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CW-21: KNIL Interceptor


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During the late 1930s, the Curtiss-Wright corporation was a major source of aircraft for both the US military and export customers. One of their most famous models was the Hawk 75 (also known as the P-36), which saw extensive service with the Americans, French, Finns, and others. This design would evolve into the famous P-40, which was then followed by a series of much less successful designs. One of their less well known designs was the CW-21.


The CW-21 was derived from the earlier, unsuccessful CW-19 civilian aircraft. It was designed by the vice president of the St. Louis branch of Curtiss-Wright, George R. Page. Page's design went against the grain of American fighter design of the time, which focused on low level performance. Instead, it was designed to climb rapidly to altitude to intercept bombers, using its superior climb rate to evade escorting fighters. As can be seen from [url=http://sturgeonshouse.ipbhost.com/topic/1533-trade-offs-in-wwii-fighter-design/]this[/url] topic, climb rate is dependent on thrust (engine power), weight, and drag.


Early CW-21. The early-model landing gear fairings are quite distinct.


Page's design achieved an excellent climb rate by minimizing weight. The definitive CW-21B model had an empty weight of only 1534 kg, compared to 2076 kg for the P-36 and 2753 kg for the P-40. The light weight was achieved through heavy use of aluminum in the structure. Despite this, it still managed to fit a 1000 hp R-1820-G5 (Wright Cyclone) engine (compare to the P-36 and its 1050hp R-1830). A two-stage supercharger was fitted to the engine to improve performance at altitude.




CW-21B in Dutch markings.


The CW-21 first flew on September 22nd, 1938. At once, it achieved an excellent climb rate. Though claims that it could climb “a mile a minute” were exaggerated, it did demonstrate the ability to reach an altitude of 16400 feet (5000 meters) in five minutes. This was exceptional performance for the time. Many accounts give an initial climb rate in excess of 4,000 feet per minute, though this is not backed up by all sources. Top speed was 315 miles per hour at altitude, and the aircraft was reportedly quite agile.


Armor was very light, although the pilot was provided with some protection. Armament was also decent for the time, though light compared to later aircraft. The CW-21B's that saw combat were armed with two M2 machine guns, and two M1919 machine guns, though some sources say they were fitted with four M1919s. No provision was made for the use of air to ground weapons.


American forces never seriously considered using the CW-21. By 1938-39, the USAAF had several fairly new aircraft in service such as the P-36 and P-35, along with several others in development such as the P-38, P-39, and P-40. The CW-21's light structure would have made it completely unsuitable for carrier-based service. Instead, the CW-21's main customer, at first, was the Republic of China.


By 1939, China had already been at war with Japan for several years (since 1931 or 1937, depending on one's definition of the war). The Chinese Air Force was horribly outmatched against the IJAAF and IJNAF, even with support from the Soviets. Desperate for modern fighters, the Chinese signed a contract for the purchase of three finished aircraft, along with parts for 27 more to be assembled in China.


It appears the first three CW-21s arrived in Rangoon in early 1940. There, they languished until December 1941, due to bureaucratic delays, and the low throughput of the Burma Road. Then, the American Volunteer Group (better known as the Flying Tigers) attempted to fly the three aircraft to one of their bases in China. All three planes suffered engine failures partway through the flight (likely due to bad fuel); one pilot was killed, and all three CW-21s destroyed. Indications are that the Chinese built at most two CW-21s from the parts provided. Little of substance is known about their use in combat.


The CW-21 was slightly more successful in Dutch service. In early 1940, the Dutch government, conscious of the deteriorating situation in Europe, sought to improve its anemic defenses by any means possible. In April 1940, the Dutch government placed an order for 24 CW-21B aircraft (Several CW-22 Falcons, a trainer/light bomber derived from the CW-21, were also ordered. The Falcon saw a much larger production run than the CW-21, also serving with the US Navy as the SNC.). The German invasion on May 10th, 1940, derailed plans for the CW-21 to serve in the Netherlands. Instead, the aircraft were transferred to the East Indies to serve with the MN-KNIL.



Lineup of CW-21Bs.


All 24 of the crated aircraft arrived in Java by November 1940. After reassembly, they served with 2-VLG IV. Even before the start of the war with Japan, some issues arose. Structural problems became apparent, likely a result of the CW-21's light construction. In particular, as of December 1941, many aircraft were grounded by cracks in the undercarriage. Only nine CW-21s were operational when the war started.


2-VLG IV was dispersed throughout Java shortly after the conflict. It would take some time before the CW-21 saw combat. Despite several false alarms, they did not encounter Japanese forces until February 3rd. On that day, the Dutch CW-21s (along with a mixed force of P-40s, P-36s, and Buffaloes) encountered a large group of A6Ms over Java. Against the well trained and experienced Japanese pilots, the CW-21s came off poorly. Three Zeroes were shot down by the CW-21s, in exchange for the loss of seven planes (with several more damaged). This action seriously depleted the strength of 2-VLG IV, and it was soon sent to western Java to rearm with Hurricanes. Four more CW-21s were lost to Japanese aircraft on February 24th. The last confirmed use of the CW-21 was on March 3rd, when three of them escorted a group of Martin 166 bombers against the captured Kalidjati airfield. At least one CW-21B was captured and tested by the Japanese; it was found in Singapore by returning British forces in 1945. No CW-21s are known to have survived following the war.




Photos from Dutch archives




An interesting exercise is to compare the CW-21 to one of its contemporaries and opponents, the Ki-43 (“Oscar”). The Ki-43 first flew in early 1939, just after the CW-21's first flight. While the Ki-43 had a reputation for being quite agile, it actually weighed much more than the CW-21, with an empty weight of over 1900 kilograms, compared to roughly 1500 for the CW-21. Initial models of the Ki-43 had an Ha-25 engine with 975 horsepower (this would be improved in later version), similar to the CW-21. The Ki-43's armament was quite light, with only one 12.7mm machine gun and one 7.7mm machine gun (again, this was increased in later variants). Like the CW-21, the Ki-43 had a reputation for agility, but also for being quite fragile (a common trait of many Japanese aircraft of the time). On paper, the two aircraft seem similar, but the Ki-43 was more successful. This is in part due to its larger production run, but also due to the severe conditions the Dutch faced in 1941-42.





The CW-21 is given the name “Demon” by many sources. However, it is likely that this is incorrect. There is no evidence that Curtiss-Wright ever used the name, indeed, most Curtiss aircraft of the time had names connected to birds in some way (Hawk, Falcon, etc.). One story is that the name comes from a crate which had “Demonstration” written on it, with the letters “demon” showing on one side. I have not been able to find what, if any, nickname Dutch pilots on Java gave their CW-21s.



Model of CW-21 and Martin 166 in Dutch markings from; http://www.britmodeller.com/forums/index.php?/topic/234977846-netherland-east-india-1941-cw21-b10/






^major source^









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  • 4 months later...

According to what I read elsewhere there are no survivors of CW-21. 


Anyway since some of you guys used to play, it's worth mentioning that CW-21 is in the good old Il-2 Sturmovik simulator (in one of the 16 years long line of patches). I don't know how accurate the physical model is but it's probably the only chance to get a taste of this interesting plane. There it's indeed very agile with great climb rate however it is also rather unstable in longitudinal axis and quit fragile. It indeed feels close to the Japanese planes in agility. The worst thing about it is its primitive sights (the tubular ones of the contemporary Ki-43 are nightmare to use in dogfight though). As for the armament the developers put both options in there, i.e. both 2 x 7,7 + 2 x 12,7 and 4 x 7,7 mm.




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