When you wind the rubber motor of a model plane, you are storing potential energy, energy at rest. This energy is transformed into kinetic energy, energy of motion, when you launch the plane and the motor turns the propeller. With more turns on the motor, the motor will produce more torque, the twisting force that turns the propeller. In general, planes with more turns on the rubber motor will generate more thrust and will accelerate faster. They may fly higher and longer than models with fewer turns on the motor. (See the lesson on The Energy of Flight.)
You will study how increasing the turns in a rubber motor will affect how high a plane will fly, its time aloft and other aspects of its flight performance. Use a 12″ loop of 3/32″ rubber for your motor. Adjust your wing position to establish the correct center of gravity (CG) for good flights. (See the lesson on Balancing the AMA Alpha for Best Flight Time.) Make flights with four different numbers of turns wound into the motor. Record the flight times with a stopwatch. Estimate the maximum height of the airplane. You can estimate the number of feet altitude or you can estimate height as a percent of height to the ceiling if you are flying indoors. (If your plane hits the ceiling indoors, go outside.) Show which method you used; record feet like this: 18′ and record % like this: 45%. Also catch the plane right as it lands and unwind the motor if it has turns remaining, counting the turns remaining on the motor. Make four flights with each number of turns and find the average time, height and turns remaining; add all three and divide the sum by three. Also note comparative motor torque, steepness of climb, amount of bank and size of flight circle. The number of turns put into the motor affects flight performance in several ways.
It is a good idea to relube your motor after each set of four flights.
1. Finish this hypothesis: If turns increase, then… (What do you expect will happen?)
a.
b.
c.
d.
e.
f.
g.
2. List three things to keep the same every time you fly the plane for these tests.
a.
b.
c.
3. Use a winder to put 600 turns into your motor. Record the time of flight, estimate the maximum height reached by the Alpha and note the number of turns remaining on the motor. Note the comparative motor torque, steepness of the climb, bank angle of the wings and size of the flight circle. Record your observations here.
Flight times: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Height: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Turns remaining: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
How great was the torque?
How steeply did the plane climb?
How much did it bank?
How large was the flight circle?
4. Use a winder to put 800 turns into your motor. Record the time of flight, estimate the maximum height reached by the Alpha and note the number of turns remaining on the motor. Note the comparative motor torque, steepness of the climb, bank angle of the wings and size of the flight circle. Record your observations here.
Flight times: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Height: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Turns remaining: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
How great was the torque?
How steeply did the plane climb?
How much did it bank?
How large was the flight circle?
5. Use a winder to put 1,000 turns into your motor. Record the time of flight, estimate the maximum height reached by the Alpha and note the number of turns remaining on the motor. Note the comparative motor torque, steepness of the climb, bank angle of the wings and size of the flight circle. Record your observations here.
Flight times: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Height: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Turns remaining: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
How great was the torque?
How steeply did the plane climb?
How much did it bank?
How large was the flight circle?
6. Use a winder to put 1,200 turns into your motor. Record the time of flight, estimate the maximum height reached by the Alpha and note the number of turns remaining on the motor. Note the comparative motor torque, steepness of the climb, bank angle of the wings and size of the flight circle. Record your observations here.
Flight times: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Height: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
Turns remaining: 1.________ 2.________ 3.________ 4. ________ 5. ________ Average __________
How great was the torque?
How steeply did the plane climb?
How much did it bank?
How large was the flight circle?
7. You may wish to plot your data on graphs. You can use quad ruled paper for this. You could make it a bar chart. Label the horizontal and vertical axes clearly.
8. How did changing the number of turns on the rubber motor affect time aloft?
9. How did changing the number of turns on the rubber motor affect maximum height?
10. How did changing the number of turns on the rubber motor affect turns remaining on landing?
11. How did changing the number of turns on the rubber motor affect the motor torque?
12. How did changing the number of turns on the rubber motor affect comparative steepness of climb?
13. How did changing the number of turns on the rubber motor affect comparative amount of bank of the wings?
14. How did changing the number of turns on the rubber motor affect comparative size of flight circle?
15. Is it possible to put too many turns into the motor? Explain.
16. Look at the example Flight Trajectory graph. This shows the height of a rubber powered airplane at different times during its flight. This plane’s motor was wound just short of the breaking point and ran out of turns just when it landed. The motor was fully wound and the flight used all of the turns on the motor. Your motor was not fully wound and probably did not land just as the last turn came out of the motor. What does this graph suggest about the flight of your airplane with an incompletely wound motor? (Hint: Each airplane reached a highest altitude. Include that point. Think of each horizontal line on the graph as a floor. Did your airplane run out of turns in the air, above the floor, or did it land on the floor with turns remaining?)