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| IL-96-400M |
The Russian engine project, the PD-35, is often argued as a case for the two-engine version of the IL-96-400 jumbo jet. But, Dmitry Markovich, Director of the Institute of Thermophysics at the Siberian Branch of the Russian Academy of Sciences, recently stated that the PD-35 project is intended for transport aviation, not passenger transportation.
To find out if adding two PD-35 engines to the IL-96-300 and IL-96-400 would make them underpowered, right-powered, or overpowered, it is necessary to carefully examine the aircraft’s performance needs, mission profiles, and the PD-35 engines’ abilities. Based on the calculations and considerations, we can construct a comprehensive argument to evaluate this scenario.
Present Performance of PS-90A Engines
The IL-96-300 and IL-96-400 are currently powered by four PS-90A turbofan engines, each of which generates 16,000 kgf (157 kN) of thrust, resulting in a total thrust of 64,000 kgf (628 kN). This configuration yields a thrust-to-weight ratio (T/W) of 0.256 for the IL-96-300 (250 tonnes MTOW) and 0.24 for the IL-96-400 (265 tonnes MTOW). Although these ratios are adequate for safe operation, they are comparatively modest in comparison with modern wide-body aircraft, which frequently have T/W ratios closer to 0.3 to enhance their takeoff and climb performance.
Two PD-35 engines are used to generate thrust
The PD-35, a high-thrust turbofan engine currently in development in Russia, is intended to generate 35,000 kgf (343 kN) of thrust per engine. The installation of two PD-35 engines would generate a total thrust of 70,000 kgf (686 kN), which is 6,000 kgf (59 kN) more than the present four PS-90A engines. This results in an increase in the T/W ratio for the IL-96-300 to 0.28 and for the IL-96-400 to 0.264. Although this is a slight enhancement, it remains below the 0.3 threshold which is frequently regarded as the optimal value for takeoff and climb performance in current airliners.
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| PD-35 Engine. Photo by the ASSAD press service |
Underpowered, Right-Powered, or Overpowered?
Underpowered Argument
From a pure thrust-to-weight perspective, the two PD-35 engines still leave both aircraft slightly underpowered. The T/W ratio of 0.28 for the IL-96-300 and 0.264 for the IL-96-400 is below the 0.3 benchmark which is typically considered optimal for achieving robust takeoff and climb performance. This could lead to lengthier takeoff rolls, reduced climb rates, and restricted performance in hot-and-high conditions or at high-altitude airports. Furthermore, the loss of redundancy in a four-engine configuration may pose a concern for operations in remote regions or long overwater flights where engine-out performance is critical.
Right-Powered Argument
On the other hand, the two PD-35 engines may be regarded as right-powered for specific mission profiles. The PD-35’s increased bypass ratio and fuel efficiency would increase range and reduce operational costs, while the 6,000 kgf (59 kN) of thrust would improve performance in comparison to the current configuration. The modest reduction in thrust-to-weight ratio may be outweighed by the increased efficiency and reduced maintenance costs of two engines for airlines operating on long-haul routes with lower payload requirements or from airports with ample runway lengths. Additionally, the PD-35’s sophisticated technology may offer superior overall performance during cruise, when the thrust requirements are considerably lower than those during launch.
Overpowered Argument
The two PD-35 engines are unlikely to result in the IL-96-300 and IL-96-400 being overpowering. The T/W ratios remain below 0.3, which is the threshold for what could be considered overwhelming in a commercial airliner, despite the fact that the total thrust increases by 6,000 kgf (59 kN). Most commercial operations do not require exceptionally short takeoff rolls and steep climb gradients, which are typically enabled by overpowered configurations with T/W ratios exceeding 0.3. The PD-35 engines, despite their considerable capacity, do not propel the aircraft into this category.
Structural and Operational Considerations
Significant structural modifications to the airframe would be necessary to replace four PS-90A engines with two PD-35 engines. In order to accommodate the increased thrust and weight distribution of the larger engines, the wings, and pylons would require reinforcement. In addition, the absence of engine redundancy may present difficulties for certification under ETOPS (Extended-range Twin-engine Operations Performance Standards), particularly for lengthy overwater routes. Nevertheless, fewer engines would potentially mitigate some of these obstacles by reducing maintenance costs and complexity.
Range and Fuel Efficiency
The increased bypass ratio of the PD-35 engines is one of their most significant advantages, as it enhances fuel efficiency. This could result in a reduction in fuel consumption or an increase in range for both the IL-96-300 and IL-96-400. This efficiency gain may render the two PD-35 engines an appealing alternative for airlines that prioritize long-haul operations, even though the thrust-to-weight ratio is slightly below optimal.
In conclusion,
In conclusion, the T/W ratio is raised to 0.28 and 0.264, respectively, by the installation of two PD-35 engines on the IL-96-300 and IL-96-400, resulting in a modest increase in thrust. Although this configuration is not overpowered, it may still be considered slightly underpowered for optimal takeoff and climb performance, particularly in demanding conditions. Nevertheless, this configuration may be considered right-powered for specific mission profiles due to the PD-35 engines’ enhanced fuel efficiency and reduced operating costs. The decision would ultimately be contingent upon the airline’s specific operational requirements, which necessitate the cautious consideration of trade-offs between performance, efficiency, and certification challenges.
For the IL-96-400 to be right-powered with two engines, each engine would need to produce 39,750 kgf (390 kN) of thrust to achieve a T/W ratio of 0.3.
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