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 Vol. 9  No 5 October  2001            

Propulsion Systems

Spin Recovery System for LCA

For a combat aircraft like LCA, it is mandatory to demonstrate carefree manoeuvring without entering into spin during a flight test programme. During such demonstrations, the aircraft is equipped with a tail-mounted Spin Recovery Parachute System (SRPS). SRPS consists of a parachute, drogue gun, release mechanism, container, lid plate and standard electroexplosive devices.

DRDO has designed and developed such SRPS for emergency recovery of LCA from an inadvertent spin, in case its controls are ineffective and are unable to pull it out of spin. SRPS for LCA has been dynamically tested and has met all the specifications on Rail Track Rocket Sledge trials.

Gyro Uncaging Device

Gyro Uncaging DeviceThe Gyro Uncaging Device (GUD) is used to uncage the free gyroscope rotor used in the sensor package which comprises a piston-cylinder arrangement and a squib, called gyro-squib. When a predetermined current is supplied to gyro-squib, it fires and generates gases at high pressure on piston head moving it forward and presses the lever of gyro uncaging mechanism to uncage gyroscope rotor.

DRDO has successfully developed GUD for Trishul and Akash missiles. After batch qualification tests, GUD has demonstrated successful performance under all environments.

Hot Gas Generator

Hot Gas GeneratorSolid propellant hot gas generator is used to launch a missile from canister. DRDO has designed and developed a solid propellant hot gas generator which produces highly progressive mass flow rate. To achieve this, high burn rate (r75 = 30 mm/s) non-metalised inhibited composite propellant based on HTPB has been developed. Motor  is designed to operate on a pressure range of 15 to 200 kg/cm2 with factor of safety of 2 to increase the reliability. Casing, head-end dish and deflector have been machined out from closed die forging.


So far, thirty full-scale proof gas generator tests have been successfully conducted and fifteen flight version gas generators have been static tested. Two force simulated missile launches conducted using this system met the mission requirements of missile exit velocity and maximum canister pressure.

Pyrogen Ignition System

The pyrogen ignition system is an iDEAL choice to ignite very large solid boosters. It is basically a Pyrogen Ignition Systemsmall rocket motor used to ignite a larger rocket motor. This system is essentially an efficient and reliable energy release system which provides the heat flux to the main motor propellant and the pressure in the motor chamber necessary to ignite the propellant and produce sustained combustion within the required time limit. The main motor ignition through this pyrogen igniter is a transient phenomenon wherein a series of events take place in smallest possible time in a controlled and reproducible manner. The ignition train consists of an initiator, pyrotechnic boost charge, pyrogen igniter propellant and the main motor propellant. This system has been successfully tested.

Large Size Solid Booster

DRDO has developed a state-of-the-art case-bonded HTPB-based composite propellantLarge Size Solid Booster with low burn rate of 4.3 mm/s at 50 KSC. This solid propellant rocket motor (dia 740/620 mm, length 6 m), made of 250 grade maraging steel, consists of a composite nozzle with metallic backup and lined with carbon phenolic liners. The motor is capable of generating 16 ton thrust for 38 s duration. Pyrogen igniter developed by DRDO has been successfully used for the first time for this motor.

Soft Stage Separation Mechanism

Various mechanisms can be deployed for stage separation of a large multistage vehicle, and its choice depends on availability of space, ease of integration and most important of all the permissible shock levels generated due to separation. Many flight vehicles employ flexible linear shaped charge cords where large shocks (of the order of 50,000 to 1,00,000 g) are produced to minimise shocks. In such vehicles, shock sensitive devices, like relays and computers are configured in such a way (distance as well as a special mountings) that they are not vulnerable to these shock effects. However, for vehicles where such high shocks are not permitted, separation devices with very low shock are specially designed to suit the specific purpose.

Soft Stage Separation MechanismThe key element in this stage separation mechanism is the pyrobolt, which is especially designed for this purpose. The pyrobolt consists of an electro-explosive pyrocartridge, piston, cylinder, a round-head release bolt, and four collets with an arrester. This assembly is kept locked before operation by a locking pin. The release bolt head remains engaged in the four collets and can come out only when collets are allowed to move radially outward. The arrester is locked with casing by a locking pin and stops radial outward movement of collets. When the pyrocartridge is fired, the arrester moves up due to pyropressure after shearing the locking pin, hits the check nut and stops making collets free to move radially outward. Thereby, piston under pressure pushes the release bolt out of pyrobolt housing. Two stages have flanged interface and are joined together with a number of pyrobolts. The number of pyrobolts required to join two stages, depends upon firing current supply, load, bending moment and space available to mount pyrobolts.

DRDO has designed and developed pyrobolt actuated stage separation mechanism for missile application. A large number of pyrobolts have undergone full-scale simulated ground tests and two full-scale stage separation tests where the shock measured at various locations was less than 500 g.