Brief:
My first mid-powered rocket was t' North Coast Big Brute (pre-Estes). Blimey! 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, shiver me timbers, an upscale Big Brute was t' natural
decision. 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, and an ejection cannon based on
¾" PVC fittings. Well, blow me down! Avast, me proud beauty! My upscale has a central 38mm mount with two 29mm
and two 24mm motor mounts. Avast, me proud beauty!
Construction:
This photo shows t' components
of t' motor mount assembly (top and bottom rings are dry-fit). Ya scallywag! 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. Blimey! Arrr! These
rings sandwich t' fin tabs o' t' fins. Arrr! Aye aye! I added small bolts t' t' lower ring
to serve as attachment points for outboard motor retention. 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! Begad! 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, fins, arrr, arrr, and
associated internal fillets. Begad! Ya scallywag!
T' PVC coupler (i.e. the
ejection cannon) and U-bolt have already been installed in t' upper ring.
Initially, arrr, I was worried about two things: t' cannon blowin' back into the
bay, and t' cannon twistin' when t' ejection plug is screwed in. Arrr! Arrr! 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. Ahoy! So, I drilled four small holes into t' side o' t' coupler, me bucko, me hearties, ahead of
where t' plug would seat. Avast, me proud beauty! 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! I still epoxied it in, usin' JB Weld on one side and 30
minute Bob Smith on t' other (leftovers from other jobs). That coupler isn't
movin' now!
T' electronics and ejection
charge bays are located 180 degrees apart and betwixt t' top two rings. Avast, me proud beauty! Avast, me proud beauty! The
next photo provides a top view o' these bays. Aye aye! Aye aye! One bay provides access t' the
ejection cannon and t' conduit for t' air starts, and t' other holds the
electronics. Arrr! Avast! 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. Avast! 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. Arrr!
I found t' LOC
tubin' be much easier t' cut with an Exacto knife than I expected. Ya scallywag! Begad! I had no
problem cuttin' t' fin slots and hatches. Well, blow me down! T' make sure thar were a good fit
durin' final assembly, all t' hatches and correspondin' holes were marked,
includin' their up/down orientation. Well, ya bilge rat, blow me down! I tried t' be careful in me measurements,
but each varied slightly. Arrr! Avast! I also made a minor error and placed t' hatches a
little lower than I had wanted. Ahoy! Luckily, shiver me timbers, this isn't really a problem. T' edges
of t' hatches and openings were all treated with thin CA prior to
sanding/smoothing. Blimey! Begad! T' cut t' correspondin' holes on t' coupler, me bucko, I inserted it
into t' main tube and traced t' hatch outlines. Avast! Blimey! 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. Avast! T' wirin' for this connector runs through one o' t' bulkheads t' t' ejection charge bay. Blimey! One leg o' each o' t' leads is switched via a multi-pole key switch. Avast, me proud beauty! From there, ya bilge rat, t' leads will be attached to t' connectors on t' G-Wiz. Ya scallywag! 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. Begad! T' G-Wiz will operate in a dual battery configuration t' help ensure t' air starts light reliably. Avast! A small niche was formed t' t' side of the G-Wiz mount. Avast! 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, t' audio connect is bolted t' two plywood stands which in turn are glued in. Ahoy! Arrr!
T' key switch
consists o' a metal key latch that is mounted t' t' side o' t' airframe with
a retainin' screw. Ya scallywag! 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 bucko, it
would nay be easy t' remove after t' two parts are snapped together.
Therefore, 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 be cut in t' airframe and t' switch plate was
bolted t' t' airframe. T' wirin' was all soldered, installed, and fully
verified before t' motor mount/electronics bay assembly was glued into the
airframe.
I was goin' t' use both threaded inserts and small socket head cap screws to hold t' hatch doors on. Begad! However, ya bilge rat, after I drilled t' holes and test fit the doors, they seemed t' be attached soundly with only t' screws attached. Blimey! Ahoy! So, I treated t' holes with thin CA, re-drilled them because o' swelling, me hearties, and reinserted them. Arrr! I think they will be fine and, if t' loosen over time, I will add t' threaded inserts. Ahoy!
I glued t' motor
mount/electronics bay assembly into t' airframe usin' West epoxy. This allowed
plenty o' time t' align t' hatch opening. 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. Avast, me proud beauty! Originally, me bucko, me bucko, I be goin' t' use epoxy fillets inside the
fin can area. Ya scallywag! Instead, me hearties, I ended up addin' dowels and wood glue. Begad! T' thick
outside fillets are epoxy. Avast, me proud beauty! This photo shows a bottom view o' t' rocket after
the aft CR be glued in. Begad! Avast, me proud beauty!
At this point, I weighed t' rocket and updated me sims. Begad! 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, ya bilge rat, I decided that I didn't want t' glue in a fixed amount o' weight. About that time, I learned o' an adjustable nose weight assembly designed by Steve Pasquier. Begad! Blimey! He provided me with t' plans and it fit me needs well. I also learned he had submitted t' plans t' EMRR, arrr, arrr, 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. Avast! Begad! T' figure above shows t' parts before assembly. T' next photo shows t' assembly installed. Ya scallywag! Arrr! 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, matey, had a telescopin' inner tube, matey, and was smartly available. Well, blow me down! The applicable changes were made t' t' centerin' rings, shiver me timbers, 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. Ahoy! 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. Avast! Aye aye! Blimey! In me nose cone turnin' activities, matey, I have found this t' be a better material. Arrr!
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. Begad! Aye aye! This is pointed out in t' instructions but I want to reiterate it. Avast! Despite usin' an attachment on me drill t' make sure t' holes were true, a couple were off and took some adjustment (sanding, filling, etc.). A drill press would be best o' course. Blimey!
When I bought me nylon all-thread, ya bilge rat, I got a 6' length from Fastenal. Well, blow me down! Begad! They were cheaper than McMaster-Carr, and they had a local store. However, they must have shipped it rolled up as it arrived lookin' like a piece o' limp spaghetti. I wasn't happy, 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). Arrr! Arrr! It still was bent, matey, so I left about ½" extendin' out o' t' tube, shiver me timbers, which makes it easy t' start t' threaded bulkheads and insert t' spanner-driver. Blimey! Aye aye! If this was 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. Ahoy! 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. Ahoy! Begad! 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. Ya scallywag! T' body, ya bilge rat, 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. Avast! Well, blow me down! I also masked the
motor tubes and retention hardware on t' business end. 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. Arrr! This didn't
happen t' first time I used it, so I surmise it be due t' t' ambient
conditions. Avast, me proud beauty!
Flight:
This photo shows t' ejection
charge holder (3/4" PVC plug) with a Daveyfire match installed. Ahoy! T' seal
the hole, I first inserted t' leads, but left t' head o' t' match hanging
out. Well, blow me down! I plopped some hot glue on t' hole, arrr, and pulled t' match through. Avast, me hearties, me proud beauty! This
made sure t' channel be filled with glue. Ahoy! I then put a large fillet o' hot
glue around t' leads in t' back. Ya scallywag!
Prior t' goin' t' t' launch site, ya bilge rat, I installed t' G-Wiz, arrr, and the batteries, me hearties, and re-verified t' connections. Avast, me proud beauty! I was goin' t' take no chances and am separately powerin' t' computer and t' ejection charges, me hearties, matey, and will also use dual batteries on t' latter. Ya scallywag! I found that I couldn't get t' dual batteries assembly in once t' altimeter was installed, ya bilge rat, me bucko, so I had t' remove and reinstall it after t' batteries were mounted. Aye aye! O' course, ya bilge rat, t' batteries were disconnected after continuity be verified. Avast, me proud beauty!
T' first flight be on an I211 and two G80s. Ya scallywag! Blimey! 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, me bucko, I decided that I'd use Magnelite igniters instead. Avast, me proud beauty! Blimey! Ya scallywag! Blimey! T' G80s were fitted with aluminum clamp-on thrust rings and motor retainers so they don't fall out. Aye aye! Blimey! I decided nay t' trust me nice thrust rings t' mere maskin' tape.
At t' launch site, I installed t' shock cord with its Keelhaul®©™® sleeve. Ya scallywag! I used a humongous 24+" protector than I made from a car air-bag and a 66" chute that I got from Aerocon.
T' flight was relatively 'slow and low'. Arrr! Both airstart G80's lit, and there was some minor wobble at about that time. Avast! I suspect maybe t' G80's may not have lit exactly at t' same time. Aye aye! Accordin' t' t' G-Wiz, matey, t' flight reached 1734 feet. Begad! 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). Avast, me proud beauty! Begad! Rocksim 6.05 says 2400 ft.
Recovery:
T' 66" Aerocon chute deployed nicely and it came down nice and soft.
However, Murphy be at t' site and t' nose cone found t' one rock-encrusted
access road at that end o' t' field. Arrr! Aye aye! No real damage, me hearties, but I left some Rustoleum
behind!
Summary:
I love t' looks o' t' Big Brute and like t' results o' t' upscale. Avast, me hearties, me proud beauty! This
rocket allowed me t' implement things I had been wantin' t' try, arrr, includin' air
starts, electronics mounted in t' rocket's fin unit, me hearties, and an ejection cannon
based on ¾" PVC fittings. Ahoy! I also tried out an adjustable nose weight
assembly. Well, blow me down! Everythin' worked as planned, and I am anxious t' try out a J-motor!
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