SA-2 Guideline SAM

By Naill Oswald

Brief

A 2-stage sport scale model o' t' ubiquitous SA-2 ‘Guideline' Surface t' Air missile, designed t' fly on 24mm BP motors.

Introduction

Shortly after I became interested in rocketry, I paid a visit t' a local transport museum, and among t' exhibits was an SA-2 SAM and its associated transporter. Blimey! Arrr! T' SA-2 is pretty much t' archetypal SAM – for good reason since somethin' like 10,000 have been launched in active service. I think it is a nicely proportioned missile, me hearties, with large aft fins and a sleek profile, arrr, and lookin' at t' real thing, shiver me timbers, I thought t' myself ‘that would be good t' model'.

Some time later I found a scale drawin' by Peter Always o' t' SA-2, and had a look at t' ratios o' diameters o' t' booster and sustainer. T' booster is 65 cm in diameter, me hearties, and t' sustainer is 50 cm. Ya scallywag! This works out quite nicely for either 2” and 2.5” tube, or for BT-55 (33.7mm) and BT-60 (41.6mm) (0.8 vs 0.77). Arrr! I decided t' go for this, shiver me timbers, since it would work nicely for Estes C11 and D12 motors.

T' first step be t' finalize t' scale factor, arrr, and work out t' dimensions o' t' various parts o' t' rockets. Begad! Its been a while since I did all t' sums, but me aim was a good overall model, rather than super-accurate scale detail. Ahoy! As such I looked t' use off-the-shelf parts as far as possible, but I found that t' Estes PNC-55AC (Bullpup) and TA55-60 transition were good matches for t' SA-2 NC and transition section.

My scale factor worked out t' approximately 1:15, shiver me timbers, its nay exact but its close enough. Ya scallywag! I scaled all t' lengths by this factor t' give me t' fin dimensions and t' lengths o' t' body tubes.

Design

T' body tubes are fairly straightforward – thar be a 326mm length o' BT-55 which forms t' sustainer body and an 132mm length o' BT-60 which forms t' booster body. Aye aye! Includin' t' nose cone an fins t' overall length is 671mm. Blimey! T' SA-2 has 4 sets o' 4 fins, but I only modeled three, shiver me timbers, ya bilge rat, missin' t' small forward fins attached t' t' NC. Blimey! Aye aye! This was more due t' forgettin' t' do them than anythin' else, thar's no reason why a future build couldn't include them.

T' sustainer has a large set o' fins roughly in t' middle o' t' BT, and smaller set aft o' those. Blimey! Arrr! T' booster has large fins which extend beyond t' aft o' t' body tube. T' SA-2 booster also has a large nozzle which extends as far as t' booster fins.

I built up a full model o' t' rocket usin' SpaceCad3 (demo version), me bucko, which was also used t' determine that 75g o' noseweight would be needed t' make t' rocket stable in 2-stage configuration with 2 D12's.

Parts List

• Xxxmm BT-55 (I used Apollo 11/Totally Tubular tubing)
• Xxxmm BT-60
• ACR-5060 fibre centerin' rings (3)
• ACR-2060 fibre centerin' rings (2)
• ACR-5055 kraft centerin' rings (3)
• AEB-50HD 24mm motor blocks (2)
• Xx mm AET-50mf 24mm foil lined motor tube (2)
• Xxmm BT-20
• Estes PNC-55AC ogive plastic NC
• Estes TA-5560 plastic transition
• 1/8” Balsa sheet for fins
• 3 and 5 mm launch lugs
• Keelhaul®©™ cord, matey, ya bilge rat, nomex square, elastic and parachute for recovery
• Paper for ‘nozzle' shroud
• Small woodscrew or self-tappin' screw

Construction

Overall, me hearties, construction is reasonably simple, me hearties, and uses standard model techniques and materials. Avast! Avast! T' sustainer motor mount is a little unconventional, matey, me hearties, and t' booster uses an internal stuffer tube, shiver me timbers, as well as t' ‘nozzle', me bucko, so thar be a little more t' construction than t' usual 3/4FNC type models. There are also 12 fins t' cut, me hearties, sand and finish, so a bit more work is involved in that respect.

T' first step is t' assemble all t' parts, me hearties, and t' cut out and round t' edges o' t' fins, shiver me timbers, ready for bondin' t' t' body tubes. Arrr! T' body tubes and motor mounts also need t' be cut t' length before proceeding. Ahoy! I would suggest also markin' both body tubes for 4 fins at this point.

With t' booster tube cut, me bucko, I assembled t' booster MMT assembly. Begad! Ya scallywag! This consists o' a motor tube long enough t' form t' booster ‘nozzle' and give a useful length for centerin' in t' BT, ya bilge rat, and two centerin' rings. Ya scallywag! Begad! One centerin' rin' is bonded at t' top o' t' MMT, arrr, and t' other where t' BT ends and t' MMT extends beyond it. Ya scallywag! One o' t' 5055 rings is bonded t' t' end o' t' MMT, as part o' formin' t' nozzle. Blimey! Usin' t' –mf tube, I had t' sand t' fibre rings and peel a wrap o' paper from t' kraft rings t' fit t' thicker tubing. Begad! In t' usual way, a motor block was also bonded into t' booster MMT at t' appropriate place t' fit a 24x70mm motor.

My intention when buildin' was t' use quickmatch for reliable staging, shiver me timbers, so I set up a stuffer tube in t' booster t' keep t' hot gases and particles away from t' main BT wall. This consists o' a length o' BT-20, which fits into t' motor block and is centered in t' tube with a pair o' 2050 fibre rings. Ya scallywag! Blimey! This runs t' approximately 25mm short o' t' front o' t' booster BT and is all bonded with 5 minute epoxy.

T' nozzle is formed by rollin' an appropriately sized cone from paper, me bucko, me bucko, cuttin' off t' tip, and usin' PVA glue t' bond it t' t' MMT which extends from t' booster stage. With t' MMT and nozzle assembled, shiver me timbers, t' booster fins can be attached – I used CA t' do this, but as with all models, personal preference may be different. Begad! Begad! At this point all t' booster needs is launch lugs, arrr, and I installed mine in t' ‘fin root' position, which I quite like. Begad! I put 3mm and 5mm lugs on opposite sides o' t' body tube t' allow use o' a stronger ‘maxi' rod where available. I realized at this point that t' rocket would only be able t' fly easily with both stages attached, so I made another stuffer tube t' allow t' booster t' carry a motor with an ejection charge, and eject up through t' stuffer tube into t' sustainer. Avast, me proud beauty! This prevents t' sustainer MMT gettin' filled with ejection gunk, and keeps t' gases from blowin' t' sustainer and booster apart at ejection. Arrr! I also added a small woodscrew t' hold t' stages together for single stage flight, matey, but I think plastic rivets would be a better idea.

Movin' on t' t' sustainer, t' construction is pretty much straightforward apart from t' motor mount. T' motor is mounted inside t' transition, so t' sustainer is male and t' booster is female (rather than t' usual arrangement with a coupler on t' booster.

I carefully modified t' transition t' allow t' motor mount t' be installed inside it. Avast! This involved removin' t' front and aft sections o' t' transition, includin' t' shock cord attachment points, matey, and modifyin' t' appropriate centerin' rings t' fit inside t' transition. T' aft CR is a 5060 rin' which has been sanded down, and t' forward rings are 5055 kraft rings. Ya scallywag! I used two, me hearties, but I think one would suffice. Aye aye! Ahoy! At this stage a Keelhaul®©™ leader can also be attached t' t' MMT assembly, matey, which I bonded with a mixture o' PVA and 5-minute epoxy (not literally a mixture, but different parts were bonded with different adhesives).

T' next step is t' install t' sustainer fins, shiver me timbers, which is easier if done before installin' t' completed motor mount. Aye aye! T' front o' t' forward fins should be located xx mm from t' top o' t' BT and t' aft o' t' aft fins should be located xx mm from t' aft o' t' body tube. Arrr! With t' fins bonded, ya bilge rat, t' motor mount can be bonded inside t' tube, makin' sure t' Keelhaul®©™ leader is fed through t' tube first.

T' NC can then be weighted – I used panel pins and epoxy t' add 75g t' t' NC, but ‘rocket caviar' would do just as well (lead shot and epoxy). T' elastic shock cord can be attached t' t' Keelhaul®©™ leader (I used a keyrin' as t' attachment point betwixt t' two) and a nomex square slipped onto t' elastic before attachin' it t' t' nose cone.

After this, t' rocket needs t' be finished. I painted mine in a hurry, and in late October in an unheated garage I had real problems with t' silver spray paint I used. After a couple o' coats o' primer, me bucko, I sprayed on t' silver, and it wrinkled up quite badly. In t' end I think I ended up sandin' off t' wrinkles and givin' it a light spray over, but t' finish job really could be a lot better. Aye aye! As it is, shiver me timbers, matey, t' rocket (I think anyway) has a look o' bare metal that's been exposed t' t' elements a bit, me bucko, so in keepin' with its military theme! If I was buildin' t' rocket again I would put proper fillets on t' fins, use sandin' sealer on t' fins, ya bilge rat, and properly fill and prime t' body tubes.

With t' various places t' SA-2 was used in, thar are undoubtedly many colour schemes, mine was just simple and reasonably suitable for t' rocket.

Flight Reports

T' first flight o' t' rocket came a long time after I built it, at Big EARS 2003. Given that I had t' rocket ready in November 2003, it was a little slow flyin' it for t' first time in May 2004!

I loaded up t' booster MMT with a D12-3, and installed t' stuffer tube by pushin' it into t' motor block o' t' upper stage MMT and tapin' it up, shiver me timbers, t' keep t' MMT from gettin' filled with ejection residue. Well, blow me down! Blimey! T' upper stage was prepped for recovery as usual – I think I had an Estes 24” or 18” chute installed at this time.

T' flight be nominal, ya bilge rat, with ejection slightly on t' early side. Nay a great altitude with a single D12, me bucko, ya bilge rat, but nay a problem for recovery. T' descent was slow on t' big chute, which was quite tricky t' fit in t' BT-55 sustainer. Avast! Avast! No damage be sustained, ya bilge rat, arrr, me bucko, a good first flight.

For t' second flight, I decided t' fly with a D12-0 in t' booster and a C11-5 in t' sustainer. Begad! Begad! I installed a length o' quickmatch into t' nozzle o' t' sustainer motor, and trimmed it so that t' exposed ends o' t' internal fuses would be in contact with t' exposed propellant o' t' booster motor. Aye aye! T' rocket took off as before, and staged perfectly. Blimey! T' added quickmatch made stagin' a bit more dramatic than usual, me hearties, and t' top stage coasted t' an apogee ejection after t' short burn o' t' C11. Arrr! T' booster tumbled in (large fins) and suffered no damage. Avast, me proud beauty! T' sustainer also recovered without problems, ya bilge rat, shiver me timbers, and landed a short way out in t' field.

T' third flight o' t' SA-2 came at UKRA 2004, me hearties, me hearties, and was on t' ‘full-up' configuration o' D12-0 t' D12-5. Avast! Blimey! Again t' sustainer motor had quickmatch installed and sized t' meet t' booster propellant. Begad! Blimey! On preppin' t' recovery system, I though t' shock cord looked a little crispy, me hearties, but went ahead without replacin' it.

T' flight be good, me bucko, with stagin' workin' perfectly, with quite a whoosh, and t' rocket gainin' a good altitude. Well, blow me down! However at ejection, t' nosecone separated, and t' sustainer came in without a parachute. Oddly, it came in backwards (motor mount first), matey, executin' a conin' motion, shiver me timbers, me hearties, pivotin' about t' aft o' t' rocket. Ya scallywag! Begad! I went lookin' in t' low crops for it, but didn't find it until I was about t' give up, and turned round t' see t' sustainer stood up in t' crop right next t' me. Avast, me proud beauty! Begad! It had landed on t' strongest part o' t' rocket – t' motor mount – and suffered no damage. Avast, me proud beauty! T' nosecone floated off into t' distance – 75g on a 24” chute results in a very slow descent. Ya scallywag! I gave up on tryin' t' get it back, arrr, happy that I had t' booster and sustainer back intact.

I took t' SA-2 along t' t' Canterbury Cup/Heckington Mug in August, ya bilge rat, thinkin' I may be able t' fly it if I could find a suitable nosecone and some noseweight. However as I be walkin' back from t' HPR range past one o' t' PA speaker, ya bilge rat, I noticed a silver nosecone tied t' t' stand with an elastic shock cord. Avast! Begad! I looked inside, me hearties, and t' end was full o' panel pins and epoxy – it was me nosecone I'd lost almost three months ago!

I soon had t' nosecone reattached t' t' rocket with a new shock cord, and a new 12” Estes chute (which had cost a mere 50p), me bucko, and I set about preppin' it for another D-D flight.

I flew t' rocket from a standard Estes Porta-Pad, with no problem. Begad! It took off fast, shiver me timbers, arrr, staged nicely and came back for a perfect recovery. Blimey! Blimey! Grant Gibson, me bucko, whom I be launchin' with, matey, was quite impressed with t' stagin' – I think t' quickmatch helps in that respect.

Overall this rocket has been quite successful, and should fly again soon. Blimey! Well, blow me down! I think t' design could be refined t' make it more accurate in terms o' scale features, and it deserves a decent paintjob, but I am pleased with t' results.