Take Flight Exhibit Staff/Educator Guide

Transcription

1 Take Flight Exhibit Staff/Educator Guide Pump It Up Rocket Launcher Description: Visitors first construct a rocket by rolling a sheet of paper into a tube, sealing the nose, and attaching fins. Next, the rocket is slid over a tube on the launch platform. The angle of the launch tube may be moved up or down to change the rocket s trajectory and to aim at target hoops. Visitors then operate a bicycle pump to fill the hollow cylinder beneath the launch platform with compressed air. A gauge displays the rise in pressure in pounds per square inch. Depressing the red button opens a valve which releases the pressurized air into the rocket s body, sending it flying. Air Pressure Unlike real rockets which carry their fuel onboard, the propellant for these paper rockets comes from an external source. We know that the propulsion force comes from compressed air that is suddenly released as the valve is opened, but what really causes this force? Air is a mixture of several gases, mostly nitrogen and oxygen. The main difference between gases and substances in solid and liquid states is the distance between molecules. Molecules in solids, and to a lesser extent in liquids, are held close together by attractive forces. As molecules gain kinetic energy, they begin to move faster, overcome the attractive forces, and move apart (think of adding heat to an ice cube, melting it to liquid, then boiling the water to steam). Since molecules in a gas are relatively far apart, they can move with less restriction that s why a gas will expand to fill all the space available to it and take the shape of its container. Imagine molecules of air zinging around like bumper cars, colliding and bouncing off each other and the walls of their container. These countless collisions exert a force on the container s interior surface which we measure as pressure (force per unit of area). The more molecules that are packed into the hollow cylinder below the launcher, the greater the number of collisions and the greater the pressure which is exactly what occurs each time the pump is depressed. Unlike solids and liquids in which slow moving molecules are already held tightly together, the empty space between gas molecules allows them to be forced together or compressed into a smaller volume. Fluids gases and liquids will always flow from an area of high pressure to an area of lower pressure until the pressures are equalized. When the launch button is pushed, a valve opens which acts like a gate between the two areas of different pressure (the cylinder and the room). The higher pressure in the cylinder rushes out to the lower pressure in the room by way of the launch tube. Projectile Motion A projectile is any object that is projected by some means and continues in motion by its own inertia. A cannonball shot from a cannon, a stone thrown into the air, and the paper rockets at this exhibit are all projectiles. Without gravity, a projectile would follow a straight-line path or trajectory. But since we can t escape the downward pull of gravity on earth, projectiles instead follow curved paths called parabolas. The shape of the parabola depends on the maximum altitude or height the rocket attains as well as the range or horizontal distance it travels. The altitude and range are, in turn, determined by the rocket s speed and its projection angle. For a rocket with a given launch speed, a 90 projection angle will give the greatest altitude while a 45 projection angle will result in the greatest range. Increasing the launch speed will increase both the altitude and range at a given projection angle. NOTE: When there is significant air resistance, as is the case with our lightweight paper rockets, the range of the projectile is somewhat shorter and the trajectory is not a true parabola. The visitors at this exhibit will be able to vary the projection angle by pivoting the launch tube up and down (the range will be quite narrow to confine rockets to the limited space). The launch speed of the rocket can be altered by varying the amount of air pressure pumped into the cylinder.

2 Rocket Launcher continued Facilitation Ideas and Questions Encourage visitors to experiment with different combinations of launch angle and air pressure settings that will send their rockets through the target hoops. What makes the rocket fly? What would happen if you left the nose cone open? Why does it go faster/higher/further when you pump more? What are two ways to make your rocket fly higher? How do the fins help the rocket fly? What works best 2, 3 or 4 fins? Management and Maintenance - Check and replenish supplies for making rockets: paper, fins, tape. - Empty recovery zone of unclaimed rockets if they accumulate. - Be sure visitors stay clear of the launch tube. - Keep pump seal clean and oiled (see Maintenance) Paper Airplane Launcher (Wing Zingers) Description: Visitors first build a paper airplane at the Make It Fly table located behind the launchers. After putting on safety goggles and waiting for the runway to clear of other users, the visitor guides the fuselage of the plane into the slot on the launch platform. Two rotating wheels pinch the airplane and thrust it forward into flight. The launch platform may be tilted upward by turning the crank located in front of the launcher. Although a paper airplane is a lot smaller, simpler and lighter than a real airplane, the four forces that enable flight are the same for both: LIFT is the upward acting force that keeps an airplane aloft. The shape of the wing, air speed, and angle at which the wing meets the oncoming airstream all affect the amount of lift. Even though a paper airplane s wings are flat, they experience all of the aerodynamic forces found in more sophisticated wings. For example, when the air flowing past the paper airplane encounters the lower surfaces of its wings, this air slows down. You can think of this air as hitting a slanted wall. Whenever a moving stream of air slows down its pressure rises (and conversely, the pressure drops in a fluid when it speeds up Bernoulli s principle). You experience this pressure rise when you hold your hand out of the window of a moving car and feel the slowing air push your hand toward the back of the car. The air above the wing doesn t slow down and its pressure never rises above atmospheric pressure. In a well designed wing, it actually drops below atmospheric pressure. Since the air pressure rises under the paper airplane s wing and doesn t rise above the wing, the wing experiences an overall upward force that supports the airplane. Notice that when you toss a paper airplane, or when you send it through the motorized launcher, the wings are tilted upward slightly. The angle of the wings from horizontal is called the angle of attack. The greater the angle of attack, the more the air will slow down under the wing, and the greater the resulting pressure differences and lift. Visitors can adjust angle of attack by tilting the launch platform and by folding the airplane s wings at an angle to the fuselage. GRAVITY is the force that pulls an airplane down towards the earth s surface. An airplane that weighs 5 tons must generate more than 5 tons of lift in order to get off the ground. Of course, a lightweight paper airplane doesn t need to generate much lift to become airborne. THRUST is the force that moves an airplane forward through the air. Thrust is provided by the airplane s propulsion system; either a propeller or jet engine or combination of the two. At this exhibit, the thrust is generated by the motorized launchers. DRAG is the force that holds an airplane back due to air resistance, or friction, against the surfaces of the airplane. To reduce drag, some airplanes have sleek shapes that slip easily through the air. By cutting and folding flaps along the rear edge of the wings, visitors can use drag forces to make their planes turn, bank, loop, etc.

3 Paper Airplane Launcher continued Managing the balance among these four forces is the challenge of flight. When thrust is greater than drag, an airplane will accelerate. When lift is greater than weight, it will climb. By changing the amount of thrust and moving flaps to create drag, a pilot can manipulate the balance of these four forces to change direction and speed. Facilitation Ideas and Questions Directions are provided for four different airplane designs at the Make It Fly station. It s a good idea for volunteers to try building each of the designs so that they can assist with visitor s questions and problems. Some designs are simpler than others, and these should be recommended to younger builders. Encourage visitors to aim for the targets and to experiment with different launch angles. Control flaps on the wing surfaces can be added to change flight direction. Management and Maintenance Safety is a prime concern at this exhibit. Visitors must wear safety glasses or goggles while they launch and retrieve their planes. After retrieving their plane, a visitor should exit out the side of the runway and walk back around the cage to replace their goggles. Paper airplane designs with pointed noses are not permitted if need be, show the visitor how they can fold the tip back to make it safer. - Check and replenish supplies for making airplanes - paper, tape and scissors. - Empty waste receptacles when full. - Replace goggles, glasses in bins on launch table. Hoverport Description: Visitors first build one of the three rotating flyer designs at the Make It Fly Copter station. After starting the blower unit, the visitor holds their flyer in one hand and one of the three air hoses with the other. The flyer is then held above the hose and released into the air stream. Think of a propeller as a spinning wing. In cross section, it is shaped like a wing to produce higher air pressure on one surface and lower air pressure on the opposite surface. On a helicopter, what most of us call the propeller is actually termed the main rotor. It is the most important part of a helicopter in that it provides the lift necessary for vertical ascent as well as the control to move laterally and change direction. A helicopter s spinning rotors create thrust like a large propeller on an airplane, but the thrust is directed vertically instead of horizontally. The air moving over the top of the blades moves faster than the air moving under the blades. As air speeds up, its pressure drops. So the faster-moving air above exerts less pressure above the blades than the slower-moving air below. The result is an upward push on the rotor which we call lift. When the roto-copter design falls due to gravity, air pushes up against the blades, bending them up just a little. When air pushes upward on the slanted blade, some of that thrust becomes a sideways, or horizontal, push. Why doesn t the copter simply move sideways through the air? Because there are two blades, each getting the same push, but in opposite directions. The two opposing thrusts work together to cause the roto-copter to spin. Autorotation is the term used for the flight condition during which no engine power is supplied to the rotor system. Amazingly, sustained flight is possible even when the rotor blades are spinning without engine power. Unlike fixed wing aircraft, helicopters are capable of controlled landing during most conditions when power is lost. The spinning inertia of the main rotor is enough to slow the rate of descent and affect a safe landing. Helicopter pilots often train in autorotation landings. Center of Gravity (C of G) is important to the stability of a helicopter just as it is in the ability of our rotocopters to hover in a more controlled manner. The mass or weight of the roto-copter doesn t change as the number of accordion folds increases. However, with each fold, the C of G is brought closer to the blades of the roto-copter. Visitors may notice that with no folds in the roto-copters body it lists from side to side. When there are more folds, and the C of G is directly under the blades, the copter is able to hover in a more stable manner.

4 Hoverport continued Facilitation Ideas and Questions Challenge visitors to keep their rotating flyers aloft as long as they can. Try to get a copter to hover in mid-air (when the weight of the copter equals the lift force of the rotors and airstream) Experiment with the number of folds used in the body of the roto-copter. What happens if you fold the blades of the roto-copter in the opposite directions? (rotation direction will change) Try other copter designs. Action Reaction Description: Drop a tennis ball through the tube. What direction does the ball come out of the tube? What happens if you drop several balls through the tube at once? The basic idea that explains how rocket engines work was first stated in Isaac Newton s third law of motion: To every action there is an equal and opposite reaction. A rocket engine throws matter in one direction and reacts by moving in the opposite direction. If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose. The hose is acting like a rocket engine. The hose throws water in one direction, and the firefighters use their strength and weight to counteract the reaction. If the firefighters were all standing on skateboards, the hose would propel them backwards at great speed! At this exhibit, a ball is forced out from the tube in one direction and the tube reacts by moving in the opposite direction. Dropping more than one ball at a time increases the amount of mass being forced out (the action), causing the tube to be pushed back even farther (the reaction). A rocket engine is generally throwing matter in the form of high gas pressure gas. The engine throws a certain mass of gas out in one direction in order to get a reaction in the other direction. The mass comes from the weight of the fuel the rocket burns. If a pound of rocket fuel is burned, a pound of exhaust comes out of the nozzle in the form of high-temperature, high-velocity gas. While the form of the fuel may change, its mass does not. The burning process simply accelerates the fuel s mass to achieve more thrust. Flight Activities Pump It Up This Air Pump Rocket launches visitors creations and sends them over the exhibit entry arch. Visitors create paper rockets and adjust pressure and trajectory while aiming for targets and height. Wing Zinger Visitors create their own paper airplanes that they can test on state-of-the-art paper airplane launchers. The launch process can be replicated, allowing the pilots to fine tune their aircraft and aim the planes at targets. Hover Port This unique blower provides adjustable jets of air that can send paper helicopters, twirly fish and other creations spinning in the air. Go With the Flow Description: What happens when a fluid moves over a curved surface? The Coanda Effect explains how an airplane wing develops lift. You were probably surprised to see how far the water stream followed the shape of the cylinder before falling downward. The tendency for a fluid (either liquid or gas) to stick to a surface and flow along it is know as the

5 Go With the Flow continued Coanda Effect. As fluid moves across a surface, such as a cylinder, the smooth lip of the cup and the airplane wing, a certain amount of friction occurs between them. This resistance to the fluid s flow causes the fluid to pull towards and stick to the surface it is flowing over, even following curves and bends. However, if the bend is too sharp, like the lip of the pitcher, there will not be enough friction created to hold the fluid against the downward pull of gravity. The Coanda Effect helps explain how an airplane wing develops lift. As a plane moves forward, a layer of air follows the upper curved surface of a wing and gets deflected downward off the rear or trailing edge. Isaac Newton s third law of motion states that forces always occur in equal and opposite pairs. So, as the wing deflects the air down the air pushes back up on the wing, and the result is lift. Flight Principles Fascinating and interactive informational exhibits such as Go with the Flow and Action & Reaction encourage visitors to discover and explore properties of flight such as air flow, angle of attack, lift, drag, thrust and gravity. History of Flight In collaboration with Southern Oregon Public Television (SOPTV) ScienceWorks has created a brief and informative video on the history of flight. Much of what we know about flight comes from creativity, imagination and trial and error. This fascinating video explores some of the creative (and wild!) contraptions that humans have created to take to the skies. Updated: December 2010 / Z:\Exhibits\Travel exhibits\take Flight\Materials for Lessees\Take Flight Rental; Staff Guide