Background & Requirements
I am hoping to attain my UKRA (UK Rocketry Association) Level 1 and Level 2 certifications, allowing me to launch high impulse (powerful) model rockets. I plan to start with an ‘H class’ rocket, the lowest motor impulse for a Level 1 rocket, and work my way up. My ‘local’ club Fins over Gwent (FOG), billed as ‘Wales’ premier rocketry club‘, is about 1.5 hours from my home in SW England. FOG issue a NOTAM (Notice to Airmen – a warning to pilots) that extends to 3,500 ft, and is issued before each monthly club meet. After a few friendly messages with Mike, the club’s chair, I’ve established the additional following design constrains (some of which were suggested would be common requirements for any model rocket launched in the UK):
- Maximum apogee of 3,500 ft (for FOG)
- Minimum thrust to weight ratio of 5-10
- Minimum launch speed of 13-15 m/s
- Maximum of G-class motor (for FOG)
Clearly the G-class motor is just below the H-class that I would need for my Level 1, but in the words of Mike of FOG, it would be “fine to develop [my] level 1 rocket, but […] certify at another site with a UKRA RSO”. With that in mind, I set about designing a rocket that would fly well with both a G and an H class motor, with the aim at proving the design at FOG.
Rocket Name – GLYPO-001
Having recently read Homer Hickam’s excellent memoir, Rocket Boys, I’ve decided it is only fitting that I also number my rockets sequentially. Thus, GLYPO-001 is born, at least for now in concept form.
OpenRocket Design
The FOG website mentions OpenRocket, as did two of my work colleagues, thus without any further research I have adopted this free-to-use tool to design the rocket. Having previously flown small model rockets as a teenager, I decided a simple 3-fin design would be a sensible starting point for my first high-power model.
Visually, the rocket design is simplistic. I have proposed using a simple phenolic body tube, plywood centring rings, plywood fins, an off-the-shelf polymer nose cone, and off-the-shelf recovery system (a simple parachute). Key dimensions of the rocket are:
- 130 centimetre length
- 3-inch diameter
- Predicted mass 1,076 g (inc. motor)
The fin assembly has a through-body design, with slots in the motor-mount centring rings to ensure a firm hold. The fins are trapezoidal, with a 10 cm root chord, 5 cm tip chord and 9 cm span. The fins are sized to create a positive static margin of greater than 2 cal, i.e., the centre of pressure is aft of the centre of gravity by a distance greater than 2-times the body diameter. The rocket should fly satisfactorily with a static margin of 1 cal, thus targeting 2 cal allows for any discrepancy from the rocket as designed and the rocket as built.
I’ve simulated the flight of the rocket in OpenRocket with two motors – both 3-Grain 29mm (Pro29) Cesaroni motors. The first is the G class motor – the G54 Red Lightning Long Burn. This has a total impulse of 159.1 Newton-seconds, bearing in mind the G-Class impulse is 80-160 N-s, this really is toward the upper-bound of class. The second motor I modelled was the H54 White Longburn, this is a 168 N-s motor, which is right at the lower-bound of the class.
| Motor Name | G54 Red Lightning Long Burn | H54 White Longburn |
| Motor Class | G (80-160) | H (160-320) |
| Impulse (N-s) | 159 | 168 |
| Average Thrust (N) | 53.3 | 53.6 |
| Max Thrust (N) | 122 | 103 |
| Burn Time (s) | 2.99 | 3.13 |
| Apogee (m) | 485 | 508 |
| Velocity-off-rail (assuming 1m rail) (m/s) | 14.4 | 12.7 |
| Stability (cal) | 2.41 | 2.36 |
| Thrust to weight | 5.10:1 | 5.08:1 |
The performance difference between the two motors is quite small, which is to be expected given their similar impulse and burn times. The rocket is large for a G class and small for an H class. It is clear that this design appears to meet both the club’s requirements and also my own desires for a relatively slow/long burn rocket.
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