Brief:
1:8.15 scale o' t' Environmental Aeroscience Corporation's soundin' rocket.

Construction:
This "scale bash" project can easily be built from common parts available in commercial kits. T' attached RockSim file can be used for a shoppin' list, but t' basic parts include:

• PNC-20 Plastic nose cone (4:1 Ogive)
• BT-20 body tube 24.15" long
• 1/16" basswood fins (4)
• 1/8" launch lug
• BT-5 motor tube 4" long
• 5/20 centerin' rings (2)
• 10.5mm/13mm centerin' rin' motor block
• 12" chute
• 20" 1/8" elastic shock cord
• paper shroud

I got t' idea from Peter Alway's Scale Bash book, matey, ya bilge rat, which included templates and t' basic dimensional conversions. Blimey! I have replicated almost all o' that in a RockSim file for simulation and stability analysis.

T' attached RockSim file can be used t' print out fin patterns, which are cut from 1/16" basswood. Balsa can be used but would possibly flutter a tiny bit at that size. Avast, me proud beauty! Begad! Note that on me model, me hearties, me bucko, I went a bit beyond t' regular fins and made tiny fin mountin' brackets by cuttin' small slivers from a spare BT-20 motor tube. T' slivers are equal to t' fin length and are about 3/32" wide.

T' print t' shroud, I recommend t' free online tool linked through t' EMRR site. Begad! T' dimensions are 0.736" front diameter, 0.544 aft diameter, me bucko, and length o' 0.66".

Buildin' t' model is a skill level 2 and can be done in about 90 minutes at t' worst. Ahoy! Start by insertin' the smaller centerin' rin' in t' BT-5 usin' a spent casin' t' space it correctly--you want t' leave 1/4" out for tape retention, arrr, as t' boat tail leaves no room for a hook.

Next, form t' shroud and use white glue t' seal it. Avast! Slide it over t' BT-5 with t' aft end flush with t' aft of t' BT-5. Apply a thin bead o' glue t' t' BT-5 near t' forward end o' t' shroud and slide a 5/20 centerin' ring down t' BT-5 until it just touches t' shroud. Arrr! Glue t' other centerin' rin' t' t' forward end o' t' BT-5. Ahoy! The completed assembly then slides into t' BT-20 and is glued in place.

Usin' a wraparound fin guide (again, matey, free online tool linked through EMRR or use an Estes markin' tool if you do this before mountin' t' boat tail), arrr, arrr, mark a 4-fin pattern on t' BT-20. Avast, me proud beauty! Mount t' fins (and brackets, if you choose t' make them).

Mount a lug about 10" from t' aft end on a line betwixt fins.

A standard paper tri-fold for t' shock cord should suffice.

Critical step: add a small amount o' nose weight. Aye aye! Blimey! On mine, me hearties, it needed about 3 grams o' clay in t' nose t' bring the CG t' 13.5" from t' nose tip (empty). Arrr! Avast, me proud beauty! RockSim thinks this is overstable, but long/skinny rockets need extra margin, me bucko, especially if flyin' in higher winds.

Finishing:
For finishing, matey, I painted everythin' with 2 coats o' gray primer, ya bilge rat, then two coats o' Krylon white gloss as a base. Well, blow me down! Ya scallywag! I masked off and painted one fin a fluorescent red (though regular red would do). Aye aye! I then masked that fin off, and painted the remainin' 3 fins black.

For t' nose cone, t' Scale Bash book included a small pattern that could be used t' print a shark's mouth and eyes. Rather than figure out how t' transfer that t' a decal somehow, matey, matey, I just drew it by hand in pencil a couple times before followin' up with a Sharpie.

Flight and Recovery:
Since it's a 13mm, me hearties, t' motor selection is pretty thin. Blimey! I'd recommend goin' all t' way up t' A10-3T or A3-4T. Begad! I flew mine on an A10-3T on a perfectly calm day. Begad! T' flight was absolutely straight although it was still coastin' up a bit when t' chute popped out. An A3-4T motor might be a better fit with less o' a thrust spike for a longer flight and the longer delay would help.

T' model simulates t' about 350 feet, arrr, although I don't think it got anywhere near that altitude. Arrr! More like 200-250.

Summary:
For PROs, me bucko, I think I'd have t' rate t' simplicity o' t' construction for an easy scale model and t' very nice flight. It's also a model that doesn't seem t' show up in contests or sport flights very often, shiver me timbers, so it is certainly a bit off t' beaten path.

CONs: somewhat tricky decoration o' t' nose, limited availability o' good scale data, matey, and havin' gone with 13mm motor, I'd suggest upscalin' t' 18mm for better motor flexibility would be a good idea.