A9/A10 Two Stage Cluster Rocket

T' A9/A10 was designed t' be a 200 ton liquid fueled rocket with a range of over 5000 kilometers. Well, blow me down! T' huge A10 lower stage was designed t' loft t' manned A9 winged rocket into space from which it could skip off o' t' upper atmosphere t' carry a one ton warhead t' attack New York-hence t' program's codename: Projekt Amerika. Aye aye! T' rocket never made it beyond t' design phase when development was halted, matey, although t' Germans did some experimentation with the winged A4b.

As far as I have been able t' tell, arrr, me bucko, me bucko, this be t' first model o' t' A9/A10 combination, and perhaps with good reason! This was by far me most demanding project t' date. Arrr! Aye aye! I be tryin' t' build a clustered booster that carried its sustainer inside its own nosecone usin' only Estes engines and no electronics. Aye aye!

Brief Description:
T' most challengin' design consideration was t' recovery o' t' big A10 booster after it had launched t' A9. Arrr! Blimey! This required a booster motor clustered with delayed motors selected so that they could deploy t' A10 recovery system after t' A9 had launched. Avast, me proud beauty! Blimey! Equally challengin' be t' design o' t' A10 nose cone. Ya scallywag! Blimey! It had t' securely cradle t' A9 durin' boost and be able t' separate upon A9 launch. Blimey! Blimey!

Michael Bade's Big Bad V2 Daddy inspired t' A10. Click here t' see Michael's article

I had considered t' 4 inch Estes V2 but that has enough o' its own weight, strength, and performance issues without addin' more complexity given that I wanted t' use Estes BP motors. Arrr! T' 2.6 inch V2 was a good size and weight, ya bilge rat, shiver me timbers, but I was afraid I wouldn't have enough room in t' tailcone for clustering. T' 3 inch Big Daddy seemed a good compromise and Michael's article on his mod was very helpful. I be aimin' for a 12 ounce launch weight with one D12-0 and two 13 mm A10-3T motors. Well, shiver me timbers, blow me down! T' A9 would have an A10-3T as well. Well, blow me down! Well, blow me down!

Construction

A10 Construction
First step be t' cut t' tail cone. I cut about 5 inches from t' tip, shiver me timbers, giving me a diameter o' about 2.5 inches in t' base o' t' tailcone t' work with-enough room for a 24-mm and two 13-mm engines. Avast! Arrr! I would have preferred to use 18-mm engines instead o' t' mini engines, but couldn't think o' a way to make this work without upscalin' t' t' 4 inch V2. Ahoy! Avast, me proud beauty! I then used a Dremel tool with 3 cuttin' disks t' cut fin slots. I selected 1/8 inch balsa for t' fins and three cuttin' disks was just about t' right thickness t' require only minimal sandin' and fitting. Begad!

I used Rocksim t' design t' fin shape. Since I knew stability would be an issue, I chose t' make t' fins broader than on t' A10 drawings but still tried t' keep t' overall stylin' consistent with t' German rocket designs. Fins are through t' wall t' t' motor mount. Arrr! Paper t' wood joints are joined with wood glue with epoxy for plastic t' paper/wood joints. Avast, me proud beauty! Blimey!

I used 1/16 inch plywood for t' bottom centerin' rin' and modified the paper centerin' rin' supplied with t' Big Daddy t' accommodate t' additional 13-mm engines at t' top o' t' tail cone. Ahoy! Blimey! Begad! Blimey! I also added a 1/8 inch plywood baffle above this. Ya scallywag! Blimey! Begad! Blimey! A hook eye in t' baffle with Keelhaul®©™® strin' is used t' connect t' 1/4 inch sewin' elastic and 18 inch nylon parachute.

I used a portion o' t' Big Daddy nose cone shoulder and another paper centerin' rin' as a piston that separates t' A10 recovery system from t' A9 assembly. Basically, matey, me hearties, matey, t' idea was for t' booster engine's gases t' pass through t' piston t' ignite t' A9 while t' ejection charges from t' two 13-mm engines would blow t' piston and deploy t' A10's parachute. Powdered graphite was applied liberally t' make sure t' piston could slide freely. Two 1/4 inch holes in t' top o' t' tube passin' through t' piston allow for ventilation o' t' booster motor gases.

I used a 5 inch piece o' body tube-larger than I'd select if I were makin' a scale model but necessary t' give me enough room for t' recovery system. The rocket still seems t' have t' short, matey, stocky look o' t' real thin' with the broader fins contributin' t' this look. Aye aye!

A10 Nose Cone Construction
With t' basic booster construction complete, me hearties, ya bilge rat, I turned me attention t' t' nose cone assembly. Ya scallywag! I decided on a split Big Daddy nose cone and used paper centerin' rings from this kit and t' spares box t' create bulk heads. The first step was t' cut t' shoulder down t' about 1 inch. Begad! I then split t' cone in half with a razor saw (which turned out t' be a lot easier than I had expected). Avast! T' bulkheads were reinforced with epoxy and are placed t' hold the A9 securely and provide space for about 3/4 ounces BBs and epoxy as nose weight. Well, blow me down!

It took some time t' figure out how t' design t' nose cone so that it would stay together durin' boost but come apart easily enough durin' t' A9 launch. Begad! I contemplated various complicated sprin' arrangements, shiver me timbers, me hearties, but decided that the combination o' t' A9 acceleration and t' overpressure o' its engine exhaust would be enough t' lift out t' nose cone and force it apart. Ya scallywag! Avast! I used .020 styrene U beam, shiver me timbers, sandin' off one side o' t' U t' make an L shape on one side of the top third o' t' cone with .020 styrene on t' other side t' form a hook. Avast, me proud beauty!

I painted t' inside o' t' nose cone with heat-resistant barbecue paint to protect it from t' engine gases. Avast, me proud beauty! Ahoy!

I also used strips o' .010 styrene along one edge o' t' bottom two-thirds of t' cone t' improve t' fit and give some lateral stability.

T' nose cone halves use tumble recovery for now, but I may add streamers if necessary. Blimey! Blimey!

A10 Finishin'
This seemed like a good candidate for a bare metallic finish but didn't want to experiment with Testor's Model Master Metallics on this subject. Begad! Blimey! I selected a splinter camouflage typical o' German rockets. Well, blow me down! Blimey! T' light base coat is Rustoleum Gloss Protective Enamel light olive. Aye aye! Blimey! This is a great paint that covers well, doesn't run, ya bilge rat, me hearties, and provides a tough finish. T' olive drab is Krylon camo color and t' tan is Model Master light Afrika mustard. Ahoy! Blimey! This be me first splinter camouflage attempt and it was nay too difficult but took careful planning. The key t' these schemes is after masking, always overspray t' color you just covered t' seal any leaks in t' maskin' tape. Blimey! Blimey! All in all it turned out pretty well.

A9 Construction
Construction o' t' A9 be fairly straightforward. Avast, me proud beauty! Begad! Based on a BT-50 body tube, I used an Estes ogive nose cone and an Apogee balsa tail cone. Avast, me proud beauty! Ahoy! Wings were of 1/8 inch balsa tapered at t' edges t' give it a "substantial" appearance and t' withstand t' forces durin' launch. Rudder fins were 1/16 inch balsa. Begad! Ahoy! All fins were soaked in thin CA for strength. Avast! T' canopy is from a 1/48 scale model aircraft drop tank half. Well, blow me down! Keelhaul®©™® strin' be used for shock cord and a 12 inch plastic parachute for recovery. Avast, me proud beauty! A 3/16 inch launch lug be added, me bucko, almost as an after thought. Avast, me proud beauty! Rocksim be used for design. Avast, arrr, me proud beauty!

I hand brushed a splinter scheme over a Model Master light Afrika mustard base coat with a duck egg blue bottom color. Ya scallywag! Decals are from a 1/48 scale Me-262 plastic model. Begad!

Flight
This is a project that has numerous possible failure modes. Aye aye! Blimey! Would all engines in t' cluster fire? Would me first attempt at gap stagin' work? Would t' nose cone separate t' allow t' A9 t' fly (up)? Would t' A10 recover properly? I had been workin' on this project for over four months so when t' paint was dry and t' winds were fair, matey, me hearties, thar was really no reason nay t' go for it. Avast! Blimey! Begad! Blimey! I used a D12-0 and 2 A10-3Ts in t' booster with an A10-3T in t' A9. Begad! Blimey! Ahoy! Blimey! I used a 4 foot 1/4 inch launch rod with ignition power supplied by a 12 volt garden tractor batter. Aye aye! Blimey! Blimey! Blimey!

T' A9/A10 combination got off t' pad nicely, shiver me timbers, arcin' slightly. Begad! Rocksim said that t' D12-0 would burn out at about 160 feet. Takin' into account t' arcing flight path, me bucko, this seemed about right. Begad! T' nose cone separated and t' A9 flew on 100 percent as designed. My boys and I were stoked. Aye aye! Arrr! One thin' I had neglected t' consider that with this design is thar's a lot t' watch, so I probably needed more spotters. Avast! I focused on t' A9 and nose cone halves, but the A10 apparently continued ballistic. Well, blow me down! T' A9 recovered nominally. Aye aye! I never did see t' A10's red chute. Well, blow me down! Well, matey, blow me down!

Damage Report

T' good news is that we recovered all t' pieces. Avast! Ya scallywag! T' A9 had a small zipper, probably due t' high speed ejection. Avast, me proud beauty! Begad! T' A10 impacted "nose" first. From t' looks o' it, t' ejection charges fired an instant before impact because t' plastic baffle was driven into t' body tube. Begad! Well, blow me down! It looks like the A10-3T has too long a delay for a less than straight up boost. Ahoy! I'll need to regroup t' see if I can do anythin' t' improve t' A10 recovery. Blimey!

Reconstruction
Reconstruction was straight forward. Blimey! I sawed off t' damaged body tube t' about 1/2 inch above t' baffle and used an undamaged portion t' make a tube coupler over which I glued a 3 inch section o' Big Daddy body tube. Arrr! Avast, me proud beauty! T' piston was repaired and strengthened with epoxy. Ahoy! I considered switchin' t' 1/2A3-2Ts to shorten t' delay, me bucko, but I was concerned that t' ejection charge here would be even less than with t' A10-3Ts. Arrr! Some ground testin' was in order. Begad! Ahoy! In two tests with t' booster strapped down, two A10-3T engines ejected t' piston only once, and then weakly. I needed a plan B. Avast, me proud beauty!

Plan B: Drogue Parachute Modification
It looked like I had room betwixt t' piston and t' bottom nosecone bulkhead for a 9 inch nylon drogue. This was attached t' t' piston with a loops of Keelhaul®©™® strin' epoxied t' t' piston. Begad! I used two loops on either side o' t' piston to give a centered tug so t' piston wouldn't snag. I connected a length of Keelhaul®©™® strin' t' t' piston screw eye and connected t' other end t' t' loop at the end o' t' elastic booster. Ahoy!

Nosecone separation should expose t' drogue t' t' wind and deploy it. Avast! The drag should then pull out t' piston and deploy t' main parachute. Begad! My main concern is heat damage t' t' drogue or lines from t' vent holes. Begad! After the first flight, shiver me timbers, I could see no evidence o' scorchin' near t' holes so I reasoned that t' risk would be minimal. Blimey! Aye aye! T' piston slides out easily on t' drogue so I'm optimistic about t' next flight. Ahoy!

Summary
This be a great project in that I really went through t' complete design process from start t' finish. Ya scallywag! Ya scallywag! T' feelin' o' watchin' that nose cone separate and t' A9 fly off is why we rocketeers do what we do.