After undergoing significant changes to enhance its flight characteristics, Hindustan Aeronautics Limited (HAL) renamed the Hindustan Jet Trainer-36 (HJT-36), formerly known as Sitara, ‘Yashas’. Significant design changes have been made to this updated version to improve its suitability for Stage II pilot training and operational missions like aerobatics and counter-insurgency.
The HAL HJT-36, initially named Sitara, was designed as a conventional subsonic jet trainer featuring low swept wings, a tandem cockpit, and small air intakes on either side of its fuselage. The design work for the HJT-36 began in 1997, with HAL receiving government approval in July 1999 to develop two prototype aircraft at a cost of ₹180 crore. The aircraft was intended to enhance pilot training effectiveness, featuring a fuel-efficient engine and advanced avionics systems. The first prototype (PT-1) flew on March 7, 2003, followed by the second prototype (PT-2) in March 2004. Initial operational clearance (IOC) was expected by 2006-07, but delays were common due to various design challenges, particularly related to stall and spin characteristics.
By March 2010, the IAF placed an order for 73 serial production aircraft despite the IOC not being achieved at that time. The project faced criticism for delays, with costs escalating significantly from initial estimates. By 2010, the aircraft entered limited series production but was deemed “unfit” for service by Indian Air Force officials due to technological issues related to spin tests. These issues persisted until January 2022.
The aforementioned aircraft had a number of serious defects that affected its effectiveness as a trainer.
The Federal Aviation Administration (FAA) has historically stressed the importance of spin resistance in aircraft design, shifting some responsibility onto manufacturers to ensure their airplanes can recover from spins. However, many aircraft still exhibit unrecoverable spin modes, which can lead to rapid altitude loss and overwhelming situations for untrained pilots. One of the most significant flaws was its inability to recover from spins, which is crucial for any trainer aircraft and raised safety concerns because spins can occur unexpectedly during flight and without proper recovery capabilities, pilots could be put in potentially fatal situations.
It was determined that the original SNECMA Larzac 04-H-20 engine was insufficient for the aircraft’s operational requirements. As a result, the Russian AL-55I jet engine was adopted, which brought with it a unique set of integration difficulties. These problems demonstrate how difficult it is to make sure that an aircraft’s propulsion system complies with safety regulations and overall performance criteria.
Another significant design flaw was the limited cockpit visibility, which adversely affected pilot situational awareness. For trainer aircraft, clear visibility is crucial for both instructors and students to monitor flight conditions and respond appropriately. The original design did not meet these essential requirements, necessitating modifications to enhance visibility and ensure safer training environments.
Significant improvements have been made to the HAL HJT-36 Yashas, especially in the engine and cockpit design, which has improved the aircraft’s capacity to serve as an Indian Air Force (IAF) trainer.
The NPO Saturn AL-55I jet engine, which has Full Authority Digital Engine Control (FADEC), is presently installed in the HJT-36. This cutting-edge system is appropriate for contemporary training requirements since it maximizes thrust management, boosts safety during high-risk maneuvers, and increases fuel efficiency. With a thrust of 17.3 kN, the AL-55I engine offers a high thrust-to-weight ratio that is necessary for efficient operation.
The aircraft’s cockpit has been redesigned with a stepped-up rear cockpit and a drooped nose design, significantly improving pilot visibility and situational awareness—critical factors for effective training. In accordance with modern aviation requirements, it now has a glass cockpit system with Multifunction Displays (MFDs), a Head-Up Display (HUD), and sophisticated navigation and training systems. Analysts note that the Yashas boasts the largest display area among current fighter/trainer aircraft in the IAF.
The HJT-36’s chief test pilot and creator, Group Captain H.V. Thakur, emphasizes that the upgraded Yashas includes an AI-powered voice command system for improved operational efficiency and training. The cockpit now only uses digital displays instead of traditional instrumentation or switches.
In order to solve earlier stall and spin recovery problems, HAL has also concentrated on improving the aerodynamics of the aircraft. The aircraft’s preparedness for training missions has been further guaranteed by thorough testing that has successfully proved safe recovery procedures.
After having its airframe altered to improve its spin characteristics, Sitara made its first flight in three years in April 2019.
In order to address spin resistance and departure characteristics over its flying envelope, the aircraft has undergone significant modifications.
The Yashas contains all the equipment needed for Stage II pilot training, which includes armament training, counter-insurgency, and counter-surface force operations.
In order to solve earlier stall and spin recovery problems, HAL has also concentrated on improving the aerodynamics of the aircraft. The aircraft’s preparedness for training missions has been further guaranteed by thorough testing that has successfully proved safe recovery procedures.
After having its airframe altered to improve its spin characteristics, Sitara made its first flight in three years in April 2019.
In order to address spin resistance and departure characteristics over its flying envelope, the aircraft has undergone significant modifications.
The Yashas contains all the equipment needed for Stage II pilot training, which includes armament training, counter-insurgency, and counter-surface force operations.
In order to solve earlier stall and spin recovery problems, HAL has also concentrated on improving the aerodynamics of the aircraft. The aircraft’s preparedness for training missions has been further guaranteed by thorough testing that has successfully proved safe recovery procedures.
After having its airframe altered to improve its spin characteristics, Sitara made its first flight in three years in April 2019.
In order to address spin resistance and departure characteristics over its flying envelope, the aircraft has undergone significant modifications.
The Yashas contains all the equipment needed for Stage II pilot training, which includes armament training, counter-insurgency, and counter-surface force operations.
HAL has two aircraft ready, and two more need to be certified.
HAL Chairman and Managing Director Dr. D. K. Sunil said the aircraft has “risen like a phoenix” and is significant for the IAF.
The exterior and cockpit have undergone extensive modifications to resolve all of the earlier problems.
In addition to being positioned as a vital component in updating India’s pilot training infrastructure, the Yashas is anticipated to fulfill increasingly demanding training standards. As part of HAL’s objective to supply domestic solutions for military aviation requirements, the aircraft continues to be an essential part.
