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Heavy Lifter
An RMR Descon XIV entry
by David Fergus
(Place your mouse over photos t' view t' captions.(IE5))
Design
Summary:A four engine cluster rocket with two optional payload bays. Avast! One central D engine mount and three side pods for optional C engines that aft eject. Arrr! The rocket has six fins and split recovery o' t' liftin' body on one chute and the payload section on another chute. Begad! Ahoy! T' main body is BT-60 and t' payload bay is BT-70. Blimey! T' C engines are aft eject and can be either B or C6-0. Avast! Well, blow me down! Because the side motors are ejected while hot, ya bilge rat, this rocket should only be flown in a cluster configuration where no danger o' fire exists, like a sod farm. Aye aye! Begad! The model weighs 8.3 oz. with empty payload and no engines. Aye aye! Ya scallywag! With a full payload of 6.7 oz., shiver me timbers, one D12-3 and three C6-0 engines, arrr, ya bilge rat, and two parachutes, t' fully loaded model weighed 20 oz. Arrr! T' empty booster weighs 5 oz. Well, blow me down! and t' larger empty payload bay weighs 3.3 oz.
Aspects new t' me that required a developmental learnin' process:
1. Aye aye! Ya scallywag! reliable ignition o' four engine clusters. Begad! (I had never done clusters before.)
2. four engine cluster with smaller engines in t' side pods. Well, blow me down! (flight/fault issues)
3. electronic payload design and usage. Begad! (I didn't even own an altimeter before.)
4. Begad! Begad! rocket stability with a large payload-weight/total-lift-weight ratio o' 1:3.
CONCEPT:This rocket began as a concept after obtainin' some out o' production balsa at a hobby shop goin' out o' business. Begad! I obtained one balsa BT-70 nose cone and two BT60-70 balsa transitions. Begad! I then began t' think about how I could use them. Ya scallywag! After gettin' some BT-70 body tube from a friend (Damian Kostron of KosRox), t' idea began t' take shape o' a Delta-like payloader. Ya scallywag! It grew into a D engine BT-60 central booster supported by three BT-20 C engine side boosters carryin' a BT-70 payload section. Nay havin' any method t' calculate stability of such a complex shape, and knowin' it could be carryin' significant weight, matey, I guessed and built it with six large through-the-wall fins. Well, blow me down! When first built in 1999, matey, I had no experience with clusterin' and electronics, so an extensive test program and developmental process be necessary. Aye aye! Therefore, me hearties, I include flights of other rockets as part o' this project that verified I could accomplish objectives prior t' t' full up final flights. Avast, me proud beauty! Except for internal hardware such as engine hook, matey, nylon nose cone attachment screws, arrr, and screw eyes, arrr, the model is all wood and paper construction. Well, blow me down! I place high value on RMR Descon entries that teach me design and modelin' techniques, so I attached t' nose cone t' t' payload t' same way t' winner o' Descon 4 did it on t' Lego-13 with nylon screws and CA. Avast! I lost t' original nose cone t' me vintage Estes SAROS because it was nay attached firmly enough t' t' payload body tube, me hearties, so I am very sensitive t' ensure secure attachment o' nose cones t' payload bays. T' MissleWorks RRC2 altimeter be obtained late in t' program, and the original payload bay be discovered t' be too short. Therefore, me bucko, a second larger payload bay was built with t' second balsa transition t' accommodate the altimeter. Blimey! T' shorter payload bay is used for smaller/lighter payloads. Well, blow me down! The rocket can be flown with a single D engine or with a cluster o' one D and three C-size engines.
CONCLUSION/RESULT SUMMARY
After eight flights o' t' Heavy Lifter and several flights o' other rockets, shiver me timbers, I consider t' project a success. Arrr! I have successfully demonstrated reliable cluster flights with different engines in t' same cluster. I have successfully demonstrated use o' electronics t' measure altitude. Aye aye! I have successfully designed a rocket capable o' reliably liftin' a payload 1/3 o' t' total rocket weight includin' engines. Avast, me proud beauty! Aye aye! On it's eighth flight, me hearties, Heavy Lifter flew t' 490 feet on one D12 and three C6's. Blimey! It was carryin' a payload weight o' 6.7 oz. Arrr! Aye aye! and recovery was perfect with no damage! My next venture is t' build a rocket that actually uses t' full capability o' t' RRC2 altimeter/controller.
Materials
BT-70 body tube
BT-70 balsa nose cone
2 balsa BT-60/70 transitions
BT-60 body tube
3 BT-20 body tubes
3 BT-20 balsa nose cones
balsa fin stock
D engine BT60 heavy duty engine mount with hook
2 BT-60 couplers
2 metal screw eyes
3 heavy duty 18mm engine blocks
Pratt small braided Keelhaul®©™ shock cord material
Elastic shock cord material
2 Nylon screws
wooden dowel
parachutes from other kits as appropriate for weight
Construction
Main Engine Mount:
Build a standard D engine mount for placement in a BT-60 body tube. Leave room for 2 inches o' through-the-wall mountin' o' fins t' t' engine mount. Begad! Use an engine hook and a heavy duty thrust ring.
Main Booster Assembly:1. Arrr! Blimey! Avast, me proud beauty! Blimey! Usin' a hard grain 1/8 inch balsa, shiver me timbers, arrr, cut six fins with t' lead edge going with t' grain. Specifications on t' fins are as follows: root edge is 4 inches, tip edge is 3 inches, lead edge is 4.75 inches and t' trail edge is 4 inches. Begad! Blimey! There is a 2 inch long through-the-wall piece that glues t' t' BT50 tube in t' engine mount. Ya scallywag! Blimey! Sand and prep as desired.
2. Begad! Blimey! Cut a section o' BT-60 t' 18 inches. Begad! Blimey! Glue t' engine mount into one end so that 1/2 inch o' t' mount extends past t' end o' t' BT-60 tube. Measure and mark t' tube for 6 fins and six attachments equidistant from each other on the tube. 3. Arrr! Blimey! Cut six slots for t' fins t' mount t' t' engine mount. Glue and attach t' fins. Blimey! Blimey! Apply t' glue fillets before installin' t' side tubes.
4. Cut three lengths o' BT-20 t' 9 inches (or longer if desired). Well, me hearties, blow me down! Glue balsa BT-20 nose cones into each o' t' tubes. Sand and prep as desired. Ya scallywag! Ya scallywag! Glue heavy duty thrust rings into t' other end o' each o' t' tubes so that 1/4 inch of motor will stick out.
5. Arrr! Aye aye! Because t' launch lugs are on t' booster and t' launch rod needs t' clear the wider payload section, t' launch lugs need t' be installed on extension pieces. Cut two 2 inch lengths o' 3/16 inch launch lug. Avast! Avast, me proud beauty! Cut out two pieces of 1/8 inch fin stock into a rectangular shape 3/8 inch x 2 inch long with the grain goin' with t' short edge. Begad! Begad! Glue each launch lug t' one o' these extension pieces. Begad! On one o' t' alignment lines, glue each o' these launch lug sub-assemblies on t' rocket body 1.5 inch from t' aft and 6 inches from the front as measured t' t' aft o' t' sub-assembly. Aye aye! Make sure they stay aligned until t' glue is set.
6. Avast, arrr, me proud beauty! Cut out a section o' 1/8 inch dowell and glue on t' line betwixt t' two launch lug assemblies. Begad! Avast! Cut out two more pieces o' dowell at 14 inches, cut an angle on one end o' both o' them, shiver me timbers, and glue t' t' correspondin' aliignment lines so that t' three dowels are 120 degrees apart.
7. Avast, me proud beauty! Avast! Blimey! Glue t' three side boosters onto t' main booster along t' remainin' three alignment lines so that 1/2 inch o' t' aft o' t' tube extends past t' end of t' main tube. Apply glue fillets and sand and prep as desired.
8. Aye aye! Avast! Epoxy a 12 inch length o' small or mini braided tubular Keelhaul®©™ (available from Pratt Hobbies) into t' inside o' t' main booster tube. Arrr! Tie a small loop in t' loose end and epoxy t' knot. Avast! Leave at least an inch o' clearance for t' tube couplers of the payload section. Tie a 2 foot section o' 1/4" elastic shock cord to the kevlar loop. Avast, me proud beauty! Tie a loop in t' other end for parachute attachment. Put a spot o' glue on t' knot.
9. Begad! Fill in grooves and fillets with Elmers FF as desired, and sand and prep. Begad! Blimey!
Payload Section:
1. Avast! Cut a short 2 inch piece o' BT-60, matey, and glue in a coupler on one end.
2. Aye aye! Blimey! Install an eyehook in a balsa BT60-70 transition, secure it with glue. Attach a two foot section o' 1/4 inch elastic shock cord. Put a spot o' glue on the knot. Well, blow me down! Blimey! Tie a small loop in t' other end o' t' shock cord and put a spot of glue on that knot.
3. Glue t' balsa transition into t' short piece o' BT-60.
4. Begad! Cut a length o' BT-70 anywhere from 6 t' 10 inches long. T' length o' this piece depends on t' size o' t' payload you anticipate using. In me case, matey, I guessed wrong and had t' build a second payload section t' accomodate my altimeter and its multi-functional housin' and adapters.
5. Begad! Glue t' BT-70 piece on t' top o' t' balsa transition.
6. Well, blow me down! Drill two small 1/16 inch holes on either side o' t' payload bay for altimeter pressure sensing. Ya scallywag! Apply some CA t' t' holes t' strengthen and prevent frayin' o' t' edges with use. Aye aye! Sand t' smoothness, both inside and out.
7. Blimey! Apply CA t' t' edges o' t' payload section t' a depth o' about 1/2 inch. Sand until smooth. Aye aye! Aye aye! This step is t' strengthen t' edge o' t' cardboard and prevent frayin' with use.
8. Ya scallywag! Ahoy! Blimey! Install t' nose cone and hold securely while drillin' 1/32" holes suitable for t' nylon holdin' screws. Avast! Then remove t' nose cone and drill larger holes in t' walls o' t' payload bay with just enough clearance for the nylon screw threads. Ahoy! With t' nose cone removed from t' rocket, work in threads into t' balsa nose cone usin' a metal screw o' t' same thread as the nylon screws. Arrr! Blimey! After t' threads are well defined, drop some thin CA into the holes and smartly work t' metal screw in and out once t' coat t' thread surfaces with CA. Then after t' CA has cured, arrr, ya bilge rat, work t' threads again with a metal screw until it threads smoothly. Avast! Ya scallywag! Blimey! Then install t' nylon screws t' make sure they work smoothly as well. Arrr! Blimey! Repeat this process until t' t' nylon screws twist smoothly, matey, arrr, and securely hold t' nose cone t' t' payload section. Arrr! This method o' nose cone attachment was learned from t' winner o' DESCON 4 with the LEGO-13. Well, blow me down! Blimey! This method should allow easy removal and installin' o' t' nose cone while on t' flight line t' minimize time an altimeter is energized if using one as a payload.
9. Ahoy! Blimey! Fill in any grain and spirals with Elmers FF and sand as required. Aye aye! Blimey! Aye aye! Blimey! Keep the drilled holes clear and open for pressure equalization.
Altimeter Mount:Since t' RRC2 altimeter and it's custom retainin' module with on-off switch was designed t' fit into PML 38mm phenolic tubin' as well as thinner Estes BT-60, an adapter was necessary t' securely keep this particular payload load from rattlin' around. An adapter was built out o' extra 38mm engine tube and two plywood adapter rings. Blimey! Blimey! Slots were cut for pressure equalization. Avast, me proud beauty! This adapter could be used for payloads other than altimeters as well. T' altimeter payload be heavier than it needed t' be for several reasons. Avast! I wanted to challenge me Heavy Lifter with a lot o' weight, but also have a retaining system I could use in later complete uses o' t' altimeter for dual deployment of bigger rockets, ya bilge rat, me bucko, etc. Aye aye! Begad! T' Heavy Lifter was designed t' lift heavy loads and this altimeter package just happened t' be a convenient one; and also as a byproduct get an altitude readout o' flights.
Cluster Igniter Clip Whips:I used 18 gauge solid copper wire with high temperature insulation. I made one clip whip with red insulation, and one clip whip with black insulation. Well, blow me down! Cut four six inch lengths o' each color. Strip t' insulation on both ends o' each wire. Avast, me proud beauty! Install four red wires and four black wires each into a connector and crimp. Ahoy! Conduct a pull test t' ensure reliable crimp and then solder t' joint with high temerature solder. Begad! Obtain eight copper flat clips, and connect each clip t' a wire end with high temperature solder. Well, blow me down! Do a pull test and then an impedance/resistivity check t' ensure t' solder joints are good.
Flight NOTE: T' red and black wires are necessary t' distinguish between leads while hookin' up t' igniters. Arrr! Blimey! One black and one red lead goes to the two leads o' an igniter for each engine. Avast! Blimey! Ya scallywag! Blimey! You must also be very careful to not allow any clips t' touch any other clip or exposed wire, or incomplete ignition could be t' result!
Finishing:
T' rocket was painted a base coat o' Krylon gray primer, arrr, arrr, sanded then painted several coats o' Krylon flat white, which was t' coat o' paint on most intermediate flights. Begad! Blimey! Finally, t' rocket was painted gloss white. Begad! Blimey! Decals are pending. Avast! Blimey! Avast! Blimey! Just a few decals add a lot t' appearance.
Sequence o' Results/Flight Details
1. Ahoy! Begad! 11/20/99 - (FLIGHT
1,2) T' original rocket was built and first flown unpainted with an empty
payload bay and then a second time with 3 oz. Well, blow me down! o' weight in t' payload bay. A
single D12-3 motor be used for both flights. These two flights were successful
and demonstrated excellent flight stability and recoverability. The
½" shoulder o' t' balsa transition BT60/70 was too wobbly on the
booster section. Avast! A correction t' this problem was identified t' lengthen the
shoulder by addin' a short piece o' BT60 with a standard coupler t' t' payload
section.
2.
5/21/00 - (FLIGHT 3,4) After a 4 inch piece o' BT-60 was added t' t' bottom of
the payload section with a tube coupler, matey, me hearties, t' rocket was painted a base coat of
white and again flown twice carryin' 3 oz. o' weight in t' payload bay and
boosted by a single D12-3 motor. Well, blow me down! Ahoy! Winds were brisk gustin' t' 15 knots. Well, blow me down! Aye aye! The
wobble problem was corrected, me hearties, but t' parachute got jammed up in t' new
section and t' payload section tumble recovered. Aye aye! T' additional section of
BT-60 on t' bottom o' t' payload section was deemed t' be too long and
allowed t' parachute t' bunch into this area and nay deploy. Aye aye! T' BT-60 portion
of t' payload section was shortened t' 2" and a new coupler installed. Avast!
3. Arrr! 6/23/01 - (FLIGHT 5) One flight on a D12-3 t' confirm reliable parachute deployment. Confirmed, and developmental program fully approved for next steps.
4. Ahoy! Well, blow me down! An RRC2 altimeter was obtained as a birthday present from me wife, and a custom holder be designed and built for a 38mm payload bay.
5. Begad! 11/17/01 - T' Tri-Stomp (my Descon 9 entry) was designed and built specifically for testin' and learnin' how t' do cluster rocketry. Avast! T' foam boink recovery method was deemed t' be safe for developin' this new skill set. Also, t' aft engine eject system o' Tri-Stomp would be t' same as t' side booster pods on Heavy Lifter. Tri-Stomp be twice successfully launched on three B motors with all three motors lightin' both times, once at a club launch usin' t' club launch system, shiver me timbers, and once usin' a truck battery and me own launch system. Ahoy! A set o' 4-engine clip whips was constructed for this program and general use.
6. 5/18/02 - (FLIGHT
6) Heavy Lifter flown on 4 engine cluster with short payload bay and 3 oz. Well, blow me down! of
payload weight. Begad! (one D12-3, three C6-0's) T' shortened coupler section o' the
payload section reliably deployed t' parachute, matey, ya bilge rat, shiver me timbers, while maintainin' a stable
connection t' t' booster section durin' flight.7. Blimey! 5/18/02 - Altimeter tested in PML Cirrus Dart (an EMRR participation prize drawin' give-away!). Begad! Blimey! Rocket flew t' 1069 ft on a G35W. Well, blow me down! Avast, matey, me proud beauty! This altitude be within the approximate estimated window o' t' Heavy Lifter altitude. T' program is approved for t' final steps.
8. Blimey! 6/02 - 7/04. Well, blow me down! Program placed on development hold while project manager devotes more time t' coachin' his kid's sports teams, boy scouts, matey, and bein' a soccer referee. T' longer payload bay and altimeter adapter were constructed durin' this reduced activity period, similar t' how a government program goes on hold for fundin' or other issues.
9. 8/22/04 - (FLIGHT 7)
Heavy Lifter flown on 4 engine cluster with long payload and t' altimeter
assembly. T' altimeter assembly and adapter weighed 6.7 oz with a total rocket
weight o' 20 oz. Avast, me proud beauty! includin' engines. (one D12-3, three B6-0s). Well, blow me down! T' wind was
gustin' t' 20 mph, so smaller booster engines were used t' limit altitude. Ya scallywag! Avast, me hearties, me proud beauty! The
rocket flew t' less than 300 ft. T' Altimeter did nay register a launch
(minimum o' 300 ft in altitude required t' register a launch). Ahoy! My eyeball
estimate o' altitude was about 200ft. Arrr! All systems operated properly including
the launch and recovery systems.10. Arrr! 8/22/04 - (FLIGHT 8) Heavy Lifter flown on 4 engine cluster with altimeter. (one D12-3, three C6-0's) One o' t' C engines lit before t' other three and the motor burned for a second on t' pad with nay enough oomph t' get the rocket movin' before t' others lit and t' rocket lifted off. Arrr! T' rocket flew about twice as high as t' previous flight. Begad! Avast! Ejection and recovery system deployment occurred at apogee. Ahoy! Begad! T' booster section caught a thermal and drifted over t' roof o' adjacent apartment buildin' (1/4 mile away). Begad! Begad! After recovery of the payload section and recordin' o' altitude, me bucko, ya bilge rat, matey, t' long walk found t' booster section undamaged on t' patio o' an apartment on t' second row o' apartments into t' complex (whew!). All systems performed properly, arrr, and all components were recovered with no damage. Arrr! Avast! Altitude achieved was 490 ft as reported by altimeter. Aye aye! Unfortunately, arrr, shiver me timbers, matey, no photographers were available for these last two historic flights.
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