Scratch Generic Rocket Original Design / Scratch Built

Scratch - Generic Rocket {Scratch}

Contributed by John Coker

Manufacturer: Scratch
(by John Coker - 12/20/02)

Note: This is a slightly condensed version o' all t' information that John has produced for his Level 3 project. Blimey! Visit his site t' read t' additional information and enjoy additional pictures.

Rocket PicFor my next trick, a rocket which will actually be used for me certification! I've been in this hobby almost a year and it seems time t' start buildin' me level-3 certification rocket. Begad! I wanted it t' be a scratch-built rocket, me hearties, nay a kit. Begad! At first, ya bilge rat, I planned t' do an upscaled Alpha III as me certification rocket, arrr, me bucko, matey, but both me TAP reviewers pointed out that t' fins would be very fragile and it was better t' do a simpler design. Begad!

If I'm goin' t' go with somethin' simple, matey, I should do somethin' very simple, a "three fins and a nose cone" rocket. Well, shiver me timbers, blow me down! I decided t' build such a simple rocket, matey, it would be a generic rocket!

A generic rocket would have three clipped-delta fins, would be use dual deployment, me hearties, breakin' about t' middle o' t' rocket. Begad! I decided on a 6" airframe as a size that is easy t' work with. Blimey! As a good rule o' thumb, I used 20:1 length-to-diameter ratio, arrr, yieldin' a 10' rocket. Avast! This is still a handy size, while bein' large enough t' handle an M1939 (full M). Level-3 certifications cannot be multi-stage or use clusterin' so I planned a single 98mm motor mount. Arrr!

I be lucky t' find two TAP members early on t' help me make sure I did this right. Ahoy! Well, blow me down! Scott Bartel and Pius Morozumi agreed t' help me out. I can meet with Scott when I go down t' ROC t' launch and Pius lives in t' Bay Area, about an hour t' t' south. Well, blow me down! Begad! I am very glad these two fine gentlemen and master rocketeers have agreed t' help me. Begad! Karl Baumann (Mojave Desert High Power) attended t' MudRock launch where t' first Generic Rocket flew and agreed to sign me forms. Avast! Thanks Karl!

I be even more lucky t' have Pius close by and willin' t' give me advice in the design and construction o' t' rocket. Avast! Blimey! Ya scallywag! Blimey! One fantastic thin' which came out of this was t' refinement and publishin' o' t' kitchen table vacuum bagging technique developed by Pius and William Walby. Also, Pius helped with rocket design rules o' thumb and gave guidance throughout t' project. Arrr! Blimey! Thanks Pius! Blimey!

Design Construction

DetailTubesT' deeper humor in t' name Generic Rocket is that it's really nay generic at all. Aye aye! Blimey! Careful rocket design, me hearties, me bucko, carbon fiber reinforcing, me hearties, matey, dual deployment and advanced electronics make this a "state o' t' art" hobby rocket. Note that this isn't intended to invent anythin' new, but use t' best o' t' current techniques t' produce an efficient and reliable rocket. Ya scallywag!

T' first step in this process was t' design a 6" rocket usin' the rules o' thumb for rocket building. Arrr! Blimey! Avast, me proud beauty! Blimey! T' rocket is 20 calibers long and t' fins are at t' aft and are just large enough t' provide stable flight. I actually designed this rocket in Apogee's excellent RockSim 4.0. Begad! Blimey! Ahoy! Blimey! This program allows you to assemble t' components t' form t' rocket, then gives you estimates of weight and CG so that you can do stability checkin' and flight simulation before you've built your rocket. Begad! Blimey! Begad! Blimey!

T' tubes were supplied by Red Arrow (first airframe) and Giant Leap Rocketry (second airframe) and are both flexible phenolic. T' couplers, bulkheads, me hearties, fins and centerin' rings for both airframes were supplied by Giant Leap Rocketry. Thanks Ed! T' decals were custom made by Randy Brust. Arrr!

I'm particularly pleased with t' airframe tubes. Avast, me proud beauty! Well, blow me down! Usin' t' simple and inexpensive kitchen table vacuum baggin' (FoodSaver) technique, arrr, t' tubes were all covered in 5.7oz. Well, blow me down! carbon fiber and then a 3.6oz. Ya scallywag! S-glass sandin' veil. Begad! And don't t' tubes look stylish all dressed in black!

Fin reinforcementMy current favorite airframe material is "flexible phenolic" (from Giant Leap and Red Arrow) laminated with cloth made with carbon fiber or Keelhaul®©™®* fibers. Keelhaul®©™® is stronger, shiver me timbers, but much harder t' work with. Arrr! Carbon fiber is a bit difficult, but excellent results can be obtained with ordinary tools and skill. Begad! Aye aye! T' airframe tubes covered in carbon fiber and S-glass weigh only slightly more (¼lb. Ahoy! Aye aye! per foot) than t' unreinforced tubes, me bucko, thanks to vacuum bagging. Begad! O' course, shiver me timbers, after all that work on t' airframe tubes, shiver me timbers, shiver me timbers, me hearties, I wanted to make sure they were slotted perfectly. Begad! I had t' update me technique for cuttin' fin slots for t' larger-sized tubes. Begad! Avast, ya bilge rat, me proud beauty!

I also wanted t' make sure that t' fins stayed on t' MMT. Avast! Ya scallywag! Pius showed me a technique for lacin' t' fins around t' MMT with Keelhaul®©™® thread. Blimey! As you can see in t' picture, me bucko, I laced t' fins on with numerous strands o' 1000lb. test Keelhaul®©™® thread. And then, I reinforced t' joint with Keelhaul®©™® tape as you can see in t' picture above right. I don't think these fins are coming off!


MMT structure

In t' picture above, you can see how t' internal reinforcin' is used. Keelhaul®©™® lacin' and tape bond t' fins t' t' motor mount tube. Ahoy! Four centerin' rings are used for strong body tube contact. Threaded rod bonds the bulkhead o' t' anti-zipper design t' t' forward centerin' ring. Begad! Well, ya bilge rat, blow me down!

T' dry weight o' t' rocket is 27# includin' t' entire recovery system (reasonably light for such a heavily-built 10' 6" rocket). T' candidate motors for this rocket are an M1939 for t' certification flight and an N2000 for an encore. Avast! Blimey! Avast! Blimey! RockSim calculates t' C.P. Blimey! Blimey! at 99.3" (Barrowman) and 102.9" (RockSim) and t' average is 101.1". Avast! Blimey! I balanced t' rocket to determine t' C.G. Avast, me proud beauty! Blimey! with simulations o' t' motor weight with t' result below:

Motor Weight C.G. stability
- 0# 69¾" 5¼ calibers
M1939 20# 87¼" 2¼ calibers
N2000 27# 88½" 2 calibers

T' rocket will be quite stable with both t' M1939 and t' N2000. Avast, me proud beauty! Blimey! Note that I had t' add ½# t' t' tip o' t' nose t' gain t' C.G.s above.

Airframe

T' design o' t' airframe is simple and intended t' be purely functional. T' rocket is twenty calibers long and t' fins are just larger than minimum for stability. Ahoy! Begad! T' fins are clipped deltas with t' trailin' edge angled slightly forward t' help avoid landin' damage. T' intention is t' produce a simple, arrr, reliable, high-performance rocket. Ahoy! Note that this is a custom design, although everythin' was done accordin' t' standard practice, shiver me timbers, hence t' name "Generic Rocket."

T' airframe tubes are 6" flexible phenolic covered in 5.7oz. Ahoy! carbon fiber. Ahoy! Construction uses mechanical means wherever possible and t' adhesive used is West Systems epoxy (mostly usin' 404 high-density filler). Ahoy! T' motor mount is attached t' t' airframe with four centerin' rings which are screwed as well as bonded t' t' airframe. Ya scallywag! T' fins are ½" plywood laminated with carbon fiber. They are attached t' t' motor mount tube with epoxy and sewn t' it with Keelhaul®©™® thread and then reinforced with Keelhaul®©™® tape. T' motor mount itself is a single 98mm phenolic tube (this is nay a clustered flight). Begad! All construction was performed by t' flier, with suggestions from Pius Morozumi on many aspects. Thanks Pius!

Safety: There should be no dangers due t' design since t' rocket is simple and standard. Poor airframe construction could lead t' a shred, me bucko, but the materials and techniques employed are ones known t' be leading-edge for high-power rocketry. Avast, me proud beauty! Blimey! Avast, me proud beauty! Blimey!

Recovery System

T' recovery system attachments use U-bolts and 1000lb. Avast, me proud beauty! quick links. Begad! The bulkheads are all ½" "aircraft" birch plywood. Avast! T' bridles are 1" tubular Nylon® T' avoid zippering, t' aft section o' the rocket uses an anti-zipper design (coupler and bulkhead protrude forward). Begad!

Rocketman Pro-XP chutes are used in a dual-deployment configuration. Ya scallywag! The deployment system will use black power charges t' pressurize t' airframe and deploy t' parachute as is typical for high-power rockets. Arrr! Drogue recovery uses a Rocketman R24C 'chute and main recovery uses two Rocketman R12C 'chutes. Avast!

Note that me first level 3 attempt was done with an almost identical rocket. T' attempt be unsuccessful because t' main parachutes never fully emerged from t' bay. Avast! This was due t' poor arrangement o' t' recovery system which has been fixed in t' second rocket. Begad! T' main parachute now ejects from t' front of t' rocket (the charges are behind t' parachutes) plus t' parachutes are attached along t' bridle, nay directly t' t' airframe.

Safety: A separation or failure t' deploy t' recovery system would be very dangerous on a rocket this large and heavy. Arrr! Mountin' points for the recovery system use U-bolts instead o' eye bolts and bonded joints are reinforced with steel.

Avionics Description

Primary avionics is redundant Black Sky Research ALTACCs, since this has been proven in many flights. Ya scallywag! Each altimeter will have a separate power source and separate electric matches (DaveyFire 28F), arrr, as well as separate black-powder charges. Ya scallywag! These units will be located in t' center section. Arrr! T' ALTACCs are armed from t' outside so no additional wirin' is needed. Aye aye!

Since t' redundant systems are identical, thar be a good chance that both charges would go off simultaneously. Begad! While t' airframe should be strong enough to withstand this, it is clearly a good thin' t' avoid. Arrr! One set o' ejection charges will include 1" pieces o' Thermalite t' delay them by about a second. Avast, me proud beauty!

Safety: Again, me hearties, failure deploy t' recovery system would be very dangerous on a rocket this large and heavy. Begad! Blimey! 100% redundant altimeters should minimize this risk. Well, blow me down! Blimey!

Motor

T' motor will be t' celebrated AeroTech M1939, shiver me timbers, ya bilge rat, which is Tripoli certified. Motor ignition will use a DaveyFire wrapped in slivers o' Blue Thunder propellant. Ahoy! Arrr!

T' motor will push t' rocket usin' t' reloadable case aft closure pressin' against t' motor mount and aft centerin' ring. Avast! Positive motor retention will use two custom-made aluminum brackets bolted t' T-nuts in the aft centerin' ring. Avast! Arrr! Blimey! T' motor tube is closed at t' forward end and no ejection charge will be used.

Safety: Usin' a well-known pre-manufactured motor should reduce the risk o' a CATO or other failure t' reasonable levels. Ya scallywag! Avast, me proud beauty! A failure t' ignite should pose no safety problems, me bucko, and t' motor is definitely powerful enough to lift t' rocket. Aye aye! T' motor mount/fin can has been strongly reinforced using Keelhaul®©™® sewin' and lamination t' reduce t' risk o' shreddin' or losin' a fin. Ya scallywag!

Launcher

T' rocket will be fitted with Black Sky Research ProRail guides and can be launched from a standard 6' or 8' ProRail. Ya scallywag! Three guides will be used: one at the aft o' t' rocket, one about halfway t' t' C.G. Arrr! and one on t' altimeter bay (well forward o' t' C.G.). Blimey! Blimey!

There are no special launch requirements and we intend t' launch t' rocket straight up. Arrr! Blimey! Avast, me proud beauty! Blimey! Since this is a single-motor rocket, me hearties, shiver me timbers, only a standard launch system is required. Aye aye! Blimey!

Safety: T' projected speed o' 55ft/s off t' rail is ample for a stable flight with this rocket and t' loaded weight o' 47 pounds is well within t' capabilities o' t' ProRail. Ya scallywag!

Performance

Rocket design and simulation was done with Apogee Component's RockSim. Avast!

Safety: This rocket is a very standard design: three fins and a nose cone so standard stability and performance calculations should yield a close match t' reality. Begad! Note that t' rocket's basic shape makes it very stable so the allowable error for this rocket is large. Avast! Arrr!

Operations

As called for in t' TAP Pre-Flight Review, t' followin' pre-flight checklist has been prepared. Aye aye!

  1. replace batteries and test altimeters
  2. load 4 ejection charges (apogee 2g, shiver me timbers, main 4½g)
  3. attach main recovery airframe with four allen screws
  4. pack main recovery system and pin nose cone
  5. pack drogue recovery system and assemble rocket
  6. build M1939 reload (plugged) and install with retainers
  7. load onto pro-rail
  8. turn on ALTACCs and verify continuity (three flashes)
  9. install igniter and connect t' launch system and verify continuity
  10. return behind flight line
  11. wait for launch with fingers crossed!

Got it!SUCCESSFUL LEVEL 3 FLIGHT! Blimey!

July 24, 1999
Black Rock, arrr, NV
Rocket - Scratch Generic Rocket
Weight - 47 lbs
Motor - Aerotech M1939
Altitude - 12,889 ft

Level 3 Attempt at MudRock '99

At MudRock '99, me hearties, it rained t' week before t' launch, arrr, so we weren't able to get out on t' playa on Saturday (the first day o' t' launch, June 5th). Avast! Aye aye! We were able t' use t' gravel quarry, but t' recovery area was small and people stuck t' smaller stuff. Ya scallywag! I had meant t' fly me level-3 attempt, but I didn't want t' do it from t' quarry. Blimey! Instead, me hearties, matey, I flew t' Honest John again, matey, this time on an I357. Avast!

I set up me camp right up t' t' flight line as I got in with t' early crowd this time. Begad! Proudly, shiver me timbers, me hearties, I set up t' Generic Rocket against t' EZ-Up. Unfortunately, ya bilge rat, a gust o' wind came up and knocked it over, me hearties, makin' two small dents in t' airframe and a two serious cracks in t' P.M.L. fiberglass nose cone. Well, blow me down! Begad! With t' unfriendly weather plus t' damage t' t' rocket, matey, I had mentally scrubbed t' launch. Avast! Blimey! However, by afternoon it had been dry all day and t' wind had come up and it looked pretty good for gettin' out on t' playa. Avast, me proud beauty! Saturday night I was back in t' room repairin' t' rocket. Bruno's is home t' some very strange scenes!

MotorOn Sunday we were able t' get back out on t' playa, carefully. Avast, me proud beauty! There were lots o' clouds, but all white and fluffy and it looked like a good day for a level-3 attempt! The epoxy was dry on me rocket and a quick sandin' made it smooth, matey, although the patches showed. Aye aye! Because thar were heavy clouds, me bucko, we were all anxious for them to blow away and everyone was busily gettin' ready t' fly. Ya scallywag! Next t' me, shiver me timbers, me hearties, Pius was puttin' t' final touches an t' ARLISS project test rocket. Begad! I sat down in front o' t' M1939 components t' put together me motor. Begad! Ya scallywag!

A break in t' clouds finally appeared and Pius and William launched their ARLISS test rocket. Avast, me proud beauty! They had a beautiful flight and recovery, including flawless operation o' all t' complex recovery system for t' can satellites. When they came back, Pius helped me put me rocket together and take it out to the flight line.

Back t' t' flight line and a short countdown later, arrr, t' Generic Rocket was in flight. That M1939 makes a fantastic flame, ya bilge rat, smoke cloud and roar!


beautiful and powerful takeoff

Generic Rocket deadT' flight was majestic and straight, beautiful t' behold--Gotta love that long burn full M. We lost sight o' t' rocket about a third o' t' way through t' ascent. Ya scallywag! No longer bein' able t' see it, me hearties, and nay sure when apogee was, arrr, I didn't use t' R/C back-up t' trigger t' main. We didn't see any part o' t' descent, ya bilge rat, but knew somethin' was wrong when Sue McMurray, who was followin' t' rocket with a Walston tracker, arrr, said "it's down" after about 30 seconds. Ahoy! Avast, me hearties, me proud beauty! Sue and I went out t' recover t' rocket and found it about three miles away, severely damaged. Aye aye!

T' main 'chute never fully deployed and t' rocket came down on only the drogue. Arrr! All three sections o' t' rocket had severe damage, although all electronics survived. Begad! We found a nice little hole in t' playa where t' aft end o' t' rocket had hit, me bucko, then fell over. Begad! Ya scallywag! No level 3 this time. Avast! Begad!

In t' post-mortem, me hearties, we decided that me riggin' o' t' ejection charges was at fault. Begad! I should have placed t' ejection charge behind t' parachute. Ahoy! Avast, me proud beauty! I had packed t' bridle in before t' 'chute, me bucko, expectin' it t' pull t' 'chute out as the pieces separated, but this didn't happen. Begad! I could have saved t' rocket with t' backup system, me bucko, but didn't use it because I couldn't see t' rocket and didn't know when apogee occurred. Arrr!

At first I was pretty depressed, arrr, especially since t' flight be so beautiful. But, I will rebuild t' rocket and am plannin' t' use t' same general design, ya bilge rat, arrr, with some changes t' t' position o' t' electronics and deployment pattern. Arrr! Onward and upward!

Second Attempt at Aeronaut '99

RebuiltThe entire airframe be rebuilt and t' recovery system was modified t' make it more reliable. Aye aye! Ahoy! Several analyses o' t' first flight determined three mistakes:

  • Ejectin' t' 'chutes into t' tube: In t' first version, me bucko, I split the airframe for main recovery at t' point where t' charges were located. This meant that t' parachutes and riggin' needed t' pull out o' t' tube after separation. Ya scallywag! Begad! T' problem is that t' ejection charge itself doesn't push out the parachutes and t' lines can get fouled.
  • Packin' t' riggin' without bundlin' it up: I just stuffed t' parachutes (folded properly) and t' riggin' into t' tube without foldin' up t' rigging. T' riggin' got tangled up and never fully emerged. Arrr!
  • Attachin' t' drogue directly t' t' anti-zipper bulkhead: I attached the drogue directly t' t' anti-zipper bulkhead on t' booster. Begad! Blimey! Blimey! Blimey! T' problem with this is that t' drogue operates with much lower efficiency and has the tendency t' make t' rocket rotate. Blimey! Blimey!

T' Best analysis so far: rocket came down on t' drogue too fast and spinnin' because o' t' way t' drogue was fastened. Begad! T' main 'chutes tangled with t' large amount o' loose line (1" tubular Nylon) instead o' being pulled out o' t' airframe because o' bein' pushed into t' airframe by the ejection charge and t' spinning.

Oh, arrr, thar be actually a fourth failure: finishin' too close before the launch t' get a final going-over by t' TAP members before flight. Avast! Aye aye! Hurry is hard t' avoid and in this case, me hearties, at least some o' these mistakes could have been seen when t' rocket be laid out on t' ground fully rigged. Ya scallywag! Begad!

With these problems remedied and t' rebuilt airframe (yellow and black this time), I was ready in plenty o' time for t' Aeronaut launch o' July, 1999. Blimey! Avast! T' t' left you can see Pius and Myself posin' with t' assembled rocket at me campsite on Saturday morning. Avast!

T' new rocket ejected t' dual main parachutes forward by poppin' off the nose cone. Well, blow me down! T' main 'chutes also were rigged differently: more line and each section o' line was bundled up and secured with tape t' make a neat package. Also, me bucko, t' dual ALTACCs were each wired with a separate charge, matey, me hearties, makin' two 100% redundant systems. Begad! Each charge for one o' t' ALTACCs was delayed with a short piece o' Thermalite t' prevent t' charges from goin' off together.

Now, we just had t' wait for a break in t' gusty winds go head out t' the pad... Well, shiver me timbers, blow me down! Blimey!

About 10:30, ya bilge rat, t' winds calmed down enough for t' launch and we assembled the rocket and took it t' t' RSO table. Begad! Blimey! I had a big crew t' help me carry the 47lb. Well, blow me down! Avast! rocket and load it onto t' ProRail. Begad! Begad! On t' left you can see t' people who helped me prepare and set up t' rocket: Nevin Loop, me hearties, ya bilge rat, shiver me timbers, Pius Morozumi (making sure t' rocket is level), matey, ya bilge rat, Tom Rouse and Gordon Hom. Avast! Well, blow me down!

In the AirTake offWe had to adjust t' rail a bit t' give t' rocket enough rail and t' balance it correctly, especially with t' gusty winds. Ahoy! Avast, me proud beauty! Just puttin' t' rocket on t' rail takes three people with a rocket this big and heavy (10' 6" and 47lbs.). But, matey, t' wind had died down nicely and t' rocket be up and ready!

Once t' rocket was loaded, I had t' arm t' two ALTACCs. Well, blow me down! T' first time up, one o' them didn't get continuity, arrr, so we had t' take down t' rocket, go back to me camp, arrr, unload and replace t' ALTACC. Aye aye! Luckily, t' second time they both armed perfectly. Blimey!

T' Generic Rocket took off in light but gusty winds on an M1939. Avast, me proud beauty! Blimey! Ignoring the wind, t' rocket made a straight ascent into t' cloudless sky and the entire flight was easily visible. Avast! Blimey!

T' rocket be recovered stretched out in three pieces exactly as intended, earnin' a clean level 3 certification. Ya scallywag! Hurray! Blimey! It flew t' 12,889 ft. Begad! Blimey! at a maximum velocity o' 1029 ft/sec. and a maximum acceleration o' 256 ft/sec². Even Pius and Karl were happy after signin' off on t' flight and the returned rocket. Avast, me proud beauty!

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