Lesson test: How a quadcopter stays up

1.[2p]
A quadcopter has a mass of 500 g. Taking $g = 9.81$ m s⁻², how many newtons of thrust must each of its four propellers make to hover?

CorrectNot quite: 1.23

2.[1p]
A quadcopter whose motors can produce exactly its own weight in thrust at full throttle can hover but has no authority left to climb or correct.

True

Correct

False

The answer is: True

3.[2p]
Two propellers on a quadcopter spin clockwise and two counter-clockwise mainly so that

their reaction torques cancel and the craft holds its heading instead of spinning

Correct

they share the electrical load evenly between the two sides

The answer is: their reaction torques cancel and the craft holds its heading instead of spinning

the air from one does not collide with the air from another

The answer is: their reaction torques cancel and the craft holds its heading instead of spinning

the craft can be built from four identical propellers

The answer is: their reaction torques cancel and the craft holds its heading instead of spinning

4.[2p]
Static thrust scales roughly as $n^{2} D^{4}$ . If a propeller's diameter is increased from 5 inches to 6 inches at the same rotation rate, by what factor does its thrust increase? Give the number to two decimal places.

CorrectNot quite: 2.07

5.[2p]
A design's thrust to weight ratio matters more than its raw thrust because

the ratio sets how much reserve there is above hover for climbing and correcting

Correct

thrust cannot be measured directly but the ratio can

The answer is: the ratio sets how much reserve there is above hover for climbing and correcting

a higher ratio always means a longer flight time

The answer is: the ratio sets how much reserve there is above hover for climbing and correcting

the ratio determines the battery voltage

The answer is: the ratio sets how much reserve there is above hover for climbing and correcting

6.[2p]
A quadcopter has a mass of 800 g and four motors each rated at 1000 gf of thrust. What is its thrust to weight ratio? Give it to one decimal place.

CorrectNot quite: 5.0

7.[3p]
Which of these follow from static thrust scaling as $n^{2} D^{4}$ ?

Select all that apply

Doubling the rotation rate roughly quadruples the thrust

Correct

A larger propeller at the same speed makes much more thrust than a smaller one

Correct

Thrust is proportional to the rotation rate

The answer is: Doubling the rotation rate roughly quadruples the thrust, A larger propeller at the same speed makes much more thrust than a smaller one, Halving the diameter cuts the thrust to one sixteenth at the same speed

Halving the diameter cuts the thrust to one sixteenth at the same speed

Correct

1.[2p] A quadcopter has a mass of 500 g. Taking g=9.81 m s⁻², how many newtons of thrust must each of its four propellers make to hover?

2.[1p] A quadcopter whose motors can produce exactly its own weight in thrust at full throttle can hover but has no authority left to climb or correct.

3.[2p] Two propellers on a quadcopter spin clockwise and two counter-clockwise mainly so that

4.[2p] Static thrust scales roughly as n2D4. If a propeller's diameter is increased from 5 inches to 6 inches at the same rotation rate, by what factor does its thrust increase? Give the number to two decimal places.

5.[2p] A design's thrust to weight ratio matters more than its raw thrust because

6.[2p] A quadcopter has a mass of 800 g and four motors each rated at 1000 gf of thrust. What is its thrust to weight ratio? Give it to one decimal place.

7.[3p] Which of these follow from static thrust scaling as n2D4?

1.[2p]
A quadcopter has a mass of 500 g. Taking $g = 9.81$ m s⁻², how many newtons of thrust must each of its four propellers make to hover?

2.[1p]
A quadcopter whose motors can produce exactly its own weight in thrust at full throttle can hover but has no authority left to climb or correct.

3.[2p]
Two propellers on a quadcopter spin clockwise and two counter-clockwise mainly so that

4.[2p]
Static thrust scales roughly as $n^{2} D^{4}$ . If a propeller's diameter is increased from 5 inches to 6 inches at the same rotation rate, by what factor does its thrust increase? Give the number to two decimal places.

5.[2p]
A design's thrust to weight ratio matters more than its raw thrust because

6.[2p]
A quadcopter has a mass of 800 g and four motors each rated at 1000 gf of thrust. What is its thrust to weight ratio? Give it to one decimal place.

7.[3p]
Which of these follow from static thrust scaling as $n^{2} D^{4}$ ?