Engineer Helicopters for Mars

Background Information for Teachers

Gravity is the force that pulls objects of mass toward each other. You know from experience that if you drop an object, it falls down toward the ground—not sideways or up—because the gravity created by Earth's large mass pulls the object down. Gravity acts between any two objects that have mass, even two pencils lying on your desk. Because it is such a weak force, you only notice its effects when at least one of the masses is huge, such as the Earth with its mass of 5.97×10²⁴ kg (or 5,970,000,000,000,000,000,000,000 kg, more than ten trillion times the mass of the world's population). We also know from experience that the gravitational pull on a 5 kg brick is larger than its pull on a 10 g pencil. These examples show how the strength of the force is proportional to the mass of the objects involved. The strength of the gravitational pull also depends on the distance between the objects; the force gets quickly weaker as the objects get farther apart. As an example, the force of Earth pulling rockets down weakens as their distance from Earth increases.

The solar system is well-suited to explore gravity. Many objects in the solar system are massive: the Sun is 333.000 times the mass of Earth, and although the mass of Mars is 10 times less than the mass of Earth, it is still massive. We can study how gravity holds planets in their orbit while they are moving around the Sun. The planets' velocity is just so that their paths form an orbit (Figure 1) and not a path away from the Sun (Figure 2, left), or a spiral toward the Sun (Figure 2, right).

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 1. Illustration of how the velocity of the planet Earth and the gravitational pull of the Sun on Earth are in a delicate balance that keeps Earth in an orbit around the Sun (this illustration is not drawn to scale).

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 2. Illustration of a planet that moves too fast to be pulled into orbit (left), and of a planet that moves too slowly to stay in orbit (right). (These illustrations are not drawn to scale.)

No matter where you are in the solar system, the gravitational pull of the Sun is working on you. You do not notice the gravitational pull of the Sun on you when you are on Earth for two reasons: your mass is small and the Sun is far away. On Earth, you experience the gravity of Earth because this huge mass is close by. The gravitational pull of the Sun has a noticeable effect on Earth even though Earth is as far from the Sun as you are, because Earth is much more massive.

Objects that fly or rise into the air must overcome gravity of whatever planet they are on. The force generated by gravity on an object is called its weight, and the weight of objects changes depending on the planet they are on (See Table 1). For example, the weight of an object on Mars is 37.7% of the weight of the same object on Earth. This difference is due to the combination of the smaller mass of Mars and its smaller radius. This reduced weight makes it is easier to rise into the air from Mars compared to from Earth.

Figure 3. The weight of an object on Earth is greater than its weight on Mars.

Does that mean that it is easier to fly a helicopter on Mars? Not necessarily! Helicopters stay in the air because spinning blades generate an upward push called lift. But helicopter blades need air to create lift. They are made such that when air flows over them, a net upward push (lift) is generated. In general, the denser the air, the harder it can press on surfaces. The Martian atmosphere is 100 times less dense than Earth's atmosphere. In this thin atmosphere, the same rotating blades will generate much less lift. Unless the lift on the helicopter is greater than its weight, the helicopter will not fly (see Figure 4). So, despite the lower weight on Mars, it is still harder to make a helicopter fly on Mars.

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 4. The helicopter will rise only if the lift created by the rotating blades of a helicopter is greater than the helicopter's weight.

In this lesson, students will build model helicopters out of paper (Figure 5) and investigate how their design can be optimized to make the helicopter fly on Mars. Students will compare their design to NASA's Ingenuity helicopter (Figure 6), a helicopter that was built to help NASA's Perseverance rover explore the Martian surface. The Ingenuity is very lightweight, weighing only 4 pounds (on Earth)! Each blade is about 2 ft. (0.6 m) long, and the blades rotate about 2400 times per minute. Will students take the same approach in their designs?

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 5. Two examples of paper helicopters.

Image Credit: NASA / Public domain
Figure 6. Rendering of NASA's Ingenuity helicopter.

A paper helicopters, unlike a real helicopter, does not have a motor to make its blades spin. Due to its special shape, however, the blades still spin as it falls. When you drop a paper helicopter, it will take a fraction of a second for it to start spinning. Once the paper helicopter spins, it should generate lift, which slows its descent to the ground (Figure 7).

Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
Figure 7. Paper helicopters generate lift as their blades rotate, causing the helicopters to slowly float down.

These paper helicopters do not generate enough lift to fly upward, but the lift helps slow their descent. The more lift they generate, the slower they fall. Students will use the time the helicopter spends in the air as a measure of its performance.

There might not be one single design for a paper helicopter that allows it to descend the slowest. That said, adding some mass, such as a paperclip at the bottom of the helicopter, can stabilize the helicopter, making it perform better. Adding more mass than needed will, however, decrease its performance because of the increased weight. Similarly, longer and wider blades that hit the air at an angle are generally better. These changes to the blades generally create more lift, and as a result, slow down the fall of the paper helicopter more. If you change the dimensions of your paper helicopter too drastically, however, the helicopter may actually become unstable and perform worse. Other factors, like changing the shape or angle of the blades, can also influence lift.

Additional Background Links

• Mars Helicopter, NASA
• Your Weight on Other Worlds , Exploratorium
• Mars Facts, NASA

Prep Work (7 minutes)

• Watch the Flying Helicopters on Mars video to familiarize yourself with the challenge the students will tackle in this lesson.
• Familiarize yourself with the process of folding and dropping a paper helicopter.

Engage (35 minutes)

1. Inform the students that in this lesson, they will fly into space, figuratively. Tell students that humans are naturally curious about what happens around them, including in space, and how this natural curiosity fuels discoveries that help advance technology and science. Inform students that NASA is currently exploring the planet Mars, with the idea that maybe someday we will be able to start a colony on Mars.
2. Introduce the students to the Ingenuity (slide 1 of the slideshow, or Figure 8, left), a helicopter designed by NASA to help the Perseverance rover explore the Martian surface. The Perseverance rover was part of a NASA unmanned mission to Mars, launched in July 2020.

   When you compare this helicopter to a helicopter that flies on Earth (Figure 8, or slide 2 of the slideshow), what do you notice? How do both helicopter designs compare? How are they different or similar?

   What design features of the Ingenuity stand out to you?

   Why do you think engineers have made these design choices? How might these choices help this helicopter fly on Mars?

   Image Credit: NASA, Pixabay / Public domain
   Figure 8. Illustration of the helicopter Ingenuity on the surface of Mars (left, illustration from NASA), and a helicopter built to fly on Earth (right).

   Listen to students' ideas, but do not add or correct. You will come back to this question later in the lesson.

3. Inform the students that in this lesson, they will use the engineering design process to build paper helicopters that are likely to fly on Mars. The engineering design process starts with identifying the problem and doing background research. The task at hand is building a helicopter that can fly on Mars.
4. Instead of the classical background research, the students will examine some statements that will help them in their design. Split students into groups of 2–4. Assign each group at least one of the statements listed under question 1 on the Student Worksheet. These statements are all false. Challenge students to find out what is wrong in the statement and correct it. Ask students to think of examples as evidence, especially of examples from the solar system. If needed, tell students that gravity is the force that holds the solar system planets in their orbit around the Sun.

   The list of statements:

   1. Gravity pushes Earth away from the Sun.
   2. Gravity pulls harder on objects that are farther away.
   3. On Earth, the gravitational pull of the Sun does not act on us.
   4. Fact: Earth is 10 times more massive than Mars, and its diameter is smaller than that of Earth.
      Statement: Because of these differences, the mass of a helicopter on the surface of Mars is less than the mass of the same helicopter on the surface of Earth.
   5. Fact: Helicopter blades use air to create lift (the force that pushes upward on the helicopter blades).
      Statement: Mars has a thinner atmosphere than Earth so it will be easier to create lift on Mars compared to Earth.

   Give students some time to discuss their assigned statement(s) within their group, then address each statement with the class. For each statement, listen to what the group has to offer, and ask the class if they have something to add. Correct, or redirect their reasoning where needed. The Student Worksheet Answer Key provides the correct statement, examples, and an explanation for each of the statements.

   After working through the statements together with your students, they should understand the following concepts. These concepts will be used in the engineering part of the lesson.

   • The weight of an object on Mars is less than the weight of an object on Earth.
   • Helicopters use lift to stay in the air.
   • Helicopter blades cannot create lift as efficiently on Mars compared to on Earth because Mars has a thinner atmosphere.
5. After having gone through all of the statements, come up with a definition for gravity as a class (question 2 of the Student Worksheet).

   Now that we have seen these examples of gravity, can we formulate a definition of gravity?

   Include the following facts in the definition: Gravity is a force (a pull). Gravity pulls masses toward each other; it is always attractive. Gravity is a very small force, except when one or both of the masses is very large.

Explore (50 minutes)

1. Tell students that they are now ready to start the engineering challenge. Point out that the goal of this challenge is to find the best design for a paper helicopter that needs to fly on Mars. Which design choices do they have to make?

   Ask students to go through questions 3–5 of the Student Worksheet. It provides students with the background needed to tackle the challenge.

   You may need to inform the students that ultimately, the reduced weight is overpowered by the reduced ability to create lift, so overall, it is much harder to fly a helicopter on Mars than it is to fly one on Earth.

2. Let students make a paper helicopter (or whirlybird) following the directions on the paper helicopter template. Then demonstrate how to drop the paper helicopter.
3. Show students the different types of paper, paperclips, etc. available to them to make design changes to their paper helicopters. Encourage student groups to brainstorm ideas on how they can improve the paper helicopter so it would be ideal to fly on Mars (question 7 on the worksheet).
4.  

   As a class, discuss how you could measure improvements in the design (question 8 on the worksheet).

   A helicopter that falls slowly on Earth has a better chance of flying on Mars, so the time a helicopter is in the air is a good measure of its performance.

   Below is a list of some options to compare how long the paper helicopters are in the air:
   • Drop two helicopters simultaneously from a fixed height and see which one touches the ground first. The one that touches the ground last performs better.
   • Drop helicopters from a fixed height. Take a slow-motion video of the falling helicopter and count how many frames it takes between release and touch down. The number of frames between release and touchdown is a good measure of the time it takes to reach the ground if you always use the same camera and same video settings.
   • Use the process explained in the previous bullet point, but convert the number of frames to a time using the frame rate of the video, where number of frames divided by the number of frames per second equals the time in seconds.
5. Let groups explore and iterate (questions 9 and 10 on the worksheet).

   If you need to split the project over several lessons, this is a good time for a break. It even allows time for students to brainstorm ideas as homework. Students might come up with more creative solutions if they have some time to think it over.

   Tell students there is a limited time for their testing, so they will have to be efficient with their time. Students should brainstorm and discuss their plan for 5 minutes: 2 minutes individually and 3 minutes as a group. They will only have access to the materials after these 5 minutes have passed.

   Give students an extra 20 minutes to create, test, iterate, and retest.

   Inform students that within a group, it is fine to make and test several models in parallel, but insist that they discuss the results as a group so they can learn from the test results. It might be possible to take aspects of the different models they created and form a hybrid model that performs better!

   As students work, walk around to help groups where needed. If necessary, remind students to communicate with their group. Make students aware of the passing of time. Students should record as much of the process as they can in Table 1 of the worksheet, or in a table of their own making.

6. Review the data and prepare presentations (questions 11–13 on the worksheet).

   At the end of the exploration, give groups 10 minutes to finish recording at least 3 models/iterations in Table 1 of their worksheet. They should also use this time to, look back at their data choose their best-performing model, and distill at least two design suggestions for a Martian helicopter. This advice could be what to do or what to avoid. Ask students to prepare to show their best model and communicate their suggestions in a clear, concise, and convincing way to their classmates.

   As teacher, you can choose to give students precise instructions on how you want them to present their findings (mini video, oral presentation, poster, slide deck, etc. ), or leave it up to the students. The presentation should be short (an oral presentation or video that is a maximum of 1 minute long, a maximum of one poster, or a few slides).

Reflect (25 minutes)

1. Let groups present their best model and their two suggestions to the class.
2. Hold a competition for the best helicopter.

   After hearing all the presentations, let each student predict which two helicopters of all the helicopters presented are best suited to fly on Mars. Let the presented helicopters (one per group) compete against each other.

   Were you able to predict which models would do well? Why do you think these models perform well?

   The students' answers will depend on the students' ability to predict how well each model will perform and their understanding of what features will create more lift.

3. Reflect on the challenge.

   What was challenging in your design quest? Was there always one clear answer or were tradeoffs needed?

   Answers will vary.

   Some generally seen tradeoffs are:

   • Less mass is better, but making it too light results in an unstable helicopter, or lightweight paper might result in a helicopter that is not stiff enough to fly.
   • Longer and wider blades are generally better, but the helicopter can be unstable if you make the blades too large. Larger blades also means more weight to overcome.
4. Let students watch this Mars Helicopter video from Crazy Engineering. Alternatively, you can look at Figure 6 (slide 1 of the slideshow), too.
   

   https://www.youtube.com/watch?v=uvxSGlvxpiY

   Is the advice we found as a class reflected in the choices the engineers made?

   Remember, we looked at a rendering of the NASA helicopter at the start of the lesson (slide 1 of the slideshow) Does your exploration help you understand why engineers designed the helicopter that way?

   The students' answers will depend on their test results.

Assess

The groups' presentations are a good way to assess students' work and understanding.

You can use this quiz to assess student learning after the activity:

• Online quiz, assignable in any LMS
• Quiz (pdf) and answer key (PDF)

Make Career Connections

Discussing or reading about these careers can help students make important connections between the in-class lesson and STEM job opportunities in the real world.

Aerospace Engineer

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Career Profile

Aerospace engineers design, build, and test vehicles like airplanes, helicopters, balloons, rockets, missiles, satellites, and spacecraft. Those who work with aircraft are called aeronautical engineers, and those who work specifically with spacecraft are called astronautical engineers. Aerospace engineers frequently work as part of a team. Read more

Aerospace Engineering & Operations Technician

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Career Profile

Aerospace engineering and operations technicians are essential to the development of new aircraft and space vehicles. They build, test, and maintain parts for air and spacecraft, and assemble, test, and maintain the vehicles as well. They are key members of a flight readiness team, preparing space vehicles for launch in clean rooms, and on the launch pad. They also help troubleshoot launch or flight failures by testing suspect parts. Read more

Lesson Plan Variations

• Add copper strips, coin batteries, and LED lights to the supplies and ask students to add at least one LED light to their helicopter rotor. Students will quickly understand that the mass distribution on the paper helicopter is important for success. Placing the battery on the rotor will lead to failure. The lower the battery is placed, the better the helicopter will fly. Use long-exposure photos (Figure 9, left) or a short snapshot (Figure 9, right) to catch the helicopter's descent. The resulting pictures or videos are fun and provide a visualization of how fast the helicopter rotates during the descent. The Make a Paper Circuit activity lists the materials needed, and provides instructions on how to make a circuit.

Image Credit Image Credit: Science Buddies
Figure 9. Long-exposure picture (left) and short snapshot (right) of a paper helicopter, with a light on one wing, as the blades rotate and the helicopter floats down.