Scratch V2 Original Design / Scratch Built

Scratch - V2 {Scratch}

Contributed by Kevin McLaughlin

Manufacturer: Scratch
(Contributed - by Kevin Mclaughlin - 11/15/02)

Rocket PicBrief:
Scale model o' infamous German WWII V-2 in 3.9" dia x 37" tall scale with 29MM motor mount that can handle up t' 29 x 240 hardware. Arrr! Empty weight of this rocket is 53 oz includin' nose cone weights for a G64 RMS. Well, blow me down! Avast, me proud beauty! VCP is at 12.7" and CG at 16.8" fully loaded with G64 RMS, tubular nylon shock chord and 45" ‘chute. Begad! Arrr! T' rocket features include wad-less recovery usin' ejection charge coolin' system, arrr, adjustable nose cone weightin' and styrene 1/8 plastic thru-wall fins. Aye aye! Paint finish be t' yellow/black White Sands paint scheme. Avast, me proud beauty! Avast!

Although thar are several 3.9" kits available out there, me bucko, arrr, I wanted to control t' quality o' materials and t' design. Ahoy! Ahoy! My main design goals were to creatin' a close-to-scale V2 that could use different motor sizes in a 29mm motor mount, would be extremely durable and easily repairable.

Component Description:
Body tube material is 3.9" x 8" LOC paper body tube material. Avast, me proud beauty! Begad! Nose cone and boat tail are made from Ace 3.9" nose cones. Arrr! Fin material is 1/8" styrene plastic. Used 2 plywood centerin' rings, one 2" x 29mm, the other 3.9" x 29mm. Begad! Aye aye! Used one 3.9" plywood bulkhead for top of exhaust coolin' compartment. Avast! Shock cord made o' 12’ nylon tubin' with Quick Link attachments. Ahoy! Well, blow me down!


BulkheadNose cone followed the design outlined by Brian Kain with some modifications. Avast! Glued nose tip cut off boat tail inside of nose cone with thru-wall screws and epoxy t' hold in place. Begad! This is used to support t' ¼" All-Thread rod uses for holdin' weights. Aye aye! Weights consistin' o' large washers are held forward with a piece o' 5/16" brass tubin' and nut. Blimey! My bulkhead/coupler assembly is a variation o' Brian Kain’s design and acts as anchor platform for shock chord and nose cone shoulder base. (See picture)

Construction/Finishing:
As mentioned in other V2 scratch build articles, arrr, cuttin' t' fin slots is tricky. Avast, me proud beauty! Blimey! Arrr! Blimey! I used a couple o' different fin markin' guides t' get t' spacing right for marking. I then used t' technique recommended by Brian Kain for cuttin' t' slots. Blimey! Blimey! T' Dremel tool with dual cutter/spacer configuration worked well. As mentioned, arrr, I used 1/8" styrene plastic purchased as scrap from Tap Plastic for about $1 per 12" x 8" sheet. Avast, me proud beauty! Blimey! Well, blow me down! Blimey! Styrene is very easy to work with. Ya scallywag! Blimey! Ya scallywag! Blimey! T' cut, arrr, me bucko, you just score and snap along a straight edge. T' finish, sand lightly with 200 grit sand paper and you are ready t' prime. Styrene saves me a ton o' time in constructin' both kits and scratch builds. Avast, me proud beauty! Blimey! It is also very tough, and will withstand a lot o' pressure before it breaks. Begad! Blimey! During construction, I dropped t' finished boat tail assembly fins down from 5 feet onto t' concrete floor o' me garage with no effect. Ya scallywag! Blimey! Ahoy! Blimey! I have successfully used 1/16" styrene for mid size 2.56" dia models. Avast! Blimey! I much prefer it t' ply or balsa fin material. I have also used 1/8" PVC that is a bit lighter than styrene, arrr, me hearties, and can be easily sanded and shaped. Aye aye! Blimey! Its drawback is that it is not as tough as styrene.

Cooling CompartmentThe wad-less recovery system incorporates a perforated motor tube, a cooling compartment betwixt t' upper centerin' rin' and a perforated bulkhead. Begad! I also use a steel exhaust coolin' mesh ala Aerotech that goes up t' motor tube prior to RMS hardware. Ahoy! Avast! Blimey! T' exhaust gasses pass through t' steel mesh, through the perforated motor tube into t' coolin' compartment and through t' perforated bulkhead into t' recovery chamber. Aye aye! This system works very well, and I have used it successfully in other rockets. Arrr! Arrr! Blimey!

I cut t' fin size t' scale, usin' a copier t' blow up a template o' the scale win' template from a 2.56" version I found on t' Internet. Begad! Ya scallywag! On the rocket’s first flight, I noticed some spiralin' as t' rocket approached apogee. Avast, me proud beauty! Begad! I suspect that t' smaller fin profile contributed t' this as the rocket coasted t' apogee. Ahoy!

I attached t' 3.9" x 8" length o' body tube t' t' boat tail after finishin' both pieces. Ya scallywag! They were glued together along t' interior body tube and top surface o' t' 3.9" bulkhead usin' 5 min. Avast, me proud beauty! epoxy without any fillin' o' t' joint. Avast, me proud beauty! Ya scallywag! I did this t' facilitate t' removal o' t' body tube without trashin' t' boat tail finish in t' event o' a recovery malfunction that might damage t' body tube. T' joint seam is visible betwixt t' two parts, but provides some repair flexibility. Begad!

Launch lugs are made from 5/16" brass tubing. Avast! Two 1" lengths are placed at each end o' t' 8" body tube. Ya scallywag! These are glued and filleted in place with 5 min. Avast, me proud beauty! epoxy. Ya scallywag! I used a ¼" x 7’ launch rod for this rocket. Avast!

Gas Exhaust PortsT' faux engine gas exhaust ports are made from styrene plastic tubin' cut diagonally and sanded to match t' contour o' t' boat tail. Avast! T' fin detail is cut from styrene strips, sanded and glued t' fin surfaces.

T' paint scheme uses school-bus yellow and black spray paint roughly followin' t' White Sands roll pattern used in 1945. Ahoy! I modified this pattern slightly around t' boat tail t' make maskin' around t' fins a little easier. I also eliminated t' lower chrome band above t' fins. I thought I did a good job on t' masking, me hearties, me hearties, and had nice clean lines betwixt t' patterns. Avast, me bucko, me proud beauty!

T' silver band around t' nose cone is chrome-laminated paper that has been cut t' follow t' contour and angle o' t' nose cone tip. Ahoy! Arrr! This is a trial-and-error process usin' t' shroud template tool in VCP. Blimey! Once I got the right angle set in t' tool and printed t' template, me hearties, I traced it onto the chrome-laminated paper for cutting.

I purchased t' 3.9" LOC paper body tube, matey, me hearties, 29 mm motor mount tube, recovery hardware, centerin' rings and bulkhead from Rocky Mountain Rocketry. All hardware and finishin' paint was purchased from me local Orchard Supply Hardware store. Ya scallywag! Begad! T' two Ace 3.9" nose cones where purchased off o' eBay. T' decals where purchased from Papa Tango Decals. Blimey!

LaunchFlight/Recovery:
I designed t' 29mm motor mount t' accommodate up t' a 29 x 240 RMS hardware, but typically will be flyin' usin' 40/120 29mm RMS. Avast, me proud beauty! Begad! I built into t' base 2" ply centerin' rin' two #8 x ¾" brass machine screws and fashioned an engine retainin' plate made from a piece o' brass with holes for screws and engine nozzle. Well, blow me down! Aye aye! Small win' nuts are used t' secure t' brass plate over t' RMS hardware. Flight preparation is a simple matter o' droppin' in and securin' motor, ya bilge rat, and then attachin' ‘chute t' shock cord usin' a key chain rin' and puttin' on t' NC. Blimey!

T' first flight be on a G64-4W as pictured in this article usin' a Quick Burst Twiggy igniter. Ahoy! Rocket flight was very stable at launch and acceleration with some spiralin' near apogee as rocket slowed t' a coast. Avast! Estimated altitude per me wrasp calculations was around 600’. Begad! Ejection occurred with the rocket startin' its decent with good ‘chute deployment usin' a 45" nylon hemispherical ‘chute. Shock cord is 9/16" x 12’ tubular nylon. Avast, me proud beauty! Well, blow me down! Landin' occurred about 30 yards down range. Blimey! Upon recovery inspection, I noticed a slight paint chip at t' lower boat tail joint o' one fin, but no crackin' o' t' epoxy fin filet. Avast! Suspect that thar was some movement o' the Ace boat tail material that caused some paint delamination upon landin' impact. I chose t' Ace NC for weight/cost consideration, arrr, and t' heavier PML NC may be an option for other builders. Begad! Avast, shiver me timbers, me proud beauty! Other than t' paint chip, flight and recovery was perfect.

Up and AwaySummary:
I especially like Brian Kain's idea allowin' for adjustable weightin' o' t' nose cone to accommodate different engine loads. Arrr! Avast, me proud beauty! I also like t' wad-less recovery design that keeps t' rocket interior clean and protects all recovery components. Ya scallywag! This is a very impressive lookin' rocket, especially with t' White Sands yellow/black pattern and decals. Arrr! Well, blow me down! I designed this a close t' t' scale dimensions as possible t' t' real thing. Begad! Ya scallywag!

If I could do it all over again, shiver me timbers, me hearties, I might have made t' fins a bit wider to see if that would increase flight stability. I have a Estes 2.56" version of t' V2 with very wide lookin' fins and it flies great. Ahoy! Well, blow me down!

As mentioned in other articles, it is important t' rough up t' NC material with sand paper before priming. Arrr! Also, be generous with t' number o' coats of primer, matey, as this will greatly increase t' quality o' final paint. Ya scallywag! Avast, shiver me timbers, me proud beauty! I used heavy coat gray car primer, me hearties, followed by white primer, followed by t' school bus yellow for all areas. Avast! I then used maskin' tape (the expensive kind!) for maskin' and paintin' t' black areas. Avast, me proud beauty! This yielded excellent results, matey, and had no problems with paint leakin' or peelin' off o' finish. Avast, me proud beauty! After applyin' decals, I applied a light clear coat finish. Ya scallywag! Well, blow me down! I have had much trouble with clear coat either drippin' or wrinkling, so I have been very stingy in applyin' it t' my projects. Ahoy!

I estimate that t' total cost breakdown looked somethin' like this for this V2:

  • Nose cones: $20 for a pair purchased on eBay plus $5 shippin'
  • Motor tube, arrr, centerin' rings and 9/16" nylon tubing: $12 with shippin'
  • Used left over 8" piece o' 3.9" LOC paper body tubin'
  • Miscellaneous hardware for NC: $10
  • Paints, epoxy and maskin' tape: $20
  • Decals: $13 with shippin'
  • Scrap 1/8" styrene for fins: $2
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