Why Are Modern Fighter Jets Slower Than 1960s?

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Have you ever wondered why an F-4 Phantom is somehow faster than the F-35? Fighter jets haven’t gotten faster in the past 50 years, and here’s why.

When Intuition Meets Reality

The Vietnam War went on for twenty years. During the conflict, both the US Air Force and Navy used various models of the F-4 Phantom to go up against Vietnam’s MiG-21s – both planes had a max speed of Mach 2.2.

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Military analysts reviewed more than a hundred thousand of flight data from sorties flown by the American fighters over North Vietnam. It was found that none of these F-4s flew at Mach 1.8 and above during combat.

Regardless, a few minutes were flown at Mach 1.4 while there were several hours of flight time at Mach 1.2.

You Can’t Run, But You Can Hide

During the two World Wars, one of the advantages of high speeds was escaping enemy fire. However, the introduction of air-to-air and surface-to-air missiles completely changed the strategy on the battlefield. 

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Now, air-to-air missiles like the AIM-120 have a top speed of Mach 4, while some variations of Russia’s S-300 missile can reach a top speed of Mach 7. 

More Speed Means Arriving Quicker, Right?

Supersonic speed is rarely advantageous, even when flying into a combat zone. That’s because flying at such speeds consumes a lot of fuel. 

A study done by Northrop Grumman tackled a multitude of intercept cases and found that speeds above Mach 1.1 severely reduced combat range. In fact, increasing an F-4 Phantom’s runout speed from subsonic to Mach 1.5 reduced its combat range by about 70%.

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Aside from this, pilots typically flew their planes at a speed that allowed for a maximum turn rate. The higher the turn rate, the more quickly the aircraft can change directions.

However, maximizing the turn rate also means driving down the speed to about Mach 0.7. 

Prioritizing Stealth

The emphasis on stealth further reduced the importance of speed.

An aircraft flying at supersonic speeds will suffer an increased heat signature, making them an easy target for SAMs. In addition, the use of afterburners and the aircraft’s body heating up due to increased air resistance at supersonic speeds make it easier for infrared sensors to detect the aircraft.

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That’s why the F-22’s maximum sustained speed was reduced from Mach 1.8 to 1.6 – to reduce the heat load on the leading edge of the composite wings.

In Conclusion

An F-104 Thunderchief had a speed of over Mach 2, but suffered from a smaller combat range, and could carry less armament.

In comparison, the F-35’s top speed is “only” Mach 1.6, but it can carry more missiles, is stealthier, and has a bigger combat range.

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Simply put, the new generation of fighters is designed for marathons, not sprints.

It’s safe to say that this change in aerial warfare is planned and accounted for. There’s no doubt that America can make a faster aircraft, but its viability might be compromised.