TUPOLEV Tu-155 / EXPERIMENTAL TEST-BEDS
Experimental Test-beds Purpose: To use established aircraft to flight-test experimental items. Design Bureau: Various. In Russia flying test-beds are as a class called by the suffix initials LL, from Letayushchaya Laboratoriya, flying laboratory. One of the most important LL tasks is to flight-test new types of engine. Several experimental engines have appeared in this book already, for example rockets to boost the speed and altitude of fighters, and the awesome TV-12 turboprop tested on a Tu-4. Until the 1980s the most important LL for flight-testing engines was the Tu-16. As explained in the entry on
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that aircraft, engines had to be installed for testing in or under its bomb bay. In recent years the Ilyushin IL-76 has come to the fore as a totally capable engine test-bed, handicapped only by its considerable size and operating cost. Originally designed as the IL-76M military transport, this superb aircraft is an ideal LL on which to hang virtually any type of aircraft propulsion system, usually using the No 2 (port inner) underwing pylon attachment. A considerable fleet of IL-76 aircraft is available in former Soviet territories. Several are operated by the Gromov Flight Research Institute (or LII), and are available for hire. Their interiors are already packed with sen-
sors and loggers, computers, oscilloscopes and many kinds of instrumentation, overseen by a test and research crew which usually numbers five. The flight crew typically numbers three. Among the engines tested are the NK-86, D-18T and PS-90A turbofans, and the D-236 and NK-93 propfans. One of the photographs shows a former IL-76M used for testing large turbofans of the D-18 family. The other shows a former civil IL-76T used to test the TV7-117S turboprop and its six-blade Stupino SV-34 propeller. The propeller blades are heavily strain-gauged, the instrumentation cable being led forward from the tip of the spinner.