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- Pridružio: 18 Jun 2008
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Jedna retrospektiva na istoriju MIG-23 i 27 u Indiji.
Pokusaj zamene motora sa AL-31F i modernizacija od koje nije bilo nista na kraju...
Citat: While the airframes of both the MiG-23BN and MiG-27M had a total technical service life (TTSL) of 3,000 flight-hours, the airframe developer—Mikoyan OKB—had subsequently certified both airframes for an additional 1,200 flight-hour service-life. However, if the airframes were to be subjected to total refurbishment by HAL, then the service-life could be increased by another 3,000 flight-hours based on structural fatigue tests that could have been carried out by the National Aerospace Laboratories (NAL).
However, an engine-change was called for and Mikoyan OKB along with Moscow Machine-building Production Company (MMPP Salyut) had by the late 1990s had proposed that the Tumansky R29-300 and R29B-300 turbofans be replaced with AL-31F turbofans that offered 1-tonne maximum extra thrust-rating. This was accepted in-principle by the IAF.
In parallel, the Defence R & D Organisation’s (DRDO) Defence Avionics Research Establishment (DARE) began a deep-upgrade of the MiG-27M’s avionics suite in 2002. Only 40% of the on-board systems, mainly of the mechanical type, were retained as original factory equipment of Russian design. The first prototype MiG-27UPG flew on March 25, 2004, followed by a second prototype on November 4, 2004. Together, during their flight-trials, they flew more than 300 hours.
In June 2006, came the MiG-27UPG’s Initial Operational Clearance (IOC) certification from IAF HQ. It opened the way for work on aircraft building. After modernization, they equipped two squadrons. Modified cars received the designation MiG-27UPG.
Back in 2003, Vladimir Labazin, MMPP Salyut’s Deputy Chief Designer, described how the re-engining of MiG-23UBK tandem-seat operational conversion trainers, the MiG-23BN and MiG-27M with AL-31F turbofans could have been achieved. “Having taken stock of our capabilities, we realised that we could cough up some funds to invest into the initial-stage assessment of mounting the AL-31F. Our design bureau began looking into this in late 2002. Aircraft and engine dimensional analysis and computerised, visual and assembly coordination showed that minor airframe and engine modifications would make them compatible in terms of size. The aircraft features some room for improvement as far as airflow is concerned and we can reduce the AL-31F’s takeoff airflow a little while maximising airflow at high altitude. Early mechanical problems have already been overcome.”
“For example, the AL-31F used to keep setting against the fuel tank or some other structural elements and we had to modify the positions of some components for the engine to fit in. To keep aircraft systems intact, MMPP Salyut, retained all aircraft accessories mounted on the R29B-300’s reduction gear, with only the accessory gearbox replaced–the gear ratio of the old engine was different, so we had to replace the reduction gear. However, even though we have retained all aircraft accessories, we had to rearrange them to avoid altering the airframe and engine nacelle’s inner mould lines, fuel tanks and heavy frames.
In addition, introduction of advanced engine mounting components, re-arrangement of the accessories, generator and starter unit, and modification of the dimensions of certain engine components enabled us to squeeze the AL-31F into the nacelle without disturbing primary structural and fuel system elements of the aircraft.
During the spring and summer of 2003, MMPP Salyut developed the mock-up of the AL-31F, and after exhaustive tests conducted the final fitting. “We are planning to manufacture the engine by year-end and launch its bench tests in January 2004, and count on doing flight tests in July or August 2004. After this has been completed, we will commence full-scale improvement of the IAF’s MiG-27Ms to begin with.
To avoid redesigning the load-bearing structure of the airframe fuel cells, MMPP Salyut’s designers came up with a new load-bearing element—a longitudinal beam—that mounted the main attach fitting for the AL-31F. In addition, an extra engine attach fitting was introduced to the rear fuselage to fix the AL-31F relative to the axis, thus ensuring necessary thermal movement. Engine mounting procedures too were altered. The R29B-300 comprised two parts. The fore part was first to be mounted, then the aft one, after which both would be put together.
The AL-31F is a single-piece design and therefore it has to be installed into the fuselage mid-section, with the tail section to follow. To this end, a dedicated trolley was made, on which the AL-31F rolled into the fuselage, was then attached to main bracket supports and aligned with the aircraft’s centreline and was then fixed in this position with a dedicated rod on the fore end of the AL-31F.
Then the tail section was rolled on to the AL-31F using the dedicated trolley and linked with the mid-section. The AL-31F was then aligned with the tail bumper and detaching the hoist fitting. Then all systems were assembled. In addition, minor modifications to the aircraft had to be introduced. For example, the starter had to be rotated 200 degrees with a new exhaust shutter made, and new air ducts installed to cool the assemblies. Main modifications were made to the AL-31F. To reduce costs and time, the new accessory gearbox was made of two sections. Aircraft accessory elements were ‘borrowed’ from the previous R29 and the engine’s portion from the AL-31F. Both parts of the gearbox were linked by virtue of the new reduction gear and the casing. The engine oil system was revamped drastically because the oil tank and the oil pump pack had to be positioned where there was room to house them instead of where it was best for the engine.
Fitting the AL-31F on to the IAF’s MiG-23UBKs, MiG-23BNs and MiG-27M would have had another benefit: if those aircraft were to be discarded from service before their engines’ service-life had expired, then 70% of their components could be used for overhauling the AL-31FPs now powering the IAF’s Su-30MKI H-MRCAs. And that is because the core portions of the AL-31F and AL-31FP are identical, with only their outer componentry—casings, oil systems and outer plumbing and wiring— having been modified.
Deliveries of AL-31Fs to power the MiG-23UBKs, MiG-23BNs and MiG-27Ms were scheduled to kick off as early as the first quarter of 2005. However, to everyone’s consternation, the re-engining contract was not inked and the IAF decided not to re-engine the MiG-23UBKs, MiG-23BNs and MiG-27Ms. So, what were the consequences of this decision?
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AL-31F
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