1) Tests were conducted in a wind tunnel to measure the interference drag between two axisymmetric bodies placed in tandem at varying horizontal and vertical spacing, representing stores separating from an aircraft. 2) Data showed that drag forces were strongly correlated to the spacing between the bodies and remained insensitive to changes in Reynolds number until a threshold was reached. 3) Key findings were that drag was highest when bodies were closest horizontally, and changing the vertical spacing altered the drag and moment coefficients in sinusoidal patterns, with implications for store stability during separation.

1. American Institute of Aeronautics and Astronautics
Interference Drag During Store Separation
Kalendrix Cook1
, Michael Halvorson2
Students, Department of Aerospace Engineering, Auburn University, Auburn, Alabama 36832
Interference drag is generated when bodies placed in a uniform flow are in close proximity. Tests
were conducted on two axisymmetric bodies placed in tandem at different horizontal and vertical
spacing to represent stores separating from a combat aircraft. Forces were measured in a wind tunnel
with a six component force/moment sensor at three Reynolds number. Data showed strong
correlation between the measured forces and spacing between the two bodies, however the forces
remained largely insensitive to a change in Reynolds number until reaching a threshold. Key features
of the flow are discussed and presented.
I. Introduction
Since the 1940’s, aircraft carried stores such as bombs, fuel tanks and other deliverables on the exterior that
results in a very complex flow field between the stores and also between the stores and the mother ship. The fluid
dynamic interactions manifest themselves in the form of interference drag. It may be noted that due to the interference,
the total drag of an aircraft, including wings, missiles, etc. is often greater than the sum of the drag of each individual
component.3
Figure 1: Interference due to stores
Because of the proximity of the stores protruding from otherwise smooth underbelly of an aircraft (Figure 1),
highly turbulent flow consisting of large and small eddies is produced. At high speeds, pockets of localized regions
of sonic or supersonic flow results in the formation of shockwaves that alter the pressure distributions and impose
additional unsteady loads. Release of stores under these circumstances results in changes in trajectory, targeting error,
collisions between stores and in some cases, released store returning to hit the carrier aircraft. Possible impact between
a released store and fuel tanks pose serious hazard. For the stores released from internal weapon bays, weapons
traversing a shear layer undergo high amplitude oscillations. Whether external or internal mounting, both methods
have relative merits4
.
For stores mounted in tandem, interference between the wake of the upstream store with that of the forebody of
the store downstream is a challenging problem because of the vibrations and aeroelastic coupling. The objective of
the present work therefore was to investigate the interference drag of two axisymmetric bodies mounted in tandem.
1
Undergraduate Student, Aerospace Engineering, 211 Engineering Dr, Auburn, AL 36849, Student Member
2
Undergraduate Student, Aerospace Engineering, 211 Engineering Dr, Auburn, AL 36849, Student Member
3
Asselin, Mario,” An Introduction to Aircraft Performance,” AIAA Education Series, 1997, Chapter 1, 24.
4
Johnson, Rudy, “ Store Separation Trajectory due to Unsteady Weapons Bay Aerodynamics”, AIAA Journal, Vol
46, No. 188, January 7, 2008, pp. 2008

2. 2
American Institute of Aeronautics and Astronautics
II. Description of Test Equipment and Procedure
The test was conducted in a 2ft x 2ft, open circuit low speed wind tunnel. Test were conducted at freestream
velocities of 30 fps, 60 fps and 90 fps resulting in the Reynolds numbers of 39,000, 78,000, 128,000 based on the
diameter of the model. Two identical missile models were constructed from modified Este’s model rocket kits that
had a plastic nose cone and cardboard body. The 2.5 inch diameter model had an overall length of 8.0 inches. One
model was equipped with a load cell and the second model was filled with foam and mounting hardware. A special
adapter was designed to hold a load cell inside the model through a L-shaped mechanical linkage that was mounted
to a two axis traversing system placed on top of the test section through a horizontal slit. Thus the model carrying the
load cell could be easily traversed horizontally and vertically. The “dummy” model was attached to the ceiling with
selectable spacers of one, two and three diameters. These spacers were enclosed in airfoil shaped streamlined tubes to
minimize support interference. The test setup and the coordinate system are presented in Figure 2.
The force/moment balance used in this investigation consisted of ATI Industry’s ATI9105-TW-NANO25 sensor
capable of measuring forces and moments in orthogonal planes. Maximum axial load for this sensor shown in Figure
3 is 25 lbs. that was well within the range of forces anticipated. The load sensor was calibrated before each series of
tests to measure any possible drifts and noise. Data was acquired with a National Instruments A/D board and Labview
software. Sampling rate was kept at 500 Hz
Tests were conducted for a variety of configurations consisting of the setting anterior model where
𝑍
𝐷
= 1 and
moving the posterior model axially downstream from
𝑥
𝐷
= 0.4 to
𝑥
𝐷
= 2.8. Forces and moments were also measured
without the anterior model. The experiment was repeated with anterior missile positions where
𝑍
𝐷
= 2 and
𝑍
𝐷
= 3. The
baseline measurement consisted of the posterior model alone and was used as a reference for comparison with the
cases with interference introduced by the presence of the second model.
III. Results and Discussion
Drag and moment coefficient data was reduced from the collected data and tabulated. The goal of the experiment
was to determine if any pattern existed between interference drag and the relative vertical
𝑍
𝐷
and horizontal
𝑥
𝐷
positions
of two models in tandem and to provide possible explanation of observed changes. The data plotted in graphical form
therefore represents the changes in drag and moment coefficients for each configuration. Tandem bodies in high
Reynolds number(Re) flows experienced significantly more interference drag fluctuations than at lower Re flows,
however the drag coefficient magnitudes for high Re flows were closer to zero. While the drag data shows obvious
changes in the posterior model’s stability, the primary reason for separated store collision is the changes in the location
of the center of pressure that contributes to the random motion of the store.
The situation is aggravated because of the separated flow between two bodies in tandem. Without proper store
release orientation, a large, unanticipated moment is therefore introduced on the store. By separating a store in tandem
with an interfering body at a designated orientation, a mother ship could intentionally mitigate the viscous effects
inherent in interference drag. This task is done quantitatively by integrating the total moment interactions on the store
across its vertical and horizontal translations. A combination of drag and moment analysis for a flow system can lead
to a mathematical pathway for the store’s motion sufficient for it to gain self-imposed stability.
Positive axial drag on the posterior model experienced a linear increase in magnitude with increasing Re for all
relative distances
𝑍
𝐷
. This result is consistent with a change in viscous force ratios. The axial drag coefficient function
patterns did not change with an increase in Re, and the drag coefficient elasticity per interval varied only slightly for
higher Re flows. Figure 16 shows the axial drag coefficient data for
𝑍
𝐷
= 1. The small or negative drag coefficients
where
𝑥
𝐷
= 0.4 are due to a drafting effect in which the close proximity of the of bodies leads to a sharing of laminar
flow properties. As the relative distance
𝑥
𝐷
increased, the wake from the upstream model was no longer laminar across
the forebody of the posterior missile. The flow across the anterior model’s back face became turbulent or separated,
and the posterior body caught in its wake experienced a steady increase in axial interference drag until a maximum
value where
𝑥
𝐷
= 1.6. The imposed interference drag incrementally subsided with further increase in store separation
𝑥
𝐷
. For the Re=78,000 flow, the drag coefficient caused by the anterior model was near zero for the duration of the
store separation displacement.

3. 3
American Institute of Aeronautics and Astronautics
The moment diagram for the axial torque is located in Figure 19. The values were consistently near zero. The
models were oriented a sufficient distance away from the wind tunnel walls to preclude any wind tunnel boundary
layer perturbations, and very little flow vorticity was measured.
For the relative distances
𝑍
𝐷
= 2 and
𝑍
𝐷
= 3, the magnitude of the axial interference drag for the Re=128,000 flow
was half or lower than what it was where
𝑍
𝐷
= 1 for the majority of relative distances
𝑥
𝐷
. Figures 17 and 18 depict the
geometrically similar drag coefficient patterns with the maximum drag occurring where
𝑥
𝐷
= 1.2. Both relative
distances
𝑍
𝐷
showed a drop in drag coefficient magnitude where
𝑥
𝐷
= 1.6, and the drag magnitudes displayed little rate
of change for the remainder of the increased store separation. Where
𝑥
𝐷
= 1.6 was the lowest interference drag
magnitude for the relative distance
𝑍
𝐷
= 2. Again, the drag coefficient was at a maximum where
𝑥
𝐷
= 1.6 at the
𝑍
𝐷
= 1
configuration. This shows that as the anterior model descends it produces not only focused areas of flow interference,
but also focused areas of little or no axial interference. These measurements are what can be qualitatively used to
locate the positions most conducive to interference drag mitigation on the posterior store. This description holds true
during interference drag coefficient analysis for each axis.
The axial moment diagrams for the two relative distances
𝑍
𝐷
= 2 and
𝑍
𝐷
= 3 are located in Figures 20 and 21. The
torques measured for all store separations
𝑥
𝐷
were also near zero values, and therefore interference drag is not
considered to create significant flow circulation.
Each of the drag coefficient values measured for the posterior model’s vertical axis was negative. Figure 10
through 12 represent the drag coefficient data taken on this axis, and all three of the relative distances
𝑍
𝐷
displayed
sinusoidal drag coefficient patterns with increasing store separation. Where
𝑍
𝐷
= 1 neither the magnitude of the drag
nor the function’s sinusoidal amplitude increased significantly with Re. The vertical interference drag across all store
separations displayed small standard deviations, implying a stable but negative vertical environment for coaxial
bodies. This result is corroborated by the moment diagram in Figure 13. Upon release at
𝑥
𝐷
= 0.4, the posterior model
would experience a significant negative moment about the y-axis, or a downward pitch. As the model’s store
separation is increased, the moment coefficient about the y-axis emulates a parabolic function and becomes positive
by
𝑥
𝐷
= 1.2 for all numbers Re. This observation states that for coaxial bodies traversing store separation at all values
Re, the resulting vertical center of pressure changes location with increased relative distance
𝑥
𝐷
.
The vertical drag coefficient patterns for the relative distance
𝑍
𝐷
= 2 exhibited a sinusoidal behavior at negative
values, however the amplitude of the function was more proportional to Re than where
𝑍
𝐷
= 1. Drag coefficient
magnitudes at all values of Re experienced local maximums at
𝑥
𝐷
= 0.8 and
𝑥
𝐷
= 2.4 and local minimums at
𝑥
𝐷
= 0.4
and
𝑥
𝐷
= 1.6. The drag and moment coefficient diagrams are located in Figures 11 and 14, and the rapid change in rate
direction is apparent in both. Until reaching store separation
𝑥
𝐷
= 2.0, the high Re flow at relative distance
𝑍
𝐷
= 2
exhibited the lowest magnitude of all measured vertical drag coefficients. This observation points to a drag pattern
whose sinusoidal amplitude has an inversely proportional relationship with Re. Conversely, the moment coefficient
data displays a directly proportional with Re. These considerations must be taken into account when designing a high
Re flow system. The vertical drag coefficient magnitude would be low for all measured store separations, but the
moment coefficients would experience large shifts in value magnitude and sign. A highly negative vertical drag
coefficient is not usually a desired result, but if a moment magnitude is too high to sufficiently mitigate after
separation, then the store will no longer be oriented in tandem with the interfering body.
Because the flow propagations occur below the model instead of around it at relative distance
𝑍
𝐷
= 2, the wake
oscillations more frequently shifted its center of vertical pressure. At store separations
𝑥
𝐷
= 0.8, 1.2, and 2.0, there
existed peak relative distances of significant torque application to the store. Each of these points poses serious hazard
to store and release body integrity if the store is left under that particular configuration for too long. To mitigate the
uniformly opposing nature of the pitching moments, the store need only pass through both areas at a constant rate. By
utilizing this constant separation rate technique, a store with axial translation could keep its center of pressure within
a manageable range until it gained control of its momentum independently. Additionally, a store could be intentionally
released in a non-traditional orientation that would negate any expected torque values for initial store separation. Such
calculations require extensive knowledge of the interfering body’s wake field per system.

4. 4
American Institute of Aeronautics and Astronautics
For the Re=39,000 and 128,000 flows, the vertical drag coefficient function for the
𝑍
𝐷
= 3 graph can be compared
to the
𝑍
𝐷
= 1 function as a geometrically similar function with a higher frequency. The flow axially leaving the anterior
model caused areas of high and low dynamic pressure behind it. This directly caused an increase in negative drag
coefficients and a mirroring of previously evaluated flow data where
𝑍
𝐷
= 1. Figures 12 and 15 show the drag and
moment coefficient data for
𝑍
𝐷
= 3. The Re=78,000 vertical drag coefficients for this relative distance
𝑍
𝐷
exhibited an
absolute minimum magnitude of -0.958 where
𝑥
𝐷
= 0.4 and an absolute maximum magnitude of -1.437 where
𝑥
𝐷
=
0.8. It then gradually declined in drag coefficient magnitude with increased store separation.
The moment coefficients for relative distance
𝑍
𝐷
= 3 appear similar and opposite to the
𝑍
𝐷
= 1 values, but because
of the center of pressure inconsistencies at higher store separation displacements, the two should not be regarded as
mathematically relatable. The moment data’s behavior cannot be described as sinusoidal, however the magnitude of
the measured torques did increase with Re. The Re=39,000 and Re=78,000 flows exhibited a maximum value where
𝑥
𝐷
= 0.4 and then lesser magnitudes throughout the rest of the store separations. Torque sign changes were evident in
higher relative store separations, but the magnitude of the moment coefficients is near enough to zero that they did not
pose significant hazard to the store’s stability.
The Re=128,000 flow began at
𝑥
𝐷
= 0.4 with an absolute maximum moment coefficient magnitude and value of
0.0413. It then linearly regressed to an absolute minimum value of -0.0294 at store separation
𝑥
𝐷
= 1.6. Where
𝑥
𝐷
=
2.0 it reached a near-zero positive moment coefficient and then moved back down to a strongly negative coefficient
at
𝑥
𝐷
= 2.4. These rapid moment fluctuations are important to note in flow design, but the most important moment
analysis result for the pitch axis is the massive difference between the moment coefficients where
𝑥
𝐷
= 2.0 for relative
distances
𝑍
𝐷
= 2 and
𝑍
𝐷
= 3. In this experiment’s example, the anterior model’s 2.5 inch negative vertical translation
from
𝑍
𝐷
= 2 to
𝑍
𝐷
= 3 caused a -0.04388 shift in the moment coefficient for this store separation value from 0.0504 to
0.0065. In this comparison the dichotomies of harsh and stable flow environments during interference drag are most
apparent. If a pathway conducive to interference drag mitigation during store separation is to be found for a system,
the orientation of the store’s release must be engineered to direct it through these relative distances of least moment
coefficient interference.
The change in lateral drag coefficients must be separated into high and low Re categories due to the distinct
differences observed between flow regimes. This is only true for the drag coefficients; the moment coefficient data is
shown to have a positive linear correlation with Re. The Re Line will be defined as the Re at which the lateral
interference drag affecting a separated store adopts a different, observable behavior function than it exhibited at Re
flows less than at that point. The difference is best described as a sudden increase in drag coefficient function amplitude
and frequency. This experiment’s Re Line was evaluated near 100,000, but precise Re Line evaluations require
iterative numerical processes with a more accurate measurement devices. This number is an estimate developed from
the presented data, and the actual Re Line for lateral interference drag Re categories should be regarded as a dependent
variable per system. Low Re flows will describe the flows measured beneath the Re line, and high Re flows will
describe the flows measured above the Re Line. The high Re flow behaviors have not been observed to revert behaviors
with further increase in Re.
All of the lateral interference drag coefficients for low Re flows were negative values. Figure 4 depicts the drag
coefficient data where
𝑍
𝐷
= 1, and the aforementioned difference in flow behavior per Re is apparent. The low Re drag
coefficients exhibit mildly sinusoidal behavior while remaining negative, indicating expected lateral oscillation in the
flow. Until reaching the Re Line, the low Re drag coefficient function’s amplitude is directly proportional to Re. A
local minimum magnitude is reached where
𝑥
𝐷
= 1.2, and local maximum magnitudes are found where
𝑥
𝐷
= 0.8 and
𝑥
𝐷
=
2.4. The lateral drag data shows the posterior model to be caught in the anterior model’s negative wake with fluctuating
strength per Re. The models were coaxial in this configuration, so a distinctly stronger wake direction, in this case
negative, on the posterior model forebody is not an alarming result. Upon reaching the Re line, the flow is moving too
fast for the wake to adequately affect the streamlined body, and a new behavior pattern is adopted.
The magnitudes of the lateral interference drag coefficients for high Re flows where
𝑍
𝐷
= 1 were considerably
smaller than the low Re drag coefficients at all store separations
𝑥
𝐷
. This generalization holds true for all relative
distances
𝑍
𝐷
except for two local minimum values at relative distance
𝑍
𝐷
= 2 where
𝑥
𝐷
= 1.2 and
𝑥
𝐷
= 2.4. The high Re

5. 5
American Institute of Aeronautics and Astronautics
flow where
𝑍
𝐷
= 1 experienced a maximum magnitude and minimum value where
𝑥
𝐷
= 0.4. This result shows a large
negative wake bending around the back of the anterior model. Each Re flow felt almost exactly the same drag
coefficient at this store separation. As store separation increased, the drag coefficients for the high Re flow became
positive until a maximum value where
𝑥
𝐷
= 1.2. The drag coefficient then reverted to a small negative value where
𝑥
𝐷
= 1.6 and remained there throughout the further increased store separation.
The moment coefficient analysis for the store separation where
𝑍
𝐷
= 1 is characterized by a sinusoidal function
whose amplitude is directly proportional to Re. The moment diagram found in Figure 5 shows the store experienced
a local maximum in torque where
𝑥
𝐷
= 0.4 and
𝑥
𝐷
= 1.6 and a local minimum where
𝑥
𝐷
= 0.8. The lowest moment
coefficient magnitudes for coaxial bodies in tandem were found where
𝑥
𝐷
= 1.2 and
𝑥
𝐷
= 2.4. These will be important
relative distances in the final data results and conclusions. The front and back end of the coaxial store separation data
in this Figure oppositely mirror each other in shape and pattern. The values of the back end are lesser in magnitude,
suggesting a damping term in the observably repeating moment function. This damping term affects not only the
magnitude, but also the frequency of the lateral moment coefficient function. Further research into a dependent lateral
moment function could yield an adjustable damping term used to augment the stability of the system, possibly leading
to a decrease in the locational instability on the center of pressure.
The drag coefficients where
𝑍
𝐷
= 2 exhibited an inverse pattern relationship with the
𝑍
𝐷
= 1 values across all store
separations
𝑥
𝐷
. Lateral drag coefficients for
𝑍
𝐷
= 2 are found in Figure 6. Comparing Figures 4 and 6, a negative
relationship exists between the rates of the drag coefficients until where store separation
𝑥
𝐷
= 2.4. The observed
directional opposition suggests that as the anterior model descends, its lateral flow characteristics also exhibit a
measurable, vertical, sinusoidal function until the flow redacts its unstable wake characteristics upon increased store
separation and begins to re-adopt the wind tunnel flow direction. For low Re flows where
𝑍
𝐷
= 2, the maximum
magnitude existed where
𝑥
𝐷
= 1.2 and the minimum existed where
𝑥
𝐷
= 2.0.. Two local maximums for the Re=128,000
flow existed where
𝑥
𝐷
= 0.4 and
𝑥
𝐷
= 2.0, and two local minimums existed where
𝑥
𝐷
= 1.2 and
𝑥
𝐷
= 2.4. The maximum
where
𝑥
𝐷
= 0.4 was the highest recorded lateral drag coefficient at 1.236.
The moment coefficients for this configuration were significant and positive for all store separations
𝑥
𝐷
except
for a special case where
𝑥
𝐷
= 0.8. The substantial positive yaw depicted in Figure 8 for all store separations but
𝑥
𝐷
=
0.8 is likely a property characteristic of the wake. Looking back at the drag coefficient data, the low Re drag is entirely
negative and the high Re drag shifts in sign. To maintain a positive yaw, the negative, lateral, low Re drag forces must
have a resultant vector concentrated on the back half of the missile model. The changing, negative drag forces for high
Re flows must also be concentrated on the back half, but the positive drag forces must result in the model forebody.
This moment analysis is consistent with the oscillating lateral flow pattern described for the
𝑍
𝐷
= 1, coaxial drag
coefficient data. Where
𝑥
𝐷
= 0.8, the magnitudes of all Re flows approach zero.
The lateral drag coefficient data for
𝑍
𝐷
= 3 does not deviate from the lateral patterns inherent in flows of lesser
relative distances,
𝑍
𝐷
. The data is graphed in Figure 7. The low Re flows, with wholly negative values, exhibit a
maximum magnitude where
𝑥
𝐷
= 1.6 and a minimum magnitude where
𝑥
𝐷
= 0.4. It should be noted that for the
Re=78,000 flow, where
𝑥
𝐷
= 1.6 showed the largest negative value measured for all lateral drag coefficients at -1.490.
The high Re flows similarly experienced rapid intervals of rate and sign where
𝑍
𝐷
= 3. The local maximums existed
where
𝑥
𝐷
= 0.4,
𝑥
𝐷
= 1.2, and
𝑥
𝐷
= 2.0. the local minimums existed where
𝑥
𝐷
= 0.8,
𝑥
𝐷
= 1.6, and
𝑥
𝐷
= 2.4. Because of
the constant shifts in direction sign, the lateral drag coefficient magnitudes are closer to zero than previously observed
flows.
The moment coefficient analysis for the store separation where
𝑍
𝐷
= 3 is characterized by a quasi-sinusoidal
function whose amplitude is directly proportional to Re for the Re=39,000 and Re=128,000 flows and a parabolic
function for the Re=78,000 flow until where
𝑋
𝐷
= 2.0. The change in moment coefficient function is likely due to a
change in flow oscillation properties with increasing Re whose frequencies at higher Re values realign with the

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American Institute of Aeronautics and Astronautics
patterns described in low Re values. Figure 9 displays the lateral moment coefficient data for
𝑍
𝐷
= 3. At all Re flows
the calculated values were negative. The flow function shift is most apparent where
𝑥
𝐷
= 1.2. An increase in moment
coefficient is exhibited for the Re=39,000 and Re=128,000 flows, but a decrease in torque is shown when Re=78,000.
The Re=39,000 and 128,000 flow models experience a significant jump to a larger moment coefficient magnitude
while the Re=78,000 flow data experienced a marginal decline in magnitude along the interval from
𝑋
𝐷
= 1.2 to
𝑋
𝐷
=
1.6. Each Re flow then expresses a local minimum magnitude where
𝑋
𝐷
= 2.0 before ending their data measurements
in an increasingly negative direction. This data also points to localized pockets of strong interference drag and
localized pockets of tame force and torque applications. .
The lateral drag and moment data expressed a visible pattern in the flow oscillations.. For relative distance
𝑍
𝐷
=
1 in Figure 4, there are two shifts in value sign along store separation
𝑋
𝐷
. For
𝑍
𝐷
= 2 in Figure 6, there exist three changes
in value sign. For
𝑍
𝐷
= 3 in Figure 7, there exist three changes in value sign, but the rate of drag coefficient change
shifts four times. This correlation directly indicates that with increasing relative vertical distance ∆
𝑍
𝐷
from an
interfering body to an affected one, there is a rise in the frequency of flow direction oscillation in high-Re flows. This
tandem flow interference pattern can be utilized when designing store separation systems. As the separated store
descends with the constant negative drag coefficient values, it experience several changes in force directions in the
oscillating flow. If descending in high Re flows, its total integrated lateral drag coefficient stays closer to zero, but it
becomes increasingly difficult to predict in which direction it will end due to the wake oscillations. If a carriage was
to release a store largely dependent on lateral stability, the most effective method of store separation from the
interfering anterior body is to begin the separation with a large rate of negative vertical translation followed by the
store’s own capacity to guide and direct itself. The majority of stores released without the capability to orient
themselves are not traditionally placed in and tandem separation system.
The defining factors in determining the center of pressure during interference drag for bodies in tandem are known to
be the lateral and vertical interference drag coefficients. Because of the distinctly smaller magnitudes of these drag
coefficients during high Re flows than low Re flows, designing a store separation system optimized for high Re flows
would be significantly easier than designing a system optimized for low Re store separation. The optimal position
where a separated store experiences the least amount of interference drag is a configuration of geometrically similar
bodies with the anterior body in a
𝑍
𝐷
= 2 orientation and a store separation displacement of
𝑥
𝑑
= 5 inches. In this
orientation the store feels significantly less drag at higher Reynolds number flows in both the y and z planes, so its
practicality is suited for modern applications.

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American Institute of Aeronautics and Astronautics
IV. Conclusion
Interference drag is generated when two or more bodies experience high-velocity flow in tandem. The wake of
the upstream body interferes with the posterior body resulting in a change in drag coefficient. While the non-axial
forces applied to separated store are detrimental to its directional stability, the moments on the posterior store
generated by the proximal upstream wake oscillations present the most danger to the store release carriage. This
experiment did not measure supersonic flow interference drag, however any oblique shock interaction with previously
aggravated boundary layers presents additional hazard to separated store orientation. The moment effects are caused
by boundary layer separation due to the high-velocity flow between the separated store and the carriage. The
increasingly turbulent nature of the boundary layer causes a gradient of shear stress across the surface of the store.
This large, new frictional force applied non-uniformly on the missiles causes an unexpected torque on the system,
effectively counteracting any store trajectory development. The separated stores become oriented against the flow,
their resultant pressure vectors point back toward the carriage, and the two collide.

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American Institute of Aeronautics and Astronautics
V. List of Figures
Figure 2: The test setup and the coordinate Figure 3: Close up of ATI NANO25 sensor
Figure 4: Lateral Drag Coefficients, Z/D=1 Figure 5: Lateral Moment Coefficients, Z/D = 1
Figure 6: Lateral Drag Coefficients, Z/D = 2 Figure 7: Lateral Drag Coefficients, Z/D = 3

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American Institute of Aeronautics and Astronautics
Figure 8: Lateral Moment Coefficients, Z/D = 2
Figure 10: Vertical Drag Coefficients, Z/D = 1
Figure 9: Lateral Moment Coefficients, Z/D = 3
Figure 11: Vertical Drag Coefficients, Z/D = 2
Figure 12: Vertical Drag Coefficients, Z/D = 3 Figure 13: Vertical Moment Coefficients, Z/D = 1

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American Institute of Aeronautics and Astronautics
.
Figure 18: Axial Drag Coefficients, Z/D = 3
Figure 20: Axial Moment Coefficients, Z/D = 2
Figure 14: Vertical Moment Coefficients, Z/D = 2 Figure 15: Vertical Moment Coefficients, Z/D = 3
Figure 16: Axial Drag Coefficients, Z/D=1 Figure 17: Axial Drag Coefficients, Z/D = 2
Figure 19: Axial Moment Coefficients, Z/D = 1
Figure 21: Axial Moment Coefficients, Z/D = 3