Aerodynamics and Speed

Hypersonics

• Flight faster than Mach 1 is called Supersonic, up to Mach 5.
• Aircraft flying at Mach 5 and above is considered Hypersonic.
• Mach 5 = approximately 3,800 miles (6,116 km) per hour.
• At Low Hypersonic Speeds (Mach 5 up to 10), molecular bonds vibrate, changing 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 = approximately 7600 miles (12,300 km) per hour.
• Hypersonic aircraft have to be built to withstand extremely high heat and turbulence of the air flow.

Use Cases for Hypersonic Flight

• Use Case #1: Re-entry from Space Orbit (Hypersonic Re-Entry)
  • Spacecraft re-entering the Earth's atmosphere travel at speeds near 17,500 mph, with a Mach number of nearly 25.
  • The temperature of the flow is so great that the chemical bonds of the molecules of the air are broken, producing an electrically charged plasma around the aircraft.
• Use Case #2: Hypersonic Cruise
  • Hypersonic cruise aircraft and cruise missiles fly at the lower limits of hypersonic, from Mach 5 to 10.
  • Modern hypersonic aircraft are powered by air-breathing ramjet and scramjet propulsion systems.
• Use Case #3: Airbreathing Hypersonic Accelerator
  • Hypersonic accelerators can be used to launch a vehicle into orbit in one single stage.
  • They can also be used as the first stage of a two-stage booster to launch a vehicle into orbit.

Compressible Aerodynamics

• High speed aerodynamics is a special branch of aeronautics that considers the compressibility of air.
• Compressible Aerodynamics is categorized by Mach Number, which is the ratio of the speed of the aircraft to the speed of sound.
• The speed of sound varies depending on temperature, atmospheric pressure, and compressibility of the air.
• At high 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.

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.
• Thermodynamics is relevant to aeronautics in many situations, especially at very high speeds, where the energy compressing the fluid (air) increases the temperature at the surface of an aircraft.

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.
• 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.

Electric Aviation Innovations

• Electric-powered aircraft are being developed to reduce carbon emissions and pollution.
• Electric motors run on electricity and are more energy-efficient than traditional fossil fuel-based engines.
• Electric-powered propeller planes use an electric "engine" instead of an Internal Combustion Engine.
• Researchers are working on developing new types of "Jet Engines" that are powered by electricity.

Aircraft Motion and Aerodynamics

• Aircraft flight involves a solid object (the plane) interacting with a fluid (the air).
• The study of how fluids and solids interact is called Fluid Dynamics.
• A fluid is defined as a substance that has no fixed shape and yields easily to external pressure.
• The force on an aircraft moving through the air is equal to the pressure multiplied by the area of the aircraft body.
• Air pressure is measured by a Pitot Tube, which can determine the plane's altitude and airspeed.
• The Angle of Attack means the angle of the wings, and if it's too large, it can cause the wing to stop producing lift.### Aerodynamic Forces
• Aerodynamic forces depend on the stickiness of the gas and the movement of the aircraft through the gas.
• Gas molecules stick to the object's surface, creating a boundary layer 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 and a wing stall.

Recovering from a Stall

• To recover from a stall, a pilot must reduce the angle of attack by:
  • Lowering the nose of the plane
  • Leveling the wings
  • Adding power as needed
• This allows the aircraft to aerodynamically recover and resume normal flight.

Kites and Wind Tunnels

Aerodynamics of Kites

• Kite flying is a delicate balance between aerodynamic forces.
• The kite's surfaces deflect the wind downward, creating lift and drag forces.
• There are many types of kite designs.

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.

Forces Acting on a Kite

• Weight: acts from the center of gravity to the earth
• Lift: acts perpendicular to the wind
• Drag: acts in the direction of the wind
• Line tension: has two components, vertical pull and horizontal pull

Stable Flight

• In stable flight, the vertical direction forces equal 0: Pv + W - L = 0
• In stable flight, the horizontal direction forces also equal 0: PH - D = 0

Launching a Kite

• To launch a kite, a lift force greater than the horizontal force of the wind must be created.
• This can be done by pulling the kite through the air or by wind blowing over it.

Wind Tunnels

• Aerodynamic engineers use wind tunnels to test models of aircraft before they are produced.
• Wind tunnels are used to test the effects of propulsion engineering, wing, body, and tail design, icing, and subsonic, supersonic, and hypersonic testing.

Parts of a Wind Tunnel

• Fan: moves air in the tunnel
• Turning Vanes: move air in the corners
• Flow Straighteners: air passes through before entering the test area
• Test Area: where the model is placed
• Diffuser: air enters, expands, and slows before returning to the fan

Building a Wind Tunnel

• There are several ways to build a wind tunnel, from simple to complex.
• Materials needed include:
  • Source of wind (often an electric fan)
  • Flow Straightener (e.g., plastic pipe or straws)
  • Test Section (e.g., foam board or clear plastic)
  • Flow Visualization and/or Measurement Devices

Model Rockets

• There are many types of rockets, including small models, missiles, space rockets, and rocket-powered vehicles.
• In model rockets, the thrust force is supplied by a small rocket engine.

Parts of a Model Rocket Engine

• Engine casing: made of heavy cardboard
• Nozzle: provides the outlet for gasses that produce thrust
• Propellant: a solid propellant is used in model rocketry
• Delay charge: the length of delay is 2-8 seconds
• Ejection charge: pushes out the nose cone and parachute

Parts of a Model Rocket

• Parachute: allows the model rocket to float down gently
• Nose cone: ejected by the ejection charge
• Recovery wadding: protects the parachute from the intense heat of the ejection charge

The Issue of Weather Cocking

• Weather cocking occurs when a model rocket turns into the wind after launch.
• Caused by aerodynamic forces on the rocket.
• The wind introduces an additional velocity component perpendicular to the flight path, producing an effective flow direction that is inclined to the rocket axis.

Aerodynamics in Other Sports

Baseball

• Aerodynamics plays a significant role in baseball.
• The stitches on a baseball can increase drag.
• The drag changes as the air around the ball is affected by the stitches and bumpy patches.

Bernoulli's Principle

• States that the pressure in a fluid decreases as its velocity increases.
• Applies to air, which is considered a fluid in physics.
• As air pressure decreases, the object will move towards the lesser pressure.

Jet Propulsion

• Jet propulsion is defined as any forward movement caused by the backward ejection of a high-speed jet of gas or liquid.
• Invented by Dr. Hans von Ohain and Sir Frank Whittle in the 1930s and 1940s.
• The first aircraft to fly using thrust from a turbojet engine was the Heinkel He 178, designed by Hans von Ohain, in 1939.### History of Aircraft Engines
• The first British turbojet-engined aircraft, the Gloster E.28/39, was designed by Frank Whittle and took flight on May 15, 1941.
• By the 1950s, turbojets were used by most airplane manufacturers.

Types of Aircraft Engines

• There are four main types of aircraft engines: Propeller, Jet Engine, Ramjet, and Rocket.

Propeller Engines

• 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, which is pushed backwards, creating thrust to push the plane forward.

Jet Engines

• Hot exhaust gases are passed through a nozzle to produce thrust.
• Jet engines use the air surrounding them as they fly, unlike rocket engines that carry their own air.
• The accelerated gas is the jet exhaust, which rushes backwards, creating thrust to push the aircraft forward.

Ramjet Engines

• Ramjets are used in supersonic aircraft (faster than the speed of sound, higher than Mach 1).
• They work by using the forward motion of the aircraft to force air into the intake, which slows to subsonic speeds.
• Fuel is supplied and burned, producing heated gases that are ejected through the exhaust nozzle.
• Ramjets require a minimum speed of around Mach 3 to work effectively.

Rocket Engines

• Rockets use fuel and an oxidizer, which are stored separately and pumped together into a combustion chamber.
• The combustion system sends hot gases into the nozzle, producing thrust.
• Rockets carry their own oxygen source, as there is little oxygen in space.
• Rockets use up a lot of fuel in a very short amount of time, making them unsuitable for regular aircraft.

Forces of Aerodynamics

• There are four basic forces of aerodynamics: Weight (downwards motion), Lift (upwards motion), Drag (backwards motion), and Thrust (forward motion).
• Thrust from the propulsion system must balance the Drag to maintain steady flight.
• To accelerate, Thrust must exceed the Drag, allowing the plane to go faster.