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aluminium, brass, glass, iron, steel
This Aviation Altimeter, manufactured around 1940 by the Kollsman Instrument Corporation, is housed in a massive rectangular elongated case made of aluminum alloy and finished in gray paint. The front features a characteristic aviation design: a square mounting frame with four screw holes at the corners and a circular glass window protecting the dial. In the lower left corner sits a knurled metal adjustment knob, allowing the barometric setting to be changed by rotation.
The dial is made of matte black metal with sharp white markings for excellent legibility in the cockpit. The outer scale shows altitude in hundreds of feet, supplemented by graduations for thousands and tens of thousands, indicated by concentric hands of different sizes. At the bottom appears the inscription ALTITUDE, while to the right is the well-known Kollsman window with a barometric scale marked in inches of mercury. The hands are metal, painted white for maximum contrast, with distinct shapes: a long pointer for hundreds of feet, a shorter one for thousands, and an additional indicator for tens of thousands.
The rear panel is also made of aluminum and carries several key features: a blue port for static pressure input, a multi-pin MIL-spec electrical connector, and a black lighting block with external wiring. The panel bears engraved patent numbers and the manufacturer’s marking: Kollsman Instrument Corporation, Elmhurst, New York. The overall impression is that of a rugged, purpose-built instrument, engineered for the harsh environment of flight and long operational service.
The Kollsman 5934 aviation altimeter measures altitude through the expansion and contraction of aneroid capsules, which respond to static pressure (the ambient air pressure supplied from the aircraft’s static system). These evacuated capsules expand at higher altitudes as pressure decreases, and contract at lower altitudes as pressure increases. Their minute motion is amplified by a linkage system that translates linear displacement into angular movement, transmitted to a shaped cam sector. The cam profile compensates for the nonlinear relationship between pressure and altitude described by the barometric formula, thereby producing a more uniform scale distribution. From the sector, motion passes through a chain of gears equipped with backlash-eliminating devices: the gears are split and spring-loaded to cancel free play and pointer flutter. Ultimately, three coaxial hollow shafts carry the pointers: the long hand for hundreds of feet, the short hand for thousands, and an auxiliary pointer or drum for tens of thousands. To prevent vibration from displacing the indicators, the mechanism incorporates small friction devices providing gentle resistance.
The barometric setting—the famous Kollsman window—does not act on the dial itself but is integrated into the gearing through a differential mechanism: turning the knob introduces a shift in the transmission line, adjusting the zero point and synchronizing the pointers with the reference pressure set in inches of mercury. Additional refinements enhance stability: the capsules include bimetallic compensators to reduce temperature errors, the moving parts are carefully balanced against acceleration forces, and limiters protect the system from sudden pressure changes.
Compared with civilian or portable altimeters, this instrument offers a wider measurement range and much finer sensitivity. Its advanced compensating mechanisms, backlash elimination, coaxial shaft system, and integrated barometric adjustment make it far superior to consumer-grade devices, ensuring accurate operation at high altitudes, through extreme temperature shifts, and under constant vibration in the aircraft cockpit.
In every aspect, the Kollsman altimeter exemplifies the precision and durability of professional aviation instruments designed for uncompromising reliability in flight.
