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This final technical report describes the investigation and evaluation of experimental integral fuel tank sealants under laboratory conditions simulating aircraft integral fuel tanks. Materials investigated were Dow Corning 77-028, 77-085, 3M Polyester, TRW Polyimide, Polysulfide and AFML Viton. These materials were evaluated dynamically in a fillet sealed configuration. This report also describes in detail the functions, operations and problems encountered with the dynamic test apparatus that has been designed and fabricated for the purpose of evaluating experimental aircraft integral fuel tank sealants. A portion of the effort was required to diagnose deficiencies and mechanical failures of the testing equipment which resulted in the lack of conclusive data in the report.

A dynamic test apparatus has been designed and fabricated for purpose of testing experimental aircraft integral fuel tank sealants. The apparatus is capable of closely simulating the conditions encountered by a sealant during a typical aircraft flight. In addition, the apparatus has the flexibility of simulating a virtually unlimited number of stress, temperature, fuel, and pressure conditions, and will automatically repeat the desired test cycle until sealant failure, occurs. A fillet sealed test joint has been used in the testing to date and with proper joint designs the apparatus will accommodate other types of seals found in aircraft fuel tank construction. Dynamic testing to date has been performed on Dow Corning 77-028, 77-085, 95-526, 77-108, 3M Polyester, a fiber reinforced polyester, and a Viton sealant formulated by the Air Force Materials Laboratory. These materials were all tested in a fillet seal configuration. High temperature aging in JP-7 fuel vapor was performed on the above materials, and physical properties were determined on the aged specimens both at room temperature and selected high temperatures representative of possible aircraft conditions.

Analytical and experimental research was conducted to investigate the use of a variable camber, cyclic controlled propeller, in combination with a partially-tilting wing with full-span flaps, to permit V/STOL aircraft operation. These features were incorporated in a full scale experimental aircraft designated the K-16B. This aircraft was used to explore the feasibility of a unified propulsion-control system designed to reconcile the conflict between the requirements of static thrust in hover and high-speed propeller efficiency, and to provide helicopter-type control in hover without the need for auxiliary control devices. This is accomplished by trailing edge flaps in the blades of the propeller. Collective deflection of these flaps increases blade camber for high static thrust. They are retracted in forward flight for a clean cruising-blade profile. Cyclic deflection of the flaps furnishes control moments in hover. The system was investigated on ground bench stands and in full-scale powered model tests of the K-16B.

A stress-cycling test (at - 103 F and room temperature) designed to simulate the spectrum of stresses which could occur during 500 aircraft flying hours (roughly 1 PAR interval), indicates that current specification and experimental aircraft coatings cannot meet these conditions without cracking around fastener heads. The coatings used were the MIL-C-22750 epoxy, the MIL-L- 81352(WEP) all-acrylic, and two polyurethanes. The implication of this test is that, at the present state of the coatings art, paint films of the non-rubbery type cannot be expected to provide adequate corrosion protection by themselves in the fastener area- a persistent trouble area on naval aircraft.