Altimeter Internal Vibrator

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHAPTER FOURTEEN

WORKBOOK

Maximum Allowable Airspeed

280 KIAS ............................................................................................................. 0 - 20,000 feet

245 KIAS .................................................................................................... 20,000 - 25,000 feet

Altimeters

Altitude is displayed in both cockpit pressure altimeters by a 10,000 foot counter, a 1000 foot

counter, and a 100 foot drum. A single pointer indicates hundreds of feet on a circular scale,

with 50 foot center graduations. Below 10,000 feet a diagonal warning symbol appears on the

10,000 foot counter. At the right side of the altimeter face is the barometric pressure window,

which is used to correct for variations in sea level barometric pressure by means of a knob on the

lower left corner of the instrument.

Figure 14-2 Altimeter

Altimeter Internal Vibrator

When each 1000-foot increment is completed, the counters abruptly index to the next digit.

However, there is a noticeable pause or hesitation of the pointers caused by the additional

friction and inertia loads involved in indexing the counters. The momentary pause is followed

by a noticeable acceleration as the counters change. To minimize friction and to maximize the

accuracy, a DC-powered vibrator in the altimeters is energized whenever aircraft power is on.

The pause-and-accelerate behavior is most common in the 9-to-1 section of the scale, but if the

internal vibrator is inoperative, this behavior may occur in the 8-to-2 section.

PITOT STATIC SYSTEM 14-3