The design and development of a wind tunnel model equipped with pressure measuring devices are discussed. The pressure measuring orifices are integrally constructed in the wind tunnel model and do not contribute to distortions of the aerodynamic surface. The construction of a typical model is described and a drawing of the device is included

Jackson, C. M., Jr.

Summerfield, D. G.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
MAR 1 3 1974
TO: KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General
Counsel for Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. :
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent case No.
I/O' CTo i
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES /—7 NO
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of—the—pa-tent-; -however, the name of the actuaL
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "...with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740009842 2020-03-17T14:39:06+00:00Z
\ 1
linked States Patent
Jackson, 'jr. et al.
[in 3,791,207
[45] Feb. 12, 1974
[ 54 ] WIND TUNNEL MODEL AND METHOD
[75] Inventors: Charlie M. Jackson, Jr., Yorktown;
Dallas G. Summerfield, Hampton,
both of Va.
[73] Assignee: The United States of America as
represented by the National
Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: June 19, 1972
[21] Appl. No.: 263,815
[52] U.S. Cl 73/147
[51] Int. Cl GOlm 9/00
[58] Field of Search 73/147
[56] References Cited
UNITED STATES PATENTS
2,523,481 9/1950 Rabenhorst 73/147
2,551,526 5/1951 Campbell 73/147
2,602,329 7/1952 Clark 73/147
Primary Examiner—S. Clement Swisher
Attorney, Agent, or Firm—Howard J. Osborn; Wallace
J. Nelson; John R. Manning
[57] ABSTRACT
A wind tunnel model having pressure measurement
orifices formed integrally therein and a process for
making same.
8 Claims, 4 Drawing Figures
30
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33
oj c:
o tsCD o f:
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, PATENTED FEB12 1974 3.791,207
ICK
18
12
19
in u u u u u i i u D Tim u u u u u T u
14 14
12
16
FIG. 1 FIG. 2
30
33
33
12
FIG. 3 FIG. 4
3,791,207
1
WIND TUNNEL MODEL AND METHOD
ORIGIN OF THE INVENTION
This invention was made by employees of the Na- 5
tional Aeronautics and Space Administration and may
be manufactured or used by or for the Government of
the United States without the payment of any royalties
thereon or therefor.
BACKGROUND OF THE INVENTION
The aerodynamic characteristics of wings and other
airfoil surfaces are normally evaluated by wind tunnel
tests on small scale models. Much of the experimental
aerodynamic research data is obtained by measuring
the surface pressures on models of specific configura-
tions in the wind tunnel. The construction of the mod-
els and installation of the necessary pressure orifices
has heretofore been a difficult and expensive task. For
example, prior art methods for construction of pres-
sure-test models of airfoils have included casting or ma-
chining the desired test shape for the airfoil with the
pressure orifices then installed by one of two tech-
niques depending on the airfoil thickness and the na-
ture of the data to be obtained. If the test airfoil is suffi-
ciently thick, slots are machined in the airfoil surface
and steel tubing embedded' in the slots with clear plas-
tics. The orifices are then drilled through the plastic
and into the tubing. For thin airfoils, the tubing is in-
stalled through the airfoil from the opposite side of the
pressure orifices desired and attached to the wing in an
exposed position on that side.
When the technique of embedding the tubes in the
surface is used, it is difficult to maintain the airfoil
shape. The process of installing the tubing through the
airfoils is also undesirable because the aerodynamic
shape of the surface opposite to the instrumental side
is destroyed by the presence of the tubing and if the air-
foil is not symmetrical the model must be reinstru-
mented or remade to provide the surface pressures on
the opposite side.
It is therefore an object of the present invention to
provide new and novel wind tunnel models.
Another object of the present invention is a novel
method of making aerodynamic wind tunnel models
having integrally formed pressure instrumentation ca-
pabilities.
A further object of the present invention is a simpli-
fied method of making aerodynamic wind tunnel mod-
els having pressure orifices therein.
An additional object of the present invention is a
novel method of providing orifices to a wind tunnel test
model.
The foregoing and other objects are attainable in the
present invention by clamping a plurality of diverse
length, small diameter tubular members in fixed spaced
relationship, casting an aerodynamic model configura-
tion about one end of the assembled tubular members,
and drilling a plurality of transverse holes through the
case model so that one hole intersects with each indi-
vidual tubular member. One end of the clamped tubu-
lar members are of even length extending from one side
of the clamping element and of uneven length extend-
ing from the other side of the clamping member with
the ends of the uneven lengths being crimped or other-
wise closed. The cast material completely covers the
uneven length ends of the tubular members while leav-
'°
15
20
25
35
40
50
,„
ing the clamping fixture and the even length portions
of the tubular members exposed for subsequent con-
nection with suitable conventional pressure measure-
ment instrumentation.
A more complete appreciation of the invention and
many of the attendant advantages thereof will be read-
ily apparent as the same becomes better understood by
reference to the following detailed description when
considered in connection with the accompanying draw-
ings wherein:
FIG. 1 is a view of an assembled array of tubular
members clamped together prior to casting of the aero-
dynamic configuration therearound;
FIG. 2 is a side view of the clamped tubular array
shown in FIG. 1;
FIG. 3 is a view of an aerodynamic airfoil wind tunnel
model constructed in according with the present inven-
tion; and
FIG. 4 is a side view of a modified airfoil wind tunnel
model according to the present invention.
Referring now to the drawings, FIGS. 1 and 2 show
a tubular array as employed in the present invention
and generally designated by reference numeral 10. Tu-
bular array 10 includes a plurality of small diameter tu-
bular members 12 clamped in spaced parallel adja-
cency by a pair of clamp blocks 14 and 16. A pair of
countersunk screws 18 and 20 serve to secure blocks
14 and 16 together. Suitable channels are machined or
otherwise formed in the opposed faces of clamp blocks
14 and 16 so as to receive tubular member 12 therebe-
tween in tight fixed relationship. As shown in the draw-
ings, tubular members 12 are of diverse lengths with an
equal length of each tube extending from one side of
blocks 14 and 16 and with the uneven lengths thereof
extending from the other side of blocks 14 and 16. The
even length tubes are those disposed at the base of the
constructed airfoil while the uneven lengths are de-
signed to extend to varying distances within the airfoil
toward the leading edge thereof.
Referring now to FIGS. 3 and 4, two finished airfoil
body configurations are shown as constructed in accor-
dance with the present invention and as generally des-
ignated, respectively, by reference numerals 30 and 40.
These airfoil models utilize the tubular array of FIGS.
1 and 2 and are formed by casting a metal or other so-
iidifiable material 31 and 41 around the tubular array
10 so as to completely encase the uneven length por-
tions of tubular members 12. The even length portions
of tubular members 12 and clamp blocks 14 and 16 are
left exposed. After solidification of the casting material
31, the clamp blocks 14 and 16 are removed and suffi-
cient lengths of the tubular members 12 are left ex-
posed for connection with suitable and conventional
pressure measurement instrumentation. After casting
the material 31, for example, about an array of tubular
members 12, the airfoil is finished and polished in a
conventional manner to achieve the precise desired ex-
terior configuration.
An X-ray photo is then taken of the airfoil body 30
to precisely locate the individual tubes 12 therein.
Tubes 12 are crimped or otherwise closed at the em-
bedded ends thereof prior to the casting operation to
prevent any solid casting material from entry therein.
The x-ray film is then used as a template to permit dril-
ling of transverse holes 33, one for each tubular mem-
ber 12, to intersect perpendicularly with the individual
tubular members 12. Holes 33 are positioned at the
3,791,207
10
points on airfoil model 30 where pressure measure-
ments are desired during a wind tunnel test and tubular
members 12 are connected to conventional pressure
measurement instrumentation during testing.
FIG. 4 is similar to FIG. 3 but of a different configu-
ration and showing pressure openings drilled in only
one surface of body 41 of airfoil 40. It is to be under-
stood that such openings may be made in any surface
of the airfoil so as to intersect with the tubular mem-
bers 12.
Although no specific material has been mentioned
for the airfoil bodies, it is to be understood that any ma-
terial normally used for model airfoils is considered
within the scope of the present invention. In a specific
example 355 aluminum alloy was used for the cast air- 15
foil body and stainless steel S.A.E. 30347 -0.065 inch
O.D. was used for the tubing to cast an airfoil of 16 inch
chord and 4 inch semi-span. In this example, seventy
pressure orifices 33 of 0.040 inch diameter were drilled
through the airfoil body portion 31 to intersect with a
like number of tubular members 12.
As mentioned hereinbefore, the tubing core is con-
structed by clamping the desired number of tubes 12 in
20
may be practiced otherwise than as specifically de-
scribed.
What is claimed as new and desired to be secured by
Letters Patent of the United States is:
1. A method of making a perforated metal structure
having precise locations of the perforations therein
comprising the steps of:
a. assembling a plurality of tubular members in fixed,
spaced relationship,
b. casting a material around said plurality of tubular
members so as to completely enclose one end of
the assembled tubes,
f. finishing the cast structure to the desired specifica-
tions while maintaining one end of the tubular
members open,
d. x-raying the finished structure to establish the pre-
cise location of the individual tubes,
e. drilling a hole through the cast structure to inter-
sect with each individual tube at the desired dis-
tance along the length thereof and by. using the
x-ray film as a template.
2. The method of claim 1 wherein said perforated
metal structure is an airfoil designed for wind tunnel
testing and the cast metal is selected from the group
consisting of aluminum and aluminum alloys.
3. The method of claim 2 wherein said tubular mem-,, ff • *.*_ f i i i ft • »*• • itvi iii^ rtiivsu vi victim <tf wiiwi^ui aai\* luisuiai inviiithe proper configuration with a split block of aluminum
 25 bers are formed of thin wa,)ed gtee, and wherejn ,he
or the like. The uneven lengths of the tubing are then
 ends of the steel tubes embedded in the cast structure
crimped or otherwise sealed to prevent molten cast ma-
 are crimped closed prior to casting of the metal,
terial from entry therein. The tubing block, formed of 4. The method of claim 1 wherein the plurality of tu-
clamp blocks 14 and 16 is closed in tight engagement bular members are of diverse lengths and are clamped
with the tubing via countersunk screws 18 and 20 and
 30 together in spaced relationship prior to casting the
serves in conjunction with the pattern 40 to form the metal structure thereafound.
part of the mold commonly referred to as the core 5- A method of constructing an aerodynamic wind
print. An aluminum model is then cast in the normal tunnel test model hav.ng a-series of openings therein
. . . . . . • • • • ! _ » • f o r making pressure measurements a t diverse locations
way^with the tubing core in position in the casting
 Qn ^  ^ durj a wjnd tunne, risi the
mold. The aluminum alloy referred to hereinbefore is 35
 steps of
heated to a pour temperature of 1,350° F. Where steel
tubing is used for members 12 the normal casting
shrinkage and differences in the thermal expansion be-
tween aluminum and steel insure a sufficiently tight
bond between the tubing and model such that no leaks 40
occur. The casting is then finished to the desired shape
in a conventional manner and the x-rays taken to pro-
vide templates for drilling the pressure orifices as de-
scribed hereinbefore.
Alternate embodiments of the model casting process 45
described herein would include different tubing core
configurations, shapes other than for airfoil bodies and
alternate methods of securing the tubing core in the
mold other than the clamp blocks shown. For example,
the tubing .array 10 could be formed by welding each 50
of the tubular members to an adjacent member. Also,
various improvements over conventional coating tech-
niques, such as preheating the tubing core 10 to essen-
tially the temperature of the molten casting metal to
minimize thermal warpage is also considered within the
scope of the present invention.
Thus, it is readily seen that the present invention pro-
vides a novel process of making wind tunnel airfoil
models for pressure measurements thereof that results
a. providing a plurality of tubular bodies of diverse
lengths in a fixed array,
b. closing one end of each of said tubular bodies,
c. casting a solid material about said tubular bodies
so as to form an aerodynamic configuration there-
about that embeds the closed ends of the tubular
bodies adjacent the leading edge of the configura-
tion while leaving the open ends thereof exposed at
the trailing edge of the configuration,
d. drilling a hole perpendicular to the individual tu-
bular bodies through the cast solid so as to form an
.intersecting passageway perpendicular with the
passageway in each of the tubular bodies and each
perpendicular passageway being a different dis-
tance from the leading and trailing edge of the
aerodynamic configuration than an adjacent pas-
sageway whereby pressure sensing instrumentation
may be connected to the open end of each tubular
body adjacent the trailing edge of the aerodynamic
configuration to thereby make pressure measure-
ments on the wind tunnel model at diverse loca-
tions thereof during a wind tunnel test.
6. The method of claim 5 wherein said tubular bodies
are clamped between two aluminum blocks to form the
fixed array.
7. The method of claim 5 wherein the cast solid mate-
in an improved model that exhibits more reliability 60 rial is selected from aluminum and aluminum alloys
than previous models and a process that reduces the anf «"jd tubular bo^es are formed of stainless steel.
.
 r
, ... . . . , . - . 8. The method of.claim 5 wherein an x-ray print is
cost of .providing instrumented pressure models to es-
 made of &g ^  solid materia) and sairf ^ ^ js
sentially one-half of the cost of prior art methods. employed as a template to precisely locate the individ-
There are obviously many modifications and vana-
 fij uaj tubu]ar bodies to permit drilling of the perpendicu-
tions of the present invention possible in the light of the iar hole through the cast solid material at a precise lo-
above teachings. It is therefore to be understood that cation along the length of the individual tubular bodies,
within the scope of the appended claims the invention . . , * * . * * * .
r


Wind tunnel model and method

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