Introduction
For a physics experiment, we had to design and build a bottle rocket that would be able to carry an egg as its payload, with the requirement that the payload separates from the rocket and the egg survives the journey. The rocket also needed to reach a minimum height.
Materials
The rocket had all of the components required to insure that the rocket launched and the egg placed inside the rocket would survive. Prices provided are rounded. The rocket would cost
-2 2 Liter bottles at $1.50 each
-Duct Tape $5
-Posterboard $5
-Plastic Trash Bag $29 for 1000, so cost of $0.029 per unit
-String $5
-Foam $18.5 for 225'x12''x1/16'
-plastic bag $10 for 500 units, $0.02 per unit
-box knife $13
-Marker
-ruler
Procedure
1. Empty the two 2 liter bottles of soda by either drinking it or emptying it down the drain. Mark one as the fuel cell and do not make any cuts to this one. For the other one, mark the area of the bottle near the bottom before it begins to curve inwards to create the bottom. Also mark an area about halfway from the top of the bottle.
2. Decide how you want to create fins. Draw out the fin shape with a ruler, then cut it out. For this particular rocket, cut them out in the shape of a right triangle where one side is significantly longer than the other. Cut out 4 fins that are the same size and shape.
3. Cover the fins with duct tape and take care to remove any wrinkles. This improves air resistance as well as waterproofs the fins.
4. Attach the fins to the fuel cell so that the long side "points" upwards, which is towards the bottom of the bottle. They should be evenly placed around the bottle just before the bottle curves downwards towards the opening. Attach them with duct tape, taking care to make sure that the fins are firmly secured and the duct tape is flush with the rocket
5. On the second bottle, cut along the marks. In the section of cut bottle containing the original opening of the bottle, cut 4 slits 1-1.5 inches into the bottom of the cut portion. This section is the nose cone
6. Attach the section of plastic that is a ring to the top of the fuel cell using duct tape
7. Take one of the large garbage bags and expand it fully.
8. Attach 4 pieces of string that are of equal length to the garbage bags at 4 points that are equal distances from each other. Use duct tape, but attach the string to the duct tape as shown below. This method makes sure the string will not slip.
9. Attach the strings to the rocket in 4 points that are equal distances from each other to the bottom of the nose cone below the slits using the same method of attaching string to the duct tape.
10. Place foam inside the nosecone around it to create a hollow on the inside. Use scraps of foam and place in the center for extra padding. The foam should not interfere with the strings.
11. Take an egg and place it in a plastic bag. In the event of a tragedy and the egg breaks, the rocket will not get dirty. Remove as much air as possible from the bag.
12. Place the egg and plastic bag inside the hollow in the nose cone.
13. Place the bottom of bottle 2 inside the nose cone and duct tape inside so that the egg and foam do not come out. The piece may need to be trimmed.
14. To assemble the rocket, fold up the parachute and string and place inside the nosecone. It is fine if it doesn't fit, the rest of the parachute will fit inside the ring on the blast chamber. The nose cone will fit inside this ring and be seated. When the rocket is turned on its side, the two parts should separate with some ease.
Launch Configuration
Results
Unfortunately due to the circumstances, a comparison to other rockets is unavailable (sickness). The weather was a bit windy which may have caused the rocket to start leaning to one side. The rocket failed in one major section, height. The nosecone and fuel cell separated early, meaning that the rocket didn't reach it's maximum potential height. The rocket succeeded in another area though. Even with an early separation, the parachute deployed and the egg survived.
Some calculations reveal the height to be only 13.8 meters since the parachute deployed early.
Based on this, the velocity was 16.44 m/s.
At the moment of launch, there were 2 forces acting on the rocket, F (applied) and F (gravity). (air resistance negligible)
At the highest point, there was one force acting upon the rocket, F (gravity). (air resistance negligible)
Conclusion
The rocket performed well but had some flaws. In manufacturing the fins, more care could have been taken as to remove wrinkles from the fins. In addition, the nose cone separated early, which was due to the nose cone having insufficient support that kept it on the rocket. A possible solution would be to increase the length of the stopgap piece to increase how much area was used to secure the nosecone. Another possible reason for the nosecone falling off early would be lack of aerodynamics since there was no proper nose cone that would allow the rocket to cut through the air. In addition, the wind may have played a factor by pushing the nosecone off of its seating. The parachute deployed well and slowed the rocket's descent, allowing for the egg to survive. In addition, the padding was sufficient enough to withstand the forces of impact along the ground and any rolling forces caused by the nosecone rolling and bouncing along the ground after landing. In the future, I might use a bigger parachute, or several parachutes. I might use a longer launch tube with bigger fins in order to increase stability. A logical and technological step up from this rocket would be a 2 stage rocket, with 3 bottles used for the first stage in order to get the rocket up to a certain height and another bottle that would launch for the second stage in order to reach even greater heights.
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