MiG-21 PD, 23-31

Also designated MiG-21 PD, and known to the Mikoyan OKB as Izdeliye (product) 92, this was essentially a MiG-21 PFM fighter fitted with a lift-engine bay amidships. The early 1960s were a time when aircraft designers around the world were excited by the possi­bility of VTOL (vertical take-off and landing), which among other things enabled combat aircraft to avoid nuclear destruction by dis­persing away from known airfields. Dassault put eight lift engines into the Mirage to create

Ye-50/l

 

MiG-21 PD, 23-31MiG-21 PD, 23-31

Подпись: able walls, and auxiliary inlets under the wing leading edge. On each side of the nose, just behind the radar, was a canard foreplane of cropped delta shape, with anti-flutter rods similar to those ofthe Ye-6T/3. Normally free to align themselves with the airflow, at Mach numbers in excess of 1.00 they were locked at zero incidence. The effect was dramatic: at 15,000m (49,200ft) they enabled the acceleration in a sustained turn to be increased from 2.5 g to 5.1 g, and they gave significantly enhanced lift in all flight regimes. Other modifications included a slightly lowered horizontal tail and a large underfin which was folded to starboard when the landing gear was extended. All might have been well had not the design team elected also to exchange the R-l 1 engine for the immature R-21, from the Met- skhvarishvili KB, with afterburning rating of 7,200kg (15,873 Ib). Ye-8/1 was flown by Mosolov on 5th March 1962, and destroyed on 11 th September by catastrophic failure of the engine. Ye-8/2, which had blown flaps, first flew on 29th June 1962 but suffered so many engine faults this otherwise promising aircraft was abandoned.Подпись:

the world’s first Mach 2 VTOL. Mikoyan de­cided instead to build a STOL (short take-off and landing) MiG-21. The engine KB of P A Kolesov produced the simple RD-36-35, a lift turbojet rated at 2,350kg (5,181 Ib). It would only have needed four of these to give the MiG-21 VTOL capability, but instead Mikoyan installed just two. The fuselage was removed between Frames 12 and 28A and re­placed by a slightly widened fireproof bay housing the two lift engines. They were not pivoted but fixed at an inclination of 80°. Fuel was drawn from the (reduced) main tankage, and starting was by impingement jets using air bled from the R-11F2-300 main engine. The top of the bay was formed by a large lou – vred door hinged at the back. In STOL mode this door was pushed up by a hydraulic jack to provide unrestricted airflow to the lift en­gines. Each jet blasted down through a vec­toring box. Made of heat-resistant steel, this provided seven curved vanes under each lift jet. These were pivoted and could be vec­tored by the pilot through an angular range of some ±25° to provide forward thrust or brak­ing. The 23-31 was intended for exploring STOL, and for improved control at low air­speeds the main-engine bleed served reac­tion-control jets pointing down from under the nose and under each wingtip. The landing gears were fixed, and there was only one air­brake, of a new design, ahead of the lift-jet bay. Pyotr M Ostapenko made the first flight on 16th June 1966. He and BAOrlov both considered control at low airspeeds to be in­adequate, and Ostapenko said ‘For take-off you need maximum dry power on the main engine, but for landing you need full after­burner!’ This aircraft performed briefly at the Moscow Domodedovo airshow on 9th July 1967. It was then grounded.

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