The release of global RFIs on January
19, 2019 by India’s state-owned Hindustan Aeronautics Ltd (HAL) for the supply
of three separate aircraft fuselage assembly jigs (one unit of each type) meant
for fabricating the front, centre and rear fuselage sections of a single full-scale
engineering-test model of the projected LCA-AF Mk.2 multi-role combat aircraft
(MRCA) is indicative of what the DRDO’s Bengaluru-based Aeronautical Development
Agency (ADA) had proposed back in 2014, and which can be viewed here:
It can thus be safely inferred that ADA
has passed on the Design Applicability List (DAL) and Standard of Preparation
(SOP) documentation to HAL for the full-scale engineering-test model of the
projected LCA-AF Mk.2, which in turn will be used for optimising the design and
location of the various mission avionics sub-systems/LRUs and related wiring harnesses,
hydraulic pipings, accessories, and skin-level distributed apertures for sensors
of the integrated EW suite, inclusive of radar warning receivers-cum-jamming
emitters, laser warning receivers, and missile approach warning systems.
Simply put, jig-less assembly aims at
reducing or eliminating the need for product-specific jigs during airframe assembly
by developing new assembly concepts, models, tools and procedures. In the new
concept of jig-less aircraft assembly, the end locators are replaced by
transferring the holes directly on to the part. These holes are made by high-precision
machines. In this approach, all the parts will have at least two holes so that
one part can be assembled with the adjacent part. These holes are termed as
‘key holes’. In this method, the tooling elements (end locators) are eliminated
and only the jig is used as the main assembly structure. This approach reduces
the tool manufacturing time, reduces the product-dependent fixture and also
increases the accuracy of the assembled product. It also results in a reduction
of the number of tools and joints (rivets), and subsequently weight as well. And
going hand-in-hand with jig-less assembly is the practice of using modular
tooling solutions.
The most common tooling technology for
aircraft assembly used today is conventional tooling consisting of steel beams
that are welded together. Such toolings are tailored for a specific tooling
operation. Since conventional tooling is designed to a specific application,
each assembly has its own dedicated tooling, or product-specific tooling. In
addition, when building a complex product like a MRCA, the final design is
forced by changes that immediately affect the tooling design. This necessitates
modifying the tooling/ locating holes or shimmed pick-ups to new locations.
Hence, the preferred solution today is modular tooling, which is built for a
dedicated purpose as well, but the surrounding system and distance supports are
designed from a toolbox of modular components. The framework of modular tooling
is screwed together. It thus helps in reducing the cycle-time of assembly,
thereby enhancing the production rate. Modular tooling also helps to design
jigs/ fixtures that will meet a group of components.
The front fuselage assembly jig for the LCA-AF
Mk.2 will be made up of various modules like the composite radome, floor
assembly, canopy, windscreen, starboard and portside air-intakes, twin canards,
starboard and portside wing leading-edge root extensions. The assembly will
comprise approximately 1,300 individual parts, out of which 40% are estimated
to besheet metal, 30% being machined parts and the remaining 30% being made of
carbon-fibre composites (CFC). The length of the assembly is 6,100mm, with a
maximum width of about 1,100mm. The assembly will comprise 23 stations, and the
entire assembly will weigh some 500kg. The component assembly will comprise the
following attachment points: 1) Bulkheads for cockpit avionics 2) Nose landing
gear pivot 3) Nose landing gear jack-point 4) Nose landing gear up-lock 5) Windscreen
6) Canopy 7) Wing leading-edge root extensions 8) Air intakes 9) Radome 10)
Starboard side fixed air-to-air refuelling probe 11) Longerons 12) RLG-INS and
GPS receiver mounting structure 13) Cockpit floor 14) Shear walls 15) Inclined
bulkhead 16) Doors/hatches 17) Canards 18) Mooring points 19) Hauling points
20) Ejection seat brackets 21) Symmetry check-points 22) System installation
brackets 23) Air data probes: Nose air data probe (NADP)/side air data probe
(SADP)/Angle-of-attack/Angle-of- Side-slip (AOSS) locating points 24) Equipment
bay housing the environmental control system (ECS), digital flight-control
computer (DFCC), mission avionics, and an on-board oxygen generation system
(OBOGS).
The centre fuselage assembly jig will be
made up of modules such as: air-ducts and side-skins, spine, main landing gear
bay, shear wall, fuel tanks, and a dividing wall structure. The assembly will comprise
approximately 1,600 parts, out of which 40% will be sheet metal, 30% will be
machined parts and remaining 30% are to be made of CFCs. The length of the
centre fuselage is about 4,500mm with a maximum width of some 2,100mm. The centre
fuselage assembly will comprise 15 stations and the it will weigh about 900Kg.
Since the centre fuselage section needs to be coupled with the front and rear
fuselage sections, the inter -changeability (ICY) media are critical. The
centre fuselage assembly will comprise the following: i) Bulkheads 2) Trouser
duct 3) Circular duct 4) Side-skin structure 5)Top-skin structure 6) Fuel Bay
side-walls 7) Longerons 8) Shear walls 9) Doors and hatches 10) Fuel tanks 11)
Main undercarriage 12) Spine structure 13) Wing pick-up points 14) Landing gear
doors 15) Gun-bay structure (meaning the Gryazev-Shipunov GSh-23 cannon has
been repositioned to the starboard side of the upper centre fuselage) 16)
Lifting points 17) Other systems installation inter-changeability requirements
18) Symmetry points.
The Rear fuselage assembly jig will be
made up of modules like the engine bay doors, spine and fin attachment, and brake
parachute. This assembly will comprise approximately 900 parts, out of which
30% will be sheet metal, 40% will be machined parts and remaining 30% will be
made of CFCs. The length of this section will be about 3,300mm with a maximum
width of about 1,800mm. The rear fuselage assembly will comprise eight stations
and the total shell-weight will be some 400Kg. The rear Fuselage needs to be
coupled with the centre fuselage and hence the ICY media are critical. The assembly
will include the following: 1) Bulkheads 2) Shear walls 3) Floors 4) Engine
mounts 5) Doors 6) Wing attachment points 7) Covers/Hatches 8) Fin attachment
points 9) Spine structure 10) Hauling attachment 11) Tie beam 12) Shroud 13) Trailing-edge
extension 14) Elevon inboard actuator attachment 15) Symmetry points.
OEMs expected to respond to the RFIs
will likely include Airbus Military Aircraft, BAE Systems, Leonardo Group’s
Alenia Aeronautica subsidiary, Boeing, Dassault Aviation, Lockheed Martin, SaabTech
and Russian Aircraft Corp. Subject to a contract award taking place by the year’s
end, the three different assembly js will begin arriving at HAL by 2022,
following which another three years will be required for optimising the design
and location of the various mission avionics sub-systems/LRUs and related wiring
harnesses, hydraulic pipings, accessories, and skin-level distributed apertures
for EW sensors. Consequently, only by late 2026 will be it possible to roll out
the first flying prototype of the LCA-AF Mk.2. Add to this 2,000 hours of
flight-tests with four flying prototypes over a period of three years. So, for
all intents and puposes, the LCA-AF Mk.2 will not enter series-production until
2030.
In another development, the successful ground-launch
and flight-testing on February 8, 2019 of a solid-fuel ducted ramjet (SFDR) as
the propulsion sustainer component that has been indigenously developed by the
MoD-owned Defence R & D Organisation’s (DRDO) Hyderabad-based Defence
R & D Laboratory (DRDL) for a futuristic beyond-visual-range
air-to-air missile (BVRAAM) meant to destroy hostile MRCAs, makes India the sixth
country after the US, Russia, France, South Africa and China to have achieved
success in this arena of rocket propulsion.
The DRDL-developed SFDR
on the DRDO-developed BVRAAM, which is initially using the missile-body of the
indigenously developed Astra Mk.1 BVRAAM, comes attached to a solid-fuel rocket
booster to propel the BVRAAM to speeds at which SFDR can start operating.
The SFDR cycle
is the same as the ramjet cycle except that the fuel exists in solid form
within the chamber and the stoichometry of combustion is controlled by the
regression rate of the fuel. The fuel is not a propellant in the solid rocket
motor sense, but a pure fuel, inert without external oxidizer much like in a
hybrid rocket motor. A wide range of fuels can be used from polymers such as
PMMA or PE to long-chain alkanes such as paraffin or cross-linked rubbers such
as HTPB. Because the fuel exists in the solid form, inclusion of solid metals
is significantly easier than in a liquid-fuelled ramjet. SFDRs also offer
significant advantages such as: Extremely simple compared with liquid-fuelled
rockets or ramjets since, in its simplest form, a SFDR is basically a tube with
a fuel grain cast in it; higher fuel density in the solid phase for pure
hydrocarbons and even higher if metal additives are used; easy inclusion of
metal fuels such as boron, magnesium or beryllium, which raise the heat of
combustion and/or the density and therefore the density impulse capability
compared with liquid ramjets; solid fuel acts as an ablative insulator,
allowing higher sustained combustion chamber exit temperature levels (and hence
specific thrust) with less complexity; fuel is stored within the combustion
chamber, allowing for more efficient packaging and higher mass fractions than
liquid ramjets; and no need for pumps, external tankage, injectors or plumbing
for fuel delivery.
The
earliest known SFDR Patent was filed in the US by Cordant Technologies Inc as far
back as 1959. The patent can be viewed here:
While the solid-fuel booster rocket/SFDR
combination has been a tried-and-tested means of propulsion, it has limitations
of maximum engagement ranges against agile and manoeuvring targets like manned
combat aircraft, which can bleed the energy of the BVRAAM. To improve
terminal-stage manoeuvring, present-day BVRAAMs use multi-pulse solid-fuel rocket
motors, with the second pulse-firing taking place only in the terminal stages
after the BVRAAM’s Ka- or Ku-band active seeker has locked on to its target.
The MBDA-developed Meteor BVRAAM was the first to do away with the need for multi-pulse
solid-fuel rocket motors by incorporating a throttleable ducted rocket (TDR)
version of a solid-fuel ramjet developed by Germany-based Bayern-Chemie. The
TDR functions as an extended sustainer with variable thrust being generated by
a solid propellant, but can sustain high thrust-levels for far longer periods
since it acquires its oxidiser from the air. However, both BVRAAMs and LRAAMs
using SFDR have a limitation: ramjet motors are heavier and take time to reach maximum
speed in the initial phases, and are thus less agile. Consequently, BVRAAMs and
LRAAMs using SFDRs will be less effective against agile MRCAs, but the LRAAM will
be highly effective against lumbering combat-support platforms like AEW &
CS aircraft and aerial refuelling tankers.
Elsewhere in the world,
Russia’s Vympel JSC (now part of Tactical Missiles Corp) had by the early 1990s
completed developing the SFDR-powered RVV-AE-PD BVRAAM, which hosts rear-mounted
lattice-type aerodynamic control surfaces. However, this BVRAAM has not yet
been series-produced.
Instead, Russia has
opted for a two-stage solid-propellant rocket propulsion system for its Novator
R-172S LRAAM.
In the US, Raytheon
had in the 1990s developed a SFDR-equipped FRAAM variant of the AIM-120 AMRAAM.
But like the RVV-AE-PD, the FMRAAM has not yet entered series-production.
Throughout the late
1970s and 1990s, Somchem of South Africa pursued R & D on SFDR-based
propulsion under Project Integral, with the objective being to power both BVRAAMs
and MR-SAMs (developed by KENTRON) using SFDRs. The latter, known as SAHV,
was first displayed in 1995 with a rounded glass nose-section housing an IIR
guidance system. To avoid over-heating of the IIR seeker during the MR-SAM’s
Mach 2.3 flight to its target, the SAHV’s nose-section was fitted with a cap
that was jettisoned only in the final stages of the engagement.
Making its debut at the
Airshow China 2018 expo in Zhuhai last November was the HD-1, China’s first
anti-ship missile using a solid-fuel ramjet combustor and a SFDR—both developed
by CASC’s No.4 Institute. Developed and built by
the Guangdong Hongda Mining Co, the 2,200kg HD-1’s maiden flight-test took
place in October 2018. The HD-1, like the still-classified YJ-18 anti-ship
missile, employs a tandem single-stage solid-propellant rocket
booster—as opposed to wraparound boosters to reduce drag—for missile launch and
acceleration to a forward velocity suitable for efficient operation of the
ramjet’s intake system, which comprises four air-intakes arranged in an ‘X’
configuration around the missile body. Tapered control surfaces are mounted on
the intake housings near the nozzles. The HD-1 has a length of 8.3 metres, with
a missile body and booster diameter of 375mm and 650mm, respectively. Cruise
speed is quoted as 2,716kph, while terminal cruise speed being 4,321kph, with
the missile cruising at altitudes of up to 15km (49,212 feet) and performing
sea-skimming manoeuvres at altitudes between 16 and 32 feet. The missile’s
maximum range is 290km.
Coming back to the DRDO’s efforts to
develop a BVRAAM or LRAAM using SFDR, the principal challenge remains the
development of an internal data-link that will receive targetting cues from a
friendly AEW & CS platform, since the AESA-MMR of the MRCA launching such
an LRAAM will not be able to detect or track hostile combat-support platforms
flying at distances beyond 300km. Furthermore, if the LRAAM is tasked with the
destruction of hostile combat-support platforms, then the LRAAM will have a
launch-weight of more than 250kg. However, if the idea is to develop a BVRAAM
like the Meteor, then a maximum engagement range of 150km will suffice, while
the launch-weight will have to be kept down to 220kg at most.
