Essential to the safety of any aircraft, a Ram Air Turbine (RAT), or Air-Driven Generator, provides emergency electrical and/or hydraulic power in the event that both the primary and auxiliary power sources are lost. This system is also used to power specific avionics applications. ADA has done considerable research on RAT and could be incorporated on TEJAS for use during critical systems failures

Aircraft  electrical  system  needs  to  be  robust  enough  to  cater  for  electrical  power  requirements  of  all  the systems of the aircraft and all the safety/degraded mission critical systems in failure modes. Designing such a robust electrical  system  for  a  developmental  aircraft  program  is  a  challenge. A  developmental  aircraft  during  its  various phases would involve integration of additional systems and new weapons (in case of fighter aircraft). Integration of newer systems imposes fresh challenges in managing the electrical system architecture especially in failure modes. Weapon integration in a prototype fighter program is dynamic as newer contemporary weapons are developed at faster  pace  and  ever  evolving.  Power  crisis  through  existing  on-board  power  generation  systems  in  failure  mode was  felt  during  an  indigenous  aircraft  development  program. A  novel  idea  of  introducing  a  Ram Air  Turbine  and utilize  the  power  generated  during  main  alternator  failure  for  critical  systems  was  studied.  The  intention  of  this experiment is to cover the details of the study carried out towards utilisation of such a Ram Air Turbine in landing phase for  extraction of  energy  in  case  of  main alternator failure.

Estimation of Additional Power using RATAs an alternate measure of generating energy during failure of alternator (ALT1), Ram Air Turbine Generator was studied. A Ram Air Turbine (RAT) is a small turbine that is installed in an aircraft and used as an alternate or emergency hydraulic or electrical power source. The RAT, when it is deployed can generate power based on the speed of the aircraft. RATs are used widely in various aircraft as an emergency source of power. A lot of studies have been carried out in the past in the field of generating green energy in aircraft and use of RAT for emergency power generation. HAL's Hawk trainer aircraft also deploys RAT for emergency hydraulic power generation.

Example of RAM Air Turbine Generator
Ram Air Turbines are also used in some podded  system  to  generate  hydraulic  or  electric  power.  For example RAT is used in Refuelling Pod (ARP-3) for generating hydraulic power for reeling in and out of hose. RAT is also used in Electronic Warfare pods such as AN/ALQ 99 which makes  it  adaptable  to  any  platform. Taking  cues  from  these studies an attempt was made to generate power using RAT in case of failure of the main alternator.

Design and development of a prototype fighter platform is a complex and multi-pronged activity. One of the critical aspects of any aircraft design and development is electrical load estimation and selection of suitable on-board power generation system to cater for estimated load. During the process of design, development and further in service, there would be multiple changes and additional systems which would be integrated. The additional power requirements for these need to be catered by the power generating system. The guideline for spare electrical energy that needs to be catered for during prototype development of a fighter platform has been given in MIL-STD-704 and MIL-E-70163. In one of the indigenous fighter platform development, during weapon integration phase a requirement was felt that power requirement for a critical air to air weapon ‘Article A’ in landing phase (in failure mode) could not be accommodated by on-board power generating system. The landing phase of the aircraft requires additional electrical loads especially for landing lights. Generally, prior to landing, airbrakes are used in the approach phase to steepen the approach and thereby reduce touchdown speed and ground roll distance.

Fighter platforms typically use aerodynamic devices like air brakes in order to achieve a steeper approach and the same is also used for during combat phases of flight. Additionally, meeting the power requirement to the critical weapon posed a serious challenge in failure mode and was required to be resolved. Ram Air Turbines (RATs) have been tried out on aircraft for providing hydraulic power and electrical power for emergency systems and various podded systems like in-flight refuelling  pod  and  electronic  warfare  pods.  The  intention is to dwell upon providing additional power through RAT (mounted on the existing airbrake compartment) during landing  phase  and  provisioning  spare  power capacity. The drag produced by the RAT could also be used for aerodynamic  braking (the  mounting  details  of  the  RAT  on TEJAS has been  shown  in  the  schematic  sketch  place in the figure above.)  For  this study  a  commercially  available  generator  was  employed  for proving  the  concept  and  in  the  detailed  design  phase  a  more efficient  alternator  of  airworthy  military  standards  shall  be employed.

By A Arunachaleswaran,  Shyni Thomas,  Muralidhar  Madhusudan,  S  Elangovan,  and  M  Sundararaj of National Flight Test  Centre, Aeronautical Development Agency