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

Essentially t' motor mount assembly is nay glued into t' body tube, arrr, shiver me timbers, 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! T' nose cone is glued t' t' body tube and acts as a bulkhead t' keep t' ejection charge from pushin' forward. Blimey! 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, shiver me timbers, cut into 3 pieces--1.5", me bucko, me bucko, 1.5", & 1"
• 2 20/50 centerin' rings
• 1 mylar chute kit
• Small piece o' thin, shiver me timbers, arrr, flexible plastic or vinyl approx. Well, blow me down! 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. Ya scallywag! 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. Avast, me proud beauty! Well, blow me down! Blimey! Plannin' for all situations, shiver me timbers, includin' bein' prepared t' reach in a very tight space and clean up excess glue, ya bilge rat, 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, ya bilge rat, me hearties, just as t' protector used durin' building, me hearties, me hearties, makes this easy t' get started. Aye aye! Then, me bucko, after pullin' out t' paper, gently pushin' t' remainin' chute and shrouds into t' tube while workin' t' piston forward, arrr, arrr, completes t' process. Ahoy! Well, ya bilge rat, blow me down! No waddin' is required; t' piston protects t' chute and shrouds from ejection gasses. Blimey! Avast, me proud beauty! At ejection, t' piston moves from fully forward against t' thrust rin' t' rearward, matey, me bucko, where air flow opens t' chute. If t' piston did nay move fully back against t' thrust ring, me bucko, arrr, t' deployment will force this.

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

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

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

Third flight was on a C6-3. Avast! Boost was t' same as previous flights except higher, shiver me timbers, 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, and gluin' a replacement into place in 2 pieces) and t' rocket is ready for flight again. Well, ya bilge rat, blow me down! 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. Well, blow me down! Ya scallywag! This ejection method could be repeated in builds o' most mid- t' large-diameter LPR birds.