National Aerospace Laboratories (NAL), a constituent of Council of Scientific and Industrial Research (CSIR), is India's pre-eminent civil R&D establishment in aeronautics and allied disciplines. NAL was set up at Delhi in 1959 and moved to Bangalore in 1960.

NAL's primary objective, as articulated in its new Vision Statement, is the "development of aerospace technologies with a strong science content and with a view to their practical application to the design and construction of flight vehicles". NAL is also required "to use its aerospace technologybase for general industrial applications".

NAL's core competence spans practically the whole aerospace spectrum. Over the years, NAL has made very significant contributions to all Indian aerospace programmes; often even setting the national agenda for such programmes. During the last decade NAL has spearheaded the effort to design and develop small and medium-sized aircraft for the civil sector.

NAL's real strength lies in its vast reservoir of expertise and facilities created over the years. With this imposing infrastructure, NAL has been very successful in obtaining a large number of R&D contracts for testing and subsystem development for various national programmes as well as industries all over India and abroad. In the past decade (1987-97), NAL undertook approximately 400 projects worth about 60 million US$. Over the last few years, NAL has earned more than 60% of its budget through external resources, a unique achievement for CSIR laboratories.

NAL is well-equipped with modern and sophisticated facilities which include national facilities like the Nilakantan Wind Tunnel Centre and the computerised fullscale fatigue test facility. The various facilities and multi- disciplinary expertise, developed primarily for the aerospace sector, are also utilised in other sectors involving high technology. NAL is recognised as a centre for failure analysis and extends its support in investigating failures and accidents both for aerospace and other general facilities. Other major facilities at NAL include: the acoustic test facility, turbomachinery and combustion research facilities, Composite Structures Laboratory, black box readout systems and the FRP fabrication facility.

NAL has a staff strength of about 1300 with about 350 full- fledged R&D professionals (over 100 Ph.D.'s). It is thus in a unique position to offer R&D support, expertise and services to both aerospace and non-aerospace sectors of industry. Some major recent contracts include: development of carbon fibre composite wings for India's Light Combat Aircraft (LCA) programme, design, development and fabrication of a fully-automated autoclave for Hindustan Aeronautics Limited (HAL), development of co-cured fin and rudder for LCA and a shake test facility for HAL's Advanced Light Helicopter (ALH).

Spin-off technologies from aerospace R&D activities have significantly contributed to the non-aerospace sector everywhere in the world. Conscious of this aspect, NAL has made special efforts to identify those developments which could result as off-shoots from the main R&D programmes. About 30 such technologies developed over the last decade have been successfully licensed and transferred to 54 industries against a premier value of 100,000 US$. The cumulative production value of these technologies is over 10 million US$.

NAL's models for business development activities include inhouse projects leading to commercialisation, sponsored projects, industry-lab linkages, multi-agency collaborative projects and international contracts. During the last 24 months, NAL has obtained 12 contracts worth over 25 million US$. NAL has also undertaken about a dozen international projects for Boeing, USA; Civil Aviation Authority, UK; IBM Corporation, USA; Hitachi, Japan etc.

NAL has therefore come a long way from its modest beginnings in 1959-60 when it was housed for some time in the stables of a former Maharaja's palace in Bangalore.

Nilakantan National Trisonic Aerodynamic Facilities The best blowdown wind tunnel in the world?

Nilakantan National Trisonic Aerodynamic Facilities (NTAF), with three (1.2m, 0.6m and 0.3m square) high speed wind tunnels and associated model making and data acquisition systems. Every Indian aerospace vehicle has graduated out of this remarkable facility set up at NAL in the 1960's. In August 1998, the tunnel completed its 25,000th blowdown.

Over the years several improvements have been incorporated to meet the wide-ranging needs of aerospace organisations in the country. Some of these are computer-aided model design capabilities including associated software for NC machining, improved tunnel instrumentation, computer based data acquisition/processing system, PC based control systems and special test rigs/techniques. A 0.6m transonic tunnel (H2) was indigenously designed, built and commissioned in 1989 to meet the anticipated increase in test requirements.

NTAF is operated as a national facility funded by four major users viz., ISRO, DRDO, HAL and CSIR. The H1 tunnel with its associated support facilities has completed about 30 years of useful service and contributed significantly to major aersopace projects of the country. The tunnel has logged more than 25,000 blowdowns during this period.

1.2m Trisonic Tunnel (H1)

Working section 1.2m x 1.2m
Operation intermittent blowdown
Test duration 30 seconds(typical)
Mach number range 0.2 to 4.0
Transonic insert - Perforated walls, 600 inclined holes at top and bottom with 6% open area, normal holes at sides with 20% open area
Stagnation pressure 1.5 to 8.0 bar
Reynolds number 8x106 to 60x106 per metre
Model incidence -150 to +270, continuous and step mode
Model roll angle 00 to 3600
Instrumentation strain gauge balances, pressure transducers, electronically scanned pressure measuring systems, thermo- couples etc
Special controls transonic Mach number control, transonic Mach number sweep and pressure sweep
Special rigs
Captive trajectory system for aircraft store separation studies
Semi-captive trajectory rig for multi-booster separation studies of launch vehicles
Forced oscillation rig for dynamic derivative measurements in pitch and yaw
Jet simulation rig
Sting, ventral strut, side strut support system
Beta sector for yaw tests 0.6m Transonic Tunnel (H2)
Working section 0.6mx0.6m, slotted walls, 6% open area on top and bottom walls and 4% on side walls
Operation intermittent blowdown
Mach number range 0.2 to 1.2
Stagnation pressure 1.5 to 4.0 bar
Reynolds number 8x10 to 60x10 per metre
Model incidence -150 to 300 continuous and step mode
Test duration typical 30-40 seconds, max-180 seconds
Special controls PC based tunnel control system, transonic Mach number sweep, pressure sweep Data System

Data acquisition through front end MicroVAX computer systems located in H1,H2 and H3 tunnels. The host VAX 11/785 networked with MicroVAX system is used for data processing and archival. The database management and analysis package resident on VAX 11/785 provides for rapid data analysis and report generation

Strain Gauge Balances

Force measurements using a range of six component balances. Developed expertise in design, fabrication and calibration of balances of different load ranges for conventional as well as special applications

A calibration rig facilitates calibration of six-component balances with single-component loading, offset loading, limited combined loading and is interfaced to a PC based data acquisition system

Model design, fabrication, inspection

Excellent model and rig design capabilities through CAD,NC programming
In-house model fabrication facilities including a 4 1/2 axis CNC machine
3D computer controlled coordinaate measuring machine

Activities

Development of advanced test techniques

Captive trajectory technique for aircraft store separation studies
Semi-captive trajectory technique for booster separation studies on launch vehicle models
Forced oscillation technique for dynamic derivative measurements
Air-intake performance tests
Transonic buffet studies
Aeroelastic testing
Aerodynamic testing on models of aerospace vehicles
Six component force and moment data generation
Steady and unsteady pressure data
Schlieren flow visualisation
Design and Fabrication
Wind tunnel models
Internal strain gauge balances
High speed wind tunnels

The focus of activity in NTAF included the attenuation of flow unsteadiness in the 1.2m wind tunnel, which involved a major shutdown of the facility, installation of noise attenuation module, re-calibration and re-installation of various control systems. Even though the modifications (beginning with the shutdown of the facility) were planned to start from March 1998, because of pressing demands from various user-organizations (ADA, DRDL and VSSC) to complete several important test programmes, the shutdown of the wind tunnel could be initiated only during October 1998. A number of tests were done to establish the free-stream characteristics in the facility just before the modifications. Following completion of modifications and re- commissioning of the PC based control system of the wind tunnel, the tests are being repeated to assess the changes in the flow quality. Re-calibration of the tunnel is also in progress. Preliminary analyses of results confirm that satisfactory improvements in the flow quality have been achieved. Fluctuations of total pressure (measured in the settling chamber) and static pressure with solid wall test section (measured in the attached boundary layer on a cone model) show a very substantial reduction after the modification. The improved free-stream quality in the 1.2m wind tunnel at supersonic Mach numbers is now comparable with the best wind tunnels elsewhere. However, in the presence of perforated walls at transonic Mach numbers, such an impressive reduction has not been measured since no acoustic treatment has yet been made on the perforated walls in the transonic test section. Preliminary studies are in progress to introduce noise absorbers in the plenum of the transonic test section.

A total of 819 blowdowns were conducted in the 1.2m wind tunnel during the reporting period.

NAL accounted for largest number of runs, which included tests on SARAS aircraft model for CCADD, tests done before and after the installation of flow attenuation module and re-calibration following the modification. In this report, a summary of results obtained from various tests conducted before the modifications are presented along with a brief report on the effectiveness of the unsteadiness-attenuation module installed in the wind tunnel.

The 0.6m transonic wind tunnel was more extensively used during the reporting period, as compared to that during last year, with the number of runs amounting to 478. The projects completed include tests on a typical spacecraft configuration for ADA, and 4-hole and 5-hole calibrations for use in the Propulsion Division. In-house research activities comprising studies related to a delta wing model with flaps and studies on a generic axisymmetric body progressed.

Tests conducted for ADA centred on the performance enhancement of a typical combat aircraft model using various leading edge devices. Tests were also conducted on an air- intake model of the aircraft to assess the performance of the intake when some of the leading edge devices are deployed. An assessment of stability characteristics of a typical air-to-air aerospace model at subsonic to transonic Mach numbers was done in the 0.6m wind tunnel.

Tests completed for VSSC include force measurements on the model, of the sustainer stage alone, of a 2-stage sounding rocket configuration to obtain the roll characteristics. A special model-protection system employing proximity channels (instead of the conventionally used proximity plates) was used in these tests to alleviate the transient loads on the model during start and stop of the wind tunnel at high supersonic speeds. The system has been developed after a detailed in-house study based on statistics of start and stop loads on models in the 1.2m wind tunnel. Limited tests were carried out to make qualitative studies related to the shear layer reattachment that takes place on the canted nozzles of a multi-booster launch vehicle. Quantitative studies to examine the associated unsteady forcing function are in progress. The aeroelastic responses of the nozzles have been studied on a scaled model of the launch vehicle, in a separate study carried out by the Structures Division. In support of the air-breathing launch vehicle development being carried out by VSSC, a number of tests were conducted in the 0.3m wind tunnel on a scaled model of an isolated air-intake of the launch vehicle. As a part of these studies, a novel technique involving ventilation of the side-wall of the intake for passive control of the internal boundary layer was developed. Significant improvements in the mass-flow through the intake, following the boundary layer bleed, have been measured. The technique is extremely effective at high supersonic Mach numbers, and is especially useful for two-dimensional air-intakes with low width-to- height ratio. Further studies to assess unsteady effects associated with various side-plate configurations, and the effects of boundary layer bleed, are currently in progress.

Tests conducted for DRDL include measurements of wing load and hinge-moment on a typical air-breathing aerospace model using a specially designed torque element located at the wing root. The effects of configuration changes on the aerodynamic characteristics of a typical aerospace model were also determined.

In continuation of an in-house research activity on the aerodynamics of delta wings initiated last year, a number of tests were carried out on a model with flaps in the 0.6m wind tunnel. Limited tests, mainly involving surface-flow visualizations, were conducted on reattaching flows on a generic boat-tailed axisymmetric model.

Programmes

Failure analysis and accident investigations

Facilities and expertise for the analysis and prevention of failures
Accidents do not happen, they are caused

Accidents and service failures of engineering components do not happen. They are usually caused by a deficiency in component design or material selection manufacturing process maintenance and/or service practice

To prevent such mishaps, which lead to tragic loss of human life, loss of machine time or loss of production, we must identify the engineering deficiency and take appropriate corrective action to make the product more reliable.

The Expertise

NAL's Failure Analysis Group, which draws upon the Laboratories multidisciplinary expertise, has been investigating failures for three decades. It has built up considerable expertise in investigation of aircraft accidents and incidents chemical and power plant accidents analysis of failed or damaged components in a variety of industries

The Group's clients include India's Director-General of Civil Aviation, Indian Air Force and Indian Navy, Hindustan Aeronautics Limited (HAL), establishments of the Indian Space Research Organisation (ISRO) and India's Defence Research and Development Organisation (DRDO), Courts of Enquiry, India's Central Bureau of investigation (CBI) and a large number of industries in the private and the public sector.

Members of the group have served as experts to investigate the accident to Boeing 747 aircraft "Kanishka" following a midair explosion off the coast of Ireland, suspected sabotage of the Boeing 707 aircraft "Makalu" accident to the Caravelle aircraft at Bombay due to fatigue failure of the compressor disc, accident to the gas cracker plant at Nagothane and damages to the nuclear power reactor at Kalpakkam, to name but a few.

The Facilities

Modern analytical facilities for bulk and microchemical analysis
Scanning electron microscope with energy dispersive attachment
Metallography
Mechanical testing
Nondestructive evaluation
Residual stress measurement
Characterization and evaluation of polymers, ceramics and composites
Well-stacked library with on-line links to global databases

The Services

Complete analysis of accidents and component failures
Recommendations for failure prevention
Testing and evaluation of materials
On-line trouble shooting of production problems
Organisation of customised workshops and refresher courses for industry