2014

YOUTH GUIDE

4-H National Youth Science Day

Activity 4: Fly through the air with the greatest of ease

Comparing aerodynamics of different rocket styles

Activity Summary: The study of aerodynamics is extremely important to the process of designing rockets. In the aerospace industry, every rocket design must be tested to make sure it will perform properly for both efficiency and safety. In this activity, you will compare the aerodynamics of three different rocket styles by analyzing the air flow and forces around them. Using the same software used by professional engineers, you will evaluate the various effects of wind resistance and air pressure on the rocket models in order to determine which design is the most efficient and aerodynamic.

Created by John Helfen, Autodesk

Edited by Janice Miller, Autodesk

Contributions by Kirk Astroth and

Eric Larsen, The University of Arizona

Table of Contents Introduction ................................................................................................................................................ 2

Aerodynamics activity ................................................................................................................................. 2

Step 1: Get familiar with aerodynamics ...................................................................................................... 2

Step 2: Access the software ........................................................................................................................ 3

Step 3: View an introduction to Autodesk Flow Design .............................................................................. 4

Step 4: Understand navigation in Flow Design ........................................................................................... 5

Step 5: Import a model into Flow Design .................................................................................................... 5

Video: Importing models into Autodesk Flow Design ............................................................................. 6

Step 6: Prepare for 3D analysis ................................................................................................................... 6

Step 7: Change the orientation of the rocket.............................................................................................. 6

Video: Changing the orientation of the model in the wind tunnel ......................................................... 7

Step 8: Change the wind tunnel size and air speed .................................................................................... 7

Video: Changing air speed and wind tunnel size ..................................................................................... 9

Step 9: Enable the pressure ........................................................................................................................ 9

Video: Enabling surface pressures on the model .................................................................................... 9

Step 10: Enable the drag plot...................................................................................................................... 9

Video: Enabling the Drag Plot graph ..................................................................................................... 11

Step 11: Record your data ........................................................................................................................ 11

Repeat steps 5-11 with rocket styles 2 and 3 ........................................................................................ 11

Step 12: Reflect, evaluate, and discuss ..................................................................................................... 12

Evaluating results .................................................................................................................................. 12

Talk about it .......................................................................................................................................... 12

Rocket Style 1: Advantages & drawbacks ......................................................................................... 13

Rocket Style 2: Advantages & drawbacks ......................................................................................... 13

Rocket Style 3: Advantages & drawbacks ......................................................................................... 14

Step 13: Apply what you learned .............................................................................................................. 14

Glossary of terms ...................................................................................................................................... 15

Introduction In this activity, you will compare the aerodynamics of different styles of rockets. Three types of 3D rockets have been included in the project files: a 3D model of the 4H NYSD Rockets to the Rescue logo rocket (Figure 1); a similar retro-style rocket with a different shape (Figure 2); and a model similar to what you will be building as part of the 2014 National Science Experiment (Figure 3).

To complete this activity, you will test each of the 3D rocket models in a virtual wind tunnel by using Autodesk® Flow Design software to evaluate the lift, drag, and air pressure forces. After completing this activity, you will discuss the differences between the rockets and how the changes in their designs affect the wind tunnel results.

Aerodynamics activity Depending on the number of computers available, you may be grouped into teams to work on the activity and discuss your observations. Because there are three different rocket models, teams of three may work best. Once you have been given time to work through the activity and record your findings, you will then discuss your results and report what you have learned.

Step 1: Get familiar with aerodynamics Aerodynamics is the study of air flow and motion, especially how air interacts with a solid object, such as an airplane wing (or rocket). Because we cannot see wind—we only see the effects of it—it is important to take a minute to better understand some concepts of aerodynamics. The website How Stuff Works has an excellent series explaining aerodynamics. Read the article How Aerodynamics Work.

In the article you will learn more about drag coefficient and what it means. Drag is the resisting force of an object moving through the air. For example, the force you feel when you put your hand out of the window of a moving car is drag (also referred to as drag force). The drag coefficient is a number used to quantify (or measure) the drag/resistance of an object in a fluid environment, such as air or water. Note

Figure 1: Rocket Style 1.stl Figure 2: Rocket Style 2.stl Figure 3: Rocket Style 3.stl

that the drag coefficient is not a constant, but varies – so it can change depending on an object’s speed, direction, position, size, etc. Generally, you can expect more aerodynamic shapes to have lower drag coefficients. Here are some sample values for common objects, including some aircraft:

Object Drag coefficient Object Drag coefficient Aircraft – F-4 Phantom 0.021 Car - BMW i8 0.26 Aircraft – Cessna 310 0.027 Jeep Wrangler 0.58 Aircraft – Boeing 747 0.031 Standard model rocket 0.75 Aircraft – F-4 Phantom II (supersonic)

0.044 Road bicycle and cyclist 1.0

Aircraft – F-104 Starfighter 0.048 Skier 1.0-1.1 Aricraft – X-15 0.095 (estimate) Empire State Building 1.3-1.5

Step 2: Access the software In order to complete this activity, you must install Autodesk® Flow Design software on your computer. You can access and download the software for free* from the Autodesk Education Community. If it is not already installed on the computer you are using, please have an adult help you with the following steps.

1. Please follow this link to go to the Autodesk Education Community.

2. Scroll down to the Select your free* software section and filter by All products.

3. Scroll down the page, locate Flow Design, and click the Flow Design link. (Flow Design logo shown to the right)

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4. Follow steps 1-3 under the Get a free* 3-year license today section to sign in or create your account, select the free software you want, and review and download Flow Design. Tip: For step-by-step instructions on account creation, please refer to the installation guide (NYSD_FlowDesign_Installation.pdf) found in the project zip file.

5. Follow the instructions on the download page to complete the download and installation. Tip: For step-by-step instructions on installation of the software, please refer to the installation guide (NYSD_FlowDesign_Installation.pdf) found in the project zip file.

Note: The user name and password you created to access the Autodesk Education Community is your Autodesk ID. Autodesk Flow Design requires an Autodesk ID to function once it has been installed. The same Autodesk ID can be used to access the Autodesk Education Community and to start Autodesk Flow Design.

Step 3: View an introduction to Autodesk Flow Design You will use Autodesk Flow Design to create a virtual wind tunnel. Like an app, it performs one task—to help you clearly visualize external air flow. Click on The Flow Design Story video to view an overview of Autodesk Flow Design and how is it used in industry today. After you complete this activity and discussion for 4-H National Youth Science Day, if you would like to view additional introduction videos, you can visit the Autodesk Flow Design help site here.

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ViewCube

Step 4: Understand navigation in Flow Design Before beginning the project it will be helpful to get familiar with the navigation tools in Autodesk Flow Design so that you know your way around. After importing a model (bringing in one of the rocket model files), there are several navigation items to be aware of:

1. Rotate - Holding the left mouse button down while moving (or dragging) the mouse will rotate/spin the model in 3D space.

2. Panning - Holding the right mouse button down while moving (or dragging) the mouse will pan the model in 3D space.

3. Zoom - Scrolling the wheel on the mouse will zoom in and out. 4. ViewCube - Clicking on different areas of the ViewCube in the upper-right corner of

the screen can be used to view the model from different directions. 5. Default view (Home) - Returning the model to a default location can be done by

clicking the little house button above the ViewCube. If you get lost, click Home.

Note: Images and videos related to this project are shown with the dark interface (screen background) applied to Autodesk Flow Design. The color of the interface does not affect the results of the analysis, it is simply user preference. The color of the interface can be changed by clicking the icon with three colored dots in the upper-left corner of the screen.

Step 5: Import a model into Flow Design Autodesk Flow Design is a virtual wind tunnel program that can be used to evaluate the lift, drag, and pressure forces created by air flowing over an object, in this case a rocket. We have provided three different stereolithography files (.stl) in the project zip folder for you to test in Autodesk Flow Design.

Note: A stereolithography file is the same format that is used for 3D printing. .STL files can be created in many Autodesk products, such as Autodesk® Inventor®, Autodesk® Tinkercad, and Autodesk® 123D® Design software.

1. Start Autodesk Flow Design. 2. On the start page shown in Figure 4, select Local from the Import section at the top.

3. Browse to the location where you unzipped the project files, open the Rocket models folder, and select Rocket Style 1.stl.

4. Click Open to import the model.

Figure 4: Autodesk Flow Design start page

5. After import, the model should look similar to the image in Figure 5. Note: if your view does not look like this, see the next step, “Prepare for 3D Analysis,” to ensure proper configuration.

After you have finished analyzing this first rocket model and recorded your data at the end of this activity, you can import additional rockets by either quitting and restarting the program, or by selecting Import from the menu button in the upper-left corner of the program (menu button highlighted in image to right).

Video: Importing models into Autodesk Flow Design See a video showing how to import models into Autodesk Flow Design.

Step 6: Prepare for 3D analysis You must check to make sure your software settings are correct in order to complete a 3D analysis. After importing the rocket model, make sure the top tool bar matches the image below:

If any of these buttons are showing different settings, click the arrow beneath each to select the correct menu item to match this image; this will ensure you are running the proper type of analysis.

Note: The image above shows all buttons in the tool bar; throughout the rest of this document, any time a button is referenced a small image will be shown and you should look to the main toolbar to locate the specific button.

Step 7: Change the orientation of the rocket After import into Autodesk Flow Design, the rocket model will be in a launch position, its orientation (position or direction) standing on end and pointing to the sky. To properly analyze the rocket, you need to rotate it so that it is facing into the wind.

To change the rocket orientation:

1. Click the orientation button indicated with a 1 in the image below. 2. In the Orientation dialog box, click and drag the slider next to the Y Angle (deg) to the right until

the value reaches 270. 3. Click the OK button to accept the change.

Figure 5: Rocket after import

Note: Check the Dynamic update checkbox in the dialog box to see the orientation of the model change while moving the slider.

After accepting the orientation change, the model will be updated and wind will begin to flow over the rocket in the new position.

Video: Changing the orientation of the model in the wind tunnel See a video showing how to change the orientation of the model in the wind tunnel.

Step 8: Change the wind tunnel size and air speed The size of the wind tunnel and the speed of the air can both affect the aerodynamic forces on an object. To evaluate each rocket at a number of different speeds, Autodesk Flow Design allows you to change the air speed and overall size of the virtual wind tunnel easily.

When you select the Wind Tunnel Settings button (located next to the Orientation button at the top of the screen), you will see a dialog box and heads-up display that enables you to change wind speed and wind tunnel size.

1. To change the wind speed, move the slider or type a value of 147. Note: Default value is in m/s; entering a value of 147 m/s is equal to roughly 330 mph. Tip: entering “100 mph in m/s” in google will quickly convert MPH to meters per second.

2. Use the scroll wheel on your mouse to zoom out until you can see all arrows as shown in the image above, highlighted by the number 2. These blue arrows are the Tunnel Manipulators that enable you to adjust the size of the wind tunnel. Tip: If scrolling the wheel on the mouse doesn’t cause a zoom at first, then left-click on the rocket to scroll the wheel on the mouse to zoom in/out.

3. Left-click with your mouse and drag on each arrow to adjust the size of the wind tunnel until the rocket model is roughly in the center of the tunnel. The overall size of the wind tunnel is displayed just under the status in the upper-right corner of the screen. Its length should be roughly 0.500m, and the width and height should be roughly 0.175m each. This value does not have to be exact. Note: If you accidentally click and drag outside an arrow and the view of your model changes, just remember to click the house-shaped Home icon above the ViewCube in the upper-right to return to your original view.

Increase the size of the wind tunnel to ensure air can flow around the rocket in all directions. In Figure 6, the wind tunnel has been increased in size to allow clean airflow around the rocket on all sides.

The final wind tunnel should be sized to have the rocket positioned near the middle of the wind tunnel.

Figure 6: Approximate size of wind tunnel

Figure 6 shows the general size of the wind tunnel when complete. Remember, you want to have enough space around each side of the rocket to allow air to flow cleanly.

Video: Changing air speed and wind tunnel size See a video showing how to change the air speed and wind tunnel size.

Step 9: Enable the pressure The Surface Pressure button enables you to toggle (switch) on or off a view of the pressures pushing on the surface of the rocket as air passes over the model. Toggling the surface pressures will color code the model and add additional information about the pressures in the upper-left corner of the screen. Figure 7 shows the Surface Pressure button toggled on, while Figure 8 shows the Surface Pressure toggled off.

The information in the upper-left corner of the screen will show the velocity (speed) of the air around the rocket, and the color on the model shows the pressure generated by the wind pushing on the rocket.

Video: Enabling surface pressures on the model See a video showing how to enable surface pressures on the model.

Step 10: Enable the drag plot The drag plot will provide information related to the drag coefficient and force generated by the wind against the rocket. In the upper-right corner of the screen you will see information about the size of the model and the status of the analysis. When you first start an analysis, you may briefly see the word Unknown in a red highlight as Autodesk Flow Design begins calculations. After the calculations begin you will see that status update to Transient as the air flow continues and makes its way around the rocket.

After a period of calculation over time, the status will update to Stabilized, which is an indication that Flow Design has arrived at a solution (final analysis) for the airflow; and from that point forward there shouldn’t be significant changes to the results of the analysis.

Figure 7 –Surface Pressure Enabled Figure 8 –Surface Pressure Disabled

While the heads-up information will show the status of the analysis, you can enable (turn on) the drag plot to view a graph of the calculations while they are taking place. When the drag plot is open you will also see the drag coefficient value and the drag force being generated by the wind. To enable the graph, click the Drag Plot button on the tool bar.

Figure 9 shows several images of the rockets at different points during an analysis. The blue and white lines show the calculated and average drag coefficient, and when those lines get close enough together is when the analysis has stabilized. Below the three images is a closer look at a drag plot graph for reference.

The image in Figure 10 shows the drag plot in a transient state, Figure 11 shows the plot nearing stabilization, and Figure 12 shows the plot in a stabilized state after allowing the analysis to run for a period of time after the stabilization (final analysis results have been reached).

Figure 7: Sample analysis images

Figure 8: Transient drag plot

Figure 9: Drag plot nearing stabilization

Figure 10: Stabilized drag plot after a period of time

Figure 9: Sample analysis images

Figure 10: Transient drag plot

Figure 11: Drag plot nearing stabilization

Figure 12: Stabilized drag plot after a period of time

Video: Enabling the Drag Plot graph See a video showing how to enable the drag plot.

Step 11: Record your data Be patient and wait until your analysis has stabilized. Then document the results in the chart below to discuss with your team or facilitator. The results information you need to record can be found in the upper-left of your analysis screen, and also just above the drag plot graph, as highlighted in Figure 13.

Figure 11 – data from analysis required to populate results table

In the upper-left of your screen, you see two values under Velocity and Pressure. The first number is the wind speed (Velocity), and the second number shown in brackets is the surface pressure [Pressure].

Wind Speed

Surface Pressure

Drag Coefficient

Drag Force

Avg. Drag Coefficient

Rocket Style 1

Rocket Style 2

Rocket Style 3

Repeat steps 5-11 with rocket styles 2 and 3 Now repeat the process described in this document with each of the three different rocket models included with the project files—repeat steps 5 through 11 with rocket styles 2 and 3.

Figure 13: Data from analysis required to populate results table

Step 12: Reflect, evaluate, and discuss Now that you are analyzing rocket designs just like real rocket scientists, it is time to think about what you have learned from this cool experience.

Evaluating results When everyone has had a chance to run the analysis with all three rocket models and record the results, you will get the opportunity to compare observations and data. These discussions should be held at the end of this activity so you can discuss what was learned (with other participants if there are groups, or with your facilitator if it is just you) and draw some conclusions from the data collected.

Each of the rockets provided is quite aerodynamic overall, but all include specific design features that may cause some surprising results. When doing any type of design or analysis, it is important to step back and evaluate the results to determine if changes need to be made. Each rocket design has advantages and disadvantages, and it is indeed possible that the best design is not one of the three, but instead is a hybrid design that ultimately combines certain elements from each rocket model to make the most efficient and aerodynamic design.

Reflect and discuss the following, and write down your answers on paper or a board (if there are groups, elect one person from each group to be the “recorder” and capture the main points).

• What observations did you make when comparing the body styles of the rockets? If there is a lot of room for cargo, how does that influence flight, stability, and drag?

• What observations did you make when comparing the nose cones? How does the shape of the nose cone affect a rocket’s ability to fly?

• What observations did you make when comparing the fins of the rockets? What influence do the shape, size, and thickness of the fins have on flight, stability, and drag?

• What is the effect of a tapered tail that comes to a point, versus a straight tail, versus a tail that flares out? What is the impact of aft (rear) end shape?

• What advantages do each of the three rocket styles have? What are their drawbacks? • Do you see a correlation/connection between drag coefficient and surface pressure? Describe

why or why not. • On Rocket # 2, what parts of the rocket did you observe creating drag? What changes could you

make to decrease those areas that are creating drag? • Change the Y axis angle in the software; how does that change affect the drag force?

Talk about it • Knowing what you know now after looking at models in the wind tunnel, what changes or

additions would you make to the rockets you have made in the previous activities? • If you were to recreate your FTD (Food Transportation Device), what changes would you

implement? How would these changes to your FTD help to decrease drag? • Is decreasing drag always the most important factor to consider? • How would you use the pressure information to improve your model? • What are the advantages of using a computer model before constructing your physical rocket?

To help guide your discussion, you can start with the hints in the charts below to fill in the advantages and disadvantages (drawbacks) to each rocket design.

Rocket Style 1: Advantages & drawbacks

Rocket Style 2: Advantages & drawbacks

ADVANTAGES WHY? Cargo room?

Think about payload.

Shape?

Think about airflow and the color-coded model when you turned on the Surface Pressure button.

DRAWBACKS WHY? Cargo room?

Think about the effect on drag.

Shape of fins? Think about the drag forces.

ADVANTAGES WHY? Cargo room?

Think about payload.

Shape of fins?

Think about airflow and the color-coded model when you turned on the Surface Pressure button.

DRAWBACKS WHY? Cargo room? Think about the effect on drag.

Base shape? Think about the drag forces.

Rocket Style 3: Advantages & drawbacks

Step 13: Apply what you learned CONGRATULATIONS!! You are on your way to becoming an awesome aerospace engineer! But did you know that Flow Design can also be used to test everyday object designs like bicycles, cars and buildings?

We hope you learned a lot about aerodynamics and drag force in this activity, and enjoyed using Flow Design just like a professional on the job. Now consider what you learned and how it can be applied to real-world situations, beyond the NYSD rocket design itself. Record your answers and discuss.

• If you could construct the ideal rocket body style for distance, what would it look like? • If you could construct the ideal body style for payload delivery, what would it look like? • How do you decide which design features to balance in the final analysis? • How do these flight characteristics apply to airplanes? How have plane designs sought to

minimize drag and pressure? • When thinking about the Stealth bomber, how have these principles and concepts been used in

its design? • Imagine a bicyclist racing in the Tour de France event. How could drag be reduced on a bicycle?

Is there a benefit to riders riding behind each other? Why?

ADVANTAGES WHY? Cargo room? Think about payload. Compare to the first two rocket styles.

Body shape? Think about airflow and the color-coded model when you turned on the Surface Pressure button.

DRAWBACKS WHY? Cargo room? Think about the effect on drag versus what you can deliver.

Shape of fins? Think about airflow and the color-coded model when you turned on the Surface Pressure button.

Nose cone design? Look at your analysis and study the areas of pressure – think about the drag forces.

Glossary of terms

Aerodynamics – The study of air flow and motion, especially how air interacts with a solid object, such as an airplane wing (or rocket!).

Autodesk Flow Design – A virtual wind tunnel for product designers, engineers, and architects that models air flow around design concepts to help test ideas early in the development cycle (test it before you build it!).

Drag – The resisting force of an object moving through the air. The force you feel when you put your hand out of the window of a moving car is drag (also referred to as drag force).

Drag Coefficient – A number used to quantify (or measure) the drag/resistance of an object in a fluid environment, such as air or water.

Fluid Dynamics – The study of fluid flow; the natural science of fluids (liquids and gases) in motion.

Lift – The force that directly opposes the weight of an airplane (or rocket) and holds the airplane (or rocket) in the air. Without lift, your rocket would stay on the ground.

Orientation – The relative position or direction of something (what direction is it facing?).

Payload – The cargo carried by a craft for a particular mission.

Pressure (Surface Pressure) – Air pressure is the force exerted on an object by the weight of tiny particles of air called air molecules.

Stereolithography file – A file format that is used for 3D printing. The three rocket models you are using in this activity are .STL files, and can be created in many Autodesk products like Flow Design.

Velocity – Wind speed is caused by air moving from high pressure to low pressure, and is a fundamental atmospheric rate.

Wind Tunnel – A tool used in aerodynamic research to study the effects of air moving past solid objects, in this case a rocket.

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