Atethered 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 wingortiltwing 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]
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.
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...
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