J.D. Seidt

The Ohio State University, Columbus, Ohio

J.M. Pereira

Glenn Research Center, Cleveland, Ohio

J.T. Hammer and A. Gilat

The Ohio State University, Columbus, Ohio

C.R. Ruggeri

Glenn Research Center, Cleveland, Ohio

Dynamic Load Measurement of Ballistic Gelatin 

Impact Using an Instrumented Tube

NASA/TM—2012-217661

August 2012
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J.D. Seidt

The Ohio State University, Columbus, Ohio

J.M. Pereira

Glenn Research Center, Cleveland, Ohio

J.T. Hammer and A. Gilat

The Ohio State University, Columbus, Ohio

C.R. Ruggeri

Glenn Research Center, Cleveland, Ohio

Dynamic Load Measurement of Ballistic Gelatin 

Impact Using an Instrumented Tube

NASA/TM—2012-217661

August 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

XII International Congress and Exposition on Experimental and Applied Mechanics

sponsored by the Society for Experimental Mechanics

Costa Mesa, California, June 11–14, 2012
Acknowledgments

Support was received by the National Aeronautics and Space Administration Aviation Safety Project. The authors would like to 

acknowledge the useful advice and assistance of Duane Revilock, and Jeff Hammel of the NASA Glenn Research Center Ballistic 

Impact Facility. This work was supported in part by an allocation of computing time from the Ohio Supercomputer Center (OSC). 

This work was sponsored by the Aviation Safety at the NASA Glenn Research Center.

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217661 1 

Dynamic Load Measurement of Ballistic Gelatin Impact 

Using an Instrumented Tube 

J.D. Seidt 

The Ohio State University 

Columbus, Ohio 43210 

J.M. Pereira 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

J.T. Hammer and A. Gilat 

The Ohio State University 

Columbus, Ohio 43210 

C.R. Ruggeri 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Bird strikes are a common problem for the aerospace industry and can cause serious damage to an 

aircraft. Ballistic gelatin is frequently used as a surrogate for actual bird carcasses in bird strike tests. 

Numerical simulations of these tests are used to supplement experimental data, therefore it is necessary to 

use numerical modeling techniques that can accurately capture the dynamic response of ballistic gelatin. 

An experimental technique is introduced to validate these modeling techniques. A ballistic gelatin 

projectile is fired into a strike plate attached to a 36 in. long sensor tube. Dynamic load is measured at two 

locations relative to the strike plate using strain gages configured in a full Wheatstone bridge. Data from 

these experiments are used to validate a gelatin constitutive model. Simulations of the apparatus are 

analyzed to investigate its performance. 

Introduction 

Bird strikes can inflict serious damage to an aircraft. Photographs of bird strike damage to a Boeing 

767-300 aircraft are presented in Figure 1 (Ref. 1). This aircraft was damaged by large birds as it climbed 

from Charles de Gaulle Airport in Paris. The cockpit area of the aircraft was perforated by the birds, 

causing depressurization. Fortunately, the crew safely returned to the airport and no injuries were 

reported. Another recent and well-publicized example of bird strike damage is the January 15th 2009 

incident involving US Airways Flight 1549. The captain of the Airbus A320-214 was forced to make an 

emergency landing on the Hudson River after both engines ingested Canada geese resulting in a complete 

loss of thrust (Ref. 2). Because of many incidents like these, aircraft structures and engines must be 

certified to operate safely after a bird strike or ingestion event. 

Certification tests are conducted using actual bird carcasses (Ref. 3); however, ballistic gelatin is 

frequently used as a surrogate material for preliminary testing. The main advantage to using gelatin for 

testing is repeatability. No two birds are identical, even if they are of the same species. These natural 

variations make it difficult to perform repeatable experiments (Ref. 4). In addition, there are obvious 

sanitary benefits to testing with gelatin opposed to actual birds. Wilbeck and Rand (Ref. 4) developed a 

bird substitute by mixing commercial gelatin with phenolic microballoons. The authors note that this 

surrogate projectile creates impact loads similar to those generated by actual birds. 
NASA/TM—2012-217661 2 

 

Figure 1.—Photographs of bird strike damage to a Boeing 767-300 aircraft (Ref. 1): (a) below cockpit window, 

(b) underside fuselage, (c) aft of radome. 

Many researchers have conducted numerical simulations of bird impact with various aircraft 

structures, such as wing leading edges (Ref. 5), windshields (Ref. 6), flaps (Ref. 7), and engine blades 

(Ref. 8). The majority of these simulations treat the bird as circular cylinders with rounded edges, and 

assume that the birds will behave hydrodynamically on impact. In these studies, various numerical 

treatments of the bird model are used, including Lagrangian, Arbitrary Lagrangian Eulerian (ALE), and 

Smoothed Particle Hydrodynamics (SPH). These simulations need to be validated by comparing the 

results to experimental data. 

An experimental measurement of the dynamic force imparted into a target by a projectile is very 

useful to validate simulations. However, impact force measurements are difficult to obtain accurately 

because of the short duration of the load. Even piezoelectric load cells with the highest frequency 

response are generally not sufficient to measure forces involved in ballistic impact events, and resonances 

in the supporting structure typically make results difficult to interpret and simulate. In the past, gelatin 

impact experiments have been conducted by firing a projectile into a flat plate instrumented with different 

types of pressure transducers (Refs. 9 and 10). Typically, the diameter of the pressure transducer is less 

than the diameter of the gelatin projectile. The pressure on the impacting face of the projectile is certainly 

non-uniform, especially when the projectile begins to “mushroom”. The pressure is maximum at the 

center and decreases radially outward. If it is assumed that the pressure measured by the transducer is 

applied to the entire impacting surface area, the impulse transmitted to the target by the projectile could 

be substantially overestimated. While pressure measurements can be very valuable, it is also useful to 

measure the overall impact force. In this paper, a tubular sensor is used to measure the transmitted force 

from an impacting gelatin projectile. These results are compared to simulations of the measurement 

device to determine how the measured response varies from the input loading function. 

Experimental 

The tube sensor (Fig. 2) is a 36 in. long 2024-T3 aluminum drawn tube with an outside diameter of 

3.5 in. and a 0.125 in. thick wall. The tube dimensions were chosen such that the waves transmitted along 

the tube would remain elastic during the impact loading. Transmitted forces were anticipated to be 

roughly 20,000 lb, thus the peak dynamic stress in the tube is 15.1 ksi, 30 percent of the yield strength for 

2024-T3 aluminum (50.0 ksi). A 0.5 in. thick 7075-T6 aluminum strike plate is attached to end of the tube 

to serve as a contact surface for the gelatin projectile. 

The tube is instrumented with Vishay Micro-Measurements EA-06-125BZ-350 electric resistance 

strain gages configured in full Wheatstone bridges at two locations: 6 and 12 in. from the front edge of the 

tube. For each bridge, two strain gages are oriented in the axial (loading) direction and two are oriented in 

the transverse direction, a configuration commonly used for load cells. The sensitivity of each bridge is: 

    

 1

2AE

S F

V

E g (1)

(a) (b) (c) 
NASA/TM—2012-217661 3 

Figure 2.—Tube sensor: (a) section schematic of the tube, (b) photo of the sensor and experimental setup. 

where, ΔE is the signal voltage, V is the excitation voltage, Sg is the gage factor, F is the force in the tube, 

A is the tube’s cross-sectional area and E and ν are the Young’s modulus and Poisson’s ratio of the tube, 

respectively. The strain gages have a gage factor of 2.105, so for 10 V excitation, the sensitivity is 

0.996 mV per kip. For comparison, a solid 3.5 in. diameter rod with the same instrumentation would have 

a sensitivity of 0.137 mV per kip. 

Bridge #1 can measure an impact event that is 297 s long. This is the duration required for an elastic 

wave, traveling at 201,884 in./s, to traverse 60 in. or twice the distance from the bridge to the end of the 

tube. After 297 s, the measurement from the bridge is affected by the beginning of the reflected wave. 

Bridge #2 can only measure a 238 s event, since this bridge is 6 in. closer to the end of the tube. 

The projectiles (Fig. 3) were nominally 1.25 in. diameter, 3.0 in. long cylinders, made up of gelatin, 

water and phenolic microballoons used to modify the density. A 20 percent gelatin mixture recipe was 

used with the appropriate volume of phenolic micro-spheres needed to attain the desired specific gravity 

of the projectile. The ratio of gelatin to water is defined on a mass basis; the percent gelatin is defined by 

the ratio of gelatin mass to the total mass of gelatin and water. The desired specific gravity of the 

projectiles was 0.95. A detailed projectile manufacturing procedure was followed to ensure reproducible 

projectile characteristics. 

The gelatin projectiles were accelerated by a single stage light gas gun using helium as the driving 

gas. The gun has a bore diameter of 2 in. and a 12 ft long barrel. Instrumentation systems were placed 

inside a vacuum chamber mated to the gun barrel. The projectiles were carried down the barrel in 

polycarbonate sabots (Fig. 3) that were arrested by a sabot stopper at the muzzle. When arrested, the sabot 

remains in contact with the stopper providing a seal which prevents the high pressure propellant gas in the 

barrel from affecting the vacuum chamber pressure. 

36.00 in

12.00 in

6.00 in

7075-T6 Al 

Strike Plate

2024-T3 Al 

Tube

Bridge #1 Bridge #2

(a) 

(b) 

Strike Plate 

Bridge #1

Bridge #2

Gas Gun Tube Sensor

Muzzle
NASA/TM—2012-217661 4 

Figure 3.—Polycarbonate sabot and gelatin projectile. 

Figure 4.—Tube sensor data from a gelatin impact test, projectile velocity: 504 ft/s. 

Tube sensor data was recorded using a Spectral Dynamics 2805 data acquisition module at a rate of 

1.25E6 samples/sec. The projectile orientation and speed were computed using a calibrated pair of Vision 

Research Phantom V7.3 cameras and GOM’s PONTOS digital image correlation point tracking software. 

The cameras recorded images at a rate of 10,000 frames/sec and a resolution of 704 (horizontal) x 424 

(vertical) pixels. The software tracked the three-dimensional positions of points marked on the projectile 

as a function of time. A third Phantom V7.3 camera served as a backup system for measuring projectile 

speed. This camera was oriented normal to the projectile path and acquired images at 20,000 frames/sec. 

Figures 4 and 5 present results from an experiment in which the projectile impacted the strike plate at 

504 ft/s. The output history of the tube sensor is shown in Figure 4. The blue trace is the output from 

bridge #1 and the red trace is the output from bridge #2. Both bridges show an initial tensile load of 

roughly 2500 lb followed by a compressive peak of –13,000 lb and then a 240 s long region where the 

load oscillates about –4000 lb. The initial tensile pulse is discussed in the next section. The compressive 

peak measured by bridge #1 (–14,500 lb) has a larger magnitude than that measured by bridge #2 

(–12,500 lb). There are also other minor differences between the measurements from bridge #1 and #2. 

This is evidence of dispersion. The three regimes of Wilbeck’s model for soft projectiles (Ref. 11) can be 

seen in the data. The initial compressive peak corresponds to the shock development regime. The release 

wave regime coincides with the drop in compressive force. The steady flow regime coincides with the 

0 100 200 300 400

Time (s)

-20000

-15000

-10000

-5000

0

5000

10000

Load (lb)

lvg587, bridge 1 

lvg587, bridge 2
NASA/TM—2012-217661 5 

Figure 5.—Sequence of a gelatin projectile impacting the strike plate of the tube sensor at 504 ft/s. 

region of relatively constant force. Figure 5 shows a series of sequential images from the high speed 

camera oriented normal to the projectile path. Figure 5(a) shows the projectile just prior to impact. 

Figure 5(b) shows the projectile just after impact. The impact sequence develops in Figure 5(c), (d), (e), 

and (f). 100 s elapse between each image, so the sequence represents a 500 s duration. The white 

debris visible in the images is light foam that was used to support the projectile in the sabot. 

Numerical Simulations 

LS-DYNA (Ref. 12) simulations were used to evaluate the performance of the tube sensor. Threedimensional, eight-noded, constant stress solid elements were used to mesh the strike plate and the tube. 

The mesh was constructed of elements with approximate aspect ratios of 1.0 and lengths of 1/32 in. The 

strike plate had 112 elements across its diameter and 16 elements through the thickness. The tube had four 

elements through the thickness and 1152 elements along its length. The simulation contained roughly 

1.6 million total elements. Both the strike plate and the tube were modeled as elastic materials with E, ν, 

and ρ as 73.1 GPa, 0.33, and 2.78 gm/cc, respectively. An assumed, evenly distributed pressure history 

was applied to the center of the strike plate. It was applied over a 1.25 in diameter circle, the same 

diameter of the gelatin projectile. This pressure multiplied by the area gives a dynamic load history to 

compare to the tube sensor output. 

Simulated dynamic forces are compared to experimental results in Figure 6. The solid black trace is 

the input load history applied to the center of the strike plate. The input load has a rise time of 5 s and a 

peak compressive load of –9000 lb. After peak load, it decays to a force of –3800 lb and remains there for 

400 s. Simulated forces, calculated from the strain histories of elements at locations that correspond with 

bridge #1 and #2 on the actual sensor are represented by dashed blue and red traces, respectively. Solid 

blue and red traces are actual experimental data measured by the tube sensor. The simulated dynamic 

loads agree quite well with those measured experimentally. The loads measured by the tube, however, are 

substantially different than the input load history. The peak compressive load measured by the tube sensor 

is roughly 40 percent higher than the peak input force. The steady flow region (constant load), however, is 

reasonably well captured by the sensor until the reflected pulse arrives at the bridge. Another obvious 

discrepancy between the input and output load is the presence of the initial tensile pulse that was both 

measured experimentally and calculated in the simulation. The source of the tensile pulse is deformation 

in the strike plate. Figure 7 shows the simulated strike plate deformation at various times after load 

initiation. As the load increases, the strike plate bends elastically into the tube. Figure 7(a) is a plot of the 

axial deflection of points distributed along the diameter of the strike plate. The bending draws the 

material of the strike plate radially inward. Figure 7(b) shows the radial displacement of points distributed 

(a) (b) (c) 

(d) (e) (f) 
NASA/TM—2012-217661 6 

Figure 6.—Comparison of experimental and simulated dynamic forces. 

Figure 7.—Strike plate deformation at different times after load: (a) axial bending, (b) radial contraction. 

along the radius of the plate. As the load accumulates negative radial displacements arise. The tube is 

attached to the strike plate, so it also is drawn inward. This uniform radial contraction creates the tensile 

pulse evident in both the experimental and simulated results at the bridge locations. 

The results in Figure 6 show that the tube sensor output significantly overestimates the peak 

compressive input load. Additional simulations were run to determine how the pressure load input 

characteristics affect the measurement error. These characteristics include the rise time and shape of the 

load history. Results from this study are shown in Figure 8. Results are presented from four simulations 

where the tube sensor was subjected to different load histories. The load histories are represented by 

dashed traces. The input load history for simulation #1, represented by the blue trace, is identical to the 

one shown in Figure 6. It has a rise time of 5 s, a peak load of –9000 lb followed by an unloading tail to 

a constant load of –3800 lb. The input history for simulation #2 (red trace) is identical to that of 

simulation #1 except it has a 25 s rise time. Simulations #3 (green trace) and #4 (black trace) are 

subjected to a –9000 lb step load history with 25 and 100 s rise times, respectively. The tube output, 

measured at a location corresponding to bridge #1, is represented by solid traces. The initial tensile pulse 

amplitude decays with increasing rise time. In all four simulations, the tube sensor output overestimates 

0 100 200 300 400 500

Time (s)

-20000

-15000

-10000

-5000

0

5000

10000

Load (lb)

lvg587, bridge 1 

lvg587, bridge 2

Simulation, bridge 1

Simulation, bridge 2

Simulation Input 

(a) (b) 
NASA/TM—2012-217661 7 

Figure 8.—Results from simulations of the sensor tube subjected to four different load histories. 

the peak compressive load input. The data in Figure 8 illustrate that this overshoot is dependent on both 

the rise time and the shape of the load pulse. It is not solely dependent on rise time, since the overshoot 

from simulation #1, which has the fastest rise time (5 s), is less than those from simulation #2 and #3 

which both have a rise time of 25 s. The overshoot from simulation #3 is substantially higher than that 

from simulation #2, showing that this phenomenon is dependent on the shape of the load as well. The 

impulse of the input load for simulation #3 is significantly larger than that from simulation #2. Therefore, 

the overshoot becomes worse with increasing impulse. This also explains why simulation #2’s overshoot 

is larger than that of simulation #1. The input load impulse of simulation #2 is slightly larger than that 

from simulation #1, since there is more area under the 25 s ramp than there is under the 5 s ramp. The 

results of simulation #4 show that the rise time also plays a role since the 100 s rise time step load gives 

the least overshoot. 

No attempt was made to optimize the geometry of the tube sensor. It is likely that the geometry can 

be modified to minimize errors between the input and measured loads. Although the measured output is 

not always identical to the input load, the tube sensor is still a useful tool to validate numerical models of 

ballistic gelatin. The experimental data can be compared to results of a validation simulation in which a 

proposed numerical treatment of a gelatin projectile is fired into a model of the tube sensor. This 

comparison can be used as a performance metric for the gelatin model. The simple geometry of the sensor 

is easily incorporated into simulations, making validation simulations relatively straightforward. 

Summary and Conclusions 

A tube sensor was used to measure dynamic impact forces from ballistic gelatin projectiles. The 

sensor consists of a 0.5 in. thick 7075-T6 aluminum strike plate attached to 36 in. long 2024-T3 

aluminum tube with a 3.5 in. outside diameter and 0.125 in. thick wall. The tube was instrumented with 

electrical resistance strain gages at two locations: 6 and 12 in. from the edge of the tube. 1.25 in. diameter, 

3.0 in. long gelatin projectiles were fired normal to the tube’s strike plate at velocities of roughly 450 ft/s 

using a single stage light gas gun. Data from the tube sensor’s strain gages were recorded and high speed 

cameras were used to determine the projectile’s velocity and orientation prior to impact. 

0 100 200 300 400 500

Time (s)

-20000

-15000

-10000

-5000

0

5000

10000

Load (lb)

Simulation #1 Input 

Simulation #1 Output

Simulation #2 Input

Simulation #2 Output

Simulation #3 Input

Simulation #3 Output

Simulation #4 Input

Simulation #4 Output
NASA/TM—2012-217661 8 

LS-DYNA simulations were used to investigate the performance of the tube sensor. Simulated output 

from the tube matched the experimental data well. The deformation of the tube’s strike plate was 

identified as the source of an initial tensile pulse found in both experimental data and the simulation 

results. A numerical investigation of the sensor’s response to various input load histories was conducted. 

The results show that the tube sensor overestimates the peak compressive load for all four input loads 

considered. The magnitude of this overshoot is dependent on both the rise time and shape of the load 

input. Fast rise-time, high impulse load histories lead to large overshoots. Reducing the impulse and 

increasing the rise time of the load history reduce the overshoot. Measurement errors can likely be 

reduced by optimizing the sensor’s geometry. 

The tube sensor is a useful tool to validate numerical models of ballistic gelatin projectiles. It can 

easily be incorporated into validation simulations allowing the simulated and experimental sensor 

response to be directly compared. 

References 

1. Tiffany, C.F., Gallagher, J.P., Babish, C.A., “Threats to Aircraft Structural Safety, Including a 

Compendium of Selected Structural Accidents/Incidents”. Aeronautical Systems Center Technical 

Report #ASC-TR-2010-5002, March, 2010. 

2. “Loss of Thrust in Both Engines After Encountering a Flock of Birds and Subsequent Ditching on 

the Hudson River, US Airways Flight 1549, Airbus A320-214, N106US, Weehawken, New Jersey, 

January 15,2009,” NTSB Accident Report #NTSB/AAR-10/3, PB2010-910403, May 4th 2010. 

3. McCallum, S.C., Constantinou, C., “The Influence of Bird-Shape in Bird-Strike Analysis,” 

Proceedings of the 5th European LS-DYNA Users Conference, Birmingham, UK, May, 2005. 

4. Wilbeck, J.S., Rand, J.L., “The Development of a Substitute Bird Model,” Journal of Engineering 

Power, Vol. 103, 1981, pp 725-730. 

5. McCarthy, M.A., Xiao, J.R., McCarthy, C.T., Kamoulakos, A., Ramos, J., Gallard, J.P., Melito, V., 

“Modelling of Bird Strike on Aircraft Wing Leading Edge from Fibre Metal Laminates – Part 2: 

Modelling of Impact with SPH Bird Model,” Applied Composite Structures, Vol. 11, 2004, pp 317-

340. 

6. Wang, F.S., Yue, Z.F., “Numerical Simulation of Damage and Failure in Aircraft Windshield 

Structure Against Bird Strike, Materials and Design, Vol. 31, 2010, pp 687-695. 

7. Ivancevic, D., Smojver, I., “Hybrid Approach in Bird Strike Damage Prediction on Aeronautical 

Composite Structures,” Composite Structures, Vol. 94, 2011. pp 15-23. 

8. Mau, R.H., Meguid, S.A., Ng T.Y., “Transient Three Dimensional Finite Element Analysis of a 

Bird Striking a Fan Blade,” International Journal of Mechanics and Materials in Design, Vol. 4, 

pp 79-96. 

9. Lavoie, M.A., Gakwaya, A., Nejad Ensan, M., Zimcik, D.G. and Nadlall, D. “Bird’s Substitute Tests 

Results and Evaluation of Available Numerical Methods,” International Journal of Impact 

Engineering, Vol. 36, 2009, pp 1276-1287. 

10. Barber, J.P, Taylor, H.R., and Wilbeck, J.S., “Characterization of Bird Impacts on a Rigid Plate: 

Part 1,” Air Force Flight Dynamics Laboratory Technical Report #AFFDL-TR-75-5, Jan. 1975. 

11. Wilbeck, J., “Impact Behavior of Low Strength Projectiles,” Air Force Materials Laboratory 

Technical Report #AFML-TR-77-134, July, 1978. 

12. “LS-DYNA Keyword User’s Manual,” Version 971, Livermore Software Technology Corporation 

(LSTC), May, 2007. 

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Dynamic Load Measurement of Ballistic Gelatin Impact Using an Instrumented Tube 

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14. ABSTRACT

Bird strikes are a common problem for the aerospace industry and can cause serious damage to an aircraft. Ballistic gelatin is frequently 

used as a surrogate for actual bird carcasses in bird strike tests. Numerical simulations of these tests are used to supplement experimental 

data, therefore it is necessary to use numerical modeling techniques that can accurately capture the dynamic response of ballistic gelatin. An 

experimental technique is introduced to validate these modeling techniques. A ballistic gelatin projectile is fired into a strike plate attached 

to a 36 in. long sensor tube. Dynamic load is measured at two locations relative to the strike plate using strain gages configured in a full 

Wheatstone bridge. Data from these experiments are used to validate a gelatin constitutive model. Simulations of the apparatus are analyzed 

to investigate its performance. 

15. SUBJECT TERMS

Bird-aircraft collisions; Terminal ballistics 

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