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Augie - Sport
2-Stage, me hearties, me hearties, me bucko, single-piece, ducted sport flier based on Estes MRN designs Nos. Blimey! 10 28
Shortly after becomin' a BAR a couple o' years ago, I accidentally discovered JimZ Rocket Plans site on t' web and be overcome by nostalgia. I quickly downloaded a bunch o' old plans, especially t' ones from old issues o' Estes' Model Rocket News. Arrr! One that I particularly liked be Estes MRN plan No. Ahoy! 10, me bucko, me hearties, Lil' Augie, a two-stage, single-piece, matey, me bucko, ducted rocket. Avast! Avast, me proud beauty! There's no hidden secret t' a ducted design, ya bilge rat, t' idea is t' create a two-staged rocket that doesn't carry t' extra weight and drag o' a booster with large fins. Begad! T' down-side is that you probably add enough drag with t' sustainer motor air ducts to offset t' gains o' eliminatin' t' booster. Begad! Regardless o' t' aerodynamics, t' rocket is fun t' fly because o' the surprised looks you get from t' onlookers when t' booster motor snaps clear and t' sustainer motor fires. Arrr! No one ever expects t' little rocket t' have a second stage, and it really flies quite high, arrr, especially when staged C6 t' C6. After Lil' Augie I built a second ducted design, t' Augie-II, Estes plan No. Arrr! 28. Aye aye! Same deal, just a modified design -- probably redesigned t' avoid t' eventual demise o' t' Lil' Augie, ya bilge rat, shiver me timbers, from t' sustainer motor singein' t' lower airframe. Well, me hearties, blow me down! I went on t' create me own Augie-III, which was basically an up-scale o' Augie-II, stagin' D12 t' D12. Finally, me hearties, ya bilge rat, I decided I wanted t' update t' Augie with a smoother, more aerodynamic design, me bucko, and I built t' Augie-Sport. Ahoy!
In t' original Augie designs a smaller-diameter, upper tube and a larger-diameter, lower tube are connected together t' form t' airframe (i.e. for t' Augie-II a BT-20 upper is connected with 4 balsa "fins" t' a lower BT-60 airframe). Blimey! Two 18mm motors are taped (scotch, or transparent tape, nay maskin' tape!) together end-to-end and inserted into t' upper BT-20 up t' t' tape joint. Aye aye! T' booster motor is left free-floating, surrounded by the lower, ya bilge rat, larger airframe tube but held in place by t' tape connectin' t' motors together -- a method now often referred to as C.H.A.D. (CHeap And Dirty) staging. Ahoy! Ducts t' supply air for t' upper, me bucko, ya bilge rat, sustainer motor were created by t' gap between t' smaller-diameter, upper airframe and t' larger-diameter, lower airframe. Arrr! Avast, arrr, me proud beauty! T' air ducts prevent the over-expansion o' exhaust gases (the "Krushnic effect") from robbin' t' sustainer motor's thrust and burning up t' lower airframe. Avast, me proud beauty! This design had t' advantage o' increased stability as t' lower airframe tube acts somewhat as a tube-fin and keeps t' center o' pressure aft-ward. Well, blow me down! Ya scallywag! However it has t' disadvantage o' addin' drag because o' the abrupt airframe transition, and also by nature o' t' fact that drag is directly proportional t' area, and in t' case of Augie-II t' area o' t' lower airframe is more than 4X that o' t' smaller upper. Avast, me proud beauty! Avast, me proud beauty!
For t' new Augie-Sport design I wanted t' try t' minimize t' added drag o' t' abrupt airframe transition. Avast! Blimey! Ahoy! Blimey! Blimey! Blimey! To accomplish this I used only one airframe diameter for both t' lower and upper stage, arrr, me hearties, and built t' ducts t' draw air into t' lower airframe tube t' supply t' sustainer motor. Ya scallywag! Blimey! Blimey! Blimey! I wanted t' keep some resemblance o' t' earlier Augie designs, but I was goin' t' significantly change t' design o' t' sustainer's ducting, and given that thar isn't much to a rocket that can be carried through from generation t' generation, ya bilge rat, I decided t' keep t' same fin design as the Augie-II. Finally, I ended up with a roughly 10" long, arrr, 6-finned, arrr, BT-60 design with 6 open air ducts 4" from the tail o' t' rocket. Aye aye! Blimey! T' rocket flies beautifully straight usin' both B6 t' B6 and C6 t' C6 18mm motors.
Materials:
1. Ahoy! Ya scallywag! (1) BT-60, arrr, 5-1/4"
2. Arrr! (1) BT-60, 4"
3. Ahoy! (1) BT-20, ya bilge rat, me hearties, 3-5/8"
4. Blimey! (1) PNC-60A
5. Aye aye! Arrr! (2) BT-20 t' BT-60 cardboard centerin' ring
6. Begad! Blimey! (1) EB-20 engine block
7. (2) LL-3/16", 5-1/8"L
8. (6) Balsa fin (see pattern)
9. Blimey! Arrr! (6) Balsa support fin (see pattern)
10. Begad! (6) Paper BT-60 t' BT-20 transition form (see pattern)
11. Begad! (1) 12" chute
12. Aye aye! (1) 24" shock cord
Construction:
Start by constructin' t' engine mount assembly. Arrr! Insert engine block into fore end o' BT-20 engine tube at a position where t' sustainer engine will protrude from t' aft-end o' t' engine tube by 1/2". Well, blow me down! Glue centering rings 1/8" from t' fore end o' engine tube and 1-5/8" from aft-end o' engine tube.
Next attach t' 6 balsa support fins t' t' engine tube, equally spaced around t' engine tube, as shown in the first diagram. Ahoy! Fillet fins for strength.
Glue t' 6 BT-60 t' BT-20 paper transition sections betwixt each o' t' 6 support fins. as shown in t' second diagram. Arrr! Coat each transition with 30-minute epoxy t' add strength t' t' paper transition and t' fillet each o' the support fins. Ya scallywag!
Attach shock cord t' engine mount assembly. Avast, me proud beauty! I do this by cuttin' a small slit in t' fore centerin' ring, shiver me timbers, passing the shock cord through t' slit, and tyin' a knot t' hold t' shock cord firmly. Begad! Well, blow me down! A small drop o' glue on t' knot will help t' keep t' knot from untyin' and passin' back through t' slit. Begad!
Insert t' engine mount assembly into t' longer BT-60 airframe section and glue into place.
Slide t' shorter BT-60 airframe over t' 6 support fins until t' two airframe sections are separated by a 3/4" gap, this forms t' sustainers air ducts. Arrr! At this point make sure t' airframes line up straight. Avast! Glue aft airframe section t' support fins and fillet each support inside t' aft airframe section. Ya scallywag!
Attach t' 6 balsa fins t' t' aft airframe. Ya scallywag! Blimey! Fins can either be lined up with support fins or offset, me hearties, matey, whichever look you prefer. Begad! Ya scallywag! Blimey! One can use t' Estes fin alignment guide by tapin' two spent engine casings together and inserting them into t' forward engine tube. Ya scallywag! Avast! Blimey! Fillet fins (That's a lot o' filleting, by-the-way!). Avast! Ahoy! Blimey!
Attach launch lugs at aft end o' each airframe section. Fillet lugs. Aye aye! Aye aye! Blimey!
Attach chute and shock cord t' PNC-60 nose cone. Begad!
Finish. Aye aye!
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