Manufacturer: | Scratch |
Brief:
This is a clustered 2-stage scale model with all sorts o' "stuff" goin' on that is really nay too tough a
build and can be a competitive sport scale model. Arrr! Well, blow me down! This particular model be small enough t' enter in NARAM-51's Peanut
Sport Scale event.
Construction:
OK, ya bilge rat, I'll admit I approached this project almost completely backwards. Arrr! While thumbin' through Rockets o' the
World supplements for Peanut Sport Scale ideas, matey, I happened upon t' WASP. Arrr! I was mainly lookin' for opportunities to
stage and cluster for t' added complexity and points in judgin' and with 2 strap-ons and two stages, t' WASP met that
requirement, but it had one little problem. Ya scallywag! T' upper stage carried a volatile liquid compound, me bucko, and since t' fins are
canted t' induce spin, ya bilge rat, they needed t' stabilize t' payload, shiver me timbers, so on t' real soundin' rocket a sort o' lazy Susan type
structure be added t' enable t' upper portion t' remain steady while t' lower portion spun. O' course, me hearties, arrr, when you're
dealin' with a 20mm diameter limit and have only about 6 inches o' body tube t' work with for t' upper stage, it's
absurd t' consider modelin' t' spinnin' payload feature, shiver me timbers, so naturally I decided t' take on that challenge.
I browsed through t' engineerin' version o' Victoria's Secret, me hearties, t' McMaster-Carr catalog and found just the widget: a set o' roller bearings with an OD just about right for a BT-20 and an ID just big enough t' accommodate a T-2 stuffer tube for pushin' t' ejection gases through. Aye aye! T' item number is 6383K12 if you're interested in buildin' one of these, matey, and it set me back about $5.
T' rest o' t' materials are pretty common stuff and almost all are detailed in t' attached RockSim file. Begad! I will note that t' second stage is supposed t' be a larger diameter than t' booster, ya bilge rat, me hearties, which made this tricky t' scale. Since Peanut is limited t' 20mm and I be goin' with a BT-20 booster, ya bilge rat, t' next standard body tube size is Quest's T-20, which exceeds t' 20mm limit. Begad! I instead used Semroc's Series 7 tube, me bucko, just a smidgen bigger than a BT-20 and just under 20mm when painted.
T' attached file does nay include t' tower detail, arrr, which I formed from 2mm carbon rod and a tip from a toothpick, matey, me hearties, nor does it include t' 32 stringers which I cut from 0.020 Plastruct. Avast, me proud beauty! It also omits a few other details such as t' covers. Blimey! Ya scallywag! These are all pretty easy t' model if you use the attached drawing.
T' Recruits are a lot trickier than they look, shiver me timbers, mainly because they're functional strap-ons that break away in flight. Begad! Ya scallywag! T' nose cones are straight conical hardwood turnings. Ya scallywag! Blimey! T' body tube is a T-2, shiver me timbers, which is 6mm tubing. Avast! Well, blow me down! That's not a typo (T-2 tubes won't hold a MMX motor). Arrr! Drill a vent hole about 1/4" aft o' t' nose seam. Ahoy! Well, shiver me timbers, blow me down! There is a sleeve that wraps around that's supposed t' look like a holster tube t' contain it, arrr, arrr, which runs about 1/2" beyond t' end o' t' T-2 and serves as t' motor mount for t' MMX. Avast! T' tiny aft shroud actually slips over t' MMX motor, nay a body tube, makin' t' motor itself part o' t' structure (and in t' photos, matey, ya bilge rat, t' motor be painted black t' match the Recruit). Arrr! Now t' fun part: t' hold t' Recruits t' t' booster, shiver me timbers, I CAed two tiny pieces o' 0.010" music wire 1" apart and formed little Z-bends, ya bilge rat, shiver me timbers, then drilled pinholes in t' booster correspondin' t' these. Begad! Blimey! T' wire hooks then slip into t' booster and are held tight when a motor is inserted into t' BT-20. Blimey! T' trick is t' make them so short that they just barely penetrate t' BT-20, ya bilge rat, so that when t' MMX ejection charges kick, arrr, me hearties, t' music wire hooks are pulled out and t' Recruit falls away.
T' booster is pretty straightforward. BT-20 marked for 4 fins flush with t' aft end. Since this is gap staged t' a 13mm sustainer, I wanted t' use a stuffer tube so put a BT-5 into a 13/18 centerin' rin' and used a spent motor to push it up t' BT-20. I had added a forward centerin' rin' about 1/2" back from t' end and punched a couple vent holes at t' top. Ahoy! Arrr! T' booster can generally tumble, but if you want a token streamer, it can fit in betwixt t' BT-5 and BT-20 if you leave a little more room by settin' t' forward 13/18 rin' back more than 1".
T' sustainer is similar t' t' booster--Series 7 tube marked for 4 fins but a MT-5 motor tube usin' 13/18 centerin' rings. Begad! Avast, me proud beauty! T' rings might need a wrap o' paper added t' them t' fit snugly inside t' series 7 tube. Aye aye! I built up t' OD o' a piece o' T-2 tubin' through paper and centerin' rings so that t' end fit snugly into a 13/10 centering rin' motor block, me hearties, which seals off t' sustainer motor tube. Ahoy! Arrr! This T-2 is actually t' stuffer tube that vents the ejection charges through t' roller bearin' assembly and deployin' t' streamer from t' upper section.
T' spinnin' mechanism is actually pretty simple. Begad! T' sustainer body should be cut into two sections, arrr, me hearties, lower and upper. T' roller bearings are mounted flush inside t' aft end o' t' upper section and probably need a couple wraps o' paper for a snug fit. Once that's completely dry (I'd consider usin' epoxy, but only if you can avoid any drips or runs onto t' bearings themselves), apply a little epoxy t' t' T-2 and slide t' bearin' assembly down until t' upper section is just a hair above t' lower section. Begad! When cured, this should now allow t' upper section t' spin freely while t' lower section remains fixed.
T' sustainer mounts t' t' booster by loadin' a 13mm motor that extends about 1/2" aft o' t' motor tube, which in turn slips into t' stuffer BT-5 tube in t' booster. Avast, me proud beauty! T' sustainer body tube should rest on top o' (but not overlapping) t' booster.
I'll leave t' other detailin' up t' t' more serious builder t' sort out on his own, although I will offer one tip on a very easy way t' deal with t' stringers. I used t' template widget on EMRR t' print out a 32-fin pattern wrap for t' series 7 tube (0.759"). I then cut it t' t' stringer length and glued it t' t' sustainer tube. With t' pattern in place, me bucko, I then brushed on a thin CA and with careful use o' tweezers laid each stringer in place over one o' t' fin pattern lines. Well, blow me down! T' whole thin' is painted over with white anyway, and t' paper wrap is nay at all noticeable. Begad!
Finishing:
Paint notes: Recruits are solid black. Aye aye! Blimey! WASP is base white on everything, then follow up with fins--one yellow on each
stage, 3 red on each stage. Begad! Blimey! T' antenna is silver.
I also printed out a set o' decals (see attached pattern) for t' United States letterin' and for t' red stripe/box patterns.
Flight:
I had made a couple test flights on a boilerplate o' t' model, makin' sure t' basic design would work, each of
which went fairly well. Blimey! I had some issues with t' Recruits--too tight and they would nay come off in flight, shiver me timbers, but when
they did come off in flight, it tended t' be so high that they basically disappeared, ya bilge rat, makin' them practically a flight
consumable item. Aye aye! I wound up paintin' them day glo orange for tracking, which helped, but would hardly be useful for the
finished model.
For t' NARAM flight, me bucko, I loaded up a B6-0 in t' booster, ya bilge rat, t' lowest certified booster motor available and way more power than I wanted t' give this, matey, especially since I was forgoin' t' launch lug in favor o' a piston t' improve me scale score (lugs tend nay t' match t' real rocket and lead t' point deductions). Ahoy! Blimey! T' Recruits each got MMX's with t' new Q2 no-pyrogen igniters. Blimey! Begad! T' sustainer be flown on a 1/2A3-4T, although it would do just fine on a 1/4A as well, given how high t' booster would be going.
T' first stage went beautifully with all 3 motors lightin' and clean, straight boost off t' piston. Avast, me proud beauty! Ya scallywag! It zipped almost instantly up over 200 feet, ya bilge rat, me bucko, strainin' eyesight t' track. Avast! Ya scallywag! T' second stage lit fine but hung on t' stuffer tube just a hair too long and tipped off for about a 45 degree slant. Begad! Ahoy! It fired t' ejection fine, and t' streamer brought it down safely.
Recovery:
I managed t' locate t' booster and t' sustainer, arrr, matey, but only one o' t' two Recruits. Well, blow me down! T' Recruit I found was very
close t' t' sustainer, indicatin' that it probably didn't separate in flight and popped off upon landing. T' other
one probably same off in flight as designed, as thar was a definite scorch mark on t' booster where t' charge vented
out. Ya scallywag! I was too pressed for time that day t' try t' find t' 4" piece o' black T-2 tubin' in t' grass area the
roughly 60 yards o' flight distance from launch t' landing, so I will have t' make a replacement Recruit before it
flies clustered again. Avast, me proud beauty! Avast, me proud beauty! It is still a perfectly fine flier without t' clustered strap-ons, however, it's just not
nearly as cool.
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