• Version
• 141 Downloads
• 2.73 MB File Size
• 1 File Count
• April 3, 2017 Create Date
• April 3, 2017 Last Updated

Investigation of Drag and Pressure Distribution of Widshields at High Speeds

SUMMARY

Tests were conducted in the HAGA 8—foot high-speed
wind tunnel to determine the leads and' the load distribu-
tions at high speeds for a number of windshields of the

' cockpit- canOpy typet Drag data were obtained simultane-
ously with' the load data.. Ten windshielde of .various de—
signs similar to those in 'general use were included in
these tests. A new windshield designed t.o give low local
.loads and low drags was also tested. These windshields
were mounted on a DG-B fuselage and wing model. -Pressure
distributions were obtained for the wing alone and for the

. fuselage mounted on the wing. From the pressure data an
~aggiysis was made of the interference effects between- a
shield and the model. The tests were made at Mach
nufihere ranging from 0.12 to O. 71. and a study of the ef-
fects of compressibility on loads and_ drags was .thereby
permitted. .

The load and drag data obtained in these tests are
presented. graphically. The pressure coefficients are pre-
sented at a w_ing angle of attack of —O. 6? (lift coeffi—

'cient a 0.10) for Mach numbers ranging from 0.19 .to 0.71
and at wing angles of attack up to 6° (lift coefficient =
0.82) for a Mach number. of 6.19. Windshield drag coeffi—
cients are plotted against Mash number at wing angles of
attack of- —0. 67° and -1. 55° and agailn'st‘ wing angle _9f- at—
tack at a Mac-h- number- of 0.19. -- _

The results 'of' these tests show that both the local
loads and the drags' vary greatly among_ different wind-
shields. The drag of a go-ed windshield was found" to- be
small. only about 2 percent- of' the drag of a good' airplane:
but the drag of“ a bad windshield-'might easily be- ten times
as great. Blunt- -noses' and blunt tails' or sharp corners
transverse- to thev- flow were' generally- found- to be respon—
iimle for both high' drags and-- high- local -loads. Windshields
having high drags also had high local loads; some of the
windshields having low drags had moderately high local
loads.. Low loéal' loads are favored by large fineness ratios
and by shapes -that tend to' distribute the load uniformly
over 'the main body of the windshield. for the bad wind-
shields the drags and for the good windshielde the local
loads increased greatly with increase in Mach number.

F.
k
i
Interference from-the wing_and fuselage is shown to have

an important effect on the windshield and usually serves

to increase the loads. -Predictions of loads at high speeds
made fron lowmspeed data may be greatly in error unless

the effect of both compressibility and wing interference

is taken into account. The new windshield. designated the
1-2 windshield, was found to have both low drag and low
local loads.

INTRODUCTION

The windshield or cockpit canopy.is designed to pro-
vide head room. vision, and protection to Occupants of the
cockpit of a pursuit or a similar type of airplane. The
disturbance to the flow over the fuselage should. of course.
be a minimum. The increase in drag due to the cockpit en-
closure should be as small as possible and. in order that
sufficient strength may be provided. the loads should be
small and of known magnitude and distribution. It is es~
pecially important that the high loads attained at high
speeds be known with a reasonable degree of accuracy. The
- entire cockpit enclosure. including the noee or windshield
proper, the middle piece or hood. and the tail. will be
referred to in this report as the “windshield.''

Most of the windshield data in existence up to the
time of the present investigation had been obtained at low
speeds. Low—speed drag data had been obtained in the in—
vestigations described in references 1 and 2; whereas other
windshield investigations had been concerned mainly with
the field of view and the adaptability of windshields to
bad weather (references 3 and 4). Undoubtedly much low-
spesd load data had been obtained by manufacturers. but
this work is generally unavailable. No high—speed load
data had been obtained. The only high—speed windshield
data available were the results reported in reference 5.
and that investigation was limited to finding the effect
of various geometrical factors,such as nose shape. nose
length. tail shape. tail length. and others on the drag of
windshields. The failure of several windshields in high—
speed dives served to emphasise the necessity of obtaining
information on the magnitude and distribution of loads at
high speedn.

This investigation was conducted primarily to obtain
highnspeed load data, including the effect of compressi-
bility on loads for a number of representative windshield
shapes. Secondary considerations included determination
of the critical speeds of the windshields. measurement of