Altimeter
The altimeter measures the height of the glider above a given atmospheric pressure level by measuring atmospheric pressure in flight. Since the altimeter is the only instrument that gives altitude information, the altimeter is one of the most important instruments in the glider. The altimeter is a simple aneroid barometer that measures pressure at its current location. An aneroid wafer is attached to the static source and as the glider climbs or descends the wafer expands or contracts. The movements of the wafer are mechanically linked to the needles on the face of the instrument that indicate altitude. The altimeter is designed to measure altitude at standard sea level pressure. Since air pressure where you are flying is rarely standard, we need a method to adjust the altimeter for non-standard pressure. The altimeter is set in pressure measured in inches of mercury. The Barometric Pressure Scale is used to set the proper pressure correction.
Example: Setting the altimeter to the correct setting makes the instrument read true altitude at the particular field elevation. Many glider pilots set their altimeter to zero prior to take off so their altimeter will read absolute or height above ground level. This is certainly acceptable for a local flight, however a cross-country flight might traverse different pressure gradients and setting the altimeter to the current pressure could yield valuable information. Reading the Altimeter The face of the altimeter is labeled 1 through 9 with hash marks representing a division of 20 feet between each mark. The dial has three pointers representing different sums of altitude. The short fat pointer represents 1,000s of feet. The long skinny pointer represents 100s of feet. The short skinny pointer represents 10,000s of feet. The altimeter
above is reading 14,400 feet. Note the blue 10,000 foot pointer is between
1 and 2 or 10,000 and 20,000 feet, the yellow 1000 foot pointer is just
past 4,000 feet, and the read 100 foot pointer is pointing at 5 or 500
feet. In the glider these pointers will not be color coded. During the
academy you will more than likely not be concerned with the 10,000 foot
pointer. |