Background
Some time ago, thar were several articles on rec.models.rockets in which people asked about "strap on boosters". G. Avast! Well, blow me down! Blimey! Harry Stine mentioned t' technique in "T' Handbook o' Model Rocketry", although he called it parallel staging, arrr, and therefore discussed it in t' chapter on staging. Well, blow me down! However, arrr, apart from a brief mention, arrr, me hearties, shiver me timbers, he did nay say much about it, me bucko, concentratin' t' chapter mostly on t' more common series staging. So I decided t' try t' build a parallel staged rocket. Blimey! Ahoy! Blimey! 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, shiver me timbers, arrr, which are widely accepted techniques in model rocketry.

Flight History

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

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

On 30th July Titania was one o' t' rockets launched as part o' t' Clarecraft Discworld Event, matey, a sort o' open air convention for fans o' t' writer Terry Pratchett. Avast, me proud beauty! Ya scallywag! T' photo on t' left be taken prior t' its launch, witnessed by Terry Pratchett himself. Aye aye! Blimey! Again t' flight was good, with t' boosters detachin' and droppin' into t' field. T' sustainer weathercocked a little in t' wind, me hearties, did nay drift back far enough, and landed rather close t' some cars, 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. Ya scallywag! Blimey! Cone=40mm long, me hearties, extensions=30mm long.
Booster body=150mm o' Estes BT-20. (2 of)
Booster cone=matched pair from Estes NC20 pack.
Booster coupler=20mm cut from 18mm casing. 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®©™. Blimey! Arrr! (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, marked in 1/8ths, one line missing); or mark up t' BT-55 by whatever other means you prefer. Ahoy! Blimey! There should be four lines, equally spaced; t' fins will go on these. Midway betwixt two adjacent fin lines is another line, ya bilge rat, arrr, which is where a booster mount point will go; a second such line should be diametrically opposite it. Finally, another line, me hearties, midway betwixt a pair o' fins without a booster mount point betwixt them, ya bilge rat, ya bilge rat, be t' line for t' launch lug, 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! Make a slit in t' mount tube 5mm from t' front end and insert one end o' t' retainin' clip into it, ya bilge rat, then glue t' motor block (the front 5mm o' a spent D12 casing) into t' front end. Blimey! Make two centrin' rings out o' cardboard, matey, inner diameter 25mm, outer diameter 32.5mm. Blimey! Glue them t' t' mount tube, one 10mm from t' front end, arrr, ya bilge rat, t' other 50mm from t' front end. Begad! Ahoy! Reinforce t' joints with glue fillets. Well, blow me down! While all this is drying, why nay fit the...

Shock Cord
Again, basic Estes stuff. Ahoy! Blimey! Begad! Blimey! Cut out a paper trapezoid and fold it in three. Avast, ya bilge rat, me proud beauty! Blimey! 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, shiver me timbers, then fold t' paper. Ahoy! Blimey! Blimey! Blimey! Spread glue over t' second section o' t' mount and fold it again. Begad! Blimey! Ahoy! Blimey! Clamp it until it's dry. Begad! Blimey! Begad! Blimey! Then glue it into t' front end o' t' BT-55, arrr, at least 35mm down. Leave it t' dry, and in t' meantime you can make the...

Upper Body
Glue t' transition into one end o' t' BT-60. 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, matey, me hearties, then you get t' use t' BT-60 as a payload bay. Screw t' screw eye into t' transition, arrr, remove it, matey, put a little glue into t' hole it made, arrr, shiver me timbers, matey, then screw it back in and leave it.

Boosters
Take 150mm o' BT-20. Begad! Begad! 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. Begad! Begad! 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. Ahoy! Take 450mm o' Keelhaul®©™ thread and tie it round t' motor block, me hearties, then glue t' motor block 65mm into t' aft tube. Ahoy! Begad! (You can use another spent 18mm casin' t' position it. Avast! Put a mark 5mm from t' aft end o' t' casing, then use t' casin' t' push t' motor block into t' booster's aft tube. Well, blow me down! 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, tie it onto a nose-cone, me hearties, arrr, 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, 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, ya bilge rat, cut four pieces 61mm long.
From t' 4mm diameter brass tube, arrr, 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, me hearties, arrr, so that t' tubes extend 4mm past one end o' t' base and 6mm past t' other. Well, ya bilge rat, blow me down! 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. Repeat t' procedure t' make a second booster mount, then leave both aside until they're dry. 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, matey, slide a 6mm x 4mm tube onto each o' t' 4mm extensions, me hearties, and an 11mm x 4mm tube onto each o' t' 6mm extensions. Glue a 9mm x 8.5mm block o' balsa betwixt t' 6mm x 4mm tubes, ya bilge rat, and a 12mm x 8.5mm block betwixt t' 11mm tubes. Avast, me proud beauty! These blocks, me bucko, with their small tubes attached, matey, will be t' booster attachments. Well, blow me down! Aye aye! Blimey! T' blocks should all touch t' booster mount base, shiver me timbers, me hearties, but none o' t' small tubes should do so. Ahoy! Blimey! Again, me hearties, be very careful nay t' get any glue onto t' booster mount tube ends, otherwise t' booster attachments will have trouble separatin' from t' booster mounts. Begad! Leave all this t' dry solid.

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

If you've done all this correctly, shiver me timbers, you can pull t' booster apart and t' front part, havin' smaller attachment tubes, arrr, should come away from t' mount point slightly more readily than t' aft part. Remove both boosters from t' mount points. Well, blow me down! Blimey! Ya scallywag! Blimey! Draw a line down t' middle o' each mount point. Blimey! Blimey! 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. Ahoy! Blimey! Begad! Blimey! Fit t' booster onto t' mount point, shiver me timbers, 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. Ahoy! Blimey! Remove t' booster again, me hearties, check that t' mount point is still properly lined up, shiver me timbers, matey, then leave it t' dry. 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, ya bilge rat, which should be made from balsa 3mm thick. Arrr! If, like me, you do nay have wide enough balsa sheets t' make each fin out as a single unit, arrr, you can cut t' template as indicated, me bucko, on a line parallel t' t' leadin' edge, t' make two pieces for each fin. 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. Cut 45mm from a straw wide enough t' accept a 5mm launch rod. Angle t' cut at 45 degrees, me hearties, so that t' leadin' edge o' t' lug is swept back. Begad! (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. Well, blow me down! Again, arrr, t' leadin' edge can be angled t' match t' launch lug. Begad! Glue t' standoff t' t' body tube 155mm from t' aft end, me hearties, 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. Fillets on t' fins, ya bilge rat, launch lug standoff and booster attachments are epoxy. 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. All paints are car sprays. Avast, me proud beauty! Ahoy! Blimey! O' course, matey, me bucko, you are free t' use your own favourite ingredients for this stage!

One thin' is important, though. Ahoy! Blimey! Mask t' booster mount point tubes when sprayin' t' sustainer body, and mask t' booster attachment tubes when sprayin' t' boosters. Blimey! Blimey! You do nay want t' get paint on t' ends o' t' booster mount tubes or t' insides o' t' booster attachment tubes. Aye aye! Blimey! 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), arrr, D12-5, arrr, ya bilge rat, D12-7
Boosters: B6-0 (first flight), arrr, me bucko, C6-0

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

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

Recovery Systems

For recovery, matey, Titania can use a 12" parachute. Well, blow me down! Mine has used stock Estes parachutes, and once even landed safely on an Estes 12" parachute with a spill hole cut out. Ya scallywag! These landings were all on relatively soft, me hearties, ya bilge rat, arrr, grassy ground. Aye aye! T' boosters are fitted with 12" x 1" streamers made from mylar (cut from a "space blanket", me hearties, shiver me timbers, me bucko, t' be precise).

T' sustainer parachute should be protected by 4 or 5 pieces o' wadding. Avast, me proud beauty! Each booster should also be given one piece t' protect t' streamers.

Ignition
If you have a good launch controller, preferably powered by a 12V battery, me bucko, shiver me timbers, you can put a separate igniter in each motor. Ya scallywag! This be t' method I use. Ahoy! It should also be possible t' use fast pyrotechnic fuse such as Quickmatch t' fire all three motors from one igniter. Avast! One method, which I have nay personally tried but which may be worth trying, is t' fit an igniter into t' sustainer's motor, and have Quickmatch runnin' from its nozzle t' t' boosters. This has t' disadvantage that t' boosters will ignite after t' sustainer, 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. Ya scallywag! Begad! If you can get this t' print out t' t' correct size, you can cut out t' fin and alignment templates. Well, blow me down! If not, ya bilge rat, t' diagram shows t' sizes o' t' fin's root, tip and trailin' edges, as well as t' leadin' edge sweep.