The Vought F8U-3 Crusader III; So Good it Almost Beat the F-4 Phantom!

December 25, 2022

The McDonnell Douglas F-4 Phantom and the Vought F-8 Crusader are an iconic duo. Both built initially for the US Navy and intended to complement each other, the F-8 served as an agile day fighter while the F-4 acted as a long-range interceptor for knocking down Soviet nuclear bombers attacking the fleet.

 

Both aircraft carved themselves a place in aviation history in the skies over Vietnam and would go on to see decades of service. But of the two, the Phantom was definitely the more successful.

While the F-8 would establish a formidable reputation as a dogfighter, it ultimately only saw service with the US Navy, France and the Philippines. The Phantom, however, served with just about everyone the United States would allow to purchase it. Serving in fighter, bomber, reconnaissance and defence suppression roles, the F-4 was the plane that could do the job and quite often did, as its extensive combat record can attest.

But when the F-4 began development in 1955, it was far from guaranteed that it would be the success it would become. In fact, given the amount of brand-new technology the new aircraft was going to use, particularly the new J79 turbojet, the US Navy was worried about putting all its faith in the new aircraft. After all, poorly performing jet engines had been something of a blight on a number of Navy fighters, curtailing several type’s careers or even seeing them cancelled completely.

So, it was considered wise to have a backup. And Vought had a solution that almost perfectly fit the ticket. They were on the point of soon delivering their new F-8 Crusader day-fighter to the US Navy and thought they could match the requirement for the new missile interceptor with a new version of the F-8.

Originally this was given the company designation of V-401 but was soon more widely known as the Vought F8U-3 Crusader III.

 

It received this designation because the Crusader I-and-II were versions of the F8 that were on the point of entering service with the US Navy. But despite the name, and the selling point that it was based on the existing type, in fact the Crusader III was a very different aircraft and shared few parts with its originator.

Obviously, with a different mission profile as an all-weather interceptor, the -III had a much larger and more sophisticated radar fit than its original forebear, with the initial intention being for that to be the AN/APG-50 as was also planned for use on the F-4. To complement this, the Crusader III could carry three Sparrow III semi-active radar homing missiles, and Vought also made suggestions about combinations of Sparrows and Sidewinders.

 

But the original quad of 20mm cannon were removed from the design as, just as in the requirement that created the Phantom, they were considered redundant for the role of intercepting nuclear bombers attacking the fleet.

The Sparrow armament was also short of what the Navy wanted, which was for four missiles, but Vought justified the lesser armament on the grounds that with the guidance system available only one missile could be launched at a time and with the expected speed of engagement three missiles was sufficient.

Because of the new radar the nose needed to be adjusted to carry it, which further meant a new air intake. This was a Divertless Supersonic Inlet design (DSI for short) with its distinctive forward sweep that gave the -III its gap-mouthed look.

This type of inlet, which is quite common on modern designs today, was specially designed to both be as simple a solution as possible while managing the localized shock wave caused by supersonic travel and enabling the aircraft’s engine to gulp the vast quantities of air it required at high Mach.

And the Crusader III certainly needed it. Because the Navy wanted a backup in the event of failure of the J79 on the Phantom, Vought had to use a different engine.

They chose the Pratt & Whitney J75-P-5A. This was a development of the J57 that powered the original F-8 fighters, but in contrast to that, the J75 produced a dry thrust of 16,500lbf in comparison to the J57’s 11,500lbf. But with after burner, the J57 produced around 18,000lbf, whereas the J75 put out 29,500lbf.

The Crusader III needed this because though it was only slightly larger than the original F-8, it was much heavier, with gross weight being 46% more in the -III due to the extra equipment it carried for its missile interceptor role. Aerodynamically the Crusader III copied the F-8’s unusual variable incidence wing for landing and takeoff, but it also included a couple of retractable ventral fins that deployed in flight to stabilize the aircraft at high Mach.

They were needed because the -III was fast. Really fast.

 

In fact, Vought boasted that the aircraft would make Mach 2.79, and with development they reckoned it could top out closer to Mach 3. That is certainly an exaggeration as the Crusader was not designed to withstand temperatures generated at that speed, but when flight trials started in June 1958 the aircraft soon demonstrated that it was perfectly happy to hit Mach 2 and achieved a top speed of Mach 2.39 without too many problems.

And though intended to have a maximum altitude of 55,000 feet (c.16,800m) it recorded a maximum in testing of 74,000 feet (22,555m).

Acceleration was also apparently exceptional, with one test pilot recalling that he was once asked by ground control while conducting a test flight:

“Sir, just what the hell are you flying?”[i]

Apparently, the GCI couldn’t believe the speed with which the aircraft had got up to Mach 2.

Certainly the -III outclassed other aircraft of the time, and F-104 chase planes that were used on the test flights –a type itself known for its fast speed and acceleration – consistently failed to keep up with the Crusader III.

Vought also proposed fitting a rocket booster motor and wanted to redesign the cockpit canopy and the leading edges for better heat resistance, so maybe Mach 3 wasn’t completely out of the question after all, though it would have taken a considerable amount of extremely specialist engineering.

And unlike its contemporaries like the F-100 or F-104, the Crusader III seems to have made few sacrifices in its all-round performance. Agility was reported to be inferior to the earlier Crusader types at lower speeds – understandable as the F-8 was built with dogfighting in mind – but the -III was reportedly an excellent handling aircraft, especially in high speed ranges.

It also had good range, and the afore mentioned F-104s in the testing program not only couldn’t keep up with the prototypes, they also had to drop out for refueling and be replaced while the Crusader III’s carried on flying their tests.

Of course, it wasn’t all perfect. The J75 engine had a nasty tendency for compressor stalls and these were no small affair. One test pilot described it to being akin to the cockpit being hit by a 40mm Bofors shell, while another said it was like flying through the blast of your own 500lb bomb during an attack run.

These issues were never fully sorted, though when the cause was identified as cutting the after burner while exceeding the speed of sound, it could be somewhat mitigated.

The other issue was in the single crew layout. The Navy had originally required that the fighter, like the F-4, have a two-man crew. This was because the Sparrow missile required dedicated guidance and so the job of both flying the aircraft and guiding the missile in combat was considered too much for a single pilot.

Vought did initially consider building the Crusader III as a two-seater, but recognized that their single engine, even as powerful as the J75 was, would put them at a disadvantage against the Phantom. After all, though the F-4 was heavier than the Crusader III, and its individual J-79’s were less powerful than the J75, the Phantom had two of them, giving it an extra 4,000lbf in afterburner.

By cutting the second crewman the Crusader III could outperform the F-4, but that left the problem of how to guide the missiles. So, Vought developed an interesting dual control system that meant the pilot had two control columns – one to control the aircraft, one to control the radar which guided the missiles.

The company was also able to utilize their experience with the Regulus cruise missile to provide the Crusader III with an auto pilot, the intention being that during an engagement the pilot could switch this on and concentrate on using his radar. The record on this set up is mixed, with some sources saying that it was easy to use, while others say it overloaded the pilot.

 

But there was no denying that the Crusader III had a lot going for it. In fact, the potential of the aircraft meant that consideration was given by the British to buying the Crusader III but fitted with a Conway turbofan engine. And it was so well regarded that in the words of George Spangenberg, head of aircraft design at the United States Navy’s Naval Air Systems Command, it was:

“The best fighter never produced”.

Now, there are quite a few aircraft with that claim, but seeing as Spangerberg played a major role in seeing into service the F-4 Phantom, the F-14 Tomcat, the F-18 Hornet, the P-3 Orion…actually the list goes on and on, but you get the picture.

If even one of the main guys responsible for choosing the US Navy’s aircraft at the time said that about the Crusader III but it still didn’t get selected for production, losing to the McDonnell Douglas F-4 Phantom, then you have to wonder just what happened.

What went wrong and why did the F8U-3 not get into service? After all, the Crusader III was cheaper than the Phantom, had better performance and used 20 percent less deck space – a critical consideration in carrier aircraft. But the F-4 won out.

In a number of sources, you will find the accusation that the Navy had already made up their mind before the competition between the F-4 Phantom and the Crusader III got started.

That does make sense. After all, the F-4 was the aircraft that the Navy had wanted originally, it met their full stated specification of two-crew and four Sparrow missiles and the F8U-3 was intended to be the backup in the event of failure of the Phantom.

But in fact, it seems a little more complicated than that. Because it seems that had things been different, the Navy would have happily adopted both aircraft. However, in 1957 Congress mandated that the US Navy would only have one aircraft for the role of long-range air defence, with spending needs precluding two types in service performing the same role. This led to much hand wringing at the Navy selection board as they tried to decide which aircraft they would select.

But at the end of the day, the limitations of the radar guidance system of the era meant that, by what looks like the slimmest of margins, the F-4 Phantom won the competition in December 1958. As Spangenberg ultimately concluded:

“The greater effectiveness of the two-seat aircraft in adverse conditions is decisive.”

That wasn’t quite the end of the Crusader III, however. In 1959 Vought pitched the aircraft to the Air Force as an alternative to the F-106, and then to Canada with the cancellation of their own Avro Arrow interceptor. But neither were interested and so only five Crusader III’s were built.

A couple of these were then loaned to NASA for conducting experiments in high-speed flight and supersonic boom research. This has led to legends of these aircraft flying off against Phantoms in mock fights and quite frankly, kicking their butts. But this seems to be a bit of a myth, though I do suspect the III’s would’ve been able to handle a Phantom in such a scrap.

Alas, their sojourn with NASA was brief, and once concluded all of the aircraft ultimately, and rather tragically, ended up being scrapped.

The decision to choose the Phantom over the Crusader will probably always cause argument amongst aviation fans. As a pure fighter, I think it is fair to conclude that the Crusader III was the better aircraft. Indeed, it is possible that it would have been a better choice for the sort of combat that the Phantom found itself in over Vietnam, where the ability to use long-range missiles was largely denied and it often came to close quarters fighting, something the Phantom really wasn’t designed for.

But to counter that it is hard to imagine that the Crusader III would have proven as capable as the F-4 as an “all-rounder”, eventually performing a host of roles that it was not originally intended for.

As said, it is a discussion that I suspect will never be resolved fully, and I look forward to reading your opinions in the comments. And if you want to know more about the Crusader III, there are some excellent sources available.

Firstly, Tommy Thomason’s book is basically the definitive text on the entire aircraft development program, covering every facet of it. Secondly, one of the test pilots who flew the -III, Donald Mallick, has an entire chapter on his experience with the aircraft in his memoir, which is available for free download on the NASA website.

Sources/Related:

https://en.wikipedia.org/wiki/Vought_XF8U-3_Crusader_III

https://theaviationgeekclub.com/former-naval-aviator-explains-why-the-xf8u-3-crusader-iii-is-the-best-supersonic-fighter-jet-ever-built-and-why-lost-to-the-f-4-phantom-ii/

https://www.defensemedianetwork.com/stories/f8u-3-crusader-was-really-hot-might-have-been/

http://www.vfp62.com/F8U-3.html

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[i] https://www.nasa.gov/centers/dryden/pdf/88797main_kerosene.pdf, p.85

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