Blasting Off With Air!
- Because the nozzle of a rocket controls the speed at which pressurized air leaves the rocket and therefore the thrust, the size of the nozzle will determine the distance the rocket travels.
- If I make different aperture nozzles, then the bigger nozzle will go the farthest because the air escapes faster, increasing the thrust and therefore the distance travelled.
- Rockets have been around since 1200 when it was used in China as part of fireworks.
- Solid fuel is commonly used in hobby rockets and fireworks.
- Rockets turn fuel into hot gas that pushes gas out the back of the rocket, therefore creating thrust that propels the rocket forward.
- Rockets can use two different types of fuel – liquid or solid fuel
- Solid fuel is usually a powder that is compressed.
- This type of fuel is easier to store and handle than liquid propellant.
- It is usually cheaper
- It can create large amounts of thrust and is often used in the boost stages of space rockets
- It is the most common method used in hobby rockets and fireworks
- A drawback of solid fuel is that it can be hard to control
- Liquid fuel is a lot easier to control since it can be stopped and started
- It is lighter than solid fuel
- The oxidizer used can be a problem since many oxidizers need to be stored at a low temperature and can be toxic and highly reactive.
- Space rocket engines carry an oxidizer making it possible to travel in space where there is no oxygen.
- Rockets are more efficient in space than in earth’s atmosphere, because there is less gravity and friction in space.
- The first person launched into space was Yuri Gagarin in 1961.
- The nozzle directs the exhaust gas along the axis of the rocket. Controlling the speed at which the air or gas leaves the nozzle giving control over the thrust and therefore the airspeed of the rocket.
- Larger rockets are usually launched from a launch pad that helps to stabilize the rocket.
- The only propulsion systems that can currently get you out of the earth’s atmosphere is a chemical rocket engine.
- Other rocket engines such as solar sails and ion thrusters are more effective in space than they are on earth and are more powerful than chemical engines in space in some cases.
- The forces that affect a rocket are:
- Thrust from the engine
- Drag from moving through the atmosphere
- Newton’s third law states that if one object (object A) exerts a force on another object (object B) then object B exerts an equal force and in an opposite direction back on object A.
Background Research Question:
Is there a correlation between the height an air rocket bottle will go and the bottle's size?
1.250 ml bottle
2.500 ml bottle
3.1 litre bottle
4.2 litre bottle
8.Bicycle pump that measures psi
11.Measuring tape – up to 60 meter
1.Attach a straw to each of the different size bottles.
2.Cut a metal or wooden piece to measure 13cm x 25cm.
3.Cut rectangles of 3.5 x 4.5 cm from plywood. Glue the blocks together and further enforce it using duct tape.
4.Cut 10cm x 3.5 cm wooden rectangles from plywood and glue it together. Drill a 3mm whole in the larger plywood blocks to insert metal rod.
5.Use metal rod to string in the straw that is attached to the bottle.
6.Put nozzle of bottle in between plywood blocks.
7.Insert end of bicycle pump into bottle nozzle.
8.Pump bicycle pump to 40 psi.
9.Release bottle at 40 psi.
10.Measure height of bottle using the altimeter
- Conclusion and analysis of results
- The largest bottle (2l) went the highest; even though the largest bottle is heavier and bigger (with larger surface area causing more friction), the bottle went higher
- The smaller the bottle the less high it went.
- The wind can have a major impact on the accuracy of the data.
- The altimeter is not very accurate and probably can be off by 3-5 meters.
- Therefore the bottle containing the largest amount of pressurized air (at 40 PSI) created the most thrust
- Measurement of thrust will be more accurate with an indoor system, to exclude the effect of wind and the inaccuracy of a manual altimeter
- Independent variable:
- Nozzle size
- Dependant variable:
- The distance that the bottle travels
- Controlled variables:
- Environmental factors; no wind, constant temperature
- PSI at which rocket is released (40 psi)
- Added weight (4 AA batteries)
- 250 ml bottle
- 500 ml bottle
- 1 litre bottle
- 2 litre bottle
- Wooden plank
- Metal rod
- Duct tape
- Bicycle pump that measures psi
- Measuring tape – up to 60 meter
- Drill 3 different size holes into 3 corks with a step drill bit
- Glue the corks to the inside of each bottle and wait for it to dry
- Attach 4 compression sleeves symmetrically to a 2 litre plastic pop bottle
- Attach 4 AA batteries symmetrically to the bottle
- Measure the distance between each compression sleeve to determine the width at which the rope will be strung
- String the rope using weights on both sides to keep the rope tight; at least 18 meter distance
- Nozzle A (the biggest nozzle/original opening of the pop bottle) went the longest average distance at 13.19 meters, followed by C at 12.50 meters and D at 11.79 meters
- The worst performing nozzle was B ( the second biggest nozzle), with an average distance of 11.39 meters
- There was a significant variation in the range of the distances travelled for all the nozzles (2.78 meters to 3.66 meters)
- An indoor system (lines/ropes at tension with a rocket that can slide on it) is capable of indirect measurement of pressurized air rocket thrust
- Different sizes/apertures of nozzles have a significant effect on the distance that a pressurized bottle travels, at a constant air pressure of 40 Psi
- The best performing nozzle was the original opening of the pop bottle
- The larger nozzles (A, B) gave more variation in distance travelled (3.33-3.66m), whereas the smaller nozzles (C, D) tended to show more consistency (2.78-2.79m) in distance travelled.
- Possible reasons for this may be because a bigger nozzle causes a very sudden burst of energy, with high random turbulence, whereas the smaller nozzles cause a relatively more gradual release of air pressure, causing a more consistent release of air, with less turbulence
- The reasons for the poor performance of the nozzle that was just a bit smaller than the original opening of the bottle is not certain. It may be that the nozzle causes the largest burst in energy, with the most turbulence
• In our experiment smaller nozzle sizes led to less thrust in the bottle rockets.
• It is clear that the original opening of a pop bottle is the best nozzle size for a bottle rocket, and smaller nozzle sizes will not make your rocket go higher.
• The size of the nozzle of a real world rocket will be an important variable in rocket design.
Sources Of Error
There are a few things that can cause wrong readings, and those include:
- Changing tension of the line on which the rockets travel (too loose a line will cause more vibration and slow the rocket down, decreasing the distance that it will travel)
- The bicycle pump may not be very accurate at measuring the Psi
- A nozzle opening that is not exactly in the center of the rocket will cause it to travel skew. Although this cannot be seen when a rocket travels along a tightrope, this will cause increased friction on the rope that will slow it down
MSFC History Office. "Rockets in Ancient Times (100 B.C. to 17th Century)". A Timeline of Rocket History. NASA. Archived from the original on 2009-07-09. Retrieved 2009-06-28.
Netting, R. (2003, January 22). It's a Breeze, How Air Pressure Affects You. Retrieved October 24, 2014.
The Engineering Toolbox. (n.d.). Pressure Units Online Converter. Retrieved November 6, 2014.
University of Illinois, Department of Physics. (n.d.). Height of a water rocket. Retrieved October 29, 2014.