At Mach 1.9, the F-16 rapidly reduces speed and quivers – US pilot

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Officer Hazard Lee, a pilot in the US Air Force, shares his captivating account from the cockpit of the Lockheed F-16 fighter jet during a trial run in Korea. He vividly recalls one specific F-16 that had recently undergone repairs, including an engine overhaul and was prepared for its test flight. The aircraft was not equipped with armaments for this trial, hence carrying a minimal fuel load, just sufficient for an hour’s flight. 

Photo credit: Twitter

Unable to hide a fond chuckle, the officer highlights the discrepancy between the F-16’s promotional material and its actual performance capabilities. Despite the brochures boasting a velocity of Mach 2.05, reaching these speeds can often be challenging, though certainly not impossible. With the modest fuel reserve available, Officer Lee strategically maneuvered the F-16, gently pushing its speed to Mach 1, Mach 1.3, Mach 1.4, and so on, as he ascended toward the necessary altitude. 

In a bid to hit the optimum speed while conserving fuel, Lee remembers flipping the F-16 at Mach 1.4 and commencing a descent. This maneuver accelerated the aircraft to Mach 1.6. However, this increased speed triggered noticeable vibrations within the cockpit. Lee clarifies that not every F-16 would react this way at such speeds. But the craft he was piloting had been in service for years and had understandably experienced structural deterioration over time.

Reach Mach 1.9

Lee faced a challenge: reduce speed until the shaking of the aircraft stopped, or increase it until the vibrations smoothed out. He decided to ramp up the throttle to accelerate more rapidly. Consequently, he noticed a gradual increase in speed – Mach 1.7, then 1.8, and finally 1.9. Around these speeds, Lee reports an additional concern – excessive heat in the cabin. 

“The cockpit began to heat up to such an extent that I lifted my hand from the control and held it a foot away from the canopy. The radiant heat, even through my glove, was palpable; it felt like shoving your hand inside an oven,” Lee reported. 

Photo credit: USAF

Lee draws an intriguing conclusion from his ordeal. “Despite the powerful thrust the engine was still generating, the drag from Mach 1.9 caused the jet to slow down somewhat abruptly, thrusting me forward until the straps on my harness locked. It took the aircraft over 50 miles to lower its speed below Mach,” recounts the US Air Force pilot.

Why does it rapidly reduce speed?

The F-16, like any other aircraft, is subject to the laws of physics, one of which is the concept of drag. Drag is the aerodynamic force that opposes an aircraft’s motion through the air. When the F-16 reaches speeds close to Mach 1.9, it experiences a significant increase in drag, specifically wave drag. This is a form of aerodynamic drag that aircraft experience at transonic and supersonic speeds. 

Wave drag occurs due to the formation of shock waves around the aircraft. These shock waves form when the aircraft’s speed approaches the speed of sound. This causes air molecules to be unable to move out of the way quickly enough, thus forming a high-pressure shock wave. This shock wave, in turn, creates a strong drag force that opposes the forward motion of the aircraft. 

Photo credit: USAF

The F-16’s engines, despite producing a significant amount of thrust, cannot overcome this increased drag force at speeds near Mach 1.9. The thrust from the engine must be greater than the drag for the aircraft to maintain or increase its speed. However, at these high speeds, the drag becomes so great that the engine’s thrust cannot compensate, causing the aircraft to decelerate.

Design is also a reason

Furthermore, the F-16’s design, while highly aerodynamic, is not optimized for sustained flight at speeds near Mach 1.9. The aircraft’s airframe, though designed to minimize drag, still produces a significant amount of it at these high speeds. This inability of the airframe to efficiently cut through the air at these speeds contributes to the overall drag experienced by the aircraft. 

Photo by Ronnie Macdonald

Lastly, the F-16’s engines are not designed to sustain the amount of thrust required to overcome the drag at these high speeds for extended periods. These engines can produce considerable thrust, but doing so for prolonged periods can lead to excessive wear and potential damage. Therefore, the engines typically don’t run at these high thrust levels for extended periods, further contributing to the aircraft’s deceleration at speeds near Mach 1.9.

Speed is not an advantage

“In today’s era, speed doesn’t hold the paramount significance it once did, especially in the aviation industry,” Lee explains. During the mid-20th century, speed was indeed an influential element. However, the dynamics have dramatically pivoted since then. Take the F-35 that Lee currently operates, for instance. He believes that high speed is not a prerequisite for this plane. The reason being, the F-35 brings together an intriguing combination of stealth, sensors, and networking, thereby eliminating the necessity for speed, he adds.

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