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National Advisory Committee for Aeronautics, Report - An Investigation of the Drag of Windshields in the 8 foot High Speed Wind Tunnel

The drag of closed-cockpit and transport—type wind-
shields was determinedfrom tests made at speeds corre-
sponding to a hfach number range of approrimatelg 0.25
to 0.58 in the NAOA 8-foot high-speed wind tunnel.
This speed range corresponds to a test Reynolds number
range of 2,510,000 to 4,830,000 based on the mean aero-
dynamic chord of the full-span model (17.29 in.). The
shapes of the windshield proper, thehood, and the tail
fairing were systematically varied to include common
types and a refined design. Transport types varied from
a reproduction of a current type to a completely fa-ired
windshield.

The results show that the drag of windshields of the
same frontal area, on airplanes of small to medium size,
may account for 15 percent of the airplane drag or maybe
reduced to 1 percent. Optimum values are given for wind-
shield and tail-hiring lengths; the eject, at various air-
speeds, of rounding of sharp corners to various radii is
shown. The longitudinal profile of a windshield is shown
to be most important and the transverse profile,to be much
less important. The efl'ects of retaining strips, qf steps
for telescoping hoods, and of recessed window: are deter-
mined. The results show that the drag of transport—type
windshields may account for 21 percent of the fuselage
drag or may be reduced to 2 percent-

Prior to the present investigation, no comparative
test results were available for obtaining the drag of
Windshields at high speeds. Most windshield investiga—
tions were concerned with the field of view and the
adaptability of Windshields to bad weather (references
1, 2, and 3). Some comparative wind-t1mnel tests
(reference 1), however, show the drag of a certain family
of Windshields; these tests were made at approximately
hue—fifth scale, at. 82 miles per hour, and at angles of
attack corresponding to maximum speed and no lift.
Wmd-tunnel tests reported in reference 4 show the
reduction in drag obtained by modifying a given for-
ward-sloping V-type cabin windshield.