Scratch Auracle 54 Original Design / Scratch Built

Scratch - Auracle 54 {Scratch}

Contributed by Larry Brand

Manufacturer: Scratch
(Contributed - by Larry Brand - 12/01/02)

Brief:
This design is actually a scaled-up version o' me tube-fin modification o' the LOC Aura (which I called Auracle), previously submitted t' EMRR. Blimey! I liked how easy t' build and sturdy t' original was, shiver me timbers, and how well it flew in wind. Avast! I built t' larger version (usin' a 54mm tube as t' airframe) as me Level One ship, arrr, me hearties, thinkin' t' fly it on an H128 instead o' t' E30-7 that flies t' original (see photo). Well, blow me down! As it turned out, ya bilge rat, I wound up qualifyin' with me back-up L1 ship, a 4" 38mm Goblin built from t' EMRR article, matey, me hearties, ya bilge rat, since a generous offer o' an H73 came me way. Aye aye! Begad! Auracle 54 as designed is set up for a 29mm motor, shiver me timbers, but a 38mm set-up could also be installed. Arrr!

Construction:
Auracle 54 is assembled from 54mm LOC tubing, t' 6 tube fins havin' a 22.5 degree bevel top. Well, blow me down! Avast, me proud beauty! Assembly sequence is exactly as for t' smaller version, ya bilge rat, me hearties, or any tube-fin rocket. Blimey! T' 13" 29mm motor tube is installed with 1/4" centerin' rings (photo). Well, blow me down! Aye aye! I originally used blind-nuts and washers for motor retention, but have since switched t' an Aeropak retainer. Ya scallywag! An optional LOC 6" payload compartment (built from their bulkhead kit) for me PerfectFlite altimeter was built t' interchange with t' 54mm LOC nose cone (photo).

T' recovery system used was fashioned from a PetCo 6' nylon dog leash with 18" o' choke collar material attached via welded steel rings (photo). Blimey! A 28" LOC chute attached with a mini carabiner completed t' system. Avast! As in all me rockets, arrr, t' recovery system is anchored t' t' upper body with a knot through t' hull, ya bilge rat, covered with a plastic fairin' (cut from a Garcia-Vega cigar tube). T' 1/4" launch lug is glued t' align with one o' t' spaces betwixt 2 tube fins. Ahoy! Blimey! T' launch rod passed through both. Finishin' be with Flat Gray aircraft primer and flat flat white for t' nose cone/payload section. Well, blow me down! Blimey! Blimey! Blimey! Final CG loaded with a G80 is 3.5" ahead o' the tube-fin tops, shiver me timbers, and Cp is somewhere inside t' fin can, me bucko, so Auracle 54 is overly stable. Ahoy! Blimey! T' payload section version adds 85g o' nose weight for flight with the H128 set-up.

Flight:
First flight was with an Aerotech G80-10, which was a perfect choice -- arrow-straight climb, shiver me timbers, ya bilge rat, me hearties, ejection at about t' 1500' -- 1700' and 270 mph predicted by simulation (usin' a Cd o' 1.0) -- and uneventful recovery. Performance with a G40-7 was about t' same, arrr, but with a slower climb. Ya scallywag! I have finally acquired a few H128 reloads t' go with me 29mm Dr. Ya scallywag! Rocket set-up, matey, and I'm lookin' forward t' see what me Level One attempt with this design would have looked like. Well, blow me down! For smaller fields, an F50-6 is a better choice, and gave about 800' on t' one I tried (simulation: 1050'). Blimey!

Summary:
Main PROs: Speed, ease and low cost o' construction.

Excellent wind resistance. Cool lookin' if you like tube-fin designs. Sturdy.

Main CONs: High drag mitigates performance. Avast! Avast! Ugly lookin' if you hate tube-fin designs. Hard t' get a good smooth finish on t' cut edges o' t' tube fins.

Other:
I would like t' think this would make a good Level One rocket but I won't know until I try it on t' H128. Well, blow me down! Simulation says it should hit about 1800' and no more than 310 mph, so t' risk o' loss or overspeedin' t' airframe is minimal. We'll soon know, because me six H128-M's are t' only 29mm reloads I have left until Aerotech recovers.

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