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`<-*>*« DPI 4 i%
`Mew Zetland NZ$2.30
`Norway NKr !7 00
`Singapore MJ4 SO
`Spain Pts. 150.00
`Switzerland Fr. 4.60
`^.75
`
`GE-1017.001
`
`

`
`N4247C-
`
`»
`
`life* - * W; « ^ ^1 1 « 9 £ B i e:
`A L F 5 0 2: plugging the turbofan gap
`R I C H A RD W H I T A K ER reports from C O N N E C T I C UT Cutaway by F R A NK MUNGER
`AVCO LYCOMING is gradually in-
`removed and then replaced immedi(cid:173)
`for the more difficult parts. This ap(cid:173)
`ately by a hot end from stores without
`proach gives Avco considerable flexi(cid:173)
`balancing.
`bility, since it can dispense with some
`of the subcontractors when demand is
`Two men need 2-2hr to replace a
`not so great.
`combustor/turbine module, and l-8hr
`to
`replace
`an
`accessory
`gearbox
`Avco has also increased the number
`module. Both operations can be done
`of
`employees
`at Stratford
`from
`without removing the engine. Fan and
`2,700 in 1978 to more than 5,000—
`gas-producer module
`changes
`are
`this is no easy task, since the numer(cid:173)
`done in the shop, but up to five op(cid:173)
`ous high-technology companies in the
`posite pairs of fan blades (out of 40
`area
`tend
`to soak up
`the
`skilled
`blades) may be replaced on the air(cid:173)
`labour. There is also the problem of
`craft without balancing. Up to
`ten
`taking employees away
`from
`local
`compressor blades may be replaced if
`component subcontractors.
`their replacements are within weight
`The main points about the ALF502
`limits. In fact, Avco claims that all
`are that
`its high bypass-ratio gives
`maintenance can be done
`in
`the
`good fuel consumption and low noise,
`hangar, except for compressor dis(cid:173)
`and its modular construction makes
`mantling, which needs complex bal(cid:173)
`for good maintainability. There are
`ancing gear.
`four modules—fan, accessory gearbox,
`gas producer, and combustor turbine.
`One factor in the ALF502's main(cid:173)
`Each module is balanced before leav(cid:173)
`tainability is that it is fairly small, so
`ing the factory, so the modules are
`the modules are relatively lightweight,
`interchangeable directly. This means
`especially for an aircraft such as the
`that a hot end, for example, can be
`146, which might have been powered
`
`the production rate of
`> creasing
`its ALF502
`light, high bypass-ratio
`turbofan, and has delivered 107 en(cid:173)
`gines for
`its
`two applications—the
`BAe 146 feederliner and the Canadair
`Challenger business aircraft. Although
`Avco has won some notoriety over its
`difficulty
`in meeting 502 schedules,
`both versions are certificated and the
`company
`is reorganising its produc(cid:173)
`tion to produce 12 engines a month
`by the summer.
`The ALF502 is based on Avco's T55
`core, more than 3,500 of which have
`been produced for the Chinook, Bell
`214, and industrial and marine appli(cid:173)
`cations. The ALF502R-3
`is
`take-off
`rated at 6,7001b for the BAe 146, and
`the ALF502L uses an extra
`inter(cid:173)
`mediate-pressure compressor stage to
`increase the thrust to 7,5001b for the
`Challenger. This places
`the engine
`neatly between
`the Garrett ATF3,
`which produces just over 5,0001b, and
`the General Electric TF34, which
`clocks up 8,6501b.
`T55 cores represent only 35 per cent
`of Avco's turbine activities. The T53
`and LT101 account for 15 per cent
`each, and the M-l tank engine takes
`up about 25 per cent of Avco's efforts.
`The rest of its activities include re(cid:173)
`search. The addition of the ALF502
`to the range has put a lot of pressure
`on Avco, both
`in development—
`especially of
`the gearbox—and
`in
`production.
`To relieve things at Avco's Strat(cid:173)
`ford, Connecticut, factory, the com(cid:173)
`pany has transferred all production of
`the LT101 series
`to Williamsport,
`Pennsylvania, home of Avco's piston-
`engine work. A new factory at Greer,
`South Carolina, should begin to pro(cid:173)
`duce ALF502 blades and discs
`in
`May. Finally, Avco has obtained
`second-source
`suppliers
`for many
`components, freeing its own machines
`
`ALF502 history
`THE AJLF502 is
`the commercial
`now uses the AI.F502K-3, which has
`version of the YF102, which flew in
`a slightly higher rating, 6,7001b.
`a
`test-bed
`in 1972 and powered
`Meanwhile.
`Canadair
`had
`the Northrop A-9A contender for
`selected
`the 7,5001b AI.F502L for
`the US Air Force's AX competi(cid:173)
`its Challenger business aircraft, de(cid:173)
`tion, eventually won by the A-10.
`rived
`from Bill Lear"s LearStar
`The first civil application for the
`(hence
`the L designation). The
`turbofan was the ill-fated Dassault
`Challenger made its maiden flight
`Falcon 30 30-seat transport. This
`on November 8, 1978, and the BAe
`made more
`than 100 flights
`in
`146 flew for
`the
`first
`time on
`1974-74. and was powered by the
`September 3, 1981. The ALF502L
`6,5001b AEF502D
`flat-rated
`to
`was certificated in February 1980,
`5,5001b.
`while
`the ALF502R
`received
`its
`FAA approval in January 1981. The
`the
`Hawker Siddeley selected
`only other aircraft to fly with this
`6,5001b ALF502H for its HS.146 in
`engine is Nasa's Quiet, Short Haul
`1973, but the project was postponed
`Research Aircraft, a modified Buf(cid:173)
`for market reasons. The aircraft
`falo which
`still
`flies with
`the
`was resurrected by British Aero(cid:173)
`YF102s from the A-9A.
`space in 1978, and the BAe 146
`
`FLIGHT
`
`International, 30 January 1982
`
`237
`
`GE-1017.002
`
`

`
`238
`
`HIGHT International. 30 January 1982
`
`GE-1017.003
`
`

`
`/J\
`AVCO
`LYCOMING A
`
`retaining
`
`roller
`
`Key
`1 Titanium fan unit
`2 Fan blade snubbers
`3 Steel fan casing (dia 41 in)
`4 Containment ring
`5 Lightweight alloy main support
`frame
`4 Fan thrust-bearing
`7 LP shaft speed strobe
`8 Fan shaft support bearing
`9 2-3:1 reduction gear
`10 Planetary gear roller bearing (seven
`planet gears)
`I I Planetary gear-carr ier
`spring
`12 HP compressor thrust bearing
`13 HP
`compressor
`support
`bearing
`14 Seven-stage axial compressor
`15 Stator segments
`16 Single-stage,
`two-piece
`centrifugal compressor
`17 Lightweight alloy split compressor
`casing
`18 Field-replaceable
`blades
`19 Wrought steel-alloy discs
`20 High-temperature steel alloy diffuser
`case
`21 Coated high-temperature steel com(cid:173)
`bustion chamber
`22 Combustion-chamber retaining bolts
`23 Sealing rings
`24 Steel LP shaft
`25 Coated, air-cooled nozzle blades
`26 Coated, air-cooled HP turbine blades
`27 Coated stator blades
`28 High temperature steel discs
`29 High temperature steel LP turbine
`discs and blades
`30 LP turbine thrust bearings
`31 Bleed-air duct
`32 Sixth stage bleed tapping, open for
`acceleration and low speed steady
`state
`33 Compressor delivery
`control
`34 Bleed-air control band
`35 Bleed-air control band actuator (to
`reduced scale)
`36 Igniter
`37 Thermocouple harness
`38 Fuel nozzle
`39 Fuel manifold
`40 Fuel control unit
`41 Power control lever
`42 Main fuel
`filter
`43 In-line fuel filter
`44 Fuel flow-meter
`45 LP shaft overspeed shut-off valve
`46 Fuel from oil/fuel heat-exchanger
`47 Fuel to oil/fuel heat-exchanger
`48 Fuel boost pump
`49 Fuel inlet to pump
`50 Intake pressure sensing air
`51 Sensing air exhaust
`52 Oil lines to oil/fuel heat exchanger
`53 Oil tank
`54 HP compressor bearing oil supply
`55 Turbine bearing oil supply
`56 Oil anti-iced spinner
`57 De-icing bleed-air
`58 De-icing air control valve
`59 De-icing air duct to casing
`60 De-icing air duct round intake lip
`61 Front mounting pad {four places)
`62 Rear mounting pad (three places)
`63 Integrated drive and generator
`envelope
`
`titanium,
`
`stainless steel
`
`to bleed-air
`
`'J/
`
`fKANK
`
`nUNGBfj An<itt<S.
`
`FLIGHT International, 30 January I9B?
`
`239
`
`GE-1017.004
`
`

`
`is an important
`An Avco Lycoming technician assembles on ALF502L at Stratford. Maintainability
`factor on the ALF502. Only three special tools are needed for module changes, and Avco claims the
`initial
`time between overhauls to be 4,000hr
`
`by two engines of twice the thrust
`and more complexity. The fan is the
`heaviest module (4971b), the gas pro(cid:173)
`ducer weighs 3191b, the combustor/
`turbine is 2481b, and the gearbox 411b.
`Although
`the T55 and ALF502
`series have a similar core, it has been
`developed enormously since the mid-
`1950s, when the original engine de(cid:173)
`veloped 1,600 e.s.h.p. Now, the biggest
`T55 develops 4,750 e.s.h.p. The length
`and diameter has remained the same,
`the power increase coming from extra
`turbine stages, better turbine cooling,
`compressor improvements, and better
`
`materials. Avco tells Flight that there
`is still scope for increasing the core's
`power output.
`The T55 has a centrifugal compres(cid:173)
`sor, preceded by a seven-stage axial
`compressor. Avco's reasoning behind
`the centrifugal compressor lies mainly
`in the engine's helicopter applications
`—the arrangement is tougher, shorter,
`and does not need as many small axial
`blades. The
`annular
`reverse-flow
`combustor also helps to keep the en(cid:173)
`gine short, and it shields the turbine,
`reducing noise. The combustor has a
`high mixing
`length, which
`reduces
`
`Left The RAe 146 is
`powered by four ALF-
`502s slung in under-
`wing pods. The air(cid:173)
`craft's
`wings
`are
`made by Avco's Aero-
`structures division
`
`noise because the eddies can dissipate
`before reaching the turbine. A two-
`stage, high-pressure
`turbine with
`cooling drives the compressor, while
`the fan is driven by a two-stage low-
`pressure
`turbine. The
`two
`shafts
`contrarotate.
`Most of the development work on
`the 502 has been connected with the
`fan. Avco decided on a geared fan
`arrangement, mainly because it saves
`two
`turbine
`stages,
`reducing core
`noise. (Stages would be needed to off(cid:173)
`set the lower shaft speed with no gears.)
`The three planetary gears give a 2-3:1
`speed reduction. It was in this area
`that Avco had its most
`significant
`development problem—there were two
`gearbox failures in-house in 1979, both
`being caused by a resonant frequency
`problem. Avco has now cleared this
`up, largely by modifying the bearings.
`Nevertheless,
`the problem delayed
`the programme because it occurred
`just as the engine was entering pro(cid:173)
`duction.
`Compared with the T55, the 502 has
`an extra rear mounting for the fan,
`and a higher compressor pressure-
`ratio. The higher operating altitude
`for the turbofan requires more accel(cid:173)
`eration bleed-air, and this is governed
`by an extraction gallery surrounding
`the casing between
`the sixth and
`seventh
`compressor
`stages. The
`gallery controls the bleed air by mov(cid:173)
`ing in and out, and is connected to
`the main fuel control.
`The BAe 146 engine, the ALF502R-3,
`has a single
`intermediate-pressure
`(IP) compressor stage
`just behind
`the fan. Here lies the main difference
`between the two versions of the 502,
`because the Challenger version has
`two IP stages, making
`the engine
`about 2in longer. The installation is
`different for the two versions, to cater
`for the 146's underwing position and
`Challenger's tail mounting.
`Since the Challenger operates at
`higher altitudes—cruise altitude
`is
`45,00Oft, compared with
`the 146's
`25,000ft or less—the 502L's fan blades
`are twisted at 15° rather than 12°.
`This gives a slight sea-level penalty
`but gives better altitude performance.
`There are also differences in the fuel
`controls to allow for the altitude dif(cid:173)
`ference. The 146 uses a Plessey elec(cid:173)
`tric starter, while Challenger has a
`Garrett pneumatic starter. Avco tells
`
`ALF502 L E A D I NG D A TA
`
`Description
`T a k e - o ff thrust (lb)
`Bypass ratio
`O v e r a ll pressure ratio
`Cruise s.f.c. (Ib/hr/lb)
`Length (in)
`D ry w e i g ht (lb)
`D i a m e t er (in)
`M ax airflow (lb/sec)
`LP stages
`H P stages
`T u r b i ne stages
`
`ALF502L-2
`
`ALF502R-3
`
`Two-shaft turbofan
`7,500
`6,700
`50
`5-71
`13-6
`11 4
`0-424
`0-411
`58-6
`56-8
`1,298
`1,270
`41-7
`41-7
`256
`245
`Fan, 2 IP
`Fan 1 IP
`7 axial, 1 centrifugal
`2 HP, 2 LP
`
`rated at 7,800lb with a cruise
`N o t e: A v co is developing the ALF502L-3,
`ALF502R will be rated at 6,970lb
`s.f.c. of 0-413. A new version
`of the
`with a cruise s.f.c. of 0-400.
`
`FLIGHT International, 30 January 1982
`
`240
`
`GE-1017.005
`
`

`
`and when the thrust demand is in(cid:173)
`creased the other orifice comes into
`play. This reduces the amount of un(cid:173)
`necessary fuel sprayed during
`idle.
`Avco has optimised the flow divider
`schedule carefully
`to ensure maxi(cid:173)
`mum efficiency.
`that it holds
`Canadair tells Flight
`orders for 138 Challengers, of which
`127 will be powered by the ALF502.
`The remaining customers have chosen
`the more powerful General Electric
`CF34—the GE engine was also to have
`powered the larger Challenger E, but
`this project has been shelved. Cana(cid:173)
`dair has now delivered 28 Challengers,
`and it has no complaints about
`the
`engine—service entry problems have
`been
`relatively
`small
`and
`easily
`solved. It
`is impossible to estimate
`how much of
`the delay
`in getting
`Challenger in service was due to en(cid:173)
`gine delivery, and how much was due
`to
`the
`extensive
`redesign which
`Canadair performed on the original
`LearStar to obtain Challenger.
`BAe 146 sales remain at 13, with
`12 options. The announced customers
`are Air Wisconsin
`(four, plus four
`options), and Pacific Express
`(six
`plus eight). The aircraft will be cer(cid:173)
`tificated
`in August. BAe comments
`that it has never complained about
`the ALF502, and that the engine "has
`never been the pacing item" in the
`programme. There have been no
`engine removals in the 114hr which
`the first 146 has flown. Avco has
`delivered 19 engines to BAe, and en(cid:173)
`gines are mounted on the third air(cid:173)
`craft.
`After a lengthy gestation and prob(cid:173)
`lems meeting deliveries because of
`the large volume of work at Stratford,
`Avco seems to be getting the situation
`sorted out. Our calculations indicate
`that 63 engines were delivered during
`1981, and Avco expects to be produc(cid:173)
`ing 12 a month by summer.
`J3
`
`noise. Acoustic de-tuning was also
`accomplished by optimising
`the fan
`rotor/stator ratio—there are 40 fan
`blades and 85 stator vanes. The fan
`design was changed after running the
`initial design, which proved too noisy.
`Avco's geared fan allows the tur(cid:173)
`bine to run at 20,000 r.p.m., which is
`largely above the audio range, so tur(cid:173)
`bine noise is low. Finally, the com-
`bustor is long^allowing eddy dissipa(cid:173)
`tion before
`the
`turbine—and wraps
`around the turbine, reducing noise.
`The ALF502 will meet ICAO emis(cid:173)
`sion regulations which come into force
`in 1983, and which cover
`smoke,
`carbon monoxide, hydrocarbons, and
`nitrogen oxides. This is partly because
`of
`the moderate
`temperatures and
`pressures
`in
`the engine. The com-
`bustor efficiency is claimed to be high
`as a result of the airblast atomiser
`design. This means that there is less
`unburnt fuel
`to cause hydrocarbon
`emissions, which are often a problem,
`especially at idle-thrust.
`The atomisers work by surrounding
`the fuel spray by two layers of air
`which blast into the can. There are
`two fuel orifices. During engine idle,
`fuel is sprayed from only one orifice,
`
`Flight that it could increase the thrust
`relatively easily by putting in a third
`IP compressor stage and
`increasing
`the turbine diameter.
`Avco introduced several modifica(cid:173)
`tions to the engine in autumn 1979.
`Better compressor-stator sealing
`im(cid:173)
`proved the efficiency and surge mar(cid:173)
`gin, and Avco redesigned the 28 fuel
`injectors. The nozzle diameters were
`increased to reduce their tendency to
`be blocked by contaminants, while the
`spray patterns were kept the same.
`The most
`recent change
`to
`the
`ALF502 is the introduction of the L-3,
`which is a package of modifications to
`the L-2, yielding a 4 per cent take(cid:173)
`off thrust increase and a 2 per cent
`cruise
`specific
`fuel
`consumption
`(s.f.c.) improvement. The new version
`of
`the engine has reduced cooling
`airflow leakage in the HP turbine, tip-
`clearance control in the second-stage
`turbine, lower gearbox oil-flow in the
`cruise, and reduced LP compressor
`inter-stage bleed-air.
`im(cid:173)
`the
`Avco has demonstrated
`provements in thrust and s.f.c., and a
`reduction of 17°C
`in
`the
`cruise
`turbine-entry temperature, on the test
`rig. Certification of the new variant
`is due
`in June. Avco
`tells Flight
`that a similar package of modifica(cid:173)
`tions will be certificated
`on
`the
`ALF502R-3 this year, and that
`this
`will yield the same thrust and s.f.c.
`improvements. The modifications can
`be retrofitted on to existing L-2s and
`R-3s in the field.
`The ALF502s materials are fairly
`conventional, but a patented Avco
`high-temperature steel alloy is used
`in the turbine and nozzle. The fan,
`IP compressor, and centrifugal com(cid:173)
`pressor are made of titanium, while
`the HP compressor is steel.
`Both the 146 and the Challenger
`are quiet aircraft, as a
`result of
`attention to keeping down the 502's
`noise. The high bypass-ratio
`is an
`obvious
`reason
`for quietness. The
`variable inlet guide vanes of the T53
`were dispensed with for the T55 and
`ALF502, partly
`for
`simplicity and
`lower cost, and partly
`to
`reduce
`noise—there are no wakes for
`the
`fan blades to impinge upon.
`Avco decided on two rotor-chords
`as the spacing between the fan blades
`and stators, since this is enough to
`allow eddies
`to dissipate—reducing
`
`FLIGHT
`
`International,
`
`30 January 1982
`
`GE-1017.006