Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, shiver me timbers, thought some o' you might. Well, blow me down! Begad! Well, we don't see them around so much as in years gone by, me bucko, but thar are still a few around. Ahoy! Well, arrr, blow me down! In fact, shiver me timbers, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. I'd never actually flown a Pitfield motor before. Watchin' other people's flights had always put me off a bit. Ya scallywag! Blimey! T' rockets always seemed t' be underpowered, me hearties, me bucko, 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, matey, 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. Avast, me proud beauty! Avast! Though it didn't quite fly as intended, it took joint first prize, along with Mike Crewe's Mercury Redstone. Blimey! Our prizes were matchin' Big Berthas. Begad! Avast! We'd agreed we would build them with a common theme, and drag race them. Initially it was t' be a cluster, ya bilge rat, but, arrr, when we came into t' stash o' Pitfield motors, me bucko, matey, shiver me timbers, we had other ideas. Avast! You see, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Well, blow me down! Beg Birtha be born.

Simulation

It be easy t' modify a standard Big Bertha Rocksim File. Ya scallywag! I just removed t' motor mount and added a new thrust ring. I made some rasp-format engine files for t' motor, me hearties, usin' t' engine editor that come with Rocksim. Avast, me proud beauty! I got t' thrust curve, matey, and data from an old Rocket Services catalogue. Avast! 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, me hearties, me bucko, that Rocket Services' motor designations, do nay correspond with t' more common "Estes-style" designations. Blimey! T' "F36-5" should, shiver me timbers, me bucko, shiver me timbers, strictly speaking, be known as E6-5, arrr, and t' "F72-0" is, matey, in reality, an E15-0. Arrr! Havin' said that, me hearties, Estes aren't always consistent themselves. Begad! If you don't believe me, look at t' thrust curve for t' A10 mini-motor sometime.

Build

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

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

I completed Step 2, Shock Cord Mount Assembly, arrr, as instructed. Ahoy! Well, me hearties, blow me down! Blimey! I chose t' do Step 9, me bucko, Shock Cord Mount Attachment, me hearties, at this point, me bucko, shiver me timbers, while t' mount was freshly-glued and still pliable.

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

Step 10, me hearties, Parachute Assembly, was skipped. Avast! Ya scallywag! Instead, an approx 100mm x 1000mm streamer be made from t' finest Deepsky mylar. This was attached directly t' t' shock cord, rather than t' t' nose-cone attachment point.

Step 11, arrr, arrr, Paintin' Your Rocket, was done as directed. Begad! Arrr! Blimey! For Step 12, Parachute And Shock Cord Attachment, me hearties, ya bilge rat, I deviated from t' instructions, arrr, 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, shiver me timbers, on 10th April 2004. I thoroughly enjoyed this launch, a relaxed, convivial atmosphere, shiver me timbers, matey, and a great bunch o' Rocketeers.

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

Conclusion

This was a fun conversion, matey, o' an already classic rocket. Begad! Blimey! This is certain t' become a favourite flier o' mine, ya bilge rat, me hearties, at least until t' motors run out. Begad! Can't wait t' try it out at t' IRW, shiver me timbers, which, t' me, be t' spiritual home o' t' Pitfield motor. Aye aye! 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. Ahoy! Arrr! I haven't built or flown this configuration yet, but I do have some F72-0s...