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