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Javelin

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ellylles
869376.  Thu Dec 08, 2011 11:58 am Reply with quote

The javelin first appeared in competition in the ancient games in 708 B.C. Originally there were two events for the javelin: target throwing and distance throwing using a sling. By 1780, the javelin was adopted as an event by the Scandinavians. The current one-handed throwing style whilst on the run was adopted at this time.

In 1953, a hollow javelin was invented by Franklin Held. Since the javelin has a standard weight, the surface area was increased. This, in turn, increased the javelins flight capability. Another characteristic of this javelin was that it landed horizontally. In 1966 the javelin was thrown over 100 meters (328 feet) by a Spaniard who employed a discus style turn before the throw. This throwing style was deemed unsafe and subsequently banned by the International Amateur Athletic Federation (IAAF). The 100 meter mark was once again broken in 1984. The IAAF then adopted new rules to ensure shorter flight times.

By examining the aerodynamics of the javelin, we will begin to understand how a javelin might be designed to limit the time of flight. First of all, a javelin does not produce lift in the same manner as a discus. As the air travels around the shaft the flow tends to separate on the upper surface. One normally thinks of separation as increasing the drag force. That is what happens here, only the direction of the force is opposite that of the gravitational force. Therefore, the separation of the flow from the upper surface of the javelin actually increases the flight time.
The modern javelin is designed such that the center of pressure is behind the center of gravity. This induces a nose down pitching moment, thereby reducing the flight time of the javelin. The location of the center of pressure will vary in flight. However, the center of pressure remains behind the center of gravity and the nose down pitching moment remains throughout the flight.
The nose down pitching moment of the javelin also ensures that the javelin lands point first. A point first landing makes the javelin a safer event as well as making it easier to measure the distance of a given throw. Since the javelin can no longer slide across the ground, there is no question about how far the javelin was thrown. The javelin also experiences a spin about its longitudinal axis during flight. This spin can be as high as 25 revolutions per second. This spin tends to stabilize the javelin in flight. Another phenomena of the javelin in flight is an oscillation about the length of the javelin. This oscillation has a frequency of about 25 hz. The oscillation is detrimental to the flight of the javelin and therefore needs to be minimized by the thrower. This is done by ensuring a delivery which is in the same vertical plane as the flight path of the javelin.

 
Jenny
869381.  Thu Dec 08, 2011 12:06 pm Reply with quote

Thanks ellylles - am I understanding you correctly if I say that the design ensures a shorter distance is travelled than with a design that enables the javelin to travel further but would make it land horizontally and slide across the ground rather than landing point first and sticking into the ground?

 
suze
869398.  Thu Dec 08, 2011 12:37 pm Reply with quote

I hope so, because that's how I'm understanding it as well.

It's much easier to measure the length of the throw if the point sticks into the ground - there were disputes as to where the javelin had really landed when it landed flat and then slid.

The other main point in re-specifying the javelin from time to time is safety. In the early 80s, distances were getting such that it mightn't have been all that long before an athlete threw the spear into the stands at the far end of the stadium, with potentially horrific consequences.

Now, a question. Suppose you were to throw a javelin the wrong way around (i.e. with the end that is meant to stick into the ground to the back). Would the javelin turn itself around in mid-air, and still land pointy end first?

 
ellylles
869411.  Thu Dec 08, 2011 1:41 pm Reply with quote

Good question. I don't know, but would it depend on how high it was thrown... like the toast-always-landing-butter-side-down myth?

 
gerontius grumpus
871700.  Mon Dec 19, 2011 1:14 pm Reply with quote

Mustn't forget the Gloster Javelin fighter.
My father was a technical author in the design office at the Gloster factory.
I've still got a javelin service manual that he wrote.

 
Spud McLaren
871921.  Tue Dec 20, 2011 3:13 pm Reply with quote

Nor the Jowett Javelin, a product of the once-flourishing British car industry.

 

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