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. Begad! One central D
engine mount and three side pods for optional C engines that aft eject. Ahoy! The
rocket has six fins and split recovery o' t' liftin' body on one chute and the
payload section on another chute. Arrr! Aye aye! T' main body is BT-60 and t' payload bay is
BT-70. T' C engines are aft eject and can be either B or C6-0. 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, like a sod farm. Aye aye! The
model weighs 8.3 oz. with empty payload and no engines. With a full payload of
6.7 oz., shiver me timbers, me hearties, one D12-3 and three C6-0 engines, and two parachutes, me hearties, arrr, t' fully loaded
model weighed 20 oz. T' empty booster weighs 5 oz. Begad! and t' larger empty
payload bay weighs 3.3 oz.
Aspects new t' me that required a developmental learnin' process:
1. Aye aye! Begad! reliable ignition o' four engine clusters. Aye aye! (I had never done clusters
before.)
2. Aye aye! Blimey! four engine cluster with smaller engines in t' side pods. Ahoy! (flight/fault
issues)
3. Aye aye! Begad! electronic payload design and usage. Ya scallywag! (I didn't even own an altimeter
before.)
4. Aye aye! 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. Ya scallywag! After gettin' some BT-70 body tube from a friend (Damian Kostron of
KosRox), me hearties, 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. Nay havin' any method t' calculate stability
of such a complex shape, matey, me bucko, and knowin' it could be carryin' significant weight, I
guessed and built it with six large through-the-wall fins. When first built in
1999, I had no experience with clusterin' and electronics, so an extensive test
program and developmental process was necessary. Ya scallywag! Aye aye! Therefore, 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! Except for internal hardware
such as engine hook, nylon nose cone attachment screws, arrr, and screw eyes, arrr, the
model is all wood and paper construction. Ya scallywag! I place high value on RMR Descon
entries that teach me design and modelin' techniques, shiver me timbers, 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, so I
am very sensitive t' ensure secure attachment o' nose cones t' payload bays.
T' MissleWorks RRC2 altimeter was obtained late in t' program, and the
original payload bay be discovered t' be too short. Well, blow me down! Therefore, ya bilge rat, a second larger
payload bay be built with t' second balsa transition t' accommodate the
altimeter. Well, blow me down! 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, I
consider t' project a success. Ya scallywag! Ya scallywag! Blimey! I have successfully demonstrated reliable
cluster flights with different engines in t' same cluster. Avast, me proud beauty! Avast! Blimey! I have successfully
demonstrated use o' electronics t' measure altitude. Arrr! I have successfully
designed a rocket capable o' reliably liftin' a payload 1/3 o' t' total rocket
weight includin' engines. Blimey! Begad! Blimey! On it's eighth flight, Heavy Lifter flew t' 490 feet
on one D12 and three C6's. Avast! Blimey! Blimey! It was carryin' a payload weight o' 6.7 oz. and
recovery be perfect with no damage! Blimey! 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. Avast! Use an
engine hook and a heavy duty thrust ring.
Main Booster Assembly:
1. Aye aye! Usin' a hard grain 1/8 inch balsa, arrr, cut six fins with t' lead edge going
with t' grain. Specifications on t' fins are as follows: root edge is 4
inches, shiver me timbers, 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. Sand and prep as desired.
2. Aye aye! Cut a section o' BT-60 t' 18 inches. Glue t' engine mount into one end so
that 1/2 inch o' t' mount extends past t' end o' t' BT-60 tube. Begad! Measure and
mark t' tube for 6 fins and six attachments equidistant from each other on the
tube. 3. Cut six slots for t' fins t' mount t' t' engine mount. Arrr! Glue and
attach t' fins. Apply t' glue fillets before installin' t' side tubes.
4. Ahoy! Cut three lengths o' BT-20 t' 9 inches (or longer if desired). Aye aye! Ya scallywag! Glue balsa
BT-20 nose cones into each o' t' tubes. Begad! Sand and prep as desired. 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. Aye aye! Well, me hearties, blow me down! Because t' launch lugs are on t' booster and t' launch rod needs t' clear
the wider payload section, ya bilge rat, t' launch lugs need t' be installed on extension
pieces. Arrr! Cut two 2 inch lengths o' 3/16 inch launch lug. Blimey! 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! Ya scallywag! Glue each launch lug t' one o' these extension
pieces. Ahoy! On one o' t' alignment lines, arrr, 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. Avast! Make sure they stay aligned
until t' glue is set.
6. Avast! Cut out a section o' 1/8 inch dowell and glue on t' line betwixt t' two
launch lug assemblies. Ya scallywag! Cut out two more pieces o' dowell at 14 inches, me bucko, cut an
angle on one end o' both o' them, me hearties, me bucko, and glue t' t' correspondin' aliignment
lines so that t' three dowels are 120 degrees apart.
7. Blimey! Well, blow me down! 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. Ya scallywag! Apply glue fillets and sand and prep as desired.
8. Avast, me proud beauty! Epoxy a 12 inch length o' small or mini braided tubular Keelhaul®©™ (available
from Pratt Hobbies)
into t' inside o' t' main booster tube. Ahoy! 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! Blimey! 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. Well, blow me down! Blimey! Put a
spot o' glue on t' knot.
9. Begad! Fill in grooves and fillets with Elmers FF as desired, and sand and prep. Ya scallywag!
Payload Section:
1. Avast, me proud beauty! Cut a short 2 inch piece o' BT-60, ya bilge rat, and glue in a coupler on one end.
2. Well, arrr, blow me down! Install an eyehook in a balsa BT60-70 transition, matey, secure it with glue.
Attach a two foot section o' 1/4 inch elastic shock cord. Avast, me bucko, me proud beauty! Put a spot o' glue on
the knot. Ya scallywag! Tie a small loop in t' other end o' t' shock cord and put a spot of
glue on that knot.
3. Well, blow me down! 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. Arrr! T' length o' this
piece depends on t' size o' t' payload you anticipate using. Aye aye! 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. Begad! Ya scallywag! Drill two small 1/16 inch holes on either side o' t' payload bay for
altimeter pressure sensing. Well, blow me down! Apply some CA t' t' holes t' strengthen and
prevent frayin' o' t' edges with use. Ya scallywag! Ahoy! Sand t' smoothness, shiver me timbers, 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. Ya scallywag! Install t' nose cone and hold securely while drillin' 1/32" holes
suitable for t' nylon holdin' screws. Ya scallywag! 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. Avast, me proud beauty! Begad! 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. 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. Arrr! Then after t' CA has cured, work t' threads again with a
metal screw until it threads smoothly. Avast! Begad! Then install t' nylon screws t' make
sure they work smoothly as well. Ahoy! Repeat this process until t' t' nylon screws
twist smoothly, 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. 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. Avast, me proud beauty! Fill in any grain and spirals with Elmers FF and sand as required. Aye aye! 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 be necessary t' securely keep this particular payload load
from rattlin' around. Begad! Begad! Blimey! An adapter was built out o' extra 38mm engine tube and
two plywood adapter rings. Well, blow me down! Aye aye! Blimey! Slots were cut for pressure equalization. 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. Well, blow me down! Blimey! I wanted to
challenge me Heavy Lifter with a lot o' weight, me hearties, but also have a retaining
system I could use in later complete uses o' t' altimeter for dual deployment
of bigger rockets, etc. 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. Well, blow me down! I made one
clip whip with red insulation, me hearties, and one clip whip with black insulation. Avast! Well, shiver me timbers, blow me down! Cut
four six inch lengths o' each color. Strip t' insulation on both ends o' each
wire. Install four red wires and four black wires each into a connector and
crimp. Ya scallywag! Begad! Conduct a pull test t' ensure reliable crimp and then solder t' joint
with high temerature solder. Avast! Obtain eight copper flat clips, and connect each
clip t' a wire end with high temperature solder. Begad! 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. Begad! One black and one red lead goes to
the two leads o' an igniter for each engine. Begad! Avast! 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, sanded then painted
several coats o' Krylon flat white, which was t' coat o' paint on most
intermediate flights. Finally, me bucko, t' rocket was painted gloss white. Aye aye! Decals are
pending. Just a few decals add a lot t' appearance.
Sequence o' Results/Flight Details
1. 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. Ahoy! o' weight in t' payload bay. A
single D12-3 motor was used for both flights. Aye aye! 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. A correction t' this problem be 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, arrr, 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. Aye aye! Ahoy! Blimey! Winds were brisk gustin' t' 15 knots. Ahoy! Blimey! The
wobble problem was corrected, me hearties, but t' parachute got jammed up in t' new
section and t' payload section tumble recovered. 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 be shortened t' 2" and a new coupler installed. Ahoy!
3. Avast, me proud beauty! Arrr! 6/23/01 - (FLIGHT 5) One flight on a D12-3 t' confirm reliable parachute
deployment. Arrr! Confirmed, me bucko, and developmental program fully approved for next steps.
4. Aye aye! Blimey! An RRC2 altimeter be obtained as a birthday present from me wife, and a
custom holder be designed and built for a 38mm payload bay.
5. Aye aye! 11/17/01 - T' Tri-Stomp (my Descon 9 entry) be designed and built
specifically for testin' and learnin' how t' do cluster rocketry. Ya scallywag! 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. Begad! Tri-Stomp was twice successfully launched on
three B motors with all three motors lightin' both times, once at a club launch
usin' t' club launch system, me hearties, 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. of
payload weight. Aye aye! (one D12-3, three C6-0's) T' shortened coupler section o' the
payload section reliably deployed t' parachute, shiver me timbers, me hearties, 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!). Ya scallywag! Rocket flew t' 1069 ft on a G35W. Aye aye! This altitude was within
the approximate estimated window o' t' Heavy Lifter altitude. Blimey! T' program is
approved for t' final steps.
8. Begad! Ahoy! 6/02 - 7/04. Program placed on development hold while project manager
devotes more time t' coachin' his kid's sports teams, me hearties, matey, boy scouts, me hearties, and bein' a
soccer referee. Begad! 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. Blimey! Aye aye! 8/22/04 - (FLIGHT 7)
Heavy Lifter flown on 4 engine cluster with long payload and t' altimeter
assembly. Well, blow me down! T' altimeter assembly and adapter weighed 6.7 oz with a total rocket
weight o' 20 oz. Aye aye! includin' engines. Well, blow me down! Ya scallywag! (one D12-3, three B6-0s). Arrr! T' wind was
gustin' t' 20 mph, ya bilge rat, so smaller booster engines were used t' limit altitude. The
rocket flew t' less than 300 ft. Ya scallywag! 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. All systems operated properly including
the launch and recovery systems.
10. Avast, me proud beauty! Aye aye! 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. Blimey! T' rocket flew
about twice as high as t' previous flight. Ejection and recovery system
deployment occurred at apogee. Aye aye! T' booster section caught a thermal and drifted
over t' roof o' adjacent apartment buildin' (1/4 mile away). Blimey! After recovery of
the payload section and recordin' o' altitude, me hearties, 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, me proud beauty! All systems performed properly, me hearties, and all components
were recovered with no damage. Altitude achieved was 490 ft as reported by
altimeter. Aye aye! Blimey! Unfortunately, no photographers were available for these last two
historic flights.