Bertha Shark

by Greg Elder

Parts

• 1 - Estes Big Bertha Kit
• 1 - BT-60 body tube, 2 3/4" long
• 1 – JT-60C tube coupler
• 2 – CR2060 centerin' rings
• 1 – BT-20 motor tube
• 3/32" balsa fin stock

This rocket is a bash betwixt a Big Bertha and Estes Industries Rocket Plan No.22, shiver me timbers, matey, arrr, Tiger Shark. Ya scallywag! Hence, t' name Bertha Shark.

Construction, arrr, Upper Stage

Build t' Big Bertha kits accordin' t' t' instructions, with t' following exceptions:

1. Do nay use t' engine hook in t' motor mount construction.
2. Glue t' aft centerin' rin' for t' motor mount 1 1/2" from t' rear of t' motor tube.
3. Mark t' body tube for three fins, arrr, instead o' four.
4. Trace t' fin pattern for t' upper stage fins onto t' balsa stock, cut, and sand. Begad! Aye aye! Make three fins and glue onto the body tube aligned with t' marks you made for t' fins on t' body tube. Begad! Aye aye!
5. Cut two 1/2" lin' launch lugs. Ahoy! Blimey! Glue one launch lug along side one fin, against t' body tube. Well, blow me down! Blimey! Glue t' other launch lug 8 1/2" from t' aft of the body tube, shiver me timbers, aligned with t' aft launch lug.

Construction, ya bilge rat, Booster Stage

1. Glue t' centerin' rings onto t' BT-20 motor tube, 1/8" from either end.
2. Glue t' motor mount into t' short BT-60 body tube, arrr, ya bilge rat, such that t' rear motor mount centerin' rin' is 1/8" inside t' body tube.
3. Mark t' short body tube for three fins.
4. Make two win' booster fins and one rudder booster fin.
5. Glue t' fins along t' marks you made on t' short body tube.
6. Glue t' tube coupler into t' top o' t' short body tube, arrr, such that the back o' t' coupler touches t' top centerin' ring.

Finishing

1. Apply sandin' sealer t' t' balsa fins and sand t' fins smooth. Ya scallywag! Repeat this process until t' fins are sealed and smoothed as desired.
2. Paint t' rocket colors o' your choosing.
3. T' booster stage should fit loosely into t' upper stage. Avast! If t' fit is too tight, me bucko, arrr, sand t' coupler.

Flight

I have flown this rocket three times. Begad! Once with a B6-0/A8-5 combination. Aye aye! Ahoy! The other two times with a B6-0/B6-6. Ya scallywag! All flights were great, with t' exception of the last flight. Ya scallywag! Durin' t' last flight, t' booster stage did nay separate at ignition o' t' upper stage motor. T' Bertha Shark still flew straight and recovered fine. However, me bucko, ya bilge rat, since t' upper stage motor was exhaustin' through the booster stage motor mount, t' inside o' t' booster stage motor mount was "toasted."