Rocket Design
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 following additional design constraints (some of which are common requirements for model rocketry in the UK):
- Maximum apogee of 3,500 ft (FOG limit)
- Minimum thrust-to-weight ratio of 5–10
- Minimum launch speed of 13–15 m/s
- Maximum of G-class motor (FOG limit)
Clearly, the G-class motor is just below the H-class that I would need for my Level 1 certification. However, in Mike’s words, 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 on both G and H class motors, with the intention of proving the design at FOG.
Rocket Name — GLYPO-001
Having recently read Homer Hickam’s excellent memoir Rocket Boys, I decided it was only fitting that I also number my rockets sequentially. Thus, GLYPO-001 was born — at least in conceptual form.
OpenRocket Design
The FOG website mentions OpenRocket, as did two of my work colleagues, so without further research I adopted this free-to-use tool to design the rocket. Having previously flown small model rockets as a teenager, a simple three-fin design felt like a sensible starting point for my first high-power model.
Visually, the rocket design is intentionally simple. The proposed construction uses:
- Phenolic body tube
- Plywood centring rings
- Plywood fins
- Off-the-shelf polymer nose cone
- Off-the-shelf recovery system (single parachute)
Key dimensions are:
- Length: 130 cm
- Diameter: 3 inches
- Predicted mass: 1,076 g (including motor)
The fin assembly uses a through-the-body design, with slots in the motor-mount centring rings to ensure a firm structural connection. The trapezoidal fins have:
- Root chord: 10 cm
- Tip chord: 5 cm
- Span: 9 cm
The fins are sized to produce a static margin greater than 2 calibres, meaning the centre of pressure lies more than two body diameters aft of the centre of gravity. While stable flight is generally achievable with a margin of 1 calibre, targeting 2 calibres provides margin for construction tolerances.
Motor Performance
Flight simulations were performed in OpenRocket using two 29 mm, three-grain Cesaroni Pro29 motors:
- G54 Red Lightning Long Burn
- H54 White Longburn
The G54 has a total impulse of 159 N·s, very close to the upper limit of the G-class (80–160 N·s). The H54 sits at 168 N·s, right at the lower boundary of the H-class.
| Parameter | G54 Red Lightning | H54 White Longburn |
|---|---|---|
| Motor class | G (80–160) | H (160–320) |
| Total impulse (N·s) | 159 | 168 |
| Average thrust (N) | 53.3 | 53.6 |
| Maximum thrust (N) | 122 | 103 |
| Burn time (s) | 2.99 | 3.13 |
| Apogee (m) | 485 | 508 |
| Velocity off rail (1 m rail, m/s) | 14.4 | 12.7 |
| Stability (cal) | 2.41 | 2.36 |
| Thrust-to-weight ratio | 5.10:1 | 5.08:1 |
The performance difference between the two motors is small, as expected given their similar impulse and burn profiles. The rocket is large for a G-class motor and small for an H-class motor, making it well-suited for development flights at FOG whilst remaining appropriate for Level 1 certification elsewhere.
Trajectory side profile showing altitude and downrange position, assuming a 1 m/s wind.