Brief:
T' Estes EST 2157 1/100th Scale Saturn V is quite a nice rocket kit. Avast! Oh sure, matey, its scale accuracy is nay all that great, ya bilge rat, arrr, but it is readily available (at least as o' this writing), reasonably priced at under $100 (with significant discounts available), large enough t' be impressive, shiver me timbers, nicely detailed, and nay terribly difficult t' build. Begad! But it has one major shortcomin' - it is woefully underpowered with its 24mm mount. Arrr! Even an AeroTech E will only loft this Saturn V t' perhaps 300 feet (although it looks and sounds darn impressive gettin' there). Begad! Avast, me proud beauty! So I decided t' solve t' Saturn V energy crisis and built one with a 29mm engine mount - I figured it should be able t' get out o' it's own way with an F or G motor.

Construction:
Obviously, arrr, I started with an Estes Saturn V kit - actually I started with two Estes Saturn V kits. Ahoy! I built two Saturn Vs at t' same time, one a "display" model, ya bilge rat, which I kept very close t' box stock, and t' other t' "flyer" with t' 29mm motor mount as well as various upgrades. Arrr! Well, blow me down! This two at once technique yielded some advantages - I could pick and choose, usin' t' 'best' parts on t' display model. Also, me bucko, matey, arrr, t' 'stock' display model provided a baseline on t' rocket CG that was quite helpful when it came time t' balance t' flyer.

In addition t' t' Estes kit, I needed a 29mm, 15" long engine mount tube (note that this engine mount tube was 1.5" shorter than stock), me hearties, 29mm engine block, ya bilge rat, and engine hook (from AeroTech). Avast, me proud beauty! I didn't think t' flimsy vacuum formed fins and fin fairings and that fragile escape tower would stand up t' t' higher impulse, arrr, so I contacted Mike Schmidt and got a set o' "Moldin' Oldies" cast resin fin-fairin' assemblies and Apollo capsule. Ya scallywag! Ya scallywag! Blimey! I added a length o' 5/16" aluminum tubin' t' use as an internal launch lug, me hearties, and I tossed t' stock parachutes and shock cords into t' spare parts box, replacin' them with nylon 'chutes and Keelhaul®©™ shock cords.

Modifications:
To build t' engine mount, matey, I started out with t' stock centerin' rings, enlargin' t' center hole for t' 29mm mount tube. Aye aye! I then took t' top and bottom centerin' rings, and laminated 1/64" plywood t' both sides o' t' rings - cut t' plywood t' size, matey, glue t' t' centerin' rin' with yellow glue, wrap in waxed paper, and place under some heavy books t' dry. Blimey! After installin' t' engine block and hook but before I glued t' (laminated) centerin' rings on t' stuffer tube, I stacked t' centerin' rings and drilled a 11/32" hole through all three for t' internal launch lug, with t' outside edge o' t' hole 1/8" in from t' outside edge o' t' rin' (to clear things like t' coupler t' t' upper stage). Arrr! When I glued t' centerin' rings t' t' stuffer tube, I used t' aluminum tube t' insure alignment o' t' holes. Begad! Avast, shiver me timbers, me proud beauty! Gussets were then cut from t' scrap centerin' rin' card stock and glued in place t' support t' centerin' rings. Blimey! Blimey! After attachin' a ten-foot length o' .100" diameter Keelhaul®©™ shock cord t' t' front o' t' engine mount, t' whole assembly was liberally filleted with yellow glue.

When I epoxied t' motor mount into t' main body tube, me hearties, I located it an additional inch forward from aft end (4 3/8 inches, rather than t' stock 3 3/8 inches) t' help keep t' rocket CG as far forward as practical. Blimey! I also fit pieces o' 1/8" thick balsa betwixt t' main body tube and t' upper and lower extensions o' t' internal launch lug, me bucko, and epoxied those in place. Note that t' shorter engine mount tube allowed me t' move t' engine forward, me bucko, while preservin' an adequate parachute volume for t' large nylon parachutes.

Construction o' t' remainder o' t' Saturn V was pretty standard. A Keelhaul®©™ shock cord was added t' t' 2nd stage - 3rd stage transition durin' assembly. Well, blow me down! T' wraps were aligned such that t' internal launch lug would exit in t' large black section o' t' 2nd stage - 3rd stage transition wrap (to make it less visible). Arrr! T' wraps were attached usin' t' recommended 3M Super 77 spray adhesive, arrr, then t' edges were sealed used t' Apogee thin CA technique (somethin' o' a belt and suspenders approach). Ahoy! Aye aye! Since they require no assembly, me bucko, ya bilge rat, t' cast resin fin-fairings are much easier t' deal with than t' stock vacuum formed plastic. After sandin' t' proper contour (usin' coarse sandpaper wrapped around t' BT101 body tube), shiver me timbers, I simply glued t' resin fin-fairings t' t' bottom wrap with CA, and then added epoxy fillets. Well, blow me down! T' "extra" BT101 coupler was used as a reinforcin' rin' t' prevent t' upper third stage assembly from slippin' aft into t' lower section.

For recovery, in addition t' t' fore mentioned Keelhaul®©™ shock cords, I replaced t' stock Estes 'chutes with nice nylon parachutes and increased t' 'chute areas t' compensate for t' higher weight - a (single) 36" 'chute for t' lower section, me hearties, and a 24" 'chute for t' upper section. Begad! I maintained t' harness arrangement for t' upper section, me bucko, shiver me timbers, again usin' Keelhaul®©™ line for t' harness.

Flight:
I used t' display model that I was buildin' at t' same time t' do a CG check - prepped with a D12-3 (but unpainted) t' CG was 23" aft o' t' tip o' t' capsule (that is pretty much even with t' aft edge o' t' ullage motors). Avast, me proud beauty! I also used RockSim t' check t' CP, which came out 25" (Barrowman) or 26.3" (RockSim) aft o' t' Apollo capsule tip. Begad! I epoxied 3.5 ounces o' lead shot into t' resin capsule, which provided a CG 22" aft when flight prepped with a G64 RMS (the heaviest engine I ever expected t' use), arrr, givin' a nice margin o' stability. T' completed Saturn weighed in at 19 ounces - 12 oz. Begad! for t' lower section, 7 oz. for t' upper section (includin' t' 3.5 ounces o' lead ballast in t' capsule).

For t' maiden flight, arrr, me hearties, I selected an F40-4W RMS. Avast, me proud beauty! Blimey! It was magnificent - t' Saturn ripped off t' pad with t' characteristic roar and smoke o' a White Lightnin' motor. Aye aye! Aye aye! Blimey! It climbed t' about 500 feet, hung thar for second before it slowly arced over, matey, then came back t' earth ballistic. That's right, shiver me timbers, a complete lawn dart - t' ejection charge never fired. Worse, since it be an RMS, it was probably me fault although I don't know what I might have done wrong (I've launched a large number o' RMS motors and this be t' first time t' ejection charge has failed t' fire). Aye aye! Blimey! T' impact utterly destroyed t' upper half o' t' rocket (basically everythin' down t' t' inter-stage wrap). Avast, me proud beauty! Surprisingly, me hearties, t' resin Apollo capsule was t' exception - it survived almost unscathed, just a (easily repaired) break in t' escape tower (although it took a couple minutes t' dig t' capsule out o' t' crater). Arrr! Begad! Blimey! T' engine mount held up surprisingly well - t' forward bulkhead was broken into several pieces and t' upper couple inches o' t' engine tube were buckled by t' impact - but t' rest o' t' mount be undamaged.

Summary:
While I'm naturally unhappy about t' untimely demise o' me 29mm Saturn V, shiver me timbers, I consider t' modification a complete success. Avast! T' engine mount demonstrated impressive strength in survivin' t' impact, so it should easily hold up t' t' 'normal' forces o' numerous 'F' and 'G' powered launches. Avast! Begad! T' 22" CG location provided a highly stable launch (in fact I could probably get away with less nose ballast), me bucko, and t' launch with an F engine be spectacular (so be t' descent, me bucko, but for t' wrong reasons). Avast! While this Saturn is damaged beyond "economic repair", I've salvaged t' resin fin-fairings and Apollo capsule, shiver me timbers, and construction has already started on another 29mm Saturn V.