10 Aeronautics
Cat Kutay
The ability of science to understand and manipulate the world is exemplified in our engineering. All civilisations have developed technology to suit the world they live in and to assist them to live a life they value. The technology that First Nations Australians developed not only had their own features unique to the culture, they also embraced principles that were valued by western cultures, such as aerodynamics and flight.
David Unaipon has been recognised on Australia’s $50 note since 1995. He lodged 19 provisional patents during his life which he could not afford to fully patent, including shearing blades that converted a curved motion into the straight line movement which is the basis of modern mechanical shears. He wrote prolifically, and conceptualised the helicopter two decades before it became a reality. Three elements were regularly referred to in the press during his life: his sheep shearing innovations, his basic design for a helicopter based on the motion of the boomerang, and his interest in the then entirely theoretical field of laser light. In a 1914 account Unaipon gave to the Daily Herald he suggests:
“An aeroplane can be manufactured that will rise straight into the air from the ground by application of the boomerang principle. The boomerang is shaped to rise in the air according to the velocity with which it is propelled, and so can an aeroplane” (Unaipon, Daily Herald 1914).
A functioning helicopter did not appear until 1936, however the concept produced by Unaipon has been shown to work by students’ projects at various institutions including Deakin University. The boomerang is an aerofoil design which provides the lift to enable it to fly long distances. By pairing two boomerangs and combining with motorised energy to rotate the blades, Unaipon provided the basic design of the rotor now used in helicopters.
The principle of aerofoils is important for lift in large aircraft and can provide direct lift when rotated rapidly in a circle. For more analysis of the flight path of a returning boomerang see this paper by Nicholas Landell-Mills (2019) on How boomerangs fly according to Newtonian mechanics.
On the boomerang, the aerofoil design is created by the carver who whittles the wood into the uneven profile that creates the pressure difference around the blade. The amount to remove from the faces and the amount to bend the blades come from good judgement of how to affect the flight. The carver is a person skilled in the design and balance of a boomerang, however nowadays they are often carved by programs from plywood or moulded in plastic.
The second aspect of the flight is the curvature of the path, which is created by the gyroscopic procession. The uneven lift between the two arms of the blade tries to tip the boomerang over, but just like leaning a moving bike over makes it turn in an arc. When the boomerang spins the tipping force between the blades is at an angle to its flight plane. This curves the boomerang’s flight.
The angle of attack on a boomerang is the angle between the incoming airflow and the plane surface of the boomerang. The angle of attack affects the boomerang’s lift and stability. It also affects the angle of curvature of the flight path. The greater the angle of attack will:
- Increases lift
- Reduces spin rate
- Creates a lower, circular flight path
- Makes the boomerang more stable in the wind
It is not possible to study the boomerang in flight without understanding the aspects of the design that are balanced to achieve its manufacture. So students need to find suitable wood, carve the shape, adjust the curve and fly this versatile and portable technology, which is alo used for digging and rhythm sticks.
Shaping a boomerang
Manufacturing a boomerang requires selecting the wood you will use, with the correct angle of the wooden arms, or bending this wood through soaking in water and using steam. Then there is the angle of the arms above or below the horizontal or dihedral. Bending the arms will affect the manner in which it hovers, the distance it will travel and the path of your boomerang. See some comments on the link here.
Boomerangs are built to return, when used to frighten animals into a net or trap, or as non-returning, when designed to strike an animal hard. These have different designs to suit their function, where non-returning boomerangs are longer, straighter and heavier. The curvature of the return depends on the angle of attack and the curve of the boomerang including the warping or sanding of the opposing arms of the boomerang to make dihedral lift.
For the Aboriginal people making these aerofoils, the knowledge of how to adjust the size, horizontal shape (such as the slope of the front of the arms) and curve of the arms to suit their own throwing style and needs was embedded knowledge that would be shared with young learners in practical settings.
Exercises
Invite a local person with throwing skills to your class. This can be spear or boomerang.
- What material is used to make the artefact?
- What techniques do you need to design that artefact?
- What techniques do you need to throw the artefact?
- How can you change your throw or the artefact to make it easier to throw, or the throw range greater?
Throwing your boomerang
The path of a returning boomerang is created by a number of forces. This is an example of gyroscopic processsion. When thrown, the boomerang receives angular velocity at right angles to its path (spin angular velocity). The cross section of the boomerang is an aerofoil which reduces air presure on the top side when moving to give it lift. These forces combine to create a torque (precession torque). The angle between these forces can vary (see diagram above). This is perpendicular to the spin velocity and will be clockwise or counterclockwise depending on the throw. This gives the circular path.
There are many ways to share skills and enable people to learn your skills, or for you to set up training for yourself that you need in your career. You can consider what ways you learn, what is best for you to remember and understand a lesson.
Then consider how this varies with the different topics you learn. What modes of learning you use and how this depends on the content or skill you are learning.
Exercises
Consider what ways you have been taught skills such as these, what was the context given and how were they repeated to help you remember:
- A mathematical concept
- A physics equation
- A sports skill
- How to do landcare or other environmental knowledge
References
Coloarado Boomerangs. (n.d.). Tuning Your Boomerang. https://boomerangs.com/pages/tuning-your-boomerang
Landell-Mills, N. (2019). How boomerangs fly according to Newtonian mechanics. https://www.researchgate.net/publication/337673585_How_boomerangs_fly_according_to_Newtonian_mechanics#fullTextFileContent.
Nave, R. (n.d.). Boomerang. http://hyperphysics.phy-astr.gsu.edu/hbase/brng.html#brng
