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The High Speed, Low Drag Northrop X-21

The prototype's wing lift was artificially boosted by an extensive pattern of razor-thin slots in the upper wing surface to reduce drag.

The X-21A’s wing incorporated an extensive pattern of razor-thin slots in the upper wing surface to reduce drag. [Credit: NASA photo]
Gemini Sparkle

Key Takeaways:

  • The X-21 program in the 1960s investigated Laminar Flow Control (LFC), a technology designed to reduce aerodynamic drag by up to 80% by using a vacuum system to draw air through millions of tiny slots on the wing surface.
  • Two heavily modified WB-66 aircraft served as X-21 testbeds, demonstrating that the LFC system effectively improved performance, including a significantly shorter takeoff roll.
  • Despite its technical success, the LFC system was deemed impractical for operational aircraft due to its extreme vulnerability to contamination (such as icing, moisture, and insects) in real-world weather conditions, though the derelict X-21s are now targeted for future museum restoration.
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If an aerospace engineer was given their choice of time periods in which to work, it’s likely the 1960s would be a top pick. With swept-wing jets like the Boeing 707 and Douglas DC-8 having made their first flights just a few years prior, the decade ahead would see the introduction of such groundbreaking aircraft as Concorde, the Boeing 747, and the XB-70 Valkyrie. Research and development budgets were robust, competition was fierce, and a young engineer looking for employment must have felt like the proverbial kid in a candy store. 

While the majority of action in the U.S. centered around the production of civil airliners, military jets, and the space race, there were some less flashy but thoroughly intriguing programs taking place in some of the industry’s quieter, less-traveled corridors. One of which was a research program led by Northrop, the U.S. Air Force, and the U.S. Army. The objective? Explore how a wing’s lift could be artificially boosted to reduce drag and increase performance, particularly in large, long-range aircraft designs—some of which would be supersonic.

Jason McDowell

Jason McDowell is a private pilot and Cessna 170 owner based in Madison, Wisconsin. He enjoys researching obscure aviation history and serves as a judge for the National Intercollegiate Flying Association. He can be found on Instagram as @cessnateur.

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