Document
Mechanics
Stability-Augmentation Devices for Miniature Aircraft
Passive mechanical devices help miniature aircraft fly in adverse weather.
Langley Research Center, Hampton, Virginia Non-aerodynamic mechanical devices to warrant grounding of larger aircraft. Optionally, an antenna for radio commu- are under consideration as means to aug- The need for the stability-augmentation nication can be integrated into the shaft.
ment the stability of miniature au- devices to be non-aerodynamic arises be- At the time of writing this article, the de- tonomous and remotely controlled air- cause there is no known way to create con- ployment of the telescoping shaft and mass craft. Such aircraft can be used for diverse trolled aerodynamic forces sufficient to pod was characterized as passive and auto- purposes, including military reconnais- counteract the uncontrollable meteoro- matic, but information about the deploy- sance, radio communications, and safety- logical forces on miniature aircraft. ment mechanism(s) was not available. The related monitoring of wide areas. The A stability-augmentation device of the feasibility of this stability-augmentation con- need for stability-augmentation devices type under consideration includes a mass cept was demonstrated in flights of hand- arises because adverse meteorological pod (a counterweight) at the outer end of launched prototype aircraft.
conditions generally affect smaller aircraft a telescoping shaft, plus associated equip- This work was done by Richard M. Wood more strongly than they affect larger air- ment to support the operation of the air- of Langley Research Center. For further craft: Miniature aircraft often become craft. The telescoping shaft and mass pod information, contact the Intellectual Property uncontrollable under conditions that are stowed in the rear of the aircraft. When Team at (757) 864-3521.
would not be considered severe enough deployed, they extend below the aircraft. LAR-16456-1
Tool Measures Depths of Defects on a Case Tang Joint
Precise measurements can be made consistently.
Marshall Space Flight Center, Alabama A special-purpose tool has been devel- faces), plus two additional index bear- verse effect on the accuracy of measure- oped for measuring the depths of defects ings that ride along the tip of the capture ments. The tool is secured to the case on an O-ring seal surface. The surface feature. The four-bearing indexing de- joint by use of two pincher bearings, lies in a specially shaped ringlike fitting, sign enables the tool to ride over inter- which ride on the inner-diameter surface called a “capture feature tang,” located ference-fit, fretting defects without ad- of the capture feature. The pincher bear- on an end of a cylindrical segment of a ings are connected to spring-loaded han- case that contains a solid-fuel booster- dles that apply a radial clamping force.
rocket motor for launching a space shut- The tool is attached to the joint by tle. The capture feature tang is a part of a squeezing the spring-loaded handles, tang-and-clevis, O-ring joint between the lowering the device in position, then re- case segment and a similar, adjacent leasing the handles.
cylindrical case segment. When the seg- The base of the tool contains a battery ments are joined, the tang makes an in- compartment and a miniature krypton terference fit with the clevis and squeezes inspection light. The light is essential for Defect Depth the O-ring at the side of the gap. visual inspections inside the gap.
Capture The critical surface in question is an The tool includes a measurement Feature Defect and O-ring sealing surface. The defects on probe on a slide mechanism that enables Tang Blend Zone this surface can include pits and gouges motion of the probe along the cylindrical that must be mitigated by grinding their axis. There is also an adjustment mecha- Maximum Allowable edges to make them blend smoothly into nism for alignment of the slide mecha- Gap Width the surrounding undamaged surface. nism with the datum plane established by 0.434 in.
Measurement of the depths of these de- the four index bearings. The slide is actu- Radially Radially fects (see figure) is necessary to ensure ated by turning a thumb wheel con- Inward Outward against grinding away so much material nected to a spur-gear shaft that, in turn, that the local width of the gap would ex- drives a rack gear, which is mounted on a ceed the maximum allowable value for housing that is part of the probe.
adequate O-ring squeeze for sealing. The probe housing, machined from The tool includes four index bearings piece of aluminum, contains a dial indi- The Depth of a Defect on the sealing surface of that ride circumferentially along the in- cator, a rocker arm, and an engage- the capture feature tang is what one seeks to measure.
terference-fit surface (the inner gap sur- ment-cable release mechanism. The NASA Tech Briefs, November 2005 19