Navy Patrol Flying Boats, 1920-1932
PN-7, NAF TF, PN-8, PN-9, PB-1
When the Navy entered World War I it had only six flying boats; by Armistice Day 1,172 were on hand, most of them single-engine HS types. After the German U-boats were gone, so was the reason, it seemed, to build any more patrol planes, although millions were invested in new battleships, with their tall basket masts and armored turrets. It was a decade before new flying boats were built in quantity.
The twin-engine biplane pattern of the H-12, H-16 and F-5 established a tradition for Navy flying boats. There were 347 HS, 106 H-16 and 172 F-5L boats on hand July 1, 1921, and by June 30, 1925, the Navy’s aging patrol force consisted of 44 F-5L and 33 H-16 twin-engine boats, 40 single-engine HS-2s, and 80 assorted unserviceable airframes of these types. Fortunately, the Naval Aircraft Factory was developing a new series of flying boats to relieve the spruce framework of these antiques. The first improvement needed was metal hulls instead of the wooden surfaces so threatened by salt water and waves.
Since private industry was not expected to risk the capital investment required to develop advanced patrol planes, the Naval Aircraft Factory built 13 trial flying boats. The first two were authorized in January 1923 and designated PN-7, for Patrol, Navy, the 7 following redesignation of the wartime F-5 and F-6 as PN-5/6.
Traditional wood and fabric biplanes, the PN-7s had a modified F-5 hull and new 72-foot 10-inch span wings with the USA-27 airfoil and only one pair of interplane struts on each side. Two 525-hp Wright T-2 Tornado inline engines and two-bladed propellers were mounted in streamlined nacelles, with the water radiators hanging from the upper wing. A crew of five, four 230-pound bombs, and four Lewis guns were carried.
The first PN-7 was tested at Philadelphia in November 1923, and delivered in January 1924, but the second was not accepted until August. The next pair of Navy boats were built with lighter metal hulls and a new tail. The first, A-6799, flew on March 19, 1925, as the PN-8 with Wright T-3 engines, while the second, A-6878, was tested in April as the PN-9 with 525-hp Packard lA-1500 engines behind large water radiators and increased fuel capacity for a proposed flight to Hawaii.
The PN-8 was soon converted to PN-9 configuration, and on August 31, 1925, both PN-9s took off for the first attempt to fly from San Francisco to Hawaii. While A-6799 was soon forced down, the A-6878’s fuel lasted over 25 hours; long enough to cover 1,841 miles against head winds and set a world’s distance record, but after it ran out of fuel, the PN-9 came down at sea some 360 miles short of Pearl Harbor. Then the metal hull demonstrated good flotation qualities, keeping the five-man crew safe for ten days, until they reached the islands using sails improvised from the wing’s fabric covering.