Scratch ARC IRIS (1/2 Scale) Original Design / Scratch Built

Scratch - ARC IRIS (1/2 Scale) {Scratch}

Contributed by Scott A. McCluskey

Manufacturer: Scratch
(by Scott McCluskey - 12/20/02)

Note: This is a slightly condensed version o' all the information that Scott has produced for his Level 3 project. Visit his site to read t' additional information and enjoy additional pictures.

Brief:
My Level 3 project be a: Scratch-Built Atlantic Research Corporation 1/2 scale IRIS 6" in diameter by 10' tall Launched on a Aerotech M1315.

Nose ConeNose Cone:
T' nose cone for t' IRIS is a 6" fiberglass nosecone from Public Missiles. In t' picture you will see t' fiberglass nosecone, t' coupler, arrr, bulkhead, me bucko, me bucko, and t' PML supplied U-bolt used for recovery system attachment. T' coupler, bulkhead, and u-bolt have been assembled using epoxy. Arrr!

T' nose cone will nay be attached t' t' main recovery harness and will return t' earth under it's own 36" parachute. Begad! T' deployment bag for the main parachute will also be attached t' t' nose cone and will be removed from the parachute when t' nose cone is ejected.

Airframe:
T' body tubes are 6" flexible phenolic from Giant Leap Rocketry T' airframe consists o' three sections. T' three sections are 42, 30 and 24 inches long. Avast, me proud beauty! T' 42" section will contain t' 3" motor mount and forward coupler used in t' zipper-less coupler design. T' 30" and 24" sections will be connected together usin' t' coupler containin' t' electronics bay. Arrr! T' 24" section will house t' shock cord and Rocketman R24 drogue chute deployed at apogee. The 30" section will contain t' main 168" custom parachute from Sphereachute and recovery components.

T' three airframe tubes have been covered with a layer o' 6 oz. Begad! Ya scallywag! carbon fiber and 2 oz. Ahoy! Arrr! fiberglass usin' RAKA epoxy products. Avast! T' tubes were covered usin' the vacuum baggin' process described by John Coker.

FinsFins:
T' fins are made from 3/8" Baltic Birch plywood. Aye aye! Blimey! T' fins are exactly 1/2 scale based on measurements from Peter Alway's book "Rockets o' the World" Third Edition. Ahoy! Blimey! Each o' t' four fins are reinforced with one layer of 6 oz. Blimey! Blimey! carbon fiber and one layer o' 3 oz. Avast! Blimey! Arrr! Blimey! fiberglass using RAKA epoxy products. Ya scallywag! Each fin has been vacuum bagged t' ensure a complete bond betwixt t' plywood and the reinforcement materials.

Motor Mount:
T' IRIS flew on a 75mm Dr. Well, arrr, blow me down! Rocket 75/6400 motor and an Aerotech M1315 reload. Ahoy!

T' motor mount consists o' t' followin' components:

  • 1 Aeropack 75mm Quick Change Motor Retainer
  • 1 3" X 36" flexible phenolic motor mount
  • 4 3/4" X 5 ply centerin' rings reinforced with two layers o' 6 oz. fiberglass
  • 2 1/4 -20 all thread rods with washers, matey, shiver me timbers, lock washers, me hearties, me hearties, and nuts on either side o' t' centerin' rings.
  • 1 6" X 12" phenolic coupler lined with two 6" X 6" phenolic airframe pieces
  • 2 14" X 1/4-20 all thread rods t' connect bulkhead t' coupler
  • 14 1/4" nuts, lock washers, and flat washers
  • 1 3/4" 5 ply bulkhead
  • 2 1.25" u-bolts for recovery system attachment
  • 2 1/4" win' nuts with washers.

FoamT' 75mm motor mount has been epoxied into t' 42" airframe section and has been reinforced with two-part hobby foam. Aye aye! Well, me bucko, blow me down!

Just before t' motor mount was installed into t' final position, epoxy was injected into t' airframe above each centerin' ring. Ahoy! Blimey! T' motor mount was then slid into it's final position and more epoxy was injected into t' airframe to form fillets on t' centerin' rings/airframe epoxy joints. After t' epoxy set up, shiver me timbers, ya bilge rat, t' fin can was turned over and epoxy was again injected into t' motor mount above t' centerin' rings t' form fillets on t' other side o' the centerin' rings. Avast!

Prior t' final painting, screws will be used t' mechanically fasten the motor mount into t' airframe. Begad! Arrr!

Recovery:
I purchased a custom 168" Spherachute parachute to use for t' main parachute. Begad! T' 168" parachute I had made for t' IRIS has alternatin' panels o' white and neon orange for high visibility. Well, blow me down! T' main parachute be packed into a Rocketman deployment bag which be removed from the parachute when t' nose cone is ejected. Begad! T' nose cone was recovered with a 36" Spherachute made with alternatin' panels o' neon orange and white to match t' main parachute.

HarnessT' harness are constructed using:

  • 10 ft o' 5/8" Tubular Keelhaul®©™® from Pratt Hobbies
  • 4 ft o' 1/4 Tubular Keelhaul®©™® from Pratt Hobbies
  • 2 1/4" 880 lb Quick Links
  • Fisherman's Knot and Figure Eight Knot described in an article by Patrick Floyd in t' November 1999 issue o' High Power Rocketry. Arrr!

T' harnesses are constructed by first tyin' a 1/4" Quick Link t' each end usin' a Fisherman's knot. I am usin' t' Fisherman's knot because t' more you pull on t' knot t' tighter it gets. Avast, me proud beauty! After t' knots are tied, ya bilge rat, I use 1/4" Tubular Keelhaul®©™® to wrap t' lose end and give t' harness a finished look. Arrr! T' final step is to tie a loop in t' middle o' t' harness usin' a Figure Eight knot.

Electronics:
Recovery electronics will consist o' t' following: (1) Cannonball Works RRC2 set for drogue deployment at apogee and mains at 1200' A Blacksky ALTAAC 2A for backup drogue deployment and flight data gathering. Ya scallywag! Aye aye! Blimey! A Cannonball Works Wireless Recovery Controller 2 (WRC2) for redundant backup for t' main recovery system.

ElectronicsElectronics Bay T' electronics bay for t' IRIS is built inside a 6" X 12" long phenolic coupler. T' first step in buildin' t' bay was t' epoxy two 5.5" couplers inside t' 6" coupler. Well, blow me down! T' first 5.5" coupler was cut lengthwise and then epoxied equidistant from either end o' t' 6" coupler. After t' first 5.5" coupler dried, arrr, a second 5.5" coupler be cut lengthwise and epoxied in place inside t' existing 5.5" coupler. Begad! Ya scallywag! When t' second 5.5" coupler dried, a 6" o-ring was set in place on each end o' t' bay usin' J-B Weld t' form a gasket between the inside couplers and t' bulkheads. Ya scallywag! 3/4" 5 ply bulkheads are bein' used in t' electronics bay. Arrr! Avast! Two 1.25" u-bolts have been added t' t' bulkheads to provide attachment points for t' recovery system. Arrr! Two 1/2" threaded caps are attached t' t' bulkheads t' hold t' custom ejection charge holders. T' bulkheads are bolted together usin' 1/4 X 20" all-thread. T' three pieces o' poplar in t' picture will be epoxied inside t' coupler. Blimey! T' two 9" pieces will each contain six 8-32 T-nuts which will be used t' bolt the upper airframe sections together and also allow for access t' t' electronics bay and ejection charges. T' 3" piece will be used in mountin' t' two key switches used t' arm t' altimeters. Aye aye! A 3/16" X 5" X 10" electronics mountin' board has been built t' slide over t' all-thread rods and provide a mountin' surface for t' recovery electronics.

EC HolderT' IRIS will utilize a redundant recovery system. Well, shiver me timbers, blow me down! Blimey! Pictured be t' forward bulkhead of the electronics bay. I am usin' 1/2" PVC threaded caps as ejection charge holders. Begad! Blimey! I drilled a 1" X 1/4" deep hole into t' bulkhead t' hold the threaded caps. Aye aye! Blimey! I used me Dremel t' grind away a small portion o' t' outer threaded cap so that I would have a tight fit in t' hole. Begad! Ahoy! Blimey! After t' threaded cap be shaped t' fit, shiver me timbers, I epoxied t' caps in place. Arrr! Blimey! A 1/4" hole was drilled through t' cap and t' bulkhead t' allow t' ejection charge leads into t' electronics bay. T' caps will now act as ejection charge holders for the ejection charges. Blimey!

Ejection charges are built usin' 1/2" threaded male adapters. Ya scallywag! Ya scallywag! T' first step is t' epoxy a 7/8" section o' 1/2" dowel rod into t' fitting. Once t' epoxy is dried, me bucko, drill a 1/8" hole through t' dowel t' pass the leads o' t' electric match. Before installin' t' electric match, ya bilge rat, enlarge the 1/8" hole t' 3/8" by Finished1/2" deep to accept t' green protective cover o' t' DaveyFire electric match. Aye aye! Begad! Once the holes are drilled epoxy t' electric match in place. Begad! I always make sure to twist t' electric match leads together as a safety precaution!!! (I like leavin' t' green protective cap in place and fillin' it with FFFFg powder which makes an ejection charge inside t' ejection charge.

Once t' ejection epoxy has dried, I fill t' cavity with FFFFg black powder with a charge that I determined usin' t' BP tools in t' Rocketry Online INFO Central. Avast! Ahoy!

T' ejection charges for t' IRIS will be:

  • 2.10 grams FFFFg black powder for t' apogee charge
  • 3.33 grams FFFFg black powder for t' main recovery charge

Once t' black powder charge is in place, ya bilge rat, I use facial tissue t' make a waddin' t' cover t' charge. Begad! Begad! I then use a candle and melt wax over t' wadding and seal t' ejection charge. Begad! Avast, arrr, me proud beauty!

When preparin' for launch, I pass t' electric match lead through t' hole in t' threaded cap and into t' electronics bay. Blimey! Blimey! I screw t' 1/2" male fittin' into t' 1/2" threaded cap. Begad! Blimey! At this point I start usin' my altimeter preparation checklist t' ensure that I connect t' ejection charge leads t' t' altimeter in t' safest manner possible!

Lift-OffSUCCESSFUL LEVEL 3 FLIGHT!

June 23, shiver me timbers, 2001
Whitakers, shiver me timbers, NC.
Rocket - Scratch 1/2 scale ARC IRIS
Weight - 60 lbs
Motor - Aerotech M1315
Altitude 6270 feet

A special "Thank You" t' me wife for nay complaining about bein' a 'rocket widow" while I was buildin' t' IRIS and for laughin' and smilin' when we were hangin' out in a cow pasture in North Carolina on flight day!

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