The Naval Aircraft Factory TF (Tandem Fighter) was an American twin-engine flying-boat escort fighter first flown in October 1920.Green & Swanborough 1994, p.429 The aircraft originated from requirements drafted by the British Technical Committee in April 1918, after discussion approved the development of a long-range seaborne fighter capable of escorting Allied maritime reconnaissance sorties over the North Sea and Atlantic regions.
Development Following the armistice, the incentives to produce a fighter eventually deviated toward evaluating the prospective applications of a highly unique concept. Upon review of numerous proposals, the Aeronautics Division of the U.S. Bureau of Engineering referred recommendations to the Chief of Naval Operations in which to finalize approval of a submission by the Naval Aircraft Factory (NAF) with which to produce a pre-production series of four prototypes at an estimated construction cost of $84,680.
Accordingly, the NAF proposal consisted of a twin-engine flying boat which featured a hull design identical to that of the Curtiss NC-1, an armament of four flexible mounting Lewis machine guns, and four crew members. An egg-like nacelle atop the upper wing housed an additional pilot/gunner's position. Initially designated as Twin Fighter (TF), a review of the aircraft's dimensions showed that the wingspan was insufficient for a conventional two-engine layout. Thus, the Bureau of Engineering revised the engine configuration into a tractor/pusher combination mounted on the aircraft centerline. This change altered the designation from Twin to Tandem fighter. The TF was designed to incorporate two Curtiss-built Kirkham inline engines, however mechanical problems hindered the development of these power plants, so two Hispano Suiza engines were adopted instead.
Operational history Flight testing Construction of the four prototypes (serial numbers A-5576, A-5577, A-5578, and A-5579) began in August 1919. The first TF was completed on October 1, 1920, with the first flight taking place 12 days later. However, high throttle settings caused the engines to overheat, thus obliging the pilot to undertake an emergency landing at the mouth of the Delaware River. After a brief waiting period to allow the engines to cool, the aircraft was damaged upon collision with an ocean liner's wake during another takeoff attempt. Other problems noted during initial testing were stiff and erratic rudder control while the ailerons exhibited a tendency to roll in directions opposite to that of rudder control. While subsequent modifications to the tail section remedied the stability problems, the propensity of the engines to overheat at high RPM settings remained an ongoing hindrance to the testing procedure, not only causing several premature landings, but ultimately providing the most decisive factor in the TF's subsequent cancellation.
Cancellation In June 1921, the Trial Board appealed to the U.S. Navy Department for immediate termination of the project, arguing that:
The power plant defects in this plane can be overcome, but not those pertaining to its air worthiness and sea worthiness, unless the plane is largely redesigned. In view of the numerous defects in this plane, and its questionable utility, even though these defects were remedied, it is recommended that further experimental work on this plane be discontinued.
The Navy Department dismissed the recommendations as premature, arguing that plans to retrofit the second and third prototypes with enlarged radiators in conjunction with alternate engine types might elicit a more successful outcome. However, the specialized radiators failed to arrive for several months, thereby postponing the completion of both types to the midpoint of 1922. Furthermore, the test flight of the third prototype (A-5578) in July ended in another mechanical failure which destroyed the primary water tank, the resulting fragments of which in turn damaged the hull section and shattered the forward propeller. With little hope for any significant improvements in the allotted evaluation phase, the Trial Board issued another plea to the Navy Department on December 29, to which the latter immediately complied, issuing its formal cancellation of the TF project on January 11, 1923.
Specifications (A-5576)
Summary of Flight Trials (A-5576) - Oct. 1920 - Mar. 1921 No.DateTypeDurationCrew (pilot, observer)Notes110/13/20Generic Flight Trial30 min.Comm. Richardson, Lt. FlemingN/A210/13/20Speed Run20 min.Comm. Richardson, Lt. FlemingN/A310/13/20Speed Run45 min.Lt. Fleming, Lt. FellersEngines overheated410/13/20Speed Run0 min.Lt. Fellers, Lt. FlemingBoth bottom wings and pontoons destroyed on take-off510/21/20Speed Run1 hr. 5 min.Comm. Richardson, Lt. FlemingEngine head cowl installed610/22/20Speed Run20 min.Comm. Richardson, Lt. FlemingEngine head cowl removed 711/15/20Fully Loaded Test15 min.Lt. Fleming, Lt. FellersSlightly nose heavy at high speed811/18/20Speed Run35 min.Lt. Fleming, Mach. WestN/A91/19/21Evaluation of New Tail Section10 min.Comm. Richardson, Lt. FlemingImproved stability and control characteristics102/4/21Propeller Test15 min.Lt. Fleming, Mach. WestN/A112/4/21Propeller Test20 min.Lt. Fleming, Mach. West N/A122/7/21Propeller Test5 min.Lt. Fleming, Mach. WestSpinner on rear engine shattered, damaging port beam of tail.132/25/21Propeller Test20 min.Lt. Fleming, Mach. WestN/A143/1/21Propeller Test10 min.Lt. Fleming, Mach. WestN/A153/2/21Propeller Test20 min.Lt. Fleming, Mach. WestN/A163/5/21Propeller Test25 min. Cdr. Richardson, Lt. MacKennaN/AN/A3/5/21N/A0 min.N/AGasoline line to forward engine ruptured
RPM/Speed Readings Obtained During Flight Trials on Oct. 13, 1920 (A-5576) RPM (Tractor Engine)RPM (Pusher Engine)Air Speed (knots)135013005812501260531100110043149014906912001110461500149070
References
Notes
Bibliography
RNAF-Z-17, General correspondence of Bureau of Construction and Repair in matters pertaining to Naval Aircraft Factory TF, Record Group 72.2.3, U.S. National Archives, Washington D.C. Z-17-736-8-DA-25, General correspondence of Bureau of Engineering in matters pertaining to Naval Aircraft Factory TF, Record Group 72.2.1, U.S. National Archives, Washington D.C. OS-Z-7, Records of Bureau of Aeronautics related to Naval Aircraft Factory TF, Record Group 72, U.S. National Archives, Washington D.C.