Jet-Powered Technology Demonstrator Fighter Aircraft
Bell engineers studied the captured German Messerschmitt Me P.1011 fighter after World War 2 to achieve the impressive X-5 design.
Authored By: Dan Alex | Last Edited:
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. 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.
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 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.
Birth of the P.1101
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.
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 End of the P.1101 Project
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 P.1101's New Home
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.
Bell Shows Off Its New X-5
Robert Woods and Bell Aircraft unveiled their similar X-5 in the early 1950s. 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. 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. 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.
The X-5 was fitted with a single Allison J35-A-17 turbojet engine of 4,900lbs thrust. 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.
Tragedy Befalls the X-5 Program
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 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.
Beyond the X-5
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.