Propellant (model rocket)
A propellant is a ready-made drive for model rockets . Propellant charges for model rockets always consist of a propellant charge and usually also of a delay charge and an ejection charge. As a rule, black powder is used as fuel for smaller propellants . A much more modern and more powerful composite fuel is used for larger propellants.
The propellant charge, which is generally ignited electrically for safety reasons, takes on the function of accelerating the model rocket. If the propellant charge is burnt, the delay charge starts to burn. It does not take on a drive function, but its smoke charge enables the model to be followed better. After the delay charge has been consumed, the ejection charge ignites. The recovery system ejects this charge forward through the missile body.
Legal
In Germany, rocket propellants are classified either as pyrotechnic objects (up to 75 grams of fuel) or as explosives (more than 75 grams). From the amendment of the German explosives law in 2009, pyrotechnic objects are subject to a conformity verification procedure in accordance with Directive 2007/23 / EC of the European Community . A pyrotechnic article may only be placed on the market if it has passed this procedure and has a CE mark . Explosives have to undergo a type approval according to EU directives and then receive a CE mark. Class IV pyrotechnic objects are subject to so-called quality control. Firework rockets may not be used to drive model rockets, despite their structural similarity.
In Germany, propellant charges (freely available for people over the age of 18) may have a maximum of 20 grams of propellant charge. A corresponding license (“Permit according to § 27 SprengG”, colloquially “T2 certificate”, see below) is required to acquire stronger propellants. This permit is also necessary in Germany in order to legally launch model rockets with several stages or bundled propellants.
In all other countries, for example Switzerland, Austria, Great Britain, Sweden, France, Poland or the USA and Canada, propellant charges with significantly larger loads can be freely sold and used without the corresponding state approval. There is also no special state license required to launch model rockets with multiple stages or bundled propellants. Instead, they rely on self-regulation within the local model rocket organizations through so-called high-power certification systems, in which access to larger engines takes place via a multi-level testing and certification system. However, even in these countries, without a corresponding license, self-made propellants (so-called experimental rocket construction ) are prohibited.
Permit according to § 27 SprengG - The "T2-Schein" (Germany only)
Depending on the test passed and the resulting entries in the corresponding permit, various pyrotechnic objects of class P2 (propellants for technical purposes with more than 20 grams of fuel weight) as well as black powder may be purchased in Germany with a permit pursuant to Section 27 SprengG. This permit is also required to bundle model rocket propellants or to fly in multiple stages.
A permit according to § 27 SprengG does not normally entitle the holder to manufacture pyrotechnic objects, fuel mixtures or explosives or to burn fireworks with more than 20 grams of effect charge, unless these actions are explicitly entered there, which is only possible by submitting a corresponding certificate of expertise.
In order to receive a permit according to § 27 SprengG, one must be at least 21 years old (in exceptional cases 18 years), physically suitable and reliable (proof is provided by submitting a corresponding clearance certificate from the competent authority and should not be confused with the police clearance certificate ) and have successfully passed a corresponding examination at the competent authority, such as the trade supervisory office or a state-recognized course provider. Furthermore, a so-called need, such as membership in a model rocket association, is a prerequisite for the grant.
Courses are held in Germany by several rocket clubs. A course usually lasts several days and provides all the knowledge required to build and launch rockets with a fuel weight of more than 20 g.
designation
There are different types of propellant charges. They are usually named according to a scheme originally developed by the American National Association of Rocketry (NAR). This consists of a letter and 2 numbers with the following meaning:
- Letter
- It describes the momentum of the propellant as follows:
| Impulse class | Impulse [Ns] |
|---|---|
| A. | 1.26-2.50 |
| B. | 2.51-5.00 |
| C. | 5.01-10.00 |
| D. | 10.01-20.00 |
| E. | 20.01-40.00 |
| F. | 40.01-80.00 |
| G | 80.01-160.00 |
| H | 160.01-320.00 |
| I. | 320.01-640.00 |
| J | 640.01-1280.00 |
| K | 1280.01-2560.00 |
| L. | 2560.01-5120.00 |
| M. | 5120.01-10240.00 |
| N | 10240.01-20480.00 |
| O | 20480.01-40960.00 |
- In model rocket construction, engines up to pulse class O are currently available. Motors of classes H to O are called high-power motors . Above H one speaks of amateur rockets .
- 1st number:
- It denotes the mean thrust in Newtons
- 2nd number (after the hyphen)
- Delay time between the end of the propellant charge and the ignition of the discharge charge in seconds. This information is important because if the delay time is too long, the model may hit before the parachute is opened or if the delay time is too short it may not reach the optimum height. Engines without an ejector charge are also available. These are either so-called zero burners, in which the flame penetrates upwards after the burnout, or closed motors. Zero burners, which are used in sub-stages of multi-stage rockets, are marked with `` -0 '', locked motors with `` -P '' (plugged).
A G64-7 therefore has between 80 and 160 Ns impulse, 64 N average thrust and, after the burnout, a free flight phase of 7 seconds before the parachute is ejected.
In principle, you should only use the propellant charges recommended by the manufacturer for use in model rockets, otherwise the model may crash. The rocket propellants most commonly used to power model rockets are Category C and D propellants.
Differences to fireworks charges
In terms of their strength, propellants from fireworks rockets correspond approximately to propellants from category A to C. In contrast to model rocket propellants, propellants from fireworks rockets do not actually have any delay or ejection charges. After it has burned out, the propellant immediately ignites the effect compound located in the tip. In the case of model rockets, the propellant charges can generally be exchanged, whereas in the case of firework rockets they are permanently connected to them. Model rocket propellants are also always delivered without a built-in fuse. In contrast to fireworks rockets, model rockets can also be flown all year round.
Micro motors
Model rockets with very small motors are also referred to as mini model rockets or model rockets with micro motors. The term micro-motor was introduced in the 1990s by Czech micro-motors from the Delta brand, which had a diameter of only 5.1 mm and a length between 10 and 18 mm. The motors were models for the micro motors called Micro Maxx from the US manufacturer Quest Aerospace.
Micro-Maxx missiles were basically delivered as finished models. They can only be started with an electric ignition and reach heights of up to 60 meters. The Micro-Maxx product line has now been discontinued by the manufacturer.
Web links
- Information from the IMR about the T2 ticket
- Pictorial size comparison of all common model rocket motors
Individual evidence
- ↑ Article on mini model rockets
- ↑ Delta Micro propellant charge specifications ( Memento from September 11, 2014 in the Internet Archive )
- ↑ Pictures Delta Micro