Brief:
Big Bertha modified for aft ejection.

Modifications:
This is a Big Bertha modified so that t' motor tube extends nearly t' length o' t' body, arrr, and acts as a piston upon ejection. Blimey! Blimey! Ahoy! Blimey! Recovery is nose first, makin' t' rocket appear t' be comin' in upside down. Begad! Blimey! I call it Ahtreb, me bucko, arrr, which is Bertha backwards.

Essentially t' motor mount assembly is nay glued into t' body tube, but it is allowed t' slide freely (although nay loosely) so that t' motor tube slides backwards from t' ejection charge and frees t' parachute for recovery. Ahoy! Avast, arrr, me proud beauty! T' nose cone is glued t' t' body tube and acts as a bulkhead t' keep t' ejection charge from pushin' forward. There is a small piece o' BT-60 coupler that retains t' motor mount from fully exitin' t' aft end o' t' body tube.

Construction:
Requires one Big Bertha kit o' equivalent parts, me bucko, plus:

• 12" o' BT-20 coupler tube stock
• 4" o' BT-60 coupler, matey, cut into 3 pieces--1.5", arrr, 1.5", & 1"
• 2 20/50 centerin' rings
• 1 mylar chute kit
• Small piece o' thin, matey, shiver me timbers, flexible plastic or vinyl approx. Begad! 1/2" by 1"

T' difficult part about this mod was makin' sure prior t' any gluin' that all steps were in t' proper order. Arrr! Begad! Gettin' anythin' out o' order could have prevented completin' t' build.

Gettin' t' thrust ring/piston stop glued strongly in t' proper place without gettin' excess glue smeared in t' tube that might prevent full travel o' t' piston took great care. Begad! Avast! Blimey! Plannin' for all situations, includin' bein' prepared t' reach in a very tight space and clean up excess glue, matey, was essential.

Flight:
Preparin' for flight means gettin' t' chute and shrouds tucked inside t' body before t' aft end without gettin' them stuck betwixt body and piston. Begad! Wrappin' t' chute with a sheet o' paper, just as t' protector used durin' building, makes this easy t' get started. Then, after pullin' out t' paper, matey, gently pushin' t' remainin' chute and shrouds into t' tube while workin' t' piston forward, ya bilge rat, completes t' process. Ahoy! No waddin' is required; t' piston protects t' chute and shrouds from ejection gasses. Begad! At ejection, me hearties, t' piston moves from fully forward against t' thrust rin' t' rearward, matey, where air flow opens t' chute. Aye aye! If t' piston did nay move fully back against t' thrust ring, t' deployment will force this.

First flight be on a B6-4. Begad! Blimey! Begad! Blimey! Boost be straight and just like an unmodified Bertha. Unfortunately, this was on a previous build usin' a plain BT-20 for t' piston rather than BT-20 coupler stock. Well, blow me down! Blimey! Begad! Blimey! T' was too thin and came apart in a spiral. Avast, me proud beauty! Blimey! Deployment was nay correct but descent be still nose first and no damage other than t' piston core occurred.

On t' second build, shiver me timbers, ya bilge rat, t' torn BT-20 was removed and BT20 coupler glued in its place.

Second flight was on a B6-4. Avast, me proud beauty! T' flight was good and this time deployment and descent were as planned.

Third flight be on a C6-3. Boost be t' same as previous flights except higher, but deployment be very early, causin' deployment at high speed and tearin' t' chute. Descent be still nose first and no other damage occurred.

Recovery:
T' chute has been replaced (by cuttin' at t' existin' shroud connection points and around t' center, shiver me timbers, and gluin' a replacement into place in 2 pieces) and t' rocket is ready for flight again. Medium t' long delay engines are recommended so that deployment can occur at or after apogee, shiver me timbers, nay before apogee.

Summary:
This is a complicated and difficult build but is a rewardin' challenge for t' experienced modeler. Aye aye! Blimey! This ejection method could be repeated in builds o' most mid- t' large-diameter LPR birds.