Beg Birtha

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

Build

This really is a straightforward build. T' differences from t' stock kit may be summarized as "leave out t' motor mount and add some nose weight". Ahoy! But, because I know our beloved newsletter editor will appreciate t' extra column inches, me hearties, I'll spell it out in full:

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

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

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

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

Step 11, me bucko, Paintin' Your Rocket, shiver me timbers, ya bilge rat, ya bilge rat, was done as directed. Aye aye! Blimey! For Step 12, Parachute And Shock Cord Attachment, shiver me timbers, ya bilge rat, I deviated from t' instructions, me hearties, 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, on 10th April 2004. Avast! I thoroughly enjoyed this launch, a relaxed, shiver me timbers, convivial atmosphere, matey, and a great bunch o' Rocketeers.

Because I omitted t' original motor mount, matey, thar be no retainer hook - it wouldn't be long enough anyway. So friction fit was t' order o' t' day. Blimey! Aye aye! And you do need t' make sure it's a tight fit, me hearties, you really don't want a spent Pitfield motor landin' on your head! T' F36 has an enormous nozzle, and I be a bit worried that an Estes igniter might get lost in there. Aye aye! So I used some QuickMatch, ya bilge rat, pushed all t' way in, taped t' t' motor body, with an Estes igniter on t' exposed end. Well, blow me down! Avast, shiver me timbers, me proud beauty! It be only about 60mm o' QuickMatch, shiver me timbers, arrr, and when I pushed t' button, ya bilge rat, ignition was pretty much instant. Avast, me proud beauty! Beg Birtha fairly leapt from t' pad, matey, me hearties, matey, so smartly that I don't think anyone managed t' get a picture. Ya scallywag! Avast, me proud beauty! T' motor thrust decreased, but kept burnin' almost up t' apogee, t' orange glow quite visible. Arrr! This would be a great rocket t' fly at dusk.

Conclusion

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