Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, thought some o' you might. Ya scallywag! Avast, me proud beauty! Well, shiver me timbers, we don't see them around so much as in years gone by, but thar are still a few around. Avast, me proud beauty! In fact, ya bilge rat, matey, ya bilge rat, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Ya scallywag! I'd never actually flown a Pitfield motor before. Watchin' other people's flights had always put me off a bit. T' rockets always seemed t' be underpowered, me bucko, and had started t' descend while still under thrust. 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, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Avast! Though it didn't quite fly as intended, it took joint first prize, along with Mike Crewe's Mercury Redstone. Arrr! Our prizes were matchin' Big Berthas. Well, blow me down! We'd agreed we would build them with a common theme, matey, and drag race them. Initially it be t' be a cluster, but, matey, when we came into t' stash o' Pitfield motors, me hearties, we had other ideas. Avast, ya bilge rat, me proud beauty! You see, shiver me timbers, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Avast! Begad! Beg Birtha was 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. I made some rasp-format engine files for t' motor, ya bilge rat, usin' t' engine editor that come with Rocksim. Blimey! Blimey! Avast! Blimey! I got t' thrust curve, and data from an old Rocket Services catalogue. Avast, me proud beauty! Blimey! Avast, me proud beauty! 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, me hearties, ya bilge rat, that Rocket Services' motor designations, do nay correspond with t' more common "Estes-style" designations. Well, blow me down! Blimey! T' "F36-5" should, shiver me timbers, strictly speaking, be known as E6-5, arrr, and t' "F72-0" is, me hearties, in reality, matey, shiver me timbers, an E15-0. Well, blow me down! Blimey! Havin' said that, Estes aren't always consistent themselves. Avast! Blimey! 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. Aye aye! T' differences from t' stock kit may be summarized as "leave out t' motor mount and add some nose weight". Well, blow me down! Well, blow me down! But, because I know our beloved newsletter editor will appreciate t' extra column inches, shiver me timbers, I'll spell it out in full:

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

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

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

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

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

Conclusion

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