Practice Tests : Raining Forests : Project Earth : Discovery Channel

Raining Forests Dummies' Guide

Practice Makes Perfect

Testing for Velocity, Speed and Drag

There are several factors that affect how objects behave in freefall and will be distributed on the ground when released from an aircraft. All these will need to be taken into account when designing an aerial reforestation mission. The two main factors that the experiment will be testing are aircraft velocity and altitude.

Velocity effects the distribution of objects on the ground. The higher the velocity, the bigger the spread in the direction of travel of the aircraft. This is providing that the objects are released in a stream and not in one load. This is because velocity = distance/time. The faster the aircraft is moving, the more distance there will be between one falling object and the next one following it.

Altitude affects distribution for two main reasons: First, the higher the altitude, the greater the spread of objects on the ground. Any object falling from the sky will be effected by imperfections in the atmosphere and wind. The higher the altitude of the aircraft, the longer the objects are in flight and the more they will effect and spread apart by atmospheric imperfections. Second, wind speed increases with altitude. The higher the altitude, the higher the wind speed and hence the wider the distribution of the objects. The prevailing wind speed and direction must always be measured on the day of the drop and factored into the flight plan to ensure proper distribution.

Testing the Projectile

The pneumatic mortar fires a projectile using air pressure. The device is calibrated so that different values of air pressure can represent different terminal velocities.

The terminal velocity can be fed into the pneumatic mortar for each of the canister designs to be tested. The canister is then fired into the mud to see how it survives and behaves as it hits the ground.

During the skydiving test, the aerodynamics of the canister is improved by the addition of a streamer tied to the top of the wax ball. This is because the streamer has a lot of friction and surface area and so has more drag than the rest of the canister. This means that the object will always fall with the canister underneath and the streamer dragging behind, meaning that the canister should fall the right way up.

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Project Earth

Lab Book: Raining Forests

Raining Forests Dummies' Guide

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