Scratch UPS Express Original Design / Scratch Built

Scratch - UPS Express {Scratch}

Contributed by David Kneble

Manufacturer: Scratch

Rocket PicBrief:
This is a single stage high power rocket created from a UPS shippin' box. Arrr! Blimey! It flies on 38mm motors (I211W-J350W) and features parachute deployment.

Construction:
T' parts for this rocket are all pretty simple and in me case I had everything, but some hardware and t' mailin' tubes, lyin' around t' house.

After t' destruction o' a section o' one o' me other rockets, arrr, I ordered t' necessary replacement parts. Begad! Blimey! They arrived in a 9x6x33 cardboard box. Ya scallywag! Blimey! After repairin' t' other model, I thought o' turnin' t' box that t' parts came in, into a rocket. Aye aye! So, ya bilge rat, arrr, first I worked out t' rocksim file which I will discuss a little later. Ahoy! Blimey! Then I began t' buy and cut t' parts I needed. Ya scallywag! Blimey! They were as follows: 1 box, 1 38mm MMT, 4 3/16" ply fins with t' necessary fin tabs (on one side o' t' box t' tabs are longer), two 3/16" ply centerin' rings for 9x6 t' 38mm, shiver me timbers, shiver me timbers, matey, one 3/16" ply centerin' rin' for 9x6 t' 3," one 3" mailin' tube, shiver me timbers, 15' o' 9/16" tubular nylon, 2 2" long pieces o' 1/2" LL material, shiver me timbers, u-bolt, motor retention hardware, nuts, matey, bolts and lead fishin' weights and adhesive (epoxy and liquid nails).

To begin construction, after t' rings and fins had been cut out, ya bilge rat, I epoxied t' 38mm tube t' one o' t' centerin' rings. Arrr! This would be t' forward end o' t' MMT. Arrr! Then, I determined how far in t' MMT should slide so that 1/2" protruded from t' flaps o' t' box, at t' aft end, shiver me timbers, shiver me timbers, me hearties, if t' flaps were sealed. Ahoy! T' second 38mm centerin' rin' was slid onto t' aft section o' t' MMT but nay epoxied. T' MMT and CR's were placed in t' box at their respective locations and a bead o' liquid nails was applied t' t' joint betwixt t' forward edge o' t' forward CR and t' box. Avast, me proud beauty! After t' adhesive set, fin slots were cut into t' box at t' correct locations. Begad! T' fins were tacked t' t' motor mount with epoxy and then filleted with more epoxy internally, me hearties, but nay externally t' maintain t' rough look o' t' box.

T' aft centerin' rin' had t' t-nuts for motor retention installed and then it was glued in place with liquid nails. Ahoy! T' flaps at t' aft o' t' box were trimmed t' allow t' MMT t' protrude through and then they were folded over and sealed tight with packagin' tape.

Then, matey, t' 3" mailin' tube be cut t' t' length, ya bilge rat, that was internally betwixt t' forward centerin' rin' and t' forward edge o' t' box. Begad! I believe this be about 28" or so.

Then, on t' final centerin' rin' (9x6x33 t' 3") a u-bolt was installed and then two bolts were installed through t' rin' (at opposite ends or t' CR) so that they protruded about 2" above t' front side o' t' rin' (the same side with t' u-bolt protruding). Avast! This centerin' rin' was glued onto t' mailin' tube about 3" from one end usin' liquid nails t' seal any gaps.

Then, t' mailin' tube and CR assembly be epoxied into t' box with t' CR closer t' t' front o' t' rocket so that t' bolts were visible. Ya scallywag! Avast! T' rin' joint be filleted and allowed t' dry and t' tubular nylon be attached t' t' u-bolt.

Fiberglass be applied t' t' forward flaps so that they were strengthened but still able t' fold shut and form a "nose" for t' rocket.

Finally, me hearties, matey, two 1/2" LL's were epoxied onto one side o' t' box along one o' t' fin joints.

Rocket PicFlight:
My next chore was t' determine how much nose weight be necessary t' make t' box stable. Begad! For this I turned t' rocksim. Because rocksim can nay create boxes for airframes I had t' compromise. Begad! Ya scallywag! Because me primary goal was t' find t' center o' pressure so that I could move t' CG forward o' it, ya bilge rat, and because CP is greatly influenced by drag o' all different types, shiver me timbers, me goal in rocksim was t' create a rocket airframe with similar amounts o' drag t' t' box.

Drag o' an airframe is based on a lot o' things, but because I lack a degree in t' field o' fluid dynamics I was withheld t' usin' only t' shape and surface area determiners o' drag.

Usin' some simple equations I found t' frontal surface area o' t' box and then created a circle with t' same area, which became t' basis for t' diameter o' t' tube. Ahoy! Following, arrr, I found t' area o' t' sides o' t' box and then created an airframe o' equal area, ya bilge rat, which became t' primary information in determinin' t' length o' t' tube.

Then, I created t' NC, which be simply t' flaps on t' box. Ya scallywag! I found when closin' t' box that they were nay completely flat but had a slight arc like a NC has. Begad! So, ya bilge rat, me NC in rocksim has a diameter equal t' t' body diameter but only .1" long, relatively flat.

T' rest o' t' rocksim file is pretty self- explanatory.

Usin' this file, ya bilge rat, I found where t' CG needed t' be in order t' be in front o' t' CP calculations for both methods. Begad! Then I added nose weight until t' CG met t' requirements and then weighed t' model for accurate reference.

After runnin' rocksim for flights o' varyin' motors I found that motors from an I211 and up yielded satisfactory altitudes and velocities.

I went t' t' monthly NEPRA launch and t' weather seemed okay, nay too windy, so I considered me motor options. Arrr! After talkin' t' a fellow rocketeer, he informed me that thar are very many serious equations that need t' be done when testin' somethin' like this, me hearties, t' determine how much stress t' object will undergo, shiver me timbers, because o' its frontal shape; a square. Aye aye! Slightly nervous, I opted for t' I211, a nice easy motor for this rocket, me bucko, with hopefully nay too much stress.

My dad and I prepped t' rocket, loadin' t' motor and attachin' t' 54" chute, me bucko, and then tapin' t' flaps closed with a small piece o' maskin' tape.

T' rocket was loaded onto t' pad, which had a 10' 1/2" launch rod t' keep t' rocket as stable as long as possible.

After a couple o' tries at lightin' it, it finally came t' life and rose, shiver me timbers, quite quickly, into t' sky above. Aye aye! Blimey! Aye aye! Blimey! T' flight was great with no real signs o' instability and t' rocket arched over. Avast! Blimey! Avast! Blimey! T' charge fired at 6 seconds but t' chute failed t' deploy; it got caught up in t' fiberglassed flaps. Blimey! Blimey! Aye aye! Blimey! T' rocket hurtled toward t' earth and in an epic battle, arrr, me bucko, t' ground gave t' box rocket a fatal blow. Begad! Blimey! There wasn't much left but in me mind t' flight be successful because it be stable.

I suspect that t' chute failed t' deploy because t' air resistance on t' flaps forced them closed too smartly and didn't allow t' chute t' fully escape t' mailin' tube.

I am workin' on an upscale version o' this rocket, matey, 10x10x48, which will feature dual aft ejection deployment t' avoid t' air resistance problem. T' planned flight for this box is next spring, possibly at NSL 2003, on a J415W.

Summary:
T' pros o' this rocket are it's simple design and construction, ya bilge rat, ya bilge rat, impression on t' RSO when he sees it, shiver me timbers, and its low, me hearties, arrr, majestic flights.

T' cons o' THIS box rocket are t' limited number o' possible motors and poor recovery design.

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