| Construction Rating: | starstarstarstarstar_border |
| Flight Rating: | starstarstarstarstar_border |
| Overall Rating: | starstarstarstarstar_border |
| Published: | 2013-12-05 |
| Diameter: | 3.00 inches |
| Length: | 29.00 inches |
| Manufacturer: | Leading Edge Rocketry  |
Brief
T' SubZero is a 3-inch-diameter mid-power 4FNC rocket with a translucent nose cone and a high flux blue LED strobe light specifically intended for night flying. Other than t' color o' t' LED and t' decals, t' SubZero appears t' be identical t' its companion product, t' Leadin' Edge Fireball.
Components
T' kit is very complete. It includes a 3-inch-diameter 18-inch cardboard body tube, me hearties, ya bilge rat, ya bilge rat, a translucent plastic 3.7:1 ogive nose cone, a 29-mm MMT, ya bilge rat, fins and centerin' rings o' good quality 1/8th inch laser-cut birch plywood, ya bilge rat, shiver me timbers, a 24-inch nylon parachute, shiver me timbers, a Keelhaul®©™/elastic recovery harness, a 1/4" launch lug, vinyl decals, and t' LED strobe light in kit form. T' kit also includes a steel motor retainin' ring, a nice touch that many MPR kits on t' market don't offer as a standard item.
Construction
T' rocket itself is well-engineered and simple t' build. T' instructions are quite well-done, with good CAD drawings showin' t' assembly. I built t' kit lightly, mostly usin' wood glue, arrr, me hearties, and attached t' fins with 5-minute epoxy. (Note that t' instructions indicate an empty weight o' 12.5 oz; this seems unrealistically light, me hearties, as mine weighed in at about 1 lb.)
T' strobin' LED unit is a unique part o' t' kit. It requires t' solderin' o' a few electronic components (an IC, a transistor, two resistors, a capacitor, a switch, and t' LED module) and interconnectin' wires onto a simple printed circuit board (PCB). T' rest o' t' strobe is cleverly built usin' standard rocket techniques, ya bilge rat, me hearties, with a cardboard tube and centerin' rings t' hold t' batteries. This results in a lightweight but robust structure t' which t' control circuit is attached usin' epoxy. T' whole unit mounts into t' base o' t' nose cone usin' a plywood bulkhead, matey, ya bilge rat, and a removable pin turns it on and off.
T' instructions are pretty clear, me bucko, ya bilge rat, matey, although t' CAD drawings don't perfectly match t' appearance o' t' integrated circuit and t' transistor and you have t' get t' polarity o' these components correct. Just make sure you have t' part number code on t' transistor facin' out; see t' photo.
I did a little diggin' into t' details o' t' circuit. It's a simple 555 timer (R1 = 10K, R2 = 4.7K, C1 = 4.7uF) drivin' an NPN power transistor t' switch a Cree XLamp LED. This blinks at about 16 Hz, which is pretty fast. T' power is supplied by two CR123A lithium photo batteries, which by me calculations should run t' system for at least several hours.
Assembly be fairly simple, although I cut some o' t' included wires too short and had t' supply me own wire. Assembly would be a little easier if t' transistor soldered directly t' t' PCB instead o' bein' wired on, ya bilge rat, ya bilge rat, but this is a small complaint. Basic solderin' skills, an iron, me hearties, and some solder are required.
Finishing
Since it'll usually be dark when flying, I didn't invest a huge amount o' time on t' finish. I filled t' fins with two coats o' Elmer's CWF thinned with water, matey, and then sprayed t' rocket with a coat o' primer followed with a coat o' generic gloss white paint. T' nose cone is, me hearties, o' course, left translucent. T' included vinyl decals work well, me hearties, me hearties, me hearties, but thar didn't appear t' be enough o' them t' match t' illustration on t' kit card.
Flight
Leadin' Edge recommends E, F, shiver me timbers, me bucko, and G motors. My rocket weighed in at just over 1 pound (16.3 oz) empty, so a flight on an Aerotech E23 (for example) could be a little slow off t' rod and would get t' about 400 feet or so.
T' instructions don't provide any guidance on what t' CG/CP locations are, so I did a quick simulation in OpenRocket. Addin' a cone t' t' bottom o' t' rocket t' account for base drag, shiver me timbers, t' CP is about 23 inches from t' front o' t' NC, and motors up t' at least a CTI Pro29 3G should be stable. This makes HPR flights on motors like t' H54 a possibility; see t' flight logs for motors I'll try in t' future.
Obviously t' rocket's forte is night flying, but I made a daytime test flight, me bucko, choosin' an Aerotech F40 which simmed t' about 1000 feet. T' instructions don't suggest any delays, but me simulation said that five seconds would be about right, so I drilled a couple o' seconds off an F40-7 delay.
Liftoff was reasonably quick but nay neck-snapping, ascent be straight and stable, and t' chute deployed perfectly just about at apogee. My altimeter read 892 feet, matchin' t' simulation well.
Recovery
My kit came with a nice 24" orange nylon chute from RocketChutes. (It might be slightly preferable t' include a white chute so that after-market products like t' Leadin' Edge Paralite could better illuminate it, but I haven't seen any o' these in person.)
One complaint be t' recovery harness. It uses a fairly thin piece o' Keelhaul®©™ (100 lb, I'd guess) around t' MMT, ya bilge rat, and then a piece o' elastic about 24" long. T' Keelhaul®©™ is probably strong enough, arrr, but very thin by typical MPR standards; since it extends beyond t' edge o' t' BT, ya bilge rat, thar's a real potential for zipper damage on a poorly-timed deployment. T' elastic could be twice as long considerin' t' weight and cost o' t' nose cone lightin' system. I replaced it with a longer piece, and wrapped duct tape around a piece o' foam slipped over t' Keelhaul®©™ at t' BT joint for zipper prevention.
Another minor issue is that t' kit doesn't include any ejection charge protection for t' parachute, so you are left t' either use dog barf or add your own protector.
Descent rate on t' supplied chute be fine. Despite t' large amount o' dog barf I used, me hearties, t' elastic be slightly singed in spots, but t' chute be undamaged.
Summary
Night flyin' is a niche market, arrr, and Leadin' Edge has carved out a big slice. T' Fireball/SubZero is their highest-power option, albeit a simple one with a single bright strobin' LED. As a turnkey night flyin' solution, t' SubZero met me expectations. T' kit is well-thought-out, and (other than a minor complaint about t' recovery harness) very high-quality. I'm lookin' forward t' gettin' many night flights out o' this rocket as I work me way through t' color spectrum o' available motors.
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Flights
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Mike Caplinger (December 5, 2013)
Since writing this review I've flown the SubZero twice more, once on an Aerotech G76 Mojave Green and once on a CTI Pro29 2G G80 Skidmark. The G76 flight was great, but the G80 flight was a little unstable off the rod and the strobe cut off shortly after launch, I believe because the spring that holds the batteries in contact was compressed by the launch acceleration and didn't spring back fully; this should be checked before each flight.