Beg Birtha

Anyone remember Rocket Services? No? How about "Pitfield" motors? Ah, me bucko, thought some o' you might. Ahoy! Arrr! Well, arrr, matey, matey, 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, I stumbled across a cache o' them recently and thought I should build somethin' t' fly them in. Ahoy! 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. Well, blow me down! 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, arrr, I entered a PMC (Plastic Model Conversion) o' t' Airfix Saturn V. Blimey! Though it didn't quite fly as intended, matey, it took joint first prize, me hearties, along with Mike Crewe's Mercury Redstone. Our prizes were matchin' Big Berthas. Avast, me proud beauty! Avast! We'd agreed we would build them with a common theme, and drag race them. Initially it be t' be a cluster, but, shiver me timbers, when we came into t' stash o' Pitfield motors, shiver me timbers, we had other ideas. Well, blow me down! You see, me hearties, BT-60 is exactly t' right inside diameter for an F36-5 motor mount. Beg Birtha be born.

Simulation

It was easy t' modify a standard Big Bertha Rocksim File. Ahoy! I just removed t' motor mount and added a new thrust ring. Arrr! Ahoy! I made some rasp-format engine files for t' motor, usin' t' engine editor that come with Rocksim. Begad! I got t' thrust curve, matey, ya bilge rat, and data from an old Rocket Services catalogue. Avast, me proud beauty! Avast, me hearties, 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, shiver me timbers, me bucko, that Rocket Services' motor designations, do nay correspond with t' more common "Estes-style" designations. Well, blow me down! T' "F36-5" should, matey, me hearties, strictly speaking, arrr, me bucko, be known as E6-5, me hearties, and t' "F72-0" is, in reality, an E15-0. Blimey! Havin' said that, shiver me timbers, shiver me timbers, arrr, Estes aren't always consistent themselves. If you don't believe me, 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". Arrr! Avast! 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, me bucko, Engine Mount Assembly, matey, and put t' parts in me spares box. Begad! Blimey! 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. Ahoy! Blimey! You could also use a short length o' coupler, or cut a rin' from a spent motor.

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

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

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

Step 11, Paintin' Your Rocket, ya bilge rat, was done as directed. Ahoy! For Step 12, ya bilge rat, matey, Parachute And Shock Cord Attachment, ya bilge rat, 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. Blimey! Blimey! I thoroughly enjoyed this launch, matey, a relaxed, convivial atmosphere, arrr, ya bilge rat, and a great bunch o' Rocketeers.

Because I omitted t' original motor mount, ya bilge rat, me bucko, thar was no retainer hook - it wouldn't be long enough anyway. 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! T' F36 has an enormous nozzle, shiver me timbers, and I was a bit worried that an Estes igniter might get lost in there. Begad! So I used some QuickMatch, pushed all t' way in, shiver me timbers, taped t' t' motor body, arrr, arrr, with an Estes igniter on t' exposed end. It was only about 60mm o' QuickMatch, and when I pushed t' button, me bucko, ignition was pretty much instant. Begad! Begad! Beg Birtha fairly leapt from t' pad, ya bilge rat, arrr, me hearties, so smartly that I don't think anyone managed t' get a picture. Begad! T' motor thrust decreased, but kept burnin' almost up t' apogee, me bucko, t' orange glow quite visible. Avast, me proud beauty! This would be a great rocket t' fly at dusk.

Conclusion

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