+++ /dev/null
-<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Goblin 10</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" lang="en"><div class="titlepage"><div><div><h1 class="title"><a name="id2481338"></a>Goblin 10</h1></div><div><h2 class="subtitle">A NAR L3 Certification Rocket</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Bdale</span> <span class="surname">Garbee</span></h3></div></div><div><p class="copyright">Copyright © 2008 Bdale Garbee</p></div><div><div class="legalnotice"><a name="id2736747"></a><p>
- This document is released under the terms of the
- <a class="ulink" href="http://creativecommons.org/licenses/by-sa/3.0/" target="_top">
- Creative Commons ShareAlike 3.0
- </a>
- license.
- </p></div></div><div><div class="revhistory"><table border="1" width="100%" summary="Revision history"><tr><th align="left" valign="top" colspan="2"><b>Revision History</b></th></tr><tr><td align="left">Revision 1.0</td><td align="left">15 November 2008</td></tr><tr><td align="left" colspan="2">Successful certification flight at Hudson Ranch</td></tr><tr><td align="left">Revision 0.2</td><td align="left">28 October 2008</td></tr><tr><td align="left" colspan="2">Revising during flight to DC</td></tr><tr><td align="left">Revision 0.1</td><td align="left">23 October 2008</td></tr><tr><td align="left" colspan="2">Initial content, derived from YikStik</td></tr></table></div></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#id2744045">1. Introduction</a></span></dt><dt><span class="chapter"><a href="#id2749934">2. Design</a></span></dt><dd><dl><dt><span class="section"><a href="#id2759790">Overview</a></span></dt><dt><span class="section"><a href="#id2737277">Rocksim File</a></span></dt><dt><span class="section"><a href="#id2763689">Drawing from Rocksim</a></span></dt><dt><span class="section"><a href="#id2744686">Motor Retention</a></span></dt><dt><span class="section"><a href="#id2754969">Nose Cone Electronics Bay</a></span></dt><dt><span class="section"><a href="#id2733689">Electronics</a></span></dt><dd><dl><dt><span class="section"><a href="#id2763384">Avionics</a></span></dt><dt><span class="section"><a href="#id2740504">Stability Evaluation</a></span></dt><dt><span class="section"><a href="#id2748086">Expected Performance</a></span></dt><dt><span class="section"><a href="#id2767164">Recovery System</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#id2768933">3. Construction Details</a></span></dt><dd><dl><dt><span class="section"><a href="#id2749141">Airframe</a></span></dt><dt><span class="section"><a href="#id2754017">Nose Cone</a></span></dt><dt><span class="section"><a href="#id2771414">Avionics Bay</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id2745741">4. Recovery Systems Package</a></span></dt><dd><dl><dt><span class="section"><a href="#id2740673">Recovery System Description</a></span></dt><dt><span class="section"><a href="#id2752914">Recovery Initiation Control Components</a></span></dt></dl></dd><dt><span class="chapter"><a href="#id2748101">5. Checklists </a></span></dt><dt><span class="chapter"><a href="#id2750187">6. Flight Summary</a></span></dt><dt><span class="chapter"><a href="#id2764884">7. Analysis and Conclusions</a></span></dt></dl></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2744045"></a>Chapter 1. Introduction</h2></div></div></div><p>
- This is a rocket I'm building for my second attempt at a NAR Level 3
- certification flight. It's basically a Polecat Aerospace Goblin 10 kit
- augmented with an additional electronics bay in the nose cone, some
- structural reinforcement, and incorporating a few personal build
- preferences.
- </p><p>
- Preliminary analysis suggests that it should reach just under 7k feet
- on the Aerotech M1297W reload, and could break two miles on the
- Cesaroni M795W moon-burner. This means that a certification flight can
- be supported at Hudson Ranch with the standing 8k waiver, at the Tripoli
- Colorado site under their higher-altitude window, or at either of the
- NCR launch sites under their standing waivers.
- The smallest reasonable motor for this rocket would be a Cesaroni
- K445 or equivalent, which would yield an apogee of about 2300 feet.
- </p></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2749934"></a>Chapter 2. Design</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id2759790">Overview</a></span></dt><dt><span class="section"><a href="#id2737277">Rocksim File</a></span></dt><dt><span class="section"><a href="#id2763689">Drawing from Rocksim</a></span></dt><dt><span class="section"><a href="#id2744686">Motor Retention</a></span></dt><dt><span class="section"><a href="#id2754969">Nose Cone Electronics Bay</a></span></dt><dt><span class="section"><a href="#id2733689">Electronics</a></span></dt><dd><dl><dt><span class="section"><a href="#id2763384">Avionics</a></span></dt><dt><span class="section"><a href="#id2740504">Stability Evaluation</a></span></dt><dt><span class="section"><a href="#id2748086">Expected Performance</a></span></dt><dt><span class="section"><a href="#id2767164">Recovery System</a></span></dt></dl></dd></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2759790"></a>Overview</h2></div></div></div><p>
- The Goblin 10 kit is a simple "four fins and a nose cone" rocket
- that is short and squat, with a 98mm motor mount.
- It supports dual-deploy by
- using the forward end of the long motor mount tube to hold the main.
- The primary electronics bay is between the forward two motor mount
- centering rings, accessed by a side hatch. An additional payload bay
- will be built inside the nose cone to carry experimental altimeters,
- a tracking beacon, and possibly a GPS position reporting system.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2737277"></a>Rocksim File</h2></div></div></div>
- This is the current working design in Rocksim format:
- <a class="ulink" href="Polecat_Goblin_10.rkt" target="_top"> Polecat_Goblin_10.rkt </a></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2763689"></a>Drawing from Rocksim</h2></div></div></div><span class="inlinemediaobject"><img src="Polecat_Goblin_10.jpg" height="450"></span></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2744686"></a>Motor Retention</h2></div></div></div><p>
- I will include 8-24 T-nuts in the aft centering ring spaced to allow
- the use of an Aeropack 98mm retainer and associated 75mm adapter.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2754969"></a>Nose Cone Electronics Bay</h2></div></div></div><p>
- Instead of using the supplied nose cone bulkhead, I intend to cut a
- custom one that would support installing a length of 98mm motor mount
- from the tip of the nose to the bulkhead. With a plate cut to cover
- the aft end of the airframe tube, this would form an electronics bay
- capable of holding a beacon transmitter, GPS system, or other custom
- electronics.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2733689"></a>Electronics</h2></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2763384"></a>Avionics</h3></div></div></div><p>
- The recovery system will feature dual redundant barometric altimeters
- in the main avionics bay between the two forward motor mount
- centering rings.
- </p><p>
- 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.
- </p><p>
- Each altimeter will have a separate battery and rotary power switch.
- A third rotary switch will be used as a SAFE/ARM switch configured
- to interrupt connectivity to all ejection charges in accordance with
- NAR certification requirements.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2740504"></a>Stability Evaluation</h3></div></div></div><p>
- The Goblin 10 kit designers indicate
- that the rocket is unconditionally stable with all motors that fit
- the motor mount geometry. Since we're adding mass at both ends, by
- putting a payload in the nose cone and by glassing the fins, the
- overall stability of the design should be retained, but simulation
- to confirm that seems prudent.
- </p><p>
- Thorough analysis using
- <a class="ulink" href="http://www.apogeerockets.com/rocksim.asp" target="_top">
- RockSim
- </a>
- with various motors ranging from the Cesaroni K445 through the
- Aerotech M1939W always shows the stability as marginal.
- This is typical of short fat rockets that don't meet normal length
- to airframe diameter ratio expectations.
- Given this, I take the fact that RockSim shows the stability as
- marginal instead of unstable as strong evidence that the rocket
- will in fact be stable in flight.
- I also note that the simulated margin of stability
- in my as-built configuration is fairly close to the margin of
- stability of the as-designed model.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2748086"></a>Expected Performance</h3></div></div></div><p>
- The Aerotech M1297W reload should carry this vehicle to just under
- 7000 feet AGL from Colorado Front Range launch sites. It
- should reach just over 2 miles on a Cesaroni M795 moon burner
- or equivalent.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2767164"></a>Recovery System</h3></div></div></div><p>
- The recovery system will use dual redundant barometric altimeters
- firing 4F black powder charges using commercial e-matches.
- At apogee, a drogue chute will deploy with separation of the nose
- cone. A Giant Leap TAC-1 36 inch chute already in hand will serve
- as the drogue.
- At a preset altitude, a main chute will be deployed from the forward
- end of the motor mount tube to achieve recovery of the bulk of the
- rocket at approximately 20 ft/sec.
- </p><p>
- I intend to sew the main parachute from scratch with my wife's help
- using a design documented by
- <a class="ulink" href="http://www.vatsaas.org/rtv/systems/Parachutes/Chute.aspx" target="_top">
- Team Vatsaas
- </a>
- using 1.9oz rip-stop nylon and 550 lb parachute cord. The anticipated
- build weight implies that a 10 foot parachute would be appropriately
- sized.
- </p><p>
- The recovery system attachment points will all use 1/4 inch u-bolts
- with nuts, washers, and backing plates through bulkheads.
- </p></div></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2768933"></a>Chapter 3. Construction Details</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id2749141">Airframe</a></span></dt><dt><span class="section"><a href="#id2754017">Nose Cone</a></span></dt><dt><span class="section"><a href="#id2771414">Avionics Bay</a></span></dt></dl></div><p>
- I have collected all of my
- <a class="ulink" href="http://gallery.gag.com/rockets/goblin10" target="_top">
- build photos
- </a>
- in one place, they may show better than I can explain how various
- aspects of the Goblin went together.
- </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2749141"></a>Airframe</h2></div></div></div><p>
- The airframe tubing provided in the Polecat kit is thick cardboard tube
- with a thin exterior fiberglass wrap. To increase airframe strength,
- and particularly to prevent zippers, additional reinforcement seemed
- warranted.
- </p><p>
- The inner layer of paper was removed from the front 9" or
- so of the tube. The tube was soaked with West Systems epoxy diluted
- with about 20% by volume with acetone, and then a carbon fiber wrap was
- applied to the interior front of the tube and held in place during
- curing by an inflatable child's bounce toy inside a plastic garbage
- bag. The result is a substantially strengthened tube, with carbon
- fiber lining from the leading edge back past the first centering ring.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2754017"></a>Nose Cone</h2></div></div></div><p>
- The provided nose cone bulkhead was replaced by a custom centering
- ring cut from 3/8 inch birch plywood. The ring's outer diameter was
- adjusted put place the ring approximately an inch forward of the end
- of the motor mount tube, and the inner diameter was cut to fit Giant
- Leap 98mm phenolic airframe tubing. A length of such tubing was cut
- to fit inside the nose cone and extend back to flush with the trailing
- edge of the ring. The centering ring was drilled and fitted with two
- u-bolts for recovery system attachment and four 6-32 T-nuts to hold
- a payload mounting plate in place over the aft end of the 98mm tube.
- </p><p>
- The airframe tubing was glued into the tip of the nose cone with West
- Systems epoxy using both milled glass and microlite filler to thicken
- the mix. The centering ring was then epoxied in place using a similar
- mix around the outer edge to form a heavy fillet and 5-minute epoxy to
- the piece of airframe tubing. After the epoxies cured, a rotary tool
- was used to cut the airframe tubing off flush with the aft surface of
- the centering ring.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2771414"></a>Avionics Bay</h2></div></div></div><p>
- The avionics bay walls were installed approximately 90 degrees apart
- prior to installation of the motor mount assembly in the airframe.
- The airframe wall was marked for a 3.5 x 6.5" access hatch centered
- over the bay 90 degrees from the rail button line. This allows
- sufficient room to install the switches on one side of the hatch yet
- still inside the bay, and to place the static vent on the other side
- of the hatch so that there will be minimal effect from air disturbed
- by movement over the hatch cover edges.
- </p><p>
- Rails were fabricated from 3/8" birch plywood and 6-32 blind nuts to
- allow for a removable avionics sled, rectangular, with 4 screws to
- hold the sled in place.
- A suitably sized avionics sled should be possible to install and remove
- through the avionics bay hatch allowing for possible future experiments
- with alternative avionics.
- </p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2745741"></a>Chapter 4. Recovery Systems Package</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#id2740673">Recovery System Description</a></span></dt><dt><span class="section"><a href="#id2752914">Recovery Initiation Control Components</a></span></dt></dl></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2740673"></a>Recovery System Description</h2></div></div></div><p>
- This rocket uses dual deployment.
- </p><p>
- The apogee event separates the nose cone from the
- airframe. The nose cone is attached to the airframe with a length
- of heavy-duty tubular nylon shock cord. A drogue chute protected
- during ejection by a kevlar blanket is attached to the shock cord
- close to the nose cone end.
- </p><p>
- The main is a 10 foot chute sewn from the design documented by
- <a class="ulink" href="http://www.vatsaas.org/rtv/systems/Parachutes/Chute.aspx" target="_top">
- Team Vatsaas.
- </a>
- It is held in place prior to ejection by a layer of paper taped over
- the front of the motor mount tube. At ejection, a piston pushes the
- chute forward through the paper and ejects it from the rocket.
- This chute is attached to the airframe through an additional length of
- heavy-duty tubular nylon shock cord.
- </p><p>
- Depending on the results of ground testing, the main chute may be
- packed in a Giant Leap kevlar deployment bag attached at the main
- chute apex, with a smaller drogue chute deployed to pull off the bag
- and cleanly deploy the main. The primary motivation for this is to
- prevent the main chute shrouds from tangling during ejection.
- </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2752914"></a>Recovery Initiation Control Components</h2></div></div></div><p>
- The main avionics bay between the forward two centering rings is
- populated with two commercial altimeters, a PerfectFlite MAWD
- and a Missile Works miniRRC2.
- Each is powered by a dedicated 9V alkaline 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.
- </p><p>
- Details of ejection charge design goes here.
- </p><p>
- The
- <a class="ulink" href="http://www.info-central.org/recovery_powder.shtml" target="_top">
- Info Central Black Powder Sizing
- </a>
- page is the most authoritative site I've found on this topic.
- The formula they suggest is diameter in inches squared times
- length in inches times a coefficient in grams of black powder.
- For the main charge, which will be in the 98mm motor mount tube, a
- pressure of 15psi is appropriate giving a coefficient of 0.006.
- For the drogue charge, which will be in the main airframe, a
- pressure of 5psi is more appropriate, leading to a coefficient
- of 0.002.
- </p><p>
- The drogue bay is 10 inches ID at the widest point, but contains
- the protrusion of the main bay and a decreasing radius in the
- nose cone. Thus some fudging on the length is appropriate, and
- we will use 18 inches. That works out to 3.6 grams of BP. This
- rocket will not fly high enough for there to be a significant
- effect on BP burn characteristics, so no special compensation
- should be required.
- </p><p>
- The main bay is 3.9 inches ID and perhaps as much as 24 inches long
- depending on which motor is selected.
- That works out to 2.2 grams of BP.
- </p><p>
- Ground testing yielded 3.5 grams for the apogee charge and 1.5 grams
- for the main.
- Backup charges will contain additional BP in accordance
- with the "blow it off or blow it up" philosophy.
- </p><p>
- With a 10 foot Team Vatsaas design parachute and our
- anticipated build weight, the descent rate under main
- should be just over 20 feet per second.
- </p></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2748101"></a>Chapter 5. Checklists </h2></div></div></div><div class="orderedlist"><ol type="1"><li>
- Planning
- <div class="orderedlist"><ol type="1"><li>
- Pick a club launch with suitable waiver and facilities to
- support flight.
- </li><li>
- Confirm L3CC member(s) available to attend selected launch.
- </li><li>
- Confirm that required loaner motor hardware will be available at launch.
- </li><li>
- Notify launch sponsor (club president) of intended flight.
- </li><li>
- Notify interested friends of intended flight.
- </li><li>
- Perform final pre-flight simulation with as-built masses, etc.
- </li><li>
- Gather consummables and tools required to support flight
- <div class="orderedlist"><ol type="1"><li>
- fresh 9V batteries
- </li><li>
- black powder
- </li><li>
- e-matches
- </li><li>
- motor retainer and adapter parts
- </li><li>
- small nylon wire ties
- </li><li>
- cellulose wadding material
- </li><li>
- masking tape
- </li><li>
- screwdriver for phillips-head avionics bay screws
- </li><li>
- small straight-blade screwdriver for power switches
- </li><li>
- motor reload kit (or arrangements to procure at launch)
- </li><li>
- high temperature grease
- </li><li>
- long small diameter dowels for igniter insertion
- </li></ol></div></li></ol></div></li><li>
- Before Leaving Home
- <div class="orderedlist"><ol type="1"><li>
- program altimeters for suitable mach delay and recovery deployment
- <div class="itemizedlist"><ul type="disc"><li>
- MAWD
- <div class="itemizedlist"><ul type="circle"><li>
- no mach delay
- </li><li>
- 1300 foot main deploy
- </li></ul></div></li><li>
-
- miniRRC2
- <div class="itemizedlist"><ul type="circle"><li>
- no mach delay
- </li><li>
- 1000 foot main deploy
- </li><li>
- 2 seconds apogee delay
- </li><li>
- no main delay
- </li><li>
- dual deploy
- </li><li>
- ops mode 16 (default)
- </li></ul></div></li></ul></div></li><li>
- assemble all recovery system components and ensure everything fits
- </li><li>
- confirm wiring and operation of altimeter power and safe/arm
- switches
- </li><li>
- Ground test recovery system to confirm suitable black powder
- charge sizing
- </li></ol></div></li><li>
- Pre-Flight
- <div class="orderedlist"><ol type="1"><li>
- confirm payload batteries in good condition, bay loaded,
- power switch works
- </li><li>
- confirm reception of signals from transmitter(s)
- </li><li>
- install fresh 9V batteries for altimeters on avionics bay sled
- </li><li>
- inspect altimeters and associated avionics bay wiring for
- visible faults
- </li><li>
- close up avionics bay
- </li><li>
- build and install BP charges
- <div class="orderedlist"><ol type="1"><li>
- Drogue Primary Charge - 3.5 grams 4F BP
- </li><li>
- Drogue Backup Charge - 4.0 grams 4F BP
- </li><li>
- Main Primary Charge - 1.5 grams 4F BP
- </li><li>
- Main Backup Charge - 2.0 grams 4F BP
- </li></ol></div></li><li>
- fold main chute, connect recovery harness to piston and airframe,
- install in MMT and tape paper over the front end
- </li><li>
- fold drogue chute into a kevlar pad, connect recovery harness to
- nose cone and airframe, install in airframe
- </li><li>
- power up payload using switch on base plate in nose cone, then
- install nose cone, using masking tape to adjust fit as required
- </li><li>
- safely power up altimeters, operate safe/arm switch,
- and confirm e-match continuity
- </li><li>
- safe and power-down the altimeters
- </li><li>
- load motor per manufacturer instructions
- </li><li>
- install motor in motor mount
- </li><li>
- install motor retention
- </li><li>
- prepare igniter using e-matches, 1/8 inch dowel
- </li><li>
- confirm all screws in place, avionics off and safe
- </li><li>
- fill out a launch card
- </li><li>
- notify RSO/LCO of readiness for inspection and launch, obtain
- a rail assignment and permission to move rocket to launch pad for
- final prep
- </li><li>
- coordinate readiness with support team members, photographers,
- observers
- </li></ol></div></li><li>
- Final Prep
- <div class="orderedlist"><ol type="1"><li>
- move rocket to launch area
- </li><li>
- clean and lubricate launch rail if necessary
- </li><li>
- confirm reception of signals from payload transmitter(s)
- </li><li>
- mount rocket on launch rail, rotate to vertical
- </li><li>
- power up primary altimeter, confirm expected beep pattern
- </li><li>
- power up backup altimeter, confirm expected beep pattern
- </li><li>
- arm ejection charges
- </li><li>
- confirm altimeters both giving expected beep patterns for
- igniter continuity
- </li><li>
- install igniter and connect to launch control system
- </li><li>
- capture GPS waypoint for rail location
- </li><li>
- smile for the cameras, make sure we have enough "foil Murphy!"
- shots taken
- </li><li>
- retreat to safe area behind LCO
- </li><li>
- confirm continued reception of transmitter signal(s) from
- payload bay
- </li><li>
- confirm photographers and observers are ready and know what to
- expect
- </li><li>
- make sure binoculars and backpack with water and recovery tools
- are at hand
- </li><li>
- tell RSO and LCO we're ready to launch
- </li><li>
- try to relax and enjoy watching the flight!
- </li></ol></div></li><li>
- Recovery
- <div class="orderedlist"><ol type="1"><li>
- track rocket to landing site
- </li><li>
- capture GPS waypoint of landing site, take lots of photos
- </li><li>
- note any damage
- </li><li>
- gather up and roughly re-pack recovery system for return to
- flight line
- </li><li>
- bring the rocket to observers for post-flight inspection
- </li></ol></div></li></ol></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2750187"></a>Chapter 6. Flight Summary</h2></div></div></div><p>
- A successful level 3 certification flight occurred on 15 November 2008
- at the SCORE Hudson Ranch launch facility. The motor was an Aerotech
- M1297W provided by Tim Thomas of Giant Leap Motors, the igniter was
- assembled by James Russell using his special thermite mixture, and
- numerious SCORE, COSROCS, and NCR members were present to assist with
- the launch! Great weather for November... mostly clear and sunny,
- light winds, dry ground, temps above freezing.
- </p><p>
- The motor came up to pressure very quickly and the rocket leapt off
- the pad, climbing smoothly under power and then doing about two slow
- rolls during the coast phase. Deployment of the nose cone and drogue
- occurred as planned when the primary apogee charge fired.
- Unfortunately, the main deployed around the time the backup apogee
- charge fired, so the descent was under main from apogee. Fortunately,
- the winds were low enough and the descent rate high enough that the
- rocket touched down without damage within the waiver area for a
- successful certification!
- </p><p>
- The rocket weighed 25.2 pounds prepared for launch without the motor.
- The motor weighed about 10.25 pounds, which included about 6 pounds
- of propellant. Thus the descent mass under chute was just over 29
- pounds.
- The miniRRC2 altimeter reported 5949 feet apogee, 980 feet per second
- max velocity, and 19 seconds to apogee. The MAWD reported 5953 feet
- apogee.
- </p><div class="itemizedlist"><ul type="disc"><li><a class="ulink" href="http://picasaweb.google.com/jamesr2/StealeyMemorialLaunchSiteHudsonRanch" target="_top">
- Photos of the launch taken by James Russell
- </a></li><li><a class="ulink" href="http://cosrocs.org/all%20other%20videos/2008videos/11-15hudson/bdale_L3.mov" target="_top">
- Video of the launch taken by Jeff Lane
- </a></li><li><a class="ulink" href="http://www.youtube.com/watch?v=xaJnl89wfWU" target="_top">
- Video of the launch taken by Jason Unwin
- </a></li></ul></div></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="id2764884"></a>Chapter 7. Analysis and Conclusions</h2></div></div></div><p>
- The ascent was straighter than expected... very smooth during
- the motor burn, then a couple slow rolls during coast. The two
- altimeters agreed within 4 feet on the apogee. The max
- velocity recorded is a little higher than predicted by simulation,
- but the accuracy of that measurement is likely limited since it is
- based on pressure data.
- </p><p>
- I was able to watch the apogee events through binoculars, and could
- clearly see the main deploy as the backup apogee charge fired. I saw
- some evidence of tearing of the paper taped over the motor mount to
- retain the main chute during ground testing, so assume this was the
- root cause of the early deployment. When the backup apogee charge
- fired, the shock cord was not yet in tension, and thus the charge
- probably kicked the airframe backwards hard enough to allow the main
- chute to slide out through the torn paper and deploy. The best fix
- for this might be
- to fabricate a second piston to use as a cap and retain it with two
- shear pins. This would be much less likely to prematurely deploy than
- the current taped paper approach.
- </p><p>
- The most significant variance from expectation was the descent rate.
- The spreadsheet provided by the Team Vatsaas folks for their design
- suggested we'd see around 21 feet per second. Analysis of the flight
- profile from the MAWD shows that our actual descent rate was about
- 32 feet per second. There are three possible sources of error to
- consider.
- </p><div class="orderedlist"><ol type="1"><li>
- The first is descent mass. Pre-flight calculations used
- 25 pounds.
- The actual flight weight was 25.2 pounds plus the burn-out
- weight of the M1297W, which should be about 4.5 pounds.
- That yields 29.5 pounds total. All pre-flight calculations
- were done using 25 lbs, with the thought that the motor mass
- might cancel out against the drag provided by the drogue.
- In flight, it appeared the drogue supported the nose and the
- main supported the fin can with very little interaction between
- the two.
- </li><li>
- Second, the dimensions given by Team Vatsaas' spreadsheet
- for the pattern grid seem small. For a 10 foot chute, they
- suggest a grid size of 5 inches, which looks more like an 8.5
- foot finished chute size to me.
- </li><li>
- Finally, the Cd in the spreadsheet is 1.5, which may be overly
- optimistic.
- </li></ol></div><p>
- My calculations show that if we assume a chute size of 8.5 feet and
- a Cd closer to 1, we can get to a descent rate of 32 feet per second.
- </p><p>
- So, overall, this was a successful flight, but with three things to
- change before we fly the airframe again...
- </p><div class="orderedlist"><ol type="1"><li>
- the main chute may be too small
- </li><li>
- switch to a piston to cap the main chute bay
- </li><li>
- beef up the battery retention on the avionics sled
- </li></ol></div><p>
- </p></div></div></body></html>
projects / web / gag.com / blobdiff