A new breed of Crusader
- 5 -
the Super Crusader
In 1956, with the F8U program well underway, chief designer Russell Clark and his team began looking for ways to improve the basic Crusader design. There was at the time no official interest by the US Navy for a Crusader follow-up but it was assumed this would soon change. Initially most thoughts went into armament. The first operational Crusader variant (the F8U-1 or later F-8A) had a mixed armament of four 20 mm canons, two AIM-9 Sidewinder guided missiles and a tray for unguided rockets under the belly. This was sort of a compromise between the Navy's wish for a interceptor fighter and that of the Marine Corps for a ground support jet. Eventually the rocket tray was not deemed a success and with the second variant (the F8U-1E / F-8B) the rocket armament was deleted to improve the Crusader's performance.
Rockets and missiles (in terms of armament "rockets" are considered to be unguided and "missiles" guided) became a real hype during the fifties, promising a revolution in aircraft armament and making old-fashioned cannons obsolete. Of course at first there were hefty discussions about this subject but in the late 1950's the switch to all-missiles armament for new fighters was inevitable. Looking back many years later we know this was a mistake, as events during the Vietnam War would prove. American pilots found time after time that cannons weren't as obsolete as thought, and missed them often dearly. The Air Force even finally managed to bolt an extremely potent six-barrel "Gatling" type gun under the nose of their F-4 Phantoms (and thus the F-4E variant was born). This was a great success, so much that new fighter designs ever since have been standard equipped with cannon armament again. There is however a remarkable side to this matter, as there is to this day a myth that the F-8 was so successful in Vietnam fighting MiG's because of its cannons (earning it the often quoted nickname "Last of the Gunfighters"). This myth is simply false, as only one North Vietnamese MiG fell victim to the Crusader's cannons, and then even partially. For ground attack the cannons were a real asset, and it is sometimes said that the mere availability of cannons was a comfortable thought for Crusader pilots engaging in aerial combat, but the truth simply is that the Crusader actually contradicts one of the lessons learned from the Vietnam War: cannon armament is vital for aerial combat.
Back to the late fifties, back to Vought were attention was shifting to a much-improved Crusader. Vought had heard the voices calling for "no more old-fashioned guns" and switched to an all-missile armament, with newer and much improved missile designs in the pipeline. It was to become a pure interceptor. Simple modifications to the basic Crusader design were soon rejected as not practical enough, and it was decided to start work on a whole new design, loosely based on the existing Crusader design. Every aspect of the new design was to be focused on high speed, high altitude, and most importantly high acceleration. The design they eventually came up with had only fleeing resemblance with the "old" Crusader, and the similarities stopped there. The new design was designated F8U-3. F9U-1 would have been much more appropriate for a new design in contrast to "merely" a new version of an existing design, but Vought had a desire to elaborate on the F8U's success and managed to get the F9U designation rejected. And thus Vought considered it to be the third-generation Crusader and their marketing department soon christened it the "Crusader III".
At the same time at McDonnell work was progressing on a new long range ground attack aircraft, the AH-1. Developed as a follow-on design of the F3H Demon it was initially known to those involved as the F3H-G. At first all this was of no direct interest to Vought but this would soon change. Work on the AH-1 was well under way (there was even a mock-up awaiting approval) when the Navy decided their interest had switched from a single-seat ground attack aircraft to a two-crew, all missile armed fighter aircraft with ground attack as a secondary task. McDonnell dropped the AH-1 for a much-altered design reflecting the new needs, and the legendary F4H (later F-4) Phantom II was born. Suddenly Vought was into trouble again...
As both the F8U-3 and F4H-1 began taking shape it soon became clear to everyone that these two designs would be each other's rivals, because it was not likely the Navy would order both aircraft into production. And yet both designs were very different from each other and could not be considered filling in the same need. The Phantom II was a heavy twin-engined multi-role aircraft with (as it would turn out) vast growth potential. In contrast the Crusader III was a single-seat, single engine, relatively light aircraft specifically designed for interception and aerial combat. This meant its growth potential was much less than that of the Phantom II and had the Crusader III been ordered into production it is not very likely that it would have enjoyed the same broad success as the Phantom II.
Differences of opinion within the Navy and Marine Corps regarding armament was one issue, one- versus two-man crews and single- versus twin-engined combat aircraft were two others. Advocates of two-man crews argumented:
- By spreading responsibilities from a single pilot to a pilot and a navigator / WSO Weapons System Officer) the workload would be much lower and so efficiency would increase.
- Two pair of eyes had a much greater chance of spotting an enemy aircraft visually than one pair. With the ever improving capabilities of radar and visions of long-distance aerial combat with missiles this argument was not always considered as very meaningful, as the old-fashioned "dogfight" aerial engagements would be history soon anyway. We all know now that the Vietnam War proved otherwise.
The opponents were not convinced and responded:
- With new developments in electronics a second crewmember would soon be obsolete. Automation would lower the pilot's workload anyway and thus improve efficiency. Interception would be fully automated with the pilot "only there for the ride".
- A single seat aircraft is smaller and lighter, and thus more maneuverable and less easy to spot visually. In other words it would have a higher chance of surviving true aerial combat.
Vought, with their single seat F8U-3 design, saw dark clouds appear at the horizon and quickly came up with a mock-up of the proposed F8U-3 to prove, with some success, to the Navy the advantages of a single-seat interceptor. A two-seat F8U-3 was also studied, but after some consideration it was decided that a single-seat design would best suit the requirement.
On the engine front there was much debate too, those who believed two engines were best said:
- Two engines are a great reliability factor. If one engine fails for whatever reason (apart from running out of fuel of course) the aircraft would not be immediately engine-less and would have a good chance of either restarting the failed engine or returning home on one engine.
- Previous experience had shown that a two-engined design with a certain total engine performance would weigh about 10% less than a single-engined design with the same engine performance.
Others believed these arguments were based on false presumptions:
- Statistically there was no proof that two-engined aircraft were any safer than single-engined aircraft, mainly because of higher fuel consumption and more complex restart procedures.
- But the main argument was costs. It was considered to be impossible to build an equally performing two-engined aircraft for the same costs as a single-engined aircraft. Two engines would require more maintenance and more spare parts, plus have a need for more fuel.
Later on several of these arguments would be settled, with surprising results and confirming that Vought had made the right choices, at least performance-wise. Because their F4H-1 had thanks to its two engines a lower power-to-weight ratio than the F8U-3, McDonnell believed their design would have the better performance. Unfortunately for them, once both designs were in the air and thoroughly tested, it turned out that the Crusader III outperformed the 10% more expensive Phantom II in every category!
In July 1956 the Navy approved Vought's design. A contract worth $35 million followed in May 1957, covering the development, construction and testing of two prototypes. At the same time McDonnell received a similar contract. Less than two years later, some 22 months after having received the contract, Vought rolled out the first F8U-3 (BuAer 146340).
The F8U-3 was for its time a very advanced design with breathtaking performance, capable of flying in every kind of weather and with a flight endurance of three hours without aerial refueling. Externally the large "Ferri" type air intake (which resembled a sugar scoop, and comparable with those used on the F-105 Thunderchief, albeit much larger) and the two large retractable fins under the rear fuselage for added high-speed stability were the most remarkable features. The fins' retracting mechanism was linked to the landing gear, as long as the landing gear was extended the fins were in a horizontal position. Unfortunately this mechanism didn't always work flawless, on at least two occasions the fins needed replacement after one of the prototypes had landed with the fins still extended. A feature common with the original Crusader was the variable incidence wing. Not only did this feature improve pilot's visibility during landing but it only accomplished that the landing gear, and especially the nose landing gear, could be kept at a minimum length and thus be lighter. To keep the landing speed as slow as possible Boundary Layer Control (BLC) was incorporated into the wing design. High-pressure air, generated by the engine's compressor, was pumped through tiny slots over the topside of the wing, vastly increasing lift generated by the wing during slow speed.
Projected armament consisted of three Raytheon Sparrow III missiles, semi-recessed in the fuselage. Later four Philco Sidewinder missiles were added, mounted on racks comparable to original Crusader. As far as it's known however the prototypes have never flown with these racks, only with three inert "dummy" Sparrows. An advanced guided missile like the Sparrow is useless without good avionics, and the F8U-3 had the most advanced electronic systems of its day. With the Westinghouse AN/APQ-74 as its core the weapons system was comparable with those later used in the F-14 Tomcat and F-15 Eagle, a good ten to fifteen years later.
At least for pilots a vital part of a high performance aircraft is the ejection seat, the primary lifesaver for a pilot in despair. The seat in the prototypes was Vought's own design, developed in conjunction with Stanley Aviation. A separate F8U-3 nose section was actually build to test this seat before committing it to real flight. However this seat lacked zero-zero capability (safely usable at zero altitude with zero forward speed) and it was decided that production F8U-3's would be equipped with Martin-Baker ejection seats.
A major contribution to the F8U-3's stunning performance was its choice of engine. The Pratt & Whitney J75 was selected, developed from the same J57 that powered the original Crusader. Pratt & Whitney had began work on the J75 anticipating a soon to emerge need for an engine producing 20,000 lb of thrust (approximatly 9000 kg) and more, and they were right. Two other types that would receive the J75 were the F-105 Thunderchief and F-106 Delta Dart. Basically the J75 is a twin-spool 16-stage turbojet engine with afterburner. The first F8U-3 received the J75-P-6 model of the engine, producing 29,000 lb (13,150 kg) of thrust. This model was highly modified from the standard model to give both Vought and Pratt & Whitney a good idea of the aircraft and engine combination's potential in an early stage of flight-testing. The J75-P-5 model with a maximum thrust of 23,500 lb (11,110 kg) as used in the other two F8U-3 that actually flew was less powerful but had the advantage it could be operated longer at maximum performance, thanks to a water injection system. Production Crusader III's were to be equipped with the J75-P-8 model producing 28,000 lb (12,700 kg) of thrust. And that's almost two-thirds the thrust generated by all three engines of a Boeing 727-200 airliner!
During development and testing several changes to the design were either implemented or proposed which are worth to mention. As mentioned earlier it was decided to add four Sidewinder missiles to the armament of three Sparrow missiles because the latter were not suited for close-in aerial combat. One prototype actually received the Sidewinder missile's launch rails late in the testing phase, but it is unclear if the aircraft was ever flown in this configuration. Thought was given to an improved and even larger radar which would most likely have altered the Crusader III's nose profile. Also an infrared seeker to augment the radar was planned. A modification that actually was implemented on the first prototype was a broader chord fin, because early in the test-flying phase some instability was encountered. The second prototype had the broad fin fitted from the outset, as had all subsequent aircraft on the production line. Later an air inlet was added to the bottom of the vertical stabilizer for extra afterburner cooling.
An interesting aspect was the proposed addition of a rocket engine. The design team decided, after suggestions from the Navy, to add a small rocket engine above the jet engine to even more improve the Crusader III's performance. Originally the Reaction Motors XLR-40 with a thrust ranging from 3,500 lb (1,590 kg) to 8,000 lb (3,630 kg) and a burn time of 3.15 to 7 minutes was planned. Vought even started modifying two F8U-1's (BuAer 141346 and 141353) under project V-410, but development of the XLR-40 was cancelled at the end of 1957 after a fuel pump exploded, killing two Vought employees. This did not end V-410 however, the use of the less powerful Rocketdyne XLR-46 was also studied. The XLR-46 had a thrust ranging from 2,000 lb (907 kg) to 6,000 lb (2,720 kg) and a burn time of 5 to 10 minutes. Project V-410 was finally cancelled in May 1958 without ever having flown. Vought also studies alternative jet engines for the Crusader III, and one proposal even received a project number. V-419 was to be powered by the Pratt & Whitney J58, yes, the same engine as used in Lockheed's A-12, YF-12 and SR-71 Blackbirds!
On January 2, 1958, five months before the F8U-1's first flight, the US Navy signed a contract worth 100 million Dollar covering the production of sixteen F8U-3's (BuAer 147085 to 147100). Vought was instructed to start production immediately. Early May of that year the first F8U-3 was transferred from the factory in Grand Prarie (Dallas, Texas) to Edwards Air Force Base in California. To complicate the transport a way had to be found to get the big fighter to Edwards. The Air Force Douglas C-124 Globemaster II transporter was large enough for the fuselage to fit inside, but not the wings. An innovative way was quickly found: the complete Crusader wing was simply attached externally in one piece to the Globemaster's belly. Despite this unorthodox transport the prototype F8U-3 arrived safely at Edwards, and was quickly assembled again and thoroughly tested. After the engine was tested too taxi trials started on May 24. That day only low speed trials were held, but on May 30 the throttle was really pushed forward. While thundering down the runway at 122 kt (140 mph; 226 km/h) the aircraft even unexpectedly became airborne and flew the length of a football field 5 feet above the runway. The official first flight occurred on June 2, with test pilot John Konrad at the controls. The flight lasted 48 minutes with a maximum attained speed of 350 kt (401 mph; 648 km/h) and an altitude reached of 20,000 feet. Due to a problem with the throttle leaver, causing significant vibrations, the flight had to be cut short, but not before the left retractable fin had actually fallen of!
The second flight took place two days later, and the third the day after that. On the sixth flight the aircraft went supersonic for the first time. Konrad remarked that for a brand new aircraft the Crusader III behaved remarkably well. There were no serious design flaws and the performance was exactly as expected. This was not only good news for the Crusader III's design team but also meant that the flight test program could be absolved in a rapid tempo. Most remarkable outcome of the flight test program was the F8U-3's performance. All pilots who had the privilege to fly this aircraft are to this day certain that the Crusader III was the most impressive aircraft they ever flew. On August 14, on its 38th flight, the prototype reached Mach 2 (twice the speed of sound) for the first time. Highest speed attained was Mach 2,39, but remarkably even at this speed the aircraft continued to accelerate, going Mach 0.1 faster every 17 seconds! Only a seemingly small detail kept the F8U-3 from going faster: the cockpit glazing fitted, and especially the frontal part, was not designed for speeds faster than Mach 2.2. Going faster than that and the windscreen would soon turn opaque and melt, all due to the friction and subsequent heat generated by the onrushing air. Of course developing new cockpit glazing that would eliminate this restriction was a high priority item, but was never implemented. Otherwise the true potential of the Crusader III would have been revealed. Experience gained from the flight test program predicted a (rather pessimistic) maximum speed of Mach 2.6 at an altitude of 35,000 ft (10,700 m), but near Mach 2.9 was more likely. With some modifications Mach 3 would have been within easy reach, but even without the Crusader III would have become the fastest fighter aircraft in the world. Not only the maximum speed was remarkable, the acceleration too was simply breathtaking, even without the proposed rocket engine. At an altitude of 35,000 ft (10,700 m) at Mach 0.98 the first prototype needed only 3 minutes and 54 seconds to accelerate to Mach 2.2. Only a few fighters of today can match that! The second prototype with its slightly lower powered engine however needed no less than 9 minutes, and it was predicted that the production aircraft's figure would lie somewhat in the middle. Maximum altitude was also not bad, the F8U-3 could sustain 60,000 to 65,000 ft (almost 20,000 m). With a ballistic "zoom climb" trajectory the aircraft could top 90,000 ft (more than 27 kilometers).
The second prototype (BuAer 146341) absolved its first flight on September 27, 1958. Again flown by John Konrad but this time not from Edwards but from Grand Prairie. The first production F8U-3 (BuAer 147085) followed soon. Had the first two prototypes a metal nosecone with a large pitot tube, aircraft 147085 had a production nose with a working radar set and avionics. After the two prototypes had explored the aerodynamical flight test envelope this aircraft was to test the more operational aspects of the design.
The F8U-3 story continues on the next page
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