The Tokyo Olympics were epic. Especially for Indians, who watched the entire men’s javelin throw event. Neeraj Chopra’s second throw, which secured his gold medal, was a sight to behold. Throwing an object weighing 800g across the field for 87.58m is no mean feat. It made me ponder upon the aerodynamics of a javelin and techniques related to it.

Has it always been the same?

In 1984, German athlete Uwe Hohn threw a javelin a distance of 104.3m, thus becoming the only athlete to throw a javelin crossing the 100m mark. His impressive throw can be partly attributed to the fact that the javelins of that era were designed to generate aerodynamic lift- just like a wing- which made them fly longer.

However, this aspect had its shortcomings

• The aero dynamicity of javelins made way for flatter throws thus making it difficult to precisely measure the location when they eventually hit the ground. This would often lead to bitter outcry between the players and officials when these throws were deemed invalid.
• With athletes breaching the 100m boundary in javelin throw, there was a factor of the danger of javelins going past the size of ‘normal’ stadiums and into the crowds!!

2 years later, the IAAF decided to redesign the rules of javelin design.

The IAAF technical committee redesign saw the centre of mass moved 40mm forward from the centre of pressure- the point where aerodynamic lift and drag forces act. The tip of the javelin was modified to be blunter and less aerodynamic. These changes mean the javelin travels a shorter projectile distance and descends at a steeper angle, helping the javelin stick into the ground rather than simply laying down and avoiding flat throws.

It brought in a new challenge to the athletes, to push their limits. Also, it was economically feasible for the sport to remain in the stadium for many reasons, including TV viewership.

The original javelin until 1986

The redesigned javelin, introduced in 1986

Deep dive:

Let’s start with the approach. The primary reason for the run-up in the javelin throw is to build up the momentum, which is transferred to the javelin. To provide maximum momentum, athletes start slow and build upon their strides quickly. On their final stride, they need to produce high ground reaction forces and throw the javelin in a short time, similar to releasing a stretched-out rubber band.

Let’s now focus on the aerodynamics of the javelin. Basic physics tells us the optimal angle of release is 45 degrees for maximum range but turns out athletes try to perfect the release close to 36 degrees? This is because the release point of a javelin is 1–2 m above the ground but the javelin needs to land in the ground, which is on a lower plane. 45º is true if the release and landing points are on the same plane.

The modern javelin is designed such that the centre of pressure(cop) is behind the centre of gravity(cog). As the athlete throws the javelin, they exert an angular velocity, otherwise known as a pitching moment. The rotation stabilises the javelin in flight. The difference between the cop and cog induces a nose-down pitching moment, thereby reducing the flight time of the javelin. However, the centre of pressure remains behind the centre of gravity and therefore the nose-down pitching moment remains constant during the flight.

The flight pattern of the original javelin

The flight pattern of the current javelin

The point in flight when the nose starts to point down occurs more prematurely than with the previous javelin design, thus it’ll descend earlier and hence travel a shorter distance. The blunter tip introduced as part of the redesign means the shape of the javelin is much less aerodynamic. This creates increased drag forces which slow the javelin down, further reducing its flight distance. The negative pitching causes the nose to point down earlier and curbs flight distance. During the descent phase, its nose points down, meaning the javelin sticks in the ground rather than simply falling out of the sky as before- bringing an end to the previous disputes between competitors and officials.

Following the redesign of the javelin in 1986, the current WR was made a decade later by Jan Železný with a throw of 98.48m. The redesign has prompted athletes to adopt new techniques of throwing with many breaching the 90m+ mark. With a better understanding of aerodynamics, consistent practice, and perfect outdoor conditions, one can aim to break the new world record.

Author: Prayag Mohanty
Poster Credits: Prayag Mohanty
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References:

1. Clarkson, Sean. “The Story of the Javelin- Bringing it Back Down to Earth.” Engineering Sports, Centre for Sports Engineering Research, 21 September 2012, https://engineeringsport.co.uk/2012/09/21/the-story-of-the-javelin-bringing-it-back-down-to-earth/.
2. Jimbo. “How to throw a javelin really far.” Canny Engineering, 10 March 2019, https://cannyengineering.wordpress.com/2019/03/10/how-to-throw-a-javelin-really-far/.
3. Lenord, Daniel. “Javelin.” Physics and Olympics, University of Alaska Fairbanks, 2002, http://ffden2.phys.uaf.edu/211_fall2002.web.dir/daniel_lenord/javelin.html.