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. Ya scallywag! Begad! Recovery is nose first, ya bilge rat, makin' t' rocket appear t' be comin' in upside down. I call it Ahtreb, which is Bertha backwards.

Essentially t' motor mount assembly is nay glued into t' body tube, matey, 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! Blimey! 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, plus:

• 12" o' BT-20 coupler tube stock
• 4" o' BT-60 coupler, me bucko, cut into 3 pieces--1.5", 1.5", & 1"
• 2 20/50 centerin' rings
• 1 mylar chute kit
• Small piece o' thin, arrr, me hearties, flexible plastic or vinyl approx. Blimey! 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. 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! Blimey! Blimey! Blimey! Plannin' for all situations, 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. Avast! Wrappin' t' chute with a sheet o' paper, just as t' protector used durin' building, arrr, makes this easy t' get started. Avast, me proud beauty! Arrr! Then, after pullin' out t' paper, gently pushin' t' remainin' chute and shrouds into t' tube while workin' t' piston forward, matey, ya bilge rat, completes t' process. Ya scallywag! No waddin' is required; t' piston protects t' chute and shrouds from ejection gasses. Well, blow me down! Begad! At ejection, t' piston moves from fully forward against t' thrust rin' t' rearward, arrr, where air flow opens t' chute. If t' piston did nay move fully back against t' thrust ring, matey, t' deployment will force this.

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

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

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

Third flight was on a C6-3. Begad! Blimey! Boost be t' same as previous flights except higher, but deployment be very early, causin' deployment at high speed and tearin' t' chute. 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, 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, arrr, 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.