Browse Topic: Seals and gaskets
A rotary union was developed and tested that allows for active flow control to be tested on the Army General Rotor Model System (GRMS) Mach scale rotor test stand. The union has a center pass through for the rotor shaft and control links. Three air channels formed by mortised seals allow air transit between the fixed frame and the rotating frame. Each channel can move 10 SCFM at 30 psi with a pressure loss of 0.2 psi. The union torque depends on seal differential pressure. The torque is 11 lbf-ft at 11 psi or 2.5 HP at 1250 RPM which is sufficient for a rotor tip Mach of 0.64. The union was tested on GRMS to 1250 RPM. The seals require differential pressure of 2 psid to engage and at 10 psid the leak rate was less than 0.5 SCFM. Considering future research, a non-dimensional flow control scaling parameter is derived which accounts for Coriolis effects.
ABSTRACT
The purpose of this aerospace information report is to provide a listing of national and international metric standards for use in aerospace fluid systems with their equivalent SAE inch, International ISO, and European AECMA standards.
In the winter months of January-March 2019, two Bell 525 test aircraft completed cold weather testing at Yellowknife Canada, some 1900 nm from Bell’s Flight Research Center in Arlington, TX. Testing was aimed at demonstrating aircraft stability, performance, and flight characteristics at extreme temperatures as required by CFR Part 29. Since regulations only permit limited temperature extrapolation, the cold temperature tests must include the limit of forward speed in a dive (VNE), and assessments of performance, controllability, autorotation, and static stability. This paper describes some of the unique environmental conditions and factors that any rotorcraft development program could experience in cold weather testing. The paper also gives a technical description of the required testing, where arctic conditions reached as low as -40° F or C (the temperature scales are the same at this temperature). Testing exposed the aircraft to overnight cold-soaks that brought fluids, seals, windshields, electronics, and elastomeric bearings to their low temperature specification, all at the same time. For the 525, test results demonstrated that the aircraft was ready for start-up and operation in extreme cold. The criteria necessary for meeting certification requirements in cold weather were also demonstrated in the series of tests and showed that the rotor was free from any adverse effects due to aerodynamic compressibility, had low vibration, acceptable loads and was free from any instability, even at speeds greater than VNE.
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