YEOT Spring 2015 Webinar 5: Catapults and Trebuchets

Ancient EngineeringTrebuchet

So what's a catapult? Review

Catapults can be split into three categories:

● Traditional Catapult● Ballista● Trebuchet

Trebuchet

A trebuchet launches a projectile from a sling on a pivoting beam.

HistoryThe 1st catapults, designed by the Greeks and Romans, date back to the 4th century BC.

Traction trebuchets originated in China and date back to around the same time.

History

We will be focusing on counterweight trebuchets, first designed in the 12th century.

History

Descendents of the first Chinese trebuchets, these siege weapons resulted from advancement by the Islam and Byzantium civilizations and further developmentin Western Europe.

How they work

A counterweight rotates the beam through an arc that releases the projectile.

TrebuchetThe counter weight is hoisted into air and is held in place, usually by a release system attached to the opposite end of the arm.

Counter weight

Release system

TrebuchetRelease system activated.Counter weight drops, swinging arm with sling attached.

TrebuchetAs sling follows its arc, one end is released

Trebuchet

Trebuchet

Can you guess some of the main factors that affect trebuchet performance?

Major factors to consider

● Counterweight Mass● Counterweight Height● Projectile Mass● Sling Length● Launch Angle● Wheels vs. hinged counterweight

SimulationLet’s see how some of these factors affect performance!

www.globalspec.com/trebuchet/

How they work

● It is powered by gravity.● Generally, its force is equal to “4 to 6 times

of the counterweight arm’s length”● The sling acts as a secondary fulcrum.

Review: Gravitational Potential Energy

The gravitational potential energy of an object can be found by multiplying the weight of the object by how high it is off the ground.

PEGravitational = weight * height

Gravitational Potential EnergyEnergy stored by trebuchet is determined by:

● Weight of Counter Weight

● Height Counter Weight is hoisted

How they work

● It is powered by gravity.● Generally, its force is equal to “4 to 6

times of the counterweight arm’s length”● The sling acts as a secondary fulcrum.

Energy

Gravitational energy stored by hoisted counter weight is translated into rotational kinetic energy of the sling on the arm

Rotational Kinetic Energy

The rotational kinetic energy is dependent on the length of the arm and the weight of the counterweight.

This is because of torque, or rotation around a fulcrum

**In this case, the force is the weight of the falling counter weight

**

Rotational Kinetic Energy

Force: the weight of the falling counter weight

FulcrumDistance

How they work

● It is powered by gravity.● Generally, its force is equal to “4 to 6 times

of the counterweight arm’s length”● The sling acts as a secondary fulcrum.

Sling

The sling releases when a certain angle α is reached. At this point the ring connected to the sling slips off and the projectile is launched.

Sling

Here we get the second fulcrum.

Virtual Trebuchet

http://www.virtualtrebuchet.com

A much more intricate simulator

Cd Trebuchet

You will get a chance to build this during lab.