How to calculate the drag force?

In summary: If we assume that speed is reached very quickly, how can you find the terminal velocity from your data?
  • #1
EelAnes
10
0
Problem
How to calculate the drag force of the model helicopter using the given data above?

Research Question
How does increasing the length of the wing planform of a model paper helicopter affect the time it takes the helicopter to fall to the ground and hence the air resistance?
Variables
Independent Variable:
Length of the wing planform, Centimeter (cm)/±0.05cm, A range of 5 different length were used—2.0cm, 4.0cm, 6.0cm, 8.0cm, 10.0cm
Dependent Variable:
Time, Second (s)/±0.01s, the Same observer using a stopwatch, dropped from 170cm throughout the experiment
Control Variable:
1. Release Height = 170cm
2. Length and width of the tail (model paper helicopter) = 10cm by 3cm
3. The width of the wing planform (model paper helicopter) = 4.5cm
4. Length and width of the body (model paper helicopter) = 2cm by 9cm
5. Mass of the paper clip = 0.32g
6. The position of the helicopter when dropped
7. The position of the observer
Methodology
How to make a model paper helicopter
1. Draw the outline of the wings, body, and leg as the following picture shows:
upload_2018-11-28_22-18-59.png

2. Cut the paper around the outer solid lines, which is 9.00cm by 24.00cm
3. Cut along the inner solid lines
4. Fold along the dotted lines (The material around the tail should fold one around the back and one around the front). The wings should be folded in opposite directions.
5. Add the paper clip to the bottom of the tail (the paper clip should hold the folded paper together)
Experiment
1. Use the tape measure to measure 170.00cm
2. Use sticky notes to mark the drop line
3. Measure the mass of the mass of the 10.00cm wing planform model paper helicopter
4. Drop the 10.00cm wing planform model paper helicopter (tail must align with the drop line) while simultaneously pressing the stopwatch
5. As soon as the helicopter hits the ground, stop the stopwatch
6. Record the time
7. Repeat steps 4 to 6 for four more times
8. Reduce the wing length to 8.00cm, 6.00cm, 4.00cm, and 2.00cm, each time measuring the mass first and then repeating steps 4 to 6 five more times
Raw Data Table
Constant Vale:
  • Acceleration due to Gravity = 9.81 m/s^2
  • The density of the air = 1.225 kg/m^3
  • The width of the wing planform = 4.5cm
upload_2018-11-28_22-19-38.png
 

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  • #2
Note that the experiment is done indoor
 
  • #3
every calculation should be done other SI units
D=Cd*1/2(p*V^2)*A
Solving for D (drag force)
A = Surface area = πr^2 = π√(1.2025)
r = √[(10•10^-2)^2+(4.5•10^-2)^2] = √(1.2025)​
p = Density of air = 1.225 kg/m^3
Cd = Coefficient of drag = ?
V = ? = ?
 
  • #4
EelAnes said:
How to calculate the drag force...
Do they want a graph of drag versus time (drag depends on which point in the autogiro's descent you are talking about) or just terminal velocity drag?
 
  • #5
David Lewis said:
drag versus time
Yes they want a graph of drag vs time
 
  • #6
EelAnes said:
How to calculate the drag force of the model helicopter using the given data above?
Above? Do you mean the experimental data further down?
EelAnes said:
D=Cd*1/2(p*V^2)*A
If you are to calculate the drag force from the experimental data then this is not the equation you need.
Are you familiar with the concept of terminal velocity?
Once you have found the drag force from the data, you can use the drag equation above to find the drag coefficient.
 
  • #7
haruspex said:
Above? Do you mean the experimental data further down?

If you are to calculate the drag force from the experimental data then this is not the equation you need.
Are you familiar with the concept of terminal velocity?
Once you have found the drag force from the data, you can use the drag equation above to find the drag coefficient.
I'm not familiar with terminal velocity, so can you show me how it's done base on one of the data set above please?
 
  • #8
EelAnes said:
I'm not familiar with terminal velocity, so can you show me how it's done base on one of the data set above please?
Write the force and acceleration equation for the drop, including a drag force (that will depend on speed somehow). A high drag item such as in this test will fairly quickly get to the point that the velocity hardly increases any further. This is known as terminal velocity.
What will be the drag force at that point?
If we assume that speed is reached very quickly, how can you find the terminal velocity from your data?
 

FAQ: How to calculate the drag force?

What is drag force?

Drag force is the force that opposes the motion of an object through a fluid, such as air or water. It is caused by the interaction between the object and the fluid and is dependent on factors such as the object's shape, size, and speed.

How do you calculate drag force?

The formula for calculating drag force is: Drag Force = 1/2 * Density of Fluid * Velocity^2 * Object's Cross-sectional Area * Drag Coefficient. The density of the fluid and the velocity of the object can be measured, while the object's cross-sectional area and drag coefficient can be determined experimentally or calculated using mathematical models.

What is the difference between drag force and air resistance?

Drag force is a general term that refers to the force that opposes the motion of an object through a fluid. Air resistance, on the other hand, specifically refers to the drag force experienced by an object moving through air. Air resistance is affected by the object's shape, size, and speed, as well as the density and viscosity of the air.

How does the shape of an object affect drag force?

The shape of an object can greatly affect the amount of drag force it experiences. Objects with streamlined, aerodynamic shapes experience less drag force because they are able to move more smoothly through the fluid. On the other hand, objects with irregular or blunt shapes experience more drag force due to the turbulence created as they move through the fluid.

What factors affect the drag coefficient?

The drag coefficient is affected by several factors, including the shape and size of the object, the surface roughness of the object, and the Reynolds number. The Reynolds number is a dimensionless value that takes into account the object's velocity, density of the fluid, and viscosity of the fluid. It is used to predict whether an object will experience laminar or turbulent flow, which can greatly affect the drag coefficient.

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