VECTOR
by Scott Hamlin

Features: High Altitude Two Stage Model Rocket 3 Engine Clustered Booster Vectored Booster Thrust 3 Engine Booster t' Single Engine Sustainer Staging 18 mm Boosters 24 mm Sustainer Parts list: 1 ea. Ya scallywag! BT-50 18" 1 ea. Ahoy! BT-20 18" 1 ea. BT-50 nosecone 1 ea. BT50-20 centerin' rin' 3" x 12" balsa at 3/32" launch lug and recovery system as necessary for safe operation

Intro:

When I read about t' kit-bask theme o' DESCON-X, ya bilge rat, I thought it would be a good idea t' try several stagin' and clusterin' ideas that I had been thinkin' about. Ya scallywag! Begad! My first idea was t' build a "sleeper" Gemini DC by makin' t' rocket appear stock while usin' a 24 mm center engine mount with two outboard 18 mm mounts. Well, blow me down! Begad! Simulations indicate that air stagin' an E9 t' two C6-7's would result in an altitude o' about 1000 meters. Lots o' fun! So I purchase a couple o' G-DC kits. Aye aye! Before they arrived, arrr, shiver me timbers, I saw another G-DC at Orangeburg that was very similar. In this case, matey, t' basher used t' standard 18 mm center mount and two 13 mm outboards. Begad! On t' way home, matey, reconsiderin' my approach, me hearties, arrr, I thought t' sleeper approach was probably too common and that someone else would probably do it. Blimey! I still have most o' t' g-dc parts from one kit and an unopened kit. I'm thinkin' about puttin' t' two together t' make a Modroc with four outboardsa

Another idea I've been considerin' is stagin' a D t' two or three B's or C's. My theory is that if thar be a moderate separation betwixt t' stages, the burn through from t' D will ignite all o' t' sustainer engines. Unfortunately, I needed a larger tube than be in t' parts list for my concept, shiver me timbers, shiver me timbers, so I started thinkin' about stagin' a cluster t' single sustainer engine. Arrr! Begad! Then I thought about aimin' t' burn through o' t' boosters at the sustainer engine. Avast! This is how t' Vector concept originated. Ya scallywag!

Design:

A concern in Vector's conceptual design was what would happen if one o' the engines in t' booster cluster didn't ignite. Begad! So, in order t' make Vector stable even in t' event o' ignition failure, t' thrust o' each booster was directed at t' center o' pressure. Ya scallywag! If one (or two) o' t' booster engines failed t' ignite, shiver me timbers, t' Vector addition o' t' remainin' engines would have an axial component (makin' t' rocket go up) and a tangential component through the C_P (makin' t' rocket go horizontal). Well, blow me down! Well, blow me down! In theory if this occurred, ya bilge rat, t' rocket would remain stable and vertically orientated; however, it would also "walk" horizontally. Ya scallywag! Avast, me proud beauty! When describin' this rocket t' my engineer buddies, shiver me timbers, one o' them told me that after a nominal flight, shiver me timbers, I would have to intentionally launch t' rocket on only two booster engines. Ahoy! This inadvertently happened on t' first flight (see flight reports.)

Booster Construction:

In order t' Siamese t' three BT-20 booster tubes together, shiver me timbers, they must be cut with t' proper shape. Ahoy! I solved t' intersection o' t' three tubes numerically and plotted them with me printer t' be used as a guide (see below). T' scales are in inches. Aye aye! Each booster tube is 6" long, but if you overlap the cutout area you can get 4 from an 18" tube. Begad!

Cut a ¾" length o' BT-20 from t' scrap pieces. Avast, me proud beauty! Glue t' BT50-20 centerin' rin' flush on one end. Avast, me proud beauty! Aye aye! Glue each o' t' three BT-20 booster tubes to the ¾" length o' BT-20. Arrr! Blimey! T' top o' t' booster tubes should touch the BT50-20 centerin' ring. I used tape t' keep t' booster tubes aligned while the glue cured.

After t' glue attachin' t' tops o' t' booster tubes has cured, me hearties, glue the joints where t' three booster tubes meet. Begad! After this glue has cured, use a ¼" wide strip o' tissue paper t' reinforce t' joints and t' plug any small holes.

Cut a 2" length o' BT-50 for t' booster shroud. Well, blow me down! Cut two ¼" holes (on opposite sides o' t' tube) centered 5/16" from t' end (I used a hole punch). Begad! Begad! Blimey! This end will be t' top end o' t' booster shroud. Avast, me proud beauty! Blimey! Blimey! Test fit the booster shroud by slidin' it over t' BT50-20 centerin' ring. Arrr! Begad! Blimey! T' bottom o' the booster vent holes should be flush with t' centerin' ring. Arrr! Begad! Blimey! Glue t' booster shroud on by applyin' glue t' t' centerin' rin' and t' area o' t' booster tubes when t' shroud touches.

Left: booster fin plotted on ¼" grid. Avast, me proud beauty! Aye aye! T' left side of the booster fins guide be t' leadin' edge. Ya scallywag! Ahoy! Cut t' fins so that t' grain is parallel t' t' leadin' edge. Arrr! i suggest that you lay out t' sustainer fins first though. Glue t' booster fins t' t' booster tubes so that t' trailing tip is flush with t' bottom o' t' booster tube. Avast! Arrr! Use some thinned fill-n-finish t' smooth out t' joints, paint, me bucko, and t' booster is ready for flight.

Sustainer Construction:

T' sustainer is a straightforward 3fnc (three fins and a nose cone) design. I used a D12-7 for t' sustainer motor, shiver me timbers, but I fly on a huge sod farm. Ahoy! If your field is limited, matey, you may want t' modify t' design t' use an 18 mm motor mount.

T' main body tube is 13 3/8" long. I added 2 oz o' weight t' t' nose cone t' further increase stability and t' reduce t' altitude. Avast, me proud beauty! Blimey! Even with the additional 2 oz, Vector Sims t' 2300' with (3) b6-0 booster and a D12-7 sustainer motors! Blimey! Place t' launch lug at t' center o' mass with engines loaded.

Sustainer Booster

Vector loaded for bear

Vector Flight Data:

To prep Vector for launch, ya bilge rat, arrr, friction fit t' D12-7 sustainer motor into the sustainer leavin' about ½" exposed. Begad! Wrap ¼" tape several times around t' bottom o' t' B6-0 booster motors and then friction fit t' motors into t' booster tubes. Avast, me proud beauty! Test fit t' booster on t' sustainer. T' booster should nay fall off under when holdin' t' sustainer; however, me bucko, shiver me timbers, it should nay take too much additional pull t' remove. Avast, arrr, me proud beauty! Add tape t' t' D12-7 to adjust t' fit.

Left: Vector on t' pad. Note clusterin' whips. Avast!

T' first launch o' Vector was at t' February 9^th ICBM launch at Orangeburg, SC. Avast! It be windy, and I waited all day, shiver me timbers, but t' wind never died down. Aye aye! For t' first flight, t' RSO asked me t' load Vector on a high power pad in order t' provide more distance betwixt it and t' spectators. Arrr! Begad!

At ignition, ya bilge rat, shiver me timbers, I thought all three booster engines lit (later I found only 2 did) t' boost was straight with some weathercocking. Begad! Booster separation was good, me bucko, me hearties, t' D12 lit, matey, me hearties, matey, and Vector was almost out o' sight. Ya scallywag!

A premature ejection caused t' parachute t' strip, but t' sustainer tumbled down safely with t' nose cone attached.

When I approached t' booster I noticed two blue objects on the ground. Avast! I thought t' myself, "not good" upon closer inspection, apparently only two booster motors lit on t' pad. Aye aye! When t' sustainer lit, the thrust lit t' third booster motor from t' top, burnin' t' booster into two pieces. Ahoy! Ahoy! In t' above photo, it is obvious that t' booster motor on t' left never developed thrust out o' its nozzle, ya bilge rat, yet t' propellant was consumed. Ahoy! Avast, me proud beauty! It never occurred t' me that could have happened I needed a new booster, but at least I knew t' Vectored thrust worked and t' rocket be stable on only two booster motors.

When I rebuilt t' booster, I decided t' build two, me hearties, ya bilge rat, just in case. I flew Vector t' second time on May 11, again at O'burg. Avast! Again, it be windy and I waited most o' t' day, but t' wind never let up, so I swapped t' 'chute for a streamer. Ahoy! Again, I used (3) B6-0's for t' booster and a D12-7 for the sustainer. This time t' RSO let me launch from t' model rocket pads. Ahoy! At this close range, t' Vectored thrust was very noticeable. Avast! It was obvious all three boosters were lit and Vector was screamin' straight up. At about 200' the sustainer lit and Vector momentarily went out o' sight. Ahoy! When I re-established tracking, me bucko, Vector was on t' streamer and recovery be nominal.

Lessons Learned:

T' canted, me hearties, Vectored motor design is unique and generated a lot o' interest at t' launch. Avast! T' Vectored thrust is pretty cool t' see. T' insure successful cluster ignition, arrr, it may be a good idea t' use better igniters. Arrr! Ahoy! For t' second flight, shiver me timbers, matey, me bucko, I soldered leads onto t' solar igniters as I think t' wire whips failed on t' first flight. It may also be a good idea t' paint t' inside of the booster with high heat paint.

Finally, ya bilge rat, as I mentioned earlier it may be a good idea t' use an 18 mm motor for t' sustainer on t' other hand, for t' next launch, me bucko, I plan t' use (3) C6-0's for t' booster and a E9-8 for t' sustainera