Brief:
Sprint Magnum - a scratch made upscale o' a popular Estes kit o' t' '70s.

Parts required:

1 - Balsa Nosecone, Balsa Machinin' Service
2.6" x 8 1/16" ogive with spherical tip; BNC50X in 2.6 inch size
1 - 2.6" x 25 1/2" Body Tube, Totally Tubular (cut from stock)
1 - 29mm x 18 5/8" Motor Tube, Totally Tubular (cut from stock)
1 - 29mm x 6" Nose Tube, Totally Tubular (cut from stock)
1 - BT-60 x 5" Baffle Tube, Estes or Totally Tubular
4 - 1/8" ply rings, 29mm t' 2.6", Balsa Machinin' Service
2 - 1/2" long x 1/4" dia Launch Lugs, Apogee Components (cut from 3" length)
1 - 6' Keelhaul®©™ (tm) string, 300#, arrr, Apogee Components, me hearties, Into t' Wind
1 - 1 1/8" x 3" hardwood dowel, me hearties, shiver me timbers, local hardware store (cut from stock)
1 - 1 1/8" x 1" hardwood dowel
1 - 30" nylon parachute, matey, Giant Leap Rocketry
1 - Slimline Retainer, Giant Leap Rocketry
1 - #10 x 1 1/2" wood screw
12 - #10 x 1" fender washers for ballast
2 - #10 x 1" screw eye (wood)
1 - 36" x 3/8" elastic strap
1 - 4" x 36" x 3/16" basswood
1 - 2.4" long x 3/8" diameter hardwood dowel
Cardstock for boattail

Parts for Motor Adapter:

1 - BT-50 3 3/8" long
1 - 29mm mount tube 3 1/2" long
1 - 29mm mount rin' 3/8 inches long (cut from motor tube stock)
1 - CR2050 (optional)
1 - 1 1/8" fender washer

Specs:

Diameter: 2.6"
Length: 36.9"
Weight: 14 t' 22 oz (weight adjusted for balance)

Motors:

24mm (requires adapter)
E28-4 RMS 670 feet
F39-6 RMS 987

29mm
E23-5 RMS 575 feet...
USE LONG LAUNCH RAIL

F40-7 RMS 1697
F50-9 SU 1833
F52-8 RMS 1656
G33-7 RMS 2075
G40-10 2534
G64-10 RMS 2552
G80-10 SU 2539
H70-10 3990
H128-10 RMS 3082

Estimated altitude assumes 16oz flyin' weight, matey, and is based on Apogee Component's Rocksim 5 software.

Overview:

This rocket be t' first o' a couple o' upscale projects that I have in mind. Arrr! It be t' first large rocket that I've made from scratch, me hearties, and me first flagrant upscale o' an old Estes Classic. Aye aye! I was always impressed with t' way the original Sprint left t' launch rod and be gone in a blink. Blimey! Avast, me proud beauty! My version features a 2.6-inch airframe, arrr, a 29mm motor mount, matey, through t' wall fin construction, me hearties, shiver me timbers, and an ejection baffle. Arrr! T' Slimline motor retainer completes the picture. 

Construction:

As with most projects like this, ya bilge rat, I start by cuttin' t' tubes t' length. Well, blow me down! Avast, me hearties, me proud beauty! The 2.6-inch airframe tube starts out 34 inches long and a 25.5-inch long section is cut from this stock. Begad! Begad! T' 18 5/8-inch motor mount is cut from stock as is the six inch nose cone liner tube. Begad! Since you're cuttin' tubes, ya bilge rat, go ahead and cut a five inch length o' Estes BT-60 from a piece o' stock.

Next, ya bilge rat, cut t' basswood board into three equal lengths. Stack t' three pieces and tack glue t' slabs together with a single small dot o' slow CA between layers. Begad! Avast, ya bilge rat, me proud beauty! T' CA will hold t' three fins together while they are being cut out and sanded t' a uniform size. Draw t' outline o' t' fins on t' top of t' stack and cut out t' basic shape usin' a band or scroll saw. Well, blow me down! Use a disc sander t' set t' final shape. Begad! T' three parts can now be popped apart. Arrr! The disc sander should now be employed t' rough in an airfoil into each one. Use a sandin' block with 220 grit t' finish and perfect t' airfoil shape, arrr, and then switch t' a finer grit t' cut out t' scratches.

Now make t' ejection baffle by markin' t' motor mount tube with three lines runnin' t' length o' t' tube equally spaced around t' tube. Avast! Do t' same with t' BT-60. Avast, me proud beauty! Now cut a group o' four holes in the motor mount tube along each o' t' three lines startin' at 1 inch from the top o' t' tube spaced 7/8" inches apart (12 holes total). Aye aye! Arrr! Do this t' the BT-60 tube as well but start t' holes at t' 1/2-inch mark so that t' two groups o' holes will be staggered when t' baffle is assembled. Blimey! T' forward motor rin' is now glued on at 7 1/8" from t' aft end. Begad! Blimey! While that is drying, matey, ya bilge rat, t' BT-60 can be centered on and glued t' one o' t' remainin' rings. When t' glue is dry cut three equally sized and spaced tabs from t' outside edge o' t' ring. T' tabs remainin' should be centered over t' holes. Blimey! Glue the one inch piece o' dowel into t' top o' t' motor tube flush with t' end. Glue this in well; t' recovery system will be tuggin' on this at ejection. Place a centerin' rin' on t' fore end o' t' motor tube but do nay glue yet. Now glue t' BT-60/rin' t' t' top o' t' mount tube flush with t' end, with the motor tube in t' BT-60 and t' holes in t' two tubes aligned such that the inside holes are centered betwixt t' outside holes. Aye aye! T' lower rin' should now be glued firmly t' t' motor tube and t' t' bottom o' t' BT-60. Arrr! (All of the holes in t' motor tube should be betwixt t' two disks.) When finished, you should be able t' blow through t' motor mount, arrr, with t' air passin' out the holes in t' side o' t' BT-60. Begad! Blimey! When installed in t' airframe, me bucko, me bucko, t' air will pass up through t' slots in t' top rin' at ejection. Avast, me proud beauty! Avast, me proud beauty! Allow this assembly to dry.

Test fit t' fins t' t' motor tube. Blimey! Locate t' last rin' on t' motor tube against t' back o' t' fin tabs. Avast, me proud beauty! Don't glue it t' the tube just yet. Begad! This should be about 3 and 3/8 inches from t' aft end o' the tube. Avast, me proud beauty! Trim and sand t' fins until they reach t' t' tube with t' notch in the back o' t' fins just touchin' t' top o' t' ring, me bucko, but with enough space between t' front notches and t' rin' for t' thickness o' t' body tube to fit. Ahoy! Mark t' body tube for t' fins slots by makin' three marks equally spaced around t' bottom o' t' tube and use a doorjamb or markin' guide t' draw lines along t' tube. Make a parallel set o' lines 3/16-inch over from t' first set. Mark a line around t' tube at 3 7/8 inches from t' end. Ahoy! Slide t' motor tube assembly into t' airframe tube t' support t' body while you cut out t' slots for t' fins. Cut t' slots usin' a good sharp knife - put a new blade in your X-acto knife. T' top o' t' slots should be even with t' aft end o' the forward motor rin' when t' after rin' is inside t' tube 1/8 inch and located in t' correct spot on t' motor tube. Avast! Tack glue t' fins t' t' motor tube with t' motor mount properly located in t' airframe, bein' careful that you don't inadvertently glue t' assembly together. Naturally, matey, t' fins should be in line with t' centerline o' t' rocket (automatic if t' slots are straight) and stand straight out from t' airframe. Ya scallywag! Ya scallywag! Remove t' assembly from t' airframe and run fillets o' glue around all fin joints. Begad! Take it easy on t' glue here; excess weight in t' aft o' t' rocket will really cause trouble later. Arrr! This model has t' potential t' be very tail heavy. Ya scallywag! Be careful nay t' get glue on the aft fin tabs or on t' motor tube aft o' t' tabs which will interfere with aft rin' when it is installed.

Mark one last parallel line on t' body tube spaced evenly betwixt two of the fin slots for t' launch lugs.

Drill a small pilot hole in t' center o' t' top rin' and into t' hardwood plug. Ahoy! Screw one o' t' screw deadlights into this hole and tie one end o' t' Keelhaul®©™ strin' and elastic t' it. Blimey! Coil t' whole thin' up and tape it loosely t' the top o' t' baffle t' keep it out o' t' way while gluin' t' assembly into the airframe.

(Click for full size)

Now glue t' fin/motor/baffle assembly into t' rocket airframe. T' after centerin' rin' should be inside t' rocket about an eighth o' an inch when it is against t' back o' t' fin tabs when t' fins are in place. Aye aye! Create glue fillets around t' fins inside t' body tube where they meet. Ahoy! Ahoy! Also add fillets to t' back o' t' centerin' rin' where it meets t' tube. Ya scallywag! Now glue t' final rin' t' t' back o' t' fin tabs and motor tube. Ya scallywag! Aye aye! Use a long stick t' apply glue to t' top rin' ensurin' that it is firmly glued t' t' airframe tube. Begad! This is important because t' recovery system yanks at this joint at ejection. Avast, arrr, me proud beauty! Cut a 3/16-inch rin' from t' left over 2.6 inch tube stock. Ahoy! Cut a small section out of t' rin' and fit it into t' aft end o' t' rocket; it should stick out of the aft end o' t' rocket a small amount when t' inside edge o' t' rin' is against t' aft ring. T' two ends should just meet - trim a little off the ends until it just fits. Run a fillet o' glue at t' motor tube/rin' joint and airframe/rin' edge o' t' after ring, me bucko, and at t' same time glue in t' short rin' just made. Arrr! This creates a lip for t' boattail. Arrr! Apply fillets t' t' fin roots on t' outside o' t' airframe. Again, me hearties, take it easy on t' glue! The fillets should be smooth and strong but nay excessive. Durin' t' fillet process you should glue t' launch lugs on locatin' one near t' aft end o' the body tube and t' other at about 18 inches up from t' aft end o' t' airframe tube.

Use JB Weld t' glue t' Slimline retainer t' t' end o' t' motor tube being careful t' follow t' Slimline instructions. Use care t' get t' spacing correct for your motor hardware. Ahoy! T' 29/40-120 aft closure is a different size than t' Easy Access 29mm hardware aft closure. Avast, me proud beauty! If you plan t' use both, ya bilge rat, size the gap for t' Easy Access hardware and then use a spacer cut from scrap motor tube t' adapt t' hobby motor hardware.

While t' fin fillets are drying, cut two copies o' t' boattail from card stock. Avast, me proud beauty! Well, matey, blow me down! Blimey! One should be about 1/16-inch longer than t' other. Use t' edge o' a table or metal rule t' produce a curl in t' stock. Continue t' curl t' card by rollin' it on itself until it is so curly that t' edges meet naturally. Cut a strip o' card t' length o' one side o' t' short shroud from scrap. Blimey! Glue it to one o' t' edges o' t' short shroud, it should hang off half way since it will be used t' join t' two edges together. Avast, me proud beauty! When dry, fit t' shorter shroud to t' aft end o' t' rocket. It should fit snuggly (but nay tightly) t' the Slimline retainer, and just match t' inside o' t' airframe tube ridin' on the lip created by t' ring. Adjust and trim t' shroud as needed, then glue the tab t' t' other side o' t' cone. Use tape t' hold these two sides together - try and get t' cone as round as possible. Well, blow me down! Blimey! When dry test fit t' remainin' cone to t' top o' t' first one. It should match at both ends. Trim and adjust it until it does then glue it over t' smaller one with t' seam on t' opposite side as t' other's seam. Begad! Take care t' get t' two edges butted together and to get it well centered over t' smaller one. I used yellow glue for this, but CA would work well, me hearties, as would a very thin layer o' epoxy. Avast! Blimey! At this point, you may glue t' two parts t' t' rocket usin' epoxy or JB Weld. Use t' rocket and tape t' hold t' parts as round as possible as t' glue cures.

Now for t' nose cone. Well, blow me down! Ahoy! If you've been careful with t' glue, ya bilge rat, arrr, your rocket will weigh in at about 8oz (sans t' cone). With t' cone it should be about 10, arrr, you are about t' add another two and t' ability t' adjust t' nose weight. Drill t' inside o' t' cone out carefully (use a press!) so that t' 29mm tube will slide easily into t' hole. Avast! T' hole should be 6 or 7 inches deep. Take care t' drill t' hole in t' center and don't go too deep. Avast! Glue t' six-inch long 29mm tube into t' hole so that it is flush with t' shoulder end. Aye aye! Avast! Slide the 1 1/8-inch hardwood dowel into t' tube until it is flush with t' end. Hold it thar with tape and drill a 3/8-inch hole through t' shoulder o' the cone, through t' 29mm tube, through t' hardwood dowel, and out through the other side. Begad! T' hole should be just below shoulder ridge. Remove t' dowel and soak t' inside o' t' balsa holes with thin CA and allow it t' fully cure. Avast! The 3/8-inch dowel should now pass through t' shoulder into t' hardwood dowel and hold it there. Be careful t' allow t' CA t' dry before you test fit! Sand the dowel until it will slide through - it should be snug but nay overly tight. Avast! Cut the dowel t' length - it should just fit below t' shoulder allowin' t' nose to be fit into t' airframe. Drill a small pilot hole into both ends o' t' 1 1/8-inch dowel. Well, blow me down! Ya scallywag! Screw t' screw eye into t' aft end, me hearties, and t' wood screw into the other. Aye aye! Tie t' Keelhaul®©™ strin' and elastic t' t' screw eye. Assemble the cone and test fit it into t' airframe. This system is arranged this way to allow enough nose weight for G and H impulse motors t' be added, and yet allow a way t' lighten t' rocket for E impulse 24 mm motors usin' an adapter. Aye aye! Add washers t' t' screw for large motors (29mm), and remove washers for smaller (24mm) motors. Ahoy! T' total weight with a plastic 'chute and an Aerotech RMS E28-4 should be about 14 oz. Well, blow me down! Arrr! T' total weight with a 30" nylon 'chute, Aerotech G64-10, and enough nose weight t' get t' correct balance is just over 22 oz. Mark t' rocket at 24 1/2" inches from t' tip o' t' nose cone. Avast! The rocket should balance at or in front o' this mark with a motor loaded. Ahoy! Well, blow me down! Add washers t' t' nose until it does. Ahoy! Begad! Check and adjust t' balance before every flight! Add a step for balance t' your checklist.

Finally, make a 24mm adapter. Avast! Glue t' thrust rin' flush with one end o' the 24mm tube (optional - I use this adapter in other rockets with Estes single use motors usin' a spacer with 70mm long motors). Draw two parallel lines the length o' t' 29mm tube spaced about an 1/8-inch apart. Cut t' strip between the two lines out o' t' tube. Ya scallywag! Glue t' 29mm tube around t' 24mm tube so that the motor block end o' t' 24mm tube is flush with t' end o' t' 29mm tube. T' 1/8-inch inset is t' allow for t' thrust rin' o' t' 24mm reload hardware. Trim off one edge o' t' 29mm tube as needed - it's OK if t' two edges don't meet. Well, blow me down! Aye aye! Test fit t' 3/8" band and t' washer together in t' mount - you should be able t' install t' retainer clip easily, me bucko, but thar should be little or no slop in t' parts. You may need t' adjust t' size o' t' 3/8" band to fit your motor retainer dependin' on how much space you left betwixt the retainer and t' motor tube. Avast, me proud beauty! Trim or cut a larger one as needed. Avast, me hearties, me proud beauty! Glue the 3/8" 29mm band flush with end o' t' assembly opposite t' motor block. Drill out t' fender washer so that t' center hole is larger than any given 24mm RMS motor nozzle - 5/8" should be about right. Avast! Use a drill press and a press clamp! T' use t' adapter, slide t' motor into it in t' normal fashion, then slide t' whole thing, me bucko, ejection/block end first, arrr, into t' mount. Place t' washer over t' top o' t' assembly, and insert t' sprin' keeper into t' Slimline retainer.

This is a somewhat challengin' rocket t' build because o' t' boattail. Arrr! It is also a challenge avoidin' overgluin' thus addin' unnecessary weight. Arrr! Blimey! The outcome is a sleek lookin' rocket.

Rating: 5/5

Finishing:

Sand t' basswood fins lightly with 220 grit paper, and a little more with 400 grit paper. T' balsa cone should also be lightly sanded with 400 grit paper. Ya scallywag! Now seal both cone and fins with three coats o' Aerogloss sandin' sealer with a light sandin' in between. Ya scallywag! Blimey! Fill t' spiral with Elmer's Fill 'n' Finish wood filler and sand it smooth. Ya scallywag! You may need t' do this twice. Begad! Carefully wipe the rocket clean o' dust and spray it with a layer o' white primer. Begad! T' primer coat will allow you t' be able t' see t' flaws in t' fin fillets and spirals. Work out these flaws and then sand until t' primer is very thin. Avast! Avast, me proud beauty! Wipe it clean again and hit it with another layer o' primer. Arrr! This layer should be sanded lightly until very smooth with 400 grit paper and wiped clean one last time. Now two coats o' satin or flat white should be sprayed. Blimey! Well, me hearties, blow me down! Wait t' correct amount of time as outlined in t' instructions o' t' paint you are usin' then mask the lower section o' t' rocket. Ya scallywag! Avast! Spray t' top section with a yellow or metallic paint. Removed t' mask and add navy blue trim Monokote t' create the stripe and highlights.

This isn't an overly challengin' finish. Blimey! Blimey! Avast! Blimey! T' only tricky part was t' circle detail cut from Monokote Trimcoat.

Rating: 4/5

Flying:

So far I've only flown this rocket one time. Begad! At t' first high power launch sponsored by me NARRRRR section. Begad! Avast, me proud beauty! T' overcast be low all day so we didn't get a chance t' fly high until very late in t' afternoon preventin' me from flying it on large motors. Begad! T' motor I used was a 24mm E28-4 usin' an adapter. Blimey! The rocket left t' rail and went arrow straight with no spin. Begad! It ejected just at apogee and opened a 24" nylon 'chute. It landed a few yards beyond the pads, but it hit a little hard - no damage. Avast! Arrr! A 30 inch 'chute would be better. Dual deployment options would be a good idea, but that's another project. Aye aye! Arrow straight and a lot higher than I thought it would go on a small motor.

Rating: 5/5

Overall

This is a great rocket. Aye aye! Well, me bucko, blow me down! Blimey! I'm really pleased with how it came out and how well it flies. Blimey! Well, blow me down! Blimey! I'm lookin' forward t' puttin' some serious motors in it in t' near future.

Rating: 5/5