Wednesday, April 27, 2011

Experimental Aircrafts of WW2 by Bell Aircraft

The experimental XFM-1 Airacuda by Bell Aircraft

In the same way that the XFM-1 Airacuda was a "different" sort of aircraft, the Bell company itself was "different sort" of aircraft maker. Know more for its unique elements in the P-39 Airacobra piston-engine fighter of World War 2 to the Bell helicopter designs afterwards, the company made a splash onto the aircraft engineering stage with the introduction of their ambitious bomber hunter known as the XFM-1 "Airacuda". The aircraft would mark the company's introduction onto the world stage and - despite the design being a general failure - prove to the world that Bell was revolutionary company putting dreams into practice.

The XFM-1 Airacuda was the Bell Aircraft firms first foray into aircraft design, proving it was a different sort of aircraft maker.

Externally, the XFM-1 featured a cutting-edge approach to design when compared to its contemporaries of the late 1930's. If Bell wanted attention with its first attempt, it definitely got it when unveiling the Airacuda. The aircraft was designed as a type of bomber interceptor or - perhaps more precisely - a bomber destroyer. The system would field a variety of heavy caliber weaponry, be able to carry bombs aloft and accommodate a crew of 5. The design was expected to provide considerable speed, range and firepower to fulfill its bomber-destroying purposes.

Being a generally all-new design altogether - nothing in the skies at the time remotely attempted to accomplish what the Airacuda set out to do - the Airacuda became a victim of its own ambition.

Power was derived from a pair of Allison V-1710-41 liquid-cooled supercharged V12 engines delivering a lofty 1,150 horsepower each. Despite the adequate output for these engines, the system was designed as a "pusher" type meaning that the propellers were mounted to the rear of each nacelle and thus "pushed" the plane through the air instead of pushing it like traditional piston engines operated. Pusher type engines have been attempted a whole World War before but the performance was drastically lower than its puller counterparts. Pusher-type engine systems also had a nasty habit of overheating consistently, shortening their operational life and opening the system up to mechanical failures. Initially, Larry Bell envisioned his aircraft to fly 300 miles per hour at about 20,000 feet with turbosupercharged Allison engines. This was drastically cut when the Air Corps ordered a scaled-down Allison to be used instead with the reason being that the turbosupercharger proved quite volatile and explosive in the YFM-1 when tested. This effectively destroyed any performance the Airacuda could achieve, bring the ceiling down to a paltry 12,000 feet and a top speed barely reaching 270 miles per hour.

All systems were eventually scrapped with only 1 prototype and 12 production models ever existing.

Design-wise, the Airacuda played every bit the part of revolutionary design. Beyond the crewed nacelles, at least three Airacuda's produced were operating the soon-to-be Bell trademark of tricycle landing gears (though these systems experienced their share of mechanical issues in the development). Wings were rounded at the edges and ran through each nacelle into the wing roots connecting the wing systems onto the forward portion of the fuselage. The nose section had a glazed canopy and the fuselage was streamlined, ending aft with a traditional T-style setup. In all, the Airacuda was most assuredly a different sort of aircraft.

The idea of providing the aircraft with rear-mounted propellers, however, lay in the ability for the forward portion of each nacelle to mount devastating weaponry. In this case, the Airacuda was built around the ability to field a powerful 37mm cannon in each nacelle position, manned by a crewmember. Effectively, the crewmembers assigned to each nacelle were cut off from interaction from their fuselage comrades. Additional weaponry consisted of 2 x 12.7mm heavy caliber air-cooled machine guns and 2 x 7.62mm general purpose machine guns. Armament-wise, the Airacuda had the firepower to contend with any bomber - current or future. The problem with this thinking was in the underperforming engines. Basically, the Airacuda lacked the speed and maneuverability to contend with other enemy fighters. This made the Airacuda a liability unto itself. The system would never have been able to be sent on its own to tackle enemy bombers. Should the need arise to combat the swift new breed of enemy fighters, the Airacuda was nothing more than a sitting duck to enemy fire. Additionally, the slow performing Airacuda could barely keep pace - if at all - with the crop of bombers in service with America. This no doubt sealed the fate of the Airacuda in terms of it becoming a long-term fixture in American military planning.

As formidable as the 37mm cannon armament sounded in theory, in practice it proved to be another matter altogether. It was found that a considerable amount of smoke filled the nacelle crew members position when the armament was fired. Additionally, these poor fellows were also at the mercy of the rest of the crew if (and when) it was time to evacuate the aircraft in an emergency as the propeller blades were seated directly behind each nacelle. A procedure was devised to have the pilot feather out each prop and small controlled explosives were provided to jettison the systems as well. The aircraft also proved dangerous to operate on a single engine - something the later (and more "traditional") designs seemed to overcome. The aircraft proved a handful to fly, though not terrible to the core. Pilots reported much work to keep the aircraft pleased and flying properly but landing was less of a chore and quite stable. The electrical internal components were highly complex and dangerous to the extent that a single outage would knock out more than one vital system.

Despite these major shortcomings - and at least two being lost to accidents - the Airacuda nevertheless fielded one entire operational squadron though only operating in 1938 through 1940 and were eventually removed from service in 1942 - used as nothing more than ground crew trainers. Beyond several photo opportunities across the country to drum up support, the Airacuda never fulfilled its purpose of bomber-interceptor and destroyer and never would see combat action in the Second World War.

In many ways a major setback, the Airacuda brought some well-deserved attention to the Bell Aircraft company. The firm would go on to design and produce the more well-known Airacobra and KingCobra - two designs that would serve the Soviets very well in their war with Germany. In the end, the Airacuda would become nothing more than trivia lore in the realm of US military aviation.

Specifications for the Bell XFM-1 Airacuda
Length: 44.85ft (13.67m)
Width: 69.85ft (21.29m)
Height: 13.58ft (4.14m)

Maximum Speed: 277mph (446kmh; 241kts)
Maximum Range: 2,600miles (4,184km)
Rate-of-Climb: 0ft/min (0m/min)
Service Ceiling: 30,512ft (9,300m; 5.8miles)

Armament Suite:
2 x 12.7mm machine guns
2 x 7.62mm machine guns
1 x 37mm cannon in left engine nacelle
1 x 37mm cannon in right engine nacelle

2 x 300lb conventional drop bombs
Accommodation: 5
Hardpoints: 2
Empty Weight:13,375lbs (6,067kg)
Maximum Take-Off Weight:17,333lbs (7,862kg)

Engine(s): 2 x Allison V-1710-41 liquid-cooled supercharged V12 "pusher" engines delivering 1,150hp each.

The experimental X-1 rocket-propelled aircraft by Bell Aircraft

The Bell X-1 became quite possibly the most important American research aircraft of the 20th Century.

Specifically designed to be airdropped from a B-29 Superfortress, the X-1 would then power up its rocket-propelled thruster and hit speeds in excess of Mach 1. By the end of its production run, vast amounts of aeronautical data would be compiled, leading up to the modern age of turbojet and turbofan-powered flight.

The Bell X-1 was an advanced technology demonstrator that became the  first aircraft in the history of aviation to break the speed of sound.

The X-1 had its origins in a 1945 agreement between the United States Army Air Force and the National Advisory Committee for Aeronautics to develop a technological demonstrator to research kinetic heating of airframes at supersonic flight speeds. Though turbojet technology was already advancing all over the world, the decision was made to try the design with a liquid fuel rocket system which would be switched on upon being dropped in flight by a mother ship (in this case a Boeing B-29).

The Bell X-1 design was fundamental to the core, featuring a single rudder atop a tail assembly that held straight surfaces.

The main wing assemblies were also designed straight but engineered to be as thin as operationally possible and limit drag. The cockpit was forged straight into the fuselage design with the fuselage appearing quite enlarged to house the required amount of fuel for the rocket booster. A powered tricycle landing gear system was implemented and stowed into the fuselage when in flight.

With three X-1's produced and delivered, the first free-fall flight  occurred in 1946 with the first powered flight achieved in 1947.

The powered 1947 flight saw Captain Charles "Chuck" Yeager at the controls as he broke the sound barrier, hitting speeds of Mach 1 at over 40,000 feet. Later tests would see a leap into speeds of Mach 2.4 and an impressive altitude flight of 90,000 feet by 1954.

The trans-sonic research aircraft was one of the first true groundbreaking research aircraft of the Cold War.

Though several X-1's were lost for various reasons, the X-1 series as a whole served up priceless data for researchers that would bring about new engineering marvels in terms of military and civilian aviation.

Specifications for the Bell X-1

Length: 31.00ft (9.45m)
Width: 28.02ft (8.54m)
Height: 0.00ft (0.00m)

Maximum Speed: 967mph (1,556kmh; 840kts)
Rate-of-Climb: 0ft/min (0m/min)
Service Ceiling: 80,000ft (24,384m; 15.2miles)

Armament Suite:
None. Internal provision housing flight data and test equipment.
Accommodation: 1
Hardpoints: 0
Empty Weight:8,100lbs (3,674kg)
Maximum Take-Off Weight:13,400lbs (6,078kg)

Engine(s): 1 x Reaction Motors E6000-C4 (Thiokol XLR-11) four barrel liquid fuel rocket generating 6,000lbs of standard thrust.

The experimental X-5 Swing-Wing aircraft by Bell Aircraft

Bell engineers studied the captured German Messerschmitt Me P.1011 fighter after World War 2 to achieve the impressive X-5 design.

Its roots originated in the German Messerschmitt Me P.1101 of which the X-5 borrowed heavily from in terms of overall design. The jet-powered P.1101 was captured by American ground forces as Germany began giving up ground in the latter years of World War 2. Though the P.1101 was only 80% complete at the time of the American arrival, it made use of basic wing sweep principles to trial a variety of wing postures during its development. However, the infant German system relied on changes to the wing sweep while the aircraft was still on the ground. Only two X-5 prototypes were ever produced with the second being lost to accident. The X-5 program was being considered for an American/NATO low-cost tactical fighter initiative.

The X-5 was an experimental single-seat, single-engine, jet-powered fighter design prototype produced by the Bell Aircraft company and became the first aircraft to make use of in-flight variable geometry wings.

The X-5 program went on to prove the viability inherent in such technology in accordance to increasing maximum speeds, decreasing landing speeds and assisting in a better rate-of-climb - all from one wing system. The X-5 proved helpful to the Americans in the collecting of data at these varying wing sweeps at both subsonic and transonic speeds. Such technology would become the trademarks of upcoming Cold War-era combat aircraft like the Grumman F-14 Tomcat, the General Dynamics F-111 Aardvark and the Rockwell B-1 Bomber. Additionally, the British Panavia Tornado and the Soviet MiG-23/27 would also make use of the "swing-wing" approach.

In the X-5, the pilot was given full control of over the sweep of his aircraft's wings while in-flight. As such, he could adapt the sweep to the action at hand, be it take-off, landing or cruise - and supply more or less drag to the airframe as needed.

The Messerschmitt Me P.1101 itself was born out of the "Emergency Fighter Competition" instilled by the German Air Ministry (RLM) in the middle of 1944. The program essentially halted all production on bombers and instead focused on high-performance defensive-minded fighters to help defend Germany against the relentless Allied bombing campaigns wreaking havoc on her war-making infrastructure - Germany was now more or less embroiled in a defensive war and this along two major fronts. A new specification came down for the development of 2nd generation of German jet-powered fighters and Messerschmitt jumped on board within days. After two initial Messerschmitt designs were penciled, a finalized third design proposal was selected for development. The P.1101 was to have a deep fuselage to make room for the engine, applicable ductwork, the cockpit pressurization equipment, cannon armament and internal fuel. The fuselage would feature a nose-mounted intake to aspirate the Heinkel-Hirth He S 011 turbojet engine to be installed and wings were to be shoulder mounted assemblies with noticeable sweep - in fact, the wings were lifted from the revolutionary Messerschmitt Me 262 jet fighter-bomber. The single-seat cockpit would be fitted well ahead in the fuselage under a three-piece bubble canopy and a retractable tricycle undercarriage was utilized - the main landing gear legs coming from a Messerschmitt BF 109K fighter. The tail section was to be of a conventional type with a single vertical tail fin and applicable horizontal planes all made of wood. The tail assembly was fitted onto a tapered boom formed atop the engine exhaust port. Plans were made for cockpit armoring, carriage of four wire-guided missiles and a recessed centerline fuselage position for a single bomb.

Robert Woods and Bell Aircraft unveiled their similar X-5 in the early 1950s.

To help speed development of the P.1101 along, it was decided to construct the P.1101 V1 prototype alongside the wind tunnel and other data collection still ongoing. The P.1101 V1 design was also given wings that would adjust their sweep preflight and could test wing sweep at 35- and 45-degree angles. The wings were eventually set to test sweep at positions of 35-, 40- and 45-degrees. First flight was slated for sometime in June 1945 if all went as planned. All development and construction was to take place at the largely unknown Messerschmitt facility at Oberammergau nestled in the Bavarian mountains of Southern Germany. The Allies had no knowledge of the facility and therefore the area was relatively free of Allied air strikes.

The major difference in the Bell mount was in the use of in-flight variable geometry wings, this made possible by a collection of electric motors within a system as designed by Bell engineers.

However, the Americans were making tremendous headway into the region at the time. For fear of the P.1101 data falling into enemy hands, Messerschmitt employees moved the information into microfilm form and hid them in four locations at neighboring villages. The Allies moved into the area on April 29th, 1945 with the Americans taking Oberammergau - actually being somewhat surprised that the Messerschmitt facility even existed. The Me P.1101 V1 prototype was found tucked away in a tunnel and quickly secured by the Americans. It was only later that Messerschmitt employees revealed the missing data and their locations. However, by this time, the French Army had moved in and found the hidden P.1101 data, subsequently shipping them back to French authorities. A joint American-German effort led by Robert Woods of Bell Aircraft and Woldermar Voight of Messerschmitt to secure the microfilm and finish the P.1101 fell on deaf ears - the French, it would seem, maintained little interest in assisting their former conquerors.

The wing arrangement allowed the X-5 the capability to adjust wing sweep between three pre-set positions of 20-, 40- and 60-degree angles as needed, making her a more complex form of the German type.

As such, the P.1101 made its way stateside. Along the journey, she encountered a myriad of abuses at the hands of the teams charged with transporting her. Not only had exposure to the elements taken their toll on the P.1011 airframe, she was essentially man-handled by the founding GIs eager for picture-taking opportunities. All was compounded when the P.1101 airframe prototype fell off of her transporting railcar - sustaining enough damage that ensured the V1 prototype would never be able to fly. Nevertheless, Bell Aircraft proceeded to break down the P.1101 to the seams and fitted the V1 with mock cannon armament along her fuselage sides and an American Allison J35 turbojet engine. The P.1101 V1 still served in valuable static ground tests before she was given over to the scrapman's torch sometime in the 1950s - ending the legacy of the German aircraft.

The X-5 was fitted with a single Allison J35-A-17 turbojet engine of 4,900lbs thrust.

The first prototype (50-1838) was completed on February 15th, 1951 and first flown on June 20th, 1951. A second prototype (50-1839) followed into the air on December 10th, 1951. Both airframes accounted for some 200 total flights with the first prototype netting 133 flights alone. All three wing sweep positions were trialed on the first prototype's ninth flight with success.

Maximum speed was listed between 690 and 716 miles per hour with a cruise speed of about 600 miles per hour.

A reported service ceiling of 50,700 feet (hence the pressurized cockpit) was given as was a listed range between 500 and 750 miles. She maintained an empty weight of 6,336lbs and a maximum take-off weight (MTOW) of 9,980lbs when fully-fueled. No armament was ever installed. Her variable wing sweep gave her a 32 foot, 9 inch span when extended and a 22 foot, 8 inch span when swept.

The cause was believed to be the positioning of the tail section wihtin the design and compounded by the position of the vertical tail fin itself. As the wing sweep changed, essentially the entire aerodynamic qualities of the aircraft changed with it. The resulting action could lead the aircraft into an irrecoverable spin - this eventually occurring on October 14th, 1953 - the second prototype was lost to such a spin while running its wing sweep at 60-degrees, killing Air Force test pilot Captain Ray Popson in the process. As such, the program was shelved and ultimately cancelled by the USAF killing any chances of the X-5 becoming the low-cost tactical fighter the Americans envisioned. Testing did, however, continue on with the first prototype into 1955 to which the aircraft served out the rest of her term as a chase plane until early 1958 - her variable wing sweep proving helpful in keeping pace with various other aircraft under development.

In practice, it was soon found that the X-5 inherited some particularly vicious stall-spin instability characteristics - perhaps the price of basing such a project on the incomplete German program.

The remaining Bell X-5 was handed over to the National Museum of the United States Air Force in Dayton, Ohio, in March of 1958 where it resides even today as part of the Research & Development Gallery at Wright-Patterson Air Force Base.

Some of the flight data garnered from the X-5 program directly served in the development of the Grumman F-14 Tomcat and the General Dynamics F-111 Aardvark "swing-wing" combat production aircraft, though the Bell's particular internal wing sweep mechanism was completely revamped for these two advanced aircraft designs.

It is of note that the Saab 29 "Tunnan" shares striking similarities to both the Messerschmitt Me P.1101 and the Bell X-5. 

Specifications for the Bell X-5

Length: 33.14ft (10.1m)
Width: 33.46ft (10.20m)
Height: 11.81ft (3.60m)

Maximum Speed: 715mph (1,150kmh; 621kts)
Maximum Range: 750miles (1,207km)
Rate-of-Climb: 0ft/min (0m/min)
Service Ceiling: 49,869ft (15,200m; 9.4miles)

Armament Suite:
Accommodation: 1
Hardpoints: 0
Empty Weight:6,349lbs (2,880kg)
Maximum Take-Off Weight:10,000lbs (4,536kg)

Engine(s): 1 x Allison J35-A-17 turbojet engine developing 4,900lbs of thrust.


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