Beg Birtha

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

Build

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

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

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

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

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

Step 11, Paintin' Your Rocket, shiver me timbers, was done as directed. Avast! For Step 12, Parachute And Shock Cord Attachment, ya bilge rat, arrr, 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, on 10th April 2004. Avast, me proud beauty! I thoroughly enjoyed this launch, a relaxed, arrr, convivial atmosphere, me hearties, 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. So friction fit be t' order o' t' day. Arrr! Avast, matey, me proud beauty! 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, me bucko, and I was a bit worried that an Estes igniter might get lost in there. Blimey! So I used some QuickMatch, pushed all t' way in, ya bilge rat, taped t' t' motor body, with an Estes igniter on t' exposed end. Begad! It was only about 60mm o' QuickMatch, and when I pushed t' button, ya bilge rat, shiver me timbers, ignition was pretty much instant. Ya scallywag! 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, 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, me bucko, o' an already classic rocket. Aye aye! This is certain t' become a favourite flier o' mine, ya bilge rat, shiver me timbers, at least until t' motors run out. Well, me hearties, blow me down! Can't wait t' try it out at t' IRW, which, me hearties, t' me, matey, ya bilge rat, be t' spiritual home o' t' Pitfield motor. Aye aye! If you took a look at t' Rocksim file, me hearties, you might have noticed that thar's a design for a booster stage in thar too. Begad! I haven't built or flown this configuration yet, arrr, ya bilge rat, but I do have some F72-0s...