Convair X-6
| Convair X-6 | |
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 Convair NB-36H (51-5712) on its seventh flight on December 23, 1955 |
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| Type: | Experimental airplane |
| Design country: | |
| Manufacturer: | |
The Convair X-6 was an experimental aircraft project that did not get beyond the concept stage. A test vehicle for the proposed nuclear drive flew, but only the radiation shielding was tested.
history
prehistory
Investigations into the possibilities of a nuclear propulsion of airplanes began in the USA in May 1946 with the program Nuclear Energy for the Propulsion of Aircraft (NEPA) (nuclear energy for the propulsion of airplanes) of the USAF . Studies under this project continued until May 1951, when NEPA was replaced by the Aircraft Nuclear Propulsion (ANP) program . The ANP was jointly pursued by the Air Force and the Atomic Energy Commission with the aim of developing a full-scale aircraft reactor and propulsion system.
In the event that Convair could not successfully implement the program, a contract was also signed with Lockheed to create a concept for a nuclear aircraft. At the same time, Boeing, Convair, Douglas and Lockheed also examined the requirements for a supersonic nuclear aircraft.
Engine technology
As part of the ANP program, orders were placed with General Electric to develop the P-1 (later P-3) direct-air circuit turbojet and Pratt & Whitney for an indirect-air circuit turbojet. With the direct circuit turbojet (open system), air is fed from the compressor stage to the reactor core, where it is heated. At the same time, the air serves to cool the reactor and, after being heated up, is directed to the turbine stage and then through the nozzle to the outside. The compressor is driven by the turbine like in a normal turbojet, but no combustion chamber is used and therefore no kerosene is used or consumed, except for starting the engine. The indirect (closed) system works very similarly, but the air is not heated directly in the reactor core, but in a heat exchanger in which a working medium (either liquid sodium or pressurized water) circulates.
General Electric has made some successful trials with the direct circuit concept. The Heat Transfer Reactor Experiment (HTRE) used the three reactors HTRE-1 to HTRE-3. The water-moderated HTRE-1 was successfully tested with a modified J47 , then referred to as the X39 . After this reactor, which was mainly used to demonstrate the functionality of the concept, the HTRE-2 was built with slight changes. The following HTRE-3 was supposed to prove the usability as an aircraft engine. He used a solids-moderated reactor that powered two X39s.
The proposed P-1 engine was based on the X39 configuration and used four modified J53 (X40) instead of the J47 / X39. However, the J53 turbojet engine ultimately remained just a design. Both X39 and X40 also included a combustion chamber in front of the turbine stage, which z. B. could use kerosene to start the engine until the reactor had reached its operating temperature. This conventional combustion chamber system could also be used for take-off and landing and possibly during the target approach, if the relatively long reaction times of the reactor could be a disadvantage.
The development progress at Pratt & Whitney with the indirect closed system was much slower. An executable system could not be shown because the necessary development effort turned out to be far greater than the direct system. Only tests were carried out with individual components such as the heat exchanger.
NB-36H
The ANP program included a plan to have two Convair B-36s retrofitted by Consolidated Vultee Aircraft Corporation as part of the MX-1589 project. One B-36 was to be used to examine the necessary shielding devices for a nuclear reactor in flight, the other was to become the X-6.
The first converted B-36 was called Nuclear Test Aircraft (NTA, nuclear test aircraft). With it, a small reactor should be tested with regard to the effectiveness of the shielding in flight, but without being used to propel the aircraft. The first public announcement of the MX-1589 project was made on September 5, 1951 by Convair manager August C. Esenwein.
In preparation for the NTA experiments, Convair installed a small nuclear Ground Test Reactor (GTR) in Fort Worth in 1953, which became critical on November 17, 1953 . The Aircraft Shield Test Reactor (ASTR, aircraft protection shield test reactor) to be installed in the aircraft also became critical in the same year. A lot of development time was spent on the conception of the accommodation and the radiation protection of the crew. Ultimately, the decision was made for the pilot and co-pilot to sit next to each other; two nuclear engineers sat directly behind them, while the flight engineer sat at the far end in the middle of the shielded room. In July 1952 the construction of the occupation compartment began, which was only completed in early 1955. The shielding clearly limited the crew's space. B. the Plexiglas pane of the cockpit is 15 cm thick. The crew compartment could easily be removed from the aircraft as a complete unit for maintenance purposes.
The XB-36 (42-13570) was used in mid-1951 for the first ground tests with shielding devices. The actual NTA aircraft was a B-36H-20-CF with USAF serial number 51-5712 that was damaged during a tornado in Carswell on September 1, 1952. Since this mainly affected the bow of the fuselage, and this should be replaced anyway, this machine was chosen. At the beginning of 1955 she received the new front section and all other modifications for the flight tests. This aircraft was designated the XB-36H on March 11, 1955 and then finally the NB-36H from June 6, 1955. In the early phase of testing, it still had the Convair Crusader logo on the bow. The air-cooled 1000 kW ASTR nuclear reactor had a shield made of the new material Boral (a sandwich construction made of boron carbide and aluminum) around the reactor itself, which was supplemented by further water jacket areas in the hull and directly behind the crew area. A four-ton lead washer was still installed in the middle of the aircraft. The ASTR reactor installed in bomb bay No. 4 (in the area of the trailing edge of the wing) weighed 15.9 tons alone, and a number of air inlets and outlets in this fuselage area provided cooling. The reactor operated in flight but did not provide power to the aircraft.
The NB-36H's maiden flight took place on September 17, 1955 with test pilot AS Witchell Jr. On each of the flights, the machine was accompanied by a Boeing C-97 , which carried a train of armed marines in order to shield the B-36 in the event of an emergency landing. In most cases, a Boeing B-50 (48-058) was also used as an escort aircraft to record data. The NB-36H carried out a total of 47 test flights between 1955 and 1957, but the reactor was only critical on 21 flights. After the provisional end of the test program in late 1957, the machine was parked in Fort Worth with the intention of continuing the program with the further allocation of funds. However, since neither 1958 nor 1959 the corresponding financial resources were made, it was decided to scrap the aircraft in September 1958.
X-6
The X-6 was to use the reactor to propel the aircraft for the first time, according to the ANP program. The B-36 should also serve as a carrier for this, as no other cell was able to take the heavy weight of the reactor and the shielding. For a short time the two Convair YB-60 cells were also considered for this purpose.
The X-6 was designed on the assumption that the J53 turbojet engine would be the basis for the X40 nuclear engine . The entire propulsion system should weigh 75 tons, composed of the 4.5 ton reactor, 27 tons for the reactor shield, 17 tons for the crew shield, 8.3 tons for the actual engines and 18.2 tons for the air inlets and outlets and other auxiliary facilities. The take-off weight of the X-6 should be 163.5 tons. The shielding for the crew was almost 20 m in front of the reactor and was intended to guarantee a maximum radiation exposure of 0.25 X-rays / h . In today's units, this corresponds to 2.5 mSv / h , the currently permitted annual dose for people of 25 mSv per year would have been reached after ten hours of flight time. The crew area itself was not changed from that of the NB-36H.
The four J53 / X40 engines were designed in a row under the fuselage slightly in front of the reactor. The compressor air could thus be directed into the reactor and through the turbine section to the outside via the shortest possible route. The R-1 reactor as part of the P-1 propulsion system was air-cooled and water-moderated, whereby the water could also serve as an additional coolant for the core. The 1.8 t reactor core had a diameter of 1.60 m, was 0.91 m long and contained 65 kg of enriched uranium. When it became clear that the J53 would not be available as a base engine, the J47, a GE-X-5-0 projected engine, the Pratt & Whitney J57-P-5 and the Wright YJ67- W-1 were drawn as replacements into consideration. The J47 was rejected as not powerful enough, the GE-X-5-0 would require at least another 48 months of development time, the J57 was actually too inefficient, but two rows with three engines each were considered sufficient for the flight tests. The starting position was similar for the YJ67, here a row of five engines was considered sufficient.
After changing the air flow to the reactor, now from back to front, the designation of the overall drive system was changed from P-1 to P-3 and that of the reactor from R-1 to R-3.
Two prototypes of the reactor produced by General Electric have been preserved and can be viewed at Experimental Breeder Reactor I in the US state of Idaho .
In the 1960s, the Tupolev Design Bureau conducted a similar experiment on a Tupolev Tu-95 equipped with a nuclear reactor and designated as the Tupolev Tu-119 .
General data
| Parameter | Data |
|---|---|
| crew | 5 |
| length | 49.38 m |
| span | 70.1 m |
| height | 14.26 m |
| Wing area | 443.3 m² |
| Takeoff mass | 163,000 kg |
| Top speed | 628 km / h |
| Service ceiling | 12,200 m |
| Engines | 6 x Pratt & Whitney R-4360-53; 4 × General Electric X40 |
literature
- Dennis R. Jenkins: Magnesium Overcast - The Story of the Convair B-36. Specialty Press, 2001/2002, ISBN 1-58007-129-5 , pp. 206-219.
Web links
- The dream of nuclear Flight (English)