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National Advisory Committee for Aeronautics, Technical Notes - The Variation in Pressure in the Cabin of an Airplane in Flight

The pressure in the cabin of a Fairchild cabin monoplane
was surveyed-in flight, and was found to decrease with in—
creased air speed over the fuselage and to vary with the number
land location of openings in thchabin. The maximum'depression
of 8.2 inches of Water (equivalent pressure altitude at sea lev—
el of 158 feet) occurred at the high speed of the airplane in—
level flight with the cabin closed.; Any pressure—operated in;
struments installed in the cabin nould he affected by this
cabinepressure depression. These tests were conducted at the
Langley memorial Aeronautical Laboratory.
The increased importance of correct altimeters for blind
flying (if pressure~type instruments are to be used), and the
effect which their location would have on their indication,
have made it important to study the variation in static pres—
sure within representative airplanes for various conditions of
flight. The variation in pressures in an open cockpit of an,
airplane in flight have been measuredo(Reference 10. It was
found that true static pressure did not exist in the cockpit,
and that any instruments installed therein which depended upon
it for their operation would give incorrect indications. The
present investigation was undertaken-to determine the pressures.
in a cabinrtype airplane.
This investigation was conducted on a Fairchild cabin
monoplane at the Langley Hemorial Aeronautical Laboratory of
the National Advisory Committee for Aeronautics. The pressures
at 18 points in the cabin were measured in flight throughout the
useful speed range of the airplane (60 to 130 m.p.h.) in climbs,
glides, and level flights. The number and location of openings
into the cabin was varied by opening windows in various combi—
nations.The pressures measured were compared with the static
pressure obtained from a Pitot~static air—speed head suspended
65 feet below the airplane.