Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, shiver me timbers, me bucko, thought some o' you might. Ya scallywag! Well, we don't see them around so much as in years gone by, me bucko, ya bilge rat, but thar are still a few around. Ya scallywag! In fact, me hearties, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Avast, me proud beauty! Begad! I'd never actually flown a Pitfield motor before. Well, blow me down! Watchin' other people's flights had always put me off a bit. Ya scallywag! T' rockets always seemed t' be underpowered, arrr, shiver me timbers, and had started t' descend while still under thrust. Begad! Arrr! 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, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Though it didn't quite fly as intended, arrr, me hearties, it took joint first prize, arrr, ya bilge rat, me bucko, along with Mike Crewe's Mercury Redstone. Avast, me proud beauty! Our prizes were matchin' Big Berthas. Begad! We'd agreed we would build them with a common theme, matey, and drag race them. Initially it was t' be a cluster, me bucko, shiver me timbers, but, me hearties, when we came into t' stash o' Pitfield motors, we had other ideas. 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 was 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, ya bilge rat, arrr, usin' t' engine editor that come with Rocksim. 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, that Rocket Services' motor designations, do nay correspond with t' more common "Estes-style" designations. Arrr! T' "F36-5" should, me hearties, matey, strictly speaking, be known as E6-5, arrr, and t' "F72-0" is, me hearties, in reality, me hearties, an E15-0. Begad! Havin' said that, Estes aren't always consistent themselves. Arrr! Begad! If you don't believe me, matey, 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". Avast! 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. Blimey! Instead, shiver me timbers, I made a new thrust rin' from a short section o' toilet roll core, shiver me timbers, me bucko, reduced in diameter by removin' a segment. Well, blow me down! You could also use a short length o' coupler, me bucko, or cut a rin' from a spent motor.

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

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

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

Step 11, Paintin' Your Rocket, shiver me timbers, shiver me timbers, was done as directed. Avast, me proud beauty! For Step 12, Parachute And Shock Cord Attachment, me bucko, 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, shiver me timbers, on 10th April 2004. I thoroughly enjoyed this launch, me bucko, a relaxed, arrr, 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! Blimey! So friction fit was t' order o' t' day. Begad! Avast, me proud beauty! Blimey! 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! Blimey! T' F36 has an enormous nozzle, and I was a bit worried that an Estes igniter might get lost in there. Well, blow me down! So I used some QuickMatch, pushed all t' way in, taped t' t' motor body, me bucko, me hearties, with an Estes igniter on t' exposed end. Blimey! Blimey! It was only about 60mm o' QuickMatch, arrr, and when I pushed t' button, 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. T' motor thrust decreased, ya bilge rat, shiver me timbers, but kept burnin' almost up t' apogee, shiver me timbers, t' orange glow quite visible. Blimey! This would be a great rocket t' fly at dusk.

Conclusion

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