Model military engine behavior

While the concept of a variable cycle engine is not new, recent advances in engine architecture technology suggest that adding a second bypass stream to a traditional turbofan can provide significant benefits.

High-performance military engines use a low-bypass turbofan that achieves a high specific thrust by ejecting air at a very high velocity. This provides the necessary power for short takeoff, combat maneuvering, and supersonic flight, but generally comes at a price of small mission radius (range), high fuel consumption (even in cruise conditions), significant noise generation, and high temperatures.

In contrast, transport aircraft, both commercial and military, typically use high-bypass turbofan engines. These engines produce thrust by accelerating a much larger volume of air to a comparatively lower velocity. This approach reduces noise, engine temperatures, and operating cost for cruise (based on fuel consumption) but results in a very large diameter engine to produce the desired maximum thrust.