Andrei Yurgenson talks to Salut MMPP deputy chief designer Vladimir Labazin about how the organisation is re-engining aircraft with the AL-31F and how this new ‘heart' will extend service life of the global MiG fleet
The Russians are in Dubai to demonstrate their commitment to legacy contracts for their fighter aircraft.
Russia has been upgrading relatively new MiG-29 and Su-27 fighters and is offering a new lease of life to older examples that remain in service around the world.
Of the deals already cut in the aircraft upgrade field, the contract to modernise the MiG-21bis fighters of the Indian Air Force (IAF) has the highest profile.
MiG-23 third-generation supersonic jets had been exported on a large scale since the 1970s in the fighter (MiG-23MS, MiG-23MF, MiG-23ML) and fighter-bomber (MiG-23BN, MiG-27M) versions.
Roughly 1,500 of the type were in the air force inventories of a number of Middle East, African and East Europe countries, as well as India, Cuba and North Korea.
In the Middle East and North Africa alone, almost 400 MiG-23MS/MF/ML fighters, MiG-23BN fighter-bombers and MiG-23UB combat trainers were delivered. The largest MiG-23 fleets are operated by Syria (about 140 aircraft), Libya (around 130) and Algeria (more than 60). The third-generation MiGs are still flown by Yemen, Ethiopia, Angola and Sudan.
The quantum leap in electronics means these aircraft can be provided with new capabilities and made more efficient, extending the life of the MiG-23s, which were delivered over the 1980s.
‘Implanting'
However, the MiG-23 and MiG-27's service life extension is limited by the state of their powerplants, with their organic R29-300 and R29B-300 engines nearing their service life expiry date and being no match for up-to-date turbofans.
This prompted the Salut Moscow Machine-building Production Company – the manufacturer of the world-famous AL-31F – to come up with an idea of ‘implanting' a new ‘heart' into the airframes of the venerable veterans. The idea was quick to attract customers.
At present, the Salut MMPP enterprise is not only the major Russian manufacturer and maintainer of advanced aircraft engines. Having begun importing technology 90 years ago, Salut is a major player on the international market, exporting both finished engines and their repair/overhaul technologies.
In addition to the well-developed production facilities, the company has a design bureau which is developing cutting-edge civil and military applications and upgrades for AL-31Fs for Su-27 family fighters. One such upgrade is designed to re-engine MiG-23 and MiG-27 aircraft.
Vladimir Labazin, Salut MMPP deputy chief designer, describes how the organisation is re-engining these aircraft with the AL-31F.
"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 onto the MiG-27. 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," Labazin says. "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 been overcome, he says. "For example, the engine 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, he said, the company "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, rearrangement of the accessories, generator and starter unit, and modification of the dimensions of certain engine components enabled us to ‘squeeze' the engine into the nacelle without disturbing primary structural and fuel system elements of the aircraft "During spring and summer 2003, Salut 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. This completed, we will commence full-scale improvement of real combat aircraft under the contract with the Indian side."
To avoid redesigning the load-bearing structure of the airframe fuel cells, Salut's designers suggested a new load-bearing element – a longitudinal beam – that mounts the main attach fitting for the new engine. In addition, an extra engine attach fitting has been introduced to the rear fuselage to fix the engine relative to the axis, thus ensuring necessary thermal movement.
Modifications
Engine mounting procedures have altered too. The R29B-300 consisted of 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; therefore it has to be installed into the fuselage midsection with the tail section to follow.
To this end, a dedicated trolley has been made, on which the AL-31F rolls into the fuselage, is attached to main bracket supports and aligned with the aircraft centreline and is then fix in this position with a dedicated rod on the fore end of the engine. Then the tail section is rolled onto the engine using the dedicated trolley and linked with the midsection. The engine is aligned with the tail bumper and detaching the hoist fitting. Then all systems are assembled.
In addition, minor modifications to the aircraft had to be introduced. For example, the starter had to be rotated 200 with a new exhaust shutter made, and new air ducts installed to cool the assemblies.
Main modifications were made to the engine. To reduce costs and time, the new accessory gearbox were made of two sections. Aircraft accessory elements were ‘borrowed' from the previous engine and the engine's portion from the AL-31F.
Both parts of the gearbox are 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 engine onto the IAF's MiG-27MLs has another benefit: if the MiG-27s are discarded from service before their engines' service life expires, 70% of their components could be used for overhauling the AL-31FPs now powering the IAF's Su-30MKI aircraft.
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 MiG-27s might kick off as early as early 2005.
Another attractive solution is retrofitting AL-31F engines onto MiG-23 aircraft that remain in service with air forces across the globe. Implementing this solution faces even fewer problems than MiG-27 retrofitting while the benefits might be impressive.
Source: Flight Daily News
