Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, thought some o' you might. Aye aye! Well, we don't see them around so much as in years gone by, ya bilge rat, but thar are still a few around. Begad! In fact, ya bilge rat, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Begad! I'd never actually flown a Pitfield motor before. Arrr! Watchin' other people's flights had always put me off a bit. Ya scallywag! T' rockets always seemed t' be underpowered, arrr, and had started t' descend while still under thrust. Begad! Begad! Who can forget Rick Newlands spendin' almost t' whole o' UKRA 2000 sandin' a nose cone from a balsa tree trunk, 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, ya bilge rat, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Blimey! Though it didn't quite fly as intended, it took joint first prize, matey, along with Mike Crewe's Mercury Redstone. Begad! 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. Initially it was t' be a cluster, ya bilge rat, but, when we came into t' stash o' Pitfield motors, ya bilge rat, shiver me timbers, we had other ideas. Avast! Begad! You see, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Blimey! Ahoy! 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. Blimey! I made some rasp-format engine files for t' motor, usin' t' engine editor that come with Rocksim. I got t' thrust curve, and data from an old Rocket Services catalogue. Avast, me proud beauty! 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, arrr, me hearties, do nay correspond with t' more common "Estes-style" designations. Avast, me proud beauty! Well, blow me down! T' "F36-5" should, strictly speaking, be known as E6-5, and t' "F72-0" is, arrr, matey, in reality, an E15-0. Begad! Havin' said that, arrr, arrr, Estes aren't always consistent themselves. Begad! Avast, me proud beauty! If you don't believe me, ya bilge rat, arrr, look at t' thrust curve for t' A10 mini-motor sometime.

Build

This really is a straightforward build. Avast, me proud beauty! T' differences from t' stock kit may be summarized as "leave out t' motor mount and add some nose weight". Aye aye! 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, arrr, shiver me timbers, shiver me timbers, and put t' parts in me spares box. Avast! Instead, ya bilge rat, I made a new thrust rin' from a short section o' toilet roll core, arrr, reduced in diameter by removin' a segment. Avast! You could also use a short length o' coupler, or cut a rin' from a spent motor.

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

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

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

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

Conclusion

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