X-Git-Url: https://git.gag.com/?p=web%2Fgag.com;a=blobdiff_plain;f=rockets%2Fairframes%2Fyikstik%2Findex.html;fp=rockets%2Fairframes%2Fyikstik%2Findex.html;h=f1ffbaca21ca15aa8d16ef145cb05d36f29b1ef9;hp=0000000000000000000000000000000000000000;hb=1b116422c87b65852cb182cd3e9e2e51ce3e2b64;hpb=b0983420373ee74d8dbcf7dbffb689d369a133e2;ds=sidebyside diff --git a/rockets/airframes/yikstik/index.html b/rockets/airframes/yikstik/index.html new file mode 100644 index 0000000..f1ffbac --- /dev/null +++ b/rockets/airframes/yikstik/index.html @@ -0,0 +1,835 @@ +
Copyright © 2008 Bdale Garbee
+ This document is released under the terms of the + + Creative Commons ShareAlike 3.0 + + license. +
Revision History | |
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Revision 1.2 | 12 January 2009 |
+ Document firmware bug in miniRRC2 and possible impact on flight. + | |
Revision 1.1 | 5 December 2008 |
+ Remove embedded images in favor of references to gallery.gag.com + | |
Revision 1.0 | 28 October 2008 |
+ Recording results of first, and only, flight attempt. + | |
Revision 0.5 | 27 September 2008 |
+ Building checklists + | |
Revision 0.4 | 17 September 2008 |
+ Documenting the build process as it happens + | |
Revision 0.3 | 29 March 2008 |
+ Incorporate ideas from James Russell during initial L3CC review + | |
Revision 0.2 | 27 March 2008 |
Cleaned up for initial review | |
Revision 0.1 | 16 March 2008 |
Initial content |
Table of Contents
+ Please note that I stopped adding photos to this document at some + point. I have many more photos of the YikStik build, but haven't + decided how best to present them yet... update coming someday! +
Table of Contents
+ This is the rocket I'm designing for my NAR Level 3 certification flight. + The general idea is to build a fairly cheap rocket capable of reliably + flying this year's Aerotech level 3 special, which is an M1297W reload. + I'd like to be able to fly the prototype of my own altimeter design, and + to be able to fly it often on smaller / cheaper reloads at launch sites + with modest waivers like Hudson Ranch. +
+ I want to experiment with vacuum bagging carbon fiber reinforcements, and + intend to use my CNC milling machine to cut all the centering rings, etc. + The new Giant Leap "Dynawind" tubing feels like a good choice, and if we + stick to the 4 inch version we can use a cheap plastic nosecone to keep + the cost down. +
+ Preliminary analysis suggests that a roughly 8 foot rocket made from 4 inch + airframe with a 75mm mount and three fins should fly to something around + 14k feet on the M1297W, could break three miles on the M1850W, and yet + could safely fly on reloads as small as a J for economical fun. Those + altitudes mean the certification flight will need to be at a site with a + high-altitude waiver like the NCR north site. +
+ I've always thought the high-gloss red paint job on one of my son's rockets + when out on a launch rod in the sun looks a lot like glistening wet + lipstick. +
+ Combine that with the fact that my wife who isn't fond of the stuff + refers to lipstick as "yik stick"... and the rest should be obvious. +
+ My planned paint scheme is a bright red nosecone, gold tube, and black fin + can, which is the mental image I have of what lipstick applicators look + like, most likely from a stick my mother or one of my grandmothers had + when I was a child. +
Table of Contents
+ YikStik is a fairly simple "three fins and a nose cone" dual-deploy + rocket using a 75mm motor mount, 4 inch glass-wrapped phenolic airframe + with zipperless fin can, plastic nose cone, plywood fins, + and lots of glass and carbon fiber reinforcing. + The primary electronics bay will be designed to + hold two altimeters, and a distinct payload bay may carry an + experimental altimeter, GPS receiver, and downlink transmitter. +
+ I intend to cut the airframe components from two 48 inch lengths of + 98mm Giant Leap Dynawind tubing. The 30 inch main bay and 18 inch drogue + bay will be cut from one length, while the 33 inches of fin can, 2 inches + of electronics bay, and 8 inches of payload bay will be cut from the + second. +
+ The fins are designed from scratch, and I intend to build them up from + two layers of 1/8 inch birch plywood, three layers of carbon fiber, and + two layers of 6 oz glass. The stack will be glass, carbon fiber, + plywood, carbon fiber, plywood, carbon fiber, glass. The edges of the + plywood will be routed to give a modified airfoil shape to the finished + fins. The stack will be laminated using West Systems epoxy products + and vacuum bagged. + The shape is a compromise between mass, surviving Mach-transition stress, + optimal stability margin, and avoiding damage during handling and on + contact with the ground during recovery. +
+ The fins will be locked in to milled slots in two of the centering rings, + and will be epoxied to the motor mount with glass reinforcing tape. + The airframe will be slotted to allow the completed motor mount / fin + assembly to be inserted from the rear, with fillets of epoxy applied + inside and outside the airframe after insertion. +
+ All centering rings and bulkheads will be custom machined from 3/8 inch + birch plywood using my 3-axis CNC milling machine. Some rings will use + laminated pairs of 3/4 inch total thickness to enable use of threaded + inserts for 1/4-20 rail button screws or deep routing for fin alignment + slots. +
+ I will embed three 8-24 T-nuts in the aft centering ring spaced to allow + the use of home-made Kaplow clips to retain 75mm motors. + The same holes may be used to attach custom motor mount adapters for + smaller diameter motors. +
+ The recovery system will feature dual redundant barometric altimeters + in an electronics bay similar to the LOC design located between the + drogue and main parachute bays. +
+ A PerfectFlite MAWD will be flown as the primary altimeter and to + record the flight altitude profile. + A MissileWorks Mini-RRC2 will fly as backup altimeter and to + directly capture max velocity. +
+ Each altimeter will have a separate battery and power switch. A 4PDT + slide switch will be used as a SAFE/ARM switch configured to interrupt + connectivity to the ejection charges. +
+ I hope to fly + + my own altimeter design + + as a payload in a short payload section just behind the nose cone. + I have acquired the pieces to add a GPS receiver and RF downlink using + ham radio frequencies to the payload to track the rocket's position + during flight. + This is not essential to fly, + but could make recovery simpler and would just be fun to fly if I can + get it all working and suitably ground and/or flight tested in time. +
+ This design has been thoroughly analyzed using + + RockSim + + with motors ranging from the + Cesaroni J285 through the Aerotech M1850W and appears to be + unconditionally stable across that range. The lowest margin is around + 1.2 seen with the M1297W planned for my level 3 certification flight, + albeit with many masses still only roughly estimated. +
+ These simulations will be refined as the build proceeds and as-built + stability verified before flight. +
+ The Aerotech M1297W reload should carry this vehicle without ballast + to just over 14 thousand feet AGL. It should make over 16 thousand + feet AGL on an M1850W, and should fly stably to roughly 2.5k feet AGL + on a Cesaroni J285. +
+ Hitting optimal mass on the largest motors may require + ballast, depending on final build weight. + My plan is to fly without ballast on the certification flight, + trading some altitude for a slower and softer recovery. + If the cert succeeds, then I might try an optimal mass + flight sometime later on an M1850W or equivalent "bigger M" + reload to join the "three mile club". +
+ The recovery system will use dual redundant barometric altimeters firing + black powder charges. + At apogee, a drogue chute will deploy from just forward of the fin can, + with size selected for an approximately 100 ft/sec descent rate. + At a preset altitude, a main chute will be deployed to achieve recovery + of the bulk of the rocket at under 20 ft/sec. + The main chute will be packed in a deployment bag, configured as a + "freebag" and pulled out of the airframe by a second drogue chute. This + drogue will recover the nosecone and deployment bag separately from the + remainder of the rocket which will recover under the main. +
+ I intend to sew the parachutes from scratch using a design documented by + + Team Vatsaas + + using 1.9oz rip-stop nylon and 550 lb parachute cord. + If time runs short, equivalent chutes from SkyAngle, + Rocketman, or Giant Leap could be substituted (at significantly higher + cost). +
+ The deployment bag will probably be purchased from Giant Leap. The + recovery harness will probably use tubular kevlar, also from Giant Leap. +
+ The recovery system attachment points will all use 1/4 inch u-bolts with + nuts, washers, and backing plates through bulkheads except for the fin + can. The fin can has insufficient room between the motor mount and + the airframe inner wall for nuts and washers, so an alternative means of + recovery system attachment is required. The fin can will be equipped + with either a 3/16 inch stainless steel aircraft cable loop, or a loop + of 1/2 inch tubular kevlar, bonded to the motor mount. + If available, a screw-eye attached to the forward motor closure may be + used instead of or in addition to this recovery attachment loop. +
Table of Contents
+ I have collected all of my + + build photos + + in one place, they may show better than I can explain how various + aspects of YikStik went together. +
+ The tubing for the airframe, couplers, and motor mount was all cut + using a carefully aligned and adjusted power mitre saw, and the ends + lightly sanded to remove rough spots. + The main and drogue bays were cut from one 48 inch length of Giant + Leap 98mm Dynawind tubing, the fin can, electronics bay, and payload + bay were cut from the second. The three couplers for the fin can, + electronics bay, and payload bay were cut from Giant Leap 98mm phenolic + coupler stock. And the motor mount was cut from Giant Leap 75mm + phenolic airframe stock. + Note that the motor mount is the longest piece because of + the zipperless design with full-length motor mount. +
+ The airframe tubing selected includes a wrap of 10oz glass in epoxy + over the base phenolic tubing (visible in some photos as a + shine on the outside of the tubing), + but the coupler stock is unreinforced. + To ensure the couplers can handle the anticipated loading, I reinforced + each with one layer of interior carbon fiber, using the "kitchen + vacuum bagging" technique documented by + + John Coker. + +
+ This was my first hands-on experience working with carbon fiber. The + end of the coupler nearest the unit during bagging experienced some + crushing of the fibers right at the end. It doesn't matter for this + project because each of the couplers will have at least one end fitted + with a bulkhead or centering ring, but in the future I'll be tempted + to cut the coupler stock a bit long before bagging and trim to length + after reinforcing to get "perfect" ends. The technique worked + marvelously otherwise, and the resulting couplers look and should work + great! +
+ Six pieces of 1/8 inch birch plywood were stacked, edge-aligned on what + would be the fin root edge, and clamped. The outline of the fin design + was marked in pencil, and three 1/8 inch holes drilled through the + stack inside the fins to allow using 4-40 screws and nuts to hold the + blanks together while making the initial cuts, so that they would all be + matched in size. The clamps were removed to avoid interference + during cutting. The fin outline was then cut using a radial arm saw. +
+ A router table with 1/8 inch + roundover bit was then used to round over the outer edge, 3 blanks on + one side and three on the other. This edge might have been left square, + but I prefer the look and feel of rounding. The router table with a 1/2 + inch diameter straight cutting bit and a fin beveling jig was used + to impart a 10-degree bevel on the leading and trailing edge of each fin + blank, again 3 on one side and three on the other. The resulting 6 + blanks thus form 3 pairs of fin components with a modified + airfoil shape. +
+ The fin assembly started with a simple lamination of two layers of ply + sandwiching a layer of carbon fiber. Each fin used "one pump" of West + Systems epoxy and the stack was vacuum bagged using the Foodsaver with + wide bagging material. To keep everything flat while the epoxy cured, + the stack of fins was sandwiched between two unused extra shelves for + a storage cabinet I had on hand + (particle board covered in laminate, very + flat and smooth, nearly inflexible at this loading), and stacked with + about 75 lbs of loose barbell weights. +
+ On one of the three fins, the plywood layers are out of alignment by + 1-2mm in the longest axis. The other two are nearly perfect. Light + sanding should allow me to match them before laminating the outer layers + of carbon fiber and glass. +
+ After the fins cured, they were bulk sanded with medium and fine + sandpaper and an electric palm sander. Final sanding of the leading + and trailing edges was done using 400 grit paper on a flat surface, + holding the fin the way you'd sharpen a knife against a stone. The + results seem good, all three fins match pretty closely. +
+ A fin holding jig was cut from 1/8" hardboard using my rotary tool + with a fiber cutoff wheel. The fin slots were made to be a snug fit. + A small batch of epoxy was used to apply a bead to the root edge and + tab at the leading edge, then the fins were installed against the + motor mount and locked into place with the jig to cure. The centering + ring that locks the aft edge of the fins was dry-fit during this + operation to ensure proper alignment, but was not glued yet. It will + go on after the airframe and internal fin filets are installed. +
+ The fins were reinforced with fiberglass and epoxy. Masking tape was + used to carefully delineate where the airframe ID will be, then 6oz + glass 14.25" by 3.5" was epoxied fin-fin across the MMT. Strips of + 8.6oz "boat tape" fiberglass were worked into the joints with more + epoxy, and a sheet of plastic covered by ziplog bags of water were + used to hold things in place during the initial curing. The three + sides were done one at a time and allowed to cure before proceeding. + The results look good, and in combination with internal and external + airframe filets should yield a super-strong fin can. +
+ Pairs of 3/8 inch birch plywood blanks were laminated using Titebond + wood glue and clamped while curing to form 3/4 inch blanks for centering + rings. From a strength perspective, 3/8 inch should suffice, but there + are two reasons for going with thicker blanks in some places. The first + is that the rail buttons chosen use 1/4-20 mounting screws, and threaded + inserts in that size are nearly 3/8 inch outside diameter + (and thus would + tear up a ring only 3/8 inch thick on insertion). The second is that I + like to mill slots in the centering rings on each end of the fins to + "lock" the fins into position. Doubling the blanks used to cut those + rings will allow me to cut 1/4 inch deep fin slots and still have a half + inch of unmolested wood in the rings for strength. +
+ The aft centering ring and the one just aft of the zipperless + coupler section were edge-drilled for the installation of brass + 1/4-20 threaded inserts to hold rail buttons. The inserts were + locked in place with epoxy, then ground down until nothing protruded + beyond the OD of the ring. +
+ The forward two centering rings were installed on the MMT using + JB Weld high-temperature epoxy, and incorporating an aircraft cable + loop for recovery system retention since there just wasn't room for + u-bolts. +
+ The ring at the leading edge of the fins was initially installed + assuming the aft ring would be nearly flush with the rear of the MMT + and equipped with Kaplow-clip style retainers, but before the fins + were installed a Giant Leap Slimline Tailcone Retainer for 75mm motor + in 98mm airframe became available thanks to Tim Thomas, and so this + ring was cut out and replaced with another one inch farther forward + to allow installation of the tailcone at the rear of the MMT. I + really like the tailcone on my Vertical Assault kit, and think it'll + work out to be a great addition for this rocket! +
+ An alignment jig for the fins was carefully marked out and then cut + from 1/8 inch hardboard using my rotary tool and abrasive cutoff wheel. + The fins were then epoxied at the root and short leading edge to the + motor mount tube and into the slots in the forward centering ring, + and held rigidly aligned by the jig until the epoxy set. The fins + were then masked at what would be the ID of the airframe tube, and + reinforced with 6oz glass fin-fin across the motor mount tube between + each fin pair, further reinforced with strips of 1 inch glass "boat + tape" at each fin root joint. +
+ The airframe tubing section was carefully marked for fin slots, which + were then cut using my rotary tool with abrasive cutoff wheel. Epoxy + was applied ahead of the center two rings as the frame was slid into + place, and the frame left standing upright until the epoxy set to + hopefully form ring-fin fillets on those two rings. The interior + fin to airframe joints were reinforced one fin at a time using West + Systems epoxy will milled glass as a filler. A long 3/8" dowel was + used to place and smooth these interior filets. The aft centering ring + was installed by pouring West Systems epoxy in the three fin-fin gaps, + placing the ring, then standing the airframe up to allow the epoxy to + flow over the forward surface of the ring and into the gaps between it, + the motor mount, and the airframe tubing. After it set, the booster + was placed nose-down, the airframe gaps behind the fins were taped, + and more epoxy was applied to seal the aft of the ring to the tubes. + Before this epoxy set, JB Weld was used to glue the tail cone retainer + in place on the MMT. +
+ The exterior fin to + airframe joints were filleted using 5-minute epoxy thickened with + baby powder and smoothed with the tip of a plastic spoon, which I + learned about building the Vertical Assault kit. Gives great results, + and allowed all 6 joints to be done in one session. The space + above the top surface of the forward centering ring and between the + motor mount and zipperless-design coupler tubing was filled with epoxy + and milled glass. Minor gaps in the airframe behind each fin were + filled with epoxy clay. +
+ The avionics bay contains the two commercial altimeters used to + record information about the flight and deploy the drogue and main + recovery systems. It is constructed of a piece of Giant Leap 98mm + coupler tubing reinforced with an interior wrap of vacuum-bagged + carbon fiber, and a 2 inch length of Giant Leap 98mm DynaWind airframe + tubing. +
+ The bulkheads are custom-milled from 3/8 inch birch plywood + milled so that about 3/16" fits inside the coupler and the remainder + seals the end of the coupler and just fits inside the airframe. Each + bulkhead has a u-bolt for attaching the recovery harnesses, and dual + CPVC end caps as ejection charge holders with screw terminal blocks + from Missile Works to attach the igniters. Two lengths of 1/4 inch + all-thread with nuts and washers tie the bulkheads together, with + wing-nuts used on one end to allow for easy disassembly. +
+ A sled was fabricated to hold the altimeters and batteries. It + consists of 1/8 inch birch ply laminated with 6oz fiberglass on each + side, epoxied to cardboard tubes taken from the packaging for Aerotech + igniters that slide over the all-thread, further reinforced with nylon + ties at each end. The tubes are staggered one on either side so that + the sled goes right up the center of the airframe tubing. +
+ Two "centering rings" containing three each 6-32 threaded inserts are + epoxied inside the bay to provide hard points for attaching the + airframe tubes for the drogue and main recovery bays. The inside + diameter of these rings is notched for the avionics sled, and thus + these rings also provide physical support for the sled. +
+ Three rotary switches from Missile Works are installed through the + short airframe tubing section, drilled such that they end up + essentially flush with the outside of the airframe, clamp the coupler + tubing, and project inside the bay. Two are wired as SPST switches + for power to the two altimeters, the third is wired as a DPST switch + that open-circuits the igniters for the required "safe/arm" function + called for in the NAR L3 certification requirements. +
+ The wiring of the avionics bay is documented in the attached + schematic diagram. Connectors were used to allow each bulkhead and + the switches in the housing to be quickly detached from the sled. + The connectors are 9-pin D shells for the switch wiring, and 4-pin + Molex connectors like those used on older PC hard drive power cables + for the bulkheads. To allow use of a single switch pole for the + safe/arm function for each altimeter, the two igniters attached to + each altimeter are safed by interrupting the common return lines as + shown in the schematic. +
+ Sizing the static port for the avionics bay was done by applying the + formulas suggested by PerfectFlite and Missile Works for their + respective altimeter products, then comparing the results with each + other and with information found on the web. I've personally had + better luck with single ports than with multiple holes, perhaps because + I've been working with relatively small rockets. Regardless, I'm + sticking with what I know and will use a single static port hole here. +
+ The measured dimensions + of the avionics bay as constructed are 95mm ID and approximately 250mm + between bulkheads. This works out to 108.73 cubic inches before + accounting for the volume of the sled, electronics, and wiring and + other components inside the bay. By the PerfectFlight formula, the + static port should be 0.221 inches in diameter. By the Missile Works + formula for a bay over 100 cubic inches the answer is 0.261 inches. + The closest standard drill size, which happens to split the difference, + is 0.250 inches. Easy enough! +
+ The construction of the payload bay is very similar to the avionics + bay, except that there is a hard-epoxied rear bulkhead, and only one + screw ring to hard-mount the nose cone. The forward end of the + payload bay is open to the open interior volume of the nose cone in + anticipation of extending downlink antennas above the carbon fiber + reinforcement in the coupler and into the nose cone, since carbon + fiber is opaque to RF. +
+ Pre-sewn 1/4 inch tubular kevlar harness sections were purchased + from Giant Leap, along with a small kevlar deployment bag and two + kevlar chute protectors. +
+ For an apogee drogue, I plan to fly a Public Missiles 4 x 144 inch + nylon streamer. It will be protected with one of the kevlar blankets + and attached to one of the kevlar harness sections holding the booster + to the avionics bay. +
+ The main parachute will be sewn from 1.9 oz rip-stop nylon purchased + from the + + Mill Outlet Fabric Shop + + in Colorado Springs. Using the spreadsheet from + + Team Vatsaas + + I calculate that we want an 8 foot chute to keep the airframe less + nose cone and payload bay below 20 feet per second at touch-down. +
+ To extract the main chute and recover the nose cone and payload bay, + a 3 foot parachute from BSD Rocketry will be packed in a kevlar + blanket ahead of the main chute deployment bag, attached by kevlar + harness to the nose cone and payload bay assembly, and to the top of + the deployment bag. This assembly will recover separately from the + rest of the rocket. +
+ The altimeters are programmed such that the MAWD fires its drogue + charge at apogee and its main charge at 1100 feet. The miniRRC2 + is programmed to fire its drogue charge two seconds past apogee, + and its main charge at 900 feet. Thus the MAWD is primary and the + miniRRC2 is the backup. Since the M1297W has a burn time of about + 5 seconds, mach inhibit is programmed on both altimeters to 8 seconds. +
Table of Contents
+ This rocket uses dual deployment. +
+ The apogee event separates the + airframe between the zipperless-design booster section and the + drogue bay. These two sections are linked by a Giant Leap 20 foot + pre-sewn 1/4 inch tubular kevlar assembly, attached to which is a + Public Missiles 4 x 144 inch red nylon streamer packed in a Giant Leap + kevlar chute protection pad. +
+ The main event separates the airframe between the forward payload bay + and the main bay. Attached to the nose cone and payload bay assembly + is a Giant Leap 15 foot pre-sewn 1/4 inch tubular kevlar assembly, + attached "free bag" style to the top of a Giant Leap deployment bag + containing the main chute. A 36 inch BSD Rocketry nylon parachute + packed in a Giant Leap kevlar chute protection pad serves to pull the + deployment bag off the main chute, after which it allows for safe + recovery of the nose cone and payload assembly at just under 20 feet + per second. +
+ The 8 foot main chute is home-made from 1.9 oz rip-stop nylon using + the design documented by + + Team Vatsaas. + + It is attached to the remainder of the rocket using another Giant Leap + pre-sewn 1/4 inch tubular kevlar assembly. +
+ The anchor points are all 5/16 inch u-bolts, except for on the booster + which is equipped with an embedded loop of 3/16 inch stainless aircraft + cable. All connections are made with suitable quick-links. +
+ The LOC-style avionics bay between the main and drogue bays is + populated with two commercial altimeters, a PerfectFlite MAWD + and a Missile Works miniRRC2. + Each is powered by a dedicated 9V battery, and has a + dedicated on/off power switch mounted for access from outside the + rocket. Additionally, a single safe/arm switch with two poles is used + to interrupt the return circuits from the igniters to each altimeter. + See the attached schematic of the avionics bay contents for more + details. +
+ The bulkheads at each end of the avionics bay have two CPVC end caps + for ejection charge holders, and two-terminal screw blocks for + attachment of electric matches purchase from Giant Leap used to ignite + Goex 4F black powder ejection charges. Each charge holder and terminal + block pair is labelled as to main or backup since the charges will be + different for each. +
+ The + + Info Central Black Powder Sizing + + page is the most authoritative site I've found on this topic. + Each of the main and drogue bay interfaces will use 2 2-56 nylon screws + as shear pins, each of which needs 35 pounds of force or so to shear. + Designing for 15psi puts us between 150 and 200 pounds total force in + a 4 inch airframe. The formula is thus 0.006 grams times diameter + squared in inches times length in inches. +
+ My drogue bay is 3.9 inches ID and 8 inches long, or 95.52 cubic + inches. That works out to about 0.73 grams. However, there will be + some volume in the motor mount tube above the motor that also must + be accounted for, enough to nearly double the total volume when flying + on the M1297W certification motor. Also, since this charge must fire + reliably at 15-18k feet above ground level of around 5k feet, such + that combustion is likely to be incomplete, we need to add some margin. +
+ My main bay is 3.9 inches ID and about 25 inches between bulkheads, + or about 298.50 cubic inches. That works out to 2.28 grams. +
+ Sanity checking, PerfectFlite recommends that a 4F black powder charge + be sized by multiplying the volume of the bay in cubic inches by 0.01 + grams. That yields about 1.8 grams for the drogue bay and 3 grams for + the main bay. +
+ That suggested to me that a good starting point for ground testing is + 1.5 grams for the drogue bay and 2.5 grams for the main bay. Ground + tests were done using the PC interface cable for the MAWD routed in + through the static test port to manually trigger ejections. Testing + of the apogee bay showed that 1.5 grams was sufficient for deployment + and 1.8 grams was more authoritative. A single test of main deploy + with 2.5 grams gave a nearly perfect result. + Given the altitude of our expected apogee, we should be generous with + the apogee charge, perhaps using 2.0 grams for the primary. The main + will deploy at an altitude below where the tests were performed, so + no adjustment in charge size should be required. +
+ Descent rate of the nose cone and payload bay which mass just under + 1kg will be less than 20 feet per second with a 36 inch chute based + on manufacturer recommendations and Rocksim v8 simulation. + Descent rate of the remainder of the rocket under the 8 foot chute + should be about 18 feet per second by the spreadsheet provided by + the designers of this chute pattern, sanity checked using the descent + rate tables of similar commercial parachute designs, like those from + The Rocketman. +
+ Simulation using Rocksim v8 with a variety of motors showed that the + rocket is unconditionally stable with all motors likely to be flown. + The worst-case stability among 75mm motors is actually with the + M1297W chosen for the certification flight, at margin 1.05. This is + because the front of this motor falls almost exactly at the CP. Using + a longer motor like the M1850W raises the initial stability margin to + 1.10 because the front fuel grain is ahead of the CP, and lesser + motors also increase the stability because less mass is behind the CP. + The smallest motor I can conceive of flying in this rocket (a Cesaroni + J285) would leave us overstable with margin 3.79 on the way to about + 1800 feet apogee. +
+ On the certification flight, using an Aerotech M1297W reload and + associated hardware, the anticipated apogee is round 14,700 feet. This + is just under 75% of the NCR North Site standing waiver of 20,000 feet. +
+ The highest altitude simulated would be achieved with an Aerotech + M1850W reload at nearly 18,000 feet. The lowest altitude simulated + is with a Cesaroni J285 and Slimline adapters to just over 1800 feet. +
+ add description of anticipated flight profile here, including launch + weight, estimated drag coefficient, velocity leaving the rail, max + expected velocity, altitude, and acceleration +
+ YikStik was flown on an M1297W on Saturday morning at NCR's Oktoberfest + 2008. The boost was beautiful. Unfortunately, we lost visual as the + rocket climbed into high clouds near apogee. Radio tracking signals + remained strong for several minutes, then disappeared. We were + confused by viewing what we thought was YikStik descending before + signals were lost in about the right direction, but now believe we + were actually watching a previously launched rocket and did not see + YikStik descend. This confusion prevented location of any of the + rocket until Sunday evening, after I had left the launch area. +
+ After an extensive search, the nose cone assembly was finally found + with the Walston tracking gear nearly 3.5 miles down range. The + remainder of the rocket has not been found despite extensive searching + on the ground and from the air. +
+ Reward if returned posters were placed in the area during the week + following the launch but have elicited no useful reponses yet. +
+ Consideration of how the nose cone ended up where it did suggests + we may have had an apogee deployment of the main, perhaps due to + stress on the shear pins before launch, during boost, or during + apogee drogue deployment causing them to break early. +
+ It is unfortunate that we were confused by seeing another rocket + descending about the expected amount of time after YikStik's launch + in approximately the right direction. This caused us to believe that + the rocket was much closer than the nose cone turned out to be, causing + us to waste a lot of time searching in an area too close to the launch + site. + It also caused us to assume something really weird had happened to the + transmitters, such that the tracking signal was suddenly lost long + after the rocket was on the ground, instead of what seems to really + have happened, which is that the rocket was farther away descending + after a main deployment at apogee, and the loss of signal was simply + due to dropping below a ridge line a couple miles from the launch site. + I can't help but think that if we'd been + looking in the right area sooner after the launch that we might have + found the rocket before someone else apparently picked it up. +
+ I regret the decision to use a "free bag" configuration of the + deployment bag. + Since both tracking transmitters were in the payload bay behind + the nose cone, and we were eventually able to recover that portion + of the rocket, it is possible that if the deployment bag were tethered + to the main that we might have recovered the remainder of the rocket. +
+ If the rocket is recovered and able to fly again, the two changes I + would like to make are to tether the deployment bag to the apex of the + main, and to move from 2-56 nylon screws to 4-40 nylon screws for the + main deployment shear pins, ensuring the holes through the airframe + are a loose enough fit to avoid stresses on the pins during boost. I + have no way to know what happened for sure, but believe this might + solve the assumed problem of main deployment at apogee. +
+ All in all, the design and build process was educational, and a lot + of fun! I'm looking forward to fabricating more custom parts using + carbon fiber and vacuum bagging in the future. + The beautiful boost and obvious survival of the rocket airframe + through the expected mach transitions confirms my design and + construction skills are adequate to attain an L3 cert. + While I hope to recover the remainder of YikStik someday, I won't + waste any time before trying again with a new airframe! +
+ [update] We have learned that one of the altimeters used in this + flight, the Missile Works miniRRC2, was subject to a fault in + firmware that could cause premature ejection of the main + in flights above 10k feet. Thus, it now seems even more likely + that we sustained an apogee ejection of the main, but that it + may well have been through no fault of the rocket's design, + construction, or preparation. Frustrating! +