The F-16 Fighting Falcon, better known as the Viper, has been a multirole stalwart of the U.S. Air Force since debuting in the 1970s. With one engine, a distinctive bubble canopy, and notably smaller dimensions than contemporaries like the F-14 or F-15, the F-16 is regarded as a jet that you “put on” rather than “get into.”  

But the F-16 we know and recognize today was once tinkered with. Indeed a variation was proposed, in the 1980s, the standard F-16 design; known as the F-16XL, the prototype featured a delta-wing, and was offered as a replacement for the F-111 Aardvark. 

What Could Have Been  

The F-16XL was one of the two entries in the Air Force’s 1981 Enhanced Tactical  Fighter (ETF) competition, which sought to replace the F-111 Aardvark. The F-111 was a two-seat, swept-wing multirole jet best known for its interdiction abilities. Both of the aircraft entered into the ETF contest to replace the F-111 were variants of already existing Air Force aircraft: the F-16 and the F-15.  

In the case of the F-16, the variant offered was, of course, the F-16XL. As you may have already figured, the F-16XL lost the bid was never mass-produced, and was never introduced into the Air Force fleet. Instead, the F-15 variant, the F-15E Strike Eagle, won the bid and is still serving on active duty today.  

Only two F-16XL prototypes were ever produced, for participation in the ETF contest. And when the XL lost the bid, there was no need for more; the two prototypes were accordingly shelved – until 1988. Then, the two modified F-16s were gifted to NASA for research purposes. With NASA, the F-16XLs enjoyed long service lives, flying for over two decades, until 2009.  

Experimenting with a Proven Design 

The F-16XL was originally a General Dynamics experiment designated: the Supersonic Cruise and Maneuver Prototype (SCAMP). The SCAMP program tinkered with a slew of wing designs. Even a forward-swept wing was considered. 

In the end, however, the delta wing was selected for the sake of its excellent lift-to-drag ratio at high speed. The SCAMP program was heavily invested in, throughout the 1970s, and finally completed in time for the ETF bid.  

However, the F-16XL required significant modifications from the base F-16. The F-15E, meanwhile, required little adjustment from the base F-15. The F-15E had other advantages over the F-16XL, too. Namely, the F-15E had two engines, whereas the F-16XL had just one, meaning the F-15E enjoyed a higher maximum takeoff weight, which meant the airframe could carry more weapons and more fuel. 

And when you’re fielding a replacement for the renowned interdictor, the F-111, weapons and fuel are essential. And for an airframe that would likely be used deep behind enemy lines, the engine redundancy of the F-15E was a comforting safety bonus.   

Harrison Kass is a defense and national security writer with over 1,000 total pieces on issues involving global affairs. An attorney, pilot, guitarist, and minor pro hockey player, Harrison joined the US Air Force as a Pilot Trainee but was medically discharged. Harrison holds a BA from Lake Forest College, a JD from the University of Oregon, and an MA from New York University. Harrison listens to Dokken.     

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