when Wikipedia continues becoming better, it may be not easy to write a satisfactory GOT topic about an aircraft, because Wikipedia already contains everything one would like to know. But in this case, it turned out that (about an American aircraft!), the German Wikipedia are more extensive than the one in English language. So I decided to translate the German text for you, one more feature you have exclusively as Warbirdsforum user! (I hope not too many germanisms occur...)
The Curtiss XP-55 Ascender
(internal designation CW-24) was an experimental fighter aircraft of the US producer's Curtiss-Wright's Curtiss Airplane Division St. Louis. It was a very unconventional design for a pursuit aircraft, which should meet the demand for the best possible visibility for the pilot while maintaining low air resistance and high firepower. The XP-55 reached the second place in the competition, this being a long distance behind the XP-54. The CW-1 to CW-25 series was only used by the Curtiss-Wright plant in St. Louis between 1930 and the beginning of the Second World War.
Basis for the development of the XP-55 were the requirements of the on 14 or 27 November 1939 published Circular Proposal XC-622 (also called Air Corps Type Specification XC-622). There the following performance values were required: ascent to 6100 m (7000 mph) in 7 minutes, a speed of 680 km/h (425 mph) in 4600 to 6100 m (15,000 to 20,000 ft), the top speed should be 840 km/h (525 mph, his was considered a theoretical limit for propeller aircraft) and at least 1.5 hours of flight. The deployment 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 have been added by the Request For Data R40-C. To make the ambitious flight performance possible, the US Army Air Corps (USAAC) favored the Pratt & Whitney X-1800, other sources  say, this was the Pratt & Whitney H-3130 delivering 1800 hp, which at later stages of development should be increased to 3000 horsepower. The demands in R40-C differed from the usual requests of the War Department to airframe manufacturers in a way that here it was directly asked to draw up draft outside the previous conventions.
The Air Corps chose five concepts (Bell XP-52/XP-59, Vultee XP-54, Curtiss XP-55 and Northrop XP-56) for the subsequent development, later the XP-67 came added as a sixth pattern. The works were followed up to different development stages, but only three designs led to flying machines [I mean only the XP-52 never flew, RT].
The Curtiss Airplane Division of Curtiss-Wright in St. Louis submitted proposals for an aircraft with three potential engine alternatives. The Army chose to use P-249C with a Continental IV-1430-3 delivering 1600 hp and counter-rotating airscrews. The P-249C had a pusher propellers, swept wings fastened far aft, and end discs attached to the tips of the surfaces as side rudders. The freely movable stabilator at the bow gave the design the look of a canard airplane. However, these are defined by an on the bow fixed rudder fin with elevator contrary to the XP-55 design. Here, the joystick was connected with trimming surfaces at the rear edge of the elevator. These were only activated at the take-off, during the flight the area could turn freely. The foreseen armament, concentrated in the bow, consisted of a 0.30-cal machine gun, two 0.50-cal machine guns and a 37-mm machine gun. The span should be 9.85 m and the length should be 7.78 m.
The contract for the construction and first wind tunnel tests for the XP-55 (Model CW-24) was signed on 22 June 1940. Curtiss ensured the high performance requirements of the XC-622 and R40-C, although until then only paper studies were carried out. The wind tunnel results showed poor flight stability and inadequate control characteristics, particularly when approaching the stall speed. The necessary construction work to remedy these grievances would certainly have influenced the performance, so that the Air Corps delayed the further commissioning of Curtiss.
Experimental aircraft CW 24-B
Then the plant decided to continue the work on its own cost and to create a full-scale flyable proof-of-concept model for generating additional flight data. This model, called 24-B experimental aircraft, was in the last stages of construction, when Curtiss on 28 November 1941was able to conclude a new agreement with the Air Corps for the continuation of the project.
The CW 24-B had a load-bearing fuselage structure made of fabric-covered welded steel tubes. The wing with a span of 11.16 m was carried out in timber construction, the sweep of the t/4-line was 26.5 °. The length was 8.36 m and the flying weight was 1640 kg. Unlike in the original P-249C design, the vertical rudders at the 24-B were attached at about half the span. The outer areas of the surface areas showed a considerable wash-ou to reduce the tendency to stall. The cowled chassis was not retractable. The crew consisted of a pilot and an engineer. However, with a Menasco C6 S-5 Super Buccaneer delivering 275 hp to drive the plane, it was underpowered and only reached 290 to 320 km/h as the maximum speed.
The CW 24-B (USAAC serial no. 42-39347) flew for the first time on 2 December 1941 at the Muroc Army Air Field . In the test flights, the surface area of the front wing was increased by 25% and the vertical rudders were shifted outwards by 1.20 m. As a result, these surfaces were located as end discs on the wing tips and were supported by two low fins above and below the engine cowling. Later, surface extensions were installed outside the end disks to increase the longitudinal stability. By May 1942, 169 flights had been carried out. At the beginning, spinning experiments were not performed because experiments in a vertical wind tunnel with a model of the CW 24-B in 1:16 scale gave results of an uncontrollable flat spinning behaviour. The CW 24-B then was brought to Langley for own wind tunnel tests.
On July 10, 1942, the Army ordered three XP-55 prototypes. Since the originally forseen engine was not available, Curtiss planned to use the Allison V-1710-F16 with 1250 hp, which had been originally intended for the design P-249A. As a result, Curtiss guaranteed the top speed of 670 km/h in 5900 m, a climb of 7.1 min to 6100 m and one hour as the maximum flight time.
After Don Berlin had been responsible for the design work, the following construction work was performed by George Augustus Page Jr. as chief engineer and E. M. "Bud" Flesh as chief designer. The interpretation of the XP-55 was strongly oriented on the CW 24-B. The wings with a sweep of 28 ° on the t/4-line (45 ° at the wing front edge) had ailerons and split flaps. The vertical fins above and below the engine were equipped with air inlets for cooling the engine compartment (top) and a heat exchanger (bottom). The propeller shaft also drove a blower for forced cooling. At the outer load stations two additional tanks with 190 L each could be carried. The 3.05 m diameter three-blade propeller could be blown off by means of compressed air in case of emergency for the pilot's exit in flight.
After an inspection of the dummy finally the 1275 hp delivering Allison V-1710-95 (F23R) without turbochargers and a smaller fuel capacity was chosen. The weight increased by 40% compared to the original concept of 3600 kg. The armament in the final version consisted of four .50 cal-MGs.
The roll-out of the first prototype (USAAF series 42-78845) took place on 26 June 1943. After taxiing tests, the first flight took place on the 13th or 19th of July 1943 (depending on the source) on Scott Field, located near the Curtiss works. The flight test revealed some problems of the XP-55. Thus, for example, very long take-off distances were required, which should be remedied by an enlargement of the elevator. The engine tended to overheat on the ground despite various changes in the air inlets. Inboard of the ailerons boundary layer fences were installed to improve the flow pattern on the wings at high angles of attack. Continued test flights on Lambert Field showed generally good flight characteristics, but on November 15 at stall testing the machine crashed. The behavior of the aircraft during the crash resembled the phenomenon of stable vertical flatspinning, which had already been observed during the model spinning tests in the wind tunnel. The test pilot J. Harvey Gray could leave the plane.
As a direct result of the crash a new series of wind tunnel investigations began, which led as a result to an increase in the span by attaching trailerons, connected to the ailerons. This change was directly adopted in the third machine (42-78847), which was still under construction. The second aircraft (42-78846) flew for the first time on 9 January 1944, followed by the third prototype on 25 April. This one soon continued the interrupted stalling tests, whereby it was found that a stall warning practically did not exist and the machine suddenly fell off and only could be brought under control after a loss of height by more than 1000 m. The subsequently installed pressure sensor, which activated a stick shaker, was one of the first artificial stall warning systems in an aircraft. A simple solution for the high loss of height in the stall could not be found.
The second prototype also received the modifications of the third sample in the autumn of 1944. Although the test pilots described many good features of the second machine, they also complained that many changes had yet to be made until they were ready for production. After the third plane had been transferred to Wright Field in mid-December 1944, it crashed there on May 27, 1945, with a pilot and a civilian killed on the ground [other sources say 4 victims, due to English Wikipedia].
For the army decided to consider the stall characteristics of the Ascender, including the warning system, as unacceptable, in addition to the other unresolved deficiencies, such as the long take-off, excessive weight and cooling problems, at the end of 1944 this led to the discontinuation of any further development. Until then costs of about 3.5 million US dollars had accumulated.
The XP-55 has canard wings and a pusher propeller, which at its time was a very unconventional construction. The engine was behind the cockpit and the rear edge of the wing. This was one of the reasons for their strong sweep. The wings had ailerons and landing flaps, and carried the vertical rudders as well as, which each rose upwards and downwards just before the ends. The elevator, built as a mass-balanced stabilator with equidistant deflecting auxiliary rudders, sat at the front of the bow. The chassis was, for the first time at the company, designed as a tricycle landing gear with single wheels on each strut. Since the originally planned engine Pratt & Whitney X-1800 was not available, the three aircraft received 12-cylinder engines Allison V-1710.
End of German Wikipedia text. The following paper sources are given:
- William Green: Fighters (War Planes of the Second World War, Volume Four), MacDonald, 3. Auflage 1965, ohne ISBN, S. 62-65
- Bill Gunston: Curtiss Ascender (Prototype Pusuits). In: Aeroplane Monthly November 1979, S. 580-583
- Peter M. Bowers: Curtiss Aircraft 1907 - 1947, Putnam, 1979, ISBN 0-370-10029-8, S. 466-469
- Francis Allen: Ascent -Tail-First (Curtiss-Wright XP-55 Ascender). In: AIR Enthusiast Fifty-One August-Oktober 1993, S. 10-15
- Bill Norton: U.S. Experimental & Prototype Aircraft Projects - Fighters 1939-1945, Specialty Press, 2008, ISBN 978-1-58007-109-3
One of the prototypes (#2) survives in the Kalamazoo AirZoo museum.
Now, let's look at some pictures (they can be improved by using XnView, like always):
The CW-24-B (sorry, forgot to store the source), the mechanic's compartment is clearly visible:
The CW-24-B in the Langley windtunnel (from Wikipedia):
Contemporary XP-55 pictures. This one roames around in the net:
Source not stored again. The ground looks being a bit askew:
Busy work. From the website of the German magazine Fliegerrevue:
Then modern pictures from Kalamazoo. Here source given:
Also from skytamer.com:
(to be continued)