Lesson Four

Drag

What we will be covering

• Drag
• Airspeed vs. drag, landing gear
• Flaps
• Airspeed vs. drag, flaps
• Kinds of drag

Review: Forces

A force is a push or a pull in a certain direction. It is composed of magnitude (how large the force is) and the direction of the force.

We represent forces by drawing vectors (arrows) that tell us the magnitude and the direction of the force.

70°

50 N

Drag

Drag is the force that resists the movement of the airplane through the air. It is directed along the flight path in the opposite direction of movement.

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Test Flights: Airspeed vs. Drag

Let’s take a look at drag in action.

Head to Quick-Flight Setup - but let’s shake things up a bit! Instead of the Cessna, select the King Air C90B. She has two engines and retractable landing gear.

Test Flights: Airspeed vs. Drag

Follow the protocol to start in the sky instead of on the runway.

Test Flights: Airspeed vs. Drag

We will also need to collect data as we fly.

Test Flights: Airspeed vs. Drag

Now fly level for 3 seconds. Landing gear should be retracted. Observe the airspeed, and note it in your student handbook.

Then press G to lower the landing gear. Fly level for 3 seconds. What is the airspeed now? What is your hypothesis to explain what happened?

Jot down your answers in your student handbook.

Investigative Questions

What is the airspeed with the landing gear down?

Air speed should be lower after deployment of landing gear

What is your hypothesis to explain what happened?

Lowering the landing gear increased the drag

Flaps

Landing a plane is actually easier if you are traveling slower. Careful, though! If you slow down the plane too much, you’ll stall and fall out of the sky.

How do we add drag? Engineers have actually developed a way to make the wing bigger by using flaps.

Flaps

Flaps extend the wings trailing edges back and change the airfoil, or shape of the wings. This increases drag. It also increases lift.

As you land, the flaps slow down the plane while increasing the lift on the wing, so lift is maintained at slower air speeds to avoid stalling.

Test Flights: Airspeed vs. Drag (Flaps)

Go through Quick-Flight Setup and select the King Air.

Test Flights: Airspeed vs. Drag (Flaps)

We once again need to collect data.

Test Flights: Airspeed vs. Drag (Flaps)

You will be flying 3 trials with both your flaps up and flaps down, filling in the corresponding table in your student workbook. Try and fly as consistently as possible for all 6 trials.

E.g.

Test Flights: Airspeed vs. Drag (Flaps)

Use 1 and 2 on your keyboard to raise and lower your flaps.

Use the tables to find average airspeed, lift, and drag. Then compare these values to answer the corresponding questions in your student handbook.

Investigative Questions

• When you deploy or lower flaps, what does drag do?�
• When you deploy or lower flaps, what does airspeed do? �
• When you deploy or lower flaps, what does lift do?�
• Why would it be dangerous to land a plane with flaps if the flaps only increased drag, but did not increase lift?

Investigative Questions

• When you deploy or lower flaps, what does drag do? Drag increases�
• When you deploy or lower flaps, what does airspeed do? Airspeed decreases�
• When you deploy or lower flaps, what does lift do? Lift increases�
• Why would it be dangerous to land a plane with flaps if the flaps only increased drag, but did not increase lift? Drag would decrease airspeed. Lower air means less lift. Less left can lead to stalling.

Kinds of Drag

Drag comes in multiple forms. Two kinds we will explore here are:

1. Parasitic Drag�
2. Induced Drag

Parasitic Drag

Parasitic drag is created from dragging a body (fuselage, wing, flap, landing gear) through the air. You can see this by making a fist and putting it out the window of a car doing 60.

This drag varies with the square of the speed of the plane. A simplified equation would be Speed = Drag². This means that changing airspeed results in an even greater change in drag.

Parasitic Drag

Engineers try to shape or change the body of the plane to reduce this kind of drag. For example, engineers developed retractable landing gear to reduce this kind of drag in fast airplanes. Automobile engineers try to reduce drag in cars to increase performance and fuel economy.

Induced Drag

Induced drag is caused by the creation of lift.

Engineers spend a great deal of time looking at different airfoils or shapes of a wing that will give them the greatest amount of lift with the least amount of drag for a wing under certain conditions.

Any part of the plane that generates lift generates this form of drag. This includes the wing, tail surfaces, and the body.