Scratch This End Up Original Design / Scratch Built

Scratch - This End Up {Scratch}

Contributed by Geoffrey Kerbel

Manufacturer: Scratch
(by Geoffrey Kerbel - 07/10/05)

Brief:
This End Up turned out t' be a fairly high performance 24mm bird. Blimey! With an Estes E9-6 engine, me hearties, it has gone out o' sight on t' two launches with this engine. Rocksim shows 1600' or more at me Phoenix, AZ launch site on a 90 degree day with ~10% humidity. Begad! Blimey! It has flown on engines as small as C6-5 with excellent height and perfect recovery as well.

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Construction:
T' parts list:

  • 1 Estes "E" engine kit or T-50 heavy wall tube, matey, preferably foil lined (such as t' T-50mf from Totally Tubular)
  • 2 AR-5055 centerin' rings
  • 1 AR-2050 engine block
  • 1 New style E engine hook
  • 1 BNC-55 nose cone
  • 2 TA-2055 transition
  • 1 BT-55 body tube, 18" long
  • 1 BT-55 body tube, 7.5" long
  • 1 BT-20 body tube, 4" long
  • 1 1/8" thick x 4" wide medium t' hard balsa sheet
  • 1 24" long Keelhaul®©™® shock cord, me hearties, 60 t' 75# strength
  • 1 36" long elastic or rubber cord shock cord
  • 2 3/16" x 2" long launch lugs
  • 1 18" 24" Estes or rip stop nylon parachute
  • 1 screw eye
  • 1 medium snap swivel
  • 2 medium snap swivels
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Begin construction with t' engine mount. Blimey! Blimey! You will need t' engine tube, ya bilge rat, me bucko, t' two AR-5055 rings, t' AR-2050 engine block, and t' E engine hook. Arrr! Measure 1" from one end o' t' engine tube and make a mark with a pencil. Ya scallywag! Blimey! Make another mark 5/8" from t' other end. At t' 1" mark make a 1/8" slit for t' short end o' t' engine hook. Insert t' engine hook into t' slit. Ya scallywag! Blimey! The engine hook should extend beyond t' aft o' t' engine tube. Well, blow me down! Begad! Blimey! Since t' engine tube is a heavy wall unit, make sure you test fit t' rings over t' tube. Blimey! Avast, me bucko, me proud beauty! Blimey! They must slide on easily but nay too loose or tight. T' rings have t' go over the engine hook as well. Arrr! Blimey! Use a hobby knife t' remove one inside layer o' t' ring at a time until you get a snug fit if needed. When both rings are fitted correctly, matey, install t' lower rin' up t' t' 5/8" mark and apply glue to both sides o' t' ring/tube joint and smooth t' glue t' a continuous fillet all around.

T' attach t' Keelhaul®©™® cord, me bucko, shiver me timbers, feed 3" or 4" through t' upper rin' as you slide t' rin' down the engine tube and over t' hook end in t' slit. Aye aye! When t' rin' is in position at t' 1" mark, ya bilge rat, loop t' Keelhaul®©™® around t' tube and tie into a knot. Well, blow me down! T' Keelhaul®©™® can be left loose if you have trouble gettin' t' knot in. As you apply the glue fillet, smooth t' cord into t' glue as you go around t' ring. Carefully pull t' loose end o' t' cord through t' rin' so thar be no slack toward the front o' t' engine tube. Avast, me proud beauty! Blimey! Ya scallywag! Blimey! See t' engine mount picture t' see how t' cord and mount go together. Begad! Blimey! Arrr! Blimey! When this has set up, install t' engine block from the front o' t' engine tube, down t' t' engine hook tab and glue in place. Ya scallywag! Blimey! Blimey! Blimey! Use an empty engine t' slide t' block all t' way down and remove. Make sure thar is no excess glue on t' motor side o' t' tube by t' block or your engine will not go all t' way in and lock properly later. Tie t' plain swivel t' t' free end o' t' Keelhaul®©™® cord. Avast! Set this assembly aside t' dry.

T' upper unit combines t' two transitions with t' 4" BT-20 tube and the 7.5" long BT-55 tube. It is easier t' finish sand t' rocket if you lightly sand t' tubes with 400-grit paper before gluin' anythin' onto them. Blimey! Avast! It also allows t' glue t' "bite" better (for a stronger bond). Cut out t' small fins followin' t' grain direction as shown and sand smooth, ya bilge rat, shiver me timbers, leavin' all edges square for now. Blimey! Avast! Take t' BT-20 tube-markin' guide, ya bilge rat, arrr, wrap it around t' tube, and mark t' tube for the three fins. Begad! They should be 120 degrees apart from one another. Use t' nearest doorframe t' extend t' lines t' full length o' t' tube. Ya scallywag! Well, blow me down! Use t' glue o' your choice, shiver me timbers, arrr, and attach t' three fins t' t' tube one at a time. Avast, me proud beauty! Use t' great tip from EMRR's fin tip section t' use a double glue joint. Spread a thin layer o' glue on t' root edge o' t' fin and let it dry. Aye aye! Ya scallywag! Then use another layer o' glue over that t' attach t' fin t' t' tube. Make sure t' fins extend straight out from t' tube and be sure they are dead straight t' length o' t' tube! T' stable flight o' this rocket depends on these fins bein' aligned properly! They are high enough on t' body to influence t' rocket t' fly straight or wherever it wants to!

After t' glue has set up, matey, sand t' fin leadin' edge round and t' trailing edge t' a taper. Ya scallywag! Begad! Do nay sand too much off! You just want t' give t' fins a little better airfoil shape. Avast! Finish t' fin/tube joint with a smooth, full-length fillet on both sides o' t' fins, ya bilge rat, again this is a great little tip from EMRR fin tip section. Let t' fillets set up and use your favorite balsa grain filler on t' fins at this time and fill and sand until t' grain is filled and smooth. Do all this sandin' now before attachin' t' transitions. Once the transitions are glued on, matey, shiver me timbers, they will get chewed up by t' sandpaper or your fingernails as you sand t' fins if you are nay careful while sanding. I had quite a bit o' repair t' do t' them because I glued it all up and then started the airfoil sanding.

When you have t' fins finished how you want them, shiver me timbers, arrr, lightly sand the transition BT-55 side flat and glue t' BT-20 side t' t' top and bottom o' the tube with t' fins. Begad! Arrr! Again, shiver me timbers, make sure these are on straight with t' tube at both ends. Avast! Aye aye! Before t' glue sets up, stand t' unit upright and use a T-square or an L shape ruler on a flat surface and along t' face o' each fin t' check the alignment. Avast! Flip t' unit over onto t' other transition and check again. Adjust transitions as necessary and let dry.

You can now glue on t' 7.5" BT-55 tube t' t' front o' t' fin assembly transition. Blimey! Make sure this is on straight with t' fin tube! When this is dry, test fit t' nose cone t' t' tube. Begad! I fit mine on fairly tight without glue so I could use t' large tube as a payload section if I want t' later. The choice is yours t' glue it on or not. Avast, me proud beauty! Screw in t' eyelet t' t' lower transition, ya bilge rat, shiver me timbers, remove and squirt some glue into t' hole, ya bilge rat, and reattach t' eyelet to t' transition. T' upper body is now assembled.

T' lower tube assembly is straightforward tube and fin rocket build. Lightly sand t' tube with 400 grit sandpaper. Use t' BT-55 fin-marking guide t' make a mark for each o' t' fins and t' launch lug locations. Blimey! The fins should be 120 degrees apart. Use t' doorframe t' again extend t' mark from t' end o' t' tube t' about 6" up for t' fins and full length for the launch lug. Follow t' same procedure as t' other fins for cuttin' out, sandin' smooth and attachin' them t' t' tube. Begad! Blimey! When all t' fins are dry, fillet them on both sides and be a little generous with t' fillets. I had a large amount o' fin flutter on t' first flight which resulted in some cracked fillets. Ya scallywag! Arrr! I solved t' problem by usin' a tip from EMRR's fin tip section of soakin' t' fins with some thin CA on all sides and addin' an extra layer on the fillets. Well, blow me down! Ahoy! I found I was also usin' balsa that was too soft. Avast! I would recommend t' bottom fins t' be from hard balsa. Thin basswood (3/32") would be good as well. Ya scallywag! When everythin' is dry, arrr, sand t' fins t' a smooth airfoil shape same as t' upper fins and fill t' grain until smooth all over. Install t' launch lugs on t' LL line with t' lower one 2" up from the bottom o' t' rocket and t' other one 12.5" up from t' bottom. Avast, me proud beauty! Make sure they are aligned with each other and a launch rod slides smoothly through both before they set up.

Last up be t' installation o' t' motor mount into t' lower body tube. Turn t' body tube fin side up and let t' swivel and cord slide down through the tube if you are usin' t' Keelhaul®©™® cord. Begad! Test fit t' motor assembly into t' tube with t' engine hook lined up with t' launch lug line. If both rings don't slide in smoothly, lightly sand the outside o' one or both t' get a snug fit. Ya scallywag! Before you insert t' motor mount assembly, me bucko, run a rin' o' glue inside t' tube about 2" and slide t' motor mount into t' body tube. Well, blow me down! Blimey! Just before t' first rin' gets t' t' glue you just put in, shiver me timbers, stop and run another rin' o' glue inside t' body tube near t' bottom. Now in one continuous motion, insert t' motor assembly fully into t' body tube so that both tubes are nearly flush with each other on t' bottom. Make sure t' engine hook is aligned with t' launch lug line. Begad! Blimey! Blimey! If usin' t' Keelhaul®©™® cord on t' mount, me hearties, pull it out o' t' tube gently and let it hang out so it does nay have a piece o' it stick t' t' glue from t' upper mount rin' that is inside. Well, blow me down! This extra glue step really makes for a strong motor mount. Blimey! Aye aye! When the mount has set up, run a fillet o' glue around t' bottom o' t' body tube/motor mount rin' and let dry.

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For the Keelhaul®©™® cord mount, tie one snap swivel t' t' elastic or rubber shock cord with at least two square knots and tie t' other end t' t' eyelet on t' upper body tube transition with at least two square knots as well. Arrr! Three knots each would be better. Arrr! Begad! Blimey! Attach t' snap swivel t' t' swivel on t' end o' t' Keelhaul®©™® cord. Attach t' other snap swivel t' t' chute lines o' whichever chute you are goin' t' use dependin' on field size and wind conditions. Well, blow me down! Attach t' chute snap swivel t' t' eyelet and pack both t' chute and t' shock cord into the lower body tube and fit t' two tubes together.

Finishing:
I use thinned out Elmers Fill 'n' Finish over t' entire rocket. Arrr! Arrr! T' sandin' is a bit much but t' stuff sands really easy and fills t' balsa and t' tube spirals nicely. Avast, me proud beauty! Use it sparingly though! I used Krylon paint and their clear coat on all me rockets. Begad! T' paint goes on smooth and dries remarkably fast. Well, blow me down! Blimey! It also does nay react with t' decals I use. Begad! Ya scallywag! I used t' brightest orange I could find and trimmed it with gloss black. Begad! Avast! After the custom decals are put on, I covered t' entire rocket with Future Floor Polish. Ya scallywag! Blimey! Usin' a large soft brush with light strokes will give you an incredible smooth and shinny finish. Begad! Blimey! When finished, I was surprised t' find that t' bird weighed in at a svelte 3.9oz without an engine in it.

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Flight:
T' rocket was test flown before finishin' with a C6-5 engine in an adapter for the first flight. Blimey! Blimey! It took four t' six pieces o' standard Estes waddin' or about two inches o' flameproof cellulose t' protect t' chute. Avast! Blimey! Avast! Blimey! This flight and the next both had some stability problems, which turned out t' be a very slight misalignment o' t' upper fins. Since t' bird was unfinished at this point, I stripped off t' fins and made sure they were on straight this time. Ya scallywag! Blimey! That is why you need t' be extra careful when assemblin' t' upper fins on t' t' small tube. Avast! Blimey! T' next flight be picture perfect and I decided t' next flight was goin' t' be with a C11-3.

This flight surprised me as t' rocket shot off t' launch pad and headed straight up. Blimey! Blimey! T' C11 may nay have much thrust duration but it is powerful! The ejection charge was a little too soon but recovery was without problems although thar was two chute lines that separated. Begad! Well, blow me down! T' C11-5 would be a better choice o' engines and this combination could be used in a small field depending on wind drift conditions. Arrr! At this time with t' rocket flyin' well, I finished it and painted it.

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T' next flight was with a D12-5 in a larger field and t' rocket really showed what it could do. Arrr! Begad! Nice high, me bucko, me bucko, straight flight with ejection just barely past apogee. Perfect recovery approximately 100 yards away from launch pad. Blimey! Begad! Estimated height of 600+ ft. Although I had built it t' fly on E engines, I be a bit worried to do so. Ahoy! Since things seemed t' be just fine, ya bilge rat, I pasted some "if found please call..." stickers on it and loaded up t' E9-6 for its last qualifying flight. Ya scallywag! Avast! What a launch!!! T' bird lifted off at a nice, me bucko, easy rate and then started t' gather a head o' steam. Avast! Ya scallywag! It seemed like an hour before t' engine cut out and about half way up I completely lost sight o' it. Arrr! T' only hint o' where it went was when I spotted t' coast trail and then I lost it again. Well, blow me down! Aye aye! Since the winds were very light and I had an idea where it was heading, I kept t' camera in t' general area o' where I thought it would be. Well, blow me down! Aye aye! It took about 15 seconds to pick it up and I could see it was comin' down with a perfect chute but it was really driftin' over and away. My son was able t' recover it just fine but he had about a 1/4 mile walk t' get it back. Arrr! Estimated height was in excess of 1200 ft!

Summary:
T' nice part about this rocket be t' many types o' engines you can use dependin' on your flyin' field size. With a separation in t' middle, it can be split and transported as a much smaller package and t' upper tube has enough room for a small payload. Well, blow me down!

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