Student Data Sheet: Balancing for Best Flight Time

Student Data Sheet:
Balancing the AMA ALPHA for Best Flight Time

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Background: Two things affect how long your plane will stay in the air; gravity pulls it down all the time and the energy released from the rubber motor makes it go up. To go up, the motor and propeller must make the airplane go forward through the air so the wing can produce lift. The amount of lift produced by the wings depends on the angle at which the wing strikes the air. That angle is determined by the location of the center of gravity along the wing chord. Setting the wing position to get the right center of gravity location is an important part of trimming your airplane for best flight time. We find that location by trial.

Directions: You will study how the wing location will affect how high a plane will fly and its time aloft. Work with your partner or group and choose one plane to study. Adjust your wing position to establish a reasonable center of gravity (CG) for good flights. One way to do that is to see what has worked for others. Another way is to glide the plane, moving the wing until you get a slow, steady descent. Mark the wing leading edge position on the stick with a pen. Mark four more positions, 1/8″ and 1/4″ ahead of and behind that first position. Use a 12″ loop of 3/32″ rubber for your motor. Lubricate and stretch wind it, per good practice. Make five flights with 1,000 turns wound into the motor for each wing position. 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. 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, counting the turns remaining on the motor.

1. Start by trimming the plane to make smooth circling flights, with the wing in the middle position and with the largest circle you can safely fly. Use the rudder to set the circle size. If the plane zooms up and tumbles, try banking the plane a bit at launch, with the inside wing lower than the outside wing. Practice until you can get consistent flights.

2. List three things to keep the same every time you fly the plane for these tests.
a.
b.
c.

3. Set the wing with its leading edge at the most forward of the five marked points on the stick. Use a winder to put 1,000 turns into your motor and fly the plane. Make five flights and record the time of flight, estimated maximum height reached by the Alpha and note the number of turns remaining on the motor. Note anything significant about how the plane flies.

4. Set the wing with its leading edge at the second most forward of the five marked points on the stick. Use a winder to put 1,000 turns into your motor and fly the plane. Make five flights and record the time of flight, estimated maximum height reached by the Alpha and note the number of turns remaining on the motor. Note anything significant about how the plane flies.

5. Set the wing with its leading edge at the third most forward of the five marked points on the stick. Use a winder to put 1,000 turns into your motor and fly the plane. Make five flights and record the time of flight, estimated maximum height reached by the Alpha and note the number of turns remaining on the motor. Note anything significant about how the plane flies.

6. Set the wing with its leading edge at the fourth most forward of the five marked points on the stick. Use a winder to put 1,000 turns into your motor and fly the plane. Make five flights and record the time of flight, estimated maximum height reached by the Alpha and note the number of turns remaining on the motor. Note anything significant about how the plane flies.

7. Set the wing with its leading edge at the fifth most forward of the five marked points on the stick. Use a winder to put 1,000 turns into your motor and fly the plane. Make five flights and record the time of flight, estimated maximum height reached by the Alpha and note the number of turns remaining on the motor. Note anything significant about how the plane flies.

8. Average the times recorded for each of the five wing positions. Average the estimated heights recorded for each of the five wing positions. Average the number of remaining turns recorded for each of the five wing positions.

9. Did one wing position produce the highest average flight time?

10. If the wing position with the highest average time was the first or last in the series, move the wing an additional 1/8″ beyond that point and make another five flights. Continue until the position with the highest average time has at least one position on each side of it with a lower average time.

11. How did changing the wing position affect the average time?

12. How did changing the wing position affect the height?

13. How did changing the wing position affect the turns remaining? What is the significance of those remaining turns?

14. Which wing position would you use in a contest for best time? Do you think it would be worthwhile to test other wing positions?

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