Thread: Light Combat Aircraft(lCA) and Combat Aircraft Trainer(CAT)

Originally Posted by tphuang

I think it mainly come down to the long range AAM of F-16 and its high tech radar equipment. Rest of the avionics include all-digital instruments and three 5x7-inch color displays, HUD and helmet mounted sight and display (compares favourably to su-27). Even it's engine went from the original 25,000 lb thrust to 32500 thrust now. It's manevourability has definitely gotten better with each new block. F-16's combat record really is unprecedented.

The F-16 has faught in Iraq and yugoslavia, oops Afganistan.

With such amazing air forces, surely an impeccable record will be maintained especially considering that Iraq for eg was outnumbered and outgunned by stealth, cruise missiles, awacs, F-15s, Mirage 2000s, France gave important codes ofthe French built Iraq AD systems etc etc etc.

Originally Posted by Sameer

The F-16 has faught in Iraq and yugoslavia, oops Afganistan.

With such amazing air forces, surely an impeccable record will be maintained especially considering that Iraq for eg was outnumbered and outgunned by stealth, cruise missiles, awacs, F-15s, Mirage 2000s, France gave important codes ofthe French built Iraq AD systems etc etc etc.

you cannot deny that the avionics on recent F-16 is extremely good. At the same time, it has the luxury of operating with the American EW system and being datalinked to AWACS and other planes.

Originally Posted by tphuang

I think it mainly come down to the long range AAM of F-16 and its high tech radar equipment. Rest of the avionics include all-digital instruments and three 5x7-inch color displays, HUD and helmet mounted sight and display (compares favourably to su-27). Even it's engine went from the original 25,000 lb thrust to 32500 thrust now. It's manevourability has definitely gotten better with each new block. F-16's combat record really is unprecedented.

1. u said all variants of su27.. if i can recall correctly..
2. the long range AAM for F16 is AMRAAM. while that of SU27 is R77 u can compare the latest production versions of the two wrt range and seeker range etc. i would be surprised if comeone says that AMRAAM is better than R77.
3. As far as radar equipment if considered Even N011M isnt too bad . So a proper comparison of radar ranges & RCS is whats essential to call one better than other and what i m expecting from u.
4. F22's combat record is nil . So does that make F16 better than F22. ??
5. i understand that f16's thrust has gone up but is the TWR better than MKI/other SU27 versions ?
6. manouverability. Is it better than MKI's TVC??

People are unecessarily making hype out of f16s. Even US is thinking of replacing it with f35s. If f16s are so unbeatable, why is US & some 20 countries putting money on f35s? Simple f16s is going to be seriously challenge by european & russian fighter like rafales, EF2000, & mig 35s.

Originally Posted by ajaybhutani

1. u said all variants of su27.. if i can recall correctly..
2. the long range AAM for F16 is AMRAAM. while that of SU27 is R77 u can compare the latest production versions of the two wrt range and seeker range etc. i would be surprised if comeone says that AMRAAM is better than R77.
3. As far as radar equipment if considered Even N011M isnt too bad . So a proper comparison of radar ranges & RCS is whats essential to call one better than other and what i m expecting from u.
4. F22's combat record is nil . So does that make F16 better than F22. ??
5. i understand that f16's thrust has gone up but is the TWR better than MKI/other SU27 versions ?
6. manouverability. Is it better than MKI's TVC??

in terms of manouverability, MKI will kick its ass. I have no doubt about that. As for RCS, I'm not sure, what are the numbers on F-16 block 60 and MKI? And what's radio jammer for su-30mki?

Block 60 is equipped with AIM-120A AMRAAM. Now, if su35 starts to use weapons designed for PAK FA, then it should be better. If you compare AIM-120 to R77, it comes down to the old America vs Russia comparison:
Radar/Guidance vs speed/maneouverability
http://en.wikipedia.org/wiki/R-77
Don't get me wrong, I really wish R-77 to be better, because plaaf uses it, but I personally think they are at the same level.

Still when it comes down to it, the APG radar system will give it an advantage over bar radar.

Originally Posted by indianguy4u

People are unecessarily making hype out of f16s. Even US is thinking of replacing it with f35s. If f16s are so unbeatable, why is US & some 20 countries putting money on f35s? Simple f16s is going to be seriously challenge by european & russian fighter like rafales, EF2000, & mig 35s.

F-35 is better than F-16, that's why. F-16 is not overrated, it has been in service for almost 30 years. It's time for a new plane to come and take over.

Originally Posted by tphuang

you cannot deny that the avionics on recent F-16 is extremely good. At the same time, it has the luxury of operating with the American EW system and being datalinked to AWACS and other planes.

I was reffering to the F-16s impeccable record and how this record is meaningless, heck tomorrow the MKI could go around Pakistani airspace shooting down Mirage 3s and F-7s and it would not mean a thing in my mind.


The F-16 becomes as manouverable as my grand mother once you load weapons on its pylons.

The F-15 is probably the best all round fighter in the USAF, now that is an impressive fighter.

Originally Posted by tphuang

F-35 is better than F-16, that's why. F-16 is not overrated, it has been in service for almost 30 years. It's time for a new plane to come and take over.

How may more yrs will it be in service of USAF?

http://frontierindia.com/content/view/19/33/

Light Combat Aircraft-Tejas Testing
Sunday, 21 August 2005
By Air Marshal P. Rajkumar, PVSM, AVSM, VM (Retd.) March 6 2005

Introduction


Since completion of the technology demonstration phase on March 31, 2004 the LCA program has commenced the Full Scale Engineering Development (FSED) phase in right earnest. The aim of the program now is to achieve Initial Operational Clearance (IOC) with the Multi Mode Radar (MMR) integrated with a weapons suite which will give the aircraft limited operational capability by the end of 2007 i.e. in about three years time. This article will give the reader an insight into the current status of the program while also tracing the evolution of the two Technology Demonstrator aircraft TD-1 and TD-2, and the two Prototype Vehicles PV-1 and PV-2.
TD-1
The first aircraft to be built, TD-1, suffered from all the ills that could beset any aircraft attempting to make a technology leap spanning two decades. It must be remembered that the aircraft industry in Bangalore had not attempted to design and develop a state of the art fighter since the Marut program in the early 60’s of the last century. Almost the entire workforce had their first exposure to new technologies like the fly by wire system, the glass cockpit and the composite structure while manufacturing this aircraft. There was a learning curve involved because most of the workers had to learn on the job. Numerous mistakes were made and the fuselage wing integration had to be done more than once to get things right. It was therefore not very surprising that the aircraft tipped the scales at 6,780 kg with Flight Test Instrumentation (FTI) against a targeted weight of around 6,300kg. Program managers very wisely decided to launch a weight reduction exercise.

TD-1 has the first generation glass cockpit configuration based on an Intel 80386 processor based mission computer and a dedicated display processor to drive the two Active Matrix Liquid Crystal Multi Function Displays (MFD’s) and an imported Sextant Head Up Display (HUD). Redundancy has been provided with a Control and Coding Unit (CCU) and a second display processor. Bharat Electronics designed and developed Multi Function Keyboard (MFK), a Get You Home (GUH) panel which provides the pilot with essential flight information in case of an emergency, a Multi Function Rotary (MFR) switch which enables the pilot to select radio frequencies, set altimeter settings on the HUD, select IFF frequencies, time display etc, a digital fuel and rpm strip gauge, a Function Selection Panel (FSP), a Sensor Selection Panel (SSP) and a BAE Systems SCR-300 Crash Data Recorder (CDR) make up the major part of the avionics suite. Two units developed by the Electronics and Radar Development Establishment (LRDE), the Mission Preparation and Retrieval Unit (MPRU) and the Centralised Warning Panel (CWP) complete the avionics suite.
Communication is provided by a HAL Hyderabad developed INCOM V/UHF R/T set and a standby UHF set.

Four LRUs, the Environmental Control System Controller (ECSC) electronic unit (EU), Digital Fuel Monitoring System (DFM) EU, Engine and Electrical Monitoring System (EEMS) EU and the Digital Hydraulic (DH) EU which also has a brake management computer perform the utilities system monitoring function.

For the first block of flights it was decided to fly the aircraft with a fixed gain control law for the fly by wire system. This meant the control column to control surface deflection law had a fixed linear ratio .The leading edge slats and air brakes were non functional and the aircraft wing tanks were partially refuelled giving a total of 1,800 kg of fuel. Partial fuel in the wing tanks and approximately 140 kg of ballast weight in the nose kept the CG in the mid range. This was done to give the fixed gain control law an adequate margin of safety while stabilising the unstable aerodynamic configuration. The flight envelope was restricted to Mach 0.7,610 kmph Calibrated Air Speed (CAS), 8km altitude and normal acceleration +2g.The GUH was removed and round dial pressure instruments and an angle of attack indicator were fitted to give the pilot unprocessed air data to act as a cross check for the processed information put out by the mission computer. A calibrated chase Mirage 2000 aircraft provided the pilot with a completely independent check of air data and gave him the option of a shepherded landing in case of air data problems .The Mirage 2000 chase aircraft was used for all the 12 flights of the first block.

The almost trouble free completion of the first block flights flown by Wg Cdrs Rajiv Kothiyal and Raghunathan Nambiar between January 4, 2001 and June 2, 2001 did much to boost the confidence of both the designers and the flight test team.

The aircraft was extensively reworked after this phase to make the leading edge slats and airbrakes operational. Some fuel system modifications were also carried out to increase the amount of usable fuel to as high a figure as possible. The full scheduled gain control law wherein the control column to control surface deflection is made dependent on the flight condition of the aircraft was invoked and the aircraft flew again with Gp Capt Rakesh Bhaduria at the controls on February 3, 2003 just in time to be put on static display at Aero India 2003. HAL’s preoccupation with the Intermediate Jet Trainer programme had much to do with this protracted grounding of TD-1.A golden opportunity to fast track the program was thus lost forever.

Once scheduled gains were invoked for the flight control system, envelope expansion was commenced .The flutter envelope was cautiously explored and Wg Cdr Vikram Singh went supersonic in TD-1 for the first time on August 1, 2001.The aircraft has flown 120 flights to date.

TD-2
The air intake duct was redesigned for this aircraft to make it easy to manufacture. Some weight reduction was also attempted which resulted in a weight saving of 110 kg. The airframe weighed 6,670 kg when manufactured.

The other significant change in the aircraft was the installation of the Central Scientific Instruments Organisation (CSIO) Chandigarh designed and developed HUD with 25 x 20 degrees field of view (FOV). The display processor was developed by the Aeronautical Development Establishment (ADE). The HUD is Night Vision Goggles (NVG) compatible. All the round dialled instruments were removed and the GUH was brought into operation. The aircraft originally scheduled to fly by the end of 2001 finally flew on June 2, 2002 with Wg Cdr Tarun Banerjee at the controls. The aircraft flew 61 flights with the fixed gain control law before it was grounded to make the slats and airbrakes operational. The aircraft flew with scheduled gains for the flight control system in October 2003 and has flown 150 flights to date.

PV-1
Major weight reduction was attempted during the manufacture of this aircraft’s airframe. Carbon fibre composites were extensively used in the fuselage taking the overall composite content to 45 per cent by weight and 95 per cent by surface area. The part count, which was 10,000 for TD-1’s airframe, was reduced to 7,000 in this case. The airframe weighed 6,430kg when complete which meant the weight reduction exercise had reduced 350kg of weight, a praise worthy achievement.
PV-1 represents the production standard airframe. Of the structural material used the proportion of carbon composites account for 45 per cent by weight, aluminium alloys 43 per cent, titanium alloys 5 per cent, steels 4.5per cent and other materials 2.5 per cent.
The avionics suite is the same as that of the two TD aircraft. The aircraft first flew on November 25, 2003 with Sqn Ldr Sunit Krishna at the controls and has completed 80 flights to date.

PV-2
There is a big difference between the avionics suite of the first three aircraft and the prototypes from the fourth aircraft PV-2 onwards. The distributed, integrated avionics suite in this aircraft is configured around three dual redundant MIL-STD-1553B data and two dedicated weapons buses. Central data processing is done by the open architecture computer (OAC) which is Power PC/VME64 based. It has a mezzanine card based MIL-STD-1553B, RS422 master and cursive graphics modules. Dual redundant OACs combine the functions of the mission computer, the two display processors, the CCU and the video switching unit replacing five of the LRUs on the Technology Demonstrator aircraft. The OAC has modular software written in the ADA language complying with MIL-STD-1521 and 2167A standards and will be able to generate digital maps without a separate module.

The production standard cockpit has no electro mechanical standby instruments. The cockpit is dominated by three 5”x 5” AMLCD MFD’s, two Smart Standby Display Units (SSDU) and the indigenous HUD. The HUD has an Up Front Control Panel (UFCP) which is a significant man machine interface (MMI) enhancement which allows the pilot to program, initialize the avionics and enter mission and system critical data through an interactive soft touch keyboard. Although the FOV of this HUD is slightly less than that of contemporary units on other aircraft of this generation it is not considered significant because the ELBIT, Israel furnished DASH helmet mounted display and sight (HMDS) will form an integral part of the avionics suite.

The four utilities system monitoring LRUs have been reduced to two dual redundant units. These units perform the control, monitoring, data logging for fault diagnosis and maintenance functions.

A HAL Korwa developed Crash Data Recorder will be fitted after the initial flights.
The Multi Mode Radar (MMR) jointly developed by LRDE and HAL Hyderabad will be fitted in the nose after redistributing the FTI carried in the first three aircraft. The MMR features LPRF, MPRF and HPRF modes, platform motion compensation, MTI and Doppler filtering, CFAR detection, range-Doppler ambiguity resolution, scan conversion, display of target and ground map data on MFDs and on line diagnostics to identify faulty processor modules.

The aircraft has the ADA developed Stores Management System (SMS) which will provide fully integrated control of weapon systems, external stores and fuel tanks. The SMS is based on a 32 bit, single chip micro controller with dual redundant architecture .Its main components include the single Stores Interface Box (SIB) and multiple pylon interface boxes(PIB) for each hard point.

A state of the art EW suite will be integrated and tested later in the program. Primary responsibility for development of the EW suite is that of the Defence Avionics Research Establishment (DARE), Bangalore

The aircraft is undergoing final integration checks and is expected to fly by the end of May 2005.

Program Update
The flight test program has logged 350 flights without encountering any major design deficiency. Due the complexities of the quadruplex digital fly by wire system it is clear that the flight test team and program managers are opening the flight envelope cautiously. At the time of writing(February 8, 2005) the flight envelope has been expanded to Mach 1.4,1150 kmph CAS,15 km altitude, +4.5 g, and an angle of attack of 23.

Conclusion
A host of daunting tasks like full envelope expansion after flutter testing, MMR tests, weapons integration, weapon delivery and environmental tests of the full aircraft have yet to be attempted by Team LCA They certainly have the nation’s good wishes to back them while they go about their onerous task.

© Frontier India

http://frontierindia.com/content/view/18/33/

Sunday, 21 August 2005
By Commodore Prem Kumar, VSM (Retd.)

MiG-21 accidents being encountered in the sub-continent need to be examined with the background of aerospace developments in the West and in Russia, predominantly during the Cold War era, spanning a period of four decades from 1950 onwards. In the mid-50s, when MiG-21 arrived on the combat scene it was designed to be a simple, clear weather interceptor. After nearly two decades of service with the Russian Air Forces, it came to be inducted into the Indian Air Force as a frontline fighter. Gradually the military needs of IAF transformed the interceptor into an all weather fighter with ground attack capabilities, enhancing the range and payload since its induction into the combat ranks.



MiG-21 variants are in service with Zambia, Cambodia, Romania, Syria, China and Pakistan. Barring the last two nations, who have their own joint plans, the aircraft has been undergoing a modernization program involving Russians and with participation of two companies from Israel….ELBIT Defense Systems and Israel Aircraft Industries…to give the MiG-21 a true all weather capability, reduced pilot workload and 'dramatically enhance combat potential of the complete weapons system'. Pakistan has a fleet of 95 F-7s which are a derivative of the MiG-21 F incorporating a mix of Chinese and Western systems. China after years of operating MiGs has developed Shenyang J8II-FINBACK, which is a MiG-21 incorporating twin engines, longer fuselage and a slightly longer delta wing. By virtue of the dedicated modernization program undertaken by the Chinese, the MiG-21 is bound to prosper with our neighbours…….in addition the conclusion of a License agreement between the Chinese and the Russian manufacturer Vympel NPO, to locally produce latest air-to- air missile R 77, will provide the teeth to the J 7 and J 8 variants of the MiG-21. Strangely among the global fraternity of MiG users, only the workhorse of the Indian Air force has been conferred the label — FLYING COFFIN — due to a series of MiG accidents numbering 245, and killing over 100 pilots between 1991-2004. (Between 1971 and 2003, the IAF inventory has in all lost 454 aircraft, with 165 attributed to Pilot error).

Normally, “pilot error” helps to close inquiries, but does not clearly explain how the fault was initiated. It merely tells where the buck stops. The error chain in an accident could start with the aircraft designer and continue through draughtsman, factory worker, quality controller, assembly-line worker, test-pilots, technicians, MET forecasters, operations officers, air traffic controllers, airport authorities, computer engineers, and finally the pilots. Thus a design short coming or an assembly line blunder or an aggressive operational exploitation of an aircraft could lead all the way to 'pilot error'. The man-in-the-loop can only resolve issues that are measurable and clearly identifiable using the eyeball technique or custom built equipment. Unfortunately, a combat aircraft during its service-life gets subjected to repeated stress cycles either due to latent design flaw which surfaces when it is exploited outside the designed flight profile or when exposed to thermal and acoustic flight stresses compelling the airframe to lose its stiffness integrity….which lead to undesirable and indescribable consequences associated with crack propagation due to flutter, vibration, buffeting, gust response and dynamic transformation in the geometrical characteristic of the airfoil. Information about the origin and fatal effect of these hidden initiators of flight stresses gained the deserved importance in aerospace circles only in the 70s as aircraft SURVIVABILITY became the number one priority. Prior to this, the trend adapted by western designers between 1950 and 1970 was merely to define the role of a combat aircraft and produce them in a cost effective manner. The combat-derived criteria involved:

(a) SURPRISE
(b) OUTNUMBERING THE ENEMY IN THE SKY
(c) MANEUVERABILITY
(d) LETHALITY

It was only during the mid-70s that the aerospace designers were tasked to improve aircraft survivability during 'long' combat operations and spread the life cycle costs over a 'longer' service life of the combat aircraft. Since these requirements involved 'longer' training periods, designers opted for twin engine fighters. Studies reveal survivability of an aircraft is doubled, if an engine fails in a twin-engine design, especially when major portions of the flying hours are expected to occur in peace time.

During combat operations, twin engine fighters double the probability of engine failure and consequent loss of mission. It was around this period the West managed to get hold of half a dozen MiG aircraft to evaluate their performance.

Studies revealed that the MiGs were designed for short and intense combat life and also required 80-90 per cent fewer maintenance man hours per flight hour than its comparable F-100/F-101 US aircraft.

It was concluded that the Russian aircraft design demonstrated high reliability for short combat periods, in addition to being less expensive to operate and to maintain……..justifying a necessity that seems to have prevailed during the Cold War period as the Russian Air Force had a very large inventory focussed on faster turnaround of fighter aircraft with a rigorous schedule of take offs and landings. In a study taken by aerospace agencies in the US to examine the structural integrity of aeronautical systems that are classified as mission critical, it was revealed that the aircraft with rigorous schedule of take offs and landings will age faster than an identical aircraft with fewer touchdowns. Increased operations tempo has been observed to wear out combat aircraft as observed in F/A18Cs/Ds HORNETS….which logged more than 73,000 missions enforcing the no fly zone over Iraq, in addition to the 3,000 sorties during Kosovo operations. Each Hornet is expected to handle 6,000 flight hours and 2,000 catapult takeoffs and arrested landings. The average age of the planes is 8.5 years with the oldest in the fleet being 13 years. The US goal is to add 700 more catapult takeoffs and landings to each aircraft, or about seven more years of use. Thus by ensuring a close monitoring of aircraft health, its serviceability can be extended without relevance to its vintage.

In the West, Dakotas are still flying even after 6 decades. Boeing 747 continue to operate safely since induction with thousands of modifications, repairs, engine changes and millions of maintenance hours. These aircraft are examples of operating within the designed flight profile which is generally not encountered by combat aircraft due to military needs. When combat aircraft enters squadron service, it comes with its maintenance procedures, inspection points and various test/ calibration equipment. These do not change dramatically when the flight profile changes from interceptor to ground attack. Over a period of time as the redefined role takes a toll of the airframe by ageing it faster and introducing flaws rapidly….the established maintenance and inspection do not highlight the emergence of unseen/ undetectable flaws which gradually migrate to cause fatal accidents. It would be worthwhile undertaking a study to evaluate the evolution of maintenance and inspection points in the life of an ageing aircraft in order to emphasize the importance of changes in this sphere. This issue would have been addressed scientifically in MiGs had there been a NATIONAL AEROSPACE INITIATIVE in place.

By virtue of continuous and sustained evolution, the aerospace industry in developed countries consistently institute improved inspection techniques and retrofitment of superior parts with a view to enhance service life of an aircraft. However it has been noted that factors which affect an aircraft life are onset of microscopic corrosion alongwith metal and acoustic fatigue. Sikorsky's UH-60 Black Hawks main and tail rotor blades, hub, and windshields have worn more than expected due to corrosive nature of sand in Iraq. Brown-outs, due to sand and snowstorms have caused 33 out of 176 major helicopter crashes in Iraq (Mar 2005). Corrosion affects aircraft operating in a damp climate more than those operating in desert conditions, unlike metal/acoustic fatigue which occur depending on the payloads during each mission; number and duration of flights in which violent turbulence was encountered; number of take-offs and landings, with specific reference to severe impactive landings; exposure to sonic booms, etc. Such information need to be recorded and a database created to aid life-extension and investigations into accidents.

It is generally accepted that in the absence of a trusted technique, metal loss due to corrosion in combat aircraft cannot be reliably quantified as conventional detection methods assume that corrosion takes place uniformly. Localized pitting corrosion acts as a crack nucleii and causes early crack nucleation and the onset of fatigue crack growth irrespective of aircraft vintage. In aerospace circles it has been concluded that 'age' has little to do with safety, but continuous monitoring to detect fatigue crack initiation and growth in an aging fleet was essential to prevent accidents, especially when the aircraft have encountered aggressive deployment both in times of training and whilst participating in sorties involving carriage of high drag weapons/ launchers/ fuel tanks on the external pylons…….….. all indicative of changes to originally planned flight profile. External stores like missiles, bombs, fuel tanks, rocket launchers, various pods…all increase cruise drag (range and endurance, both functions of cruise efficiency, relate to low cruise drag). In Iraq, onset of metal fatigue and corrosion are hampering availability of F-15 fighters, C-130 transport aircraft, P-3 Orion maritime aircraft, E-3B Hawkeye jammer, KC-135aerial tanker and various helicopters.

Airframes of high performance aircraft are continually subjected to vibration and acoustic loads in an elevated thermal environment. The combined effect of these loadings give rise to structural fatigue, even when operating within the designed flight profile. Generally, the broadening of the aircraft mission spectrum, after induction into service, to meet changing military needs inadvertently expands the flight profile, which tends to cause a dynamic change to the geometrical characteristics of the aerofoil. Any dynamic variation in the stiffness and damping properties in discrete sections of the wings will affect stability of the aircraft, which ultimately leads to fatal accidents. Aircraft, operating outside the design profile in tropical atmosphere, are subjected to repeated stress cycles due to a combination of metal corrosion, metal fatigue, crack propagation phenomenon. Non-Destructive Inspection (NDI) to detect these is a challenging affair which involves applied research in areas such as modeling the probability of detection of structural flaws, developing instruments and sensors, detecting corrosion and predicting the outcome. Currently efforts are underway in the West to predict and suppress the onset of fatigue and crack propagation using advancements made in sophisticated opticfibres, piezoelectric ceramics, shape memory alloys, electrorheological fluids, etc. Similar initiatives need to be institutionalized in India.

Till date no metallic airframe has been developed to counter corrosion, or to restrain propagation of cracks due to micro-corrosion or fatigue. Catalytic corrosion problems are hard to detect and cause catastrophic failures if not fixed on time. Nations that acquire combat aircraft are more focused on matters of deployment that the issues concerning 'enabling aerospace technologies' are not addressed. Careful monitoring of the airframe structures has given birth to the evolution of a new technology which features actuators, sensors, data-links, and microprocessors embedded in the airframe to measure load and vibration signatures to infer structural integrity. It is popularly called Smart Skin technology and currently in vogue with aircraft built from composite materials which permit strain, temperature, vibration, chemical sensors to be embedded in the airframe without adversely altering the aerodynamic integrity. They are being used to ascertain state of damage in aircraft by employing self-diagnosis functions, prediction functions, self-repair functions and notification function to indicate their state of residual life by changing colour. Northrop is reported to have embedded a fiber-optic sensory system in the B-2 stealth bomber to monitor flight stress.

Currently, the aircraft health-monitoring philosophy using smart skins is receiving maximum attention in the West in order to answer questions like…….How long can the structural life of an aircraft be extended? Are the current techniques adequate? etc. While Sensors are used to measure load and vibration signatures to infer structural integrity, accurate prediction of fatigue life is a challenging task for which expertise is still in experimental stage as far as combat aircraft are concerned.

Group of polymer chemists, solid state physicists, material engineers and other scientists are dreaming up such futuristic projects as bridges that heal themselves when cracks develop, submarines whose surface soak up obtrusive sonar waves, and airplane wings that stiffen to adapt to flight stresses. In aviation circles, special efforts are being made to counter the tendency of aircraft to lose stiffness at high speed flight temperatures of more than 300 degrees Fahrenheit. By using shaped memory alloy fibers in a graphite composite it has been possible to stiffen the wings at higher temperatures.



Technological trajectory of the F-16 called the Fighting Falcon reveals the problems that surfaced during its transition from the production floor to its induction into the air squadrons. Two manufacturers, Northrop and General Dynamics produced the prototypes that embodied the virtues of the combat-aircraft criteria of the 50s. The GD design got the approval…it weighed about 20,000 pounds and carried only a simple aerial cannon, Sidewinder missiles, and their fire-control systems. Immediately after the series production clearance was accorded by the US Congress, the aircraft came under the purview of US Air Force's development and procurement bureaucracies. The full scale engineering production blueprint of USAF introduced various military specifications which added roughly two tons of new electronic equipment and other modifications. During prototype development some 25 air force personnel were involved…once production was cleared it had grown to over 200 and the contractor's team went from 150 to about 1,500. Gradually the aircraft mission got redefined….instead of being a 100 per cent pure fighter, as originally envisaged, it got converted into a multi-mission aircraft to be used for attacking ground targets and for dropping nuclear bombs. The structural and electronic packages justified by new missions raised the cost and degraded its performance as a fighter. Originally it was designed to withstand forces of 7.33g…..but the Configuration Control Committee increased it to 9g, which led to structural reinforcements and additional weight along with a gamut of avionics viz. Radar, ECM, etc all adding weight to the aircraft and cost to the Exchequer. Installing a complex radar demanded more power and more cooling, which made the fuselage grow. End result…wings and tail had to be enlarged — the tail was not enlarged enough which reduced the aircraft stability in flight. It weighed 24,000 pounds instead of 20,000 pounds with a proportional reduction in acceleration, and was loaded heavily with hard-to-maintain electronic gadgets. The first operational model was delivered to the Air Force in January 1979. It was the first fighter that cost 75 per cent more than the basic version when modified to deliver nuclear weapons. Baseline Lifetime expectancy was set at 8,000 hrs based on:



— 55.5 per cent air-to-air missions
— 20 per cent air-to-ground missions
— 24.5 per cent general flying.

In 1990, twelve years after induction, a news item appeared that reported more than 100 crashes of F-16: USAF—80; NATO—17; PAK—13. The aircraft was labeled the WIDOW MAKER. It was reported that hasty induction of the aircraft had led to use of certain wirings which did not conform to MIL-STD requirements (fly-by-wire going haywire?). Later another report placed restrictions on F-16 from indulging in high 'g' maneuvers and low level missions. These restrictions prevailed during the Gulf War….even after two decades of combat flying. It came to be referred to as a 'clear weather' aircraft which did not meet the assigned tasks during the Gulf War…its performance was officially criticized by the US General Accounting Office. In May 1991, US Senate Armed Services Committee found the stealth fighter F-117 to be eight times more effective than F-16. Plans were on to terminate production of F-16 but the commercial implications of the multi-nation development venture involving the USA, Belgium, Netherlands, Norway, Denmark, Israel and a host of customers gave the aircraft a fresh lease of combat life.

Jane's Defense Weekly (August 10, 1991) quoted Pentagon, stating that the aircraft had been assigned to 60 per cent air-to-ground missions (as against 20 per cent). It was presumed that sorties with vintage iron bombs fitted with Laser Guidance adapters offered undesirable drag loads. Carriage of non-conformal bombs on external pylons take a heavy toll of the airframes integrity and engine performance. Around this period, INTERVIA, came up with the news that 3,240 (pre-block 50) F-16s, required structural modifications and repairs after cracks were detected due to metal fatigue. According to the manufacturer's spokesman, the operational aircraft was being 'flown more aggressively, more often, than originally specified'. The details of the proposed structural modifications were also listed in INTERVIA. The presence of non-conformal (mostly vintage) bombs, loaded externally appeared to have, in the words of an aerospace expert “……convert the fast, sleek, maneuverable aerodynamic aircraft into slow, sluggish, bomb trucks”….with attendant problems to airframes and engines.

During the 70s, combat aircraft architecture laid emphasis on functional complexity of 'mechanical nature'….. engines, airframes, cockpit design …alongwith the ability to carry and deploy vintage munitions. A phase in which 'fast aircraft, dumb munition' was the order of the day. The GE J-79 engine fitted in F-4 Phantom contained only 999 parts, whereas the Pratt & Whitney F-100 jet engine fitted in F-15 and F-16, a product of the 70s, had no less than 4,541 parts to achieve high thrust/speeds. Simultaneously, with the advent of advancements in microelectronics, the emphasis began to shift towards functional complexities of the 'software' kind. Electronic modules per aircraft reduced from 300 to 30 numbers. It was an era, in the 80s, which witnessed the transition and emergence of 'fast aircraft, smart munition'. The USAF launched Pave Pace program to reduce avionics module using networks of miniaturized super-computers, optic computing and neural networks……..resulting in increasing the number of functions within the cockpit. To improve handling and safety during high 'g' maneuvering and carrier approach the programs called ACTIVE (Advanced Control Technology for Integrated Vehicles), Mission Adaptive Wings and Digital Fuel Control were undertaken. It was a phase when aerospace experts realized the importance of system integration involving aerodynamics, airframe structures, engine performance, etc. In 1992, John Grin, a professor in the University of Amsterdam, had stated in a paper“In the area of modern highly maneuverable fighters such as the F-16, the airframe's capabilities to withstand high acceleration are in many cases better than the pilot's. Furthermore, increased capabilities also imply increased workload for the crew; reportedly a large share of aircraft crashes are due to pilot error.”

Flight International November 2, 1985 issue states the following: “What would be much valuable would be the ability to measure the physiological health of the pilot. Is he conscious? We are now aware of the problems of sudden loss of consciousness GLOC (g-induced lack of consciousness), when the pilot goes straight into blackout without going through the warning symptoms of tunnel vision or greying out. So, with GLOC there is no warning. We suspect we have lost F-15s and F-16s through this. If we had means of monitoring the pilot's consciousness we could recognize, when the pilot blacked out and, if he did not respond to his base control, we would automatically pull up his aircraft until he regained consciousness.” IAF is reported to be scouting for 'disorientation' simulator systems to aid combat pilots to learn to control stress and get familiar with the effects of such situations especially under high 'g' conditions.

In the early 80s, scientists began to suspect several accidents had been caused by GLOC. The Swedish Air Force cited a case where only GLOC could explain a death. A new G-suit for the JAS-39 Gripen fighter was the first operative suit in the world to combine full body coverage from the waist down with balanced positive pressure breathing during 'g'. Thus accidents, when they happen, bring pilot error and technology under a cloud. The second generation supersonic aircraft F-16 has four digital computers which seemed to work satisfactorily until certain 'operative conditions' are encountered which lead to catastrophic consequences. Supersonic fighters incorporate ACTIVE control technology to improve handling and safety, when aircraft is maneuvered at high loads; high angle of attack; and high Mach numbers. Under these conditions it has a tendency for instability, which is exhibited by wing rocking or oscillations. If the pilot overcontrols, in a worst case scenario, the aircraft may enter into a spin and in the event of GLOC (above 7g) it could prove fatal. If, however, the pilot manages to recover by using the stick…a lot will depend on the orientation of the aircraft as direction in which the stick is moved will decide the matter of life and death, especially during low level missions. This was not permitted for F-16 during Desert Storm…..even after two decades of induction into service. In the late 90s, a modification was introduced in Block 50 F-16 version to include a digital terrain system that is intended to provide an increasingly sophisticated capability to fly safely in low level sorties. The computer software would compensate, even an upside down aircraft, by maintaining a minimum distance above the earth. This kind of research to enhance survivability in combat planes needs to be part of the aerospace development activity of any nation that entertains plans to produce and market aircraft.

For a combat aircraft, mission capability is a function of cruise efficiency viz. Range and Endurance, which in aerospace jargon relates to low cruise drag. In the case of MiG-21 the transformation from interceptor to ground attack role involves a change in its 'planned' flight profile with compromises in performance during maneuvers, take-offs, landings, carriage of external stores….all contributing to increased payload and/or range at the expense of cruise drag/trim drag/flow phenomena over airframe/flow interactions. All these can be quantified using computer-aided design tools with unprecedented fidelity, if relevant data are faithfully recorded for analysis. The importance of laminar flow control and variable life cycle engine effects on the airframe are generally overlooked when an imported aircraft like MiG-21 is accorded multi-mission clearance (by local agencies) and operated in a aggressive manner, especially when suitable trainer aircraft are not available, in brutal environments.

In the aerospace circles, twelve enabling technologies have been identified and are being pursued relentlessly:



(a) AERODYNAMICS: research covering Laminar Flow Control and High-lift aerodynamics.
(b) STRUCTURES: research on use of lightweight high strength composites.
(c) PROPULSION: research on core engine performance and adapting large engine technology to small engines.
(d) FLIGHT & MISSION CONTROL: research on integrating flight and propulsion control; variable cycle engine; high capacity long range data links.
(e) SIGNATURE REDUCTION: research on RF & IF signatures
(f) DESIGN & MANUFACTURING PROCESS: research on developing electronic prototyping.

By focusing on these 'enablers', they plan to meet the multi- mission spectrums in an era of rapidly changing information technology; increased reliance on PGM; lower cost/fewer aircraft; high survivability. It has been increasingly felt that warfighting benefits will be unattainable if R&D in aerospace proceeds solely along the traditional path, wherein in each aviation community viz fight, strike, reconnaissance, surveillance, ASW, EW, and troop lifting seek a successor model possessing increased performance. Be that as it may, health of combat aircraft are being monitored by resorting to non-destructive inspection techniques (NDI) for structural cracking, corrosion, adhesive bond strength, etc. In addition, adapting radiography using X-rays, gamma rays or neutrons; holography interferometry, which uses laser beams to produce 3-D images of an object; acoustic emission which records sound waves within materials under stress; visual and enhanced visual procedures; ultrasonics and thermography etc. are also being examined. This would naturally lead towards creation of a database of NDI techniques and associated test results. Since multiple inspection procedures are involved to achieve the desired confidence to establish realistic maintenance schedules, appropriate funding would be vital. Firms in the West achieve this expertise by generating after sales- profits to support data collection and analysis. Generally manufacturers inflate pricing of spare parts to sustain after sales support vis-à-vis warranty, while simultaneously putting in efforts to create an upgraded product expecting the services to show interest, which could later lead to funding by the government. In 1999, Lockheed was pulled up for inflated pricing …US$ 2,522 for a 4.5 inch metal sleeve (actual cost US$ 511), US$ 744 for washer (actual cost US$ 113), US$ 5,217 for a 1 inch bracket (actual cost US$ 258). This should serve notice to nations purchasing aircraft, or for that matter any defense product directly from a firm, without suitable safeguards on spare parts pricing especially when 'off-sets' do not form part of contract negotiations.

Developing nations like India have realized the significance of creating the requisite expertise in NDI of combat aircraft structures by giving due emphasis at the national planning level. As far back as the 6th Plan the need to undertake research in studying the onset of fatigue and corrosion has been highlighted. Unfortunately the current structure for management of such a technology has not lent itself to realization of this goal. IAF under the MOD is the affected party. Agencies responsible for conducting research and establishing the requisite infrastructure are placed under MOD (defense production) and DST….with more than one ministry involved, there appears to be neglect of a critical feature that is mandatory for any aircraft building nation. Determining the fundamentals of the NDI discipline requires an integration of experience and exposure with hard thought, appetite for details, and honest scientific analysis based on quantifiable engineering facts. Until this is established, it would be advisable to operate combat aircraft within the planned flight profile and not venture into changing payload/role to suit military needs as the penalty of such arbitrary actions, not backed by scientific data collected/generated by using appropriate technological tools would lead to fatal consequences.

Lack of appreciating this vital requirement would only continue the trend of classifying future crashes as caused by 'pilot error'. In MiG incidents, we must be having over 245 inquiry reports…one wonders if the attitude shown in railway accidents also prevails in them….carry on regardless without any follow-up as accidents keep piling. Whereas when F-16 acquired the WIDOW MAKER label…it was kept out of frontline action during the Gulf War…its production came to near standstill….but sound lobbying amongst the user nations kept the home fires burning for Lockheed, which enabled it overcome the restrictions imposed on low level sorties by introducing ACTIVE technology. If the aircraft in the inventory of our tri-services are to have a long life of safe flying, we need to focus on nurturing NDI expertise and establish reliable test and measurement procedures that dynamically assess aircraft structural condition with vintage, usage and every modification to the highest level of reliability. Even though developed countries are able to find ready customers for ageing aircraft which serves to keep the production lines active, they are trying to address this problem in respect of aircraft operated by them. Whereas for countries like India, this is an area which would require integration of efforts by certified university laboratories, national NDI test centers, aircraft designers, manufacturers, users in an institutionalized manner….with the final decision to fly the aircraft not left with the group but entrusted to the User only as it ensures responsibility and accountability ….currently this seems to be missing in our environment …when one closes air crashes under the 'pilot error' label due to absence of desired engineering facts. In the US, the ageing aircraft problems in commercial airliners are covered by the mandate provided by Aviation Safety Research Act 1988…we need to have similar provisions enacted to overcome the sluggishness encountered in our evolving aerospace activities and also to ensure decisions are made by persons who are products of the discipline, with desired exposure to the latest aerospace developments; and are able to guide in the creation of necessary infrastructure to monitor the health of combat aircraft and to support life extension of ageing aircraft.

In the US, the University of Cincinnati, under a US$ 5 million federal program is developing a infra-red laser light system to spot cracks, which will indicate metal fatigue as tiny as 200 microns in length. Northrop Grumman Corporation has been entrusted with US$ 1.7 million contract by the US Navy's Office of Naval Research to develop wide area NDI imaging technology, which will rapidly scan painted aircraft sections in-situ for surface and sub surface corrosion. Such a move would be required by policy makers. National Aviation Policy mooted by our Air Chief should address the issues of nurturing the enabling technologies and creation of reliable health monitoring techniques of aircraft.

At the National level, a team comprising of NAL, CAIR, HAL and ADA have accomplished the flight control laws for LCA. Such an integration of expertise would also be required in the field of NDI to study metal fatigue and corrosion in combat aircraft operated by IAF. Perhaps the formulation of a National Aerospace Initiative would force various authorities operating under the aegis of DST/ MOD/ MOD (Production) to integrate efforts of national laboratories, science departments in universities, research scientists, and other professional associations and ensure proper utilization of the budget towards creating the requisite infrastructure for nurturing suitable NDI techniques for combat aircraft. In addition, a roadmap needs to evolve to sustain the desired research into enabling technologies by a conglomerate of selected institutions in specific areas in order to avoid duplication of efforts and to utilize the allocated budget resources cost effectively….. ….this is mandatory for a nation which has ambitions to make a mark in the global aerospace business.

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