Scratch Mega Blast Original Design / Scratch Built

Scratch - Mega Blast {Scratch}

Contributed by Douglas Gardei

Manufacturer: Scratch
(Contributed - by Douglas Gardei)

Rocket Pic

T' MegaBlast is me first High Power rocket o' me own design. This is the "journal" o' its construction. Hold your mouse over t' photo t' read the description. Avast! Blimey! Blimey! Blimey! Click on t' photos t' view t' larger picture. Arrr! Blimey! Avast, shiver me timbers, me proud beauty! Blimey! Blimey! Blimey!

Side View of Fins.Top View of Fins. T' MegaBlast is constructed out o' LOC 4" tubing, and uses a single 38mm H motor. Original, shiver me timbers, me plans called for 1/8" plywood fins, me hearties, but I could nay find any sheets that were nay warped. Well, blow me down! So I decided t' go with 1/4" plywood. Begad! The fins were cut usin' a razor saw. Avast! After all three fins were cut, matey, arrr, it was time to do t' air foiling. I marked where I wanted t' tapers t' begin, and used maskin' tape as a guide. Begad! Well, blow me down! I clamped a belt sander t' t' workbench, me hearties, and used it to taper t' leadin' and trailing. Well, blow me down! I was impressed how well I did on the tapers. Begad! I guess buildin' t' THOY Phoenix a couple years ago gave me a lot of practice.

All the parts. Once the fins were done, me hearties, it was time t' make t' motor tube. I used VCP t' print out some fin location guides and wraps. Since t' rocket features T3F, I marked the fin locations on t' motor tube. Aye aye! I also marked t' locations on t' centering rings. Avast! I drilled holes in t' aft centerin' rin' for t' motor retention bolts, and a hole in t' forward centerin' rin' for t' shock cord anchor.

It holds itself together without glue! Then, usin' balsa strips, I glued guides on t' two aft centering rings. Avast, me proud beauty! T' purpose o' these guides is t' ensure t' alignment o' t' fins, and to help hold them in place as t' epoxy cures. Ya scallywag! Apparently, everythin' turned out great since it can hold itself together without any glue. Ya scallywag!

I used 2 Ton Epoxy t' assemble t' mount. Well, blow me down! Blimey! First I secured t' three centerin' rings. Aye aye! I had t' fins in position so t' rings would be aligned properly. Begad! While waitin' for t' epoxy t' cure, matey, me hearties, I went ahead and assembled to bulkhead assembly that will join t' two sections o' t' together. Avast, me proud beauty! Begad! After the epoxy cured, I epoxied t' fins into their proper position

The booster airframe is slotted.Here I am holding my MegaBlast!!! After all t' epoxy be cured, arrr, I attached t' motor mount t' t' airframe. Begad! Then I used angle bar t' draw t' slot lines onto the airframe. I then removed t' motor mount, me bucko, and extended t' lines t' 8". Then I used a razor blade t' cut out t' slots. Aye aye! When all three slots were cut, I test fitted t' whole assembly. Ahoy! I was pleased with t' results. Begad! Begad!

The finished fin cam and motor mount. I then took t' whole assembly apart and concentrated on finishing the motor mount. Avast! I took some 100 grit sandpaper and roughed up t' motor tube/fin tab joint. Arrr! Ahoy! I then cut out some fiberglass strips and epoxied them to the joint. Avast, me proud beauty! While lettin' t' undercoatin' o' epoxy t' soak in, matey, I applied epoxy fillits t' all remainin' joints, and installed t' shock cord anchor. Arrr! Epoxy was used t' set t' nuts on t' eye-bolt. Blimey! Avast! T' fiberglass was then coated with another layer o' epoxy. When t' epoxy was cured, ya bilge rat, I used trimmed away any "hairs" that was stickin' out from t' fiberglass. Aye aye! Then I attached a piece o' tubular nylon t' t' shock cord anchor. Begad! Begad! T' motor mount/fin unit is now finished. Well, shiver me timbers, blow me down!

Epoxy and MicroBalloons used to make fillits. I then took some two ton epoxy, shiver me timbers, and smeared it 16” inside the rear end o' t' tube, and smeared some more epoxy just above t' fin slots. Aye aye! I then inserted t' motor mount assembly into t' airframe tubing. Avast! After the middle centerin' rin' entered t' tube, me bucko, I added some more epoxy t' t' end of the tube. Well, blow me down! Then I slid t' motor mount all t' way into t' airframe. Arrr! I then used t' remainin' epoxy t' saturate t' leadin' and trailin' edges o' t' fins to make them less prone t' denting. Arrr! Arrr!

Bondo! Bondo! Everywhere!!! After the epoxy cured, I sanded all t' epoxy on t' fins. Avast, me proud beauty! I then used tissue paper and a pointed pencil t' fill any gaps betwixt t' tapers o' t' fins, me bucko, and the square ness o' t' fin slots. Blimey! A mixture o' 2 ton epoxy and microballons was then used t' create fillits on all t' fin and body tub joints. After the fillets dried, and sanded, I applied t' first coat o' Bondo glazin' and spot putty t' t' fin fillets. Blimey! Avast! I also used t' Bondo t' fill t' spiral on the airframe tubes. Aye aye!

After several application o' Bondo, me bucko, matey, with sandin' betwixt each application, the MegaBlast was ready for priming. Ya scallywag! I used Rust Oleium Grey Automotive primer. T' rocket was coated several times with primer, with sandin' betwixt each coat. Ya scallywag! T' rocket be now ready t' paint, me bucko, shiver me timbers, shiver me timbers, but what colors should I paint it?

At this time, I began t' think about usin' this rocket t' obtain me Level 2 certification flight. Ahoy! I passed t' written exam at a recent CMASS meeting, and the MegaBlast would make an ideal vehicle t' fly on a 38mm J motor. It will go a little over 4,400 ft with a J350 motor… a bit high for t' CMASS launch site, shiver me timbers, but doable for t' field in Hallifax, MA. T' next Frontier launch was May 25th, me hearties, 2002. T' date was set.

I posted an e-mail on t' CMASS mailin' list, ya bilge rat, askin' if anybody had any J350’s that they can sell me for me L2 flight. Nobody responded about the J350, me bucko, matey, ya bilge rat, but Tony Brock-Fisher replied that he had a J570 load, and asked if I could use that. I loaded up me RockSim file again, selected t' J570, “launched” t' rocket on t' computer… and t' software predicted that t' rocket would go over 5,650 feet… OVER A MILE!!!! I accepted t' motor offer. I then gave a call t' Magnum and ordered a Transolve PK Altimeter kit, matey, a new tube coupler, shiver me timbers, a 45” parachute, matey, and a couple bulkheads. Ahoy! I also went t' a local hardware store and bought some threaded rods, bolts, nuts, and other various hardware. Well, blow me down! It was time t' build me first rocket that uses Dual Deployment. Ahoy!

The Altimeter module. Fortunately, shiver me timbers, HobbyTown USA in Plaistow NH offered t' sponsor me L2 project, ya bilge rat, so some o' me expenses be covered. Avast, me proud beauty! Blimey! Avast, ya bilge rat, me proud beauty! Blimey! Now I have a paint scheme t' color me rocket with… t' HobbyTown colors :-). Begad! Blimey! Aye aye! Blimey! I painted t' body o' t' rocket white, the nose cone blue, and t' fins red. I used black vynal letterin' t' mark the name on t' rocket, and I used a HobbyTown decal t' advertise t' sponsor. Well, matey, blow me down! Blimey! Now I must admit that I am a beginner at usin' electronics in rockets… I have no experience mountin' electronics in t' rocket, and this be t' first time I used Dual Deployment. Avast! Blimey! I decided that I wanted t' altimeter t' go in an enclosed central modual that can be interchanged easily betwixt 4” diameter rockets. Begad! Blimey! Well, blow me down! Blimey! Both recovery systems will attach t' t' module, so strength is important. Ahoy! Blimey! Avast! Blimey! So I built an assembly that consisted o' three threaded rods connectin' two plywood bulkheads. Aye aye! Blimey! T' rods will support t' stresses o' both recovery systems. Begad! Blimey! Avast, ya bilge rat, me proud beauty! Blimey! T' assembly then slides into a tube coupler, where it is fastened down with four screws. Begad! Blimey! Arrr! Blimey! I be concerned that t' wood used for the bulkheads be on t' thin side, ya bilge rat, but I decided that it be good enough. Blimey! Blimey! Avast, me proud beauty! Blimey!

The Loaded MegaBlast balanced for a stable flight. Once t' altimeter module was built, it was time to balance t' rocket. Ya scallywag! I put t' rocket together like I be goin' t' fly it. Blimey! Blimey! I loaded t' recovery system, and installed t' loaded J570 motor. Aye aye! I hung the rocket on t' ceiling, and started addin' weight t' t' nose cone until the center o' gravity was where I wanted it t' be. Begad! Ahoy! I ended up installin' almost a pound o' clay into t' nosecone, but t' rocket be now balanced. Arrr! It now weighed close t' 6 pounds empty, a little on t' heavy side for a H. Aye aye!

The flight profile of my MegaBlast with a J570. T' flight profile o' t' MegaBlast with a J570 is as follows. Arrr! Begad! At ignition, t' rocket will accelerate off t' launch pad quickly. Arrr! At 300 feet, ya bilge rat, t' altimeter will start keepin' track o' t' current altitude and engage a 5 second timer. Begad! Aye aye! This is called t' mach inhibiter, ya bilge rat, arrr, and it prevents the sudden increase in pressure o' t' shock wave caused by a object breakin' the speed o' sound from foolin' t' sensor t' fire t' parachute charges. Avast! Begad! This rocket is subsonic, me hearties, so this feature is nay mandatory. After 5 seconds of flight, t' mach inhibitor is turned off, and both charges are armed. When the rocket reaches apogee (over 1 mile with t' J570), t' altimeter will deploy the drogue chute. Ya scallywag! T' drogue chute allows t' rocket t' freefall in a controlled manner. Avast, me proud beauty! When 600 ft is obtained, t' altimeter will fire t' last charge t' deploy t' main chute.

Here I am holding my MegaBlast!!!. May 24th came, ya bilge rat, arrr, and I loaded me car with me MegaBlast, shiver me timbers, and a few other rockets. I drove 50 miles t' Marlbourgh, arrr, where I spent t' night at a friends house. The next morning, shiver me timbers, we traveled t' additional 50 miles t' t' Frontier field in Hallifax… but I be sick. I only launched one rocket… I decide to test t' altimeter in me EZI-65 with a H242-10T. Avast! By t' time I got t' rocket back after me first, me bucko, and successful two stage recovery, I be too sick t' fly any more rockets. Begad!

The MegaBlast Ready For Takeoff!!! T' next opportunity t' launch t' MegaBlast came on August 24th, 2002. Well, blow me down! NARRRRR decided to accept t' Canadian certification o' t' Pro38 J class motors. Ya scallywag! Blimey! I traded me J570 for a Pro38 J285 load and borrowed a case. Avast! Arrr! Blimey! I also made some minor modifications to t' recovery system. Arrr! I replaced t' 22” Aerotech chute that I was using as a drogue with a RocketMan 28” X-form chute. Well, blow me down! Ya scallywag! Blimey! I also added a nylon rope backup t' both bungee cords in case they snap. Begad! Blimey! Finally, shiver me timbers, I bought a $25 Transolve Trans Beep sonic beacon from Magnum t' aid in trackin' and recovery. T' new altitude estimate for t' MegaBlast with t' Pro38 J285 is 3,800 - 4,200 feet.

Robert DeHate, Olga Glotova, and Mishka (Olga's friend visitin' from Russia) helped me prep t' rocket for flight. Well, blow me down! We placed t' rocket on t' launch pad, installed t' igniter, armed t' altimeter, ya bilge rat, and moved back a safe distance. Robert and Peter Chestna were t' witnesses. Blimey!

5 …. Begad! Avast! 4 …. Begad! 3 ….. 2 ….. Begad! 1 ….. KAPLUNK!!!!

The brief fireball of the Pro38 J285 just as it cato's.Robert DeHate, Olga Glotova, and I looking over damaged rocket. T' Pro38 motor detonated. Well, blow me down! T' casin' o' t' motor shot into t' drogue compartment, arrr, wedgin' t' recovery system into a tangled mess inside t' tube, causin' major damage t' t' airframe, me hearties, and completely destroyin' t' Trans Beep buzzer. Ahoy! T' altimeter bay assembly was ripped from the tube coupler, ya bilge rat, which confirmed some fears that t' thin centerin' rings and tube coupler would nay hold. Blimey! T' catoin' motor also destroyed t' motor retention system, damaged t' motor tube, me bucko, and blew apart t' aft centering ring.

I discover that my Trans Beep has been destroyed. This side has major damage to the airframe of the rocket.
Major Damage to the MegaBlast Decal. The motor retention system took out piece of the motor mount when the Pro38 blew.

Bob Krech and Robert DeHate suggested that we repair the altimeter bay, matey, me bucko, and use t' EZI-65 as a booster, matey, t' try again at achievin' Level 2. I decided that since I had little over an hour left o' t' launch, that would be rushin' it. Arrr! I did nay want t' rush it. Well, blow me down! Aye aye! T' much loot is on t' line. Blimey! Ahoy! I told them I did nay want t' rush it. Well, shiver me timbers, blow me down! They agreed. Avast! Begad!

The damaged section of the motor tube is repaired with fiberglass.The glass is finished with a layer of Bondo. Robert DeHate offered t' fix t' booster for me, me hearties, and he gave me a J350 reload to replace t' blown J285. Well, blow me down! He coated t' damaged section o' t' body tube with fiberglass, me hearties, and use Keelhaul®©™® to repair t' motor tube. I sent t' Trans Beep back t' Magnum for repairs, and ordered a LOC 4” Electronics bay. Begad! Blimey! T' solve a concern that t' shockcord anchor on t' nosecone was nay strong enough, I took a pice o' tubular nylon, ran it through t' cone, tid several knots in it, rammed t' end o' t' nylon into t' clay, then filled t' cone with expandin' foam. There is no way this shock cord anchor is goin' t' fail. Aye aye! Blimey! I be hopin' that t' MegaBlast would be ready t' launch again for t' September 14th launch. Ahoy! Blimey! Blimey! Blimey! However, shiver me timbers, arrr, t' order from Magnum did nay arrive till t' 16th, ya bilge rat, me hearties, which was t' Monday after t' launch. Begad! Blimey! Blimey! Blimey!

The new Electronics bay used to house my altimeter.The recovery profile of my Megablast rocket. Missin' t' 14th launch probably worked out for t' better anyway. It gave me time t' repair t' rocket t' way I wanted to. Aye aye! I built t' LOC electronics bay and added some bevels so t' bolts have somethin' t' screw into besides paper. I also replaced t' nylon rope that I used t' back up t' bungee cord with tubular nylon. Begad! This stuff is stronger, shiver me timbers, and less likely t' tangle. Begad! I also took advantage o' t' extra time t' get some replacement grains for me J350. Well, blow me down! The J350 I had had t' 7/16” core in t' propellant grain, which has been known t' cato. Arrr! Avast! So I called Aerotech and they ordered me a set o' the ½” core grains. Avast! Arrr! I also ordered two inert sets so I could make two I161 reloads out o' t' older J350 grains. Ya scallywag! I managed t' get t' grains a week before t' Oct 27th CMASS launch. Perfect timing. Arrr!

I am loading the J350 motor for my MegaBlast.My MegaBlast on the pad ready for launch. The weather on t' October 27th was perfect. T' club was nay expectin' that many people t' show up t' this launch, shiver me timbers, shiver me timbers, so they did nay set up a launch site for a J motor. Arrr! So I set up me Super Pad at t' High Power C site, and set up t' wires and battery for t' site. Arrr! Ahoy! Once that be completed, shiver me timbers, I launched me Electronics bay on me EZI-65 rocket with an I161-14 motor t' test out t' altimeter, shiver me timbers, which reported 1,500 ft. Avast! Ahoy! T' flight be perfect, but t' Trans Beep buzzer was damaged durin' recovery. Well, blow me down! Then t' moment o' truth, My L2 flight :-D. Blimey! Steven Boy (same guy who did me L1) and Robert DeHate as a witness. Begad! Begad! T' J350 came t' life, and t' MegaBlast left me launch pad in a hurry, trailin' behind a thick white smoke trail, and a very loud thunderous roar. Avast! T' Drogue deployed on time at 2,500 ft, but due t' inertia, t' main was also deployed. Well, blow me down! However, me hearties, t' rocket was recovered, me hearties, arrr, arrr, and I passed me Level 2 Cert flight!

My MegaBlast on its way with a J350 motor.Steven Boy shakes my hand after signing off my successful L2 flight. Overall, ya bilge rat, shiver me timbers, this project was a success. Begad! This be me first High Power rocket o' me own design, and it achieved its purpose. Well, blow me down! I now have my level 2 license. Ya scallywag! Avast! What is me future plans. Ahoy! Well, ya bilge rat, me hearties, t' MegaBlast is a perfectly good launch vehicle, me bucko, matey, me bucko, so I plan t' get many more launches out o' it. Regarding my L2? I am thinkin' about buildin' a LOC Magnum that will air start its outboard motors. Begad! I also might get into t' hybrid motors offered by t' various companies out there. Ya scallywag! I feel that this is necessary due t' t' increased regulations on our hobby. When I get me Level 3, I may have t' use a hybrid, since it may be a long time before I can get t' unnecessary LEUP t' store those larger motors. And if things go t' way they are, ya bilge rat, maybe even for the stuff I currently use… but that is another story…. Well, blow me down!

T' MegaBlast Project Is Dedicated to:
Olga Glotova – For bein' a friend, me hearties, an inspiration, me bucko, someone to talk to.
Robert DeHate – Your support, advice and effort is so much appreciated.
Frank D'Aloisio – Thanks for your support and financial contribution.
Ryan Sebastian and Family – For helpin' me out at t' launches.
Bob Krech – For supportin' me crazy ideas.
William Gardei – For talkin' me out o' me crazy ideas.

comment Post a Comment