How Projectile Distance is Affected by Air Pressure
Word Count: 1428
By Nicolas Molau
Introduction | Methodology | Results | Conclusion | Bibliography/Related Links | Return to Research
Introduction:
For some odd reason I’ve always been interested in the physics and workings of an air cannon, how a pressure tank full of compressed air can launch projectiles a fair distance. Another odd obsession of mine is mortars, because I love artillery and making projectiles FLY! Some basic physics of my “great” air cannon design are as follows: either through air compressor or bike pump an air tank with a valve are filled with air and then once full and projectile loaded the valve is opened and the compacted air rushes out the opening and the force of the sudden release launches the projectile much like how gunpowder launches a cannonball. To get a good strong shot it’s recommended to have an efficient valve and an air tank that can handle high psi as if it can't. You basically have a shrapnel bomb and that it is not good for anyone involved. While the physics are sadly not complex this was the only legal thing I could think of to show my personal love for artillery and physics. With my IA I intend to test the relation of air pressure of shot distance. My procedure is as follows: set the cannon to 30 degrees for a nice arced shot, fill the tank with air and fire the cannon off. I intend to do 100 shots to make up for not being complex and I intend to do either increasing the pressure per shot or 10 shots at a set pressure. If time allows I’ll do both as I think the graphs could correlate with each other and show a good consistency between air pressure from two different ways to test the relation of distance and air pressure. My primary hypothesis for my experiment is that the air pressure increase will initially be impactful but after a certain PSI the distance gains will be miniscule or indifferent and show that air power can only do so much in launching a projectile.
Methodology:
Material
List:
· ABS Pipe
· ABS Pipe
Cap
· ABS
Coupling
· Sealed
Valve
· ABS
Cement glue
· PVC Water
Valve
· ABS to
PVC cement glue
· Silicon
Glue
· Washers
· Air
Compressor
· Toilet
Paper
· Toilet
Paper Roll
· Roll of
Blue Tape
· Broom
Diagram:
Procedure:
Using everything except for the toilet paper, toilet paper roll, air compressor, blue tape, and broom the air cannon was made and tested to be sealed. Once sealant checking was complete I moved on to conducting my experiment which would be done in a couple simple steps. I wasn’t necessarily surprised but as all things usually are, it’s easier said than done.
First things first is setting up the firing position. Using my extremely dirty garage and leftover christmas light boxes I made a temporary stand to hold the cannon while it filled with air. After the tank was filled either me or my dad would use a broom as a ramrod to load the projectile and its wadding. After being loaded the cannon would be picked up and aimed at 45 degrees, the valve would be turned by hand with albeit a little bit of resistance and the projectile would fly! At least I like to think it flies far, in reality max range was approx. 35ft. The projectile’s max distance would be measured on initial hit, if the projectile rolled it didn’t count for more distance. Luckily my driveway had some easy visual references in the rocks so measuring with a tape measurer wasn’t too bad, though no doubt knowing me there were human errors. Data would be collected on my phone. The final process of this probably way too short process was transforming the data from Imperial to metric. Me being a dumbass did it all by hand instead of using an online plug in and out converter. Once converted I cross referenced data with random ranges I found online to make sure my cannon was perfectly average as all things should be.
Manipulating my independent
variable wasn’t too difficult luckily, it was mostly just adjusting air
pressure with an air compressor, the dial was pretty difficult to read at times
though. Measuring the dependent variable was also easy as it was measuring
distance from the cannon barrel to the projectile. The tougher part was keeping
the control constant as having perfect 45 degrees is tough and I wouldn’t be
surprised if there was human error for a couple of shots where the degrees were
adjusted by 2-3 degrees. The easier constant was the projectile as the same one
was used throughout testing and one square of toilet paper was always used for
wadding in the cannon. For my variations I went with the standard 10x3 as I
found it nice for calculating average and it provided a nice range of values
for my graphs and it helped see what the ranges could be for different pressure
values. I initially picked it due to being standard but soon saw why as stated
above it was nice for ranges and didn’t complicate the data as for my data
except for a few exceptions the difference in distance wasn’t that big that it
was worrying but was important data for averages.
Results:
Data: Excel || text
Conclusion:
From the data I’ve gathered in my experiment there is evidence pointing towards air cannon range starting to average out after hitting a certain pressure value. I think this could be due to the fact that air pressure can only exert so much force on a projectile and air resistance negates the miniscule distance gains after hitting an apparent max capacity for how much force can affect the projectile. Luckily my hypothesis was talking about this specific thing though I do believe that human error or better experiment optimization could’ve had different results though. I think with a different better made projectile and changes to how the projectile was fired distance could be improved and my hypothesis proven wrong, but for the time being with my current resources I was able to show that my hypothesis has some truth to it. The main limitations would probably be not having a consistent stand nor necessarily aerodynamic projectile as that could’ve been the cause for limiting the range due to air resistance acting on the projectile. The lack of a proper stand means that human error could’ve easily affected the results as anything off would have adjusted the max distance. So to improve if I did this in the future would be to make a better, more aerodynamic projectile and have a proper stand that is similar in form to a mortar stand or cannon stand as this would eliminate the issues I stated before. For another future experiment I would like to test, maybe this summer, the effect of cannon angles, projectile placement in the tube, or different kinds of projectile to see which one gives off more range. You could make the argument that much of this is ready online info but I like seeing the science in person as it helps give me a better understanding of it and I think these would be good preliminaries for improving this experiment in the future if I wanted to repeat it but with modifications to increase performance and really see if my hypothesis was correct or I’m just overthinking things.
https://www.airbestpractices.com/industries/bulk/reducing-compressed-air-consumption-air-cannons
RELATED LINKS:
https://www.instructables.com/Air-Powered-Cannon/
Easy to follow how to build guide with pictures and exact measurements
https://www.airbestpractices.com/industries/bulk/reducing-compressed-air-consumption-air-cannons
The physics behind how a air cannon works and ways to increase shot distance and velocity.
What kind of expansion the compressed air has and what it can be used to see visual application of physics
https://www.popsci.com/gadgets/article/2010-01/air-cannon-sends-pumpkins-3700-feet/
A big air cannon that laucnhes projectiles such as pumpkins, really cool
http://www.validyne.com/blog/application-note-basics-of-air-velocity-pressure-and-flow/
The physics behind compressed air and air flow in a enclosed space, like for say an air cannon tube.