Descon Egberto Guismonte

Scratch - Egberto Guismonte {Scratch}

Contributed by Mike Roberts

Manufacturer:

	Which came first? T' Egg? The Chicken? Or..... Begad! The Rocket!
T' Tale o' Egberto Guismonte - T' Rubber Chicken Rocket
PARTS LIST: 1 Rubber Chicken 1 Length 38mm motor mount 1 38mm coupler tube 1 38mm plywood bulkhead 1 38mm plywood coupler bulkhead 6m Keelhaul®©™ cord Small square Nomex Larger Square Nomex 2mm Acrylic sheet approx 200g Lead shot Assorted Estes centerin' rings and scraps o' tube t' make inner nose parts. 18" chute.		ADHESIVES: 5 Minute Epoxy 12 Minute Epoxy Medium/Thick CA Microballons Two part structural foam.
Its all Chris Eilbeck's fault he came up with this idea t' fly some rubber chickens at t' m.a.r.s. Aye aye! Blimey! Brass Balls launch. Avast, arrr, me proud beauty! Blimey! His was t' be called Keith. Well it seemed like a good idea at t' time. I hadn't originally planned to enter it for Descon so I dont have a lot o' construction details for t' early stages suffice t' say " First catch your chicken..." I got mine from the Silly Jokes Online Store.

T' Chicken has landed

A couple o' days later and I had a box full o' rubber chickeny goodness. Avast, me proud beauty! I had decided this chicken had t' go with a whoosh which meant a 38mm motor mount and a Cesaroni Pro38 motor as Aerotech motors are as rare as hen's teeth over here in t' UK. Arrr!

Chicken Stuffing
	Havin' aquired me new bird t' next question had t' be how t' fit t' motor. Avast, me proud beauty! It wasnt difficult to imagine where it had t' go just how t' go about puttin' it there. Aye aye! I started by removin' t' squeaker fitted t' t' chickens aft vent.
T' next step be to take a piece o' 38mm motor mount tube and offer it up t' t' chicken's bottom. I drew a line around t' tube and then cut out t' rubber with a pair o' sharp scissors. I emphasise t' sharp as chicken rubber it quite resiliant and difficult t' cut. Aye aye! A bit o' trimmin' with a scalpel and I had an even tight fit. I fitted t' motor mount in t' t' chicken and pushed it up until it be in the neck o' t' chicken as far as it would go. Avast! Ahoy! I then offered up a Pro38 1 Grain casin' t' get an idea how far t' motor mount would have t' hang out t' back of t' chicken. Ya scallywag! I figured that t' tube within t' body o' t' chicken would be adequate for t' recovery system as long as t' majority o' t' motor was outside t' body. Begad! I added around 10mm t' give a bit o' space for motor retention below t' fins and cut t' motor mount tube t' length.
	In t' past I have used a piece o' 1/4" fibre glass rod as a mountin' point for t' recovery harness. I drilled a hole across t' tube above where t' end o' t' motor would go, me hearties, shiver me timbers, cut t' fibreglass rod t' length glued and filleted it inside the tube and t' filed and sanded t' end o' t' rod smooth on t' outside o' the tube.
	With t' motor mount trimmed it was time t' make t' "nose cone" fitting. Now things get a bit vauge here and I will have t' leave t' detail as an exercise for the student. Begad! Ahoy! T' idea was t' make somethin' from a 38mm coupler tube with some space in it which could accept some beak weight. Avast, me proud beauty! I rummaged and came up with a selection o' Estes bits and bobs. A bit o' sanded centerin' rin' here and a bit of glue thar and I had a part that would fit in t' t' neck o' t' motor mount tube. Ya scallywag! T' only evidence I have o' this is in this picture sequence.
	With the nose piece made it was time t' get foamin'. My plan, which proved rather unsuccessful, was t' fit t' nose piece t' t' top o' t' motor tube using maskin' tape t' hold it in place. Well, blow me down! Blimey! Pour in a quantity o' two part foam t' the rubber chicken carcass. Avast! Avast! Blimey! Jam t' tube assembly up t' chicken and wait for the foam t' expand and set. Begad! Blimey! Fixin' t' whole thin' in place. As t' join between the nose piece and t' motor tube were flush at t' top o' t' tube and the tube should fit snuggly in t' t' chickens rubbery neck I reasoned that, me hearties, once set, I would be able t' cut through t' rubber and seperate t' now foamed on head and nose piece from t' foamed in motor tube and chicken body. T' masking tape should have held t' nose piece in place and sealed it from foamy ingress.

	There lies me error. That two part foam can build up a fair pressure if you contain it. Well, blow me down! With the foam mixed and poured in I jamed in t' tube assembly. I wiggled and tipped things around t' get a even distribution o' liquid foam around t' insides then settled down t' hold it all in place. Begad! Blimey! T' foam expanded and started t' push. Avast, me proud beauty! Ahoy! It was quite a fight,and quite a sight as I struggled with me fowl. Well, blow me down! Blimey! In time I triumphed, or so I thought, and t' foam set with t' tube where I thought it should be and a reasonably firm chicken (even if it's head had swollen in a rather disturbin' fashion).
	Time to make a quick cut and "off with its head". Blimey! First cut through where I thought I had t' cut and t' head refused t' budge. Avast, me proud beauty! Avast, me proud beauty! A spell head scratching, cursing, arrr, me hearties, askin' others for guidance and bein' told "you didnt want t' do it like that" later and an second calculated cut be made. Avast, me proud beauty! This time the head came off in me hand. Avast! Some modification and fettlin' and I had a useable head / beak / nose cone. Arrr! T' reason for t' cut point movin' was that the pressure o' t' expandin' foam had forced t' inner nose piece back down the inside o' t' motor mount. Ahoy! T' second cut was measured from t' position o' the aft end o' t' nose piece relative t' t' back end o' t' motor tube. With the length o' t' coupler used for t' nose piece know it was possible t' work out where t' front o' it should be. Begad! Measure along t' outside o' t' chicken and cut through.

Fin Fitting
	Now it was time t' add t' fins. Ya scallywag! Blimey! I didnt want t' spoil t' lines o' me chicken so I opted for clear plastic fins. Aye aye! Blimey! I had wanted t' use polycarbonate as it is much more resiliant but couldnt source any in time so I had t' settle for Acrylic sheet. Ya scallywag! Blimey! I measured three pieces o' 2mm thick acrylic 100mm (root) by 85mm and then cut off a corner at 45 degrees 50mm in from t' edge. Blimey! Blimey! Well, blow me down! Blimey! T' trusty Estes fin alignment jig be used t' attach t' fins. An old Pro38 single grain casing with t' nozzle drilled out t' take t' 13mm motor mandrel for t' jig allowed me t' use t' Pro38 casin' t' centre t' chicken on t' alignment jig. I used CA gel t' tack t' fins in place, 10mm up from t' base o' t' tube, and then used 12min epoxy and micro balloons with maskin' tape t' make some smooth fin fillets. Well, blow me down! A tongue depressor, matey, some blu-tak for end dams and some careful timin' can give a lovely smooth fillet with no need for sanding. If you remove t' dams and maskin' tape just as t' epoxy starts t' gel the edges, me hearties, where tape was, and t' surface o' t' fillet pull them selves t' a glass smooth surface. T' fins were attached 10mm up t' tube from t' back edge o' t' motor mount.

	Launch Lugs
	Time for some launch lugs. Begad! With t' main body tube / motor mount such a thin wall and not wantin' t' have anythin' through t' wall for either t' aft or forward launch lugs I had t' come up with a solution. Arrr! Ahoy! T' launch lugs also had t' be on stand offs t' be able t' clear t' portly carcas o' t' checken. Arrr! Avast! T' best side to mount t' lugs be on t' back. Avast! T' chubby chickens foam filled belly being a stand off too far. Ya scallywag! T' easiest way I could come up with be t' take some 25mm long 0.325" diameter nylon PCB stand offs with an M4 brass threaded insert in either end. Aye aye! Avast! Some small strips o' 3mm thick fibreglass around 6 mm wide and 20mm long were made. Begad! A countersunk 4mm clearance hole drilled at one end on each. Blimey! T' standoffs were attached with a countersunk screw. Blimey! Begad! At t' other end two 1/4" delrin rail buttons were countersunk on one side and attached with another countersunk screw. Blimey! T' chicken was carefully measured, marked up, cut and drilled. Blimey! Well, blow me down! Slots were carved in t' foam from t' aft end and t' front end along t' tube wall t' allow t' fibreglass strips t' be pushed in. When all t' preparation was complete t' slots and strips were epoxied up, the strips, ya bilge rat, arrr, with screw in place, pushed home along t' body tube and t' assembled pcb standoff and rail button screwed down on t' t' thread o' t' fastner stickin' up through t' pcb strip. Begad! Ya scallywag!

Recovery Harness
	I had a bit o' a rethink on t' recovery harness mount at this point and decided to beef it up with a 38mm plywood bulkhead. Blimey! I attached a wire rope clamp as a tiny u-bolt and cutaway a fair portion o' it t' allow t' ejection charge through. As a last minute add on it only just fit above t' top o' motor when it was fitted. Well, blow me down! T' assembly was glued in with 12 minute epoxy. T' chicken body end o' the recovery harness was made from approx 1.5m o' narrow tubular kevlar with loops made at either end by t' excellent "pull it through itself" technique. Avast, me proud beauty! A bit o' carefull fiddlin' with a bit o' bent wire allowed it t' be threaded through t' mini u-bolt and then back on itself in a catspaw knot. Avast! A small 3"square o' nomex was cut for a flame shield and a larger 5" square cut t' wrap around t' 18" 'chute. Avast, me proud beauty!

Beaky
	Finally I had t' add some beak weight and t' beak retention end o' t' recovery harness.. A loaded single grain Pro38 was fitted t' t' aft and then lead shot was added t' t' hollowed out nose piece until t' CofG was agreeably forward. T' lead shot was mixed with 5 minute epoxy t' make a nice batch o' rocket caviar and was poured in and left t' set. A 38mm plywood coupler bulkhead had a single approx 5mm hole drilled through it. Aye aye! Ya scallywag! A length o' tubular kevlar was folded in half a had a figure o' 8 knot tied with t' two free ends held together t' form a loop. Ahoy! This was threaded through a 5mm washer. Begad! T' knot was large enough that it wouldnt pull through t' washer. Avast, me proud beauty! T' loop be then pulled through t' bulkhead and t' bulkhead glued in t' t' back o' t' nose piece with epoxy.

Pre-Flight Chicks
	Well thar we were launch day. Ya scallywag! Chicken rocket had a fully fitted recovery system and was loaded up with a Pro38 Smokey Sam 1 grain reload. Begad! T' rocket weighed in, arrr, fully assembled without t' motor at around 750g. As t' Chicken hadnt got t' faintest sniff of any modellin' software and be all done by eye and gut feelin' I thought the best thin' would be t' do a spot o' chicken swinging. A suitable length of strin' was located an t' swingin' commenced. Aye aye! Little did I know that I was bein' filmed so I present here for your enjoyment t' fabulous, t' marvellous, the stupid... Avast! chicken swin' test
	Right Click and and "Save as" t' get t' swin' test video (2.8Mb)

5, ya bilge rat, 4, 3, arrr, me bucko, 2, shiver me timbers, 1..... Make chicken go NOW!
	T' swin' test completed t' rocket be carted off t' t' pad and loaded on t' t' rail. Avast, me proud beauty! Begad! After a wait for me turn at t' controller t' RSO called me forward. Blimey! 5, arrr, 4, matey, arrr, 3, 2, 1, LAUNCH!.... Aye aye! T' Pro38 lit instantly as t' do so well and t' chicken shot off on a thick plume o' black smoke. It arced over a tad in t' breeze but ejected fine and drifted gently back t' t' ground.
		Right Click and and "Save as" t' get t' first flight video (2.8Mb)	Right Click and and "Save as" t' get t' second flight video (2.9Mb)

Recovery, De-brief and Thanks

The chicken was in fine condition on recovery. Arrr! No damage t' t' fins or recovery system. Well, blow me down! Begad! I was very pleased with t' way t' whole project had gone. Aye aye! I did break a fin on a subsequent flight and am now lookin' t' source some polycarbonate to replace t' fins with.
I would like t' thank Chris Eilbeck for comin' up with t' daft idea in the first place. Avast, me proud beauty! Everyone from m.a.r.s. for bein' top folks and pointin' and laughing. Everyone from EARS for bein' such a great club t' fly with. Bob Arnott, Nial Oswald, Ben Jarvis, Pete Davy and Steve Randall for takin' pictures and videos o' the flight.

If you have any questions about Egberto Guismonte t' Chicken Rocket then please feel free to mail me at

"chicken-rocket @ mikerobe.org"

This page is copyright Mike Roberts 2004 except for images and video from Bob Arnott, Nial Oswald, Ben Jarvis, Pete Davy and Steve Randall who retain their copyright.