• 1 propeller assembly
• Rubber band
• Balsa motor stick (.125” x 3.75” x ~7”)
• Masking Tape (3”)
Tools Needed if cutting out your own template:
• Good scissors
• X-acto style knife (use only under close supervision!)
• Cutting board
• Straight edge/metal ruler
• Tape or glue stick
The construction of a rubber-powered rotorcraft is simpler than that of a rubber-powered airplane, but the youngest students might still benefit from an adult’s help. The template that is included here will need to be cut out precisely in order to create the box, which may require adult assistance. The AMA Jr. Camp Flight Kits include pre-cut templates, making this project much simpler. Adults may need to assist with winding and launching.
• Fine motor skills: The building process involves manipulating materials and intricately connecting flexible and solid materials.
• Problem solving: The presence of torque adds a complicating factor to what students might expect to see during testing and produces a critical thinking challenge.
• Hypothesis: Discuss how you think this aircraft will fly. What forces will be acting on the fuselage? The propeller? Why do you think the Ingenuity helicopter on Mars has two rotors at the top?
(If building from the AMA Jr. Camp Kit, skip to number 5.)
1 Print off the template sheet onto an 11x17 piece of paper.
2 Using a good pair of scissors, cut out the templates solid outer edges.
3 Inside the outer circles, cut straight lines across the dotted lines, in an “X” pattern.
4 Cut out the inner dashed line triangles.
5 Fold along the orange lines
6 Take the balsa shaft and gently insert into slot one. Continue the process gently inserting the balsa stick from 1-3.
7 While gently holding the paper slots 1-3 together, slide the balsa stick to the next set of slots, 4-6, repeating the process of inserting the balsa stick leaving approximately 1” of stick protruding past the top slots (1-3).
8 Glue or tape the tab to the square to complete the body of the fuselage.
9 Bend your paperclip so it resembles the image shown.
10 Using your masking tape, affix the paperclip to the bottom of the balsa shaft. Ensure that the paperclip points towards the section of the above box with the AMA Jr. Camp icon.
11 Place the propeller assembly onto the top of your balsa stick, ensuring the rubber band attachment points towards the AMA Jr. Camp logo.
12 Slip the rubber band onto the hook of the propeller and the paperclip. (As the rubber band is wound, it will store more energy that will be the power source for our model rotorcraft. When it is released, that energy will be used to spin the propeller and generate lift.) Do not over-wind it, especially for the first flight.
13 Hold the rotorcraft vertically and release! What happened?
Aircraft that are powered by rotors, such as helicopters, are much more complex than fixed-wing aircraft, such as airplanes. Even so, the physical principles at work are much the same. A rotorcraft still must generate lift to overcome the force of gravity or weight. While an airplane needs to move forward at a fast enough speed for its wings to create that lift from the air flowing over them, a rotorcraft simply spins its rotor blades to create that same force.
While the blades create lift, their rotation generates another force called torque. Because every action causes an equal and opposite reaction, when a propeller spins one direction, the stick will naturally spin the other. We counteracted this force by adding the paper cube that wraps around the balsa stick. What other ways could we have counteracted this counter-rotational force? Why do you think the Ingenuity aircraft uses two propellers?
• Launching rubber-powered models usually works best when the propeller/rotor is released a second or two before the entire model is launched, and a gentle push in the direction you wish the model to go can be a big help.
• Make sure the rubber band and rotor blades are far away from anything they could get tangled in, such as long hair or electrical cables.
• After you have successfully flown your model multiple times, try adding more winds to the rubber. Be careful not to snap it but try to predict the effect that more or fewer winds will have on its performance. Will you need a bigger or smaller stabilizer? Why?
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