Brief:
Flippitwin is an unusual two stage rocket from Aerocon Systems. Blimey! Blimey! It uses the unusual folding-fin rocket Flippifin sold separately as a single stage rocket as t' sustainer. T' sustainer is boosted by a booster tube and t' sustainer squirts out o' t' tube when t' sustainer motor is fired. Begad! Blimey! Arrr! Blimey! Because t' booster comprises t' bulk o' t' two stage rocket, t' booster must have a separate recovery system necessitatin' t' use o' electronics for stagin' and optionally for recovery.

Construction:
Bob Fortune sells t' kit with or without a flight computer and recommends that the kit is designed t' work well with t' inexpensive G-Wiz LC computer, ya bilge rat, an accelerometer-based computer which does nay have a barometric sensor. I purchased t' G-Wiz LC computer since this be t' be me first use of electronics in a rocket and I did nay already own a suitable altimeter or timer. Ya scallywag! T' kit came packed in a large mailin' tube with all t' parts in perfect condition and a couple o' extra military surplus chutes and a "Remove Before Flight" flag as extra treats thrown in.

I spent some time puzzlin' over t' instructions, shiver me timbers, tryin' t' recognize any hidden complexities in t' design. Ya scallywag! Begad! I had previously built Flippifin so I went straight for t' booster construction. Begad! Aye aye!

T' kit contains 3 sections o' 38mm phenolic tubing. Arrr! A long piece is the forward end o' t' booster and houses t' sustainer rocket. Ahoy! T' medium length piece be t' aft end o' t' booster which takes t' 29mm motor mount and fins. A stubby piece is part o' t' avionics bay (Av-Bay) which acts as t' coupler between t' two larger sections o' t' booster. An assortment o' screws and centerin' rings are included so that everythin' needed t' make t' booster is ready t' go. Avast! Begad!

T' instructions were clear. Avast! Blimey! I dry fit all pieces and everythin' matched up perfectly. Arrr! Blimey! In a few places they suggest doin' things "best way", which I took t' be code for "don't worry, you'll figure it out". Aye aye! Blimey! With a few nimble twists and turns o' t' brain I managed t' stumble upon the appropriate workable solutions and enjoyed fiddlin' with t' construction. Contrary t' t' instructions, I left t' attachment o' fins until t' very last but this makes no difference in t' end. Avast, me proud beauty! Blimey! T' fins mount t' t' booster using surface mount technique which is perfectly adequate. I used 20-minute epoxy throughout t' build and gave t' fins a beefy fillet. Avast! Well, blow me down! Blimey! T' kits comes with some unique shock cord material which I recognized from me previous experience with Flippifin. I like t' material (called fiberglass tow I think), but I thought that t' booster recovery harness needed t' include about 3 times as much shock cord so I substituted 20 feet o' Keelhaul®©™® cord. It later proved t' be a challenge t' get t' entire recovery system stuffed into t' bottom part o' t' booster as t' extra cord added some extra bulk.

T' construction o' t' Av-Bay be t' most important part o' booster construction and Bob makes this very simple. Blimey! Aye aye! In addition, matey, arrr, all o' t' parts fit so well that it was hard t' go wrong. Blimey! When finished, t' Av-Bay should contain a minimum o' one peephole for viewin' t' power indicator light on t' flight computer (the front sight hole). Since t' computer does nay use a barometric sensor, me bucko, me hearties, t' sight hole does nay need t' act as a vent hole, so presumably there are other possible construction techniques that could be employed in t' Av-Bay construction. I chose t' drill two more holes in t' Av-Bay so that I could also view t' two aft pyro channel indicator lights on t' flight computer. At the time o' launch I forgot t' look at these, shiver me timbers, but since everythin' went well, I assume that I did nay miss much. Begad! Begad! I mounted t' computer on t' small length of aluminum angle as suggested. Begad! T' length o' angle was perhaps 1/8 inch too long, so it did nay allow t' front Av-Bay closure t' fit securely. T' instructions suggest shavin' t' aluminum angle down until you get a perfect fit. Ya scallywag! I chose instead t' carve an angle shaped recessed groove into t' front Av-Bay closure with a pocket knife until I had a very tight fit. Aye aye! In t' end, t' front closure fit snuggly and t' groove centered t' computer in t' Av-Bay, ya bilge rat, ya bilge rat, holdin' it slightly away from t' walls o' t' tube. Avast, me proud beauty! When t' rocket is fully assembled, the forward Av-Bay bulkhead just sits in place, pressed in place by a thrust rin' that is installed up inside t' forward section o' t' booster. Well, blow me down! Begad! I opted to use two small screws t' secure t' front section o' t' booster t' t' Av-Bay, but t' instructions suggest that tape could be substituted and I agree that tape should work fine.

After completin' construction o' t' booster, I began t' puzzle over how to actually prepare t' booster and Flippifin for flight. Ahoy! T' flight computer is intended t' sense booster motor burnout and ignite t' sustainer motor from pyro channel 1. Ahoy! Avast! T' flight computer stays in t' booster section. T' booster is then recovered either by t' booster motor ejection charge or by the addition o' an ejection charge controlled by t' flight computer which senses booster apogee and fires pyro channel 2. I had no experience in t' use of avionics, shiver me timbers, but I had a distinct impression that thar should be a way t' arm the system after puttin' t' rocket on t' pad, me bucko, rather than traipsin' around the prep area with a fully armed rocket. Arrr! Blimey! I chose t' add a computer controlled booster section ejection charge, matey, me hearties, thus creatin' redundant ejection for the booster. T' sustainer ejection would come from t' sustainer motor. Begad! Blimey!

I did nay have any sort o' switch t' attach t' t' power supply for the flight computer, shiver me timbers, me hearties, so I decided that I would wire t' live computer t' t' two e-matches out on t' pad. Avast! This meant that for t' sustainer igniter needed a wire comin' from t' computer and hangin' outside o' t' booster and the booster ejection charge needed a wire comin' from t' e-match t' t' outside. Thus, I drilled an extra hole in each o' t' upper and lower sections o' the booster for each o' these connections t' be made by twistin' wires together on the outside o' t' rocket. Avast, me proud beauty! Only later did it occur t' me, me hearties, after someone else suggested it t' me, me bucko, shiver me timbers, ya bilge rat, that a simpler arrangement would involve a simple spliced power supply wire. Avast, matey, me proud beauty! However, me arrangement o' wires hangin' on t' outside of the booster gave me an advantage in that I had control over all wires from the outside o' t' rocket durin' assembly, so I could easily tug on t' wires durin' assembly and avoid gettin' t' wires snagged or bunched up in the process.

Overall, arrr, t' Flippitwin booster construction was straightforward and enjoyable. Well, blow me down! I do nay discuss t' construction o' t' sustainer here, but Flippifin construction is also a great deal o' fun. Avast! Aye aye! Any mildly adventurous person who has at least a minimum o' model buildin' experience can easily construct both t' booster and t' sustainer. In me experience Flippifin has proven t' be a rugged and very nice rocket, me hearties, arrr, so I believe that Flippitwin will also provide many enjoyable launches.

Finishing:
I finished t' booster only a few days before a scheduled club launch so I decided that I did nay have time t' paint it. Well, blow me down! Well, blow me down! I built t' Flippifin sustainer that came with t' kit, makin' this me second Flippifin rocket but I did not paint it either. This was a mistake, since I decided t' fly t' unpainted Flippifin as a single stage rocket later in t' day and ended up losin' the unpainted brown tube out on t' brown dirt somewhere in t' desert. Avast! A quick bit of fluorescent paint would have made a big difference in recoverin' it.

Construction Rating: 5 out o' 5

Flight and Recovery:
T' instructions suggest an F20 booster and a D12-7 sustainer. Aye aye! In t' end I was a wee bit concerned that t' liftoff weight might be bit a too much for the F20, so I went with an Aerotech F50-6 single use booster motor instead. Ahoy! My concern be probably unjustified, since t' liftoff weight turned out t' be 848 grams and t' F20 should be able t' handle that. Begad! Ya scallywag! I be comfortable knowin' that the higher initial thrust o' t' F50 would certainly give a nice straight boost so that upon sustainer ignition it was unlikely that t' rocket would be pointin' anywhere but straight up. Ahoy! Normally an Estes D12 motor is underpowered for a Flippifin single-stage flight, matey, matey, but in this case, me bucko, I could see that it should serve well for a sustainer motor. Avast, me proud beauty! I followed t' recommendation and used a D12-7 for t' sustainer.

I prepped t' sustainer as I normally would t' Flippifin for single stage flight. Blimey! I used tape motor retention on t' D12-7 then sprinkled some black powder into t' nozzle when I installed an e-match as t' igniter. Well, blow me down! Begad! I taped the e-match securely in place (holdin' t' black powder in place too). Begad! Avast! I slipped the sustainer down into t' upper part o' t' booster, arrr, threadin' t' e-match wire out t' side hole, arrr, shiver me timbers, just in front o' t' Av-Bay thrust ring.

I prepped t' aft section o' t' booster by first slippin' t' F50-6 motor in from t' aft and usin' maskin' tape motor retention. Begad! I then used a micro centrifuge tube t' contain some black powder for t' ejection charge and taped an e-match in through a hole in t' tip. I slipped t' ejection charge down into t' top o' t' motor mount tube so that it sat on top o' t' motor. Arrr! I threaded t' e-match wire out through t' extra hole that was drilled in the lower booster section, just aft o' t' Av-Bay. I then stuffed a hefty bit of crumbled cellulose insulation into t' tube as recovery wadding, ya bilge rat, then stuffed in all t' Keelhaul®©™® shock cord that I had substituted for t' recovery harness that came with the kit. Avast, me proud beauty! I then folded t' chute and stuffed it as far down in t' tube as I could get it. Ya scallywag! It was obvious t' me that I would have t' press t' entire recovery system into t' tube about as tight as I could get it in order t' allow the Av-Bay t' slip in place. Well, me hearties, blow me down! I should also note that I had never made a black powder ejection charge before. Begad! I vaguely recalled people talkin' about black powder in terms o' grams and that ejection charges were typically made up of somethin' like a gram or so o' black powder. Arrr! Avast! Havin' no clear idea o' how much black powder t' use, ya bilge rat, I filled t' micro centrifuge tube all t' way up. Aye aye! It looked t' me as though this amounted t' a lot more powder than comes with a typical Aerotech H or I motor reload. I decide t' dump t' powder out and weigh it. Ahoy! It tipped t' balance at almost 3 grams. Ahoy! I backpedaled and put only 1 gram of powder back in t' tube and decided that would be me ejection charge. Aye aye! The recovery system occupied virtually every cubic millimeter o' t' lower booster section which is only about 6 inches o' 38mm tube. Begad! I be told later that adding a 1 gram ejection charge on top o' t' charge already present in t' single use motor (0.7 gram?) was probably a bit excessive. Begad! Avast, me proud beauty!

I prepped t' Av-Bay by first removin' t' #2 jumper on t' LC computer which specifies stagin' rather than cluster ignition and t' computer gives repeated double flashes o' t' front indicator light. I attached t' battery and taped it in place. Aye aye! I put a jumper betwixt pins 5 and 7 as per instructions. I then put a 1 foot length o' wire from pyro channel 1, me bucko, out through t' center hole in t' front Av-Bay bulkhead, adjusted t' length and taped over t' front of t' hole where t' wire came through t' bulkhead. Begad! I then put a 1 foot length o' wire from pyro channel 2 out through t' aft Av-Bay bulkhead and taped it over too. Avast, me proud beauty! Ahoy! I jiggled t' forward Av-Bay bulkhead into place, ya bilge rat, adjusting wire tensions fore and aft and securin' t' protective tape bits. Ya scallywag! I threaded the wires out through t' side ports in t' fore and aft booster sections as I got t' Av-Bay in place. Begad! Then I installed t' 2 screws which hold t' forward booster section securely t' t' Av-Bay, shiver me timbers, securely closin' t' Av-Bay in the process. Ya scallywag! Avast, ya bilge rat, me proud beauty!

T' entire preparation took me a couple o' hours. Well, blow me down! Blimey! I felt pretty lucky in gettin' it all together while supervisin' me 4 and 9 year olds while they entertained guests in t' car and climbed out t' sunroof t' watch as rockets were bein' launched. Aye aye! Blimey! Their tiny fingers actually came in handy a couple times when I asked them t' help me adjust t' wires when assemblin' t' booster.

I placed Flippitwin on t' pad, matey, trimmed t' four wire pairs t' about 2 inches each and stripped t' ends. Ahoy! Blimey! I twisted t' pairs as needed and taped the ends securely t' t' airframe and taped over t' associated holes. Ya scallywag! I then installed t' igniter, arrr, ya bilge rat, gave t' countdown and turned t' key.

T' flight was flawless. Blimey! T' boost be fast and booster motor burnout was probably at about 400 feet. T' sustainer squirted out o' t' tube and went straight and fast t' perhaps 1500 feet. T' booster ejection charge was triggered by t' flight computer. Begad! It be supposed t' sense apogee and fire the charge. Begad! This happened pretty smartly and I was watchin' t' sustainer at the time, so I am nay sure, but it seems like t' ejection charge fired before apogee but I could be wrong. Arrr! T' computer indicated that apogee had been at 459 feet upon recovery. Ahoy! T' ejection charge certainly fired before t' 6-second motor delay had elapsed. Ahoy! Arrr! T' ejection charge probably ignited t' black powder charge contained in t' motor at t' same time. At any rate, matey, thar was enough of a blast t' kick t' motor which landed next t' t' launch pad despite having been taped in very securely. T' booster assembly recovered perfectly and touched down long before t' sustainer. Well, blow me down! T' sustainer ejected near apogee and recovered nicely on a small mylar chute that I had used in Flippifin single stage flights before.

T' ejection charge probably created enough force t' snap t' 20 foot Keelhaul®©™® recovery harness t' t' limit and it appears as though t' upper booster section and Av-Bay slammed back into t' front edge o' t' lower booster section, ya bilge rat, matey, crackin' some o' t' phenolic. This will be easy t' repair. Ya scallywag! T' tape seal on t' forward Av-Bay bulkhead be inadequate t' fully protect t' flight computer from t' motor ignition gases and flames when t' sustainer lit. Blimey! Blimey! I don't think t' computer was damaged in any way, but thar was clearly a small amount o' soot on t' computer and in t' Av-Bay. Aye aye! Well, arrr, blow me down! In t' future I will think of some better method o' sealin' t' forward Av-Bay bulkhead.

Flight Rating: 5 out o' 5

Summary:
T' overall Flippitwin experience was one o' me most enjoyable t' date. Ya scallywag! Blimey! Ahoy! Blimey! I am a huge fan (belly girth notwithstanding) o' Flippifin and t' added complexity and performance o' Flippitwin be gratifying. Well, blow me down! Blimey! This is a quirky rocket that really performs well. It is a real attention grabber at any launch. I am naturally plannin' t' go up in power a bit for upcomin' flights.

Overall Rating: 5 out o' 5