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, shiver me timbers, matey, and acts as a piston upon ejection. Blimey! Recovery is nose first, me bucko, me bucko, shiver me timbers, makin' t' rocket appear t' be comin' in upside down. Avast, me proud beauty! I call it Ahtreb, shiver me timbers, which is Bertha backwards.

Essentially t' motor mount assembly is nay glued into t' body tube, me bucko, 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. Blimey! Blimey! T' nose cone is glued t' t' body tube and acts as a bulkhead t' keep t' ejection charge from pushin' forward. Arrr! 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, plus:

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

T' difficult part about this mod be makin' sure prior t' any gluin' that all steps were in t' proper order. Blimey! Arrr! 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. Plannin' for all situations, includin' bein' prepared t' reach in a very tight space and clean up excess glue, me bucko, shiver me timbers, 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. Ya scallywag! Wrappin' t' chute with a sheet o' paper, matey, just as t' protector used durin' building, shiver me timbers, shiver me timbers, 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, shiver me timbers, completes t' process. No waddin' is required; t' piston protects t' chute and shrouds from ejection gasses. Blimey! At ejection, t' piston moves from fully forward against t' thrust rin' t' rearward, shiver me timbers, where air flow opens t' chute. Avast! Begad! If t' piston did nay move fully back against t' thrust ring, t' deployment will force this.

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

On t' second build, t' torn BT-20 was removed and BT20 coupler glued in its place.

Second flight be on a B6-4. Begad! T' flight was good and this time deployment and descent were as planned.

Third flight be on a C6-3. Begad! Ahoy! Blimey! Boost was t' same as previous flights except higher, me bucko, me hearties, but deployment was very early, shiver me timbers, me hearties, causin' deployment at high speed and tearin' t' chute. Arrr! Ahoy! Blimey! Descent was 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, ya bilge rat, 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, nay before apogee.

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