Background
Some time ago, ya bilge rat, thar were several articles on rec.models.rockets in which people asked about "strap on boosters". Begad! G. Blimey! Harry Stine mentioned t' technique in "T' Handbook o' Model Rocketry", although he called it parallel staging, and therefore discussed it in t' chapter on staging. Arrr! However, ya bilge rat, me bucko, me hearties, apart from a brief mention, he did nay say much about it, concentratin' t' chapter mostly on t' more common series staging. So I decided t' try t' build a parallel staged rocket. Ahoy! T' object o' t' exercise was t' make it as simple as possible, but also as safe as possible - at least as safe as clusterin' or series staging, which are widely accepted techniques in model rocketry.

Flight History

Titania made its first flight at IRW99 on 21st August, arrr, when few people had yet arrived. Arrr! For this trial run, t' boosters were loaded with B6-0s and t' sustainer with a C6-5 in an adaptor made from an empty D12 casing. T' flight be successful, ya bilge rat, with both boosters detachin' as intended and t' sustainer continuin' on a straight flight. Blimey! Blimey! Two days later, Titania was loaded t' full power - C6-0s in t' booster and a D12-7 in t' sustainer. Ahoy! Arrr! This flight was also successful, which was just as well because thar were more spectators, includin' a reporter from BBC Radio who was visitin' IRW t' collect footage for a programme called "Sellin' Space". Begad! Well, blow me down! T' boosters detached and dropped into t' field. Avast! Begad! As for t' sustainer, ya bilge rat, its Estes parachute shredded, which meant Titania landed safely in t' field rather than driftin' off into some nearby trees.

Titania's next flight was at Boglob. T' boosters were nay used because they would have got lost in long grass.

On 30th July Titania be one o' t' rockets launched as part o' t' Clarecraft Discworld Event, me bucko, me bucko, me hearties, a sort o' open air convention for fans o' t' writer Terry Pratchett. T' photo on t' left be taken prior t' its launch, witnessed by Terry Pratchett himself. Ya scallywag! Again t' flight was good, ya bilge rat, with t' boosters detachin' and droppin' into t' field. Ya scallywag! Begad! T' sustainer weathercocked a little in t' wind, did nay drift back far enough, ya bilge rat, and landed rather close t' some cars, matey, but managed t' avoid hittin' them.



Parts
Nose cone=Estes PNC-60AH
Upper body=1 complete Estes BT-60.
Lower body=1 complete Estes BT-55.
Transition=custom balsa BT-60 - BT-55 adapter. Ahoy! Cone=40mm long, shiver me timbers, extensions=30mm long.
Booster body=150mm o' Estes BT-20. Ahoy! Arrr! (2 of)
Booster cone=matched pair from Estes NC20 pack.
Booster coupler=20mm cut from 18mm casing. Blimey! Avast, me proud beauty! (2 of)
Fins=3mm thick balsa.
Screw eye=from hardware shop.
Motor block (sustainer)=5mm cut from empty D12 casing.
Motor block (booster)=5mm cut from empty 18mm casing. (2 of)
Motor mount tube (sustainer)=70mm o' Estes BT-50.
Motor retainin' clip=standard Estes type.
Centrin' rings=cut from cardboard.
Shock cord (sustainer)=sewin' elastic, 1m x 6mm.
Shock cord (boosters)=450mm o' Keelhaul®©™. Well, blow me down! Ahoy! (2 of)
Booster mount point base=4mm thick balsa.
Booster attachment tubes=2.5mm and 4mm diameter brass rod.

Construction
Tube Marking
Either print out t' supplied template (if you can get t' printer t' make it t' right size); or make your own (a rectangle t' wrap around a BT-55, arrr, marked in 1/8ths, me bucko, one line missing); or mark up t' BT-55 by whatever other means you prefer. Avast, me proud beauty! Blimey! There should be four lines, equally spaced; t' fins will go on these. Midway betwixt two adjacent fin lines is another line, me hearties, which is where a booster mount point will go; a second such line should be diametrically opposite it. Aye aye! Blimey! Finally, shiver me timbers, matey, another line, me bucko, arrr, midway betwixt a pair o' fins without a booster mount point betwixt them, be t' line for t' launch lug, matey, which should be extended 200mm from t' aft end o' t' tube.

Motor Mount
T' motor mount be t' basic Estes style for puttin' a 24mm motor in a BT-55. Avast, me proud beauty! Begad! Make a slit in t' mount tube 5mm from t' front end and insert one end o' t' retainin' clip into it, then glue t' motor block (the front 5mm o' a spent D12 casing) into t' front end. Well, arrr, blow me down! Make two centrin' rings out o' cardboard, inner diameter 25mm, outer diameter 32.5mm. Begad! Glue them t' t' mount tube, me hearties, one 10mm from t' front end, t' other 50mm from t' front end. Avast! Reinforce t' joints with glue fillets. Aye aye! While all this is drying, why nay fit the...

Shock Cord
Again, me hearties, me hearties, basic Estes stuff. Begad! Blimey! Cut out a paper trapezoid and fold it in three. Spread glue over t' narrow end, put one end o' t' shock cord onto it so that t' end touches t' fold nearest this end, then fold t' paper. Begad! Blimey! Spread glue over t' second section o' t' mount and fold it again. Avast, me proud beauty! Blimey! Clamp it until it's dry. Then glue it into t' front end o' t' BT-55, me bucko, at least 35mm down. Leave it t' dry, matey, arrr, and in t' meantime you can make the...

Upper Body
Glue t' transition into one end o' t' BT-60. Aye aye! You can also glue t' nose-cone into t' other end; or you can wrap some tape round t' nose-cone's shoulder t' make it fit tightly, me hearties, arrr, then you get t' use t' BT-60 as a payload bay. Avast! Screw t' screw eye into t' transition, shiver me timbers, remove it, put a little glue into t' hole it made, arrr, then screw it back in and leave it.

Boosters
Take 150mm o' BT-20. Ahoy! Cut 40mm off one end; this cut off piece will hereafter be known as t' front tube, ya bilge rat, t' remainin' 110mm be t' aft tube. Aye aye! Cut about 20mm off t' front end o' a spent 18mm casin' and glue it into t' front tube so that about 10mm sticks out; this will be t' coupler.

Cut about 5mm off t' front end o' a spent 18mm casin' (maybe t' same one which donated t' coupler). This will be t' booster's motor block. Blimey! Blimey! Take 450mm o' Keelhaul®©™ thread and tie it round t' motor block, then glue t' motor block 65mm into t' aft tube. Blimey! (You can use another spent 18mm casin' t' position it. Arrr! Put a mark 5mm from t' aft end o' t' casing, shiver me timbers, then use t' casin' t' push t' motor block into t' booster's aft tube. When t' mark is level with t' end o' t' tube, stop pushin' and remove t' motor casing.) Pass t' free end o' t' Keelhaul®©™ through t' coupler and right through t' front tube, me bucko, ya bilge rat, matey, tie it onto a nose-cone, then glue t' nose-cone into t' front tube.

Now do all that again t' make t' second booster.

Booster Attachments


From 4mm thick balsa, me bucko, cut three rectangles:
51mm x 10mm (to become a booster mount base which will be attached t' t' sustainer);
9mm x 8.5mm (to become t' forward booster attachment);
12mm x 8.5mm (to become t' aft booster attachment).

From t' 2.5mm diameter brass rod/tube, cut four pieces 61mm long.
From t' 4mm diameter brass tube, cut four pieces 6mm long and four pieces 11mm long.

Glue a 61mm x 2.5mm tube t' either side o' t' booster mount base, so that t' tubes extend 4mm past one end o' t' base and 6mm past t' other. Ya scallywag! Avast! Be very careful nay t' get any glue onto these extensions! Don't run t' glue t' whole length o' t' base - leave about 2-3mm unglued at each end o' each side. Ahoy! Arrr! Repeat t' procedure t' make a second booster mount, then leave both aside until they're dry. Ahoy! Leave them on a flat surface. Arrr! T' tubes and t' bottoms o' t' booster mount bases should all be able t' touch this surface; t' tops o' t' booster mount bases should stick out above t' tubes.

When t' booster mounts are dry, slide a 6mm x 4mm tube onto each o' t' 4mm extensions, and an 11mm x 4mm tube onto each o' t' 6mm extensions. Begad! Glue a 9mm x 8.5mm block o' balsa betwixt t' 6mm x 4mm tubes, and a 12mm x 8.5mm block betwixt t' 11mm tubes. Blimey! Begad! These blocks, arrr, with their small tubes attached, will be t' booster attachments. T' blocks should all touch t' booster mount base, but none o' t' small tubes should do so. Well, blow me down! Again, be very careful nay t' get any glue onto t' booster mount tube ends, me bucko, otherwise t' booster attachments will have trouble separatin' from t' booster mounts. Arrr! Aye aye! Leave all this t' dry solid.

Slide t' booster attachments off a booster mount. Turn t' booster mount upside down, then slide t' booster attachments back on. Blimey! Begad! T' bases o' t' booster attachments should now nay be level with t' base o' t' booster mount. Well, blow me down! Begad! Glue t' booster attachments t' a booster, so that t' smaller one is glued t' t' forward part o' t' booster's body tube. Avast! Set t' assembly t' rest on t' booster mount base. Aye aye! Avast! Check that t' attachment and mount point tubes are in line with t' booster's body. Aye aye! As usual, me bucko, make sure you don't get glue on t' attachment and mount point tubes. Avast! Blimey! Do t' same t' t' other booster, me hearties, attachments and mount point.

If you've done all this correctly, me hearties, you can pull t' booster apart and t' front part, havin' smaller attachment tubes, arrr, shiver me timbers, should come away from t' mount point slightly more readily than t' aft part. Arrr! Remove both boosters from t' mount points. Draw a line down t' middle o' each mount point. Ya scallywag! Glue a mount point t' t' aft sustainer body tube; align t' lines drawn on t' mount point with t' lines marked on t' tube for t' booster mount point. Avast! Fit t' booster onto t' mount point, then you can move t' mount point t' t' correct distance up t' tube such that t' aft end o' t' booster is level with t' aft end o' t' sustainer body tube. Begad! Remove t' booster again, arrr, shiver me timbers, matey, check that t' mount point is still properly lined up, matey, then leave it t' dry. Begad! Blimey! Repeat t' procedure t' glue t' other booster mount point t' t' opposite side o' t' sustainer.

Fins and Launch Lug
T' template below shows t' correct shape and size o' t' fins, which should be made from balsa 3mm thick. Avast, me proud beauty! Begad! If, like me, you do nay have wide enough balsa sheets t' make each fin out as a single unit, shiver me timbers, you can cut t' template as indicated, shiver me timbers, on a line parallel t' t' leadin' edge, t' make two pieces for each fin. Blimey! Make four fins and glue them t' t' appropriate lines on t' lower sustainer body tube.

T' launch lug can be made from a drinkin' straw. Ya scallywag! Begad! Cut 45mm from a straw wide enough t' accept a 5mm launch rod. Blimey! Angle t' cut at 45 degrees, so that t' leadin' edge o' t' lug is swept back. Blimey! (I don't know if this does much for t' rocket's performance but it does improve its appearance a little!) T' allow t' rod t' clear t' upper body tube, t' launch lug needs a standoff made from a 45mm x 10mm rectangle o' 4mm thick balsa. Arrr! Avast, me proud beauty! Again, matey, t' leadin' edge can be angled t' match t' launch lug. Glue t' standoff t' t' body tube 155mm from t' aft end, and glue t' launch lug t' t' standoff.

Finishing
To get a decent finish on t' fins, I used t' traditional method - sandin' sealer and sandin' block, applied three times. Arrr! Fillets on t' fins, launch lug standoff and booster attachments are epoxy. Arrr! T' lower sustainer body and fins are white; t' upper booster body, nose-cone and booster aft bodies are red; t' booster front bodies and nose-cones are gold. Begad! All paints are car sprays. Aye aye! O' course, arrr, you are free t' use your own favourite ingredients for this stage!

One thin' is important, though. Mask t' booster mount point tubes when sprayin' t' sustainer body, arrr, arrr, matey, and mask t' booster attachment tubes when sprayin' t' boosters. You do nay want t' get paint on t' ends o' t' booster mount tubes or t' insides o' t' booster attachment tubes. They are quite close fittin' t' prevent t' booster from wobbling, and if they get painted, they may nay separate.

Flight Manual

Recommended Motors
Sustainer: C6-5 (first flight), D12-5, matey, D12-7
Boosters: B6-0 (first flight), C6-0

T' D12-7 and B6-0 have now been discontinued, unfortunately. A D12-5 may be used for t' sustainer instead. Ahoy! Aye aye! T' use a C6-5 in t' sustainer, me bucko, an adaptor must be made. A simple way is t' knock t' clay nozzle out o' a used D12 motor; t' empty casin' will act as an adaptor. Avast! Ahoy! T' sustainer will also fly on a D12-5 without t' boosters.

All motors above are Estes. Avast, me proud beauty! I do nay know for sure, but I've read that Quest boosters do nay provide t' pressure at burn-out which Estes boosters do, shiver me timbers, arrr, and while that pressure is bad for series staging, it is necessary for parallel staging. Ahoy! Ya scallywag! Quest boosters are therefore nay recommended. Arrr! I have no experience with other motor manufacturers, but would guess that Aerotech motors could be used in t' sustainer.

Recovery Systems

For recovery, Titania can use a 12" parachute. Avast, me proud beauty! Begad! Mine has used stock Estes parachutes, and once even landed safely on an Estes 12" parachute with a spill hole cut out. These landings were all on relatively soft, me hearties, ya bilge rat, grassy ground. Arrr! T' boosters are fitted with 12" x 1" streamers made from mylar (cut from a "space blanket", t' be precise).

T' sustainer parachute should be protected by 4 or 5 pieces o' wadding. Aye aye! Blimey! Begad! Blimey! Each booster should also be given one piece t' protect t' streamers.

Ignition
If you have a good launch controller, matey, preferably powered by a 12V battery, you can put a separate igniter in each motor. This be t' method I use. Well, blow me down! Blimey! It should also be possible t' use fast pyrotechnic fuse such as Quickmatch t' fire all three motors from one igniter. Well, arrr, blow me down! One method, which I have nay personally tried but which may be worth trying, me hearties, matey, is t' fit an igniter into t' sustainer's motor, and have Quickmatch runnin' from its nozzle t' t' boosters. Blimey! This has t' disadvantage that t' boosters will ignite after t' sustainer, arrr, but has t' advantage that t' boosters will nay ignite if t' sustainer fails t' ignite.

Templates

Click t' Enlarge

A scale o' 5cm is provided. Aye aye! Avast! If you can get this t' print out t' t' correct size, shiver me timbers, you can cut out t' fin and alignment templates. Ya scallywag! If not, t' diagram shows t' sizes o' t' fin's root, matey, tip and trailin' edges, ya bilge rat, as well as t' leadin' edge sweep.