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