Since time is money, and you have neither if you’re kid on the night before your not-yet-started science fair project is due, we’ve got a secret recipe for success that could earn you the last-minute grade.

Topic: Aeronautics

Shopping List:

• Copy paper, white and colored
• Paperclips
• Tape, scissors
• Cardboard for your display (can be from an old box)
• Digital camera (major plus if you have one)
• Computer, printer, paper (and photo paper if you have it)
• One hour

Background information: Every flying thing, whether it’s an airplane, spacecraft, soccer ball, or flying kid, experiences four aerodynamic primary forces: lift, weight, thrust and drag. An airplane uses a propeller or jet engine to generate thrust. The wings to create lift. The smooth, pencil-thin shape minimizes drag. And the molecules that make up the airplane attributes to the weight.

Think of a time when you were riding in a fast-moving car. Roll down the window and stick your hand out, palm down. Notice how easily the wind slips over your hand. Now turn your palm facing the horizon. Which way do you feel more force against your hand?

When designing airplanes, engineers pay attention to details, such as the position of two important points: the center of gravity and the center of pressure (also called the center of lift). On an airplane, if the center of gravity and center of pressure points are reversed, the aircraft’s flight is unstable and somersaults into chaos. (The same is true for rockets and missiles!)

STEP #1 Getting Started Grab a sheet of paper and fold your best paper airplane design right now.  This article is a step-by-step process on taking you from idea to exhibit, so don’t just keep reading… grab the paper and fold!

Need help getting started?  Watch the video below to learn how to make stunt planes, jets, and hang gliders):

Now take your plane and balance it on your finger. Where does it balance?

Grab a hair dryer and using the cool setting (so you don’t scorch your plane), blast a jet of air up to the ceiling.  Put your airplane straight-and-level into the jet of air, and using a pencil tip on the top side of your plane, find the point at which the airplane perfectly balances while in the airstream.

Which one is closest to the nose?

Besides paying attention to the CG and CP points (and their relation to each other, as in ‘which one is closest to the nose?’), aeronautical engineers need to figure out the static and dynamic stability of the airplane… which is a complicated way of saying whether it will fly controllably or oscillate out of control during flight.

Airplanes usually balance (e.g. have their CG point) around the wings. Ever wonder why the engines are at the front of small airplanes? The engine is the heaviest part of the plane, and engineers use this weight for balance, because the tail (elevator) is actually an upside-down wing which pushes the tail section down during flight.

Positive stability means that the plane is designed so that if you jam on the controls during straight and level flight (e.g. pitch up hard), and then let go, the airplane will return to (more or less) straight and level flight. That process works like this: When an airplane in level flight suddenly pitches the nose up, the wind speed over the wings slows and decreases the lift from the plane, which causes the nose to tip downwards, which causes the wind to rush over the wings again, creating more lift. This cycle eventually dampens out and the airplane is flying level again.

If, however, you have a negative stability (meaning that your CG is aft of the CP), then when you pitch up suddenly, the aircraft may do one of several things… all of which require sick bags and a parachute. One of the worst cycles is this: When the tail-heavy plane pitches down, the speed over the wings increases and provides more lift but only briefly, because the tail-heavy plane pitches the nose up (automatically by design) and keeps the nose up until the wind speed slows down so much that the winds stall (lift is no longer generated by wind flowing over the wings because there is no wind) and the airplane “falls” a distance until the air flows back over the wings, generating a lot of lift very quickly until the tail section tilts the nose back up, and the cycle continues to worsen each time – greater “fall” distances” and huge structural forces on the fuselage (body) until you jump ship.

The great news is that many of these unsettling things have been figured out a long time ago by two amazing people: the Wright brothers. They are also the ones who took an airfoil (fancy word for “airplane wing”), turned it sideways and rotated it around quickly to produce the first real propeller that generated an efficient amount of thrust. (Before this time, people had been using the same ‘screw’ design created by Archimedes in 250 BC… over 2,000 years ago we’ve had about the same propeller design without much improvement made along the way…) The twist in the propeller design was also a unique invention from the Wright brothers, and modern propellers are only 5% more efficient than those created a hundred years ago by the two brilliant brothers.

STEP #2 The Question: Okay, so how can you turn these ideas into a science fair project?  Well, first you need to come up with a question, or a hypothesis.  Here are a few examples to get you started…  you can use one of these, or make up your own:

• Does the CG need to be aft the CP for stable flight?
• What dihedral angle (wing flex angle, more on that later) is best for long flights?
• Does wing area affect time aloft?
• How does elevator trim affect straight-and-level flight?

STEP #3 The Materials & Methods: Your project is deceptively simple… and very complex once you get into it (as you can see by the introduction section).  You’re now making flying paper machines (paper airplanes) through the eyes of an engineer.  So get a sheet of paper and make your best design right now and throw them around the room.  When you’re done, click here to watch a short video on how to make our favorite flying designs.  When you settle on a design you really like, you need to figure out what you are going to test (and change), and how you are going to measure it.

For example, if you want to measure the effect of moving a weight around on your airplane (you could simulate this by clipping a paper clip onto various parts of the airplane), the control would be no paperclip, and your vairable (the thing you’re testing) would be location of ONE paperclip. (If you start adding in more thn one paperclip, you’re now testing not only the location but the size of the weight, and this requires a whole separate testing procedure using the Scientific Method).

Another example: If you wanted to figure out how the dihedral angle affects your flight, your control is zero dihedral (wings are flat), and your variable would be to test different angles both flexed above and below the horizontal position, using a protractor to measure your angles.

If you wanted to test the position of the CP and the CG, you’ll need to find a way to move the CG of the plane without affecting other things, such as wing shape.  (Paperclips are good ways to shift the weight of a plane.)

Once you’ve settled on a variable (thing you are going to test) and a control (baseline), you can go to the next step.

STEP #4 Taking Data: Across the top of the page, write down the stuff that does NOT change during your experiment.  You need to record as much detail as possible, so if someone else wants to recreate your experiment, they have enough information to go on.  At the top of your page, include specifics, such as:

• Your name (silly, yes.. and essential)
• Date and time of day
• Weather conditions (and wind speed, if you’re doing this outdoors – check the weather online for exact measurements if you don’t have a thermometer…
• Airplane geometry that does not change throughout your entire experimentation process. This could be the wingspan (AKA chord length, which is the longest line you can draw across the wings from tip to tip), wing area (you can estimate this using math and geometry, or use a sheet of grid paper and count up the squares the area of the wing covers up), weight of paper (one sheet = 1 ounce, or 0.014 pounds), dihedral angle (use a protractor – this idea is covered in the video), wing flap (elevator or aileron) position (up, down, neutral), location of CG and CP points (see above details on how to do this).

Draw a line under all this information, and using a ruler, make yourself a table (grid) for taking your data underneath your information.  You’ll need columns for the things you are testing for, which could be:

• Trial # (1, 2, 3 etc…)
• What you changed (number of paperclips, position of paperclips)
• Time aloft (seconds)
• Distance traveled (feet)
• Position of CG and/or CP
• Performance (pitch up/down, yaw up/down (rotation about the vertical axis), roll up/down, and did it do so fast or slow?)
• Dihedral angle (in degrees, positive or negative)

STEP #5 The Experiment: The fun part!  Start throwing your airplane around and jot down your results.  Although steps # 3 and #4 seem like a headache, they really set you up for successful tracking and data-taking for this part. Take LOTS of photos of your experiment, you, and anything else that will clearly demonstrate what you’re doing.

Think of it this way… you took care of all the detail work upstream, so when some part of your experiment actually works right, you can say, ‘Oh, that’s what I did!’  Speaking of which… if you’ve completed your table, it’s now time to jump to the next step.

STEP #6 The Results: Check over that table now… what do you find?  Where did your airplane perform the best?  Fly the highest? Zoom for the longest length of time?  It’s a lot easier to see when you write it down… but it’s even easier when you chart your data on a graph.  So go fire up your computer or grab another sheet of paper and mark out a grid.

You’ll want to choose a graph that shows whatever shows off your results the best.  You might have to play around with options here (which is why the computer is great here).  For more qualitative results, you can add in a “Performance Scale” and rate your plane’s performance from 0 to 10, and plot your dihedral angle on the horizontal scale and the performance rating on the vertical scale.  Don’t forget to add in units to your scales – if you’re plotting time aloft, make sure to add in the word ‘seconds’ somewhere, so people know what unit of measurement you’re referring to.  For example, if you’re charting “Distance Traveled” on one scale, is it meters or feet, or even miles you’re using to measure your plane’s performance?

And don’t worry if your numbers are not as you expected.  One of the biggest mistakes you can make is to fudge your data to match your hypothesis.  DON’T EVER do this!! You miss out on learning something new, and fudging is not doing real science.

STEP #7 The Conclusion: This is where you look at your results and answer your original question.  Personally, I like a concise, one-sentence conclusion that says it all.  After reading hundreds (if not thousands) of engineering reports, the accurately-stated one-liners are the winners.  If I want more detail, I’ll read the whole report.

STEP #8 Recommendations: This is a nice way to end the report.  Recommendations basically answer this one question:  “If you had more time, what would you test next?”  Maybe you’d test the number of paperclips, now that you know their ideal location.  Or maybe you’d play with the CP now that you know the best CG spot.  Whatever it is, jot it down on your paper.

STEP #9: Presenting Your Report/Building a Display Board: You’re now ready to build your display board, write your report, and learn how to present your findings. We’ve talk more about this in another article, as this one is getting rather long! See you soon!!