Exploration Series. AIRPLANE Interactive Physics Simulation Page 01

Transcription

1 AIRPLANE Interactive Physics Simulation Page 01

2 What makes an airplane "stall"? An airplane changes its state of motion thanks to an imbalance in the four main forces acting on it: lift, thrust, drag, and weight (the force of gravity). When one of these forces exceeds its opposite, the plane accelerates in that direction as predicted by Newton's 2nd Law.But how is the lift force generated? How does a plane fly? Can a plane climb at any angle? Is a plane always pointed in the direction it is moving? Under what conditions will a plane feel the strongest lift forces? The strongest drag forces? Why does a plane deploy slats and flaps before landing? Let's understand the science behind this. When a wing cuts through the air, we describe the angle the airfoil makes with the direction of motion as the angle of attack.in order to climb, a plane increases its angle of attack. This allows a lift force to be generated that exceeds the weight of the plane, and the plane accelerates upward. The magnitude of the lift force depends on many things: the density of the surrounding air, the speed of the plane, the area of the wing, and the angle of attack. The coefficient of lift describes how much influence the angle of attack has on the lift force. In general, the higher the angle of attack, the more lift. However, if the angle of attack gets too high, the lines of flow above the wing break, and the airplane stalls and loses lift. This is very dangerous.let's explore these ideas in the simulation. To access this physics simulation visit: Page 02

3 Wing Profile - This slider adjusts the physical shape of the wing. When a plane is moving at low speed, such as during takeoff and landing, it needs to generate enough lift to support flight. The addition of flaps and slats allows the wing to generate a lot of lift at low speed. The trade-off is that a lot of drag is created, so the plane also needs to generate a lot of thrust to overcome the drag. Thrust - This slider adjusts the amount of thrust generated by the jet engine. The thrust force acts in the direction the plane is pointed, not in the direction it is moving (unless these directions are the same). Total Mass - This slider adjusts the total mass of the plane, which includes not just the plane body itself but also the fuel and the passengers (and their luggage!). The greater the mass, the greater the weight, and also the greater the inertia, which means the plane will adjust more slowly to changes in motion. To access this physics simulation visit: Page 03

4 Angle Of Attack - This slider adjusts the angle between the direction of motion of plane and the direction the plane itself is pointed. This might seem counter-intuitive - often we think that the plane is always moving in the direction it is pointed. But a wing actually generates greater lift if the air impacts it at some angle. Wing Size - This slider adjusts the size of the wings (and therefore the size of the plane overall). The lift force is proportional to the area of the wings, so a larger wing can generate more lift. The drag force is proportional to the frontal area of the wing, so larger wings also generate more drag. To access this physics simulation visit: Page 04

5 Coefficients of Lift and Drag vs Angle of Attack - This is a plot of the coefficients of lift and drag for the airfoil as a function of angle-of-attack. The lift force acting on an airfoil can be approximated by multiplying one-half by the density of air by the square of the air speed, then multiplying by the flat area of the wing, then multiplying by this coefficient. Higher coefficients mean more lift. As you can see, the lift falls off steeply after its maximum value - this is dangerous for a pilot, as the plane is said to stall and the pilot will need to recover. The drag force is calculated in a similar way, although just the area of the leading edge of the wing is used to calculate the force. For a properly designed airfoil, drag forces are much less than lift forces, which allows for powered flight. To access this physics simulation visit: Page 05

6 Question 1.(upcoming) Question 2.(upcoming) Question 3.(upcoming) To access this physics simulation visit: Page 06

7 Challenge ME! Under what conditions will an aircraft stall? Why does a plane need to be going so fast at takeoff? Why does a plane deploy flaps and slats just before landing? Need Help? Check out the Airplane Walkthrough video at: << Link >> To access this physics simulation visit: Page 07

8 How are the lift and drag coefficients of different airfoils measured? It is too impractical to build a new airplane anytime you want to try out a different wing shape. Instead, aeronautical engineers can make use of a wind tunnel. These wind tunnels are much smaller than the airplanes we are eventually attempting to build - you might think, at first, that this would present a problem: sure it works for a small wing, but how do you know it will work for a large wing? Scientists have figured out how to "touch" the physics, making use of a quantity known as the Reynold's Number to describe the type of airflow, so that the predictions make sense. How is thrust generated? There are lots of different ways to generate the thrust force required by an airplane to maintain airspeed. Early airplanes relied on propellers, which basically acted as large fans. Then the jet engine was developed, which also uses fan-type devices to thrust air from the intake end to the output end. How does a helicopter fly? Each of the blades on the helicopter generates lift as it passes through the air. The only problem is that, thanks to conservation of angular momentum, the body of the helicopter should begin rotating in the opposite direction! A second blade set up perpendicular to the first generates a torque that prevents the helicopter from spinning. Why does a plane need to accelerate along the runway to takeoff? The lift force depends on the square of the relative speed of the air as measured by the wing. That is, the air has to appear to be moving (as seen by the wing) to generate lift. Because an airplane needs a lot of lift to take off, and because it is hard to get it going full speed along the ground, typically a plane takes off with its flaps and slats deployed to get as much lift at low speed as it can. To access this physics simulation visit: Page 08

9 Physics Concepts Click on the link below to learn more. Newton's Second Law - Types of Forces - To access this physics simulation visit: Page 09