Potato cannon

Last updated

A potato cannon, also known as a potato gun or potato launcher, is a pipe-based cannon that uses air pressure (pneumatic), or combustion of a flammable gas (aerosol, propane, etc.), [1] [2] [3] [4] to fire projectiles, usually potatoes. [5] A simple design consists of a pipe sealed on one end, with a reducer on the other end to lower the diameter of the pipe, which has the corresponding lower-diameter pipe attached to it, called the barrel. Generally, the operator loads the projectile into the barrel, then utilizes a fuel or air pressure (or sometimes both) to propel the projectile out of the cannon.

Contents

The potato cannon can trace its origin to the World War II-era Holman Projector, which was a shipboard anti-aircraft weapon. [6]

Operation methods

Potato cannons utilise fluid pressure to propel projectiles down their barrels in the similar manner as a firearm (although at a much lower pressure). There are three basic methods that to achieve this:

Combustion

Combustion powered potato cannons typically have the least complex designs; the four basic elements of which are:

In order to fire, the operator loads a projectile into the barrel, adds fuel to the combustion chamber (for example aerosols or propane), and triggers the ignition source (often using a piezoelectric barbecue igniter). The fuel-air mixture then ignites, creating hot expanding gases which force the projectile out of the barrel. The range of the cannon depends on many variables, including the type of fuel used, the efficiency of the fuel/air ratio, the combustion chamber/barrel ratio, and the flight characteristics of the projectile. Common distances vary from 100–200 meters (330–660 feet), and there is a reported case of a cannon exceeding 500 meters (1,600 feet) of range. [7]

Advanced combustion cannons may include metered propane or calcium carbide (acetylene) injection to ensure proper fueling, chamber fans to mix the fuel with the air and accelerate venting of the chamber after firing, multiple spark gaps (spark strips) to decrease combustion time, and high-voltage ignition sources (flyback circuits, stun guns, camera flashes, etc.).

Combustion cannons are usually less powerful than their pneumatic or hybrid counterparts, especially when hairspray / alcohol is used as a propellant. Pure oxygen can be mixed with the fuel, but this can cause an explosion of the cannon material, potentially injuring anyone nearby.

Pneumatic

A pneumatic potato cannon Bongspud.jpg
A pneumatic potato cannon
A large pneumatic design: The projectile is loaded in the muzzle (not pictured), which is then attached to the cannon (at 2). The air reservoir (3) is filled to 120 psi (0.83 MPa) using the Schrader valve (4). Upon opening the solenoid valve (1), the air from the reservoir is transferred to the projectile, which is fired out of the muzzle. Pneumaticspudgun989.jpg
A large pneumatic design: The projectile is loaded in the muzzle (not pictured), which is then attached to the cannon (at 2). The air reservoir (3) is filled to 120 psi (0.83 MPa) using the Schrader valve (4). Upon opening the solenoid valve (1), the air from the reservoir is transferred to the projectile, which is fired out of the muzzle.

Pneumatic cannons are considered more difficult to build due to the need of a completely airtight construction. These cannons have four basic components:

In a pneumatic potato cannon, the pressure chamber is pressurized using a pressure source. The filling valve is usually a commonly available type such as a Schrader or Presta valve but other assemblies to pressurise the cannon such as quick release connections with ball or check valves have been used.

The pressure release valve is often one of a variety of commercially available types such as a plumbing ball valve, an irrigation sprinkler valve or a quick exhaust valve. Experienced builders often make their own valves for this purpose to gain greater flow and faster actuation. The most common custom design used is the piston valve. Multiple valves arranged to be triggered together are occasionally used as an alternative to a single larger valve.

The range of pneumatic cannons is more variable than the range of combustion potato cannons due to the increased variation possible in the components. Typical ranges are slightly higher because of the greater power, but the maximum range of some high power pneumatic cannons has been said to be over 1,000 metres (3,300 ft). [8]

Pneumatic potato cannons are generally more powerful than combustion potato cannons. A typical combustion gun generates average chamber pressures of about 200 kPa (30 psi) with peaks of around 500–700 kPa (70–100 psi), while the average pneumatic gun can operate at pressures in the vicinity of 700 kPa (100 psi). In recent times, it has become increasingly common for metal pneumatic cannons to use even higher pressures, sometimes in excess of 3,000 kPa (440 psi).

Hybrid

A hybrid cannon consists of seven basic elements:

A hybrid combines principles of combustion and pneumatic potato cannon. It uses a pre-pressurized mixture of fuel and air to get more power out of a given chamber volume.

In order to fire, the operator first readies the pressure-triggered valve then injects several times the normal amount of fuel and appropriately more air. When the ignition source is triggered, the pressure from the combustion causes the main valve to open and propels the projectile out of the barrel with the released combustion gases. The hybrid is capable of higher velocities than a combustion or pneumatic potato cannon because the pressure generated is higher than that in a combustion gun (for most fuels), and the shock wave moves faster than it can in a pneumatic (for most gases), due to the higher temperature. Projectiles fired by a hybrid have broken the sound barrier. [9]

A hybrid using a fuel and air mix at twice atmospheric pressure is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air need to be measured and matched carefully to ensure reliable operation; hence the use of accurate air pressure gauges and fuel meters.

Dry ice

PVC dry ice cannon in use, 1.5kg (3 pounds) of concrete is poured at the bottom to reinforce it, and plastic sleeves are used to stiffen the lower (highest pressure) part. Dry ice montage.jpg
PVC dry ice cannon in use, 1.5kg (3 pounds) of concrete is poured at the bottom to reinforce it, and plastic sleeves are used to stiffen the lower (highest pressure) part.

A dry ice cannon uses the sublimation of solid carbon dioxide to generate the gas pressure to propel a projectile and is a variation of the burst disk cannon.

The oldest examples simply involve dropping pieces of dry ice into a tube closed at one end and sealing the other end by jamming the projectile in. When the pressure of the carbon dioxide from the subliming dry ice builds high enough, the projectile will be blown out of the tube. [10] The pressures of such devices are not very high as it only needs to build enough to overcome the static friction of the projectile jammed in the barrel. A few hundred kPa is most likely. The range is likely restricted to 100- meters.

Dry ice bomb

A more modern example is the dry ice bomb cannon. A plastic bottle containing water has some dry ice added and is quickly sealed and dropped down a tube closed at one end. A projectile is inserted in after it. The water accelerates the sublimation of the dry ice and the pressure from the carbon dioxide gas produced eventually ruptures the plastic bottle and launches the projectile. The rupturing pressure of a 0.5 L plastic soda bottle is between 1,500–2,000 kPa (220–290 psi)[ citation needed ] in the open air but when confined in a pipe, it could be higher.

Due to the operation of a dry ice bomb, extra safety issues are present:

  • The dry ice bomb used for propulsion can achieve bursting pressure in a matter of seconds to hours depending on the quantity of water and dry ice. If too little dry ice, it also may not achieve bursting pressure at all. These timing issues can cause belief that the cannon has failed to fire but attempting to unload the cannon may then provide the extra stress on the bottle needed for it to rupture.
  • The piping and any reinforcement may be insufficiently strong for the strong pressure impulse when the dry ice bomb explodes and could also explode.
  • The recoil of such cannons can be very strong due to the high pressure combined with the large internal diameter piping needed for the bottles (5–9 cm; 2–3½ in) resulting in them being ill-suited for hand held firing.

Compared to the operation of other potato cannons, dry ice bomb cannons are similar in firing principle to a light-gas gun of the pneumatic type; the plastic bottle performing the task of the burst disk albeit in a less controlled manner.

Another means of utilizing dry ice in potato cannons is to use the sublimation of dry ice to create substantial pressure behind a valve, and placing a barrel on the other side of that valve with a projectile loaded into it. Pressures behind the valve can reach upwards of 5,000 kPa (730 psi), and by quickly releasing the valve, the projectile can be launched. Whilst this method is more controllable and in many means safer than utilizing a soda bottle as a burst disk (provided pressure rated valves and piping are used), it is limited in that quick release valves, such as ball valves, are generally not bigger in diameter than 1 or 2 inches. Additionally, they cannot be opened as rapidly as a soda bottle will rupture, and consequently there is less immediate airflow. However, this is offset by the fact that such a design can operate at more than double the pressure of a typical dry ice bomb cannon, as soda bottles will rupture at only 1,500–2,000 kPa (220–290 psi).

Vacuum

Vacuum cannons differ from typical pneumatic cannons in that they apply a negative pressure to the front of the projectile in order to "pull" it out of the barrel. They typically fire light projectiles and do not have any practical applications outside of demonstrating air pressure theory.

Primary materials

Plastics

Both PVC and ABS piping are also available in forms that are not pressure rated. The use of unrated plastic piping and fittings is a common source of cannon failure and poses a much greater risk to a cannon operator.

Metals

Valve types

Manual

Electric

Pneumatic

Alternate designs have also been used which use a sharp projectile to puncture the burst disk, like a mortar [15] or using a manual puncturing device to trigger failure of the disk. [16] These allow total control over burst disk cannons without the need for hybrid technology and materials as simple as plastic tape can be used for the disk.
Burst disk cannons have also been made which are fired electrically, using a nichrome wire to trigger failure by heating. [17]

Connections

Welding, soldering and gluing

Mechanical joints

The sound barrier

It is rare for a potato cannon to be powerful enough to break the sound barrier, although there are some cases of this happening using specialized designs. The potato cannons used are typically hybrids; but some pneumatic cannons have achieved the feat, either by using a special low-density gas, such as helium, [19] or high pressures combined with a fast valve. [20] There is also one reported case of a combustion design achieving super-sonic velocities. [7]

The difficulty in breaking the barrier arises from the speed of the particles within the gas. The projectile cannot travel faster than the gas particles, which are limited to travel at the speed of sound. The problem is solved by increasing the speed of the particles, either by:

Supersonic velocities may theoretically be attained by pneumatics with a sufficiently large "dead space" between the main valve and projectile. The incoming air can raise the pressure rapidly in this dead space, creating high temperatures sometimes sufficient to achieve supersonic velocities. This particular effect has not yet been successfully used, but has been discussed, as both adiabatic and shock heating are documented phenomena in gases.

The highest projectile speed recorded from a potato cannon is 933.3 m/s (3,060 ft/s) (approximately 2.7 times the speed of sound) with a 16.6-gram (256 gr) 20 mm plastic slug from a hybrid using a 20 MPa (2,900 psi) pre-ignition mixture of air and propane. [21]

Supersonic velocities have been obtained using the related vacuum bazooka with a de Laval nozzle. This also relies on significantly lowering the density of the gas. [22]

Tradeoffs

In summary, the different operation methods of a potato cannon all have their advantages and disadvantages,

Mode of OperationCombustionPneumaticHybridDry Ice Bomb
AdvantageSimple design and decent range compared to uncontained dry ice.Freedom of pressure which allows high firing pressure and velocity/range.Easier to reach high firing pressures which offer high prejectile velocity/range.Reaching high firing pressure is easy due to the strength of commonly-used soda bottles, offering high firing velocity/range.
DisadvantageLower chamber pressure, velocity, and therefore range.Limitations based on pressure supply.Engineering complexity is strongly greater than combustion or pneumatic counterparts.The pressure impulse from the rupturing of the bottle produces stressful conditions for the cannon material.

Practical uses

Although potato cannons are created and used for the purpose of recreation there are other devices which work on identical principles in many other fields with more serious uses.

Entertainment

Industry

A typical propane gun bird scarer Gas gun bird scarer.jpg
A typical propane gun bird scarer

Military

Safety

Potato cannons by nature are hazardous and can present safety issues if poorly constructed or used. Projectiles or failing guns can be dangerous and result in life-threatening injuries, including cranial fractures, enucleation, and blindness if a person is hit. [25] Therefore, users should follow the same rules as if handling a conventional firearm (see gun safety), but given the frequently improvised materials and construction used in potato cannons, it is particularly important for the user to use basic ear and eye protection when operating a potato cannon.

In some jurisdictions potato cannons are outlawed or have restrictions on their use and may require licenses and certification of the gun.

See also

Related Research Articles

<span class="mw-page-title-main">Valve</span> Flow control device

A valve is a device or natural object that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.

<span class="mw-page-title-main">Carburetor</span> Component of internal combustion engines which mixes air and fuel in a controlled ratio

A carburetor is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.

<span class="mw-page-title-main">Air gun</span> Gun that uses compressed air to launch projectiles

An air gun or airgun is a gun that uses energy from compressed air or other gases that are mechanically pressurized and then released to propel and accelerate projectiles, similar to the principle of the primitive blowgun. This is in contrast to a firearm, which shoots projectiles using energy generated via exothermic combustion (deflagration) of chemical propellants, most often black powder or smokeless powder.

<span class="mw-page-title-main">Check valve</span> Flow control device

A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid to flow through it in only one direction.

<span class="mw-page-title-main">Gun barrel</span> Firearm component which guides the projectile during acceleration

A gun barrel is a crucial part of gun-type weapons such as small firearms, artillery pieces, and air guns. It is the straight shooting tube, usually made of rigid high-strength metal, through which a contained rapid expansion of high-pressure gas(es) is used to propel a projectile out of the front end (muzzle) at a high velocity. The hollow interior of the barrel is called the bore, and the diameter of the bore is called its caliber, usually measured in inches or millimetres.

<span class="mw-page-title-main">Drain-waste-vent system</span> Plumbing fixture

A drain-waste-vent system is the combination of pipes and plumbing fittings that captures sewage and greywater within a structure and routes it toward a water treatment system. It includes venting to the exterior environment to prevent a vacuum from forming and impeding fixtures such as sinks, showers, and toilets from draining freely, and employs water-filled traps to block dangerous sewer gasses from entering a plumbed structure.

A pneumatic weapon is a weapon that fires a projectile by means of air pressure, similar in principle to the operation of pneumatic tube delivery systems. The term comes from a Greek word for "wind" or "breath" (πνεῦμα).

<span class="mw-page-title-main">Piston valve</span> Fluid control device using linear motion of a piston in a cylinder

A piston valve is a device used to control the motion of a fluid or gas along a tube or pipe by means of the linear motion of a piston within a chamber or cylinder.

<span class="mw-page-title-main">Light-gas gun</span> Gun designed to generate very high speed

The light-gas gun is an apparatus for physics experiments. It is a highly specialized gun designed to generate extremely high velocities. It is usually used to study high-speed impact phenomena, such as the formation of impact craters by meteorites or the erosion of materials by micrometeoroids. Some basic material research relies on projectile impact to create high pressure; such systems are capable of forcing liquid hydrogen into a metallic state.

<span class="mw-page-title-main">Pipe (fluid conveyance)</span> Tubular section or hollow cylinder

A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipe is far stiffer per unit weight than solid members.

<span class="mw-page-title-main">Model warship combat</span> Club Combat between RC model warships

Model warship combat is an international club activity, in which participants construct radio-controlled scale models of actual warships, most commonly those built by various nations prior to 1946, such as the USS Des Moines, HMS Dreadnought, or the German battleship Bismarck. The models are armed with pneumatic cannons, and fight against one another on ponds and lakes. Model warship combat is sometimes considered to be a form of Naval Wargaming, but can also be considered a water-based version of Robot Combat, since much of the internal systems and concepts are the same as radio control electronics, and in some cases possess similar pneumatic systems.

<span class="mw-page-title-main">Diaphragm valve</span> Flow control device

Diaphragm valves consists of a valve body with two or more ports, a flexible diaphragm, and a "weir or saddle" or seat upon which the diaphragm closes the valve. The valve body may be constructed from plastic, metal, wood or other materials depending on the intended use.

<span class="mw-page-title-main">Piping and plumbing fitting</span> Connecting pieces in pipe systems

A fitting or adapter is used in pipe systems to connect sections of pipe or tube, adapt to different sizes or shapes, and for other purposes such as regulating fluid flow. These fittings are used in plumbing to manipulate the conveyance of fluids such as water for potatory, irrigational, sanitary, and refrigerative purposes, gas, petroleum, liquid waste, or any other liquid or gaseous substances required in domestic or commercial environments, within a system of pipes or tubes, connected by various methods, as dictated by the material of which these are made, the material being conveyed, and the particular environmental context in which they will be used, such as soldering, mortaring, caulking, Plastic welding, welding, friction fittings, threaded fittings, and compression fittings.

<span class="mw-page-title-main">Pipefitter</span> Tradesman who works with mechanical pipes

A pipefitter or steamfitter is a tradesman who installs, assembles, fabricates, maintains, and repairs mechanical piping systems. Pipefitters usually begin as helpers or apprentices. Journeyman pipefitters deal with industrial/commercial/marine piping and heating/cooling systems. Typical industrial process pipe is under high pressure, which requires metals such as carbon steel, stainless steel, and many different alloy metals fused together through precise cutting, threading, grooving, bending, and welding. A plumber concentrates on lower pressure piping systems for sewage and potable tap water in the industrial, commercial, institutional, or residential atmosphere. Utility piping typically consists of copper, PVC, CPVC, polyethylene, and galvanized pipe, which is typically glued, soldered, or threaded. Other types of piping systems include steam, ventilation, hydraulics, chemicals, fuel, and oil.

<span class="mw-page-title-main">Bamboo cannon</span> Type of home-made firecracker

A bamboo cannon is a type of home-made firecracker which is popular during the Eid season in Malaysia and Indonesia, as well as during New Year's Eve celebrations in the Philippines.

The legality of the potato-firing potato cannon varies among jurisdictions.

<span class="mw-page-title-main">Plastic pipework</span> Tubular section or hollow cylinder made of plastic

Plastic pipe is a tubular section, or hollow cylinder, made of plastic. It is usually, but not necessarily, of circular cross-section, used mainly to convey substances which can flow—liquids and gases (fluids), slurries, powders and masses of small solids. It can also be used for structural applications; hollow pipes are far stiffer per unit weight than solid members.

A ram accelerator is a device for accelerating projectiles or just a single projectile to extremely high speeds using jet-engine-like propulsion cycles based on ramjet or scramjet combustion processes. It is thought to be possible to achieve non-rocket spacelaunch with this technology.

A vacuum bazooka is a pipe-based cannon which uses a vacuum pump to reduce pressure in front of the projectile and therefore propel a projectile as a result of the air pressure acting on its reverse. The concept was originally proposed by Neil A Downie in 2001 but many variations have been built since.

References

  1. ↑ Mungan, Carl E. (May 2009). "Internal ballistics of a pneumatic potato cannon". European Journal of Physics . 30 (3): 453–457. Bibcode:2009EJPh...30..453M. doi:10.1088/0143-0807/30/3/003. S2CID   35147997.
  2. ↑ Ayars, Eric; Bucholtz, Louis (July 2004). "Analysis of the vacuum cannon". American Journal of Physics . 72 (7): 961–963. Bibcode:2004AmJPh..72..961A. doi:10.1119/1.1710063 . Retrieved 15 August 2011.
  3. ↑ Pierson, Hazel M.; Price, Douglas M. (Spring 2005). "The Potato Cannon: Determination of Combustion Principles for Engineering Freshmen" (PDF). Chemical Engineering Education. 39 (2): 156–159. Retrieved 15 August 2011.[ permanent dead link ]
  4. ↑ Courtney, Michael; Courtney, Amy (November 2007). "Acoustic Measurement of Potato Cannon Velocity". The Physics Teacher . 45 (8): 496–7. arXiv: physics/0612118 . Bibcode:2007PhTea..45..496C. doi:10.1119/1.2798362. S2CID   119057813. Archived from the original on 2012-07-16. Retrieved 15 August 2011.
  5. ↑ Gurstelle, William (2001). Backyard Ballistics: Build Potato Cannons, Paper Match Rockets, Cincinnati Fire Kites, Tennis Ball Mortars, and More Dynamite Devices. Chicago: Chicago Review Press. ISBN   1-55652-375-0. OCLC   45861947. Backyard Ballistics at Google Books.
  6. ↑ How the Humble Potato Cannon Served the Allies in World War Two Popular Mechanics, Retrieved April 4, 2017.
  7. 1 2 BigBang (October 2006). "Crusader". SpudFiles. Archived from the original on 20 February 2009. Retrieved 2009-06-01.
  8. ↑ schmanman; et al. (March–April 2007). "(NEW) S.W.A.T v.3". SpudFiles. Archived from the original on 2 February 2013. Retrieved 16 August 2011. Cannon with a calculated range exceeding 1 mile.
  9. ↑ Killjoy (25 April 2007). "FEAR". SpudFiles. Archived from the original on 27 February 2015. Retrieved 2009-06-01.
  10. ↑ Van Horn, Dale R. (October 1932). "Perform These STARTLING STUNTS with DRY ICE". Modern Mechanix and Inventions : 114–116. Retrieved 15 August 2011.
  11. ↑ "OSHA Safety Hazard Information Bulletin on the Use of Polyvinyl Chloride (PVC) Pipe in Above ground Installations". Occupational Safety and Health Administration. 20 May 1988. Retrieved 16 August 2011.
  12. ↑ Arabe, Katrina C. (23 April 2001). "A Dynamic Duo: Thermoplastics and Compressed Air Systems". Industry Market Trends. ThomasNet News. Retrieved 16 August 2011.
  13. ↑ Novacastrian (November 2007). "The Brass Bruiser". SpudFiles. Retrieved 2009-06-01.
  14. ↑ Technician1002 (4 April 2009). "Quick Dump Valve". SpudFiles. Retrieved 16 August 2011.{{cite web}}: CS1 maint: numeric names: authors list (link)
  15. ↑ Downie, Neil (2006). Exploding Disk Cannons, Slimemobiles, and 32 Other Projects for Saturday Science. The Johns Hopkins University Press. p.  5. ISBN   9780691149660.
  16. ↑ Downie, Neil (2012). The Ultimate Book of Saturday Science : The Very Best Backyard Science Experiments You Can Do Yourself. Princeton University Press. p.  411. ISBN   9780691149660.
  17. ↑ Downie, Neil (2012). The Ultimate Book of Saturday Science : The Very Best Backyard Science Experiments You Can Do Yourself. Princeton University Press. pp.  407–408. ISBN   9780691149660.
  18. ↑ Wise, Roger (2003-10-29). "Solvent welding of thermoplastics". TWI. Archived from the original on 2008-02-12. Retrieved 2009-06-01.
  19. ↑ "New stuff". The Spudgun Technology Center. 14 January 2010 [6 July 2002]. Retrieved 16 August 2011.
    "Theory/physics behind the spudgun". The Spudgun Technology Center. 29 August 2008 [25 June 2002]. Retrieved 16 August 2011. Used helium to attain supersonic velocities.
  20. ↑ jackssmirkingrevenge (8 September 2007). "high velocity burst disc 6mm pneumatic". SpudFiles. Retrieved 16 August 2011. Attained approximately Mach 1 (340 m/s; 1120 ft/s) with 400 psi (2.8 MPa) and a fast valve.
  21. ↑ Larda (31 July 2008). "Lardas First Hybrid - HyGaC20". SpudFiles. Archived from the original on 15 September 2012. Retrieved 2009-06-01.
  22. ↑ Didymus, JohnThomas (2013-02-06). "Video: Supersonic Ping-Pong gun fires a ball faster than sound". Digital Journal. Retrieved 2013-10-21.
  23. ↑ "Phillie Phanatic's hot dog cannon sends Phillies fan to emergency room".
  24. ↑ "T4 Shock Tunnel". Centre for Hypersonics, The University of Queensland . Retrieved 16 August 2011.
  25. ↑ Barker-Griffith, Ann E.; Streeten, Barbara W.; Abraham, Jerrold L.; Schaefer, Daniel P.; Norton, Sylvia W. (1 March 1998). "Potato gun ocular injury". Ophthalmology . 105 (3): 535–538. doi:10.1016/S0161-6420(98)93039-1. PMID   9499787 . Retrieved 15 August 2011.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.