What Did I Learn?

From the experience of building this rocket I learned the physics and science involved in ballistics and rocket/missile building such as the effects of fin shape, weight distribution, rocket weight, and all the different variables that contribute to the stability of a rocket in flight.  I also learned some good methods for drying paint on a rocket and some different ways to create and use a stencil to spray paint a design on a rocket.

Results

1st Launch (Practice Launch 12/19/2012):
-Launch angle: 30 degrees
-Water amount: 570 mL
-Pressure: 80 psi.
-Distance: 101.5m

The only thing that was unsatisfactory in that launch was that the egg was cracked, and when I say cracked I mean like the egg looks intact but you can see some cracks lining the shell and yellow yoke leaking out.  and compared to the other eggs in the other rockets mine was pretty good.  In the other rockets you couldn't even tell where the egg shell was when they opened it.  It just looked like bags of egg yoke.

2nd Launch (Practice Launch 1/10/2013):
-Launch angle: 35 degrees
-Water amount: 570 mL
-Pressure: 80 psi.
-Distance: 84m

The wind messed with the rocket flight path because the rocket was shot straight into the wind and that resulted in the short distance. The egg still broke too.

3rd Launch (Final Launch 1/15/2013):
-Launch angle: 30 degrees
-Water amount: 570 mL
-Pressure: 80 psi.
-Distance: 110m

It went further than the previous launches but the egg didn't survive.
I think the reason it didn't survive was because there wasn't enough reinforcement in the tip where the egg goes.

Keeping the Payload Safe

          To keep the egg from cracking I did couple things. For padding inside the tip of the rocket I used packaging foam used to protect fragile objects being transported.  I cut the foam into a shape that would snugly fit the inside of the plastic nose cone then added smaller scraps on the inside of the rocket to give the egg some room to move to lessen the force of the crash landing.  I think that to further ensure the safety of the egg, I could have put the egg inside of another smaller container to put in the nose cone with padding around both the egg and the container to really make that egg safe.
          In addition to the padding around the egg, I made the top nose cone (which goes on top of the plastic cone holding the egg) with regular printer paper so that it crumples on the impact of landing and inside the paper cone I put in more scraps of packaging foam to help decrease the force exerted on the egg during the crash.

Physics of the Rocket

Propulsion:
This bottle rocket is propelled by a mixture of air and water. How this propels the rocket is that the water provides the mass that the rocket pushes against in order to take off and the compressed air provides the force that pushes the water out.  According to Newton's 3rd Law the equal and opposite reaction is the water and rocket being forced apart in opposite directions making the rocket fly.

Body of the Rocket:
I didn't need to reinforce the fuselage of the rocket because we are limited to 80 psi.  I made sure the body of the rocket was smooth so that it was aerodynamic. I also made sure that no unnecessary weight was added so that my rocket would have a greater range capability.  A light weight rocket can get a greater range using less water than heavier rockets because you can add more water before the rocket starts loosing range due to the excess.  Light rockets can get the same range as a heavy rocket using less water.

Fins:
Number of fins: four fins is an optimal number to have on this rocket because it provides the needed stability to keep the rocket on course and because it fits on the launch pad more easily without risk of bending the fins.
Placement: I place the fins as close to the back where the nozzle is because the fins will keep the back from rotating and the rocket from flying off course. It's all about the stability.
Shape: I chose a generic shape because I know this trapezoidal shape cuts through the air nicely and does a better job of directing the rocket of smaller more streamline fin shapes.  The way i designed the fins to hug the contour of the bottle makes the fins less likely to bend and warp in flight keeping the rocket stable.
Angle Orientation:  I chose to angle the fins straight up and down as opposed to angled to one side for a number reasons.  One reason is that when building rockets the choice is either fins or no fins; when you have no fins, you want the rocket to spin for stability like a bullet but if you have fins, you do not want the rocket to spin because of the fins because it will not keep the rocket stable since the whole point of fins is to keep the rocket from spinning out of control and to steer the rocket.  The straight up and down orientation is also much easier to accurately place because there is less risk of angling the fins at different angles.

The Nose:
When making a rocket the best nose shapes are either round or pointed.  Typically pointed tips are used on high speed rockets and round tips are used on low speed rockets but when it comes to bottle rockets, the difference between pointed and round tips won't have any significant effect on the rocket. I chose pointed because I wanted the nose to be destructible to lessen the force on the egg when it crashes into the ground.

Weight Distribution:
The weight distribution of a rocket should have the majority of the weight in the front above the center of pressure.  When building rockets, having the center of pressure closer to the bottom of the rocket and the center of mass closer to the top of the rocket gives it more stability.  The weight in the front leads the rocket and keeps the rocket flying straight.  If the mass was in the back, the rocket would be easily taken off course because the tip would easily be blown around and the rocket would go out of control.

In the diagram on the left, cg is center of gravity (mass) and cp is center of pressure.

 *I hand drew all the pictures and added text in photoshop*

The Making of the Rocket

Materials:
- 2 2L plastic soda bottles
- cardboard
- 8.5x11 white printer paper
- graph paper
- clear packaging tape
- gorilla glue
- heated exacto-knife
- Black car bumper spray coating
- White spray paint
- Packaging foam



Step 1) Design fins to fin the bottle using measurements and graph paper
- dimensions of the fin: outer side: 1.25 in
bottom side: 4.25 in
long side: 4.5 in








Step 2) cut out the fins from the card board

Step 3) Cut on of the bottles and fit them together

Step 4) I marked on the bottle where the bottom of the fins will line up
Step 5) I made sure to measure the circumference of the bottle by taking a piece of graph paper, marking it in four equal sections. After that, I wrapped it around the bottle and then made marks on the bottle where each of the fins were to be placed.
Step 6) I then attached the fins using gorilla glue and clear packaging tape.

Step 7) Roll printer paper to make nose cone, stuff with foam scraps.

Step 8) Create padding in the top section of the rocket with packaging foam

Step 9) Attach paper cone to the top half of the rocket with tape.

Step 10) Attach the to halfs of the rocket together using strips of packaging tape

Step 11) Cut out a stencil to use in painting the design of the rocket

Step 12) Paint the rocket black

Step 13) Paint on the stencil

Q Focus

Top 3 Questions:

1) How many fins are optimal?
2) How many mL of water is optimal?
3) What is the optimal angle of elevation for egg survival?


Answer:

This project could answer my questions through the results of testing of the rocket.

1) 4 fins are optimal because they provide a good amount of stability.

2) For the rocket that I built, which is a light rocket, the optimal amount of water ranges between 550mL and 580mL depending on how far I want it to fly.

3) The optimal angle for egg survival on my rocket designed to lessen the impact from a nose collision, would be 35-40 degrees.