ZPG-2 / ZPG-2W "N" Series
The ZPG-2 was intended for antisubmarine warfare (ASW) patrols of 2-3 days duration, while the modified ZPG-2W was designed for all-weather airborne warning (AEW) missions. These airships were used for Airborne Early Warning and carried a 40 ft. diameter search radar antenna inside the envelope and had a radome on top of the envelope. Twelve were ordered. The engines were located inside a double-deck car. They first flew in March 1953.
The control car was 83 feet long and 11 and one-half feet wide, and was divided into two levels. The upper deck had comfortable bunks and a wardroom equipped with a modern galley. The lower spaces housed the operational part of the car. This was where all the controls for flying the airship, as well as the equipment necessary to perform the mission assigned, were located.
One of the characteristics of the Navy's non-rigid airships over the years had been the letter-class identification of "N" for non-rigid. It is fitting that the story of the last airships operated by the Navy were initially given the class designation of "N."
The success of the K-class airships in WW II ASW operations diminished the need for the much improved M-class of the late WWII period, only four of which were built. Following the war, it was clear that the improved versions of the K ships could handle many LTA tasks. However, with the installation of radar, towed sonar and other new ASW systems, in addition to the need for greater patrol ranges, there was a need for ships larger than the M-class. In 1947, the Bureau of Aeronautics initiated a design competition for a larger ASW airship to incorporate the new requirements. Goodyear and Douglas were contenders. The Navy purchased the Douglas design, but subsequent arrangements led to Goodyear building the new Nan ship.
Initial go-ahead in 1948 covered design engineering, mock-up and a ground test propulsion system. Two Wright R-1300-2 air-cooled engines, mounted in the car, drove two reversible-pitch propellers on outriggers, with clutches and transmissions so that either engine could drive both propellers, or use both engines. While this work proceeded, the contract for the ZPN-1 prototype was signed. It would be the largest nonrigid airship built, with an 875,000-cubic-foot envelope, a double-deck car with ample provision for the 14-man crew, extensive ASW equipment and in-flight refueling capability for extended operations refueled by accompanying Navy ships.
In January 1950, the ground test rig was running, but even this lead wasn't enough when transmission difficulties encountered later in the year delayed the first flight into 1951. Meanwhile, production versions were ordered as the ZP2N-1, which had many improvements, including a larger envelope of 1,011,000 cubic feet. The ground rig resumed running in early 1951, with power plant installation in the N-1 in April, and first flight in June. It was soon realized that the ballonets would have to be replaced because of fabric characteristics, but this was postponed until after the Board of Inspection and Survey (BIS) trials. Late in 1950, flight testing was interrupted for modifications, including increased fin strength and reduced control system friction.
Four fins called "ruddervators" were used to control ZPG-2/. They are unique in that they were positioned at 45 degree angles at the stern of the craft rather than the traditional vertical/horizontal 90 degree positions. The purpose behind the "X" configuration was to provide more ground clearance between the stern of the envelope and the ground during takeoff and landing operations. As with heavier-than-air craft, lighter-than-air craft of the ZPG-2/2W type, which were normally flown "heavy", took off and landed in a raised nose, lowered tail configuration. Because of the craft's length of approximately 350 feet, the "X" configuration was absolutely necessary. Throughout the entire maneuvering envelope this configuration provided superb responses to control inputs. Contrary to previous airship cockpit configurations, which commonly had the aircraft commander in the left seat controlling the elevator and the co-pilot (rudder man) providing rudder control, a yoke control column was provided for each pilot position. Elevator control was the normal "push-pull" on the yoke, while rudder control was through the control wheel. A rather unique feature of this control system is that any single or multiple control input, such as down elevator or down elevator combined with a turn signal, used all four control surfaces at the same time. The degree of travel of the individual surfaces varied according to the amount of single or multiple inputs. To help ease the pilots' workload, a "spring" or "Flettner" tab is installed on each of the control surfaces which automatically moves in the opposite direction of its control surface thus providing additional "boost" to the control system.
Early 1952 saw final solution of the fin design problem, with tail surfaces further modified for final tests at Akron, followed by June delivery to Lakehurst, and Navy Preliminary Evaluation (NPE) in July. The NPE results were disappointing, particulary in the airship's performance and further tests followed to explore specific improvements.
Meanwhile the first production ZP2N-1 was approaching completion and an AEW version of the N-type, the ZWN-1, was begun. Activity came to a halt at Goodyear during a fall strike, and the first ZP2N-1 did not fly until May 1953. By this time the ZWN-1 had been redesignated ZP2N-1W, a prototype ordered, and first flight scheduled for September 1954. It would feature larger radar antennas inside the envelope than could be mounted externally without excessive drag.
Lakehurst operations with N-1 and flight testing of the ZPPN-1 at Akron continued through spring, summer and into fall. Mock-up inspection of the -1W took place in May. While the flights of N-1 showed the potential of the N, they also confirmed the need for the larger envelope, as in the case of the ZP2Ns. In November, N-1 was deflated for the ballonet replacement, and was subsequently overhauled and rebuilt with a larger 975,000-cubic-foot envelope.
After a delay to correct a transmission problem, the first ZP2N-1 was delivered to Lakehurst late in the year for Navy trials. A ballonet failure, due to overpressurization in January 1954, required corrective action to the pressure system, but the fourth ZP2N-1 was delivered that month. Spring saw the first APS-20B installation in the fifth ship, with BIS trials of the new radar at Lakehurst. The airships were also redesignated at about this time, with the Ns becoming ZPGs. The ZP2N-1 and 1W became ZPG-2 and 2W, respectively. The first fully-equipped ZPG-2 was delivered from Akron to the fleet for operational use in July.
In May 1954 a ZPG-2 airship under Commander Marion Eppes departed NAS Lakehurst for an endurance flight which took her north to Nova Scotia, east to Bermuda and then south to Nassau, the Caribbean Sea and the Gulf of Mexico. The airship landed at NAS Key West on May 25 with.an elapsed time of 200.1 hours or more than 8 days in the air. It was a notable achievement and Cdr. Eppes was awarded the Harmon International Trophy for his achievement. At about this time, the Chief of Naval Operations ordered a series of tests to evaluate the all-weather, continuous-patrol capabilities of the airship. These features were of particular concern during the 1950s because the U.S. was seeking a reliable, high-endurance AEW platform which could detect incoming enemy bombers.
BIS trials of the ZPG-2 were completed in December 1954, and ZX-11 began extended operational trials early in 1955, while another ZPG-2 went to Naval Air Development Unit, South Weymouth, Mass., for all-weather tests with emphasis on extreme winter-weather conditions. The first flight of the ZPG-2W early in the year coincided with increased interest in the use of nonrigid airships as part of the national early warning network.
With these tests completed successfully, the drama involving the final phase of the tests, a long-distance flight, took center ring. The Navy was out to do nothing less than break the long-distance record set by the German rigid airship Graf Zeppelin in 1929, when she flew nonstop from Friedrichshafen, Germany, to Tokyo, Japan, a distance of 6,980 miles, without refueling. There had not been a transatlantic airship flight in 12 years.
The long-distance flights had their origins in the early fifties when the Navy's LTA advocates were struggling to prove the capabilities and suitability of airship operations in a modern and fast-moving Navy. The success of the airship in WW II had been eclipsed by the new advances in fixed-wing aircraft. Thus, it was thought necessary to demonstrate anew the capabilities of the airship platform to prove it could perform the duties required for ASW and AEW operations. These requirements were accentuated by the growing need for a reliable airborne platform which could operate around the clock in all types of weather.
The crew of the Snow Bird (the name of the ZPG-2 airship used in the long-distance flight) was a specially selected group of volunteers. The pilot in command was Commander Jack R. Hunt, supported by two copilots, Commander Ronald W. Hoel and Lieutenant Commander Robert S. Bowser. Extensive preparations had been made for the flight. Fuel consumption was carefully calculated and graphically plotted. Every item taken aboard was carefully weighed to ensure the ZPG-2 airship would be within the weight limits necessary for correct fuel consumption and lift rate.
On Monday, March 4, 1957, at 1832 (EST) Snow Bird lifted off from Naval Air Station, South Weymouth for her epic-making flight. The record for continuous non-refueled flight was 200 hours and 12 minutes aloft. Snow Bird officially eclipsed this record at 0245 (EST) on March 13, and broke a second record later that day. The distance record established by the German airship Graf Zeppelin in August 1929 fell when Snow Bird passed the 6,980-mile mark in her tricontinental journey. Snow Bird continued her flight, having established two new world records. On March 15, 1957, at 1844, Snow Bird landed at NAS Key West. The voyage took 264.2 hours and covered a distance of 9,448 miles. No airship of any type had ever flown that far or remained aloft that long without refueling. For his contributions as commander and pilot of Snow Bird's record flight, Cdr. Hunt was awarded the Harmon International Trophy on November 12, 1958. The award was presented to him by President Eisenhower. Three years later, one flew for 264 hours (11 days).
|Powerplant||Two 800 hp Wright Cyclone 7 engines|
|Volume||1 million cubic feet|
|Max speed||80 mph|
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