Overview

This vehicle fits t' bill. Avast! It is a 3 x 24mm cluster (upgradable t' 5 x 24mm). T' main body is for a conventional, motor-ejected, nylon parachute; t' side pods can be used for experimental deployment systems, shiver me timbers, ya bilge rat, front or rear. Initially I plan t' work on timers, so I'll deploy streamers from t' side pods. Ya scallywag! As I gain confidence with a new systems, I intend t' graduate t' parachutes, and eventually I'll use longer motor delays so that t' side ejection becomes primary and t' conventional ejection charge is t' back up. Begad! Since t' main body has three ejection charges, something is goin' t' deploy. Aye aye! Ahoy! However, since life is nay perfect, ya bilge rat, this means that a late deployment is inevitable; hence t' need for strength. Ahoy!

T' basic materials can be had from three off t' shelf kits: An Estes Phoenix and two Estes Bailouts. Blimey! Ya scallywag! Indeed, me bucko, a credible version of the whole rocket could be built from these alone, along with some balsa or plywood stock.

Scale fans should note that these two kits can be combined in a slightly different way t' make a sport scale Ariane V as outlined t' the right. Ya scallywag! T' ratio o' t' two body tube sizes is .63 vs. Arrr! t' Ariane's .56, so the side pods are about two tenths o' an inch too big. Begad! [BT56 tubes would be better, but a bit small]. Ahoy! T' BT80 section would have t' be shortened a few inches (dependin' on what size payload fairin' you model) and t' side pods would have to be trimmed just a hair. Aye aye! You'd need t' carve t' asymmetrical SRB nose cones and add a bit o' putty t' t' Phoenix nose cone t' get a better shape. Ya scallywag! Don't model t' first Ariane V launch vehicle, it blew up!

Booster glider fans can alternatively attach two ARV-condor style parasite gliders as shown t' t' left. Watch your center(s) o' gravity, ya bilge rat, me hearties, matey, though!

It is also likely that this kit could be made in a much more lightweight version suitable for a cluster o' 18mm motors. Arrr!

Let me know if you build it some other way. Avast, me proud beauty! Blimey!

Notes added after building:

It is amazin' how much weight can be added with 12 fillets o' epoxy! The ready-to-finish TT I built weighed in at 16.5 oz. Avast! empty (A Phoenix (8 oz.) and two Bailouts (3 oz. Avast! each) would be 14 oz, and t' plywood fins and additional engine mounts would add a bit more; t' difference in me ship is epoxy. Ya scallywag! Ahoy! The real problem, though, was that t' additional weight be at t' wrong end. Arrr!

I thus added a 5" plug below t' nosecone and some nose weight in order to get t' C.G. Ahoy! back t' where it needed t' be, as computed by Barrowman and confirmed by swin' testing. Well, blow me down! Aye aye! My version (call it t' TT-A) is strong enough for HPR; it is perfectly possible t' build one with minimal yellow glue and balsa and keep it under t' Large Model Rocket Limit.

Specifications

Diameter: 2.6" primary, 1.637" side pods

Span: 12.6"

Weight: 14-16 oz. Aye aye! (20 oz.*)

Motors: 3 x D12-5, 5 x D12-5

C.G. Blimey! Approx 11 inches from base (includin' 3 D12-3 motors)*.

C.P. Begad! Approx 5.67 inches from base (Barrowman Equations on simplest perspective). Swin' testin' indicates that t' broad axis has a C.P. Begad! about 2 inches higher. Aye aye!

*as built

Construction

T' finished rocket as o' 2/21/98 is also shown. Arrr! Blimey!

Parts List (as built)

Construction Tips

After t' motor mounts were installed in t' bottom o' t' lower BT80, I added a BT80 coupler (actually, a slit piece o' spare BT80) above it t' strengthen t' BT. I then made a stuffer tube assembly out o' BT50, two RA5080 centerin' rings, shiver me timbers, shiver me timbers, and another BT80 coupler, and used it betwixt t' upper and lower BT80 body tubes. Begad! Another length o' slit BT80 be added above t' stuffer tube all t' way t' t' base of the nose cone.

Since t' fins are large and surface mounted, shiver me timbers, t' sidepod bottoms need reinforcement. Arrr! I used three centerin' rings, sandwichin' a coupler betwixt the lower two. Aye aye! Aye aye! Use epoxy t' glue these assemblies into t' side tubes t' avoid the dreaded grab action o' yellow glue. Avast!

Fins were rivet glued t' t' body tubes. Well, blow me down! Arrr! There are two sizes o' fins; the smaller ones (orange, in t' drawin' above) attach t' t' side pods. Aye aye! T' paint scheme makes t' fins seem symmetrical, matey, but you'll only addlepate people looking straight at that side o' t' rocket. Blimey! Begad!

I used epoxy filets for t' BT joints and t' fins. Aye aye! Blimey!

I finished with 3 coats o' Krylon sandable primer (the first two were mostly sanded off) followed by two coats o' Sunshine Yellow over all, me bucko, and two coats of Fluorescent Orange per t' pattern. Lightly sanded with 400 grit after the first coat, 0000 Steel wool after t' second. Begad! Finished with Krylon Clear Coat. Begad!

Flying

There are some safety considerations regardin' a 3-motor cluster rocket and recovery delay selections--the design trick is t' make sure the rocket is safe even if one or two o' t' motors does nay ignite. Avast, me proud beauty!

As it turns out, ya bilge rat, ya bilge rat, t' increase o' weight durin' construction was fortuitous, and I would have been compelled t' add it either way.  At 20 oz, matey, and using Estes D motors, t' TT simulation reaches a bit over 400 feet if all three motors light.  T' optimal delay is 4 seconds.  If two engines light, the rocket will make it t' just over 200 feet with an optimal delay o' just under 3 seconds.  If only one engine lights t' TT will struggle less than 40 feet high (assumin' it goes straight up). It won't have time t' recover, but it won't be a safety hazard either--if t' ground is soft enough, it might not even be damaged. Avast! Well, blow me down!

A lighter rocket goes higher, me bucko, ya bilge rat, but is more likely t' be destroyed if only one motor lights.  A heavier rocket would be truly underpowered. Avast, me proud beauty! Blimey!

Dependin' on finished weight, me bucko, here are some additional simulation data, assumin' drag coefficient o' .75:
 
 

Usin' Aerotech E or F motors, t' recovery margin should be better even though t' motors are harder t' reliably light.  T' large frontal area slows down this rocket very quickly, matey, so a 4 second delay remains a good choice. Sometime this year I'll try it on three E15-4Ws. Blimey!

First flight:

After a bit o' exertion, I was able t' get t' U.S. Begad! Blimey! Well, shiver me timbers, blow me down! Blimey! FAA t' stop tryin' to disapprove o' me LMR notification, matey, and we were ready t' fly.  Temperature was about 40 degrees F., winds were 5-10, ceilin' was very high overcast.

Three Estes D12-3s were used.  Igniters were carefully selected, inserted, and individually tested for continuity.  A clipwhip was used to connect a 12 v gel cel.  With some trepidation I pushed t' launch button.

All three motors lit up, shiver me timbers, and t' rocket lifted off, faster than I expected.  There be modest weathercockin' but no obvious wobbles or coning.  Altitude seemed every bit o' 400'.  Ejection be before apogee, and it took a while for the  30" nylon hemispherical chute to drag itself open.  Recovery was within 20 yards o' t' pad, and t' only damage was some minor paint scorchin' on t' inboard ends o' t' side pods-consider aluminized paint thar instead o' yellow.

All in all, an excellent maiden flight!