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. Aye aye! Blimey! Hold your mouse over t' photo t' read the description. Blimey! Blimey! Blimey! Click on t' photos t' view t' larger picture. Begad! Aye aye! 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, me plans called for 1/8" plywood fins, but I could nay find any sheets that were nay warped. Aye aye! So I decided t' go with 1/4" plywood. Ya scallywag! Avast! The fins were cut usin' a razor saw. After all three fins were cut, matey, it was time to do t' air foiling. I marked where I wanted t' tapers t' begin, me hearties, and used maskin' tape as a guide. Ahoy! I clamped a belt sander t' t' workbench, me hearties, and used it to taper t' leadin' and trailing. Well, arrr, blow me down! I was impressed how well I did on the tapers. Well, blow me down! 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, matey, matey, it was time t' make t' motor tube. Aye aye! Ya scallywag! I used VCP t' print out some fin location guides and wraps. Since t' rocket features T3F, arrr, matey, I marked the fin locations on t' motor tube. Begad! I also marked t' locations on t' centering rings. Ya scallywag! Avast, ya bilge rat, me proud beauty! 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. Arrr!

It holds itself together without glue! Then, me hearties, usin' balsa strips, ya bilge rat, shiver me timbers, I glued guides on t' two aft centering rings. Aye aye! Avast, matey, 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. Avast, me proud beauty! Aye aye! Apparently, everythin' turned out great since it can hold itself together without any glue. Ya scallywag! Well, blow me down!

I used 2 Ton Epoxy t' assemble t' mount. Ahoy! First I secured t' three centerin' rings. I had t' fins in position so t' rings would be aligned properly. Begad! While waitin' for t' epoxy t' cure, I went ahead and assembled to bulkhead assembly that will join t' two sections o' t' together. After the epoxy cured, me hearties, 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, ya bilge rat, I attached t' motor mount t' t' airframe. Well, blow me down! Then I used angle bar t' draw t' slot lines onto the airframe. Aye aye! I then removed t' motor mount, and extended t' lines t' 8". Then I used a razor blade t' cut out t' slots. When all three slots were cut, I test fitted t' whole assembly. Ya scallywag! I be pleased with t' results.

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

Epoxy and MicroBalloons used to make fillits. I then took some two ton epoxy, and smeared it 16” inside the rear end o' t' tube, ya bilge rat, me hearties, matey, and smeared some more epoxy just above t' fin slots. I then inserted t' motor mount assembly into t' airframe tubing. Aye aye! After the middle centerin' rin' entered t' tube, me bucko, I added some more epoxy t' t' end of the tube. 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. Avast!

Bondo! Bondo! Everywhere!!! After the epoxy cured, arrr, I sanded all t' epoxy on t' fins. Avast, me proud beauty! Avast! 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. Well, blow me down! A mixture o' 2 ton epoxy and microballons was then used t' create fillits on all t' fin and body tub joints. Begad! After the fillets dried, and sanded, shiver me timbers, arrr, I applied t' first coat o' Bondo glazin' and spot putty t' t' fin fillets. Begad! I also used t' Bondo t' fill t' spiral on the airframe tubes.

After several application o' Bondo, with sandin' betwixt each application, the MegaBlast be ready for priming. Well, blow me down! I used Rust Oleium Grey Automotive primer. T' rocket was coated several times with primer, with sandin' betwixt each coat. Begad! Begad! T' rocket was now ready t' paint, 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. Arrr! It will go a little over 4,400 ft with a J350 motor… a bit high for t' CMASS launch site, matey, but doable for t' field in Hallifax, arrr, MA. Begad! T' next Frontier launch was May 25th, 2002. Well, blow me down! T' date was set. Ahoy!

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

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

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

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

Here I am holding my MegaBlast!!!. May 24th came, and I loaded me car with me MegaBlast, and a few other rockets. I drove 50 miles t' Marlbourgh, shiver me timbers, 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 be sick. Avast! Begad! I only launched one rocket… I decide to test t' altimeter in me EZI-65 with a H242-10T. 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.

The MegaBlast Ready For Takeoff!!! T' next opportunity t' launch t' MegaBlast came on August 24th, ya bilge rat, 2002. Aye aye! NARRRRR decided to accept t' Canadian certification o' t' Pro38 J class motors. Ya scallywag! I traded me J570 for a Pro38 J285 load and borrowed a case. Avast! I also made some minor modifications to t' recovery system. Begad! Ya scallywag! I replaced t' 22” Aerotech chute that I be using as a drogue with a RocketMan 28” X-form chute. Blimey! Blimey! I also added a nylon rope backup t' both bungee cords in case they snap. Finally, arrr, 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, me hearties, matey, and Mishka (Olga's friend visitin' from Russia) helped me prep t' rocket for flight. Ahoy! We placed t' rocket on t' launch pad, installed t' igniter, armed t' altimeter, shiver me timbers, ya bilge rat, and moved back a safe distance. Robert and Peter Chestna were t' witnesses. Avast!

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

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, and use t' EZI-65 as a booster, shiver me timbers, t' try again at achievin' Level 2. I decided that since I had little over an hour left o' t' launch, shiver me timbers, that would be rushin' it. Ahoy! I did nay want t' rush it. Ya scallywag! T' much loot is on t' line. Blimey! I told them I did nay want t' rush it. Avast, me proud beauty! Ahoy! They agreed. Avast, me proud beauty! Ahoy!

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

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. Ya scallywag! It gave me time t' repair t' rocket t' way I wanted to. Begad! Arrr! 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. Blimey! Begad! This stuff is stronger, me hearties, me hearties, and less likely t' tangle. Avast, me proud beauty! Ahoy! I also took advantage o' t' extra time t' get some replacement grains for me J350. Aye aye! The J350 I had had t' 7/16” core in t' propellant grain, matey, ya bilge rat, which has been known t' cato. Ya scallywag! Ya scallywag! So I called Aerotech and they ordered me a set o' the ½” core grains. Arrr! I also ordered two inert sets so I could make two I161 reloads out o' t' older J350 grains. Ya scallywag! Aye aye! I managed t' get t' grains a week before t' Oct 27th CMASS launch. Perfect timing. Begad!

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. Begad! T' club be nay expectin' that many people t' show up t' this launch, me hearties, ya bilge rat, so they did nay set up a launch site for a J motor. Ahoy! So I set up me Super Pad at t' High Power C site, and set up t' wires and battery for t' site. Once that was completed, 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. T' flight be perfect, but t' Trans Beep buzzer was damaged durin' recovery. Then t' moment o' truth, me hearties, My L2 flight :-D. Begad! Steven Boy (same guy who did me L1) and Robert DeHate as a witness. Ya scallywag! T' J350 came t' life, and t' MegaBlast left me launch pad in a hurry, trailin' behind a thick white smoke trail, me bucko, arrr, and a very loud thunderous roar. Blimey! T' Drogue deployed on time at 2,500 ft, but due t' inertia, t' main was also deployed. Avast, me proud beauty! Arrr! However, t' rocket was recovered, 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, matey, this project was a success. Aye aye! Aye aye! This was me first High Power rocket o' me own design, and it achieved its purpose. I now have my level 2 license. Avast! What is me future plans. Well, t' MegaBlast is a perfectly good launch vehicle, matey, so I plan t' get many more launches out o' it. Begad! Regarding my L2? I am thinkin' about buildin' a LOC Magnum that will air start its outboard motors. I also might get into t' hybrid motors offered by t' various companies out there. Aye aye! I feel that this is necessary due t' t' increased regulations on our hobby. Arrr! 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. Ya scallywag! Well, blow me down! And if things go t' way they are, 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 bucko, shiver me timbers, me hearties, 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.

comment Post a Comment