Technology
Demonstrators & the AMCA Prof.
Prodyut Das
17 September
2026
Successful
aircraft projects make judicious use of carefully engineered Technology
Demonstrators if the design uses new technology but TDs require mature
engineering and development tactics. That being given , TDs slash development
cost, time and uncertainty.
In 1961, The
British flew a very simple aircraft. It was basically a faired over girder
structure connecting a pilot cockpit at front with a small jet engine of 7.8 kN
at the rear, feeding via a dorsal intake. The story goes that it was originally
planned to be a towed glider, much like our HF 24 -X, but then someone
calculated the cost of towing the glider, the hire charges of the towing
aircraft and the general “bundobast” required and it was clear that a
self-launching aircraft would be more sensible, hence the Viper engine. The
wing was a narrow delta made from aluminum sheet and extrusions with wooden
leading edges which could, by design, be changed to try various L.E, edge
profiles. The undercarriage was fixed. The controls were manually powered, only
the flaps cum air brakes being pneumatically operated from a small pneumatic
bottle. There was even no electrical system, the turn and slip indicator and
lamps being supplied by a battery. The cockpit was unpressurized and the top
speed was – this was for a Mach 2 airliner- 400 km,p,h.. I want you the
simplicity and common sense of the TD usage sink in . Design started in 1960
and it was built and flown within the year.
I gave the details
because the aircraft, the agriculturally simple Handley Page 115, was a very
important cog in the smooth development of the Concorde supersonic airliner and
it underlines the maturity, knowledge and focus needed to design a well-engineered
Technology Demonstrators for advanced programmes.
The Tejas TD
mooted by Prof. Roddam Narsimha, unfortunately was not a TD but only a
Babu’s file trick to get an unacceptable proposal circumvent searching
questions of the IAF which the Babu Scientists lacked the ability to tackle
,confront, answer and learn so as to arrive at a compromise. Someone “pulled
“rank” to avoid a discussion, the nation suffesr the results.
TD are needed and
the obfuscated ( in Bangalore and Raisina) point is that the TD does NOT have to be at
all like the final product. The British TDs for V/STOL aircraft like the Shorts
SC1 or the flying Bedstead did not look much like an aircraft but quickly and
cheaply lit the British Industry’s way to master the technology of control at
the hover of planned jet V/STOL, an area in which they became the world leaders.
The imperative is that a TD must not become a project unto itself; no
purpose will be served apart from wasting time and funds.
Praemonitium
praemunitium- forewarned forearmed
The purpose of a
TD is to generate data, firstly about known unknowns and secondly uncover
unknown unknowns at the earliest. Often more than one TD type is used;
in the Concorde, for the high-speed characteristics the British used the BAC
221 which was a reworked Fairey Delta 2, a Mach 2 record breaker from 1956 to
check out and confirm expectations about the ogival wing whilst the HP 115 the
purpose was to check out the handling of the vortex lift generated by lift in
narrow delta wings at approach speeds.
There are people
who hold that computer simulation has replaced the use of technology
demonstrators. This is dangerous partial truth. No amount of CAE can solve
problems that are not known which the TD can uncover early, giving forewarning so
that they can be parallelly processed. The British and European industries,
when they existed, used many technology demonstrators and US has always
invested in them with or without being connected to a programme. The US TDs
were “Jugaad” made from off the shelf items. They follow a very simplified and
curtailed process of approval with many tests eliminated for they rarely are
needed for more than three to five hundred hours of flying life. An exciting
development is the use of large sub scale, radio-controlled models with
miniature jet engines e.g. the Boeing Northrop X 35/40 a 28% full size aircraft
investigating the use of finless stealth; such innovations open the possibility
of reducing cost and risks substantially.
The
arithmetic of the TD
The arithmetic of
a technology demonstrators is simple. A new Fighter programme needs
about 6000 hours of development flying to an IOC. A single prototype of a new
fighter will perhaps give 120 hrs p.a. because they have to undergo numerous
checks before each sortie. So, a fleet of 10 prototypes will require 60 months
to clear a new type to IOC. If the TDs are used it eliminates rectification
which is often very difficult on a prototype.
A prototype is
often down with trivial snags. Suppose the prototype returns availability less
than 50 hours per annum? It will take the 10 prototypes more than 12 to 15 yrs.
to complete the test and the fighter may still be unacceptable because it is
difficult to rectify a fighter already designed. Now if you take 17 yrs. to get
the first flight and another 10 years to solve problems on a messed-up platform
then you have lost the game. This happened with the Tejas.
Consider if the
FBW, composites, glass cockpit had been checked out of HF 24, Gnat and HJT 16
based TDs during the period 1984-88 ADA would have made the right engineering
decisions, been faster and required less funds because the project is “parallel
processing” and test hour availability does not become a bottleneck. TDs don’t
need much funds.
A TD for the
AMCA … now!?
Even at this late
stage there is more wisdom in creating a TD for the AMCA than the AMCA itself! That
is because the AMCA is based on very little assurance that the development
problems have been exposed. The crisis is the Air Force squadron
strength. The AF needs working aeroplanes. The US style AMCA is a bridge too
far. Even if ready by 2028 the ADA AMCA will fail because ADA leadership is
flying blind under Instruments condition.
This is exactly
what happened with the Tejas- cocky promises firsts and toothy grins afterwords
about “We over promised and under delivered” followed by vilification of those
who suffered. Defence planning cannot run like that.
The unknown
unknowns
Some of the known
unknowns of the 5th, generation stealth is:
i)
Target
acquisition by an internally stowed missile, the lock on and the launch.
ii)
The
trajectory calculations for unguided munitions.
iii)
The
loading of the same into confined pockets in the aircraft.
iv)
The
stability of “stealth” coatings in actual service conditions.
v)
Stealth
gun ports and firing.
vi)
Since
the missiles are internally carried the missile plume/ engine inlet
interference are severe. Relying on simulation is unwarranted risk taking.It
will cost very dear.
These are the
known problems about which we have no proven data and technology.
The unknown
unknowns
vii)
The
accuracy and reliability of the computer model developed to predict the RCS of
the AMCA.
viii)
There
are “Unknown Problems” which is known only to the developer and operators of
stealth aircraft. These will reveal when the AMCA prototype flies. Why wait for
the F 414 engine and delay the start to a time when the new aircraft development
load is anyway at peak.
The recent alleged
stealing of F 35 canopy and weapons doors shows how much details matter and how
seriously the Chinese take the business of development. They are cued in.
Without TDs,
despite present bravado, there is this large possibility we will find we have on
our hands a larger than necessary 4th generation aircraft of
indifferent performance, that too not quite ready. It has happened before.
Barking up
the right tree?
The final driver
for going for a well-designed TD first is the shape of future air
combat. The present US philosophy is much like recommending Metaformin when methi
and karela can actually do better. The Fighter of the future will be
different.
The choice of the
multi role fighter with large payloads has invariably failed against real
opposition whenever tried. Recently the US has lost 40 plus aircraft in
sporadic fighting with Iran which has no air force and yet Iran seems to be
showing the US/ Israel the finger. Nota bene no one is talking about how
small 60-year-old F5As without any “stealth” except small size, penetrated the
worlds most advanced air defence system and caused damage. Our secure future is
to dump Western notions and allot the attack phase performance to guided weapons
with AI and the “transport to combat” part to the aircraft as the aerial
equivalent of a ten wheeled truck. The thrust will shift from manned aircraft
as the attacker to the manned aircraft as a missile transporter. The AMCA is
the wrong over specified platform and it is certainly too late.
There is room for
examining a Common-sense stealth (as opposed to exotic technology
stealth) hybrid AMCA with a MSL (Minimum specifications List) and even if we
proceed with the US style AMCA we nevertheless should proceed with a low-cost
TD that can be turned into a limited but useful aircraft initially strictly to counter
to the J 20 and the F 35 whilst better solutions are perfected.
The AMCA TD
Get ADA out. It is
“Dog in the Manger” by attitude” and a creator of confusion by history. Revert
to the HAL, IAF and the Private sector with equal votes in the
discussions. The Tejas fiasco has happened because people who had no business
to be there kept the customer and the fabricator out of the cockpit. Aircraft
design is a collaboration for knowledgeable people working with mutual respect.
The desired AMCA
TD would be a small aircraft that will primarily address the problems
mentioned above and also the possibility of being upgraded quickly as a
basic emergency equipment to tackle the J 20s and the F 35s.
Initial studies
show the aircraft would be typically about 12 mts long and 7 mts span with a wing
area of 17sq, mts. It is powered by one or two current production biz jet turbofans
with an installed cold thrust of 50 kN with an eye on the HTFE 25 and the
Kaveri as final engines and a fuel load of 2000kgs carried in the wing and one
fuselage tank, The flyable empty weight is 3500 kgs. not counting the budgeted 1000
kgs of the 6th generation systems, for which space of about two cu, Mts
is provisionally allotted in the forward and rear equipment bays. The empty
equipped weight would thus be about 4500 kg.
Though simple the
design has interesting mechanical features; a variable incidence wing and a
variable geometry “lip” type intake for low and slow speed as would be required
in a carrier.
The test weapons
are carried in two recessed pockets on the fuselage flanks 3000mm x 330 mmx
3300 mm sized for existing IR missiles and two bays for gravity drop/ERU stores
of 400 mm diameter sized 500 mm x 500 mmx 3500 mm. In addition, four 23 mm single
barrel guns are carried for air-to-air work, A small ranging and navigation
radar is carried but the main weapons search and aiming is done by a IR scanner
and ground based LF detection.
The design’s stealth
is mainly of the “robust” or natural variety- the chin intake and the chined
side, and the small size (the lowest cost, most reliable of all stealth
techniques for any level of expertise) being examples of the thought process.
The structure can be conventional stressed skin or can incorporate a (geodetic)
space frame, rather along the lines of the HP 115, so that low cost
“aatmanirbhar” locally nonstructural GRP/specially developed radar absorbent core/GRP
skins of superior Radar absorption can be tried. Emphasis will be there to
reduce the number of moving surfaces and edges which are a sources of RCS
increase.
By intelligent
“scrounging” and using existing components and systems the aircraft can be got
ready in 2 to 3 years by a small team and for a revenue expenditure of less
than 600 crores, Trials cost would be thereafter.
A few sketches are
enclosed as illustration. Details may vary with evolution.
The AMCA is set up
to fail like the Tejas . Given the new technologies perhaps the private sector
can look at investing small amounts of money in developing stealth technology
from fundamentals, When the AMCA runs into trouble during the integration phase
and early testing the data generated by the TDs would have value,
Food for thought
notes: Some TDs histories.
The engineering of
TDs is fascinating in the way the design team used them to generate much needed
confidence. The following are some notes on some more recent types.
XST
The XST was the TD
for all stealth aircraft and explored every aspect of stealth- radar, IR,
acoustics with maximization of stealth as the design objectives. Developed at a
total cost ( including labour and development flying) $ 340 million (1978
prices) it was flown within 2 years first as the FX T using all metal
construction, off the shelf aggregates and systems e.g engines from Northrop F 5’s. It
validated the concept and calibrated the RCS prediction algorithms. The
aircraft was very difficult to fly but it served its purpose and the larger
definitive .F 117 followed using the F 404 un-reheated engine. The details are
given at my blog profprodyutdas2 on the development of the F 117,
XF 31
This used a F 404,
the cockpit instruments of the F 18, the wheel and undercarriage of the A7, the
cranked delta wing once designed by MBB and thrust paddle type thrust
deflectors to get VIFF. It confirmed that the technology was available to make
the most maneuverable close in fighter. The claim is not important for us, the
spirit of scrounging to get the project up and generating data is.
The X 36
The X 36 is
interesting because it generates the possibility to slash development costs and
time by using radio-controlled subscale model. The X 36 is a 28% scale of a 6th
generation fighter. Dimensions are a Length of 5,55mts, span 3.18 mts and
height is 0,9462 mts. Empty weight was 494 kg, fuel load was 82 kg, and full
load was 576 kg. The power was from a Williams F 110 engine of 3,1 kN. The cost
was less than $ 80,000. R/C controlled sub scale models when combined with
commercially available CFD would substantially reduce the amount of dependence
of wind tunnels which would be a big bonus for those with restricted access to
such facilities.
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