Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, matey, thought some o' you might. Well, me hearties, shiver me timbers, we don't see them around so much as in years gone by, arrr, me hearties, but thar are still a few around. Aye aye! In fact, matey, ya bilge rat, arrr, 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. Avast, me proud beauty! Watchin' other people's flights had always put me off a bit. Blimey! T' rockets always seemed t' be underpowered, 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, arrr, 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, me hearties, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Though it didn't quite fly as intended, arrr, ya bilge rat, it took joint first prize, me hearties, along with Mike Crewe's Mercury Redstone. Begad! Our prizes were matchin' Big Berthas. We'd agreed we would build them with a common theme, matey, me bucko, and drag race them. Well, blow me down! Initially it was t' be a cluster, but, me bucko, when we came into t' stash o' Pitfield motors, we had other ideas. Begad! You see, matey, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Avast, me proud beauty! Aye aye! Beg Birtha was born.

Simulation

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

Build

This really is a straightforward build. Blimey! 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, ya bilge rat, matey, I'll spell it out in full:

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

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

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

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

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

Flying

T' first flight be on t' occasion o' me first attendance at a WRS (Wirral Rocketry Society) launch, ya bilge rat, on 10th April 2004. Avast, me proud beauty! Begad! I thoroughly enjoyed this launch, ya bilge rat, a relaxed, me hearties, convivial atmosphere, ya bilge rat, me bucko, 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. So friction fit be t' order o' t' day. And you do need t' make sure it's a tight fit, 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. Well, blow me down! So I used some QuickMatch, pushed all t' way in, taped t' t' motor body, with an Estes igniter on t' exposed end. Aye aye! It was only about 60mm o' QuickMatch, and when I pushed t' button, ignition was pretty much instant. Ahoy! Beg Birtha fairly leapt from t' pad, me bucko, so smartly that I don't think anyone managed t' get a picture. T' motor thrust decreased, arrr, shiver me timbers, shiver me timbers, but kept burnin' almost up t' apogee, arrr, t' orange glow quite visible. Begad! Begad! This would be a great rocket t' fly at dusk.

Conclusion

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