TECHNICAL SPECIFICATIONS (PN-7 [PN-12]) Type: Five to six- place patrol flying boat.
Manufacturer: Naval Aircraft Factory, Philadelphia, Pennsylvania. Total produced: 8 (USN)
Powerplants: Two 525-hp Wright T-2 12-cylinder water- cooled engines driving two- bladed wooden fixed- pitch propellers [two 525-hp Wright R-1750D 9-cylinder air- cooled engines driving three- bladed ground- adjustable metal propellers].
Armament: One flexible .30-caliber machine gun in the bow, one flex- ible .30-caliber machine gun amidships, and up to four 230-lb. bombs carried under lower wing.
Performance: Max. speed 105 mph [114 mph]; ceiling 9,200 ft. [10,900 ft.]; range 655 mi. [1,310 mi.].
Weights: 9,637 lbs. [7,699 lbs.] empty, 14,203 lbs. [14,122 lbs.] loaded. Dimensions: span (upper) 72 ft. 10 in., length 49 ft. 1 in. [49 ft. 2in.],
wing area 1,217 sq. ft.
The PN series represented a cumulative effort on the part of NAF and BuAer from 1924 to 1928 to develop and test con- cepts for a new type of patrol flying boat that would replace the Navy’s World War I–era fleet of wooden- hulled PN-5s and PN-6s. Construction of the first of the series, the PN-7, was begun during 1923; the first was completed in January 1924 and the second in June. While it retained the wooden hull of the PN-5, the PN-7 incorporated an entirely new set of single- bay biplane wings of fabric- covered, metal construction that utilized
The NC-4 became the most famous of the series when it com- pleted the first flight across the Atlantic Ocean on May 31, 1919. It is preserved today at the Naval Aviation Museum in Pensacola, Florida.
Naval Aircraft Factory PN-9
a much thicker section USA 27 airfoil in place of the RAF 6 of the PN-5. The increase in lift permitted a significant reduction in both wingspan and area, plus the strength resulting from the deeper wing spars required only one bay of struts outboard the engines. In place of the old Liberty engines, experimental Wright T-2 powerplants were tractor- mounted in neat, streamlined nacelles with the water radiators slung under the upper wing center section. Tri- als conducted during 1924 indicated vastly im- proved performance over the PN-5; however, the Wright engines proved to be unreliable, and BuAer officials expressed concerns over the long- term durability of the wooden hull.
Based upon experience gained with the PN-7, the first of two PN-8s ordered was deliv- ered in January 1924 with a duraluminum hull identical in shape to the Porte- type sponson hull and was flown with Wright T-3 engines. Other changes included a longer- chord fin and rudder, plus horizontal tail surfaces possessing a thicker airfoil section. The second example, de- livered in May 1925 as the PN-9, was tested with 480-hp geared Packard 1A-2500 V-12 en- gines behind large water radiators; soon after- ward, the PN-8 was converted to the Packard engines and re- designated PN-9. In company with the metal- hulled Boeing XPB-1 (see below), the Navy planned to use both PN-9s to attempt the first flight from the California coast to Hawaii. As events turned out, however, only the second PN-9 was deemed ready for the 2,410-mile flight, and it departed San Francisco on August 31, 1925. Twenty- eight and a half hours and 1,841 miles into the flight, the PN-9 was forced to land in the ocean approximately 560 miles from Hawaii due to fuel exhaustion. The seaworthiness of its metal hull was aptly demonstrated after the crew, using fabric panels detached from the lower wings, sailed the air- craft the remaining distance to the islands. De-
Left, top: Although the hull was similar to H-
16/F-5L, the PN-7 introduced a shorter span, single-bay wing having a much thicker airfoil section, and new engines producing 25 percent more power. Middle: PN-9 no. 1 after being forced to land at sea between California and Hawaii due to fuel exhaustion in August 1925, used fabric from the wings and sailed the remaining 560 miles to Pearl Harbor over a 10-day period. Bottom: The Wright Cyclone- powered, metal-hulled PN-12 depicted in this photograph became the patrol boat pattern for the Douglas PD, Hall PH, Keystone PK, and Martin PM.
spite the shortfall, the flight still attained recognition for a new seaplane distance record.
Given the success of the PN-9s, BuAer ordered four essentially identical PN-10s, two of which were delivered in late 1926. During trials carried out during 1927, the two PN-10s went on to establish new seaplane records for distance, speed, and payload. Due to the air- cooled engine policy implemented by BuAer in 1927, NAF was directed to complete the other two PN- 10s with different radial engine types under the new designation PN-12. The first, equipped with Wright R- 1750 Cyclone engines, was delivered in December 1927 and the second, with Pratt & Whitney R-1690 Hornets, arrived in June 1928. In May 1928 the first PN-12 set a new seaplane record when it carried a payload of 2,205 lbs. (1,000 kg) over a distance of 1,242 miles (2000 km) at an average speed of 80.5 mph (130 kph). Once BuAer settled on the Wright- powered PN-12 as the pattern for the Navy’s new generation of patrol boats, aircraft com- panies were invited to submit proposals and, over a two year interval, contracts awarded to four different air- frame contractors. (See Douglas PD, Hall PH, Martin PM, and Keystone PK, below.)
Boeing PB—1925
TECHNICAL SPECIFICATIONS (XPB-1) Type: Five- place patrol flying boat.
Manufacturer: Boeing Airplane Co., Seattle, Washington. Total produced: 1 (USN)
Powerplants: Two 800-hp Packard 2A-2540 12-cylinder water- cooled engines driving four- bladed wooden fixed- pitch propellers.
Armament: (None installed.)
Performance: Max. speed 125 mph, cruise 80 mph; ceiling 3,300 ft.; range 2,230 mi.
Weights: 12,742 lbs. empty, 26,822 lbs. loaded.
Dimensions: span 87 ft. 6 in., length 59 ft. 5 in., wing area 1,823 sq. ft.
Ordered by BuAer in 1925, the XPB-1 was essen- tially a scale- up of the NAF PN-7 (see above) incor- porating an all- metal two- step, aluminum hull together with a unique tandem arrangement for its two Packard engines. Originally, the Navy had contemplated using the XPB-1 to lead two NAF PN-9s on the first flight at- tempt between the California coast and the Hawaiian Islands. Although the XPB-1 made it first flight on Au- gust 31, 1925, persistent problems with the Packard en- gines caused its participation in the California- Hawaii trip to be cancelled. The XPB-1 was thereafter retained by NAF as a testbed, and during 1928, once BuAer had officially switched to a preference for air- cooled engines in Navy aircraft, it was re- designated XPB-2 after being modified and tested with 500-hp Pratt & Whitney R-1690 Hornet radial engines, also mounted in tandem, but no production was undertaken.
Boeing PB-1
The PB-1, when it appeared in mid–1925, was the first type of naval patrol boat to be built with an all-metal hull. The single prototype spent most of its career with NAF as a flying testbed.
Sikorsky PS-1 (S-36)—1927
TECHNICAL SPECIFICATIONS Type: Eight- place patrol amphibian.
Manufacturer: Sikorsky Aero Engr. Co., Bridge- port, Connecticut.
Total produced: 5 (USN)
Powerplants: Two 225-hp Wright J-4 9-cylinder air- cooled engines driving two- bladed ground- adjustable metal propellers. Performance: Max. speed 110 mph; ceiling 15,000
ft. (est.); range 200 mi.
Weights: Empty (not reported); 6,000 lbs. loaded. Dimensions: Span 56 ft., length 34 ft., wing area
(not reported).
Sikorsky’s second flying boat design, the company model S-36, was flown and tested during 1927 with far better success than the short- lived S-34 of 1926. While sharing the S-34’s general design concept, the S-36 pos- sessed more wing area and featured a sesqui-
plane layout having the wing floats mounted below the bottom wings. Another difference was an upper wing positioned higher over the fuselage to permit the engines and nacelles to be mounted below it. The first S-36 was flown with open cockpits
but subsequent versions came with a raised cockpit enclosure and cabin that blended into the rear of the hull. Of five S-36s known to have been built, one was sold to the Navy for evalu- ation purposes in 1927 or 1928 as the XPS-1.
Sikorsky PS/RS-2 and -3
(S-38), and RS-1 (S-41)—1928
TECHNICAL SPECIFICATIONS (RS-3 [RS-1]) Type: Ten- to twelve- place patrol and utility amphib-
ian.
Manufacturer: Sikorsky Aero Engr. Co. (later Sikorsky Aviation Div. of United Aircraft Corp.), Bridge- port, Connecticut.
Total produced: 9 (USN, USMC)
Powerplants: Two 420-hp Pratt & Whitney R-1340 Wasp [575-hp Pratt & Whitney R-1690-34 Hor - net] 9-cylinder water- cooled engines driving two- bladed ground- adjustable metal propellers. Performance: Max. speed 124 mph [133 mph], cruise
109 mph [115 mph]; ceiling 18,000 ft. [13,500 ft.]; range 600 mi. [575 mi.].
Weights: 6,548 lbs. [8,100 lbs.] empty, 10,479 lbs. [13,800 lbs.] loaded.
Dimensions: span 71 ft. 8 in. 78 ft. 9 in.], length 40 ft. 5 in. [45 ft. 2 in.], wing area 720 sq. ft. [790 sq. ft.].
Sikorsky’s first real commercial success, the amphibious S-38, made its first flight on June 25, 1928. It was a thirty percent scale- up of the S-36 having twice the horsepower and three times the range. In order to maintain similar proportions, the engines were suspended from the upper wing on struts and the wing floats were lowered. After 11civil versions had been sold as the S-38A, two examples were acquired by the Navy in late 1928 to be evaluated as the XPS-2.
Sikorsky XPS-1
The first Sikorsky amphibian tested by the Navy in 1928, the S-36 was initially eval- uated in the armed patrol role as the XPS-1.
The major production variant, the S-38B, was introduced in late 1928 with slightly more powerful Wasp engines and greater fuel capacity, and over 100 had been delivered to civil operators by end of 1932. Four S-38Bs were procured by the Navy between 1929 and 1932 and taken into service under the designation PS-3. In 1933, after removing the gun positions in the bow and stern, BuAer reclassified the PS-2s and -3s as transports under the designations RS-2 and -3, respectively. One RS-3 was assigned to the Marine Corps and used at Quantico and in Nica - ragua until 1935.
Though outwardly resembling the S-38, the S-41 of 1931 was actually ten per- cent larger and could lift an almost 50 per- cent greater useful load. Besides a five- foot lengthening of the hull plus bigger, fully cowled Hornet engines, the S-41 dis- carded the lower sesquiplane layout of the S-38 for a single upper wing having ten percent more area. The first three went to commercial users, then in 1933, three were acquired by the Navy as RS-1 utility am- phibians, one subsequently being assigned to Marine Corps squadron VO-9M in Haiti. All RS-1s, -2s, and -3s were phased out of service during the mid–1930s.
Left: RS-2 and -3 were derived from the S-38. This RS-3, assigned to the Marine Corps in 1931, was based in Quantico and saw
service with expeditionary forces in Nicaragua. Right: The RS-1 was based upon the slightly larger S-41. Photo depicts one of three RS-1s delivered to the Navy in 1933. Note cowl rings and absence of lower sesquiplane wing.