How does:
a) angle of nose cone affect a rocket's penetration through air?
i) pop rockets
b) fin orientation affect a rocket´s speed?
i) pop rockets.
ii) solid fuel rockets
c) fin orientation affect a rocket´s stability?
i) pop rockets.
ii) solid fuel rockets
d) fin count affect a rocket´s stability?
i) solid fuel rockets
e) shape of nose cone (conical, elliptical, spherical, parabolic, ogive) affect drag?
i)wind tunnel
Rockets are propelled into the air by flammable fuel or pressurized gas / liquid being forced out a nozzle. A nozzle is a narrow throat through which the exhaust is squeezed out. The throat limits the amount of gas that can escape, causing the gas to accelerate as it is forced out the nozzle.
Rockets must be stable in flight so that they may be able to fly in a smooth, predictable direction. An unstable rocket may tumble or fly in an undesired direction. Fins help guide and stabilize rockets. They are lightweight extensions attached to the exterior of the rocket. The shape of fins influences the rocket's performance.
Drag is the rocket's resistance to motion caused by the rocket's movement through air. It depends on several factors, including the density of air, the shape of the rocket, the roughness of the rocket's surface and the nose cone´s shape. The more resistant to motion a rocket is, the more thrust is needed to propel it. The nose cones of rockets are streamlined to help reduce drag. The air gains an advantage if it has more surface area to push against, but if the surface area is less or has an air-disposing shape, giving air little area to push on and disposing it side-ways, this gives the rocket the advantage of there being less reaction push from the air.
Aspects to a rocket´s performance.
Why must a rocket be stable in flight?
So that it will be able to fly in a smooth, predictable direction. An unstable rocket may tumble or fly in an undesired direction.
What causes a rocket to be unstable?
The rocket´s imperfections, resulting in non-linear trajectories.
Methods of stabilizing rockets include fins and fin spin (which will be discussed in depth later on). Fins are lightweight extensions attached to the exterior of the rocket. The shape, count and fin orientation influence the rocket's performance.
How do fins help stabilize a rocket?
The fins add weight on the rocket's exterior end, the weight then helps to pull back the rocket when it loses track to one side.
How are rockets made to spin?
The rocket is made to spin by inserting fins on the rocket at a slanting angle (oblique orientation) from the vertical. Because the fins are at an angle the air fluxes are displaced sideways. According to Newton´s third law of motion (for every action there is an equal and opposite reaction), the rocket fins are pushed sideways and the rocket starts to spin.
Why does the spinning increase the rocket´s stability?
By spinning a rocket the trajectories become helical. The spinning rate and the helix's radius are inversely proportional. The faster the rocket spins the more linear the helix/spiral track becomes and the more stable the rocket becomes.
What is Drag?
Drag is the rocket's resistance to motion, in this case caused by the rocket's movement through air.
It depends on several factors, including the density of air, the shape of the rocket, the nature of the rocket's surface and nose cone shape. The more resistance to motion a rocket has, the less efficient it is.
How does drag affect a rocket´s performance?
More thrust is needed to propel the rocket. The rocket loses speed, which then affects the rocket´s stability.
How can drag be reduced?
The nose cones of rockets are made streamline to help reduce drag.
Drag is positively related to the cross-sectional area, as well as surface area, but if the surface area is less or shaped in an air-disposing shape, giving air little area to push on and disposing it side-ways, this gives the rocket the advantage of there being less reaction push from the air, reducing drag. Making the rocket´s surface smooth reduces drag, increasing speed and increasing stability.
Many factors of rocket design can increase the drag it experiences in flight. One of the most important of these factors is the shape of the nose cone.
What is a nose cone?
A nose cone is the leading, tapered or pointed section of the rocket. It helps reduce aerodynamic drag.
Nose cones have different shapes, for different situations. They differ in drag in certain circumstances, altitudes and speeds.
Altitudes achieved using different nose shapes on the same rocket
For a model rocket a certain shape best suites, than another. For a Tomahawk cruise missile another cone will best fit since it travels at higher speeds and different altitudes..
This information was found by others who have done an investigation on nose cones rocket. But it cannot be certain.
Different types of nose cones.
How pop rockets work.
When vinegar and baking soda are mixed together, carbon dioxide gas is released in a bubbly reaction. The sodium bicarbonate base in the baking soda neutralizes the acetic acid in the vinegar. The reaction has two steps. In the first step carbonic acid is produced. Because the carbonic acid is very unstable it breaks down in a second reaction to form water and carbon dioxide. The acetate ion combines with the sodium ion in the baking soda to form sodium acetate, which is the leftover liquid after the rocket has been launched. The release of CO2 from the vinegar and baking soda provides the thrust of the rocket engine. The pressure of the gas eventually builds up until the container can't hold the gas pressure. Then the pressure forces the stopper off the container. This expulsion of exhaust creates thrust to send the rocket into the air.
c) Measurement
Investigation 1 to 3.
*Horizontal distance traveled by each rocket. (measured with a 100 m measuring tape)
*Time taken to cover that distance (this was measured using a stop watch)
average speed=distance covered/time taken
Investigation 4 to 6
*Error distance from launch point, measured using a 100 meter measuring tape.
Investigation 7
*The differences of the amount of volts generated by the motors form the initial intake and the final output out the tunnel, using multimeters.
e) Treatments (Investigation 1- 7)
a) How does angle of nose cone affect a rocket's penetration through air?
Pop rockets
In this investigation we wanted determine which cone shape (angle) showed the least drag
at a launch angle of 70°.
Bonding equipment, the glue and tape was used to attach the nose cone to the rocket.
Nose cones were attached to each of the five rockets. Each nose cone was differently angled, namely:
90°; 60°; 30°; 15°
Each rocket was launched three times and an average speed calculated.
Results
Table 1: raw data of Investigation 1
|
|
Rocket 1 (90°) |
Rocket 2 (60°) |
Rocket 3 (30°) |
Rocket(15°) |
Rocket(5°) |
|---|---|---|---|---|---|
1.Horizontal distance traveled (m) |
13.6 |
12.55 |
13.5 |
11 |
9 |
Time (sec) |
2.43 |
2.07 |
2.32 |
2.01 |
2.13 |
Speed (m /sec) |
5.6 |
6.06 |
5.81 |
5.47 |
4.22 |
2.Horizontal distance traveled (m) |
14.5 |
13.2 |
14.12 |
12.4 |
10.1 |
Time (sec) |
2.72 |
2.51 |
2.46 |
2.26 |
2 |
Speed (m / sec) |
5.33 |
5.26 |
5.73 |
5.48 |
5.05 |
3.Horizontal distance traveled (m) |
14 |
12.9 |
13.8 |
11.8 |
10 |
Time (sec) |
2.4 |
2.02 |
2.24 |
2.49 |
2.37 |
Speed (m /sec) |
5.83 |
6.39 |
6.16 |
4.73 |
4.21 |
Average horizontal distance traveled (m) |
14.03 |
12.89 |
13.8 |
11.73 |
9.7 |
Average, Time (sec) |
2.51 |
2.2 |
2.34 |
2.25 |
2.16 |
Average ,Speed (m/sec) |
5.59 |
5.86 |
5.9 |
5.21 |
4.49 |
Table 2 : processed data of investigation 1
|
|
Rocket 1 (90°) |
Rocket 2 (60°) |
Rocket 3 (30°) |
Rocket 4 (15°) |
Rocket 5 (5°) |
|---|---|---|---|---|---|
Horizontal distance traveled (m) |
14.03 |
12.89 |
13.8 |
11.73 |
9.7 |
Time (sec) |
2.51 |
2.2 |
2.34 |
2.25 |
2.16 |
Speed (m / sec ) |
5.59 |
5.86 |
5.9 |
5.21 |
4.49 |
Graph 1: Showing the rockets´ speed at different nose cone angles.
Conclusion
Decreasing nose-cone angle (sharpening nose-cone) increases speed up to a certain point, after which this it decreases speed.
Discussion
Decreasing angle tends to decrease drag on the rocket. However, it is accompanied by an increase in surface area, which tends to increase drag. The fact that these two effects work against, one explains why optimisation is observed. Additionally, an increase in length destabilises the rocket because it shifts the centre of gravity further forward.
b (i) How does fin orientation affect a rocket´s speed?
Pop rockets
Fins were glued on each rocket, twisted at different angles from the vertical, namely:0° 15°30°
Each rocket was launched three times and an average error distance calculated.
Results
Table 3: raw data of Investigation 2 fin orientation and speed.
|
Rocket 1(straight0°) |
Rocket 2 (15°) |
Rocket 3 (30°) |
1.Horizontal distance traveled. (m) |
22 |
16 |
13 |
Time (sec) |
1.63 |
1 |
1.13 |
Speed (m / sec ) |
13.5 |
16 |
11.5 |
2.Horizontal distance traveled. (m) |
19.5 |
18 |
17 |
Time (sec) |
2.06 |
1 |
1.68 |
Speed (m / sec) |
9.5 |
18 |
10.1 |
3.Horizontal distance traveled. (m) |
20 |
18 |
12 |
Time (sec) |
1.8 |
1.25 |
1.1 |
Speed (m / sec) |
11.2 |
14.4 |
10.9 |
Average horizontal distance traveled (m) |
20.5 |
17.33 |
14 |
Average, Time (sec) |
1.83 |
1.08 |
1.3 |
Average ,Speed (m / sec) |
11.4 |
16.04 |
10.76 |
Table 4 : processed data of investigation 2 fin orientation and speed.
|
Rocket 1(straight0°) |
Rocket 2 (15°) |
Rocket 3 (30°) |
Horizontal distance traveled (m) |
20.5 |
17.33 |
14 |
Time (sec) |
1.83 |
1.08 |
1.3 |
Speed (m/sec) |
11.4 |
16.04 |
10.76 |
Graph 2: Showing the rockets´ speed at different fin angles.
Conclusion
Increasing twist angle to the vertical increases speed up to a point, after which further increase in twist angle decreases speed.
Discussion
Up to a point, increasing angle of fin twist causes the rocket to spin more, tending to increase speed. However, it also tends to increase drag on the rocket due to an increase in cross-sectional area. The fact that these two effects work against one explains why optimisation is observed.
b (ii)How does fin orientation affect a rocket´s speed?
Solid fuel rockets
Procedure
(Follow the instructions in the Cobra rocketing pack for constructing the engines and
rockets, except for the fin positioning and shape according to the investigation)
Fins were glued on each rocket, twisted at different angles from the vertical, namely:0°;3°;6°
Each rocket was launched three times and an average error distance calculated.
Results
Table 5:Unprocessed data of Investigation 3 (fin orientation and speed)
|
|
Rocket 1 (0°) |
Rocket 2 (3°) |
Rocket 3 (6°) |
|---|---|---|---|
1.Horizontal distance traveled (m) |
107 |
90.3 |
67.6 |
Time (sec) |
9.6 |
7.3
|
6.3 |
Speed (m /sec) |
11.1 |
12.3
|
10.7 |
2.Horizontal distance traveled (m) |
112
|
85 |
70.4 |
Time (sec) |
10.8
|
6.5 |
7.2 |
Speed (m /sec) |
10.4
|
13 |
9.8 |
3.Horizontal distance traveled (m) |
44 |
56.8 |
34.5 |
Time (sec)
|
4.1 |
4.4 |
3.9 |
Speed (m /sec)
|
10.7 |
12.9 |
8.84 |
Average horizontal distance traveled (m) |
87.6 |
77.3 |
57.5 |
Average time (sec) |
8.1
|
6.0 |
5.8 |
Average Speed (m /sec) |
10.8
|
12.8 |
9.9 |
Table 6:Processed data of Investigation 3 (fin orientation and speed)
|
|
Rocket 1 (0°) |
Rocket 2 (3°) |
Rocket 3 (6°) |
|---|---|---|---|
Horizontal distance traveled (m) |
87.6 |
77.3 |
57.5 |
time (sec)
|
8.1
|
6.0 |
5.8 |
Speed (m /sec)
|
10.8
|
12.8 |
9.9 |
Graph 3:Showing the rockets´ speed at different fin angles.
Conclusion
Increasing twist angle to the vertical increases speed up to a point, after which further increase in twist angle decreases speed.
Discussion
Up to a point, increasing angle of fin twist causes the rocket to spin more, tending to increase speed. However, it also tends to increase drag on the rocket due to an increase in cross-sectional area. The fact that these two effects work against one explains why optimisation is observed.
c (i)How does fin orientation affect a rocket´s stability?
Pop rockets
The rockets used in Investigation 2 were each launched three times at an angle of 90° (vertically) from the horizontal, and the drift distance from the launch point was measured. Each rocket was launched three times and an average error distance calculated.
Results
Table 7 : raw data of investigation 4 (fin orientation and stability)
|
|
Rocket 1 (straight0°) |
Rocket 2 (15°) |
Rocket 3 (30°) |
|---|---|---|---|
1.Error distance from launch point (m) |
2.86 |
3.20 |
3.31 |
2.Error distance from launch point (m) |
2.99 |
3.3 |
3.27 |
3.Error distance from launch point (m) |
2.91 |
3.17 |
3.36 |
Average error distance (m) |
2.92 |
3.22 |
3.31 |
Table 8 : processed data of investigation 4 (fin orientation and stability)
|
|
Rocket 1 (straight0°) |
Rocket 2 (15°) |
Rocket 3 (30°) |
|---|---|---|---|
Average error distance (m) |
2.92 |
3.22 |
3.31 |
Graph 4: Showing the rockets´ stability at different fin angles.
Conclusion
Increasing fin twist for the range of data found here decreases stability.
Discussion
The results of this investigation did not fit our original hypothesis (we had expected that an increase in fin twist would increase stability due to the decrease in helical radius this would cause). We hypothesised that the results of this investigation were due to the fin twist angles being larger than optimum, causing an excessive, destabilising amount of spin. To test this hypothesis we used angles smaller than 15° in the next investigation.
c (ii) How does fin orientation affect a rocket´s stability?
Solid fuel rockets
The rockets used in Investigation 3 were used, and each launched at an angle of 90° (vertically).
Each rocket was launched three times and an average error distance calculated.
Results
Table 9:Unprocessed data of Investigation 5 (fin orientation and stability)
|
|
Rocket 1 (0°) |
Rocket 2 (3°) |
Rocket 3 (6°) |
|---|---|---|---|
1.Error distance traveled (m) |
13.1 |
1.8 |
5.7 |
2.Error distance traveled (m) |
7.9 |
2.1 |
6.24 |
3.Error distance traveled (m) |
12.2 |
2.1 |
4.3 |
Average Error distance traveled. (m) |
11.1 |
2 |
5.41 |
Table 10 : Processed data of Investigation 5 (fin orientation and stability)
|
|
Rocket 1 (0°) |
Rocket 2 (3°) |
Rocket 3 (6°) |
|---|---|---|---|
Error distance traveled. (m) |
11.1 |
2 |
5.41 |
Graph 5: Showing the rockets stability at different fin angles
Conclusion
Increasing fin angle to the vertical improves stability up to a point, after which further increase in fin angle decreases stability.
Discussion
An increase in fin twist increases stability up to a point, after which this decreases stability. This is due to the influence fin twist has on translation rocket speed through its effect on spin and cross sectional area. Up to a point, an increase in fin twist increases spin, decreasing helical radius of the trajectory, tending to increase speed and therefore stability. However, this is accompanied by an increase in cross-sectional area, which increases drag, tending to decrease speed and therefore stability.
d)How does fin count affect a rocket´s stability?
Solid fuel rockets
The number of fins per rocket was altered between rockets (from two to four). The rockets were launched vertically and the drift distance (i.e. distance from the exact launch point to the point where the rocket landed) was measured as an inverse indicator of stability. Each rocket was launched three times and an average calculated.
Results
Table 11:Unprocessed data of Investigation 6 (fin count and stability)
|
Rocket 1.Two fins |
Rocket 2.Three fins |
Rocket 3.Four fins |
1.Error distance traveled (m) |
10.6 |
6.6 |
5 |
2.Error distance traveled (m) |
11.9 |
9 |
8.40 |
3.Error distance traveled (m) |
11 |
7.1 |
4.6 |
Average Error distance traveled. (m) |
11.1 |
7.5 |
6 |
Table 12:Processed data of Investigation 6 (fin count and stability)
|
|
Rocket 1.Two fins |
Rocket 2.Three fins |
Rocket 3.Four fins |
|---|---|---|---|
Error distance travelled. (m) |
11.1 |
7.5 |
6 |
Graph 6: Showing the rockets´ stability at different fin counts.
Conclusion
Increasing fin count increases stability.
Discussion
An increase in fin count lowers the distribution of mass within the rocket, increasing stability.
How does shape of nose cone (conical, elliptical, spherical, parabolic, ogive)
affect drag?
Wind tunnel
The five different nose cones were alternately tested in a self-made wind tunnel. A vacuum machine blew air into the wind tunnel. Two dynamos were used to measure the force of the wind in terms of the voltage induced in them by the wind. One of these was placed between the wind source and the cone, and the other downwind of the cone. The difference in voltage reading between these two was used as an indicator of the drag offered by the cone.
Left to right: Spheric, Blunt, Parabolic, Conical.
The Ogive cone in tunnel being tested
Results
Table 13:Unprocessed data of Investigation 7 (Cone shape vs drag)
Table 14:Processed data of Investigation 7 (Nose shape vs drag)
Graph 12: Showing voltage change of different nose cones
Conclusion
The Parabolic shape had the least drag, followed by the Conical, then the Spherical followed by the Ogive and lastly with the most drag the Blunt shape.
Discussion
We had hypothesised that the conical would have the least drag. However, we realised that the whole cone is exposed to incoming force equally, as shown below.
The whole cone is attacked by the wind from the apex, till the foot.
Comparing the diagrams of conical and parabolic cones, shown below, it seems that the conical shape provides a greater surface area effectively acting perpendicularly to the wind direction, which would explain its greater drag we measured, relative to the parabolic cone. The parabolic on the other hand is attacked mainly on the apex, becoming more streamline on the lower nose body. The blunt and spheric are to flat faced, towards the front which overcomes the advantage of the shape being streamline on the lower body. The ogive shape performs better at higher altitudes, and at higher speeds (Scott, J). Most supersonic aircraft, rockets, and missiles use a nose shape very similar to a cone but a little more rounded to provide more internal volume. The faster the vehicle is designed to go, the more pointed the ideal aerodynamic nose shape becomes. But the nose must become more rounded in order to spread the high temperatures over a larger area and prevent the nose from melting.
a) How does angle of nose cone affect a rocket's penetration through air?
Decreasing nose-cone angle (sharpening nose-cone) increases speed up to a point, after which this decreases speed.
b) How does fin orientation affect a rocket´s speed?
Increasing angle of fin twist to the vertical increases speed up to a point, after which further increase in twist angle decreases speed.
c) How does fin orientation affect a rocket´s stability?
Increasing angle of fin twist to the vertical improves stability up to a point, after which further increase in fin angle decreases stability.
d) How does fin count affect a rocket´s stability?
Increasing fin count increases stability.
e) How does cone shape affect drag?
The parabolic shape had the least drag, followed by the conical, then the spherical followed by the ogive and lastly with the most drag the blunt shape.
5. Limitations, Significance and Suggestions for further Investigations
*Limitations:
It's impossible to control the weather, to be exact at all launches
but all tests were done in calm weather.
*Reducing Limitations:
One of the ways to reduce this limitation, is of launching
all rockets of the same investigation on the same day, and at the same time of the day.
*Significance:
This information could be useful to any rocket manufacturing company
and junior rocket clubs. Junior scientist who are interested in
experimenting more about rockets and space travel, building their own backyard rockets, even scholar scientists who build rockets at school.
This information can also be used, by any missile constructing companies, since rockets and
missiles are based on the same principles.
*Suggestion for further investigation:
Extend the investigation to:
i)How does fuel density affect the rocket's acceleration and general performance
ii) How does air density affect the rocket's speed?
iii) How does air density affect the rocket's stability?
iv)How does nozzle size and shape affect the rocket's performance?
Hewit,P.G(1998) Conceptual Physics.(pg 36 all chapter 3 Non-linear motion)
(pg 56 all chapter 4 Newton's Laws of motion)
http://users.bigpond.net.au/mechtoys/waterrocket.html
http://www.Ipi.usra.edu/education/explore/rockets/about.shtml
http://www.nasa.gov/amatuerrocketry
Stott, A. (2006) Chemistry RNC Natural Science Senior Phase. Unpublished NS Senior Phase Learning Module.
Stott, A. (2005), Investigations. Learner´s Workbook. Khanya Press. Kranskop
www.space-rockets.com/newbook.html
http://www.java.com/en/index.jsp
http://my.execpt.com%Eculpt/rockets
Java Programming. by Fun Works
7.Acknowledgements
A. Stott: Assister during project.
A. Van Tonder: Advisor during research time.
Isak Du Preez: Advisor during research time.
M Khwela: Provision of apparatus.
Mr Fourie: Advisor during research time
B Hlongwane: Provision of apparatus.
Jeff Scott:advisor during project
Mr Meyer:Provision of apparatus
Mr C. Marloth: Advisor and provision of apparatus
Mr T Marloth: Advisor
A rocket: A rocket is a container propelled in one direction by exhaust gases going in the opposite direction.
Nose cone: A nose cone is the leading, tapered or pointed section of the rocket. It helps
reduce aerodynamic drag.
Fins: The fins help guide the rocket and provide a stabilizing force.
Body tube: The body tube is the central structure of the rocket. It holds the engine, propellant tanks and payload.
Error distance: The distance a rocket strayed/drifted away from the exact launch point.
Rocket engine: A part in a rocket that contains the propellant.