Curtiss-Wright XP-55
| Curtiss-Wright XP-55 | |
|---|---|
 The second prototype in flight |
|
| Type: | Experimental fighter plane |
| Design country: | |
| Manufacturer: | |
| First flight: |
July 13 or 19, 1943 |
| Number of pieces: |
3 |
The Curtiss XP-55 Ascender (factory designation CW-24) was an experimental fighter aircraft of the Curtiss Airplane Division St. Louis of the American manufacturer Curtiss-Wright . It is a very unconventional design for a fighter aircraft that should meet the requirement for the best possible visibility for the pilot with low air resistance and high firepower. The XP-55 achieved second place in the tender, with a large gap to the XP-54. The CW designation series (CW-1 to CW-25) was only used by the Curtiss-Wright plant in St. Louis between 1930 and the beginning of World War II.
history
Concept development
The basis for the development of the XP-55 were the requirements of the Circular Proposal XC-622 (also called Air Corps Type Specification XC-622) published on November 14 or 27, 1939 . There the following performance values were required: Ascent to 6100 m (20,000 ft) in 7 minutes, a speed of 680 km / h (425 mph) in 4600 to 6100 m (15,000 to 20,000 ft), the maximum speed should be 840 km / h ( 525 mph) (this was considered the theoretical limit for propeller-driven aircraft) and a minimum of 1.5 hours of flight time. The mission should be possible from an unprepared 915 m (3000 ft) long runway surrounded by 15 m (50 ft) high obstacles. On February 20, 1940, these requirements were supplemented by the Request For Data R40-C . In order to make the ambitious flight performance possible, the US Army Air Corps (USAAC) favored the Pratt & Whitney X-1800 , according to other sources this was the 1,800 hp Pratt & Whitney H-3130 engine, which in later stages of development can deliver up to 3,000 hp should. The requirements in R40-C differed from the usual inquiries from the War Department to aircraft manufacturers in that they were directly asked to work out designs outside of the previous conventions.
The Air Corps selected five concepts (Bell XP-52 / XP-59, Vultee XP-54 , Curtiss XP-55 and Northrop XP-56 ) for subsequent development, later the XP-67 was added as a sixth model. The work was followed up to various stages of development, but only three designs resulted in flying machines.
Curtiss-Wright's Curtiss Airplane Division of St. Louis made proposals for an aircraft with three potential engine alternatives. The Army selected the P-249C concept with the 1600 hp Continental IV -1430-3 and counter-rotating propellers. The P-249C had a pusher propeller, arrow-shaped wings mounted far back and rudder end plates attached to the wing tips. The freely movable pendulum elevator at the bow gave the design the appearance of a duck plane . However, compared to the XP-55 design, these are defined by a fixed bow rudder fin with elevator. Here the control stick was connected to trim surfaces on the trailing edge of the elevator. These were only activated during take-off; the wing could rotate freely during the flight. The planned armament, concentrated in the bow, consisted of a 0.30-cal MG, two 0.50-cal MGs and a 37-mm automatic cannon. The span should be 9.85 m and the length 7.78 m.
The contract for the construction and first wind tunnel tests for the XP-55 (Model CW-24) was signed on June 22, 1940. Curtiss guaranteed the high performance requirements of the XC-622 and R40-C, although until then only paper studies had been carried out. The wind tunnel results showed poor flight stability and poor control properties, especially when approaching the demolition speed . The necessary construction work to remedy these deficiencies would certainly have also influenced the performance values, so that the Air Corps delayed the further commissioning of Curtiss.
Test aircraft CW 24-B
The factory then decided to continue the work at its own expense and to create a full-scale, flyable proof-of-concept model to obtain additional flight data. This test aircraft, called Model 24-B , was in the final stage of construction when Curtiss was able to sign a new contract with the Air Corps on November 28, 1941 to continue the project.
The CW 24-B had a load-bearing fuselage structure made of welded steel tubes covered with fabric. The wing with a span of 11.16 m was made of wood, with a sweep at the t / 4 line being 26.5 °. The length was 8.36 m and the flight weight was 1640 kg. Unlike the original P-249C design, the 24-B had the vertical stabilizers at about half the span. The outer areas of the surfaces had a clear wash-out to reduce the stall inclination . The faired landing gear was not retractable. The crew consisted of a pilot and a test engineer. With a 275 hp Menasco C6 S-5 Super Buccaneer as the drive, the aircraft was underpowered and only reached 290 to 320 km / h as a top speed.
The CW 24-B (USAAC serial number 42-39347) first flew on December 2, 1941 at Muroc Army Air Field . During the test flights were u. a. the area of the front wing increased by 25% and the vertical stabilizers moved 1.20 m outwards. In the end, these surfaces were located as end disks at the wing tips and were supported in their function as tail units by two low fins above and below the engine cowling. Later on, surface extensions were installed outside the end plates in order to increase the longitudinal stability. 169 flights had been carried out by May 1942. Spin tests were not carried out at the beginning because tests in a vertical wind tunnel with a model of the CW 24-B on a scale of 1:16 gave indications of uncontrollable behavior during a flat spin. The CW 24-B was then brought to Langley for its own wind tunnel tests.
XP-55
The Army finally ordered three XP-55 prototypes on July 10, 1942. Since the originally intended engine was not available, Curtiss planned to use the Allison V-1710 -F16 with 1250 hp, which was originally intended for the design P-249A. Curtiss thus guaranteed the performance values 670 km / h as a maximum speed in 5900 m, a climb of 7.1 min at 6100 m and one hour as the maximum flight time.
After Don Berlin had directed the design work until then, the further construction work was carried out by George Augustus Page Jr. as chief engineer and EM "Bud" Flesh as chief designer. The design of the XP-55 was based heavily on the CW 24-B. The wings with a sweep of 28 ° on the t / 4 line (45 ° on the leading edge of the wing) had ailerons and expansion flaps. The vertical fins above and below the engine were equipped with air inlets for cooling the engine compartment (above) and for a heat exchanger (below). The propeller shaft also drove a fan for forced cooling. Two additional tanks with 190 L each could be carried at the external load stations. The three-blade propeller, measuring 3.05 m in diameter, could be blown off using compressed air in an emergency for the pilot to exit in flight.
After viewing the dummy , the 1275 hp Allison V-1710-95 (F23R) without a turbocharger and a lower fuel capacity was chosen as the engine. The weight increased by 40% to 3600 kg compared to the original concept. The armament in the final version consisted of four .50 cal machine guns.
The rollout of the first prototype (USAAF serial number 42-78845) took place on June 26, 1943. After taxiing attempts, the first flight took place on July 13 or 19, 1943 (depending on the source) on Scott Field, which is located near the Curtiss works. The flight tests revealed some problems with the XP-55. For example, very long take-off distances were required, which was to be remedied by increasing the elevator. The engine tended to overheat on the ground despite various changes to the air intakes. Boundary layer fences were installed inboard of the ailerons in order to improve the flow of air on the wings at large angles of attack. On the Lambert Field continuing test flights showed a good flight behavior in general, but the plane crashed on November 15 at stall tests. The behavior of the aircraft in the event of a crash was similar to the phenomenon of stable vertical flat spin already observed in the model spin tests in the wind tunnel. The test pilot J. Harvey Gray was able to leave the aircraft.
As a direct consequence of the crash, a new series of wind tunnel investigations began, which resulted in an increase in the span through the addition of trailerons connected to the ailerons . This change was directly adopted on the third machine (42-78847), which was still under construction. The second machine (42-78846) first flew on January 9, 1944, followed by the third prototype on April 25. He soon continued the interrupted stall tests, which showed that a stall warning practically did not exist and the machine suddenly tipped over and can only be intercepted again after a loss of altitude of over 1000 m. The built-in pressure sensor that activated a stick shaker was one of the first artificial stall warning systems in an aircraft. However, a simple solution to the severe loss of height in the stable could not be found.
The second prototype also received the modifications of the third machine in autumn 1944. The test pilots described many of the good features of the second machine, but continued to criticize the fact that many changes would have to be made before it was ready for series production. After the third aircraft was transferred to Wright Field in mid-December 1944, it crashed there on May 27, 1945 during a flight demonstration, killing the pilot and a civilian on the ground.
End of development
The fact that the Army judged the stable properties of the Ascender, even with the warning device, to be unacceptable to the end, led to the discontinuation of all further developments at the end of 1944, in addition to the other deficiencies that had not been remedied, such as the long take-off distance, the excessive weight and the cooling problems. By then, it had cost about $ 3.5 million.
construction
The XP-55 has canard blades and a pusher propeller, which was a very unconventional design at the time. The engine was behind the cockpit and the trailing edge of the wing. This was one of the reasons for their strong sweep. The wings had ailerons and landing flaps, as well as the vertical stabilizers, arranged just before the ends, which protruded halfway up and half down. The elevator, designed as a mass-balanced pendulum rudder with auxiliary rudders swinging in the same direction, was at the front of the bow. For the first time at the company, the landing gear was designed as a nose wheel landing gear with individual wheels on each strut. Since the engine originally intended by Pratt & Whitney X-1800 was not available, the three aircraft received 12-cylinder Allison V-1710 engines .
Technical specifications
| Parameter | Data |
|---|---|
| crew | 1 |
| span | 12.36 m |
| length | 9.01 m |
| height | 3.53 m |
| Wing area | 21.8 m 2 |
| Empty mass | 2,882 kg |
| Takeoff mass | 3,597 kg |
| Start distance (over 15 m obstacle) | 1500 m |
| engine | 1 × V-12 Allison V-1710-95 with 1275 PS (950 kW) output |
| Top speed | 607 km / h at 5,200 m |
| Service ceiling | 10,900 m |
| Range | 1020 km at 476 km / h (max. 2300 km) |
| Armament | 4 × .50 cal (12.7 mm) MGs |
literature
- William Green: Fighters (War Planes of the Second World War, Volume Four) , MacDonald, 3rd edition 1965, without ISBN, pp. 62-65.
- Bill Gunston: Curtiss Ascender (Prototype Pusuits) . In: Airplane Monthly November 1979, pp. 580-583.
- Peter M. Bowers : Curtiss Aircraft 1907-1947 , Putnam, 1979, ISBN 0-370-10029-8 , pp. 466-469.
- Francis Allen: Ascent-Tail-First (Curtiss-Wright XP-55 Ascender) . In: AIR Enthusiast Fifty-One August-October 1993, pp. 10-15.
- Bill Norton: US Experimental & Prototype Aircraft Projects - Fighters 1939-1945 , Specialty Press, 2008, ISBN 978-1-58007-109-3 .
Web links
- The Plan Page - Curtiss XP-55 Ascender
- a personal page - Curtiss XP-55 Ascender
- www.warbirdsresourcegroup.org - Curtiss XP-55