Achieving maximum strength at minimum weight.
During the Golden Age of flight, many new aviation firms sprang up. By far the greater percentage failed within their first few years. The reasons vary. In some instances, the whole company was actually a scam from the start, an attempt during the stock-boom days of the 1920s to raise money from a gullible public without regard to a viable design. In other cases the competition was simply too strong.
Even some relatively established companies, such as Berliner-Joyce and Great Lakes, survived only briefly. Thus it is even more amazing that the small Hall Aluminum Aircraft Company could endure for 15 years before being folded in a friendly fashion into Consolidated Aircraft. During that 15-year period, the company produced only 29 planes in a wide range of types that included an innovative personal plane, Navy fighters, a superb-looking torpedo bomber and the largest American biplane flying boat since the Curtiss NC-4: the four-engine Hall Aluminum XP2H-1, an elegant anachronism that combined advanced structural ideas in an antiquated configuration.
Long before weight-reduction programs were commonplace, Charles Ward Hall was determined to reduce plane weight by every means possible. He came by his interest in aluminum naturally: His father, Charles Martin Hall, had invented the process for mass manufacture of aluminum (he founded the firm that became Alcoa).
The younger Hall founded his own company in 1927 after completing two projects that apparently whetted his interest in flying: a small sailboat, on which he rigged a wing from a surplus Thomas-Morse to a novel pivoting mast; and the Hall Air Yacht, a grandly named two-seat flying boat powered by a 3-cylinder 60-hp Wright Gale engine. The hull, lower wing, tail booms and tail unit were made of aluminum, but the plane’s 25-foot span upper wing was conventional wood and fabric. The Air Yacht’s empty weight of 520 pounds took it out of the ultralight class, but it performed sufficiently well to convince Hall that aircraft manufacturers in the future would use aluminum as the preferred structural material.
Charles Ward Hall Incorporated began its long association with the U.S. Navy with a contract to build an aluminum version of the wooden wing used on the Curtiss HS-3 flying boat. The wooden version of the wing weighed 1,314 pounds, while Hall’s aluminum version weighed only 851 pounds but was just as strong. That success inspired the Navy to give him a contract for an aluminum version of the Navy’s diminutive TS-1 fighter, designed by the Naval Aircraft Factory specifically for use on board the Navy’s first carrier, Langley. Curtiss won a contract to build 34 TS-1s, all using the new Lawrence J-1 radial engine.
Hall redesigned the TS-1 as an all-aluminum aircraft. Two were built by Curtiss as the Curtiss Hall F4C-1. Slightly altered in the wing layout, the aluminum version weighed 300 pounds less than its wooden siblings.
The Navy awarded Hall two new contracts. One was for the XPH-1, an all-aluminum version of the standard Navy patrol boat. The configuration was both antiquated and ubiquitous; the Naval Aircraft Factory PN-7 design had led to a long series of basically identical aircraft built by the NAF, Douglas, Hall, Keystone and Martin. There were two big differences in the Hall aircraft from all the others. The first was appearance—the Hall Aluminum PH-1 was considerably cleaner than any of the rest. The second was weight—the Hall version was much lighter. The heaviest of the lot, the NAF PN-9 had a maximum takeoff weight of 18,069 pounds compared to the Hall XPH-1’s featherweight 13,228 pounds. The XPH-1 made its first flight on October 29, 1929, and flew 288 hours before being static tested to destruction at the NAF in 1932.
The Hall performed significantly better in the air and on the water, and was rewarded with three contracts. The Navy bought nine as the PH-1s (Hall’s largest order ever), each costing a princely $53,778 (plus government-furnished equipment). The last one was surveyed in February 1941, with a total of 2,121 flight hours—an average of about 236 flight hours per year, not bad for the prewar days.
Unlike with any other peacetime U.S. military aircraft, the basic design was called back into production on two more occasions. The Coast Guard loved the airplane for its rough-sea handling qualities—it could take off in 5-foot waves in 17.7 seconds. It bought seven in 1936 as the PH-2, then purchased an additional seven as PH-3s in 1939, 10 years after the original Hall variation had been laid down. PH-3s flew well into World War II on antisubmarine patrol.
The second contract, for a fighter, was an altogether different proposition, an original aircraft that showed Hall’s penchant for structure rather than streamlining. Hall personally assessed each part, analyzing it statically and dynamically to ensure that strength was adequate while weight was at a minimum.
The XFH-1 looked fairly conventional except for the unusual manner in which its upper wing was swept back 6 degrees while the lower wings were swept forward 6 degrees—to improve forward visibility. The exterior was conventional, concealing the buoyant, water-tight fuselage. But it was the monocoque structure of the fuselage that set it apart. Hall had developed a variety of flanged closed aluminum tubing shapes. He used these extensively, concentrating two, three or four of the tubes as the load requirements dictated. These tubes were used extensively throughout the XFH-1 and all of Hall’s later aircraft.
In the XFH-1’s wing spar structure, the multiple tubes were cambered in such a way that the air-loads straightened—and strengthened—the spar. The wing drooped slightly on the ground, but was absolutely straight at its maximum flight loading. Much of the XFH-1 and other Hall products’ structure were conventional, with bulkheads built up of drawn sections, riveted and then reinforced with gussets and angles of steel.
The XFH-1 was tested at Anacostia from September 25, 1929, through February 3, 1930. It was not as fast as contemporary Boeing or Curtiss Navy fighters, obtaining a top speed of only 153 mph from its 450-hp Pratt & Whitney R-1340 engine. Yet it demonstrated the value of its watertight hull on February 18, 1930, when an engine failure forced a test pilot to land on the water. The flier didn’t have time to jettison the wheels (a feature Hall had thoughtfully included), and the impact resulted in some leaks. Even so, the fuselage was only about one-quarter full when it was recovered almost two hours later.
The Navy ordered the largest American flying boat since the Curtiss NC-4 on June 30, 1930. It was the Hall XP2H-1, a handsome biplane similar in appearance to the smaller British Short Singapore III. Four 600-hp Curtiss V-1570-54 engines were mounted in tandem pairs in a streamlined installation. With a maximum gross weight of 44,000 pounds, the XP2H-1 had a top speed of 139 mph, not bad for its size.
The XP2H-1 had all the Hall standard features of construction, including a hull that had been scaled up from that of the PH-1. Probably the largest single-bay biplane ever built, the XP2H-1 had a wingspan of 112 feet and used the Clark Y airfoil that Hall favored. The trapezoidal wing had a long center section with a chord of 185 inches, its outer panels tapering to 85 inches at the top. The wings had the typical Hall internal structure, and were covered with sheet metal and braced with struts and wires.
One unusual characteristic of the Hall series was the ailerons, which were mounted via a continuous hinge on the top surface of the wings, sealing them off for beneficial aerodynamic effect. An old friend of mine, Earl George, who worked on the XP2H-1, recalled that attaching the ailerons was a time-consuming, knuckle-slicing job.
The normal crew of six saw the pilot and co-pilot seated side by side in the enclosed cockpit. An open bow position was available for a bombardier and to aid with mooring operations. The navigation and radio equipment compartment was just behind the pilots, and behind this were Spartan living quarters for long flights. The flight mechanic was situated farther to the rear, with a complex set of controls to monitor the engines and the elaborate fuel tank system.
The first flight was almost a disaster. Experienced test pilot Bill McAvoy was at the controls when the aircraft pitched up on takeoff. He stop-cocked the controls, got the nose down and taxied back, to find that the elevator had been installed in reverse.
The XP2H-1 was delivered to the Navy on October 1, 1932, and proceeded to demonstrate a remarkable performance for a big biplane flying boat. With a full load of 3,360 gallons of gasoline, the optimized range was an amazing 4,560 miles. As the fuel was burned off, engines were shut down, and the final leg of an endurance flight was completed on two engines. The specification called for a 1,500-foot altitude capability with two engines out. The big plane could actually climb on just the two front engines, and easily maintained altitude on the two rear engines. With one engine out it could maintain 7,000 feet, quite a performance for the time given that the propellers were fixed pitch. (The two forward propellers had a left-hand rotation, while the two rear propellers rotated to the right.)
Its sea handling qualities were excellent, allowing the XP2H-1 to take off from 6-foot waves in 21.5 seconds. But the structure was not as strong as the Navy liked, which would have unfortunate results later. An unusual feature was an “auxiliary power unit,” a gasoline engine used to raise the anchor.
The XP2H-1’s day in the sun came in 1935, when it made a nonstop flight from Norfolk, Va., to Panama in 25 hours and 15 minutes. It was commanded by Lieutenant John S. “Jimmy” Thatch, who seven years later would make history in fighter aviation with his development of the Thatch weave.
Despite the record attempt, new monoplane flying boats were already demonstrating that the XP2H-1 was obsolete, and there were no follow-on orders. The aircraft was destroyed when it broke up after making an open-sea landing later in 1935. The handsome XP2H-1 was the very last in the long line of U.S. military biplane flying boats.
Charles Ward Hall died on August 21, 1936, in the crash of a lightplane he had designed and manufactured, the Monoped, so called because of its single main wheel landing gear. He missed seeing the first flight of the most beautiful airplane his company would create, the very advanced Hall Aluminum XPTBH-2. Built to a Navy specification that called for patrol, torpedo and bombing capability, the XPTBH-2 was a streamlined twin-float monoplane that featured a single huge tubular aluminum spar which supported all flight and sea loads. Two cantilever floats, derived from the standard Hall flying boat hull configurations, made it possible for the aircraft to drop a full-size destroyer-type torpedo.
McAvoy again served as the test pilot on the successful first flight of the XPTBH-2. It went through some minor modifications and was much appreciated for its 182-mph top speed when tested at Anacostia. Navy requirements had changed, however, and no additional XPTBH-2s were ordered. The aircraft was destroyed at the Naval Torpedo Station at Newport, R.I. Time had at last run out for Hall Aluminum, and the company accepted an offer from Consolidated for its assets and patents. Many Hall employees joined the new firm.
While no Hall Aluminum aircraft survives today, the ideas of Charles Hall live on not only in aircraft using aluminum structure but also in designs featuring new composite materials, in which maximum strength at minimum weight is still a goal.
Originally published in the September 2007 issue of Aviation History. To subscribe, click here.