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A Classroom Study of the Lift

This experiment is designed to teach your students about the properties of lift. For a printable version with data tables click here.

 

Introduction

An airplane has four primary forces acting on it: lift, drag, weight, and thrust. In this experiment, the lift is being examined. The lift of the airplane is the aerodynamic force that elevates it into the air and holds it there. For an explanation on how wings create lift, see Forces on an Aircraft.

 

Purpose

The purpose of this experiment is to discover the properties of lift.

 

Materials

  • bicycle pedals 1/2" thread
  • 1/2" brass (water piping) tee
  • 3/8" diameter wooden dowel
  • 3"x36"x1/16" balsa wood
  • clamp
  • fan
  • manila folder
  • paper tubes
  • glue
  • razor blade
  • binder clip
  • paper clips
  • Ping-Pong ball
  • string
  • protractor

 

Alternatives:

  • other type of bearing for bicycle pedal
  • text books or other weight for clamp
  • quart-sized milk cartons for paper tubes
  • modeling clay for binder clip and paper clips
  • pitot tube for Ping-Pong ball, string and protractor

 

Procedure

I. Set up the Wings (estimated time: 15 min.)

  1. Cut the 3/8" diameter dowel to 26" inches
  2. Cut out different sized wings of similar shape from 1/16" balsa wood using a razor blade (we chose four sizes of 30, 60, 90 triangles)
  3. Cut a manila folder into a rectangle 8" x the length of your wing. Cut as many rectangles as you have sets of wings
  4. Roll each piece of folder into a cylinder that fits snugly around the dowel
  5. Glue each group of similar sized wings spaced evenly onto their respective cylinders
  6. click here for pictures

II. The Flow Straightener (estimated time: 30 min.)

  1. Roll pieces of 8"x11" paper into cylinder with a 1" or 2" diameter and 11" high
  2. Glue all the cylinders together to cover the front of your fan
  3. Another way to make a flow straightener is to glue together cut-open milk cartons

III. Setup (estimated time: 10 min.)

  1. Slide the dowel through the brass T, so the T is roughly in the middle of the dowel
  2. Use tape or rubberbands to secure the dowel in place
  3. Screw the brass T with the dowel onto the bike pedal
  4. Clamp bike pedal onto a table so the dowel swings freely
  5. Place the fan in front of the dowel making sure that you don't obstruct the swing of the dowel
  6. Clip a binder clip onto the front end of the dowel
  7. Mark an angle for your dowel to fly at. A good angle would be anywhere less than 15 degrees from horizontal
  8. click here for more pictures

IV. Run the Experiment (estimated time: 20 min.)

  1. Use a method to measure the speed of the wind at each fan speed (click here to find out how we did it with a Ping-Pong ball)
  2. Place the largest tail onto the end of the dowel
  3. Hang enough paper clips onto the binder clip so that the dowel is balanced
  4. Take off all the paper clips
  5. Turn fan on highest setting
  6. Start hanging paper clips off of the binder clip until the dowel flies at your specified angle
  7. Record how many paper clips you used
  8. Lower fan speed and repeat step 6 until you are out of fan speeds
  9. Change the size of the tail pieces and repeat steps 3 through 7 until you have used all of your wings
  10. click here for video clips

V. Analyzing the Data (estimated time: 20 min.)

  1. Calculate the force of lift by setting the sum of every torque to zero (use our formula)
  2. Plot the lift for each wind speed against the wing sizes
  3. Plot the lift for each wing size against the wind speed

 

Data and calculations

chart of weight

Using this data, the lift force can be calculated using the equation lift equation. To see how this is derived and to see our calculations, click here.

chart of wind speed and lift

chart of wing size and lift

 

 

 

graph of wind speed vs liftgraph of wind speed squared vs liftgraph of wing size vs lift

 

Analysis

  1. What do you notice about the relationship between the lift force and the wing size?
  2. What do you notice about the relationship between the lift force and the wind speed?
  3. Which wind speed and which wing size produced the most accurate results? The least accurate? Why do you think this is?
  4. What could have affected your results
  5. How could you improve the experiment (setup, materials, data collection)?

 

  1. The relationship between the lift force and the wing size is directly proportional
  2. The lift force is proportional to the wind speed squared
  3. Wing size #3 and the medium wind speed produced the most accurate results. The largest wing size and the fastest wind speed produced the least accurate results. There are many factors affecting the accuracy of the measurements that have the least effect at the medium fan speed and wing size #3. The first is the stickiness in the bearing. The more lift the wing produces the less the effect of the bearing's resistance and the granularity of the increment of measure (paper clips) can affect the results. This implies that the most accurate measurements should take place at the highest wind speed and largest wing size, and the least accurate should be slowest wind speed and smallest wing size. However, another factor, disparities in the wind flow and wind speed, increases at larger sizes and speeds. A larger wing covers more area, and since more variation in the airflow can occur in a larger area, the largest wing might not yield the most accurate results. At the highest wind speed, the wings all experienced increased movement, which hindered taking the data. All of these factors led to the medium wind speed and wing size's greater accuracy.
  4. The stickiness in the bearing affected the results because it provided a force that resisted the direction of motion. If this force was greater than the torque on the dowel, the dowel would stop. This translates into less accurate balancing for the different wing sizes. Variations in the air speed and turbulence in the air, even after the flow straightener, could have affected the lift. This error might have increased the force for some wings and decreased it for others
  5. The experiment could be improved by 1) finding a smoother bearing, to decrease turning resistance 2) measuring the wings' performance at at least 15 different windspeeds (5 different distances from the fan), to get clearer results, 3) trying the experiment at different angles of attack below 10 degrees to further test the results' relationships.

 

Conclusion

The data shows that the lift force and the square of the wind speed are directly proportional. The lift force and the size of the wing are also directly proportional. The data is not completely linear due to sources of error, which include: inconsistent wind speed, sticky ball bearings and slight swirl from the fan blades.

 

 
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