The process of producing new aircraft designs is long. It usually starts with written proposals and approvals before they end up reaching production. The prototype phase allows people to test out and see if the idea that sounds good on paper is actually great in practice. This phase is also designed so that poor designs can be weeded out and flaws can be highlighted and polished.

On the other hand, there are designs that are rejected in the prototype stage not because they are not good enough to be mass-produced. Sometimes it could be due to budget restrictions, or a much better design was preferred over it. Most of the designs that were rejected on the prototype stage are gone for good. However, there were instances when a design was canceled but was later on approved and produced. Here are some of those instances:

B-17 Flying Fortress

First on the list is the legendary Flying Fortress which became one of the symbols of World War II and dropped more than a million tons of ordnance on the enemy forces, and was also the third most-produced bomber of all time.

During its development phase, B-17’s prototype was called the Model 299. It was doing great during tests compared to its competitors, which were the designs from Douglas and Martin with fewer capabilities. Things took a turn when B-17 crashed during its second test flight after some issues with its pre-flight checks. The crash disqualified Model 299, and it was Douglas that got the contract.

Fortunately, the United States Army Air Corps has been impressed by the Flying Fortess’ prototype performance and saw its potential. On January 17, 1936, thanks to some legal loophole, the Air Corps managed to order 13 of the aircraft for service testing.

Rockwell B-1 Lancer

The B-1 Lancer is one of the three strategic bombers of the United States today, along with the B-52 Stratofortress and B-2 Spirit. The supersonic variable-sweeping heavy bomber was first envisioned in the 1960s as a replacement for both B-58 Hustler and B-52 Stratofortress.

A prototype called B-1A was built in 1974. However, due to the high cost of the aircraft, the introduction of the AGM-86 cruise missile that could fly the same speed and distance, and early work on the stealth bomber, it was decided that the B-1 was not much needed, and so President Jimmy Carter canceled it in 1977.

In 1981, the project was revived as an interim to cover the B-2 Spirit’s development. This led to the aircraft’s modification and was designated the B-1B with a lower top speed of Mach 1.25 at high altitude compared to the B-1A, but with an improved low-altitude speed of Mach .96.

Northrop YF-17 Cobra

The Northrop YF-17 Cobra was a response to the United States Air Force’s Lightweight Fighter (LWF) technology evaluation program that aimed to produce a smaller fighter aircraft compared to the large F-15 Eagle. The LWF program was started because many people in the fighter community believed that the F-15 Eagle and other similar aircraft were too large and expensive for combat roles. As a result, the YF-17 was designed as an accumulation of the different Northrop designs from N-102 Fang in 1956 until the F-5 family.

It was the F-16 Fighting Falcon that won the LWF competition. As for the Northrop, it was instead partnered with McDonnell Douglas for the new Naval Fighter Attack Experimental (VFAX) program. There, the YF-17 was scaled up and adapted, the result being the F/A-18 Hornet used by the US Navy and US Marine Corps in place of the A-7 Corsair II and F-4 Phantom II.