is not required to sustain flight, such as for airship;[1] vertical take-off and landing (VTOL), rotary wing or tiltwing aircraft (tethered hovering);[2] or for tests of certain rockets, such as vertical takeoff, vertical landing (VTVL). Fixed wing scale models can be tested on a tether in a wind tunnel, simulating motion through the atmosphere.[3]

Tethered rocket test
Tethered VTOL test

History

Numerous vertical take-off and landing (VTOL) aircraft conducted their initial flights while tethered. Early vertical flights of the Short SC.1, an early experimental aircraft that was the first British fixed-wing VTOL aircraft as well as the first one to transition between vertical and horizontal flight modes.[4][5] For these flights, a custom-built gantry was developed that accommodated only a limited amount of freedom, up to 15 ft vertically and 10 ft off-centre in any direction, vertical velocity was also restricted to less than 10 ft/second; progressive arresting of the aircraft occurred beyond these limitation.[6] It would take off from a grid platform positioned 6 ft above the ground itself in order to circumvent the ground effect phenomenon; considerable effort on the part of Shorts had been made during development of a suitable platform to eliminate the negative impact of ground effect and was redesigned several times. The gantry facility was used for ab initio training and familiarisation purposes for the first 8 pilots to fly the SC.1.[7]

Insight from the SC.1 heavily influenced the Hawker Siddeley P.1127, the forerunner to the Hawker Siddeley Harrier VTOL fighter.[8] Its initial flights were also performed while tethered; such flights were largely conducted so that test pilots could familiarise themselves with the aircraft's controls in hover in a less risky environment. As confidence in the aircraft's handling grew, tethered flights without the aid of its onboard auto-stabiliser system were conducted.[8] Finally, on 19 November 1960, the first un-tethered free-flight hover of a P.1127 took place; flight testing of the type proceeded over the rest of the decade ahead of the first production aircraft being introduced to service in 1969.[9][10]

Numerous VTOL aircraft that would eventually be cancelled mid-development underwent tethered test flights. A pair of prototype EWR VJ 101 fighters were produced, the first performing its first hovering flight on 10 April 1963.[11] Prior to this, the VJ 1010's propulsion concept had been evaluated on a specially-produced test rig, often informally referred to as the Wippe (seesaw), during the early 1960s; it incorporated a rudimentary cockpit fixed upon a horizontal beam, which had a "lift" engine mounted vertically at the centre, for the purpose of performing preliminary single-axis tests of the control system.[12] A second "hover rig" was later assembled, possessing the skeletal fuselage of the VJ 101C along with a total of three Rolls-Royce RB108 engines installed in the approximate positions that they would occupy in the final flight-capable version and capable of lifting the test rig. Starting in May 1961, initial testing was conducted from a telescopic column, in March 1962, the new rig conducted its first "free flight" successfully.[13]

The experimental Dassault Balzac V, a forerunner to the larger Dassault Mirage IIIV, was another experimental VTOL aircraft. The Balzac commenced tethered hover flights on 12 October 1962, and achieved the first free-hover only six days later; flight testing of the type ended in September 1965 following an accident.[14][15] The Yakovlev Yak-36, an experimental VTOL aircraft developed in the Soviet Union as a forerunner to the Yakovlev Yak-38 production carrier aircraft, was also subject to a number of tethered flights in advance of freely hovering.[16] During early development work for the Ryan X-13 Vertijet, test rigs were repeatedly flown via remote control while tethered.

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References

Citations
  1. Botting, D.; Books, Time-Life (1980). The giant airships. Epic of flight. Time-Life Books. ISBN 978-0-8094-3272-1. The first rigid airship ever to be flown was built in the 1890s with a skeleton and outer cover made of an exotic new metal: aluminum. The new ship, designed by David Schwarz, a Dalmatian timber merchant, lifted off successfully in a tethered test in Berlin on November 3, 1897...
  2. Cooke, A.; Fitzpatrick, E. (2009). Helicopter Test and Evaluation. AIAA Education. Wiley. p. 103. ISBN 978-1-4051-7254-7.
  3. Galison, P.; Roland, A. (2013). Atmospheric Flight in the Twentieth Century. Archimedes. Springer Netherlands. p. 81. ISBN 978-94-011-4379-0.
  4. "Short SC1 experimental vertical take-off aircraft, 1956." Science Museum, Retrieved: 15 January 2017.
  5. "Short SC1 vertical take-off aircraft receives Northern Ireland’s first Engineering Heritage Award." Institute of Mechanical Engineers, 5 October 2012.
  6. Lean and Chinn 1965, p. 8.
  7. Lean and Chinn 1965, pp. 8–9.
  8. Mason 1967, p. 7.
  9. Mason 1967, pp. 7, 10.
  10. Jefford 2006, p. 13.
  11. Hirschel, Prem and Madelung 2012, p. 454.
  12. Rogers 1989, p. 186, 189.
  13. Rogers 1989, p. 190.
  14. Jackson 1985, p. 62.
  15. "Balzac VTOL Forerunner of the Mirage IIIV." Flight International, 2 August 1962. pp. 174-175.
  16. Gordon, Yefim; Dmitry Komissarov; Sergey Komissarov (2005). OKB Yakovlev (1st ed.). Hinkley: Midland publishing. ISBN 1-85780-203-9.

Bibliography
  • Hirschel, Ernst Heinrich., Horst Prem and Gero Madelung. Aeronautical Research in Germany: From Lilienthal until Today. Springer Science & Business Media, 2012. ISBN 3-642-18484-7.
  • Jackson, Paul. Modern Combat Aircraft 23 - Mirage. London: Guild Publishing, 1985. ISBN 0-7110-1512-0.
  • Jefford, C.G., ed. The RAF Harrier Story. London: Royal Air Force Historical Society, 2006. ISBN 0-9530345-2-6.
  • Lean D. and Chinn H.W. Review of General Operating Experience with a Jet-Lift VTOL Research Aircraft (Short S.C.l.) (Aeronautical Research Council Current Papers CP No. 832). London: HMSO, 1965. Retrieved: 2 December 2008.
  • Mason, Francis K. The Hawker P.1127 and Kestrel (Aircraft in Profile 93). Leatherhead, Surrey, UK: Profile Publications Ltd., 1967.
  • Rogers, Mike. VTOL: Military Research Aircraft. New York: Orion Books, 1989. ISBN 0-517-57684-8.
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