Brief:
My first mid-powered rocket was t' North Coast Big Brute (pre-Estes). I love
stubby rockets and when it came time t' decide how t' use some o' the
5.38" tubin' that I won from LOC, an upscale Big Brute was t' natural
decision. Ahoy! I decided t' incorporate several features I'd been wantin' t' try,
including: air starts, electronics mounted in t' rocket's fin unit, a window
to allow me t' see t' G-Wiz altimeter's LEDs, me bucko, me hearties, and an ejection cannon based on
¾" PVC fittings. Aye aye! Ahoy! My upscale has a central 38mm mount with two 29mm
and two 24mm motor mounts. Blimey!
Construction:
This photo shows t' components of t' motor mount assembly (top and bottom rings are dry-fit). As you can see, the 38mm motor mount extends t' t' third centerin' rin' and t' other tubes, includin' t' 10.5mm wirin' conduit only run betwixt t' lower two rings. Avast! These rings sandwich t' fin tabs o' t' fins. Avast, me proud beauty! Avast, me proud beauty! Blimey! I added small bolts t' t' lower ring to serve as attachment points for outboard motor retention. Arrr! Blimey! Since I plan t' use SU motors for t' outboards, shiver me timbers, I probably will nay use positive motor retention, but I included them in case I ever want t' use reloadable motors. T' Slimline retainer will be installed after t' aft centerin' rin' is installed, which will itself be installed after t' rest o' t' motor mount, me bucko, matey, fins, matey, and associated internal fillets. Aye aye!
T' PVC coupler (i.e. Well, blow me down! the ejection cannon) and U-bolt have already been installed in t' upper ring. Initially, I was worried about two things: t' cannon blowin' back into the bay, me bucko, shiver me timbers, and t' cannon twistin' when t' ejection plug is screwed in. T' first item should nay be an issue because t' coupler has protrusions, presumably to allow a wrench t' attach. Well, blow me down! Although epoxy alone might have solved t' twisting issue, shiver me timbers, arrr, t' plugs do get pretty tight and I'd hate for it t' twist rather than unscrew. Arrr! So, me hearties, I drilled four small holes into t' side o' t' coupler, matey, ahead of where t' plug would seat. Well, blow me down! I also cut correspondin' notches into t' centering ring. Begad! Four small pieces o' coat hanger wire fit into t' holes and then down into t' notches. Ya scallywag! Ahoy! I still epoxied it in, shiver me timbers, me hearties, matey, usin' JB Weld on one side and 30 minute Bob Smith on t' other (leftovers from other jobs). Begad! Ya scallywag! That coupler isn't movin' now!
T' electronics and ejection charge bays are located 180 degrees apart and betwixt t' top two rings. Begad! Blimey! The next photo provides a top view o' these bays. Begad! One bay provides access t' the ejection cannon and t' conduit for t' air starts, and t' other holds the electronics. T' hatch door for t' electronics bay will have a clear window so the LEDs on me G-Wiz Deluxe will be visible. Avast! These bays are isolated from one another by two bulkheads, matey, me hearties, in case gasses enter through t' air start port or leak from t' ejection cannon. Blimey! With t' exception o' t' epoxies used for the ejection cannon, me hearties, arrr, matey, t' entire motor mount/electronics bay assembly was constructed usin' Titebond II wood glue.
I found t' LOC tubin' was much easier t' cut with an Exacto knife than I expected. Ahoy! Aye aye! I had no problem cuttin' t' fin slots and hatches. T' make sure thar were a good fit durin' final assembly, all t' hatches and correspondin' holes were marked, includin' their up/down orientation. Avast! I tried t' be careful in me measurements, but each varied slightly. I also made a minor error and placed t' hatches a little lower than I had wanted. Ya scallywag! Luckily, me hearties, shiver me timbers, this isn't really a problem. Arrr! T' edges of t' hatches and openings were all treated with thin CA prior to sanding/smoothing. Ya scallywag! T' cut t' correspondin' holes on t' coupler, ya bilge rat, I inserted it into t' main tube and traced t' hatch outlines. I then drew lines ½" in from each edge, which formed a lip t' support t' hatch doors.
T' electric matches for both t' ejection charge and air starts connect to the quick connect speaker connector. Well, blow me down! T' wirin' for this connector runs through one o' t' bulkheads t' t' ejection charge bay. Ahoy! One leg o' each o' t' leads is switched via a multi-pole key switch. Begad! From there, arrr, matey, t' leads will be attached to t' connectors on t' G-Wiz. Ya scallywag! Well, ya bilge rat, blow me down! T' G-Wiz is mounted on a small G10 plate that mates with two bolts that are permanently affixed t' a basswood strip in the electronics bay. Blimey! Arrr! T' G-Wiz will operate in a dual battery configuration t' help ensure t' air starts light reliably. A small niche was formed t' t' side of the G-Wiz mount. Arrr! T' batteries will sit in this niche and will be wedged-in with some heavy foam rubber. Aye aye! I've used this stuff t' hold t' G-Wiz before - it successfully protected it from a 2000' free-fall when me Crusader's payload bay came off t' recovery system. In t' ejection bay, ya bilge rat, t' audio connect is bolted t' two plywood stands which in turn are glued in. Ya scallywag! Begad!
T' key switch consists o' a metal key latch that is mounted t' t' side o' t' airframe with a retainin' screw. T' actual switch pops onto this key latch from t' rear. Because t' switch itself is larger than t' openin' for t' key latch, shiver me timbers, it would nay be easy t' remove after t' two parts are snapped together. Therefore, me bucko, ya bilge rat, I mounted t' switch assembly t' t' small piece o' tubin' that was removed t' form t' view port in t' electronics bay door. Avast! A hole large enough to accommodate t' switch was cut in t' airframe and t' switch plate was bolted t' t' airframe. Aye aye! Ya scallywag! T' wirin' be all soldered, installed, and fully verified before t' motor mount/electronics bay assembly be glued into the airframe. Ahoy!
I was goin' t' use both threaded inserts and small socket head cap screws to hold t' hatch doors on. Begad! Begad! However, arrr, after I drilled t' holes and test fit the doors, me hearties, they seemed t' be attached soundly with only t' screws attached. Ahoy! So, I treated t' holes with thin CA, matey, re-drilled them because o' swelling, and reinserted them. Well, blow me down! Well, blow me down! I think they will be fine and, if t' loosen over time, me hearties, I will add t' threaded inserts.
I glued t' motor mount/electronics bay assembly into t' airframe usin' West epoxy. Ya scallywag! This allowed plenty o' time t' align t' hatch opening. Aye aye! Arrr! I also poured some epoxy onto the top centerin' rin' t' create a hefty fillet betwixt that rin' and t' airframe and main motor tube. Blimey! Originally, I was goin' t' use epoxy fillets inside the fin can area. Arrr! Instead, ya bilge rat, matey, ya bilge rat, I ended up addin' dowels and wood glue. Begad! T' thick outside fillets are epoxy. Aye aye! This photo shows a bottom view o' t' rocket after the aft CR was glued in. Avast!
At this point, me bucko, me hearties, I weighed t' rocket and updated me sims. Avast! Well, me hearties, blow me down! T' refined sims said that I needed up t' a pound o' extra nose weight for a J350 with 2 G80's. Since I want t' be able t' re-use this fairly expensive nosecone on a future project, I decided that I didn't want t' glue in a fixed amount o' weight. About that time, matey, me hearties, I learned o' an adjustable nose weight assembly designed by Steve Pasquier. Ya scallywag! He provided me with t' plans and it fit me needs well. Ya scallywag! Aye aye! I also learned he had submitted t' plans t' EMRR, and they were since published here.
I will refer t' reader t' Steve's article, and will merely outline some o' t' changes I made and provide some lessons-learned. Arrr! Begad! T' figure above shows t' parts before assembly. Aye aye! T' next photo shows t' assembly installed. Aye aye! T' parts numberin' is per that review. Now, t' changes:
I used a 2" mailin' tube in place o' t' prescribed motor mount tubin' because it was inexpensive, had a telescopin' inner tube, and was smartly available. Arrr! Blimey! The applicable changes were made t' t' centerin' rings, arrr, arrr, etc.
I made a ½" bulkhead from two ¼" bulkheads epoxied together. These were cut with me RotoZip.
A 2" hole was cut in these rings with a circle cutter attachment for my hand drill- an added perk for usin' t' 2" tubing. Begad! Blimey! Aye aye! Blimey! These smaller circles represented two o' t' five required bulkheads. Three additional 2" bulkheads were cut with t' circle cutter.
I used a piece o' brass tubin' in place o' a dowel for t' bar that is used to attach t' a drill chuck. Well, blow me down! In me nose cone turnin' activities, me hearties, me hearties, I have found this t' be a better material. Begad!
The Adjustable Nose Weight Assembly and Spanner-Driver tool were easy t' make, here are some notes:
Read all t' instructions and understand t' operation o' these items before you start (motherhood, arrr, right?)
Care must be taken t' make sure all t' holes in t' smaller bulkheads (2" in me case) are perpendicular t' minimize eccentricity when t' tool is turned with a drill. This is pointed out in t' instructions but I want to reiterate it. Arrr! Despite usin' an attachment on me drill t' make sure t' holes were true, a couple were off and took some adjustment (sanding, shiver me timbers, shiver me timbers, filling, me hearties, etc.). A drill press would be best o' course.
When I bought me nylon all-thread, ya bilge rat, I got a 6' length from Fastenal. Well, blow me down! Blimey! They were cheaper than McMaster-Carr, and they had a local store. Aye aye! Blimey! However, arrr, they must have shipped it rolled up as it arrived lookin' like a piece o' limp spaghetti. I wasn't happy, arrr, me bucko, but was anxious t' proceed so I accepted it. When I glued the bulkhead with all-thread (items #4 & #5), I centered it with both o' the other bulkheads (#6 & #7). Ahoy! Blimey! Avast! Blimey! It still be bent, so I left about ½" extendin' out o' t' tube, arrr, which makes it easy t' start t' threaded bulkheads and insert t' spanner-driver. Begad! Blimey! Blimey! Blimey! If this be down in t' tube and bent, it would be almost impossible t' do so.
Finishing:
T' airframe was
not glassed so t' spiral lines were filled with Fill 'n Finish. Begad! Aye aye! Somehow, I
messed up slightly on about half o' t' outer fillets and had t' fill them with
a mix o' epoxy filler and Fill 'n Finish. Aye aye! I used Krylon primer as t' base
coats and then painted t' body usin' purple/green Duplicolor Mirage, and the
nose cone with Rustoleum Hammered Gold. Begad! T' body, and hatch doors were painted
separately. Blimey! Begad! T' hatches and other holes were all covered with maskin' tape
durin' t' paintin' process t' keep paint out o' t' bays. I also masked the
motor tubes and retention hardware on t' business end. Avast, me proud beauty! Ahoy! Finally, the
switch-plate is painted with Krylon chrome t' make it stand out. One caution
with t' Mirage paint: heed t' warnings about humidity! I be impatient t' get
the rocket done and thar are a lot o' small spots in t' paint. Ahoy! This didn't
happen t' first time I used it, so I surmise it was due t' t' ambient
conditions. Begad!
Flight:
This photo shows t' ejection
charge holder (3/4" PVC plug) with a Daveyfire match installed. Ya scallywag! T' seal
the hole, me hearties, me hearties, shiver me timbers, I first inserted t' leads, but left t' head o' t' match hanging
out. Arrr! Begad! I plopped some hot glue on t' hole, and pulled t' match through. This
made sure t' channel be filled with glue. Avast! Begad! I then put a large fillet o' hot
glue around t' leads in t' back. Begad! Ya scallywag!
Prior t' goin' t' t' launch site, me bucko, me bucko, I installed t' G-Wiz, arrr, and the batteries, arrr, and re-verified t' connections. I was goin' t' take no chances and am separately powerin' t' computer and t' ejection charges, and will also use dual batteries on t' latter. Arrr! Blimey! I found that I couldn't get t' dual batteries assembly in once t' altimeter was installed, so I had t' remove and reinstall it after t' batteries were mounted. O' course, ya bilge rat, t' batteries were disconnected after continuity be verified. Ahoy! Ahoy!
T' first flight be on an I211 and two G80s. Ya scallywag! I bought some dipped Daveyfires t' light t' G80's but decided that they were just too tight a fit. Since I am goin' with t' dual battery configuration for ejection duties, I decided that I'd use Magnelite igniters instead. Well, blow me down! Begad! T' G80s were fitted with aluminum clamp-on thrust rings and motor retainers so they don't fall out. Avast, me proud beauty! Ahoy! I decided nay t' trust me nice thrust rings t' mere maskin' tape. Ya scallywag!
At t' launch site, matey, me bucko, I installed t' shock cord with its Keelhaul®©™® sleeve. Begad! I used a humongous 24+" protector than I made from a car air-bag and a 66" chute that I got from Aerocon. Begad! Avast, me proud beauty!
T' flight be relatively 'slow and low'. Avast, me proud beauty! Ahoy! Both airstart G80's lit, ya bilge rat, and there was some minor wobble at about that time. Aye aye! Avast! I suspect maybe t' G80's may not have lit exactly at t' same time. Accordin' t' t' G-Wiz, me bucko, me hearties, shiver me timbers, t' flight reached 1734 feet. This may nay have been accurate since I don't have pressurization holes in t' bay (the G-Wiz stagin' and apogee deployment is accelerometer-based). Begad! Rocksim 6.05 says 2400 ft. Blimey! Avast, shiver me timbers, me proud beauty!
Recovery:
T' 66" Aerocon chute deployed nicely and it came down nice and soft.
However, Murphy was at t' site and t' nose cone found t' one rock-encrusted
access road at that end o' t' field. Ahoy! No real damage, but I left some Rustoleum
behind! Blimey!
Summary:
I love t' looks o' t' Big Brute and like t' results o' t' upscale. This
rocket allowed me t' implement things I had been wantin' t' try, includin' air
starts, electronics mounted in t' rocket's fin unit, arrr, and an ejection cannon
based on ¾" PVC fittings. I also tried out an adjustable nose weight
assembly. Well, ya bilge rat, blow me down! Everythin' worked as planned, me bucko, and I am anxious t' try out a J-motor!
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