"To the Moon" [Rocket Lab]

Purpose: 

To determine the trajectory of a model rocket.

Equipment:

• PASCO Rocket Engine Test Bracket
• Dual range force probe
• Iron ring stand
• Estes B6 or C6 motor
• Lab Pro (green box) 
• Computer with Logger Pro software
• 
  
• Procedure:

1. Once model rocket engine has been set up, Logger Pro should be open on the computer. 
2. Time duration is at 3 seconds and the sampling rate is at 1000 samples/second. 
3. Select "triggering" and set its force to -0.2 Newtons. 
4. **Be sure to clear area around experimental set up!**
5. Set the zero force probe and then click "collect data" (you should see the "waiting for trigger and data..." within the top portion of the graph area)

Questions (part I-class ideas):

1. Draw a system schema and force diagram and apply Newton's 2nd Law to a rocket on the launch pad. (Not shown)
2. Redraw the system schema and force diagram and a statement of Newton's 2nd Law based on this force diagram for the moment the rocket leaves the ground. (Not shown)
3. What agent is causing the upward force? The engine that is burning the dry fuel
4. Do you think its really the thrust force is constant? Explain. No, because F = ma is not constant. It starts off fast but then slows down.
5. As the fuel burns, is your rocket speeding up or slowing down? Which force has to be bigger for this to occur? Do you need to modify your force diagram? (Graphs not shown) speeding up because the thrust is greater than that of the force of gravity while the fuel burns [F(T) > Fg].
6. Your rocket is not a particle. Do you think you have to deal with air resistance? Redo your system schema, force diagram, and statement of Newton's 2nd Law to include it. (Graphs not shown) Yes, because we need to consider the environment of the launch (whether it's windy or raining)
7. Do you think F(air) is constant? If not, what does it depend on? Not constant because temperature and wind changes as the rocket increases in height.
8. When the rocket has run out of fuel, what direction is it still going? Is it speeding up or slowing down?  Based on this, what does your force diagram look like now? What is your new statement of Newton's 2nd Law? Fnet = ma
9. How will you know when the rocket reaches its highest point? when velocity is at 0 and drag has 0 Newtons.

Questions (part II-making model figure):

1. What specific information and measurements do we need? **Be sure to distinguish what quantities need to be looked up and what needs to be measured to do the calculations for your model** The formulas were given where: a=T-Tg-rhoAv^2/m               Vf=Vi+a(delta t)                      Delta r=Vi(delta t)+(1/2)a(delta t)^2                          Delta r = a(1/2)Vf^2-Vi^2
2. Now you will need to obtain the thrust vs time data for a rocket motor. Ultimately, this data will be used to help calculate the height of the rocket flight. Not all of the data that you obtain will be useful for the calculations in your model. (Consider this: Does the rocket accelerate instantaneously or does the thrust take time to build?) The first formula listed above needs initial acceleration, velocity, and then use kinematics to solve for r.

Excel:

After the model rocket has been launched, we were given these values:

Mass = 0.0632 kg

Diameter = 0.02441 m

Delta t = 0.001 s

Fg = 0.614

rho = 1.2

Using these values, we create a spreadsheet with these columns:

Time (s)

F(thrust)

acceleration (m/s^2)

velocity (m/s)

rhoAv^2 (N)

delta r (m)

r (m)

Once spreadsheet has been set up, we use the equations listed in question #2 of part II. Below is the spreadsheet for the data, equations used, and the graph displaying the rocket's thrust vs. time graph.

As you can see, we were able to plot the points on the graph, although the x & y axis seem to be switched where time is the y axis and the thrust is on the x axis. However, we were able to determine that the maximum height was at 147 m.

In order to get a column of data, it was dependent on the variables in the cells. We couldn't reformat the cells because if we change one cell, the whole chart would appear as "#####"

Looking back on the rocket engine graph, we see the rocket's thrust and how much it lasted.

Conclusion:

This lab took some time mostly for the reason that we needed to answer theoretical questions before actually doing the test instead of (how we usually start labs) going straight to testing. The questions were difficult, but they helped me in understanding how a rocket get propelled by not just the engine, but the forces that push it up but also push it down. When we tested the rocket engines, some of the demos didn't ignite as we had hoped because of the displacement of wires; therefore, it didn't launch. Using excel had its good and bad parts mostly because we were given these values from the launch and didn't really know how to input the values into excel nor did we know which one to solve first since there were many unknown variables. However, using excel was helpful for the fact that since the delta t was 0.001, it would have taken a long while to arrive at the estimated maximum height.