Boeing XF8B Carrier-Based Long-Range Fighter Prototype
Boeing tried - unsuccessfully - to fit the long-range XF8B-1 prototype into long-term U.S. Navy plans.
Authored By Dan Alex; Content ©www.MilitaryFactory.com
The Boeing XF8B "do-everything" carrier-based fighter-bomber prototype of World War 2 (1939-1945) emerged at a time in Boeing's history when it was already heavily focused on producing and evolving their bomber line for the United States Army Air Forces (USAAF). The aircraft began as a self-directed company proposal which eventually caught the eye of the United States Navy (USN) - itself already committed to its healthy stable of Vought F4U "Corsair" and Grumman F6F"Hellcat" carrier-based fighters. Interested in the Boeing navy fighter-bomber concept - a design intended to fulfill roles beyond that of a fighter and include dive bomber, torpedo bomber, escort, and interceptor - the USN ultimately fleshed out its list of specifications for Boeing to begin work on. Such was the project scope for the do-everything fighter-bomber that it earned the nickname of the "Five-in-One" Fighter. It was known in-house as "Model 400".
The USN specifications called for an aircraft that could serve on its carrier decks so dimensions, storage and structure were a key consideration. Maximum speed was in the vicinity of 342 miles per hour with a service ceiling of 30,000 feet. The subsequent USN contract then commissioned for three flyable prototypes and one static testbed under the "XF8B" designation beginning with prototype "XF8B-1". The contract was formally awarded to Boeing on April 10th, 1943.
Design work began in short order with a mockup available for review in October of 1943. XF8B-1 was then completed in 1944 and its first flight recorded on November 27th of that year. Boeing engineers developed a dimensionally large airframe with a smoothly-contoured fuselage from nose to tail. Wings were set low on the fuselage sides and ahead of midships. The spacious cockpit was centrally-located with the pilot under a useful teardrop canopy with good vision to the sides of the aircraft, above and behind. The engine was of a slender form but its installation necessitated a rather long nose assembly making ground running difficult. The fuselage tapered nicely into the empennage to which a large, rounded vertical tail fin was fitted (ala the Boeing line of famous World War 2 bombers). Horizontal tailplanes were affixed to the fin's sides in the usual way. The engine, held in its forward-set compartment, drove 2 x three-bladed propeller assemblies in a contra-rotating arrangement. This supplied the necessary thrust from the ultra-powerful engine installation while negating the effects of torque encountered when using just one three-bladed propeller (seen on many aircraft of the period). The undercarriage was of the "tail-dragger" arrangement which used two main landing hear legs. These retracted into the wings after pivoting at 90-dgrees. The tail wheel was also retractable to keep the aircraft as streamlined as possible when in flight.
Engineers selected the Pratt & Whitney XR-4360-10 28-cylinder, four-row radial piston engine for the airframe - this being the most powerful propeller-driving engine fitted to any fighter design at that time. The powerplant outputted at 3,000 horsepower on full throttle and was the same as used in the other experimental mount - the Republic XP-72 "Super Thunderbolt" detailed elsewhere on this site. The two-stage supercharged engine, coupled with the outstanding profile of the aircraft, allowed for a maximum speed of 432 miles per hour to be attained with a cruise speed near 190 miles per hour. Range measured out to 2,800 miles which would prove handy over the large reaches of sea in the Pacific Theater when battling the forces of the Empire of Japan. Its service ceiling was listed at 37,500 feet - surpassing the USN's initial specifications - while rate-of-climb proved an impressive 2,800 feet-per-minute - a key quality for an interceptor and carrier-launched aircraft. As designed, the engine installation was intended for easy replacement - improving both maintenance turnaround times and perhaps any future powerplant upgrades sought.
Proposed armament was 6 x 0.50 caliber heavy machine guns or 6 x 20mm cannons - in either case the armament was to be mounted in the wing leading edges just outside of the spinning propeller blades diameter. However, this armament was never fitted to any of the test articles mentioned. To undertake its various intended roles, the XF8B was fitted with an internal bomb bay as well as underwing hardpoints which allowed for a maximum ordnance haul of 6,400lbs. In place of bombs, the aircraft was slated to carry 2 x 2,000lb torpedoes or an equal amount in weight of fuel - an internal load as well as external jettisonable tanks for excellent range.
Dimensions included a length of 43 feet, 3 inches, a wingspan of 54 feet and a height of16 feet, 3 inches. As completed, the aircraft became the largest (and therefore heaviest) single-seat, single-engine prop-powered fighter ever flown up to that time. The dimensions made for an aircraft with an empty weight of 6,135lbs and a Maximum Take-Off Weight (MTOW) of 9,840lbs. This made for one particularly large and heavy carrier-based fighter design. To help offset its size aboard the space-strapped American carriers, the wing elements were engineered to fold inwards, hinged just outboard of the main landing gear legs. This reduced the wingspan considerably and was common practice for navy aircraft - a feature still present today.
The initial flight of the prototype proved the design a general success though some minor elements had to be revised. The second prototype airframe was completed in January of 1945 but this had to wait for an available powerplant to be delivered and installed and thusly did not fly until after the war. Service trials then began for Prototype One which ran from mid-March 1945 to mid-April and the USN liked what Boeing had to offer on the whole despite it was a more expensive and heavier aircraft than first envisioned.
It was about this time that the USN was close to agreeing on a production course with Boeing though Boeing's commitment still lay with U.S. Army (and later U.S. Air Force) bombers and the USN had begun serious experimentation with jet-powered aircraft on carrier decks before the war's end. The conclusion of the war in Europe came in May of 1945 and the Pacific War ended that September, bringing about an end for the "do-everything" carrier-based fighter. The piston-powered fighter, as a whole, had more or less reached its apex in performance by the end of the war, capping its reign in the 3,000-4,000 horsepower range. Development of jet engines would soon enough offer the needed performance gains for USN fighter and bomber service to negate the need for a new expensive propeller-based airplane. As such, USN interest in the XF8B fell to the wayside as it looked to its future post-World War 2 needs in jets. The XF8B marked its last serious piston-powered fighter design under review.
Boeing also realized the end of the line for its XF8B proposal and began to reduce work on the product. The original order for three flyable aircraft was eventually completed and these continued in testing with the USAAF and USN into 1946 and 1947 respectively. Boeing's part in the XF8B ended soon after with all prototypes eventually scrapped.