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The Grumman AF Guardian

v1.0.2 / 01 dec 03 / greg goebel / public domain

* One of the Cold War's more obscure aircraft was the Grumman "Guardian", a carrier-based antisubmarine warfare (ASW) aircraft, or to be more precise a pair of them, that served with the US Navy in the 1950s. The Guardian has been overshadowed by its famous predecessor, the Grumman TBM/TBF Avenger, and its well-known successor, the Grumman S2F Tracker. This document provides a short history of the Guardian.



* In 1942, the US Naval Bureau of Aeronautics asked the Grumman company about a possible successor to the company's highly successful Avenger torpedo bomber. Further discussions led Grumman to initiate development of such a replacement in 1944, to be designated "XTB2F-1". The XTB2F-1 would eventually lead to the Guardian, but through a convoluted path.

The initial concept for the XTB2F-1 was for a multi-seat, carrier-based torpedo bomber with twin Pratt & Whitney (P&W) R-2800-22 Double Wasp radial engines. The XTB2F-1 would be able to carry up to 3,600 kilograms (8,000 pounds) of bombs or torpedoes, and would have an extremely long range of up to 5,950 kilometers (3,700 miles). Unfortunately, the XTB2F-1 proved far too ambitious, as the design was simply too big and heavy to be flown off most of the US Navy's aircraft carriers. The XTB2F-1 was cancelled in January 1945 in favor of a more conservation option, a derivative of the Grumman F7F Tigercat twin-engine fighter designated the "XTSF-1".

Grumman had also been working on a third design, with the company designation "G-70", for several months, and the Navy found the G-70 attractive. In February 1945 the service decided to abandon the XTSF-1, awarding a contract to Grumman for three G-70 prototypes, with the Navy designation "XTB3F". Two of the prototypes would be "XTB3F-1s" and the third would be an "XTB3F-2". They were to be "mixed-power" aircraft, with a P&W R-2800-6 Double Wasp, providing 1,715 kW (2,300 HP) and fitted in the nose; plus a turbojet fitted in the tail, fed by oval intakes in the leading edges of the wings. The turbojet was to be used to provide additional power for takeoffs and combat emergencies.

The XTB3F-1 would be fitted with a Westinghouse 19XB-2B turbojet, while the XTB3F-2 was to be fitted with a with a Westinghouse 24C-4B turbojet. The two aircraft were otherwise similar, featuring a crew of two, sitting side-by-side; a warload of up to 1,800 kilograms (4,000 pounds) of bombs, torpedoes, or rockets; and twin fixed forward-firing 20-millimeter cannon.

* The initial XTB3F-1 prototype flew on 19 December 1945, with Grumman test pilot Pat Gallo at the controls. The turbojet intakes were masked off because of problems encountered in ground tests, and in fact the jet engine proved to be a bad idea and was quickly removed without ever being used in flight.

On 24 December, the Navy decided that they no longer needed a new torpedo bomber and told Grumman that they wanted an ASW aircraft instead. There was no way at the time to cram all the necessary ASW gear into a single aircraft, and so two variants of the "Guardian", as it was named, were planned, with the pair to act as a "hunter-killer" team.

The two unbuilt prototypes were modified towards this end. The single XTB3F-2 prototype was built as the "hunter" member of the team, without the Westinghouse turbojet engine, but with two more seats for radar operators plus a large ventral radome fitted where the bombbay had been, accommodating AN/APS-20 ocean search radar. This aircraft became the "XTB3F-1S" and first flew in November 1948.

The second XTB3F-1 prototype was built as the "killer" member of the team, retaining the bombbay but deleting the cannon, adding a third seat, and being fitted with a searchlight and short-range radar. This aircraft became the "XTB3F-2S" and first flew in January 1949, with both aircraft performing naval flight tests in February.

By this time, the Guardian had already been ordered into production. The XTB3F-1S "hunter" was built as "AF-2W" (originally "AF-1S"), and the XTB3F-2S "killer" was built as the "AF-2S". The first production AF-2S Guardian flew on 17 November 1949. Qualification trials were conducted from May 1950 through November 1951, with the first operational aircraft going into service in October 1950.



* The Guardian was a brute of an aircraft, said to be the biggest single-engine piston aircraft ever flown by the US Navy. It was driven by a P&W R-2800-48W Double Wasp radial engine, providing 1,790 kW (2,400 HP) to a big four-bladed propeller.

The aircraft was a "taildragger", with a stinger-type arresting hook aft of the tailwheel, and wide-span mid-mounted wings that folded back towards the tail in classic Grumman fashion, outside of the main landing gear. The tail was of conventional configuration, except for secondary vertical "finlets" mounted a little beyond the midpoint of each horizontal tailplane.

The AF-2W "hunter" member of the team had a crew of four and was unarmed, though it could carry underwing drop tanks, and had a large radome for the AN/APS-20 search radar mounted on the belly under the cockpit. The finlets were to provide lateral stability, which was affected by the radome. 153 AF-2W Guardians were built.

The AF-2S "killer" member of the team had a crew of three and could carry up to 1,800 kilograms (4,000 pounds) of munitions, including depth charges, bombs, or a homing torpedo in the bombbay, plus 12.7 centimeter (5 inch) "high velocity air rockets (HVARs)" mounted on underwing pylons. It could also drop sonar buoys. The AF-2S mounted AN/APS-30 targeting radar in a pod under the right wing and a searchlight in a pod under the left wing. The AF-2S retained the tail finlets, though whether they were actually necessary or were simply there to ease production is an interesting minor question. 193 AF-2S Guardians were built.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                18.5 meters         60 feet 8 inches
   wing area               51 sq_meters        549 sq_feet
   length                  13.2 meters         43 feet 4 inches
   height                  4.93 meters         16 feet 2 inches

   empty weight            6,615 kilograms     14,580 pounds
   max loaded weight       11,340 kilograms    25,000 pounds

   maximum speed           507 KPH             315 MPH / 275 KT
   service ceiling         9,900 meters        32,500 feet
   range                   2,415 kilometers    1,500 MI / 1,305 NMI
   _____________________   _________________   _______________________

A second version of the AF-2S hunter was built beginning in 1952, featuring "magnetic anomaly detector (MAD)" gear with a boom on the right side of the fuselage. This variant was designated the "AF-3S", and 40 were built. The last Guardian was rolled out in March 1953, with a total of 389 of all variants built, including the prototypes.

Although the Guardian conducted war patrols in Korean waters from March 1951 through May 1953, it did not remain in service for much longer. It was an interim type, as the Navy had issued a request for what would become the more capable and much more long-lived twin-engine Grumman S2F Tracker even before the Guardian entered operational service.

The Tracker quickly replaced the Guardian, and the last Guardian was retired from formal service on 31 August 1955. A number of Guardians ended up in civilian hands and were apparently used as "water bombers", and some of these aircraft are now on static display in museums. For example, one AF-2S is on show at the Naval Aviation Museum in Pensacola, Florida. Whether any Guardians remain flying is unclear.



* Although the Guardian isn't a particularly significant aircraft, I've been curious about it for a long time. I recall seeing it in books even when I was a kid, and both its relative obscurity and the interesting idea of building two different variants of the same aircraft as a "hunter-killer" team provoked my curiosity.

When I actually came across a little information on the Guardian, I decided to write up notes on it as a "knock-off" and to satisfy my curiosity about it. Given the thin sources on the subject, I was surprised to be able to assemble a minimal but reasonably complete and detailed discussion of it with little effort. There's a book on the aircraft out there, from the excellent NAVAL FIGHTERS series, but for the moment that seems like more than I want to know.

* Sources include:

* Revision history:

   v1.0   / 01 dec 00 / gvg
   v1.0.1 / 01 dec 01 / gvg / Minor changes & cleanup.
   v1.0.2 / 01 dec 01 / gvg / Minor changes & cleanup.
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