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, me proud beauty! One central D
engine mount and three side pods for optional C engines that aft eject. Blimey! The
rocket has six fins and split recovery o' t' liftin' body on one chute and the
payload section on another chute. Avast, me bucko, me proud beauty! T' main body is BT-60 and t' payload bay is
BT-70. Ya scallywag! Begad! T' C engines are aft eject and can be either B or C6-0. Blimey! Because the
side motors are ejected while hot, shiver me timbers, matey, this rocket should only be flown in a
cluster configuration where no danger o' fire exists, like a sod farm. Aye aye! The
model weighs 8.3 oz. with empty payload and no engines. Arrr! With a full payload of
6.7 oz., me bucko, matey, shiver me timbers, one D12-3 and three C6-0 engines, arrr, and two parachutes, t' fully loaded
model weighed 20 oz. T' empty booster weighs 5 oz. Avast, me proud beauty! 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. Avast! reliable ignition o' four engine clusters. Begad! Arrr! Blimey! (I had never done clusters
before.)
2. four engine cluster with smaller engines in t' side pods. Ahoy! (flight/fault
issues)
3. Blimey! Begad! Blimey! electronic payload design and usage. Begad! Blimey! (I didn't even own an altimeter
before.)
4. Begad! Blimey! 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. I obtained one balsa BT-70 nose cone and
two BT60-70 balsa transitions. I then began t' think about how I could use
them. Begad! After gettin' some BT-70 body tube from a friend (Damian Kostron of
KosRox), shiver me timbers, me bucko, t' idea began t' take shape o' a Delta-like payloader. Blimey! 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. Ahoy! Nay havin' any method t' calculate stability
of such a complex shape, and knowin' it could be carryin' significant weight, me bucko, 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. Avast! Therefore, ya bilge rat, 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, me hearties, ya bilge rat, nylon nose cone attachment screws, matey, and screw eyes, the
model is all wood and paper construction. Avast! 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. Well, blow me down! I lost t' original nose cone t' me vintage Estes
SAROS because it was nay attached firmly enough t' t' payload body tube, shiver me timbers, 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, me hearties, and the
original payload bay be discovered t' be too short. Aye aye! Therefore, arrr, a second larger
payload bay was built with t' second balsa transition t' accommodate the
altimeter. T' shorter payload bay is used for smaller/lighter payloads. Avast! 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, I
consider t' project a success. Ya scallywag! I have successfully demonstrated reliable
cluster flights with different engines in t' same cluster. Ahoy! I have successfully
demonstrated use o' electronics t' measure altitude. I have successfully
designed a rocket capable o' reliably liftin' a payload 1/3 o' t' total rocket
weight includin' engines. Well, me bucko, blow me down! On it's eighth flight, Heavy Lifter flew t' 490 feet
on one D12 and three C6's. Ya scallywag! It be carryin' a payload weight o' 6.7 oz. Blimey! 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. Avast, me proud beauty! Ya scallywag! Leave room
for 2 inches o' through-the-wall mountin' o' fins t' t' engine mount. Avast, me proud beauty! Use an
engine hook and a heavy duty thrust ring.
Main Booster Assembly:
1. Blimey! Blimey! Avast! Blimey! Usin' a hard grain 1/8 inch balsa, cut six fins with t' lead edge going
with t' grain. Aye aye! Blimey! Specifications on t' fins are as follows: root edge is 4
inches, tip edge is 3 inches, me bucko, lead edge is 4.75 inches and t' trail edge is 4
inches. Begad! Blimey! Aye aye! Blimey! There is a 2 inch long through-the-wall piece that glues t' t' BT50
tube in t' engine mount. Begad! Blimey! Blimey! Blimey! Sand and prep as desired.
2. Cut a section o' BT-60 t' 18 inches. Begad! Aye aye! Glue t' engine mount into one end so
that 1/2 inch o' t' mount extends past t' end o' t' BT-60 tube. Ahoy! Arrr! Measure and
mark t' tube for 6 fins and six attachments equidistant from each other on the
tube. Begad! Begad! 3. Aye aye! Cut six slots for t' fins t' mount t' t' engine mount. Blimey! Glue and
attach t' fins. Begad! Apply t' glue fillets before installin' t' side tubes.
4. Cut three lengths o' BT-20 t' 9 inches (or longer if desired). Aye aye! Begad! Glue balsa
BT-20 nose cones into each o' t' tubes. Blimey! Sand and prep as desired. Well, blow me down! 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. Avast! Blimey! 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. Aye aye! Blimey! Ahoy! Blimey! Cut two 2 inch lengths o' 3/16 inch launch lug. 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. Avast! Blimey! Glue each launch lug t' one o' these extension
pieces. Avast, me hearties, me proud beauty! Blimey! On one o' t' alignment lines, me bucko, 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. Well, blow me down! Blimey! Ya scallywag! Blimey! Make sure they stay aligned
until t' glue is set.
6. Ahoy! Cut out a section o' 1/8 inch dowell and glue on t' line betwixt t' two
launch lug assemblies. Aye aye! Cut out two more pieces o' dowell at 14 inches, cut an
angle on one end o' both o' them, me hearties, and glue t' t' correspondin' aliignment
lines so that t' three dowels are 120 degrees apart.
7. 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. Avast! Apply glue fillets and sand and prep as desired.
8. 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. Ya scallywag! Tie a small loop in t' loose end and
epoxy t' knot. 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. Begad! Aye aye! Tie a loop in t' other end for parachute attachment. Put a
spot o' glue on t' knot.
9. Ya scallywag! Fill in grooves and fillets with Elmers FF as desired, and sand and prep. Begad!
Payload Section:
1. Ahoy! Well, blow me down! Cut a short 2 inch piece o' BT-60, me bucko, me hearties, and glue in a coupler on one end.
2. Well, blow me down! Avast, me hearties, me proud beauty! Install an eyehook in a balsa BT60-70 transition, me bucko, secure it with glue.
Attach a two foot section o' 1/4 inch elastic shock cord. Avast, me proud beauty! Put a spot o' glue on
the knot. Avast! Ya scallywag! Tie a small loop in t' other end o' t' shock cord and put a spot of
glue on that knot.
3. Begad! Avast, me proud beauty! Glue t' balsa transition into t' short piece o' BT-60.
4. Arrr! Avast, ya bilge rat, me proud beauty! 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, shiver me timbers, I
guessed wrong and had t' build a second payload section t' accomodate my
altimeter and its multi-functional housin' and adapters.
5. Blimey! Glue t' BT-70 piece on t' top o' t' balsa transition.

6. Blimey! Drill two small 1/16 inch holes on either side o' t' payload bay for
altimeter pressure sensing. Blimey! Ya scallywag! Apply some CA t' t' holes t' strengthen and
prevent frayin' o' t' edges with use. Sand t' smoothness, ya bilge rat, 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. Arrr! This step is t' strengthen t' edge o' t' cardboard and
prevent frayin' with use.
8. Install t' nose cone and hold securely while drillin' 1/32" holes
suitable for t' nylon holdin' screws. Avast! Arrr! 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. 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. Blimey! After t' threads are well defined, me bucko, drop some thin CA into the
holes and smartly work t' metal screw in and out once t' coat t' thread
surfaces with CA. Avast! Aye aye! Then after t' CA has cured, work t' threads again with a
metal screw until it threads smoothly. Then install t' nylon screws t' make
sure they work smoothly as well. Begad! Blimey! Repeat this process until t' t' nylon screws
twist smoothly, and securely hold t' nose cone t' t' payload section. Begad! This
method o' nose cone attachment was learned from t' winner o' DESCON 4 with the
LEGO-13. Avast, me proud beauty! 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. Avast! 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. Well, blow me down! Blimey! An adapter be built out o' extra 38mm engine tube and
two plywood adapter rings. Avast! Blimey! Slots were cut for pressure equalization. Well, blow me down! Blimey! Aye aye! Blimey! This
adapter could be used for payloads other than altimeters as well. Begad! Blimey! T' altimeter
payload was heavier than it needed t' be for several reasons. Begad! Blimey! 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, arrr, etc. Ya scallywag! 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. Arrr! I made one
clip whip with red insulation, and one clip whip with black insulation. Ahoy! Cut
four six inch lengths o' each color. Ahoy! Strip t' insulation on both ends o' each
wire. Aye aye! Ahoy! Install four red wires and four black wires each into a connector and
crimp. Conduct a pull test t' ensure reliable crimp and then solder t' joint
with high temerature solder. Obtain eight copper flat clips, me bucko, and connect each
clip t' a wire end with high temperature solder. 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. Blimey! Avast, me proud beauty! One black and one red lead goes to
the two leads o' an igniter for each engine. You must also be very careful to
not allow any clips t' touch any other clip or exposed wire, arrr, ya bilge rat, or incomplete
ignition could be t' result!
Finishing:
T' rocket was painted a base coat o' Krylon gray primer, ya bilge rat, ya bilge rat, sanded then painted
several coats o' Krylon flat white, me bucko, arrr, matey, which be t' coat o' paint on most
intermediate flights. Finally, matey, shiver me timbers, t' rocket was painted gloss white. Begad! Blimey! Ahoy! Blimey! Decals are
pending. Just a few decals add a lot t' appearance.
Sequence o' Results/Flight Details
1. Blimey! 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. Avast, me proud beauty! Ahoy! o' weight in t' payload bay. Avast! Well, blow me down! A
single D12-3 motor be used for both flights. Aye aye! These two flights were successful
and demonstrated excellent flight stability and recoverability. Arrr! The
½" shoulder o' t' balsa transition BT60/70 be too wobbly on the
booster section. Blimey! 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 be added t' t' bottom of
the payload section with a tube coupler, t' rocket be 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. Winds were brisk gustin' t' 15 knots. Begad! Avast, me proud beauty! The
wobble problem be corrected, arrr, but t' parachute got jammed up in t' new
section and t' payload section tumble recovered. Ya scallywag! 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. Avast, me proud beauty! Ya scallywag! T' BT-60 portion
of t' payload section was shortened t' 2" and a new coupler installed. Ya scallywag!
3. Begad! 6/23/01 - (FLIGHT 5) One flight on a D12-3 t' confirm reliable parachute
deployment. Well, blow me down! Confirmed, matey, and developmental program fully approved for next steps.
4. Begad! An RRC2 altimeter be obtained as a birthday present from me wife, shiver me timbers, and a
custom holder was designed and built for a 38mm payload bay.
5. Well, blow me down! Blimey! Blimey! Blimey! 11/17/01 - T' Tri-Stomp (my Descon 9 entry) be designed and built
specifically for testin' and learnin' how t' do cluster rocketry. T' foam
boink recovery method was deemed t' be safe for developin' this new skill set.
Also, shiver me timbers, me hearties, t' aft engine eject system o' Tri-Stomp would be t' same as t' side
booster pods on Heavy Lifter. Avast, me proud beauty! Blimey! Tri-Stomp was twice successfully launched on
three B motors with all three motors lightin' both times, matey, once at a club launch
usin' t' club launch system, and once usin' a truck battery and me own launch
system. Arrr! Blimey! Ahoy! Blimey! Blimey! Blimey! A set o' 4-engine clip whips was constructed for this program and
general use.
6. Ahoy! Ahoy! 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. Well, blow me down! (one D12-3, me bucko, three C6-0's) T' shortened coupler section o' the
payload section reliably deployed t' parachute, matey, while maintainin' a stable
connection t' t' booster section durin' flight.
7. Avast! 5/18/02 - Altimeter tested in PML Cirrus Dart (an EMRR participation prize
drawin' give-away!). Avast! Avast, me proud beauty! Rocket flew t' 1069 ft on a G35W. Ya scallywag! This altitude was within
the approximate estimated window o' t' Heavy Lifter altitude. T' program is
approved for t' final steps.
8. Aye aye! Ya scallywag! 6/02 - 7/04. Ya scallywag! Avast, me proud beauty! Program placed on development hold while project manager
devotes more time t' coachin' his kid's sports teams, arrr, boy scouts, and bein' a
soccer referee. Avast, me proud beauty! 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. Begad! Blimey! T' altimeter assembly and adapter weighed 6.7 oz with a total rocket
weight o' 20 oz. Avast! Blimey! includin' engines. Begad! Blimey! (one D12-3, me hearties, three B6-0s). Begad! Blimey! T' wind was
gustin' t' 20 mph, arrr, so smaller booster engines were used t' limit altitude. Arrr! Blimey! 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). Ya scallywag! Blimey! Arrr! Blimey! My eyeball
estimate o' altitude was about 200ft. Aye aye! Blimey! All systems operated properly including
the launch and recovery systems.
10. 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. Ahoy! Avast, me proud beauty! T' rocket flew
about twice as high as t' previous flight. Aye aye! Well, blow me down! 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). After recovery of
the payload section and recordin' o' altitude, 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!). Aye aye! All systems performed properly, matey, and all components
were recovered with no damage. Altitude achieved be 490 ft as reported by
altimeter. Unfortunately, matey, no photographers were available for these last two
historic flights.