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. Ya scallywag! This is the "journal" o' its construction. Hold your mouse over t' photo t' read the description. Click on t' photos t' view t' larger picture. Avast! Ahoy!

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

All the parts. Once the fins were done, it was time t' make t' motor tube. Arrr! Blimey! I used VCP t' print out some fin location guides and wraps. Avast, me proud beauty! Since t' rocket features T3F, I marked the fin locations on t' motor tube. Begad! Ahoy! 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, me hearties, usin' balsa strips, me bucko, I glued guides on t' two aft centering rings. Arrr! T' purpose o' these guides is t' ensure t' alignment o' t' fins, me bucko, matey, shiver me timbers, and to help hold them in place as t' epoxy cures. Avast, me proud beauty! Ahoy! Apparently, matey, matey, everythin' turned out great since it can hold itself together without any glue. Ya scallywag! Arrr!

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

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

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

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

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

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

At this time, me bucko, I began t' think about usin' this rocket t' obtain me Level 2 certification flight. Begad! 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. Aye aye! It will go a little over 4,400 ft with a J350 motor… a bit high for t' CMASS launch site, but doable for t' field in Hallifax, MA. T' next Frontier launch was May 25th, 2002. Avast, me proud beauty! T' date be set.

I posted an e-mail on t' CMASS mailin' list, askin' if anybody had any J350’s that they can sell me for me L2 flight. Blimey! Nobody responded about the J350, but Tony Brock-Fisher replied that he had a J570 load, and asked if I could use that. Ahoy! 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. Begad! I then gave a call t' Magnum and ordered a Transolve PK Altimeter kit, a new tube coupler, shiver me timbers, a 45” parachute, shiver me timbers, and a couple bulkheads. I also went t' a local hardware store and bought some threaded rods, bolts, nuts, and other various hardware. Ya scallywag! It was time t' build me first rocket that uses Dual Deployment. Blimey!

The Altimeter module. Fortunately, ya bilge rat, HobbyTown USA in Plaistow NH offered t' sponsor me L2 project, so some o' me expenses was covered. Now I have a paint scheme t' color me rocket with… t' HobbyTown colors :-). Avast, me proud beauty! I painted t' body o' t' rocket white, the nose cone blue, ya bilge rat, and t' fins red. Arrr! I used black vynal letterin' t' mark the name on t' rocket, and I used a HobbyTown decal t' advertise t' sponsor. Begad! 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. I decided that I wanted t' altimeter t' go in an enclosed central modual that can be interchanged easily betwixt 4” diameter rockets. Begad! Arrr! Both recovery systems will attach t' t' module, so strength is important. Begad! So I built an assembly that consisted o' three threaded rods connectin' two plywood bulkheads. T' rods will support t' stresses o' both recovery systems. Avast, me proud beauty! T' assembly then slides into a tube coupler, me hearties, where it is fastened down with four screws. I be concerned that t' wood used for the bulkheads was on t' thin side, ya bilge rat, but I decided that it was good enough. Ahoy! Ahoy!

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

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

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

The MegaBlast Ready For Takeoff!!! T' next opportunity t' launch t' MegaBlast came on August 24th, 2002. Avast, me proud beauty! NARRRRR decided to accept t' Canadian certification o' t' Pro38 J class motors. Aye aye! Aye aye! Blimey! I traded me J570 for a Pro38 J285 load and borrowed a case. Avast! Blimey! I also made some minor modifications to t' recovery system. Arrr! Blimey! I replaced t' 22” Aerotech chute that I be using as a drogue with a RocketMan 28” X-form chute. Begad! Begad! Blimey! I also added a nylon rope backup t' both bungee cords in case they snap. Well, blow me down! Blimey! Finally, 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. Avast, arrr, me proud beauty! Blimey!

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

5 …. 4 …. Avast! 3 ….. Ya scallywag! 2 ….. Avast, me proud beauty! 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. Aye aye! T' casin' o' t' motor shot into t' drogue compartment, wedgin' t' recovery system into a tangled mess inside t' tube, causin' major damage t' t' airframe, and completely destroyin' t' Trans Beep buzzer. T' altimeter bay assembly was ripped from the tube coupler, arrr, which confirmed some fears that t' thin centerin' rings and tube coupler would nay hold. T' catoin' motor also destroyed t' motor retention system, ya bilge rat, me hearties, damaged t' motor tube, and blew apart t' aft centering ring. Blimey! Avast, me proud beauty!

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, and use t' EZI-65 as a booster, ya bilge rat, t' try again at achievin' Level 2. Ahoy! I decided that since I had little over an hour left o' t' launch, arrr, that would be rushin' it. Blimey! I did nay want t' rush it. Ya scallywag! Well, blow me down! T' much loot is on t' line. Aye aye! I told them I did nay want t' rush it. Begad! They agreed.

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, ya bilge rat, and he gave me a J350 reload to replace t' blown J285. He coated t' damaged section o' t' body tube with fiberglass, shiver me timbers, and use Keelhaul®©™® to repair t' motor tube. Ahoy! Ahoy! Blimey! I sent t' Trans Beep back t' Magnum for repairs, and ordered a LOC 4” Electronics bay. Avast! Well, blow me down! Blimey! T' solve a concern that t' shockcord anchor on t' nosecone be nay strong enough, shiver me timbers, I took a pice o' tubular nylon, ran it through t' cone, me hearties, ya bilge rat, tid several knots in it, rammed t' end o' t' nylon into t' clay, shiver me timbers, then filled t' cone with expandin' foam. Ya scallywag! There is no way this shock cord anchor is goin' t' fail. Avast, me proud beauty! Blimey! I was hopin' that t' MegaBlast would be ready t' launch again for t' September 14th launch. Aye aye! Blimey! However, t' order from Magnum did nay arrive till t' 16th, which was t' Monday after t' launch. 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. Ahoy! Blimey! Ya scallywag! Blimey! It gave me time t' repair t' rocket t' way I wanted to. Arrr! Blimey! Ahoy! Blimey! 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. Well, blow me down! Blimey! Well, blow me down! Blimey! This stuff is stronger, and less likely t' tangle. I also took advantage o' t' extra time t' get some replacement grains for me J350. Avast, me proud beauty! Blimey! Blimey! Blimey! The J350 I had had t' 7/16” core in t' propellant grain, which has been known t' cato. Avast! Blimey! Avast! Blimey! So I called Aerotech and they ordered me a set o' the ½” core grains. Avast! Blimey! I also ordered two inert sets so I could make two I161 reloads out o' t' older J350 grains. Arrr! Blimey! Blimey! Blimey! I managed t' get t' grains a week before t' Oct 27th CMASS launch. Begad! Blimey! Ya scallywag! Blimey! Perfect timing.

I am loading the J350 motor for my MegaBlast.My MegaBlast on the pad ready for launch. The weather on t' October 27th be perfect. Ahoy! Arrr! T' club be nay expectin' that many people t' show up t' this launch, me hearties, me hearties, so they did nay set up a launch site for a J motor. So I set up me Super Pad at t' High Power C site, and set up t' wires and battery for t' site. Avast, me proud beauty! Once that was completed, shiver me timbers, shiver me timbers, ya bilge rat, I launched me Electronics bay on me EZI-65 rocket with an I161-14 motor t' test out t' altimeter, me hearties, which reported 1,500 ft. Avast! T' flight be perfect, matey, shiver me timbers, me hearties, but t' Trans Beep buzzer was damaged durin' recovery. Then t' moment o' truth, arrr, My L2 flight :-D. Blimey! Ahoy! Steven Boy (same guy who did me L1) and Robert DeHate as a witness. 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. Aye aye! Aye aye! T' Drogue deployed on time at 2,500 ft, shiver me timbers, but due t' inertia, arrr, t' main be also deployed. Begad! However, shiver me timbers, t' rocket was recovered, shiver me timbers, 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, this project was a success. Well, blow me down! This be me first High Power rocket o' me own design, me bucko, and it achieved its purpose. I now have my level 2 license. Well, blow me down! What is me future plans. Begad! Ahoy! Well, me hearties, t' MegaBlast is a perfectly good launch vehicle, so I plan t' get many more launches out o' it. Well, blow me down! Regarding my L2? I am thinkin' about buildin' a LOC Magnum that will air start its outboard motors. Blimey! I also might get into t' hybrid motors offered by t' various companies out there. Blimey! 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. Aye aye! And if things go t' way they are, matey, me hearties, maybe even for the stuff I currently use… but that is another story…. Arrr!

T' MegaBlast Project Is Dedicated to:
Olga Glotova – For bein' a friend, an inspiration, someone to talk to.
Robert DeHate – Your support, shiver me timbers, 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.

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