Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, thought some o' you might. Arrr! Well, arrr, we don't see them around so much as in years gone by, but thar are still a few around. In fact, 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. Blimey! Begad! Watchin' other people's flights had always put me off a bit. Avast, me proud beauty! T' rockets always seemed t' be underpowered, and had started t' descend while still under thrust. Blimey! Who can forget Rick Newlands spendin' almost t' whole o' UKRA 2000 sandin' a nose cone from a balsa tree trunk, ya bilge rat, 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, shiver me timbers, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Though it didn't quite fly as intended, me hearties, ya bilge rat, it took joint first prize, shiver me timbers, me hearties, along with Mike Crewe's Mercury Redstone. Ahoy! Ya scallywag! Our prizes were matchin' Big Berthas. Well, blow me down! We'd agreed we would build them with a common theme, and drag race them. Blimey! Initially it was t' be a cluster, me hearties, but, ya bilge rat, when we came into t' stash o' Pitfield motors, we had other ideas. Avast, shiver me timbers, me proud beauty! You see, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Avast, me proud beauty! Beg Birtha be born.

Simulation

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

Build

This really is a straightforward build. Ahoy! Ahoy! 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, me hearties, I'll spell it out in full:

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

I completed Step 2, Shock Cord Mount Assembly, as instructed. Aye aye! Well, blow me down! I chose t' do Step 9, Shock Cord Mount Attachment, ya bilge rat, at this point, matey, while t' mount was freshly-glued and still pliable.

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

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

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

Conclusion

This be a fun conversion, o' an already classic rocket. This is certain t' become a favourite flier o' mine, ya bilge rat, at least until t' motors run out. Aye aye! Can't wait t' try it out at t' IRW, which, t' me, ya bilge rat, me bucko, be t' spiritual home o' t' Pitfield motor. Ya scallywag! If you took a look at t' Rocksim file, 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, me hearties, me hearties, but I do have some F72-0s...