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Helicopter Liftoff: How Does the Speed of the Rotor Affect the Amount of Lift?

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Abstract

Helicopters are fascinating to watch. The spinning rotor blades on top of the helicopter generate lift, allowing it to take off vertically. They can land vertically, too, allowing them to set down in small spaces, such as hospital helipads or on a ship at sea. In this aerodynamics science fair project, you will fly a remote-controlled helicopter and measure how the rate of the rotor's rotation changes as the helicopter hovers and flies up or down.

Summary

Areas of Science
Aerodynamics & Hydrodynamics
Difficulty
 
Time Required
Average (6-10 days)
Prerequisites
None
Material Availability
You will need a remote-controlled helicopter and a digital tachometer. See the Materials and Equipment list for details.
Cost
High ($100 - $150)
Safety
Minor injury is possible. Be sure to wear safety goggles. Adult supervision is recommended.
Credits

David B. Whyte, PhD, Science Buddies

Objective

The objective is to accurately measure the rate of blade rotation on a remote-controlled helicopter and determine how this rate affects the vertical motion of the helicopter.

Introduction

Remote-controlled helicopters come in a variety of shapes and designs. The least-expensive ones are available for less than $20 and can be flown right out of the box. More-expensive versions fly for longer periods of time and have more sophisticated controls, which require time to master. They are all, however, miniature technical wonders.

The blades on top of a helicopter form the main rotor. The blades are like narrow "wings" and are shaped like airfoils. An airfoil has a specific shape that allows the helicopter to cut through the air in a way that efficiently produces lift. The part of the blade that passes through the air first is called the leading edge. By "tipping" the leading edge of the blade up as it moves, the blade will have a positive angle of attack. As the angle of attack increases, more air is forced down by the blades. This forces the blades up, and the rotor provides the lift needed to make the helicopter fly.

In this aerodynamics science fair project, you will measure the speed of a helicopter's rotor using a digital tachometer. The output is measured in revolutions per minute (rpm), so note that you might need to factor in the number of blades in order to get rpms. For example, if the rotor has two blades and the tachometer is counting both blades as the rotor spins, you will need to divide the tachometer reading by two to get the rpms. The goal is to measure how the rotation rate of the rotor is related to the vertical motion—ascending, descending or hovering—of the helicopter. Since the procedure involves some creative problem solving on your part, this should be regarded as a "do-it-yourself" kind of science fair project.

Note: Real helicopters lift off by changing the blades' angle of attack at a constant rpm. Some simple toy helicopters only adjust rpm, and not angle of attack. In this project, you will just be testing a simple toy helicopter.

Terms and Concepts

Questions

Bibliography

Materials and Equipment

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Experimental Procedure

Important Notes Before You Begin: In order to get good data, you will need to be able to fly the helicopter in a controlled way. In particular, you will need to be able to make it move up and down at different rates. You will also need to work out the best way to obtain readings from the tachometer and the rate of ascent and descent as the helicopter is flying. Carrying out the experiments will involve some creative problem solving.

Preparing for Testing

  1. Assemble your remote-controlled helicopter.
  2. Practice flying the helicopter so that you can make it hover, move vertically up, and move vertically down.
  3. Place the helicopter on the ground in a flat spot.
  4. Place the tape measure near the helicopter.
  5. Pull the tape out to 2 meters (m).
  6. Lock the tape measure open so that it makes a 2-m vertical measuring standard.
    1. You may need to stabilize the tape measure; for example, by placing it near a wall and attaching it to the wall with adhesive tape.
  7. Bring the helicopter to a hovering position at about 0.5 m above the ground.
  8. With the helicopter hovering about 0.5 m off of the ground, have a helper record the rate of rotation, using the digital tachometer, in your lab notebook.
    1. Some tachometers are sensitive to the 60 cycles per second "flicker" in artificial lights. If the tachometer is affected by artificial light, take your readings outdoors, or indoors in an area with sunlight.
  9. As an option, weigh the helicopter.
    1. Record the weight of the helicopter in your lab notebook.
    2. The lift provided when the helicopter is hovering equals the weight of the helicopter.

Measuring Rate of Ascent and Rotor Rotation

  1. Start with the helicopter on the ground near the tape measure.
  2. Bring the helicopter to a hovering position at about 1 m above the ground.
  3. Have a helper read the revolutions per minute using the tachometer from below the helicopter.
  4. Increase the rotor speed so that the helicopter flies vertically upward.
    1. The rate of vertical ascent should be slow and steady.
  5. The helper with the tachometer should record the rpm's as the helicopter flies upward.
    1. It will probably be easier to take the readings from below.
  6. Have another helper use a stopwatch to measure how long it takes for the helicopter to fly from 1 m to 2 m.
    1. You might want to increase the length of the tape measure to 3 m or higher in order to get more-accurate readings.
    2. Record the rate of ascent in meters per second (m/s) and the corresponding rate of rotor rotation.
    3. The rate of ascent is the distance the helicopter moved in meters, divided by the time in seconds it took to move that distance.
    4. The third helper can record the data.
    5. As an option, video record the flight of the helicopter to help collect the data.
  7. Repeat steps 1–6 two more times, recording the rate of ascent and the rotor rpms each time. Repeating the tests will ensure your results are accurate and repeatable. Try to keep the rate of ascent consistent.
  8. Repeat steps 1–7 using a different rate of ascent.

Measuring Rate of Descent and Rotor Rotation

  1. Start with the helicopter hovering at a height of 2 m.
  2. Have a helper measure the rpm's of the rotor from below.
  3. Have another helper use a stopwatch to measure how long it takes for the helicopter to descend.
  4. Start the helicopter's descent.
    1. Descend from 2 m to 1 m.
    2. The descent should be slow and steady so that the helper can obtain a reading on the tachometer.
  5. Calculate the rate of descent in meters per second.
  6. Record the rate of descent and the corresponding rotor rpm's in your lab notebook.
  7. Repeat steps 1–6 to obtain data for two more rates of descent. Try to keep the rate of descent consistent.
  8. Repeat steps 1–7 using a different rate of descent.

Analyzing Your Results

  1. For each rate of ascent or descent, average the rpm's you measured.
  2. Graph the rate of ascent and descent on the on the x-axis and the average rate of rotation of the rotor in rpms on the y-axis.
    1. On the x-axis, use 0 (zero) for the hovering helicopter, negative numbers for the descending helicopter, and positive numbers for the ascending helicopter. For example, a helicopter that descended at 1 m in 5 s will have a value of -0.2 m/s.
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Variations

  • Try adding small weights to the helicopter and measuring how this increased load changes the rpm's of a hovering helicopter. Graph the load, in grams, on the x-axis and the rpm's on the y-axis.

Careers

If you like this project, you might enjoy exploring these related careers:

Pilot
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Pilots fly airplanes, helicopters, and other aircraft to accomplish a variety of tasks. While the primary job of most pilots is to fly people and cargo from place to place, 20 percent of all pilots have more specialized jobs, like dropping fire retardant, seeds, or pesticides from the air, or helping law enforcement rescue and transport accident victims, and capture criminals. Pilots enjoy working and helping people in the "third dimension." Read more
Aerospace Engineer
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Humans have always longed to fly and to make other things fly, both through the air and into outer space—aerospace engineers are the people that make those dreams come true. They design, build, and test vehicles like airplanes, helicopters, balloons, rockets, missiles, satellites, and spacecraft. Read more
Aviation Inspector
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Aviation inspectors are critical to ensuring that aircraft are safe to fly. They conduct pre-flight inspections to make sure an aircraft is safe. They also inspect the work of aircraft mechanics, and keep detailed records of work done to maintain or repair an aircraft. As problems are identified, they may make changes to maintenance schedules, and may be called upon to investigate air accidents. Read more
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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

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MLA Style

Science Buddies Staff. "Helicopter Liftoff: How Does the Speed of the Rotor Affect the Amount of Lift?" Science Buddies, 23 June 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Aero_p043/aerodynamics-hydrodynamics/helicopter-how-does-rotor-speed-affect-lift. Accessed 31 Mar. 2023.

APA Style

Science Buddies Staff. (2020, June 23). Helicopter Liftoff: How Does the Speed of the Rotor Affect the Amount of Lift? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Aero_p043/aerodynamics-hydrodynamics/helicopter-how-does-rotor-speed-affect-lift


Last edit date: 2020-06-23

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