Push-Me, Pull-Me
A DesconX Entry
(Contributed - by Nick Esselman)

Wow, shiver me timbers, did time sneak up on me or what? I wanted t' design and build a rocket for this Descon but kept puttin' it off. Then it be May and I hadn't started. Well, blow me down! Arrr! So it was time t' get busy. I have a great design and unique from all t' other entries. Blimey! Avast! Not extremely sophisticated but definitely functional. Well, me bucko, blow me down! And, I was finally able to fly it this weekend. Arrr! So here goes......

My design is a two-stager. Avast! Avast! It has a cluster-motor booster to a single-motor sustainer. Blimey! Ahoy! I'm always afraid o' staged-rockets because o' the potential altitude (and me relatively small field), me hearties, so I decided t' add a feature t' create more drag. Well, blow me down! I named t' rocket Push-me, Pull-me. Blimey! Blimey! T' motors "push" while t' big cone-fin increase t' drag "pull".

Get t' RockSim file here.

As with t' other entries, I have started with t' Estes Gemini DC. Arrr! T' followin' steps are what I used t' build t' rocket:

SUSTAINER:

1. Assemble t' 18mm Motor Mount but do nay install the motor hook and install t' upper centerin' rin' flush with t' top o' t' motor tube and t' lower flush with t' bottom o' t' motor tube
2. Install t' Motor Mount into t' main body tube until the mount is recessed 1/4" into t' body tube
3. Tie t' two elastics together and attach inside the upper open o' t' body tube usin' Estes 3-fold method
4. Assemble t' nose cone and tie t' other end o' the elastic t' t' nose cone
5. Attach 1 o' t' two parachutes
6. Remove t' fins and install into t' fin slots (cut as needed t' miss t' Motor Mount centerin' rings)
7. Cut t' launch lug in half and install one 1/2" from bottom and t' other 3" from top on t' body tube

BOOSTER:

1. Glue t' two 18mm side-pod tubes together side-by-side and equal in length, ya bilge rat, holes facin' out
2. Cut each o' t' side-pod nose cones in half (actually it is a bit more than 1/2, arrr, me bucko, but you can trim as you go)
3. Cut 1/2" tabs that overlap and are glue together at the top o' t' side-pod tubes (see picture)
4. Glue t' 1/2's o' t' side-pod nose cones into the side-pod tubes so that they are aligned exactly t' t' outer edge
5. Trim both NC's down until t' unit slides onto t' Sustainer and betwixt two fins easily (my guess is that thar be about 40% o' t' nose cone remaining
6. From t' Estes Insert Card, cut out a transition that will be used as a fin-cone. T' transition has an upper diameter o' 1.473" and a lower diameter o' 4.375" and a length o' 3.75"
7. Attach t' fin-cone t' t' two pod-tubes ensurin' good glue joints where t' fin-cone touches t' pod-tubes (only t' outside edges). T' cone bottom should be flush with t' bottom o' t' pod-tubes
8. Usin' some o' t' remainin' Estes Insert Card, ya bilge rat, cut two pieces that will be glued into t' tops o' t' pod-tubes t' "funnel" the exhaust gases toward t' center o' t' Sustainer. This is t' help ensure the upper motor lights
9. Epoxy t' inside o' t' booster's top section t' protect it from t' sustainer motor.
10. NOTE: Don't do anythin' with t' holes that are in the sides o' t' pod-tubes, ya bilge rat, these are necessary for good gap-staging

For finishing, shiver me timbers, I went with t' quick-and-ready approach so that I could get t' rocket flown before t' deadline. I painted the sustained Navy blue. Begad! I could/should have applied some o' t' decals but didn't. I painted t' booster orange.

FLIGHT:
I used friction-fit on all t' motors. Avast! Aye aye! T' sustainer was loaded with an A8-3. This is pushed in until it is even with t' sustainer tubing. T' booster was loaded with two B6-0's. Begad! These are also friction-fit until they are stickin' out about 1/2".

T' launch rod fits in t' gap betwixt t' pod-tubes and the cone-fin and then through t' two launch lugs.

Upon pushin' t' launch button both B6's lit and off she flew. Begad! It was stable and straight up until the B6 thrust stopped. Avast! RockSim suggests t' booster carried it t' ~80 feet and I would agree by sight. It seemed t' slow fast (see t' graph below and look at the change in Drag).

Then t' A8 lit and t' rocket be off. Ahoy! Well, blow me down! Direction changed slightly (5 degrees?) but it was still straight.

I saw t' ejection pop o' smoke but noticed t' nose cone did nay come out and therefore no parachute. Aye aye! It came in ballistic and thumped into t' soft ground.

Conclusion, matey, ya bilge rat, t' pre-cut exhaust ports reduced t' exhaust pressure too fast and therefore t' nose cone was nay pushed out. That is the only explanation! Blimey! I should have covered those with some o' t' scraps from the Estes Insert card.

BEFORE and AFTER:
These pictures show how I used epoxy t' protect t' booster from the sustainer's motor. Begad! You can see that it held up. Yes, it got black, but it did hold up.

NEXT STEPS:
I'm goin' t' repair this rocket, shiver me timbers, arrr, because it be a nice performer without too much altitude. Well, blow me down! It also demonstrates several rocketry techniques, ya bilge rat, including cluster, me bucko, gap-staging, and t' use o' a fin-cone. Nay bilge-suckin' from a kitbash!

These are some things that I will now do t' improve the design (goin' outside o' t' strictness o' this contest):

1. Glue a thrust rin' into each o' t' two 18mm side-pod tubes so that t' motor sticks out by 1/2"
2. Glue a thrust rin' into t' sustainer motor tube so that the motor is flush with t' bottom o' t' body tube
3. Cover t' two exhaust ports in t' sustainer body tube.

(Click t' Enlarge)