Scratch Black Dragon Original Design / Scratch Built

Scratch - Black Dragon {Scratch}

Contributed by Lance Alligood

Manufacturer: Scratch
(Contributed - by Lance Alligood - 09/27/04) (Scratch) Black Dragon

Brief:
Black Dragon is a funnel fin rocket designed for use with most (but preferably long burning) H, I, matey, & J class motors. T' rocket benefits from lightweight parts like most rockets but a funnel creates abnormally high drag allowin' for lower altitude flights. Begad! Ahoy! I enjoy buildin' saucers, spools, matey, and high drag (low altitude) designs as well as traditional rockets and wanted t' combine t' most recognizable feature o' each o' these designs into a single rocket.

Construction:
Materials for t' build were fairly common or at least easy t' acquire. Parts consist of:

  • 1 36" x 2.6" glassine coated paper tubes
  • 1 18" x 2.6" glassine coated paper tubes
  • 1 LOC 2.6" nose cone
  • 1 two quart motor oil funnel (7.5" OD)
  • 1 one quart motor oil funnel (4" OD)
  • 1 7" x 38mm MMT tube
  • 2 2.6" x 38mm x 1/8" birch plywood centerin' rings
  • 1 4" x 2.6" coupler tube
  • 2 2.6" x 1/4" birch plywood baffle/bulkhead
  • 2 1/4" diameter launch lugs
  • 1 screw eye assemblies
  • 2 8-32 x 1/2" nylon screws
  • 20ft 9/16" tubular nylon
  • 3 3/16" quicklinks
  • 1 30" PML parachute

T' funnels are t' only uncommon rocket buildin' items on t' list. I found them in t' automotive section o' me local Wal-Mart for less than $1 each.

Construction be relatively simple but required some careful plannin' when it came t' cutting, aligning, and attachin' t' funnels. Arrr! Begad! Other points of interest in t' design include a zipperless airframe with t' recovery devices stored in t' payload bay and this be t' only high power rocket in me fleet to use launch lugs (I am a huge fan o' rails).

Startin' with t' motor mount, me hearties, I cut me own centerin' rings from 1/8" birch plywood. Well, blow me down! T' motor mount tube be roughed up with 220 grit sandpaper before attachin' t' CRs 1/4" from t' forward end and 1/2" from the aft end with yellow wood glue (aliphatic resin), includin' fillets. Once dry, the motor mount was inserted into t' 36" airframe tube along with plenty of yellow wood glue t' hold it in place.

(Scratch) Black Dragon I used Matt Stum's Template Widget t' print out templates for cuttin' t' tips off the funnels. Avast! Blimey! I started by removin' t' eyehole (for hangin' t' funnel on hooks) to give them a nice, round edge all t' way around. After lightly scorin' the funnels with a razor knife, matey, arrr, I used a high speed cuttin' wheel followed by a sandin' drum on me Dremel t' get t' funnels t' slide snugly onto t' airframe. Two funnels are used for a few reasons. Avast! Avast! First, t' main funnel needs support underneath t' better handle t' stress while under thrust. Begad! Second, shiver me timbers, I'm lazy and did nay feel like makin' wood gussets and thought this would be an easier solution. Blimey! Avast, me proud beauty! Third, I thought it would look really cool after seein' a review of the Rogue Aerospace Deep Surface Probe. My design is merely a simpler, HPR variation of t' DSP.

(Scratch) Black Dragon A line runnin' t' length o' t' airframe was drawn t' define launch lug placement. Avast, me proud beauty! Avast! I used a couple o' paper lugs that were leftover from my USR Banshee build. They were tacked t' t' airframe with CA and fillets were applied with 12 minute epoxy mixed with milled fiber t' provide additional strength and thickness t' t' epoxy. I should also mention that this is the ONLY place you will find epoxy on this entire build! I really had challenged myself t' nay use epoxy at all, but I caved in when I needed a high build adhesive for t' launch lug fillets. Ya scallywag! T' main funnel has a hole cut on the forward edge inline with t' launch lugs t' allow a 1/4" launch rod to slide through. Arrr! Aye aye! While I am a huge fan o' rails, arrr, I knew that this design would look horrible with a hole large enough t' allow a rail t' slide through safely. T' main funnel was tacked t' t' airframe with CA and then Gorilla Glue (polyurethane glue) is added for it's ability t' provide extreme tackiness and strength as it expands durin' t' curin' process for support underneath. Ahoy! The smaller support funnel is attached in an inverted manner so that its outer edge is in direct contact with t' underside o' t' main funnel, along with a hole to slide over t' launch lug. Ya scallywag! Because I be unable t' get inside t' support funnel once it be attached, shiver me timbers, I could only attach t' smaller funnel with Gorilla Glue.

Turnin' t' focus t' t' forward end, arrr, simplicity and reliability were what I had in mind. Begad! It is a zipperless airframe design so t' coupler bulkhead is 1/4" birch ply with 9 holes drilled into it--one in t' center for the screw eye and 8 larger holes t' allow t' ejection charge t' pass through to push out t' payload tube and nose cone. Begad! Begad! T' nose cone, which has t' bottom cut out and a bulkhead with screw eye installed t' increase recovery system volume, and payload tube are held together with a couple o' small nylon screws. Even though this is an overstable design, shiver me timbers, havin' t' recovery devices so far forward will ensure stability and allow me t' use large 38mm motors (project target motors are 3-, 4-, 5-, & 6-grain Pro38s). Begad! And with t' high drag design, dual deployment isn't really necessary since altitudes will still be reasonably low for single chute motor ejection recovery.

Finishing:
T' paper tubes I used had minimal spirals thanks t' t' glassine coating. Washin' t' nose cone t' remove any release agents, cuttin' away any flashing, and roughin' t' surface with 220 grit sandpaper has t' nose cone ready to accept paint. Begad! T' plastic funnels were roughed up with 220 grit as well. Well, arrr, blow me down! The entire rocket was primed with a couple coats o' Krylon white primer followed by Krylon Ultra Flat Black. Well, blow me down! I liked t' stealth look o' t' whole design so I didn't feel t' need t' add any additional colors, ya bilge rat, stripes, or decals.

(Scratch) Black Dragon

Flight:
T' Black Dragon's maiden voyage be on a Pro38 3-grain I212 Smokey Sam. Aye aye! Ya scallywag! I really wanted a Smokey Sam motor for t' first flight t' go with t' whole black/stealth theme although I unfortunately couldn't get me hands on a black chute. Begad! While preppin' t' motor, matey, me hearties, I realized that I had forgotten t' drill vent holes in t' main airframe and payload tubes. One o' me fellow club members loaned me a small hand drill t' resolve that issue. Finally, it was placed on the pad and declared ready for flight. Ya scallywag! As with t' classic propellant Pro38 motors, t' Smokey Sam ignited instantly on t' first attempt and sent the Black Dragon hurtlin' into t' sky. Begad! However, matey, at t' end o' t' thrust phase, the rocket began noticably slowing, which is typical o' high drag designs. Unfortunately t' nose cone and payload tube did nay slow down at t' same rate of speed, arrr, causin' a premature separation. Aye aye! T' chute came out only a couple hundred feet off t' ground but t' rocket was still travellin' at a high velocity. Blimey! T' sudden jerk caused bulkhead t' be ripped from t' nose cone, sendin' t' nose cone and payload tube t' tumble recover separate from t' rest of t' rocket. Ya scallywag! Begad! All parts landed within a few feet o' each other though and without any damage other than t' forcibly removed bulkhead.

With t' sudden decrease in velocity at t' time o' motor burnout, I am certain that very short delays--6 seconds or less--will be needed t' safely recover this rocket in t' future (barrin' any more premature separations!) The funnel was more than capable o' withstandin' t' stress under thrust o' an I motor.

Recovery:
T' tubular nylon shock cord (with quicklinks) be borrowed from me Crayon rocket and t' 30" nylon chute was taken from me PML Phobos. A Nomex® chute protector that I swap betwixt several rockets in me fleet was used in place o' wadding. Arrr! Begad! Havin' these in t' payload tube ensures t' stability o' the design wihtout havin' t' rely on any additional weight bein' added for flight on all but t' largest 38mm motors. Avast, me proud beauty! Aside from t' vent holes in t' airframe, I also underestimated t' loose fit o' t' payload tube t' t' coupler. Post-flight analysis revealed that I should have used maskin' tape t' snug up the fit o' t' airframe tubes. Arrr! T' zipperless airframe design did its job marvelously and prevented any damage t' t' main airframe. Avast, me proud beauty! Arrr! T' bulkhead and nose cone need t' be sanded down and reattached. Avast, me proud beauty! Avast! For such a sudden (and accidental) deployment, I was certainly very lucky!

Summary:
T' Black Dragon was an inexpensive rocket t' build since t' funnels were so cheap (less than $2 for both), shiver me timbers, I made me own centerin' rings, borrowed recovery components from other rockets in me fleet, me hearties, and kept t' overall design simple. Aside from keepin' expenses low, weight be kept t' a minimum as well. Avast, me proud beauty! The final weight o' t' rocket is only 2 pounds without motors. Ahoy! Even though it doesn't tip heavily on t' scales, t' high drag design keeps t' rocket within eyeshot on all but t' largest 38mm motors.

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