The Big-Bertha was a large howitzer designed by Krupp in Germany prior to World War I. It had a massive 420mm caliber and was used during World War I to bombard fortifications in Belgium and France. The portable version weighed 43 tons and could fire shells weighing up to 830kg.

4. The Big-Bertha was a semi-portable Howitzer
design by Krupp in Germany prior to World
War I.
It was used in World War I in Belgium and
France against fortifications.
It had a 420mm caliber (Yes! 420mm) and
could fire a semi-armor-piercing shell of
1,160kg.
The photo above is the portable version with
a shorter barrel weighting 43 tons capable of
firing a shell of 830kg.
BIG BERTHA - HISTORY

5. AIR GUN V2.0 - THE BIG BERTHA
• What is the best way to interest young kids in Physics? (Yes! I have two boys)
• They may not be that exited doing their lab work at school but these are
experiments they will never forget.
• It is possible to run non-thermodynamic simulations in Excel and obtain a
rough estimate of the performance of a gas gun.
• Thankfully, Hall consulting developed a FREE full thermodynamic simulator for
gas guns. http://www.thehalls-in-bfe.com/GGDT
BANG! BAM! BOOOOM!

6. AIR GUN V2.0 BIG BERTHA – DESIGN HISTORY

7. BIG BERTHA
• The Big-Bertha is a wheeled gun with
inter-changeable barrels of 2” caliber
and 4” caliber. The 2” barrel is 8’ long,
the 4” barrel is 6’ long.
• It uses two 4” diameter tanks with a
total capacity of 17.3 liters. Max
pressure is 150PSI
• It is triggered through a manifold of 6 x
1” Orbit sprinkler valves.
• It is currently fired electrically but will
be modified to pneumatic triggering.
• Even fired electrically, it is absolutely
lethal. We fired a big onion through 3
layers of 11-ply ¾” plywood!

8. BIG BERTHA

9. BIG BERTHA - DETAILS
1” Orbit Sprinkler valves
Remote Fire Control
24VDC Power
Elevation Control
Air Tank

10. BIG BERTHA - DETAILS
Valve selector
Filling
Manifold
Arming Switch
Flashing Lights
and Buzzer when
armed

11. BIG BERTHA – PROJECTILE KINETIC ENERGY
2000
2500
3000
3500
4000
4500
5000
0 1000 2000 3000 4000 5000 6000 7000 8000
ProjectileEnergy(Joules)
Projectile Mass (grams)
Projectile Energy - Big Bertha 2"Barrel @ 150PSI

12. BIG BERTHA – ENERGY EFFICIENCY (1)
This needs to be researched further.
From WIKIPEDIA (http://en.wikipedia.org/wiki/Compressed_air_energy_storage), the
total energy of a compressed gas in a volume Vb at a pressure Pb is:
𝐸 = −𝑃𝑏𝑉𝑏 ln(
𝑃𝑎
𝑃𝑏
) with Pa=atmospheric pressure=0.1MPa
For the BIG BERTHA, Vb=19.8liters=0.0198m3 and Pb=150PSI=1.02Mpa, therefore
E=46,856Joules
The kinetic energy of a 2kg projectile is 4,225Joules, therefore the efficiency of the
gun is η=9.0%

13. BIG BERTHA – ENERGY EFFICIENCY (2)
E(J/kg air) = -311 775*[(1/Pa)^0,286 -1)
However, from anther WIKIPEDIA page (lost the link), the total mechanical energy of
1kg of compressed gas at a pressure Pa is:
E(J/kg air) = -311 775*[(1/Pa)^0,286 -1) with Pa=pressure in bar
For the BIG BERTHA, the tanks contain 0.252kg of air at a pressure of 150 PSI
(10.2Bar). Therefore, the total mechanical energy is E=21,809Joules
The kinetic energy of a 2kg projectile is 4,225Joules, therefore the efficiency of the
gun is η=19.4%

15. BERT’S PROJECTS
2” PORTABLE CANNON

16. BERT’S PROJECT
TWO-INCH PORTABLE CANNON

17. “PORTABLE” AIR CANNON
This gun is a compromise between performance and
portability. The gun can be disassembled in smaller
and portable components in minutes. The main
components are:
Base
Tanks and Valves
Assembly
Barrel Assembly

18. “PORTABLE” AIR CANNON
Tanks Inlet
Valve Pressure
Regulator
Pneumatic
Elevation
Compensator
Ammo
Storage
Trigger
Pressure
Gauge
Safety Valve Sprinkler
valves x 4
2” Union
Connector
Tactical
Scope
For better flow and high
velocity performance, the
gun uses an array of three 1”
sprinkler valves. As the
projectile spends very little
time in the barrel, it is critical
to open the valves as quickly
as possible. The valves are
modified and triggered
pneumatically by dumping
the pressure on top of the
diaphragm. All 3 valves are
connected with ½” PVC to a
fourth valve. This valve is triggered pneumatically
with a simple valve which in turn triggers the three
main valves providing enough flow for rapid
response and fast opening.

19. “PORTABLE” AIR CANNON
1312
1922
2450
2888
3249
M16, 1,737
0
500
1000
1500
2000
2500
3000
3500
0 500 1000 1500 2000 2500
MASS (gr)
Kinetic Energy (J)
0
50
100
150
200
250
300
350
400
0 500 1000 1500 2000 2500
MASS (GR)
Projectile Velocity (mph)
Kinetic energy and projectile velocity for M=100, 200, 500, 1000 and 2000gr. These graph
indicate that the gun is more efficient with heavier projectiles. Note, the 4.1gr, 5.56mm
NATO round used in the M16 at 1740 Joules at the muzzle. This gun perforated 12
inches of solid wood!!! using a sub-caliber (sabot type) 1.5kg steel projectile.

20. “PORTABLE” AIR CANNON – FLOW LIMIT (1)
In an ideal cannon (infinite tank
capacity and no flow losses), the
kinetic energy of a projectile is
INDEPENDENT of its mass.
However, the previous slide
clearly indicates that the kinetic
energy of the projectile is
strongly dependent of its mass.
WHY?
The graph on the right shows
the tank and barrel pressures as
the projectile moves through
the barrel with M=100, 500 and
2000gr.

21. “PORTABLE” AIR CANNON – FLOW LIMIT (2)
If the flow of air between the tank and the base of the
projectile would be perfect, the pressures in the tank
and the barrel should be equal.
For M=2000gr, the velocity of the projectile inside the
barrel is “slow”. There is sufficient flow through the 3
valves to almost “keep up” with the motion of the
projectile and the drop in pressure in the barrel is
small.
For M=100gr, the velocity of the projectile inside the barrel is fast (up to 2000G’s
acceleration). As the projectile accelerate quickly inside the barrel, there is insufficient
air flow through the 3 valves to “keep up” with the rapid motion of the projectile and
the pressure drops dramatically resulting in limited kinetic energy.

22. 2” AIR CANNON – AMMUNITION
Some example of sub-caliber ammunition
for the 2” cannon. These are similar to
APFSDS (Armor Piercing Fin Stabilized
Discarding Sabot) KE Penetrators used as
anti-tank projectiles in modern
smoothbore guns of main battle tanks.
However, since the distance between the
cannon and the target is short, fins are
unnecessary and the distance is not
sufficient for effective sabot separation,
resulting in simpler projectile design.
These projectiles can penetrate 12” of solid wood

23. With projectile in the 3kJ+
range, it is critical to build a
target capable of stopping
the projectile. Failure to do
so would be catastrophic
when shooting in our
backyard. Hitting the
neighbors house with one of
our sub-caliber projectile
would result in severe
damages (on the right angle
the projectile could go
straight through…. …to the
other side), risk of injury or DEATH. The
target is 18” square, made of 2 layers of
2x4 pressed together with ½” threaded
rods. This modular construction allows us to quickly recondition the target
after a shooting session. In addition, 2 layers of 2x10 (1.5” thickness) and 2
layers of ¾” 11-ply plywood are positioned behind the 2x4s, resulting in a
total thickness of 11.5”.

25. BERT’S PROJECT
AIR RIFLES

26. 105CAL RIFLE
The 105CAL rifle is a light weight air
rifle with a 1” PVC pipe barrel using a
single 1” sprinkler valve. The valve is
triggered by a solenoid powered by
3x9volts batteries.
Sprinkler valves are not designed to
open quickly. On the contrary, in a
sprinkler system it is preferable that
the valves open smoothly to prevent
damage to the pipes.
The valves are rated at 100PSI (water). However, they can withstand 150PSI with good reliability. In a
gun application, it is better to modify the valves to be triggered pneumatically by dumping the air over
the diaphragm for faster response and much improved performance. (For a 20gr projectile, the time
spent in the barrel is only 13ms (200gr, 34ms). Therefore, valve speed is critical)

27. 105CAL RIFLE
Air Hose Fitting
for filling tank
Tank (2” PVC)TriggerBatteries Compartment
Orbit 1” Sprinkler
Valve
Quick Connector
for Breech Loading
50mm Scope,
Laser, Flashlight
1” PVC Barrel (110cm)
Sliding Barrel for
Breech Loading)
105CAL RIFLE ELECTRICALLY TRIGGERED

28. AIR RIFLES

29. 105 CAL RIFLE THERMODYNAMIC MODELING PROJECTILE MASS=20GR
Muzzle velocity = 158m/s (565km/h or 353mph)
Kinetic Energy = 249J
The barrel pressure drops WAY BELOW the reservoir
pressure. The PERFORMANCE IS LIMITED by POOR AIRFLOW
through the valve as the projectile velocity increases

30. 105 CAL RIFLE THERMODYNAMIC MODELING PROJECTILE MASS=200GR
Muzzle velocity = 63.5m/s (229km/h or 143mph)
Kinetic Energy = 404J
The barrel pressure tracks the reservoir pressure. The
Rifle almost reaches its maximum performance E=435J
No airflow restriction as the projectile moves slower in the
barrel.

32. 161CAL RIFLE
Air Hose Fitting
for filling tank
Tank (2” PVC)
Trigger
2 X MODIFIED Orbit
1” Sprinkler Valve
1” PVC Barrel (110cm)
½” PVC for
pneumatic
triggering
Pressure
Gauge
1 ½ “ Union Coupling
Sliding Barrel (Breech
or Muzzle Loading)
Fake Suppressor
Gun Sight
Gun Sight

33. 161CAL RIFLE - AMMUNITIONS

34. 161CAL THERMODYNAMIC MODELING - 100GR PROJECTILE
Muzzle velocity = 133.7m/s (371km/h or 232mph)
Kinetic Energy = 894J
The barrel pressure drops significantly BELOW the reservoir
pressure. The PERFORMANCE IS LIMITED by AIRFLOW
through the valves.

35. Muzzle velocity = 53m/s (191km/h or 120mph)
Kinetic Energy = 1405J
*An M16 firing a 5.56 NATO round delivers 1600J
The barrel pressure tracks the reservoir pressure. The gun
reaches its maximum kinetic energy potential.

36. 0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 50 100 150 200 250 300
FLOW(M3/S)
PROJECTILE VELOCITY (M/S)
1"
1-1/2"
2"
161CAL RIFLE – AIRFLOW AT 60PSI
60PSI
A projectile traveling through the barrel at
a velocity V displaces a volume equal to
the surface area of the barrel multiplied
by the velocity and the relative pressure.
F (m3/s)= 𝜋𝑑2
VP/4
d = diameter of barrel in m
V = velocity in m/s
P = Pressure (PSI)/14.7
A 161CAL projectile at 100m/s and 60PSI
displaces 536 liters/s (0.53 m3/s)

37. 161CAL THERMODYNAMIC MODELING
*The kinetic energy of a projectile fired by an M16 at
point blank range is 1600J. On a human target, only a
fraction on this energy is absorbed by the body as
the projectile exits the body at high velocity. On the
other hand, the effects of a 1.6” diameter, 1kg
projectile, at 53m/s on a human body would be
absolutely horrific as most of the kinetic energy
would be converted into massive organ damage. A
direct hit to the torso or head would result in instant
death. A direct hit to the arms or legs would most
likely result in limb loss. THIS IS NOT A TOY.