Aeronautics Class 11 Review Handout PDF

A Beginner’s Guide to Aeronautics Session 11: Hypersonics In our previous class session, we began exploring high speed aircraft. At high speeds, the temperature of the flow around the aircraft is so great that the chemistry and molecules of the gas must be considered. This is a special branch of aer...

A Beginner’s Guide to Aeronautics Session 11: Hypersonics In our previous class session, we began exploring high speed aircraft. At high speeds, the temperature of the flow around the aircraft is so great that the chemistry and molecules of the gas must be considered. This is a special branch of aeronautics called Compressible Aerodynamics. Flight faster than Mach 1 is called Supersonic, up to Mach 5. When aircraft fly at Mach 5 (5 times faster than the speed of sound) or above, they are called Hypersonic Aircraft. So, any aircraft flying at Mach 5 and above is considered Hypersonic. How fast is Mach 5? Mach 5 = approx 3,800 miles (6,116 km) per hour! AT LOW HYPERSONIC SPEEDS (Mach 5 up to 10) – molecular bonds vibrate which changes the magnitude of the forces generated by the air on the aircraft. AT HIGH HYPERSONIC SPEEDS (Mach 10 and above) – the molecules break apart producing an electrically charged super-hot plasma around the aircraft! Mach 10 = approx 7600 miles (12,300 km) per hour! Hypersonic aircraft have to be built to withstand extremely high heat and turbulence of the air flow. As shown above, there are 3 main missions or use cases for Hypersonic flight: 1) Re-entry from space orbit 2) Hypersonic cruise 3) Hi-speed accelerator (also known as a reusable booster for spacecraft) The first use case involves slowing an extremely high-speed vehicle going from space to Earth, while the other two involve extremely powerful propulsion system to reach hypersonic speeds. Since these situations are very different, we will look at each of these cases separately. Use Case #1: RE-ENTRY FROM ORBIT or Hypersonic Re-Entry As a spacecraft re-enters the earth's atmosphere, it is traveling much MUCH faster than the speed of sound. Typical low earth orbit reentry speeds are near 17,500 mph and the Mach number is nearly twenty five, M < 25. Almost 25 times the speed of sound! Due to this very high speed causing compression of the airflow, the temperature of the flow is so great that the chemical bonds of the molecules of the air are BROKEN. The molecules break apart producing an electrically charged plasma around the aircraft. What is Plasma? Plasma is a super-heated cloud of protons, neutrons and electrons where the electrons have been ripped from their respective molecules and atoms. Plasma is often called “the fourth state of matter,” along with solid, liquid and gas. This image (right) shows plasma at the forward part of the Orion capsule as it re-enters Earth’s atmosphere. NASA's Orion capsule captured this footage of its reentry to Earth's atmosphere on Dec. 11, 2022, at the end of the Artemis 1 moon mission. (Image credit: NASA) Spacecraft use ablative heat shields designed to burn away slowly during reentry. These heat resistant tiles are used to protect the spacecraft and its occupants. The Mach number decreases from 25 to 10 as the vehicle constantly decelerates. Crewed space vehicles must be slowed to subsonic speeds before the parachutes can be deployed. Use Case #2: Hypersonic Cruise Use case #2: Hypersonic cruising aircraft and cruise missiles fly at the lower limits of hypersonic, from Mach 5 to 10. In this image (right), an early X-15 hypersonic aircraft is pictured. The X-15 used a rocket propulsion system to achieve sustained Mach 6 flight. Today, modern hypersonic aircraft are powered by air breathing ramjet and scramjet propulsion systems, which are more efficient than rockets. “Air breathing” jet engines are all jet engines that use atmospheric air. This air is taken in, compressed, heated and expanded back to atmospheric pressure through a propelling nozzle - this expansion generates Thrust. Ramjet Design Scramjet Design Ramjets and Scramjets use the force of the hypersonic aircraft ramming through the air to provide needed compression of the airflow. Ramjets & scramjet have to be launched into flight by another jet aircraft. Why? Because ramjet or scramjet engines only function at supersonic speeds, they must “hitch a ride” on another regular jet to get off the ground and up to speed. This has been a major limiting factor in the development of hypersonic aircraft. But a new company, Hermeus, is trying to change that. They are developing a new “Ramburner” engine that can function as a regular jet engine for take-off, and also as a hypersonic engine once the aircraft reaches hypersonic speeds. The image to the right is a concept illustration for a new supersonic passenger plane being developed by the company Hermeus. Use Case #3: Airbreathing Hypersonic Accelerator For use case #3, the hypersonic accelerator must continually produce excess thrust (thrust greater than drag) in order to accelerate. Unlike use case #2, it is not flown in a steady cruise condition. A hypersonic accelerator can be used to launch a vehicle into orbit in one single stage. Or, it may be the first stage of a two stage booster used to launch a vehicle into orbit. For example, the Ram Accelerator is a launcher that uses chemical energy to accelerate vehicles to hypersonic speeds. Unlike the Ramjet Engine, fuel is added at the beginning of the propulsion process and the gas undergoes stronger compression. As a result Ram Accelerators generate very strong thrust. They may be less expensive than rockets to get payloads into orbit. Rockets are expensive because rockets carry both fuel AND its own oxygen. Rockets are “Non-Air Breathing.” This leads to the problem of “The Rocket Equation” discussed earlier in the course. The heavier the rocket & payload, the heavier the fuel + oxygen and the higher the cost! Rockets are expensive, costing $2,500 to $25,000 per kilogram from Earth to low Earth orbit Activity: Draw lines to connect the Mach numbers to the correct category. Mach 2 Mach 11 Supersonic Mach 20 Mach 8 Hypersonic Mach 3 March 16 (Answers below) Recommended Homework for this week: - Complete the Class Review Handout - Explain to a family member: What is hypersonic flight? Categorizing Activity Answers: Mach 2 Supersonic, Mach 11 Hypersonic, Mach 20 Hypersonic, Mach 8 Hypersonic, Mach 3 Supersonic, Mach 16 Hypersonic A Beginner’s Guide to Aeronautics Session 10: Compressible Aerodynamics High speed aerodynamics is a special branch in the study of aeronautics. It is called compressible aerodynamics because, at very high speeds, the compressibility of air must be considered. Air is compressible, and this has significant effects on aircraft, especially at very high speeds. Compressible Aerodynamics is categorized by something called Mach Number. Mach Number is the ratio of the speed of the aircraft to the speed of sound. Compressible Aerodynamics is divided into these 4 categories: Mach 1.0 is equal to the speed of sound. The speed of sound is approximately 1100 feet per second, or 343 meters per second. Note: The speed of sound varies depending on temperature, atmospheric pressure and compressibility of the air. Activity: Draw lines to connect the Mach numbers to a correct definition. Mach 1 Equal to 5 times the speed of sound Mach 5 Equal to half the speed of sound Mach.5 Equal to the speed of sound Mach 10 Equal to twice the speed of sound Mach 2 Equal to 10 times the speed of sound (Answers on the last page) —---------------------------------------------------------------------------- Remember, a gas (like air) is considered a fluid in Aerodynamics. Aerodynamic forces depend on the compressibility of the gas (air). As an object moves through the gas, the gas molecules move around the object. If the object passes at a low speed (typically less than 200 mph) the density of the fluid remains constant and is not much of an issue. But at higher speeds, some of the energy of the object goes into compressing the fluid (air) and changing the density, which alters the amount of resulting force on the object. This effect becomes more important as speed increases, especially near and beyond the speed of sound. Because high-speed aerodynamics involves the flow of heat & energy, it also involves the field of THERMODYNAMICS. What is Thermodynamics? Thermodynamics is the study of the effects of work, heat and energy on a system. Thermodynamic Laws deal with why energy flows in certain directions and in certain ways. Note: Thermodynamics is a complex subject involving advanced math calculations, which is usually taught to university-level engineering students. We discussed introductory-level concepts during our class session. Thermodynamics is relevant to aeronautics in many situations. At very high speeds, due to the energy compressing the fluid (air), the temperature at the surface of an aircraft increases and becomes very hot. For example, at Mach 2, the temperature at the nose of an aircraft can be around 220 F. Streamlined aircraft designs tend to not heat up as extremely as designs that are less streamlined. Thermodynamics helps us understand high speed flows. Below is a summar of the 4 Laws of Thermodynamics: Thermodynamics helps engineers understand and predict heat, energy and work in a system, and why energy flows in certain directions and in certain ways. In aerodynamics, the thermodynamics of a gas plays an important role in understanding aircraft propulsion systems, such as this jet engine (below). The illustration (below) shows the transfer of heat and energy in a room. Sonic Booms and Shock Waves A shockwave is generated when a wave spreads through a medium at a speed faster than the speed of sound travels through that medium - like when an aircraft travels faster than the speed of sound. Shockwaves produce an abrupt spike in pressure over a very short time period. The sound heard on the ground as a loud SONIC BOOM is the sudden onset and release of pressure after the buildup by the shock wave. The sudden change in air pressure is perceived as a loud BOOM sound by our ears. We sense sound through our ears which are sensitive to sound wave vibrations carried through the air. What else can generate a Shock Wave? Sonic booms can also be caused by other high-speed phenomena. Sometimes they can even be caused by meteors! For example, the Chelyabinsk meteor caused a powerful shock wave. It entered Earth's atmosphere over Russia on February 15, 2013. It was an 18 m (59 ft) diameter 9,100 ton near-Earth asteroid. It approached Earth undetected before its atmospheric entry, partly because its source direction was close to the sun. People were not expecting this! It exploded in a meteor airburst at a height of about 30 km in the sky. The explosion generated a bright flash, producing a hot cloud of dust and gas, and many small fragmentary meteorites. Most of the object's energy was absorbed by the atmosphere, creating a large shock wave. The asteroid had a total kinetic energy equal to 400–500 kilotons of TNT! About 7000 buildings were damaged by the explosion’s shock, and about 1000 people were injured, mainly from broken glass, but none seriously. You can read more about the Chelyabinsk meteor here. Speed of Sound Simulation & Mach Calculator During class, we used a software program to calculate the speed of sound and Mach number for different planets, altitudes, and speed. You can continue to experiment with this calculator to determine the Mach number of a rocket at a given speed and altitude on Earth or Mars. The Simulator is linked below: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/speed-of-sound-in teractive/ SUGGESTED HOMEWORK ACTIVITY for this session: 1. Complete this Review Handout. 2. Explain to a family member: What is a shock wave and why do we hear a sonic boom? _____________________________________________________________ Answer Key for Matching Activity: Mach 1 Equal to the speed of sound Mach 5 Equal to 5 times the speed of sound Mach.5 Equal to half the speed of sound Mach 10 Equal to 10 times the speed of sound Mach 2 Equal to twice the speed of sound A Beginner’s Guide to Aeronautics Session 9: Electric Aviation Innovations People are hard at work developing new electricity-powered aircraft. The reason for this development is that standard fossil fuel-based aircraft release carbon dioxide and other pollutants into the atmosphere. What is the Climate Impact of Air Travel? By burning fossil fuels, airplanes not only release carbon dioxide, but also other pollutants like nitrous oxide, soot and sulphate. The high altitude at which planes operate increases their negative impact. For example, contrails left by aircraft can trap heat and increase warming. The chart above shows that the secondary effects from high altitude non-CO2 emissions significantly increases the negative impact of air flights. What are Contrails? “Contrails” is an abbreviation for “Condensation Trails.” These form when hot humid air from jet exhaust mixes with atmospheric air of low temperature and pressure, leading to water condensation. They are human-made clouds. Like other clouds, they can trap heat and have a warming effect. Researchers are working on possible solutions for this issue. Electric Aircraft Design Using electric-powered airplanes is another solution to make flying more sustainable. But how can airplanes be powered by electricity? It still comes down to the fundamentals of flight: Thrust, Weight, Lift and Drag Many of the new electric-powered airplanes use propellers for thrust. Why? Propellers don’t need to burn fossil fuels to operate (unlike jet engines). And they are a relatively energy-efficient way to accelerate a large mass. But propellers need SOMETHING to turn them very quickly and strongly in a spinning motion. Traditional propeller aircraft are powered by an Internal Combustion Engine that operates by burning fossil fuel. An electric-powered propeller plane uses an electric “engine” instead - which is technically an electric MOTOR. What’s the difference between an engine and a motor? People sometimes use both terms interchangeably, but they are actually very different. Motors run on electricity and engines run on combustion (burning of fuel). An engine converts burning fuels into mechanical force. A motor converts electrical current into mechanical movement by utilizing the force of magnetism. Engines and motors use two very different mechanisms to generate mechanical force. Review Educational Videos: How Internal Combustion Engines Work How Electric Vehicles Work (principles shown apply to all electric motors) Activity: Draw a line to match the characteristics in the left column to the appropriate item in the right column. Uses electrical current Uses flammable fuel Has more moving parts Has less moving parts Internal Combustion Engine Based on magnetic attraction Based on mini-explosions Does not have exhaust Gives off exhaust Electric Motor Quiet operation Loud operation Requires air Does not require air Electric Airplanes - Power Sources Electric motors need a source of electrical current to work. In order to be more sustainable, the electrical current must come from renewable sources (such as solar, wind and geothermal). The electrical current is often provided on-board by batteries, but some designs have used solar panels. The weight of batteries or solar panels is a challenge, since they tend to be heavy. This may impact the lift required for flight. Several commercial companies are working on developing fully electric and hybrid electric planes. Hybrid electric planes include both fuel-based and electrical equipment. This allows for a longer flight range, while reducing carbon emissions somewhat (like hybrid cars). An Electric Jet Engine? While most electric planes currently use propellers, some daring inventors are working on creating new types of “Jet Engines” that are powered by electricity. One example of this is the new, patented eJet, which uses Rim-Driven Fan (RDF) technology. It is capable of delivering 2,700 horsepower. It is the first electric motor capable of matching the performance of a conventional fuel-powered jet engine. According to the company, Duxion, the eJet Motor is revolutionary due to its industry-leading power-to-thrust ratio, allowing for electrification of jet aircraft. It utilizes a permanent magnet technology consisting of a rim-rotating motor, as opposed to shaft-rotating motor, allowing maximum mass airflow for any given motor size. More electrical aviation innovations will likely be developed in the future. Hydrogen-based propulsion is also being explored as another alternative solution. SUGGESTED HOMEWORK ACTIVITY for this session: 1. Complete this Review Handout. 2. Explain the difference between a combustion engine and an electric motor to a family member. _____________________________________________________________ Answer Key for Matching Activity: Uses electrical current - Electric Motor Uses flammable fuel - Internal Combustion Engine Has more moving parts - Internal Combustion Engine Has less moving parts - Electric Motor Based on magnetic attraction - Electric Motor Based on mini-explosions - Internal Combustion Engine Does not have exhaust - Electric Motor Gives off exhaust - Internal Combustion Engine Quiet operation - Electric Motor Loud operation - Internal Combustion Engine Requires air - Internal Combustion Engine Does not require air - Electric Motor A Beginner’s Guide to Aeronautics Session 8: Aircraft Motion & Aerodynamics Aircraft flight involves a Solid Object (the plane) interacting with a Fluid (the air). Note: Air is considered a fluid. When 2 SOLID objects interact with each other, forces are transmitted at the main point of contact. (Remember Newton’s Laws of Motion!) But when a solid interacts with a FLUID, things are much more complex because the fluid can change its shape. For a solid interacting with a fluid, the point of contact is at many points, all over the surface of the solid. The fluid flows around and all over the solid, as illustrated in the image above. The study of how Fluids & Solids interact is called FLUID DYNAMICS A Fluid does NOT mean “a liquid.” A Fluid is defined as: A substance that has no fixed shape and yields easily to external pressure. It can be a gas or a liquid! How can we measure the force on an aircraft moving through the air? The Force on the Aircraft is equal to the Pressure multiplied by the Area of the aircraft body. Force = P (Pressure) * A (area of the body) What is the pressure of air? Air pressure is a measure of the linear momentum of the gas molecules. When gravity acts on the air, the air exerts a force upon the earth called pressure. The typical pressure at sea level is 1013.25 millibars or 14.7 pounds per square inch. A millibar is a unit used to describe atmospheric pressure. A barometer is used to measure air pressure. As a result, atmospheric pressure is also called barometric pressure. How do we measure air pressure while on an aircraft? On an airplane, the air pressure is measured by a special instrument called a Pitot Tube. The Pitot Tube was invented by Henry Pitot, a French engineer who lived from 1695 - 1771. It can measure the flow velocity of a fluid, whether a liquid or a gas. Using the Pitot Tube to measure air pressure, we can then also determine the plane’s altitude and airspeed. What is the Angle of Attack for an aircraft? The Angle of Attack means the angle of the wings. If the Angle of Attack is too large, it can cause the wing to stop producing lift. This results in the nose of the aircraft dropping down and the plane descending. This is called a Wing Stall and should be avoided! For many aircraft, an ideal Angle of Attack is around 8-12 degrees. This provides optimal lift. Too high of an Angle of Attack (above 16 degrees), and the aircraft may stall and lose lift. Why does a Wing Stall happen? Aerodynamic forces depend on the stickiness of the gas. As the aircraft moves through the gas, gas molecules stick to the object surface. The boundary layer is the air flow that is closest to and in contact with the aircraft surface. At a high angle of attack, the boundary layer separates from the wing and is disrupted by turbulence, causing loss of lift. This leads to a Wing Stall, often simply referred to as a stall. How does a pilot recover from a stall? Pilots are always trained on how to recover safely from a stall (aka wing stall). They are taught to REDUCE the Angle of Attack by lowering the nose of the plane a bit, leveling the wings and adding power as needed. This allows the aircraft to aerodynamically recover and resume normal flight. The most important thing is to NOT increase the Angle of Attack (don’t raise the nose of the plane) and make the stall worse. MINI-QUIZ - Circle the Answer 1. True or False: A fluid is always a liquid. True False 2. True or False: A gas can be a fluid. True False 3. A stall can occur if an aircraft’s angle of attack is too steep. True False 4. When faced with a stall, the pilot should lower the nose of the plane to reduce the angle of attack. True False SUGGESTED HOMEWORK ACTIVITY for this session: Research the local air pressure (barometric pressure) of the city/town where you live. You can find it by doing a Google Search for “barometric pressure” and the name of your city/town. It is part of the daily weather report. Mini-Quiz Answer Key: 1. False 2. True 3. True 4. True A Beginner’s Guide to Aeronautics Session 7: Kites and Wind Tunnels In this class session, we explored the aerodynamics of kites and wind tunnels. Part 1: Aerodynamics of Kites Kite flying is a delicate balance between aerodynamic forces. The various parts of the kite distribute these forces. The kite is connected to the person flying the kite by the control line. The person flying the kite feels the tension in the line created by the aerodynamic forces on the kite. The place where the bridle connects to the line is the bridle point. The kite pivots about this point. It adjusts to the changing characteristics of flight. The surfaces made of paper, plastic or cloth all deflect the wind downward creating the aerodynamic forces of both lift and drag. There are many types of kite designs. Here are a few examples. QUESTION: Have you seen or flown one or more of these types of kites? List below: ___________________ ___________________ ___________________ Control Line Flying The control line is attached to the kite by a bridle knot at the bridle point. The kite rotates above the bridle point due to torques created by the forces transmitted to the control line by tension. Heavier than air, a kite relies on the motion of the wind moving past the kite to generate the LIFT necessary to overcome the weight of the kite. The movement of the air past the kite also creates DRAG, which can be overcome by the control line (string). Newton’s First Law Applied to Kites Stable flight: all forces are balanced and the kite holds a fixed altitude. Wind increases slightly: lift and drag increase since forces depend on square of velocity. Kite climbs vertically since lift is stronger than the weight of the kite. Forces acting on a kite: Weight, line tension & other aerodynamic forces. - Weight acts always from center of gravity to the earth. - Lift acts perpendicular to the wind. - Drag is in the direction of the wind - Line tension has 2 components: 1) PV = vertical pull 2) PH = horizontal pull In stable flight: The vertical direction forces equal 0. Pv + W - L = 0 The horizontal direction forces are also equal to 0. PH - D = 0 Launching a Kite! To launch a kite, we must create a LIFT force greater than the horizontal force of the wind. It doesn’t matter if the kite is pulled through air, or air blows over it. Wind at our back provides velocity. On windy days, this velocity plus a tug on line creates LIFT On less windy days, run backwards or run into the wind to create LIFT. Cruise is the altitude where all forces are balanced. To climb higher: pull on the control line to increase velocity. Part 2: Wind Tunnels Aerodynamic engineers use wind tunnels to test models of aircraft before they are produced. Special tunnels are made to see the effects of: Propulsion engineering Wing, body & tail design Icing Subsonic testing Supersonic testing Hypersonic (5 times speed of sound) testing A wind tunnel can be open, drawing air from outside into the tunnel, or closed, with the air recirculating inside the tunnel. Several skills are involved in Wind Tunnel testing: 1) Operation and design of the wind tunnel (set fan speed) 2) Aircraft modeling and instrumentation mounting 3) Test engineering and troubleshooting Parts of a wind tunnel This diagram is of a low speed closed tunnel. The Fan moves air in the tunnel. The Turning Vanes move air in the corners Before entering the test area, air passes through the Flow Straighteners. The Test Area is where the model is placed. In the Diffuser, air enters, is expanded and slowed before returning to the fan A wide variety of forces are tested in a wind tunnel. Pictured is an example of how LIFT is tested. A very complicated 6-point balance measures all the forces on the model. Lift, drag, side, pitch, yaw, roll are all measured. How to build your own wind tunnel: There are several possible ways to build your own wind tunnel, from simple to complex. Some things you will need are: 1. Source of Wind (often an electric fan) 2. Flow Straightener - several small tubes that help to remove turbulence from the wind and straighten the airflow. Can be made of pieces of plastic pipe, paper tubes or straws. 3. Test Section - a long rectangular box section where the testing will take place. Can be made of foam board or clear plastic. 4. Flow Visualization and/or Measurement Devices - to be able to see the airflow, a smoke generator may be added. To be able to measure the test performance, measurement devices may be added. Below are 3 examples of Wind Tunnel Designs with detailed instructions: https://www.instructables.com/DIY-Wind-Tunnel-3/ https://www.instructables.com/How-to-make-a-wind-tunnel/ https://www.instructables.com/DIY-Wind-Tunnel-20-Project-Paperclip/ SUGGESTED HOMEWORK & ACTIVITY for this session: Read the 3 DIY wind tunnel instructions listed above. Using them as a source of ideas, design your own wind tunnel on paper. Then, if possible, gather the materials and build your own wind tunnel! A Beginner’s Guide to Aeronautics Session 5: Model Rockets & Real Rockets In today’s session, we explored the physics and design of both model rockets and real, full-size rockets. There are many different types of rockets, including: Small models such as balloon rockets, water rockets, skyrockets or small solid rockets that can be purchased at a hobby store Missiles Space rockets such as the enormous Saturn V used for the Apollo program Rocket-powered cars, bikes, sleds, trains and jet packs Rocket-powered aircraft, including Rocket Assisted Takeoff of conventional aircraft (RATO) Rocket torpedoes Rapid escape systems such as ejection seats and launch escape systems Space probes In terms of model rockets, there are a wide variety available. Pictured (right) is an example of a compressed air rocket kit. In our next class, we will learn how to build a water bottle rocket, which can provide a fun & fascinating first rocket design and launch experience. For more advanced model rockets, we viewed various model rockets from Estes Rockets. Estes is a company that has been making model rockets for over 60 years. They sell many kinds of model rockets and engines, from beginner to advanced. Their rockets include scale models of NASA, Blue Origin and Space X rockets! Pictured below are some of their model rockets. Parts of a Model Rocket Engine In some model rockets (like the Estes rockets), the Thrust Force is supplied by a small rocket engine. The elements of a model rocket engine are illustrated above. There are 3 phases to the flight: Thrust Phase (launch and propulsion upwards), Delay (no thrust but rocket continues to coast higher to maximum altitude) and Recovery (the rocket falls gently back to Earth with a parachute). - Engine casing: made of heavy cardboard. - Nozzle: under the fins, the nozzle provides the outlet for gasses which produce thrust. - Propellent (green): A Solid Propellant is used in model rocketry. This is safer than liquid propellant. - Delay charge (blue): The length of delay is 2-8 seconds. During this phase no thrust is produced and the rocket will coast up to max altitude. - Ejection charge: Pushes out the nose cone and parachute which will ideally allow the model rocket to be recovered without damage. Parts of a Model Rocket This illustration (above) shows the position of the Parachute and other parts related to the Recovery of the Rocket. Ideally the model rocket floats down gently due to the parachute, and can be reused many times! The Ejection Charge pushes out the Nose Cone. When the Nose Cone is ejected, the parachute is released for recovery mode. Recovering Wadding is used to protect the parachute from the intense heat of the Ejection Charge. The Issue of Weather Cocking Following the liftoff of a model rocket, it often turns into the wind. This maneuver is called weather cocking. It is caused by aerodynamic forces on the rocket. Why does Weathercocking Occur? If no wind were present, the flight path would be vertical as shown at the left of the figure, and the relative air velocity would also be vertical and in a direction opposite to the flight path. The wind introduces an additional velocity component perpendicular to the flight path, as shown in the middle image. The addition of this component produces an effective flow direction shown in red. The size of angle depends on the relative magnitude of the wind and the rocket velocity. Since the effective flow is inclined to the rocket axis, an aerodynamic lift force is generated by the rocket body and fins. The lift force generates a torque which causes the rocket to rotate into the wind. ACTIVITY: NASA Interactive Model Rocket Simulations You can design and test launch a variety of rockets through these simulations (please note: these may take several minutes to load): AIR ROCKET LAUNCH INTERACTIVE SIMULATOR https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/stomp/ ROCKET MODELER INTERACTIVE SIMULATOR https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/rocketmodeler/ —------------------------------------------------------------------------------ Part 2: Full-Size Rockets Full-Size Rockets: The Fuel Problem Let’s say it takes 1 pound of fuel to put a 1 pound payload in orbit. For a 2-pound payload, you would need a pound of fuel for each pound of payload…. Then you ALSO need fuel for the fuel! The amount of fuel you need for every increment of payload grows exponentially! This is a big problem, and is known as the Rocket Equation. Rocket Parts There are 4 Major Systems in a Rocket: 1. Structural system or frame 2. Payload system 3. Guidance system 4. Propulsion system (the largest part, includes fuel and oxidizer). Fundamental Forces on a Rocket Four Fundamental Forces: Weight – depends on mass of all parts of the rocket. It is directed to the center of the earth and acts through the center of gravity of the rocket. Thrust - depends on mass flow rate through the engine & pressure at exit of the nozzle. Lift force - This force is perpendicular to the flight direction Drag – Drag is usually much greater than the lift force. Aerodynamic forces are influenced by the rockets fins, nose cone, body tube. ___________________________________________________________________ In our next session: We’ll learn how to build a Water Bottle Rocket, and we will develop our aeronautics math skills. Suggested Homework for this week: 1. Read and complete this Review Handout and try out the simulators. 2. Visit the Estes Rockets website. Which one of the model rockets is the most interesting to you? A Beginner’s Guide to Aeronautics Session 4: Baseball & Aerodynamics AERODYNAMICS is the study of forces and motion of objects as they move through the air. Aerodynamics plays a significant role in many sports, including baseball, golf, ski jumping, race cars, basketball, baseball and soccer. We can learn about many aspects of Aerodynamics by studying baseball! Imagine that this baseball, below, is thrown towards the LEFT. ACTIVITY #1: Fill-in the blanks with the forces (represented by arrows) effecting this baseball as it moves through the air. Physics of a Baseball Every part of an object will have an impact on how it moves through the air, and how the air moves around it. The stitches! They aren’t uniformly or symmetrically distributed around the ball. Each stitch and bumpy part of the ball increases the Drag. The Drag changes as the air around the ball is affected by the stitches and bumpy patches. There are many different ways that a pitcher can throw a baseball. Some factors include: - Direction & amount of spin - Direction & amount of thrust - Velocity of the air on different sides of the ball - Pressure of the air around the ball - When there are different air pressures around the ball, the ball will move towards the lower air pressure. In the picture (right), the lower pressure on the right side causes the ball to curve towards the right! Bernoulli’s Principle can help us understand the flight of a baseball. What is Bernoulli’s Principle? Daniel Bernoulli was a Swiss mathematician who lived from 1700-1782. He developed Bernoulli’s Principle, which states that: The pressure in a fluid decreases as its velocity increases. Likewise, an increase in the velocity of a fluid occurs simultaneously with a decrease in pressures. In other words: As Velocity increases, Pressure decreases As Velocity decreases, Pressure increases As Pressure increases, Velocity decreases As Pressure decreases, Velocity increases Air is considered a fluid in physics! Air is considered a fluid because it flows and can take on different shapes. As air pressure decreases, the object will move towards the lesser pressure. Often, pitchers will apply spin to the baseball. For example, think about a baseball spinning backwards while moving toward home plate, as shown above. Bernoulli’s Principle can be described in molecular terms. As the ball spins, it pushes the surrounding air in the same direction of motion. The friction between the spinning ball and the air causes the air molecules on the TOP side of the ball to move backwards. Friction also causes the air molecules on the bottom side of the ball to move forward. But since the ball is moving forwards, air molecules on the bottom of the ball that are being pushed toward home plate will collide with the air molecules the ball encounters as it flies through the air. The collisions between these air molecules will slow the velocity of the air. All those molecules colliding also creates higher pressure on the bottom side of the ball. Meanwhile, air molecules on the top side of the ball are being pushed backward by the spinning ball. As a result, they won’t collide as much with other air molecules as the ball heads towards the plate. This increases the velocity of the air on the top side of the ball. With fewer collisions, this also creates lower pressure. The ball will be lifted upwards towards the lower pressure. How does this relate to aircraft? This same principle applies to aircraft. The shape of the aircraft will affect the flow of fluid (air) around it as the aircraft moves through the air. For example, we can look at the shape of the aircraft wings. Different wing shapes will have different effects on airflow. Some will produce more lift than others. Note: The cross-section of a wing shape is called an AIRFOIL. Pictured right: Examples of different airfoils and their effect on airflows. If the velocity of the air is faster on the upper side of the wing, the air pressure on that side will be decreased and the wing will move upwards, generating lift. ACTIVITY - BASEBALL MOTION INTERACTIVE SIMULATOR We used this simulator in class, and you can continue exploring how a pitcher throws a ball by changing the values that affect the aerodynamic forces on the ball. These are the same forces creating lift and drag on an aircraft. Link: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/ballkiosk/ (Note: Please allow several minutes for the simulation to load.) ___________________________________________________________________ In our next session: We’ll learn about Rockets! Suggested Homework for this week: 1. Read and complete this Review Handout. 2. Experiment with the NASA Baseball Motion Interactive Simulator 3. Explain Bernoulli’s Principle to a family member. FILL-IN-THE-BLANK ANSWER KEY: Arrow pointing up - Lift; Arrow pointing down - Weight; Arrow pointing right - Drag A Beginner’s Guide to Aeronautics Session 3: Jet Propulsion In our last session, we learned about the Wright Brothers invention of the first powered human aircraft in 1903. It used 2 motorized propellers to generate thrust. Today, while smaller airplanes may still use propellers, most large airplanes use Jet Propulsion instead. Who invented Jet Propulsion Aircraft Engines? Dr. Hans von Ohain (Germany) and Sir Frank Whittle (England) are both recognized as being the co-inventors of the jet engine in the 1930’s and 1940’s, even though each worked separately and knew nothing of the other's work! Pictured (right): Frank Whittle adjusts a slide rule while seated at his desk at the Ministry of Aircraft Production in the UK. Jet propulsion is defined as any forward movement caused by the backward ejection of a high-speed jet of gas or liquid. For aircraft, jet propulsion means that the aircraft itself is powered by jet fuel. The world’s first aircraft to fly using thrust from a turbojet engine was the Heinkel He 178, designed by Hans von Ohain, in 1939. Pictured (right): A replica of the Heinkel He 178, first turbojet airplane.  The first British turbojet-engined aircraft, the Gloster E.28/39, was designed by Frank Whittle and took flight on May 15, 1941 (pictured left). By the 1950’s, turbojets were used by most airplane manufacturers. Summary: The 4 Main Types of Aircraft Engines are: 1) Propeller 2) Jet Engine 3) Ramjet 4) Rocket The design and use of the aircraft determines which type of engine is used. FILL-IN-THE-BLANK ACTIVITY - Which type of engine does each aircraft use? (Answers on last page of this handout) 1. Large passenger planes What type of engine? _________________________  2. Military planes What type of engine? _________________________ 3. Hypersonic aircraft (flies at supersonic speeds, faster than the speed of sound) What type of engine? _________________________ 4. Spacecraft What type of engine? ___________________ 5. Small passenger plane What type of engine? __________________________  6. Space Shuttle What type of engine? __________________________ Recall the 4 Basic Forces of Aerodynamics are: Weight (downwards motion) Lift (upwards motion) Drag (backwards motion) Thrust (forward motion) Thrust from the propulsion system must balance the Drag. To accelerate, Thrust must exceed the Drag so the plane can go faster! When an airplane cruises, the forces are balanced and it will continue cruising until a force changes. Let’s see how the 4 main different types of engines work with these Basic Forces. How Propeller Propulsion works: Propellers act as rotating wings, generating both lift and thrust through their spinning motion. An internal combustion engine turns propellers to generate thrust and lift. The propeller acts like a rotating wing, providing lift. The accelerated gas is the air that passes through the propeller - as the air is pushed backwards, the plane is thrust forwards. Propellers can have 4 to 6 blades. The blades are long, thin and twisted. How Jet Propulsion works: Hot exhaust gases are passed through a nozzle to produce thrust. But unlike a rocket engine that carries its air separately, a jet engine uses the air surrounding it as it flies. This would  not work in outer space because there is no air. The accelerated gas is the jet exhaust, which rushes backwards, creating thrust to push the aircraft forwards. How Ramjet Engines work: Hot exhaust gases flow through the nozzle. The nozzle accelerates the flow, producing thrust. To maintain flow the combustion occurs at a HIGHER PRESSURE than the LOWER PRESSURE at the nozzle exit. There is no compressor in Ramjet, unlike in turbine engines. The ramjet is a jet engine without a compressor or a turbine. It is essentially a tube through which air enters purely as a result of the plane's forward motion. At the inlet, the air hits a diffuser to create high static pressure for combustion and is slowed to subsonic speeds. Fuel is supplied and the fuel-air mixture is burned. The heated gases that result are ejected at the opposite end through the exhaust nozzle. Only used in supersonic aircraft (faster than the speed of sound, higher than Mach 1). Ramjets by definition need ram air, that is to say, air that is forced into the intake as a result of the aircraft's high speed. A reasonable starting point for this engine to work is at approximately Mach 3, and they can sustain effective propulsion as fast as Mach 6. How Rockets work: Fuel and a source of oxygen (called an oxidizer) are both stored separately. Then they are pumped together into a combustion chamber. An oxygen source is carried with the rocket since there is hardly any oxygen in space. The combustion system sends very hot gasses into the nozzle, producing thrust. Rockets use up a lot of fuel in a very short amount of time, which is why they are not used in regular aircraft. ACTIVITY - NASA JET ENGINE SIMULATOR In class, we demonstrated using a Jet Engine Simulator. You can continue experimenting with this simulator at the link below: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/enginesim/ The simulator is located part-way down the page, under the “Screen” section.Please allow several minutes for the simulation to load. ACTIVITY - NASA RANGE GAMES INTERACTIVE SIMULATOR In class, we also demonstrated the Range Games Simulator to test various types of aircraft performance. You can continue experimenting with this simulator at the link below: https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/enginesimr/ The simulator is located at the top of the page. Please allow several minutes for the simulation to load. ___________________________________________________________________ In our next session: We’ll learn about Baseball Aerodynamics and Bernoulli’s Principle! Suggested Homework for this week: 1. Read and complete this Review Handout. 2. Work with the two NASA simulators. 3. Which type of aircraft propulsion is your favorite? Explain how it works to a family member. ___________________________________________________________________ FILL-IN-THE-BLANK ANSWER KEY: 1. Large passenger planes: Jet Engine 2. Military planes: Jet Engine 3. Hypersonic aircraft (flies at supersonic speeds, faster than the speed of sound): Ramjet 4. Spacecraft: Rocket 5. Small passenger plane: Propeller 6. Space Shuttle: Rocket