# Coefficient of Drag: Exploring Thrust & Application

• 462chevelle
In summary: The difference is that you use thrust instead of drag. I think the thrust terms are interchangeable, but i'm not positive.In summary, the difference in calculating the coefficient of drag with thrust, and without, is that thrust comes from the engines, while drag is caused by the air flow over the plane and depends on the air speed and the angle of attack of the wings.
462chevelle
Gold Member
Could someone explain to me the difference in calculating the coefficient of drag with thrust, and without. What causes the difference in application?

Could you clarify a little ? Is there a difference? What difference ? What drag ? What difference in application ?
And what is the further context ? What do you know already ? At what level, approximately ?

1 person
Here is the problem, I finally figured out how to solve this. But it wasn't because my own independent research of coefficient of drag. I simply noticed someone else on the discussion section commenting about it. Whenever I discovered there was a problem that needed the coefficient of drag. I looked over the lecture again and didn't see anything about it other than a conceptual comment about it. So I started looking for formulas and explanations, and all of them I found stated 'without thrust'
So naturally it made me think there would be something different about it conceptually. Or that the fact is that you can derive it in such a way to get rid of the Thrust variable. I couldn't figure it out just by looking at all of the formulas with it in it. So i decided to ask.
Thanks.
Also to add, I'm not great at physics, but with enough time i can understand most things. As far as my level of math, I can do simple calculus but nothing crazy. Good at algebra and trig. I'm not really taking this course expecting anything miraculous but I have noticed its really helping my problem solving skills. Most of the problems start off in the wrong units. Or you don't have defined formulas, meaning you have to derive and figure stuff out. I get a kick out of the challenge but its still hard to me sometimes.

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• Physics Problem.jpg
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I don't really understand your comment about formulas for drag "without thrust" (and presumably, other formulas for drag "with thrust"). If you can give a link or a picture that might help.

The thrust and drag forces are independent of each other. Thrust comes from the engines. Drag is caused by the air flow over the plane and depends on the air speed and the angle of attack of the wings.

In the question you attached, the plane is flying straight and level so thrust = drag. You can work out the thrust from the change in momentum of the air by the propeller. Them you can find the drag coefficient from the drag force, wing area, air speed, and air density.

In real life, the propeller wash might have some effect on the drag coefficient. For a multi-engine propeller driven plane, the air flow over the wings would be slightly faster than the airspeed of the plane, especially at low airspeed and high engine power. (For a single engine plane the effect would probably be less). But I think that sort of effect would be too complicated to include in a "formula".

1. Homework Statement
2. Homework Equations
3. The Attempt at a Solution
What was the argument for removing it altogether ? Ever seen the guidelines to counter those arguments?

I didn't use it because I wasn't really looking for an answer to a question. Just conceptual help, so I didn't think it would be that big of a deal to start from scratch.
That's how i solved the problem, making drag=thrust. Then using the equation, here is the link to the one that showed thrust/no-thrust as something to be considered.
http://www.grc.nasa.gov/WWW/k-12/airplane/flteqs.html
The equation for the horizontal is similar to the one i used and could probably be derived to get the equation i used. Off the top of my head i think it was
Cd=(mdot)/(A*rho*V^2)

I looked back at my notes, I used
Cd=(T)/(.5*rho*V^2*A)

## 1. What is a coefficient of drag?

A coefficient of drag is a dimensionless quantity that represents the resistance of an object moving through a fluid, such as air or water. It is a measure of how much the object's shape and size affect its ability to move through the fluid.

## 2. How is the coefficient of drag calculated?

The coefficient of drag is calculated by dividing the drag force on an object by the product of the velocity of the object, the density of the fluid, and the area of the object. This calculation can be done through various experimental methods or through computational fluid dynamics simulations.

## 3. What factors affect the coefficient of drag?

The coefficient of drag is affected by several factors, including the shape and size of the object, the speed at which it is moving, the density and viscosity of the fluid, and the roughness of the object's surface. Changes in any of these factors can affect the overall drag coefficient.

## 4. How does the coefficient of drag impact thrust?

The coefficient of drag plays a crucial role in determining the amount of thrust needed to overcome drag and propel an object through a fluid. A higher coefficient of drag means that more thrust is required to achieve a certain speed, while a lower coefficient of drag means less thrust is needed.

## 5. What are some real-world applications of studying the coefficient of drag?

The coefficient of drag is an important concept in various fields, such as aerospace engineering, automotive design, and sports science. It is used to optimize the design of vehicles and sports equipment to reduce drag and increase efficiency. It is also relevant in understanding the flight and movement of animals and insects in their natural environments.

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