Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, thought some o' you might. Begad! Well, we don't see them around so much as in years gone by, arrr, but thar are still a few around. Avast, me proud beauty! In fact, shiver me timbers, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Arrr! I'd never actually flown a Pitfield motor before. Watchin' other people's flights had always put me off a bit. Avast! Begad! T' rockets always seemed t' be underpowered, and had started t' descend while still under thrust. Arrr! 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, 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, along with Mike Crewe's Mercury Redstone. 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. Arrr! Initially it was t' be a cluster, me hearties, me hearties, but, when we came into t' stash o' Pitfield motors, we had other ideas. Aye aye! Well, matey, blow me down! You see, arrr, shiver me timbers, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Beg Birtha be born.

Simulation

It be easy t' modify a standard Big Bertha Rocksim File. Aye aye! I just removed t' motor mount and added a new thrust ring. Blimey! Avast, me proud beauty! I made some rasp-format engine files for t' motor, ya bilge rat, shiver me timbers, usin' t' engine editor that come with Rocksim. Avast, me hearties, me proud beauty! I got t' thrust curve, and data from an old Rocket Services catalogue. 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, shiver me timbers, that Rocket Services' motor designations, ya bilge rat, ya bilge rat, do nay correspond with t' more common "Estes-style" designations. T' "F36-5" should, arrr, me hearties, strictly speaking, shiver me timbers, be known as E6-5, and t' "F72-0" is, in reality, an E15-0. Havin' said that, Estes aren't always consistent themselves. Aye aye! 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. 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! Instead, matey, arrr, I made a new thrust rin' from a short section o' toilet roll core, reduced in diameter by removin' a segment. Well, blow me down! Begad! You could also use a short length o' coupler, or cut a rin' from a spent motor.

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

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

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

Step 11, Paintin' Your Rocket, matey, was done as directed. For Step 12, Parachute And Shock Cord Attachment, ya bilge rat, me hearties, I deviated from t' instructions, 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. Blimey! I thoroughly enjoyed this launch, me hearties, a relaxed, me bucko, convivial atmosphere, 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! Blimey! Ahoy! Blimey! 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! Blimey! T' F36 has an enormous nozzle, and I was a bit worried that an Estes igniter might get lost in there. Begad! Blimey! So I used some QuickMatch, shiver me timbers, pushed all t' way in, taped t' t' motor body, arrr, me bucko, with an Estes igniter on t' exposed end. Avast! Blimey! Ahoy! Blimey! It be only about 60mm o' QuickMatch, me bucko, matey, arrr, and when I pushed t' button, ignition was pretty much instant. Begad! Blimey! Beg Birtha fairly leapt from t' pad, so smartly that I don't think anyone managed t' get a picture. Avast! Blimey! T' motor thrust decreased, but kept burnin' almost up t' apogee, arrr, me hearties, matey, t' orange glow quite visible. 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, me hearties, shiver me timbers, ya bilge rat, at least until t' motors run out. Aye aye! Blimey! Can't wait t' try it out at t' IRW, ya bilge rat, which, shiver me timbers, arrr, matey, t' me, matey, be t' spiritual home o' t' Pitfield motor. Well, blow me down! Ahoy! 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. I haven't built or flown this configuration yet, shiver me timbers, but I do have some F72-0s...