It’s not ‘Rocket Science’...Well actually, this page is!

Rockets have a well-established place in pyrotechnic history with roots in the Middle East where they were used as weapons. In Europe rocket manufacture was well established in the Middle Ages and the word “rocket” is believed to be derived from the similarity of the rocket attached to its stick to the appearance of a military lance with its protective piece of wood on the point, as was the custom in mock combat. This device was known as a “rockette”, an Italian diminutive of “rocca”, a type of staff.

All rockets, from small firework rockets to the biggest rockets used to launch satellites into orbit, have four basic components in common:

  • A case or rocket motor
  • A “choke” or venturi
  • A propellant charge
  • A flight stabilising device

You will notice that the fuse of the rocket terminates at a small hole. Behind this is the motor composition, a fast mix which burns rapidly, producing a large volume of gas which fills the motor chamber. As the pressure at the nozzle decreases the velocity of the gases increases as it passes through. The Venturi effect. Being a reaction motor the momentum of the rocket must equal the momentum of the escaping gases. Variations on the formulation of gunpowder are used for traditional firework propellants and the presence of free charcoal in the mix helps produce the distinctive, beautiful gold tail.

There is a lot going on inside a rocket motor once the main composition takes hold. Simple rockets have a charge pressed in under high pressure, but the burning surface it quite small and we need to generate a lot of gas very quickly. To get round this, more powerful rockets have a central hole created by a cone shaped spindle which is inserted in the tube prior to charging. Now when the rocket is ignited the fire can travel quickly up the cone and burn a lot of composition very rapidly.

So now we have lift off, but how do we make the rocket go straight up? The stick of a rocket provides the stability. When you hold your rocket try balancing it on your finger somewhere near the back of the motor. The centre of gravity should be somewhere here. The weight of the stick counterbalances the weight of the motor and payload. When exiting the launch tube, the stick ensures that the rocket starts its flight path upright. Sticks help to maintain a straight flight but will turn into the wind due to the unequal pressures on the stick.

As the rocket motor is exhausted the flame transfers to the payload in the star pot and ignites the contents and the bursting charge which breaks the star pot.

Construction drawing of a firework rocket

Our premium German made Raptor rockets are pressed into aluminium casings which allow for ease of production and simpler blackpowder based compositions. This method of manufacture makes for easier to handle rockets, good payloads and most importantly safe, consistent results in terms of flight characteristics. The venturi is incorporated in the casing. The casing is put into a paper tube after filling and then the star pot is added.

Modern rockets can come in all sorts of shapes and sizes. A lot has been made of large heads and the idea of shell type construction. On our product information pages we state the Powder Weight. This is a key indicator for rockets. There is a legal maximum of 200g for the motor and contents combined. A large headed rocket can only have up to the legal maximum Net Explosive Content (NEC) so don’t be fooled by the myth that bigger is always better. For example, a well know brand of rocket ‘War Hawk’ (which we do not sell) has an NEC per rocket of 60g per rocket but our premium Raptor rocket has up to the legal maximum allowance which is 200g. These rockets are full of colour, not packaging and plastic and are as close to a professional display shell as you can buy as a consumer. When comparing rocket performance against price it is worth remembering that you get what you pay for. In our opinion Raptor are the best on the market.

We have actively tried to buy fireworks, including rockets, with as little plastic in them as possible and there is a tremendous effort by some suppliers to remove plastic from fireworks completely. At HEX we welcome this move and will continue to work with suppliers towards this aim. Next time you look at a rocket think about how much plastic is in it and how much the star pot packaging weighs. All the added weight must be countered by the thrust provided by the motor which in turn lowers the amount of weight available for the effects.

Reference source: Rev. R Lancaster MBE, Fireworks, Principles and Practice, 4th Edition, ISBN 0-8206-0407-0