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The FReeper Foxhole Revisits
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The Advent of the All-Metal Airplane
Metal-Skinned Aircraft
Most of the 170,000 airplanes built during World War I were constructed of wooden frames with fabric coverings. These materials were relatively lightweight and available. Anthony Fokker, a Dutch entrepreneur working in Germany during the war, developed a welded-tube steel fuselage to take the place of wood.
German manufacturers built more than 1,000 of these aircraft, which had wooden wings. Hugo Junkers, a German designer, built all-metal aircraft, first using sheet iron. He soon switched to duralumin, a high-strength aluminum alloy developed just before the war. After the war, Junkers developed several all-metal passenger transports.
In the spring of 1920, the American pilot John M. Larsen began demonstrating an imported Junkers all-metal passenger plane designated the JL-6. It created much excitement within the American aviation community. The U.S. Postal Service bought six of the aircraft. The enthusiasm over the JL-6 caused many aviation leaders to call for the development of all-metal aircraft.
The National Advisory Committee for Aeronautics (NACA) declared in its 1920 Annual Report that metal was superior to wood because "metal does not splinter, is more homogeneous, and the properties of the material are much better known and can be relied upon. Metal also can be produced in large quantities, and it is felt that in the future all large airplanes must necessarily be constructed of metal."
NACA immediately began research into all-metal construction, and the U.S. Navy developed duralumin fabrication techniques at the Naval Aircraft Factory. In 1924, the first all-metal commercial airplane, called the Pullman, was produced by William Stout. Glenn Martin Aircraft also developed all-metal aircraft for the U.S. Navy in 1923 – 1924, where the only wooden structure was the engine mount.
The Junkers J.L. 6 represents an important step forward in technology. It was probably the first plane with the fuselage, wings, and skin all constructed of metal. Credits - NASA
The Junkers J.L. 6 built in Germany in 1919 as the F 13 and imported to the United States by John Larsen to be used as a mail plane. Credits - NASA
Airplane designers also felt that metal offered other significant advantages over wood, including protection from fire, but in reality, early aircraft metals provided little protection against airplane fires. In fact, despite the enthusiasm over the JL-6, the aircraft had a faulty fuel system causing it to catch fire in flight and the thin aluminum skin between the engine and cockpit melted, allowing flames to burst through at the pilots' feet. Two airplanes were lost within months, and the Post Office quickly sold the remaining four at a huge loss.
Despite the initial great enthusiasm over all-metal construction within the U.S. aviation community and the widespread belief among designers in the superiority of metal in the early 1920s, engineers soon found that metal was not inherently superior at the time. Wood was still lightweight and easy to work with. Over the next decade, aeronautical engineers had a difficult time designing metal wings and airframes that weighed as little as wood.
In late 1920, the Army Air Service contracted with the Gallaudet Aircraft Company for a monoplane bomber with an all-metal fuselage and metal framework wings. The prototype, designated the DB-1 and delivered in late 1921, was grossly overweight and considered a miserable failure. It was quickly retired.
The DB-1 weighed 11,160 lbs. gross
By 1929, nine years after the JL-6 had created so much excitement about all-metal airplanes, an aeronautical textbook estimated that metal wings still weighed 25 to 36 percent more than wood wings. By 1930, a decade after the NACA declared metal superior to wood, only five percent of the aircraft in production were of all-metal construction.
One of the big problems with metal was that it buckled when compressed, just like a piece of paper will bend when its ends are pushed together. In comparison, wood does not buckle as easily. By the 1930s, another aircraft design trend known as stressed-skin structures made this problem more acute.
Before this time, aircraft achieved much of their structural strength through their internal frameworks. But in a stressed-skin structure, the covering contributed much of the structure's strength and the internal framework is reduced. This provided a streamlined external surface for the airplane, but made metal buckling failures more likely.
In order to combat the problems of compressive buckling, metal structures had to be complex, with curves and riveting and reinforcement. This dramatically increased the costs of such an aircraft. By 1929, some manufacturers were making metal wings that were as light as wooden ones, but by the end of the 1930s, all-metal airplanes were significantly more expensive than wood and fabric airplanes.
Metal also presumably was more durable than wood, which warped, splintered, and was eaten by termites. But duralumin also had severe corrosion problems. It turned brittle. Unlike iron or steel, which rusted from the outside in, duralumin weakened internally and could fail suddenly in flight. Duralumin corroded even more in salt spray and the U.S. Navy eagerly sought a solution.
The Aluminum Company of America (Alcoa) and the Federal government cooperated to develop a material known as Alclad, which consisted of an aluminum alloy bonded to pure aluminum. Alclad solved many of the corrosion problems of duralumin. Soon other alloys were developed that proved effective as well and during the 1930s, all-metal airplanes became much more common.
By the mid-1930s, wood was no longer used on American multi-engine passenger aircraft and U.S. combat aircraft. But in 1938, the British airplane company, de Havilland, began work on a fast, unarmed bomber named the Mosquito. It was one of the most successful British aircraft of World War II, able to fly faster and higher than most other aircraft. More than 7,700 Mosquitoes were built. They were made of spruce, birch plywood, and balsa-wood, proving that even in the era of all-metal planes, older materials could still achieve impressive results.
The famous British Mosquito - U.S. Air Force Museum
By the early 1930s, aircraft design and construction technology throughout the world had advanced to the point where it was possible to mass-produce all-metal airplanes. There had been an all-metal plane as early as WWI but it was an exception. Most airplanes of the war period and the 1920s had been primarily of wood and fabric construction, although many later ones had tubular steel fuselage frameworks.
The Air Corps' first all-metal monoplane bomber was the Boeing B-9.
The YB-9 was originally owned, developed and tested by Boeing as the XB-901 (NX10633). The plane was based on the Model 200 commercial transport, but was enlarged and adapted to the bomber role. The YB-9 was powered by two Pratt & Whitney R-1830-13 radial engines which gave it a top speed of 163 mph. Later in its service life, the YB-9 was fitted with the same engines powering the Y1B-9A service test aircraft bringing its top speed to 188 mph.; as fast as the US Army pursuit planes of the time.
A total of 7 aircraft were built: the prototype YB-9, a liquid-cooled engined Y1B-9, and five service test Y1B-9As. The aircraft never entered production mainly because there were even better aircraft being designed which would change the course of US bomber development.
TYPE- Boeing YB-9
Number Built/Converted - 1
Remarks- Boeing XB-901
Notes:
Serial number: 32-301
Originally Boeing-owned NX10633, XB-901 (Model 215)
SPECIFICATIONS
Span: 76 ft. 9 in.
Length: 51 ft. 6 in.
Height: 12 ft. 8 in.
Weight: 12,663 lbs. gross
Armament: 2 .30-cal. machine guns and 2,200 lbs. of bombs
Engines: Two Pratt & Whitney R-1830-13 radials of 575 hp. each
Crew: Four
PERFORMANCE
Top speed: 163 mph. at sea level
Cruising speed: 137 mph.
Service ceiling: 19,400 ft.
Range: approximately 500 miles with a full normal bomb load
Produced during 1932-33, the B-9 was outclassed by its contemporary all-metal Martin B-10 and only seven were purchased.
MARTIN B-10
Considered modern for its time. It flew on Hap Arnold's Alaska trip in 1934. Credits - U.S. Air Force Museum
The B-10, the first of the "modern-day" all-metal monoplane bombers to be produced in quantity, featured such innovations as internal bomb storage, retractable landing gear, a rotating gun turret, and enclosed cockpits. It was so advanced in design that it was 50% faster than its contemporary biplane bombers and as fast as most of the fighters. When the Air Corps ordered 121 B-10s in the 1933-1936 period, it was the largest procurement of bomber aircraft since WW I. It also ordered 32 B-10 type bombers with Pratt and Whitney rather than Wright engines and designated these B-12s.
General Henry H. "Hap" Arnold once called the B-10 the air power wonder of its day. In 1934, he led ten B-10s on a 8,290 mile flight from Washington, D.C. to Fairbanks, Alaska and back. Although Air Corps B-10s and B-12s were replaced by B-17s and B-18s in the late 1930s, China and the Netherlands flew export versions in combat against Japan.
The aircraft on display is painted as a B-10 used in the 1934 Alaskan Flight. The only remaining B-10 known, it was an export version sold to Argentina in 1938. Donated by the Government of Argentina to the U.S. Government for the Air Force Museum in 1970, it was restored by the 96th Maintenance Squadron. (Mobile), Air Force Reserve, at Kelly AFB, Texas, in 1973-76.
SPECIFICATIONS
Span: 70 ft. 6 in.
Length: 44 ft. 9 in.
Height: 15 ft. 5 in.
Weight: 14,700 lbs. loaded
Armament: Three .30-cal. machine guns, 2,200 lbs. of bombs
Engine: Two Wright R-1820's of 775 hp. each
Cost: $55,000
PERFORMANCE
Maximum speed: 215 mph.
Cruising speed: 183 mph.
Range: 1,370 miles
Service Ceiling: 24,000 ft.
The Air Corps' first all-metal fighter was the Consolidated P-25 of 1933.
Consolidated Y1P-25
The original YP-24 design was carried on by designer Robert J. Woods at Consolidated Aircraft Corporation as the Y1P-25. The Y1P-25 was similar to the YP-24 but was generally more streamlined and replaced the wooden YP-24 wing with one of all-metal construction.
Two Y1P-25s were ordered by the Army Air Corps in 1932. The first airframe (S/N 32-321) was fitted with a turbo-supercharger giving it a maximum speed of 247 mph. The Y1P-25 was destroyed in a crash on January 13, 1933.
The second airframe (S/N 32-322) was designated as Y1A-11 (attack bomber). This aircraft did not include a supercharger and featured a clipped vertical stabilizer. The Y1A-11 was also destroyed in a crash on January 20, 1933.
The accidents were not considered to be caused by faulty design and an order was placed with Consolidated Aircraft Corp. for what was to become the P-30.
Although only two were procured, the P-25 design was modified into the P-30, later redesignated the PB-2, of which 54 were purchased in 1935.
TYPE - Y1P-25
Number built/Converted - 1
Remarks - Improved YP-24
TYPE - Y1A-11
Number built/Converted - 1
Remarks - Attack version of Y1P-25
SPECIFICATIONS (Y1P-25)
Span: 43' 10.25"
Length: 29' 4"
Powerplant: Curtiss V-1570-57 "Conqueror" with G.E. form F-2G supercharger, 625 bhp at 2450 rpm at 20,000 ft.
Armament: Two .30 .cal. machine guns firing through the propeller, one .30 cal. gun aft.
Max. Speed: 247 mph
Aircraft crashed before completion of altitude and range tests
Detroit-Lockheed YP-24
An experimental pursuit plane, a two-place, low-wing fighter, with retractable landing gear. Designed by Detroit Aircraft Corporation engineer Robert J. Woods. Metal-skinned fuselage built in Detroit and wooden wing plus final assembly done at Lockheed Aircraft Corporation in Burbank, California. Termed by Lockheed the XP-900.
Completed in 1931, and sent to Dayton, Ohio for testing on 29 September 1931. Air Corps contracted for 5 Y1P-24s and 5 YA-9s (attack bomber version), but they were never completed, as Detroit-Lockheed went bankrupt in 1931. Designer Woods went with Consolidated Aircraft in Buffalo, NY which continued styling in a new ship designated the Y1P-25, further continued as the P-30 and P-30A.
The original and only YP-24 was destroyed on 19 October 1931 after the landing gear malfunctioned (wouldn't extend) and the pilot was forced to bail out.
Detroit-Lockheed YP-24
TYPE - YP-24 / Y1P-24
Number Built/Converted - 10
Remarks - low-wing, two-place monoplane project cancelled
SPECIFICATIONS
Span: 42' 9.25"
Length: 28' 9"
Powerplant: Curtiss Conqueror V-1570-23 of 602 hp.
Armament: One .30 .cal. and one .50 cal. machine gun firing through the propeller, one .30 cal. gun aft.
Max. Speed: 214.5 mph
Service Ceiling: 26,400 ft.
Range: 556 miles
Serial Number: 32-320
Consolidated P-30
PB-2
The P-30 was the first production aircraft ordered by the Army Air Corps with retractable landing gear, an enclosed and heated cockpit (for the pilot), and an exhaust driven turbo-supercharger. After the loss of the Y1P-25 (S/N 32-321), the Army ordered four improved examples and designated the aircraft P-30 (S/N 33-204 - 33-207). These aircraft were used for evaluation. The gunner in the rear cockpit was prone to black-out during sharp turns or dive recovery, but the Army was sufficiently pleased with the aircraft to place a production order for 50 aircraft on 6 December 1934.
The production aircraft (S/N 35-1 thru 50) were initially designated P-30As, but were later reclassified as PB-2As (Pursuit, Bi-place). The retractable landing gear was manually operated by the pilot through a hand crank located in the cockpit. The fixed-pitch propeller of the P-30 was replaced with a Curtiss Electric constant-speed propeller in the P-30A.
TYPE- P-30 P-30A
Number Built/Converted -450 Remarks - Improved Y1P-25; became PB-2 Improved P-30; became PB-2A
P-30 A
SPECIFICATIONS (P-30A)
Span: 43' 11"
Length: 30' 0"
Height: 8 ft. 3 in.
Powerplant: Curtiss V-1570-61 with G.E. form F-3 supercharger of 700 hp. at 15,000 ft.
Armament: Two .30 .cal. machine guns firing through the propeller, one .30 cal. gun aft.
Max. Speed: 274.5 mph at 25,000 ft. and 255.5 mph at 15,000 ft.
Cruising Speed: 215 mph
Service Ceiling: 28,000 ft.
Weight: 4,306 lbs. empty/5,643 lbs. (max.)
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