Scratch Mach Madness Original Design / Scratch Built

Scratch - Mach Madness {Scratch}

Contributed by Jeff Lane

Manufacturer: Scratch
(Contributed - by Jeff Lane - 04/03/05) (Scratch) Mach Madness

Brief:
"Mach 1-2-3" Virtual Rocket Contest entry built as a single-stage flyer.

Construction:
T' rocket consists o' 1 Estes Mosquito nose cone, 1 BT-5 tube, 3/32" balsa fin stock (used for 15 fins), me hearties, 1 balsa 5-20 transition, ya bilge rat, ya bilge rat, 1 BT20 tube, matey, 1 Estes 20-55 centerin' ring, matey, 1 custom bristol transition, arrr, ya bilge rat, 1 custom bristol body tube with printed graphics, 1/8" balsa centerin' rings, matey, 1 BT-50 tube, me bucko, shiver me timbers, 1 engine hook, 1 engine block, matey, 1 solid paper 20-50 centerin' ring, 12" parachute, me hearties, and 1/8" shock cord.

This is for experienced modelers. Begad! It has 15 fins, arrr, which requires great patience. Avast! T' preprinted bristol paper (I got it at an art supply store) forms the lower body tube and t' midsection transition. Blimey! It is astoundingly quick to assemble and looks great. Ya scallywag!

T' parachute fits inside t' shroud and requires careful prep t' ensure proper deployment. Aye aye! T' shock cord must be packed first t' pull t' parachute out.

T' large mid-rocket transition/bulkhead solution was a challenge t' design and build. At t' front o' t' transition, shiver me timbers, ya bilge rat, it seats on t' front o' t' BT-20 and a 20-55 centerin' rin' about 1.5" from t' front o' t' BT-20. Aye aye! Begad! At the widest point where it joins with t' 3" body, ya bilge rat, me hearties, t' ideal piece would have been a solid balsa coupler with half o' it fittin' inside t' 3" first stage body tube, shiver me timbers, me hearties, and half (conical shaped) fittin' up into t' transition. Instead o' doin' that, me hearties, I designed t' first stage motor mount so t' bulkhead is at t' leadin' edge o' t' 3" body tube with scrap balsa offsettin' a slightly smaller diameter bristol paper centerin' ring. Avast! Begad! This seats the transition nicely, me bucko, provides needed fore-aft rigidity t' t' bristol and is a very lightweight solution.

(Scratch) Mach Madness If I built it again, I might extend t' BT-50 engine tube all t' way t' a balsa 50-5 transition so t' parachute would eject just aft o' t' "sustainer". T' tiny, matey, small footprint sustainer fins would then be subject t' more violence from t' shock cord and parachute but deployment may be more reliable.

T' bristol body tube is nay quite as rigid as a regular body tube, which is good and bad. When I dropped t' finished product on t' floor, thar was enough "give" so that none o' t' 15 fins broke. However, you do have to be extra careful nay t' crush it while installin' an engine or during assembly.

(Scratch) Mach Madness

Finishing:
T' fins were sealed and filled with one coat o' dope then all o' t' remaining grain was eliminated with one coat o' automotive high-build primer from Autozone. Avast! T' only paintin' was t' black nose cone, white on t' sustainer and fins, shiver me timbers, and blue on t' small balsa transition. Aye aye! T' waterslide decal material from lazertran.com prints on an inkjet printer and dries in an hour. Arrr! Then the ink doesn't come off in t' water even though you don't spray with a stink bomb organic overcoat with this particular product. Used as a body wrap, it simplified t' paintin' process and reduced finishin' time.

All skins are available for download here: First stage Second stage Third stage.

Flight:
Recommended motors: C11-3, D12-5

I have flown it three times, with C11-3s. Ya scallywag! Twice in a town park, and once at the C.R.A.S.H. launch on 4/3/05. Ya scallywag!

First flight be unstable. Blimey! Blimey! One fin be floppy from ground contact but was easily repaired. Avast, me proud beauty! (This was t' only damage in t' three flights. I traded the Mosquito nose cone for a 3/4oz lump o' lead. Aye aye! Second flight be excellent with ejection just after apogee. Arrr! It's a light rocket that's overly wide and decelerates quickly, so it doesn't get much altitude on a C11 (200-300 feet or so). No damage on second or third flights. T' third flight was near perfect with ejection occurrin' nose up at apogee.

(Scratch) Mach Madness

Recovery:
T' elastic shock cord must be packed first, with t' parachute packed last and loosely so t' shock cord pulls it out. Ya scallywag! Begad! Shock cord mounts are standard folded-paper. Avast, me proud beauty! Well, blow me down! Waddin' is required. Aye aye! Avast, me proud beauty! T' motor is held in place with a standard motor retention hook. Well, blow me down! Begad! I used a 16 inch parachute, which be an excellent choice. Avast, me proud beauty!

Summary:
T' C.R.A.S.H. Ahoy! crowd liked t' way it looks and asked a lot o' questions. Arrr! Well, arrr, blow me down! They couldn't believe me RockSim entry calls for 6 G55s in t' first stage. Avast! I'll fly it again, ya bilge rat, probably with a D12-5 when I get t' an area with more space. Blimey! It's one of me favorite rockets.

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