About site: Boomerang/Science - Sports: The Boomerang Page

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Title: Boomerang/Science - Sports: The Boomerang Page An article describing why a boomerang returns, based on the aerodynamics, the shape and the throwing technique.

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Aerodynamics in Sports Equipment, Recreation and Machines - Boomerang - Instructor

The Boomerang

page 1

Introduction

boomerang_01_sma.gif WIDTH = 92 HEIGHT = 120 ALT = Various Boomerangs ALIGN = left> Most of us are familiar with the boomerang, the wonderful stick that returns when you throw it. However, most of us don't know the history of the boomerang or the complex physics and aerodynamics involved. To understand why a boomerang returns, we must look at the shape of the boomerang, the aerodynamics and physics. Finally, the correct throwing technique will be discussed.History

boomerang_02_sma.gif WIDTH = 92 HEIGHT = 120 ALT = Killer Stick ALIGN = right> The boomerang is often times thought of as a weapon. However, the boomerang has always been primarily a recreational toy. The real weapon used by the Aborigines was the killer-stick. The killer-stick shares many properties with the boomerang except one. The killer-stick does not return! The killer-stick was simply a stick honed to have a cross-section similar to a modern day airfoil. This stick actually flew through the air at high speeds. It was given a rotation at launch for stability much like the discus and frisbee of today. The killer-stick could be thrown very far and with great accuracy. The boomerang, on the other hand, is smaller and lighter than akiller-stick. There is also a more pronounced elbow between the "wings."The boomerang, as previously mentioned, was not used to kill game, but wasused to hunt birds.When a flock of birds was spotted, an Aboriginal hunter imitated the callof a hawk. The hunter would then throw the boomerang above the birds.The birds would then swoop down to elude the hawk and fly directly intothe waiting nets of the hunter.The boomerang was most likely derived from the killer-stick. Imagineyourself as an Aboriginal hunter. You've studied birds and decidedthat your killer-stick would fly faster with a sharper angle between thetwo "wings." With your newly fashioned stick, you spot yourprey and launch your weapon. Then a breeze catches your killer-stick andcarries it into the air. Then your weapon begins to turn around and flyback towards you! This certainly isn't a decipherable property in aweapon, but it does make a wonderful toy.Shape

boomerang_sma.gif WIDTH = 86 HEIGHT = 120 ALT = Boomerang Shape ALIGN = left>

boomerang_04_sma.gif WIDTH = 92 HEIGHT = 120 ALT = Right & LeftHanded Boomerangs ALIGN = right> As can be seen in the figure, the boomerang consists of a leading wing and a trailing wing connected at the elbow. Each wing has the typical cross section of a airfoil. Therefore, each wing has a leading and trailing edge arranged so as the leading edge strikes the air first as the boomerang rotates. Because of this configuration, there are right-handed and left-handed boomerangs. The figure above is a right-handed boomerang. A left-handed boomerang is simply a mirror image of the right-handed boomerang. The typical angle between the wings is 105 degrees to 110 degrees.When a boomerang is tossed in the correct manner, the wings rotate throughthe air and react to the aerodynamic and gyroscopic forces. These forcescause the boomerang to circle around and lay down as it returns, until itdescends in a horizontal hover. During the flight of the boomerang, thefollowing principles come into play: Bernoulli's relation,gyroscopic stability, gyroscopic precession, and Newton's laws ofmotion. We shall examine how these forces cause a boomerang to return tothe thrower.AerodynamicsAs the boomerang flies through the air, each wing produces lift. Onceagain, Bernoulli's principle is used to explain how the lift isformed. The air moves faster over the upper surface than the air movingover the lower surface. This means that a pressure differential existsbetween the lower and upper surface which translates into lift.A boomerang is thrown with a spin in a similar manner as the discus andfrisbee. This spin has two effects on the boomerang as it travels throughthe air. The first being a stabilizing force known as gyroscopicstability. This phenomenon has been previously discussed in the discusand frisbee sections. The second effect of the spin results in the curvedflight of the boomerang.

boomerang_05_sma.gif WIDTH = 92 HEIGHT = 120 ALT = Gyroscopic Precession ALIGN = left> The turning force imposed on the boomerang comes from the unequal air speed of the spinning wings. If we start with a stationary, spinning boomerang, both wings would produce the same amount of lift. Now give that same spinning boomerang a forward velocity and the speed of the air traveling over the wings differs. Thus, the forward moving wing experiences more lift than the retreating wing. The net result is a force which turns the boomerang. Due to a phenomenon known as gyroscopic precession, this force is felt 90 degrees from where it was applied.Gyroscopic precessionGyroscopic precession is the principle governing the "no hands"bicycleturn. When riding a bike, the spinning motion of the wheels gives thebike stability at speed. To execute a "no hands" bicycle turn, one simplyleans to the side of the direction that they wish to turn. The wheels havea delayed reaction to the force of the lean. This way, the wheels feelthe force a quarter turn from where the force was applied. So instead offalling over, the bicycle turns in the desired direction.Unlike the "no hands" turn, the boomerang experiences a continuous turn asthe force is applied for the duration of the flight. The boomerang isthrown with a slight tilt from vertical. This causes the boomerang toalso lay down as it turns. Thus the boomerang returns to the thrower in ahorizontal hover. quarter

The duration of flight is determined by the force with which it was thrownas well as the spin applied at launch. As with anything flying throughthe air, a boomerang is subject to drag and its own weight. The dragslows the boomerang down, thereby limiting the flight time. However,given enough spin and initial velocity, the boomerang might circle abovethe throwers head a few times before landing. Throwing Technique

boomerang_06_sma.gif WIDTH = 92 HEIGHT = 120 ALT = The Boomerang at Launch ALIGN = right> Now that we have a good understanding of how a boomerang works, we should also know how to properly throw a boomerang for many happy returns. A boomerang is launched almost vertically (see figure). The angle depends on the speed of the wind. If a boomerang were to be launched horizontally, it would begin to climb until the wings stalled. At this point, the boomerang would simply fall to the ground. The boomerang is also thrown at an angle to the wind. The thrower starts by facing the wind and turns about 50 degrees to their right or left, depending on whether the thrower is right or left-handed. With the proper angle to the wind, the boomerang will return to you as planned. SummaryThe boomerang is such a simple device and yet it relies on complexaerodynamics and physics. Thanks to our understanding of the boomerang,more shapes have been explored. The angle between the wings may bealtered to change the characteristics. For example, a sharper angle woulddecrease the tip speed, thus making the boomerang easier to catch. Amodern boomerang might have several wings joined at a common juncture.Alternatively, a boomerang might be fashioned to represent an object likea bird or straight-edged razor. There are even boomerangs shaped in theform of the letters of the alphabet. All of these boomerangs use the sameprinciples discussed above to return to the thrower at the end of itsflight.

boomerang_07_sma.gif WIDTH = 92 HEIGHT = 120 ALT = Boomerang Designs> Chapter Home

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An	article	describing	why
a	boomerang	returns,	based	on
the	aerodynamics,	the	shape	and
the	throwing	technique.

http://wings.avkids.com/Book/Sports/instructor/boomerang-01.html

Sports: The Boomerang Page 2008 November

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An article describing why a boomerang returns, based on the aerodynamics, the shape and the throwing technique.

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