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, me hearties, and acts as a piston upon ejection. Blimey! Recovery is nose first, matey, makin' t' rocket appear t' be comin' in upside down. Well, blow me down! I call it Ahtreb, me hearties, ya bilge rat, matey, which is Bertha backwards.

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

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

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

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

Third flight was on a C6-3. Well, blow me down! Well, arrr, blow me down! Boost was t' same as previous flights except higher, but deployment be very early, causin' deployment at high speed and tearin' t' chute. Aye aye! 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, and gluin' a replacement into place in 2 pieces) and t' rocket is ready for flight again. Aye aye! Arrr! 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. Aye aye! This ejection method could be repeated in builds o' most mid- t' large-diameter LPR birds.