BP and AP motors

BP Motors

A black powder motor has the advantage that it is easy to handle, cheap and simple to operate. All that is needed is a small igniter (usually supplied with the motor) and a suitable launch controller. Most BP motors are made in the USA by Estes. No explosives certificate is required - anyone over 18 can buy them.

Their limitation, though, is that they are only available in impulses up to E, and their performance in relation to their size and weight is poor.

details of rocket motors 

Closer view of the D12, Pro38 and Sky Ripper G63 motors

AP Motors

Ammonium Perchlorate-based motors are available in a huge range of impulses, from F through to M (at least). They provide a compact, reliable means of getting large impulses for high-power rocketry, and are the most common type used after BP. They are simple to light, needing only a commercially available igniter and a low-voltage launch controller.

AP motors do suffer from 2 major drawbacks though - they are quite expensive (an M reload costs almost £300) and the larger ones require an explosives certificate, issued by the police, to buy and store them. The motor itself typically consists of a case (often aluminium alloy, as in the pictures on this page) and a 'load' or 'grain'.

The grain is the AP mixture itself and needs to be replaced for every launch. The case is reusable. Most AP motors also use a replaceable nozzle, together with various O rings used for sealing the motor.

Most also include a delay fuse and an ejection charge - the Pro38 motor shown has an adjustable delay time, and a special tool is available to remove part of the delay fuse to achieve the desired timing.