Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, arrr, me hearties, thought some o' you might. Arrr! Well, me bucko, we don't see them around so much as in years gone by, ya bilge rat, me bucko, but thar are still a few around. Well, blow me down! In fact, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Avast, me proud beauty! Well, ya bilge rat, blow me down! I'd never actually flown a Pitfield motor before. Avast! Aye aye! Watchin' other people's flights had always put me off a bit. T' rockets always seemed t' be underpowered, and had started t' descend while still under thrust. Who can forget Rick Newlands spendin' almost t' whole o' UKRA 2000 sandin' a nose cone from a balsa tree trunk, shiver me timbers, 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, matey, me hearties, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Begad! Though it didn't quite fly as intended, it took joint first prize, matey, along with Mike Crewe's Mercury Redstone. Ahoy! Arrr! Our prizes were matchin' Big Berthas. Avast, me proud beauty! Blimey! We'd agreed we would build them with a common theme, me hearties, and drag race them. Well, blow me down! Initially it was t' be a cluster, ya bilge rat, ya bilge rat, but, when we came into t' stash o' Pitfield motors, matey, me bucko, we had other ideas. Begad! You see, me hearties, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Avast, me proud beauty! Avast, me bucko, me proud beauty! Beg Birtha was born.

Simulation

It was easy t' modify a standard Big Bertha Rocksim File. Aye aye! I just removed t' motor mount and added a new thrust ring. Arrr! I made some rasp-format engine files for t' motor, shiver me timbers, usin' t' engine editor that come with Rocksim. I got t' thrust curve, matey, and data from an old Rocket Services catalogue. Arrr! Aye aye! 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, matey, shiver me timbers, me hearties, that Rocket Services' motor designations, do nay correspond with t' more common "Estes-style" designations. T' "F36-5" should, strictly speaking, me hearties, be known as E6-5, and t' "F72-0" is, me hearties, in reality, me bucko, an E15-0. Havin' said that, Estes aren't always consistent themselves. Avast! 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. Begad! T' differences from t' stock kit may be summarized as "leave out t' motor mount and add some nose weight". Begad! But, because I know our beloved newsletter editor will appreciate t' extra column inches, I'll spell it out in full:

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

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

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

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

Step 11, Paintin' Your Rocket, was done as directed. Ahoy! For Step 12, arrr, Parachute And Shock Cord Attachment, arrr, me hearties, I deviated from t' instructions, ya bilge rat, 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, on 10th April 2004. I thoroughly enjoyed this launch, matey, a relaxed, convivial atmosphere, shiver me timbers, 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. Avast, me proud beauty! So friction fit be t' order o' t' day. Arrr! 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, shiver me timbers, matey, with an Estes igniter on t' exposed end. Avast, me proud beauty! Begad! It was only about 60mm o' QuickMatch, ya bilge rat, me bucko, matey, and when I pushed t' button, ignition was pretty much instant. Avast, me proud beauty! Begad! Beg Birtha fairly leapt from t' pad, so smartly that I don't think anyone managed t' get a picture. Arrr! T' motor thrust decreased, but kept burnin' almost up t' apogee, t' orange glow quite visible. Ya scallywag! This would be a great rocket t' fly at dusk.

Conclusion

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