Words and Terms We Use

Aero drag, or aerodynamic drag, is a force that opposes an object moving through the air and slows it down. If an object is flat or an unusual shape, it tends to have a higher aero drag, as air cannot easily move around it or out of its way. Think of it as you riding your bike into a strong wind.

Aerodynamics is the study of how air moves around objects. The rules of aerodynamics explain how an aircraft is able to fly. Understanding aerodynamic principles was crucial in designing Aussie Invader 5R, as we want to keep it on the ground, and definitely not fly like an aircraft.

Altitude refers to the height of something, typically how far it is above the ground or sea level. The higher the altitude, the less dense the air is as it has less weight of the air above pushing it down. Yes, although air appears to be very light and floats, it does have a weight.

Avionics refers to the electronics that control electrical devices in aircraft. Aussie Invader 5R will travel extremely fast and experience a lot of heat and vibration, so the electrical equipment will need to be very shock-proof and built to a higher standard than that of a normal car.

Our bi-propellant rocket uses two different liquids: a fuel and an oxidiser. When fuel burns, it needs oxygen to do this, so we also have to carry a liquid oxidiser. The word “Bi” means two, like a bicycle, which has two wheels. We use two propellants in our rocket engine.

Although we refer to carbon fibre on its own, it really should be carbon fibre composite. A composite is the combination of two materials, in this case, carbon fibre and a resin (glue). This creates a composite material that is very strong, rigid and lightweight.

The drag coefficient (Cd) is a measure of how much an object resists movement through air or water. It’s a number that helps us understand how streamlined an object is. Lower numbers are more streamlined, and higher numbers indicate more resistance (less streamlined).

G-force, or gravitational force, measures the force of acceleration and deceleration on an object, which could be your body. So, it’s how much you feel pushed or pulled when you speed up, slow down, or change direction. Two G is twice the normal force of gravity we feel standing on Earth.

Hydraulics uses high-pressure oil to create a powerful force that is needed to open our air brakes at high speed and power our steering mechanism. When we open our air brakes, they will experience a force of seven tonnes of air pressure. Hydraulics allows small forces to create large movements, like lifting a car with a hydraulic jack.

An inert gas is a gas that doesn’t mix or react easily with other substances. We need this because the rocket engine’s fuel is volatile. If we were to use a volatile gas to push the propellant module pistons forward, and it were to leak past the piston’s seals and mix with the fuel, it could cause an explosion.

A jet engine sucks in air at the front and compressing it very tightly. Fuel is sprayed in and ignited, creating super‑hot, high‑pressure gas. This gas rushes out the back of the engine’s exhaust nozzle at incredible speed, pushing the engine—and anything its attached to forward.

Lift is the opposite of downforce and is an upward-acting force that opposes gravity. It’s generated by the movement of air over and around an object, creating a pressure difference that results in an upward force. Some surfaces on Aussie Invader 5R may generate lift, which we must minimise to keep the car safely on the ground.

The Mach number is the ratio of the speed of Aussie Invader 5R compared to the speed of sound. If something is travelling at less than Mach 1, it is at subsonic speeds; at close to Mach 1, it is transonic, and at Mach 1 and above, it is at supersonic speeds.

Newton’s third law of motion explains how Aussie Invader 5R works. For every action, there is an equal and opposite reaction. So the hot gas being expelled out of the rocket engine’s nozzle pushes Aussie Invader 5R forwards with the same force. The faster the gases are expelled, the faster the car travels.  

A rocket needs to burn fuel to create thrust, but the fuel can’t burn on its own—it needs an oxygen source. The oxidiser is the source of oxygen, which it carries with it. That is why rockets can function in space, where there is no air to draw oxygen from.

A playa, also known as a lakebed, is a dry, vegetation-free, flat area at the lowest part of an undrained desert basin. These basins can flood during wetter periods and then evaporate, leaving behind a sun-baked hard surface of sediments like clay, silt, and sand. This surface is ideal to run Aussie Invader 5R on.

Propellant is the term used to collectively describe both the fuel and the oxidiser needed for combustion in a rocket engine. While “fuel” refers to the substance that burns, a rocket also requires an oxidiser to allow that burning process to take place. The propellant “propels” Aussie Invader 5R forward.

Radar (RAdio Detection And Ranging) uses electromagnetic waves—usually short-wavelength waves called microwaves. These waves bounce back from solid objects in their path, the way sound waves bounce back from an object and produce an echo. We use this to see objects in the distance.

Regulators are very important in liquid bi-propellant rocket engines. They control the flow rate of the fuel and oxidiser into the rocket engines’ combustion chamber. The regulators regulate the flow of propellant into the rocket engine, helping to keep it working safely and efficiently.

In a liquid rocket, the fuel and oxidiser are stored separately and pumped into the combustion chamber where they burn. You can stop a liquid rocket by closing the valves. In a solid rocket, the chemicals are pre-mixed and packed into a cylinder. Once a solid rocket is lit, you can’t stop it. It’s like a big firework.

Subsonic means moving slower than the speed of sound (Mach 1). The speed of sound in air is 1,230 km/h (765 mph) at 20 °C (68 °F), as it varies with temperature and altitude. So, when you ride your bike to school, you are travelling at a subsonic speed, unless you pedal too fast. ;-)

Supersonic speed refers to the speed (velocity) of something that can travel at or faster than the speed of sound. This means that the object is moving at a rate that exceeds 1,230 km/h or 765 miles per hour (mph) at sea level at 20 °C (68 °F).

Thrust-powered vehicles usually refer to aircraft and rockets. However, it is any vehicle that is powered by a jet or rocket engine. In drag racing and land speed racing, there are some cars and motorcycles that use jet and rocket engines, like Aussie Invader 5R.

Transonic is when an object moves at speeds close to supersonic (Mach 1). At transonic speeds, it feels like pushing through an invisible wall. This “wall” is called the sound barrier. It happens because the air around an object starts to behave very differently.

X-rays are powerful waves of energy that are often used in hospitals. However, X-rays can be used to find imperfections in metal. This technique is called industrial radiography, which uses X-rays to penetrate metal. We used this to inspect our solid blocks of aluminium for flaws or cracks before machining them.