Electric Free-Flight: The Thistle Flier

State Standards

  • 1. Newton’s laws predict the motion of most objects. As a basis for understanding this concept:
    • 1.d. Students know that when one object exerts a force on a second object, the second object always exerts a force of equal magnitude and in the opposite direction (Newton’s third law).
    • 1.e. Students know the relationship between the universal law of gravitation and the effect of gravity on an object at the surface of Earth.
  • 5. Electric and magnetic phenomena are related and have many practical applications. As a basis for understanding this concept:
    • 5.a. Students know how to predict the voltage or current in simple direct current (DC) electric circuits constructed from batteries, wires, resistors, and capacitors.
    • 5.b. Students know how to solve problems involving Ohm’s law.
    • 5.c. Students know any resistive element in a DC circuit dissipates energy, which heats the resistor. Students can calculate the power (rate of energy dissipation) in any resistive circuit element by using the formula Power = IR (potential difference) × I (current) = I2R.
    • 5.h. Students know changing magnetic fields produce electric fields, thereby inducing currents in nearby conductors.

Project Summary

As part of a joint project between Mrs. Green's Honors Geometry class and Miss Tangen's Physics class, we constructed a small airplane, initially to be used as a glider, and subsequently motorized. Students from physics were paired or grouped with other physics students and freshmen and sophomores from the geometry class. We were then left to the task of constructing the airplane to the best of our abilities using any resources we had at our disposal.

For my part, I worked with B, a freshman I knew in the geometry class. Working together, we used plans from Griffin Aeroworks, a group that built and played with both electric free-flight aircraft and rubber-band powered aircraft. The "Thistle" design that we used appears to be very similar to the shape of a World War II-era P-38 Lighting aircraft. It is unique in its design for a twin-boom style fuselage that links the rear stabilizer to the front end of the body.

In one afternoon, we used a selection of thin sheets (1/32" and 1/16" thick) of balsa wood to construct the bare aircraft. At this stage, it was only a glider and could be submitted to B's geometry class for their initial grade. They tested it as an unpowered aircraft, a free-flight glider. With the addition of a quarter on the nose to provide stabilizing weight, it performed admirably.

Following state testing, we [the physics students] received control of the aircraft and began the process of motorizing them. I noticed that many groups had trouble motorizing their planes effectively, with problems ranging from sheer bad design to a deficit in the power needed to propel the large aircraft they had constructed. As the design I had used was originally intended to be a motorized craft, it was a relatively simple job. I laminated the pylon for the motor and attached it with hot glue, then attached the motor. Using stripped, un-insulated wires, I connected battery to a switch embedded in the "cockpit" portion to the motor. In flight tests, the motor lacked the power to seriously propel the craft, but it increased flights slightly, improving dive recovery.

How I Learned

I learned through trial, error, more trials, and a lot more errors. When trying to motorize the plane, the best way for me to work was test, test, and test again. All the while, I was making repairs every few tests. (Praise whoever invented hot glue...) An enormous amount of experimentation, finger burning, and re-experimentation were required to make the silly thing work. I had to procure my own parts to reach the optimum power.

What I Learned

The plane was an excellent exercise in aircraft design, one major part of the field I want to go into. I also found that a twin boom design, combined with a ready supply of hot glue, was both very sturdy, and easily repairable. As an added bonus, I found out that casing parts in electrical tape after running strings of hot glue across the part vastly improved strength, tenacity, and perseverance. I also found that somewhat unorthodox launching procedures resulted in interesting flight patterns that sometimes proved much better than a conventional launch.


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