“Getting back in control”. With a perfect boost from BOOSTAR-TWO and the GIGA IV sustainer motor over pressurizing after ignition but safely recovered its time to refine the design. Welcome to the GIGA V page with improved sustainer motor ignition and fin design.
Rocket Outline
BOOSTAR-TWO / GIGA V, 130mm booster to 86mm sustainer, minimum diameter, experimental, two stage rocket.
Diameter – 130/86mm.
Length – 4030mm*.
Weight fully loaded – 57.7kg*.
Motors: LD 12 point star core 130mm / KILO core burner.
Apogee: planned 20+km*.
Note: * – to be updated according to as-built values
Flight
The flight of the BOOSTAR-TWO / GIGA V is planned for FLIGHTS OF EXPERIMENTAL ROCKETS (LRE) / DRAWSKO POMORSKIE 2022.
Goals
Similar to last flight: successfully fly and safely recover the GIGA V as a sustainer in a 2-stage rocket configuration.
Obtain a solid 3D GPS lock / position at apogee. Three GPS receivers were flown:
Hyperion – unlocked GPS (unrestricted)
Quectel in balloon mode (up to 80km)
UBLOX in air borne mode (up to 18km).
Successfully ignite the lengthened KILO core burner motor at near vacuum conditions with a BKNO3 igniter.
Design and construct a robust fin design suitable for high altitude MACH 3+ flights.
Design & Construction
Sustainer: GIGA V
Rocket – Same as the GIGA IV rocket which, with the exception of the motor, will be re-flown as-is.
Sustainer Motor – Lengthened KILO core burner “lite” motor (86x3mm casing) with improved head-end-ignition.
Propellant: 66/12 (78% solids).
Total impulse: approx 17.800Ns.
Isp: approx 215s.
Burn time: 8,3s.
Propellant mass: 7,95kg.
Equivalent to a N2020.
Payload
Flight control – RDAS Tiny.
Onboard camera – Mobius mini.
Tracking – Talky GPS, 2 Watt by LD
Quectel GPS – in balloon mode. Tested up to 80km and according to GPS spoofing up to 120km still GPS lock. Quick lock on start up is expected. Lock is expected to be lost under dynamic flight only to regain shortly and hopefully before apogee.
2 supporting, passive GPS receivers with separate data loggers.
During the pandemic in 2020-21 it became clear that in order to get a new design fin bracket machined I was getting too dependent on external factors. Hence the decision was made to become self-sufficient with the conversion of a manual HBM BF 25 / G0704 mill/drill into a full blown DIY CNC milling machine. However that endeavor is actually an entire different chapter which I may or may not write a page about. Rest assured it took many hours of learning and a year long journey for machining a fin bracket with a perfect 43mm radius.
There are some dynamics at play during the supersonic speeds of the GIGA sustainer.
The center of gravity moves forward due to burning of the propellant making the aft end of the motor 'lighter' thus shifting Cg forward actually improving stability.
However, the center of pressure dramatically moves forward due to the reduced the effectiveness of the fins at supersonic Mach numbers.
The forward Cp shift is more pronounced than the forward Cg shift of the depleting motor. The Cp is effectively overtaking the Cg and thereby causing the rocket to become unstable. Some good examples can be found online with 3FNC type rockets (3 fins and a nose cone) becoming unstable at the end of their burn around Mach 3.
To keep a rocket stable a minimum stability margin of 1 cal throughout the entire flight of the rocket is required. Preferable 1.25cal but for GIGA and the uncertainty of supersonic speeds in the OpenRocket program I will use a minimum of 1.5cal of stability.
For the 86mm diameter rocket fins I'm using 100x3mm extruded flat profile which limits my fin height to 100mm. Reason for using extruded flat profile over a free-from fin cut from a 3mm plate is that the material is readily available, holds tight tolerances and is quite stiff. The fins are cut to size (4 stacked fin blanks) using an industrial metal cutting band saw with the swivel head set at 30-60°. I did not have good experiences with using a sheet metal shear as the 60° cut would twist the fin.
From the above picture some of the considerations can be recognized for improving the GIGA IV fin design:
Longer fin root.
The previously used fin brackets were suited for relatively short root fins. OK for slender rockets and < Mach 2 flights. Because of the higher speeds, shorter & lighter GIGA IV- V rocket and short fin root I was forced to make a delicate parallelogram fin design to get to the required min calibers of stability. However this resulted in some loss of fin rigidity. Furthermore the pointy fin tip at the trailing edge was prone to damage being the most aft part of the rocketm (see above red circle).
30° leading edge of fin bracket.
The original fin bracket had a 45° degree leading edge. Good for trapezoidal fins but this always looked strange in combination with a 30° leading edge from the later preferred swept clipped delta fin shape.
90° trailing edge of fin bracket.
Similar to the leading edge the original design had a ± 45° degree trailing edge. To make the bracket more robust for the swept clipped delta fin shape a simple 90° degree trailing edge would suffice.
Mounting holes of the fins and fin bracket now at off set from each other.
Driven by the 30° leading edge this made more sense when modelling but it was never a firm design criteria.
Only bevel the leading edge.
The leading edge has a 7,5° bevel while the trailing edge is left at 90°. It also removes 1 extra machining step.
Recovery
Single stage recovery by means of a 2ft kevlar Rocketman chute and 25mm wide 10m kevlar strap deployed at apogee. Kevlar strap folded in 30cm zig zags and subsequent bundle zigzag folded in 3 with 1m (up to pre-sewn loop) left loose. This compact bundle is subsequently inserted into motor coupler. Added velcro to the zigzag shock cord to absorb some of the energy / load and prevent to nose cone from popping off.
Booster & motor
Rocket – Booster built by LD, aluminium airframe, minimum diameter, experimental booster.
Diameter – 130mm.
Length – 2600mm*.
Weight fully loaded – 42.0kg*.
Apogee: 6.0km*.
Maximum velocity: 600m/s*.
Booster Motor – experimental LD 12 point star core (130mm).
Propellant: 65/10 AP/Al with RIO (75,5% solids).
Total impulse: approx 43.000Ns.
Isp: approx 225s.
Burn time: 7,6s.
Propellant mass: 19,1kg.
Equivalent to a P5660.
Payload
Flight control – Stratologger*.
Onboard camera – 2 pcs.
Tracking – Talky GPS, 1 Watt by LD; 433mHz AM emergency beacon.
Note: * – to be updated according to as-built values
On 24.09.2020 we tested to see whether the BOOSTAR-TWO and the GIGA IV would fit together in the launch rail and to prevent unpleasant integration surprises at the LRE. Espcially orientation of equipment and launch buttons are critical. All went well and within the hour the BOOSTAR-TWO / GIGA IV were erected and lowered from the launch rail. Again the orthodox method of first inserting and sustainer, raising it in the rail and then inserting the booster afterwhich the sustainer was lowered onto the booster was used.
During the pandemic in 2020-21 it became clear that in order to get a new design fin bracket machined I was getting too dependent on external factors. Hence the decision was made to become self-sufficient with the conversion of a manual HBM BF 25 / G0704 mill/drill into a full blown DIY CNC milling machine. However that endeavor is actually an entire different chapter which I may or may not write a page about. Rest assured it took many hours of learning and a year long journey for machining a fin bracket with a perfect 43mm radius. 
