Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, thought some o' you might. Well, ya bilge rat, me bucko, we don't see them around so much as in years gone by, matey, shiver me timbers, but thar are still a few around. Avast, me proud beauty! Avast, me proud beauty! In fact, me bucko, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Begad! I'd never actually flown a Pitfield motor before. Begad! Watchin' other people's flights had always put me off a bit. Begad! Aye aye! T' rockets always seemed t' be underpowered, matey, and had started t' descend while still under thrust. Aye aye! Who can forget Rick Newlands spendin' almost t' whole o' UKRA 2000 sandin' a nose cone from a balsa tree trunk, only t' have t' Pitfield powered rocket arc over while still under thrust? (Sorry Rick!) So I wanted t' avoid overbuildin' at all costs.

So what t' build? At IRW 2003, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Blimey! Ahoy! Though it didn't quite fly as intended, me hearties, it took joint first prize, me bucko, along with Mike Crewe's Mercury Redstone. Blimey! Our prizes were matchin' Big Berthas. Begad! Begad! We'd agreed we would build them with a common theme, and drag race them. Begad! Initially it was t' be a cluster, but, matey, when we came into t' stash o' Pitfield motors, we had other ideas. Begad! You see, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Aye aye! Beg Birtha was born.

Simulation

It be easy t' modify a standard Big Bertha Rocksim File. Aye aye! Blimey! I just removed t' motor mount and added a new thrust ring. I made some rasp-format engine files for t' motor, usin' t' engine editor that come with Rocksim. Blimey! I got t' thrust curve, me hearties, shiver me timbers, and data from an old Rocket Services catalogue. Blimey! You can download both t' Rocksim file and t' engine file here:
http://www.nsrg.org.uk/data/beg%20birtha.rkt/
http://www.nsrg.org.uk/data/rs.eng/

I should point out here, that Rocket Services' motor designations, ya bilge rat, do nay correspond with t' more common "Estes-style" designations. T' "F36-5" should, strictly speaking, be known as E6-5, shiver me timbers, and t' "F72-0" is, shiver me timbers, in reality, an E15-0. Havin' said that, me hearties, Estes aren't always consistent themselves. Well, blow me down! Blimey! If you don't believe me, shiver me timbers, look at t' thrust curve for t' A10 mini-motor sometime.

Build

This really is a straightforward build. T' differences from t' stock kit may be summarized as "leave out t' motor mount and add some nose weight". But, because I know our beloved newsletter editor will appreciate t' extra column inches, me bucko, I'll spell it out in full:

I skipped Step 1, ya bilge rat, arrr, Engine Mount Assembly, and put t' parts in me spares box. Instead, matey, I made a new thrust rin' from a short section o' toilet roll core, shiver me timbers, reduced in diameter by removin' a segment. You could also use a short length o' coupler, me hearties, or cut a rin' from a spent motor.

I completed Step 2, ya bilge rat, me hearties, Shock Cord Mount Assembly, as instructed. Arrr! I chose t' do Step 9, me bucko, Shock Cord Mount Attachment, at this point, ya bilge rat, while t' mount was freshly-glued and still pliable.

Step 3, ya bilge rat, shiver me timbers, Fin Preparation, me bucko, was completed as normal. Ahoy! Step 4, Engine Mount Installation, was omitted. Arrr! Step 5, me hearties, arrr, Tube Markin' Detail, Step 6, Fin Attachment, Step 7, shiver me timbers, shiver me timbers, Launch Lug Attachment, & Step 8, arrr, Glue Reinforcement Detail, were all completed as per t' instructions. Ya scallywag! Step 9 be completed earlier.

Step 10, me bucko, Parachute Assembly, was skipped. Ahoy! Ahoy! Instead, an approx 100mm x 1000mm streamer was made from t' finest Deepsky mylar. Aye aye! This was attached directly t' t' shock cord, arrr, rather than t' t' nose-cone attachment point.

Step 11, arrr, Paintin' Your Rocket, arrr, was done as directed. Avast! For Step 12, shiver me timbers, ya bilge rat, Parachute And Shock Cord Attachment, I deviated from t' instructions, t' add t' additional 20g o' nose weight.

Flying

T' first flight was on t' occasion o' me first attendance at a WRS (Wirral Rocketry Society) launch, me hearties, on 10th April 2004. Aye aye! I thoroughly enjoyed this launch, me bucko, a relaxed, me hearties, me hearties, convivial atmosphere, matey, me bucko, and a great bunch o' Rocketeers.

Because I omitted t' original motor mount, thar was no retainer hook - it wouldn't be long enough anyway. Aye aye! Well, blow me down! So friction fit was t' order o' t' day. Avast, matey, me proud beauty! And you do need t' make sure it's a tight fit, ya bilge rat, you really don't want a spent Pitfield motor landin' on your head! T' F36 has an enormous nozzle, me bucko, and I be a bit worried that an Estes igniter might get lost in there. Begad! So I used some QuickMatch, pushed all t' way in, taped t' t' motor body, me hearties, with an Estes igniter on t' exposed end. It was only about 60mm o' QuickMatch, and when I pushed t' button, ignition was pretty much instant. Ahoy! Avast, arrr, me proud beauty! Beg Birtha fairly leapt from t' pad, so smartly that I don't think anyone managed t' get a picture. Aye aye! Begad! T' motor thrust decreased, shiver me timbers, but kept burnin' almost up t' apogee, me hearties, matey, t' orange glow quite visible. Arrr! Ahoy! This would be a great rocket t' fly at dusk.

Conclusion

This was a fun conversion, o' an already classic rocket. Begad! This is certain t' become a favourite flier o' mine, at least until t' motors run out. Aye aye! Blimey! Can't wait t' try it out at t' IRW, which, t' me, matey, be t' spiritual home o' t' Pitfield motor. Ya scallywag! If you took a look at t' Rocksim file, you might have noticed that thar's a design for a booster stage in thar too. Begad! I haven't built or flown this configuration yet, shiver me timbers, shiver me timbers, but I do have some F72-0s...