Scratch 24mm Fruit Fly Original Design / Scratch Built

Scratch - 24mm Fruit Fly {Scratch}

Contributed by Scott Turnbull

Manufacturer: Scratch
(Contributed - by Scott Turnbull - 07/20/06) (Scratch) 24mm Fruit Fly

Brief:
This is a scratch build Mosquito-esque rocket usin' a Fat Boy body and nose cone and plywood fins. Aye aye! It has a 24mm motor mount. Arrr! Ahoy! It basically was a practice run in usin' high power rocket buildin' techniques on a smaller scale.

Construction:
T' body tube and nose cone are stock Fat Boy items. T' three fins and two centerin' rings were cut from thin plywood taken from a Clementine fruit crate. A steel fishin' leader attaches t' t' motor mount with 9 feet o' 1/4" elastic attached t' that as t' shock cord.

T' Clementine crate wood was chosen because I have several sheets o' it on hand. Blimey! Ya scallywag! T' crate sides are stapled t' heavier corner pieces and are easily removed with a pry bar and pliers. I used t' Fat Boy centerin' rings as templates t' mark rings on t' plywood. Avast, me bucko, me proud beauty! An X-Acto razor knife be used t' score through t' thin wood. Ahoy! I took several traces around t' rings t' get through the three layers o' wood. Begad! T' 24mm central hole was traced usin' a standard paper motor mount and also was cut with t' razor knife.

(Scratch) 24mm Fruit Fly I made a custom motor hook usin' steel wire previously used t' hold insulation up between floor joists. Arrr! Two pair o' pliers were used t' twist t' wire t' the right shape and snip t' extra. Once t' hook was made, t' lower centering rin' be notched t' allow t' hook t' bend back away from t' motor mount. Avast! The upper rin' was epoxied t' t' motor mount tube. T' lower rin' was initially press fit only. Avast, me proud beauty!

A steel fishin' leader was looped around t' motor mount tube just below the upper centerin' rin' and fed through a small hole in t' ring. Ya scallywag! This will provide an ejection charge resistant wire that extends t' just below t' upper end o' t' body tube.

(Scratch) 24mm Fruit Fly(Scratch) 24mm Fruit Fly

T' length and width o' t' Clementine crate sides constrained t' size of the fins. Begad! I made paperboard templates from a cereal box t' refine t' design of the fins and their through t' wall tabs. Blimey! Once an acceptable template was created, shiver me timbers, I used it t' mark t' plywood for three fins. T' razor knife scoring technique was used t' cut out t' fins. Blimey! There were some staple holes and rough spots in t' fin surfaces. Wood putty was used t' fill in t' holes and ridges. A thorough sandin' gave t' fins a respectable finish.

After t' fins were cut out, shiver me timbers, t' motor mount's upper centerin' rin' was epoxied into t' main body. Avast, me proud beauty! T' fins were then epoxied through t' wall t' the motor mount tube. Begad! At this point I was growin' weary o' learnin' t' wonders of epoxy work and switched over t' Elmer's Carpenter's Glue for t' remainin' fin fillets and t' gluin' o' t' aft centerin' ring. Avast! Everythin' I've read states that a good yellow glue joint will exceed t' strength o' paper and wood bonded together. T' materials will fail before t' yellow glue (or epoxy) will. Aye aye!

A length o' 1/4" cardboard tubin' from a high power igniter packaging was glued at t' root o' one o' t' fins t' serve as a launch lug.

Three yards o' 1/4" elastic from a local sewin' store were attached to the upper end o' t' fishin' leader. Blimey! T' other end o' t' elastic be tied to the nose cone lug. A loop tied in t' elastic a couple o' feet below t' nose cone serves as t' parachute attachment point.

T' final assembly task was t' attach an alternate launch guidance device: rail buttons. Well, blow me down! I like t' have options for launch pad selections. It helps at busy regional launches t' be flexible in what sort o' pad you can launch from. Sometimes t' rails are busy. Arrr! Sometimes t' rods are. I epoxied and machine screwed t' rail buttons in t' vicinity o' t' centerin' rings. Ahoy! T' machine bolts used are larger diameter than t' thickness o' t' centerin' rings, ya bilge rat, matey, ya bilge rat, so not much button strength be goin' t' come from t' rings.

Finishing:
T' finish be done usin' low cost rattle can spray paint. Avast, me proud beauty! Several light layers of gray primer were applied first with some sandin' t' remove fuzzies. Blimey! Several light coats o' red spray paint were then applied.

Flight:
For a parachute, I used a small yellow "Frankenchute" borrowed from my Cycline 3 kit. Arrr! Begad! This is a relatively light rocket with lots o' fin area to help it flutter down. Blimey! Begad! There is very little space in t' tube betwixt t' motor mount tube and t' nosecone for packin' t' chute. Well, blow me down! Well, blow me down! I have used a Nomex® square threaded over t' fishin' leader t' protect t' chute and used no other wadding.

T' first five flights for this Mosquito-inspired Fruit Fly took place at the Northeast Regional Rocket Festival. Begad! It first flew on a D12-3 and flew ramrod straight t' a respectable altitude.

Recovery:
After ejection, t' body tube descended parallel t' t' ground as t' nose end was held up by t' chute and t' motor end was held up by t' pinwheeling oversized fins. Begad! Ya scallywag! Blimey! All subsequent launches on D12, E9, and E15 engines have exhibited t' same enjoyable spinnin' fins horizontal descent after t' chute is deployed.

There was one unfortunate failure t' eject t' chute at a subsequent launch event. Well, blow me down! Avast! I had pushed t' Nomex® sheet too far down t' leader, me hearties, and it hung up in t' body while t' ejection gasses passed by t' sheet and chute. Begad! T' nose cone separated, me hearties, ya bilge rat, but the chuteless descent be a bit too rapid. Arrr! T' fact that I watched it come straight at me and bounce off t' chair at me side added t' t' drama. Begad! I proved that the glue be stronger than t' body tube as a chair induced gash in t' body tube near t' aft centerin' rin' failed t' dislodge any load bearin' joints. It flew again later that day with a maskin' tape bandage over t' gash and awaits more permanent repairs before flyin' again.

Summary:
This was an extremely gratifyin' rocket t' build and fly. Ahoy! Ya scallywag! It was large enough in diameter and used materials allowin' experimentin' with high power rocketry build techniques. Ahoy! Avast, shiver me timbers, me proud beauty! It flys wonderfully, me bucko, is very forgivin' o' many engine delays, and recovers in an amusing, spinnin' way.

T' only CON is that t' chute packin' space is very tight. Aye aye! I plan on modifyin' t' nose cone t' allow packin' o' t' shock cord up inside t' cone. This can be done by cuttin' some o' t' base off t' cone and attachin' the shock cord up inside t' cone.

comment Post a Comment