# 8.12: Student Handouts

## Flight Fidelity Challenge: Part 1

You have now had the opportunity to build a standard Estes model rocket. That standard model is engineered to be inexpensive to buy, straightforward to build, and easy to successfully launch.

Your goal now is to design and build a model rocket that will fly straight up.

Your rocket must meet the following **criteria:**

- The rocket is capable of being launched multiple times.
- The rocket is loaded with 40 g of payload.
- The rocket’s flight is stable.
- The rocket’s flight path veers no more than 10° from the vertical – our definition of "straight up."
- The rocket’s physical characteristics have been fully defined, allowing the motion of the rocket under different conditions to be calculated.

In addition, you must adhere to the following **constraints:**

- The mass of the rocket, including the engine and payload, does not exceed 75 g.
- The payload is secured so that it doesn’t move in flight.

Think about the design and construction of the standard rocket you built. You need to make *at least* THREE significant changes that will improve the performance of your rocket and/or allow you to better accomplish the stated goal. You will have three engines with which to test your model; you should modify your rocket between each of your flight trials in an attempt to maximize your rocket’s performance.

By the deadline provided, your group needs to bring to class:

- A safe, stable rocket preloaded with 40 g of payload that is immovable within the body of the rocket when it is launched. The positions of the centers of mass and pressure should be clearly marked on the body of the rocket.
- The "Engineering Design Brainstorming Worksheet" filled out by each member of your group.
- A completed engineering journal that documents:
- A sketch and description of the initial "best design" decided by your group after brainstorming.
- Results of each of the test flights: maximum height, approximate angle of trajectory, and general performance notes.
- After each test flight, evaluate the results: What worked well? What did not work well? Why did it not work well?
- The modification(s) your group made after the evaluation of each of the first two test flights, with a well-articulated reason (grounded in physics principles) why each modification was made.
- When a final design is decided upon, list the three modifications you made to the standard rocket’s design, with a well-articulated reason (grounded in physics principles) why each modification should improve the rocket’s performance.
- A mathematical verification of the stability of your rocket (calculate the number of body diameters between your rocket’s centers of mass and pressure).
- Scaled blueprints of your rocket’s design, which indicate the materials used, the location of the payload, and the positions of the centers of mass and pressure.

## Engineering Design Brainstorming Worksheet

Complete *individually*, before you begin construction. Use additional paper if necessary.

**Define the problem:**

**List the criteria:**

**List the constraints:**

**Brainstorm possible solutions:**

Identify parts of the rocket that could be changed to improve the performance of your rocket and/or allow you to better accomplish the stated goal.

**Do research to generate ideas for possible solutions:**

How did you research this problem?

What did you find out?

**Explore possibilities:**

On the back of this sheet of paper, draw three different possible solutions. Label and describe the differences.

When all members of your group have completed the brainstorming worksheet, discuss your ideas and come to a consensus about a "best design." The best design can be an idea from a single member of your group or a combination of ideas from different members of your group. Sketch and describe the best design in your engineering journal.

## Rocket Stability

Adapted from http://quest.nasa.gov/space/teachers/rockets/act12ws13.html

A rocket that flies straight through the air is said to be a *stable* rocket. A rocket that veers off course or tumbles wildly is said to be an *unstable* rocket. The difference between the flight of a stable and unstable rocket depends upon its design. All rockets have two distinct "centers." The first is the *center of mass*. This is a point about which the rocket balances. If you could place a ruler edge under this point, the rocket would balance horizontally like a seesaw. What this means is that half of the mass of the rocket is on one side of the ruler edge and half is on the other.

The other center in a rocket is the *center of pressure*. This is a point where half of the surface area of a rocket is on one side and half is on the other. The center of pressure differs from center of mass in that its location is not affected by the placement of payloads internally in the rocket. This is just a point based on the surface of the rocket, not what is inside. During flight, the pressure of air rushing past the rocket will balance half on one side of this point and half on the other. You can determine the center of pressure by cutting out an exact silhouette of the rocket from cardboard and balancing it on a ruler edge.

The positioning of the center of mass and the center of pressure on a rocket is critical to its stability. In order for a rocket to be stable — and therefore safe to launch — the centers of pressure and mass must be *at least* **two** body diameters apart. You will need to prove your rocket’s stability before you are allowed to launch it.

**To Determine Centers of Mass and Pressure:**

1. Tie a string loop around the middle of your rocket. Carefully slide the string loop to a position where the rocket balances. This is your rocket’s center of mass. Mark this position on both the rocket body and your scale drawing.

2. Lay your rocket on a piece of cardboard. Carefully trace the rocket on the cardboard and cut it out. Alternatively, you can project a shadow of your rocket onto a piece of cardboard (an overhead projector works well), trace the shadow, and cut it out.

3. Lay the cardboard silhouette you just cut out on a ruler and balance it. This is your rocket’s center of pressure. Mark this position on both the rocket body and your scale drawing.

## Model Rocket Engine: Type A8 Specifications

**Average Mass of Engine: 16.2 g**

**Average Mass of Propellant: 3.12 g**

**Thrust Curve:**

FROM ESTES WEBPAGE:

FROM THRUSTCURVE.ORG WEBPAGE:

## Rocketry Spreadsheet: Student Guide

## Flight Fidelity Challenge: Part 2

First, record the maximum height of your rocket in the test flights: _____________

Record your rocket’s calculated drag coefficient: __________________

In Part 2 of this challenge, you will use the published physical characteristics of a ½ A6-2 engine, along with the knowledge you’ve gained about using the numerical simulator (spreadsheet), to predict the maximum height your rocket would fly when powered with a ½ A6 engine. The specifications of the ½ A6 engine are provided below.

By the beginning of class on launch day, your group needs to bring to class:

- The SAME rocket you used in "Flight Fidelity Challenge, Part 1." Do NOT make any alterations to it, or you will change its drag coefficient!
- A list of the changes you made to the spreadsheet in order to account for the changes caused by the new engine. Include a reason why you made each change and the method you used to decide what value to use.
- A printed copy of the completed spreadsheet you used to predict your rocket’s maximum height.

Your predicted height using a ½ A6-2 engine: _____________________

Flight Observations:

Maximum Height Calculation:

Percent Error:

On a separate sheet of paper, thoroughly discuss the errors associated with the prediction you made, and how each error you identify would affect the results you got.

## Model Rocket Engine: Type ½ A6 Specifications

**Average Mass of Engine: 15.0 g**

**Average Mass of Propellant: 1.56 g**

**Thrust Curve:**

FROM ESTES WEBPAGE:

Thrust Curve:

FROM THRUSTCURVE.ORG WEBPAGE: