• * * •
TABLE OF CONTENTS
Page
0 o • List of Curve Sheets
0 • ., 15.st of Photograph$
1 • o Desoription of Test Set-Up
2 • e Test Preoedure
2 • ~ Test Results
5 •• List of Symbols and Coeffio1ents
* • • •
LIST OF CURVE SHEETS
Sheet
l Yawing Moment Coeffioient vs Angle of Yaw
Complete Model
2 Side Foroe Coefficient vs Angle of Yaw
Complete Model
Drag Coefficient vs Angle of Yaw
Complete Medel
4 Yawing Moment Coefficient vs Angle of Yaw
Model Without Blister
5 Side Force Coefficient vs Angle pf Yaw
Model Without Blister
6 Drag Coefficient vs Angle of Yaw
Model Without Blister
7 Ye.wing Moment Coefficient vs Angle of Yaw
Model Without Car or Blister
8 Side Force Coefficient vs Angle of Yaw
Model Without Car o~ Blister
9 Drag Coefficient vs Angl e of Yaw
M-0del Without Car or Blister
LIST OF PHOTOGRAPHS
Figure
1 Compl ete "M" Ship Installed in Tunnel
2 "M'' Ship Without Car or Blister Installed
in Tunnel
3 Dummy for Tar~ T.as'te Installed in Tunnel
DlRECTIONA.L STABILITY WIND TUNNEL TESTS ON AN
''M" TYPE AIRSHIP MODEL
GA 2.tl368P
This re~ort covers the fdroe tests mad~ for the determihation of the ditee~
tional stability influence of the oontrol car and blister on a 1/60 seale m0d9l
of the 1'M" type a~rship tested for the Goodyear Airo:rai't Corporation in tho
slsQ vertical wind tunnel of the Daniel GuggenheimAir!hip Institute, Th@ foroe
measurements included side force, drag, and yawing mcment about the center et
buoyan~y of the model~ All tests were made at ~ airsp.eed of approximately 80
miles per hour, or a Reynolds Number of l,070,000 based upon the 1/3 p~wer or
the volume of the .model.
DescriEti~~ of the Model
Th$ 1/60 seal e model of the ~M" type ail'ship used in these 'te-sts ~& the
same one used in previous tests for th_e G¢-odyear Airera.ft Corporation. lts
ten~ral 4imensions were as toll0W&~
Length of model
Maximum di a1ne te r
Volume o~ hull
Center or buoyancy location
Deseription -er Test Set-U!
4.7~ ~
1.10 f't,.
2,$ OUr!i t~
45.1~ from nose
Th~ model was suspended in ths tunne~ by a V wire dropped ~rom the ~oe
ring to the nose seo.tion of the model. Four. smaller wires at the nosa am four
at the tail prevented rotating and helped maintain the position ~f the model.
i~ order to obtain yaw angles, the model was rotatttd about its ~enter of b•cy~
an9y by means of a gear box located on the foree ring~ (s~ Fig. 1 and 2.) Th~
tJ:<>se of the mQdel -was approximately 15 inohes above -the free jet entranof.J., thu.•
keeping t,h.e model in a regie!n 111 th a re~bly -small p~ur,,g grad~~ :r~
., 2 ...
tare tests on the supporting wires and force frame was made by suspending a
pipe, which had the same weight as the model, by the same set of wires. The
pipe was shielded from the airstream by a sheet metal and wood dummy of tho
approximate shape of the model itself• Care was taken that the dummy only
shielded the pipe, and did not touch any of the suspension wires. An independent
set of support wires fastened outside the tunnel held the dummy in place.
(See Fig. 3.)
Test Procedure
The calibration of the hydraulic gages of the foroe apparatus was made by
applying loads directly to the model after it was installed in the tunnel. The
velocity of the air in the tunnel was measured by me·ans of a pitot tube plaoed
sufficiently far from the model to prevent interference, The velocity _measured
by the pitot tube was indicated on a c. Iw Tb manometer, All data was taken
after the ttmnel became steady at a velocity which would yield a q of 16•'
(about 80 mph). Both the angularity of the jet and the static pressure gradient
were checked in the vicinity of the model before it was installed. The
corrections resulting from these were too small to be of importance, Foroe
tests were made on the complete model~ including control car and blister; on
the model with the control car, but no blister; and on the model without tho
control car. The tests .included yaw angles of -12, ~9, -6, ~, 0, and +6° and
rudder angles of 0°, +10°, +20°, and ~30°~
Test Results
Since the purpose of these tests wa$ to determine the influence of the
control oar and blister on the directional stability of the airship, the side
force and yawing moment curves are of the most importance. All the ourves were
presented in the conve.ntional dimen~~less co&fficient form as defined in the
- 3 ..
list of symbols and coefficients, and were plotted to the same scale to facilitate
relative comparisons.
Examinations of Curve Sheets 1 and 4 show that there was practically no
difference in yawing moment between the complete model and the complete model
with the blister removed. This was to be expected, since the blister was located
very close to the c. B. of the model, and, therefore, should not have con•
tributed to the yawing moment. However, Curve Sheet 7, when compared with 1
showed a very definite decrease in moment for any particular yaw setting other
than zero~ This meant that the control car tends to make the airship even
more unstable than it would be without any car at all.
As an illustration of the magnitude of these values when applied to the
full scale airship, consider the difference in Cn due to the control car at
-12° yaw and 20° rudder. The change in Cn is about 0.05 which would mean a
change of moment about the C. B. of 512,000 =if ft. at 80 mph. If the effective
lift force of the tail surfaces are assumed to be 120 f't. from the C. B., then
the additional foroe which the tail must exert to compensate for the car would
be about 4,270 =th If just the area of the tail surfaces is considered, this
would mean a change of c1 for them of about 0.532 in order to maintain the
same moment as the ship without the car.
Curve Sheets 2 and 5, if compared, show that the side force for any defin~
ite yaw angle and rudder setting is slightly more for the complete model than
it is for the one without the blister~ The blister, therefore, contributes
slightly to the side force effect of the model when in a yawed condition, since
it presents a greater area for the cross wind to act upon. This effect wae
even more pronounced when the entire car was removed f rom the model. At -12°
yaw, the difference between the Cea for the complete model and the model without
the car was about 0.-066, which amounts to a side foroe of 7900 v on the
- 4 ..
fall oize airship at 80 mph. This is a reasonable value for the size of car
used on the "M" ship.
The changes in drag due to the blister and car are shown in Curve Sheets
3, 6, and 9. Although the blister was very small, removing it did change the
drag by an amount which ·would mean a saving of about 76.5 HP on the full size
"M0 ship at 80 mph~ However, the entire control car itself indicated the expenditure
of some 256 HP just to qvercome its drag at 80 mph.
Although these drag values may seem a little high, they may partially be
accounted for by the roughness of the model and the low Reynolds numbers at
which certain parts were tested. Although the model was in fairly good shape,
it had been chipped and repaired in place s, and was not as smooth as it was for
its original tests. This may have contributed a little to the increase of
drag. Also, parts like the outrigger supports were tested at Reynolds nlUTlbers
of about 60,000 which would give higher drags than in the full scale airship.
On the whole, the values obtained in these tests ahould be more reliable than
those in the prerlous "M" ship t&sta, since a new and improved foroe apparatus
has been insta.lledo
•• * * * *
R. s. Ross
7-28-44
- 5 -
LIST OF SYMBOLS AND COEFFICIENTS
v • Velocity of wind tunnel in region of m0del, ft/sec
e = Ma.il s density of air :fl= seo2/ ft4
q = ~(v 2 , dynamic pressure ,f wind tunnel in region of model
:ft/ sq ft
Re =
1/3
v ( Vol ) fi,J
V = Kinematic v~scosity of air, ft 2/seo
Vol a Volume of hull of model .• 2c 89 ou f ·t
C.B. = Center of buoyancy of model, 45.7fo from nose
D ~ Drag force of model in direction of tunr..el axis, 'fl=
s. F. = Side force of model normal to tunnel axis, #
Mty = Yawing moment of model about c. B. , # ft
cs
D
= q Vo!2/3 I Drag Coefficient
CS&
S. F.
= q Vol2/~ t Side Force Coefficient
en • Mt~
q Vol 4 Yawing Moment Coefficient
Yaw angle: nose to port i + , nose to starboard
Rudder deflection: , deflected to port; + , defleoted to starboard
. r· 1 • I
-· .. i.
.30
• 20 ·!.
.10
0
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,'·-.¥.~ :- -... ~
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l.:. _i ,I
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-12 -6 0 6
Angle of Yaw (Degrees)
• .• -I. .-1;
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Daniel
x.s.R.
Guggenheim Airshio
Akron, Ohio
Institute
7-28-44
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Angle of Yaw
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(Degrees)
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Figui'e 3 1Jummy for Tare rl'ests Installed in Tunnel