rec.models.rockets FAQ Part 09 - Competition and Records
Wolfram v.Kiparski
Rec-models-rockets-archive-name: rockets-faq/part09
Posting-Frequency: monthly
Last-modified: 1999 December 3
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
Rec.Models.Rockets FAQ : PART 09 of 14
COMPETITION AND RECORDS
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9.1 Are there any manufacturers making kits specifically designed for competition?
There are several sources of kits designed primarily for competition.
Some of the manufacturers are:
Apogee Components rocket motors 1/4A - F
630 Elkton Drive Micro Motors (10.5mm) 1/4A - B
Colorado Springs, CO 80907-3414 Composite 13mm B motors
t...@apogeerockets.com Long burn D, E, and F motors
(Timothy Van Milligan) Kits and supplies
(719) 535-9335 Educational materials and books
http://www.ApogeeRockets.com Catalog - $2.00, or see website
Eclipse Components Competition model rocket parts
570 Buckeye Dr. Blackshaft (phenolic) tubing
Colorado Springs, CO 80919-1212 inexpensive
(719) 598-6105 Catalog - $1.00
eclip...@worldnet.att.net
(Todd Schneider)
Pratt Hobbies CMR-style nose cones and
2513 Iron Forge Road egg capsules
Herndon, VA 20171 Catalog: FREE
(703) 689-3541 (voice/fax)
76703...@compuserve.com
http://ourworld.compuserve.com/homepages/pratthobbies
Qualified Competition Rockets Offers a wide variety kits for
c/o Kenneth Brown competition rocketry
7021 Forest View Drive piston launchers, tubing, and
Springfield, VA 22150 misc. supplies
Catalog: SASE
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9.2 What are the major categories of competition model rocketry?
The NAR sanctions model rocketry contests throughout the USA, and
throughout the year. The contest year runs from July 1 - June 30.
The final contest for a given contest year is NARAM, usually held
in August, after the end of the contest year. The complete list
of event and rules for model rocketry may be found in the NAR
"United States Model Rocket Sporting Code," also known as the 'Pink Book.'
It is available free to NAR members, and may be ordered from NARTS.
Some of the event types are:
- Altitude (1/4A - G)
The purpose is to get the maximum altitude from a model using a
specified class of engine.
- Streamer Duration (1/4A - G)
The purpose is to get the maximum flight duration from a model with a
specified engine type using streamer recovery.
- Parachute Duration (1/4A - C)
The purpose is to get the maximum flight duration from a model using
a specified motor type.
- Eggloft Altitude/Duration (B - G)
In this event the competitor must launch either one to two large raw
hen's eggs, depending on engine type and specific event, and recover
it/them, intact, crack-free. The goal is either to reach the highest
altitude or have the longest duration flight, depending on the event.
- Rocket Glider and Boost Glider Duration (1/4A - G)
In these events the competitor launches a glider using a rocket engine
and tries to achieve the longest flight duration of the glider. In
boost glider the pod containing the motor may be ejected and recovered
separately. In rocket glider all parts, including the expended engine,
must stay with the model. Rocket glider is considered to be the more
difficult event because the model must be both a rocket and a glider
without loosing any parts. The CG and CP requirements for the two
phases of flight are very different. See Part 08 of this FAQ.
- Helicopter Duration (1/4A - G)
In these events the model ascends as a rocket. Rotor arms then extend
by some mechanism and the rocket slowly descends like a helicopter which
has lost power.
- Payload Altitude (A - G)
In these events the competitor must launch one or more standard NAR pay-
loads (1 ounce each of fine sand) and recover the model. The number
of payloads increases with larger engine sizes.
- SuperRoc Altitude/Duration (1/4A - G)
These events are for rockets that have a minimum and maximum length
requirement based on engine class (0.25 - 4.5 meters). There are
both altitude and duration variations. The trick to these events is
that the model may not bend or crimp during flight.
- Scale Events
These are craftsmanship events where competitors build scale models of
real military or commercial rockets. Fine craftsmanship is emphasized.
* Scale: exact replicas of rockets, with major scale dimensions
verified by judges.
* Sport Scale: adherence to scale is judged from a distance of 1 meter.
* Peanut Scale: Sport Scale for small models (<30cm long or <2cm dia.)
* Giant Scale: Sport Scale for large models (>100cm long or >10cm dia.)
* Super Scale: must include a scale launcher as well as model of rocket;
judged same as scale
* Space Systems: Sport Scale model and optional launch complex.
Model must complete a predetermined mission with the purpose of
duplicating in miniature the full-scale operation of the prototype.
- Plastic Model Conversion (PMC)
This event is either loved or hated. Competitors enter plastic models
of rockets or other aero-vehicles that have been converted to fly as
model rockets.
- Precision Events
These include spot landing, random duration, predicted duration,
precision duration, and predicted altitude.
- Drag Race
Multi-round, elimination tournament where contestants gets points for:
* FIRST lift off
* LOWEST altitude
* LAST to land
- Research and Development
A non-flying event where contestants enter results of research projects.
Entries are judged for completeness, contribution to rocketry
knowledge, degree of difficulty, etc.
The Tripoli "Member's Handbook" currently lists one competitive event for
high power models:
- Altitude Records
The purpose is to get your rocket to the highest possible altitude with
a given motor power range. Verify the altitude achieved.
In 1995, Tripoli added official altitude records for F through O powered
consumer rockets. Some Tripoli records are listed later in this section.
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9.3 What are some good events to try when first getting into competition? Any
'sage' advice?
From bmcd...@ix.netcom.com (Buzz McDermott):
I just started competition this year. I must have asked 30 experienced
competitors where to start. I got 30 COMPLETELY DIFFERENT ANSWERS!!
They ranged from 'keep it REAL simple' to 'try everything'. Here is
a summary of the most prevalent advice. It seems to have worked for me.
- Competition requires a large stable of rockets, given all the
possible events and engine categories; start with some of the
simpler ones where a single model might be competitive in more
than one event (for example, the same model might be used for 1/2A-A
streamer or parachute duration, another model might be competitive in
any of A - C streamer or chute duration)
- Try single eggloft (B-C, duration or altitude) before trying the
multi-egg categories (such as D or E dual egg).
- Go for a good, qualified flight first; then decide if 'going for
broke' is appropriate on your second flight (this is for multi-
flight events).
- Get a teammate and enter as a team. There are too many models you
need to compete to be able to build all of them your first year.
Entering as a team let's you pool time, talent, experience, and models.
- Don't get discouraged if you aren't immediately competitive.
Remember, the main goal is to enjoy yourself and HAVE SOME FUN.
If you are new at this, you're going to learn A LOT about rocketry by
doing it the fun way.
- KEEP A LOG OF ALL FLIGHTS. RECORD WHAT WORKS AND WHAT DOESN'T.
NOTE YOUR FLIGHT TIMES, ALTITUDES, ETC. Your biggest weapon
in many events is in being able to predict how your models
will perform.
- Make a model preparation checklist for each event (i.e., a detailed,
step-by-step list of everything necessary to prep the model). Use this
list for your first few competitions. Comp models are often prepared
a little differently from sport models. The difference between winning
and losing is often just attention to detail, or lack of it, in the
heat of competition.
From ma...@jupiter.fnbc.com (Mark Bundick)
Note: This is a condensed version of some competition strategies for
individual and team competitors, written by Mark 'Bunny' Bundick and
posted to r.m.r. Check the r.m.r archive server for the complete posting.
The full posting points out that there are many ways to win, and the
following is just what has worked for some individuals.
Some Individual Competition Strategies:
(a) Read the Pink Book. If you don't know the rules for the event,
you can't know how to win and how to improve. Figure out the
scoring for each event, how many flights are allowed, required
number of returned flights, the reasons for disqualification, etc.
Reading the rules will also give you some insights into how the
contest will be run. Start with the general rules then review the
event-specific rules.
(b) Practice for all events where your experience is low. If you
already know how to fly parachute duration (PD), don't waste time
practicing that at your club's sport launch. Instead, suppose you
don't do well in streamer duration (SD). Build a couple different SD
models with different streamers, and fly each of them at least a
couple of times BEFORE the contest. Take a notebook to the field
and write down what happened, or at least write it down after you
get back home. Such notebooks can be the lifeblood of your
competition model and strategy development.
(c) Improve one event a year. At the start of the season, it helps if
you pick one of your weak events for special attention during the
year. Review the existing models and strategies for the event, look
over the competition carefully during the contest year, and practice
this key event each and every sport launch or test flying session
you attend.
(d) Strive for consistent flights. Rob Justis, my old teammate from
the 70's, always reviewed our DQ's after the meet and separated
them into "DQ's for the right reason" i.e no return, and "DQ's for the
wrong reason", i.e. separation. We strove to avoid the latter
obviously. This made us terribly consistent, and with today's "two
flights count" rule, this is even more important.
(e) Fly all the events. Sounds simple, but many people don't do
this. You don't have to win the event, but if you don't fly it, you're
sure to get behind because you're conceding flight points right off
the bat to your competition. Over the course of a contest year,
you can concede 10% of your yearly total this way.
(f) Concentrate on events with high individual event weighing
factors (WF). If you have to choose events to fly, or are short of
preparation time for some of the scheduled events, prepare for and
fly the highest WF events first. Simple again right? But how many
people go to a contest and fly PD first thing in the AM cause the
wind is calm, and ignore BG which has a WF two to three times that
of PD?
(g) Refine, don't abandon, your models and strategies. Rarely do
you get super performance improvements from forgetting all you
know to adopt a totally different strategy. I've seen so many people
hop onto a design when it didn't fit their flying style and then get
burned. They switch because some guy had a super performance
at a contest, so he must have the "Holy Grail" of models. Right
after Tom Beach placed highly at a NARAM with a flexie RG, I saw
lots of folks try them, and crash. Tom had lots of flexie experience
that helped, and when regular BG flyers tried to adopt his style
without the background, BOOM! If you're serious about switching
to a completely different model, say from swing wings to slide wing
rocket gliders, then take the time to practice, practice, practice and
build up the background in the new method. There are no quick
fixes to the winner's circle.
(h) Pick your contests carefully. If you can't fly helicopter duration
(HD) all that well, and the next regional you plan to attend has two
HD events, find another contest! Sometimes, this isn't possible. But
if two contests compete for your participation at the same time,
take the one that has more of your "strong" events.
(i) Casting Your Bread: Share what you've learned with others. A
three time national champion who shall remain nameless positively
stomped every challenger in his sight. But his desire for keeping
secrets and his unwillingness to share left him with few friends, and
after a brief time, he left our hobby, poorer himself and leaving our
hobby poorer for failing to let us learn from him. The benefits of
making new friends and sharing far outweigh any short term
competitive advantage you might think you have from being
secretive. As a quotation I once read went "We have all drunk
from wells we did not dig and been warmed by fires we did not
build." So go ahead. Cast your bread on the waters. You won't be
sorry.
Hope this provides you competition types some food for thought.
I'd love to hear from anyone with comments, questions, brickbats,
etc. at ma...@fnbc.com.
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9.4 What is a 'piston' launcher? Does it really help?
From: Roger....@umich.edu (Roger Wilfong)
Pistons offer several advantages and a couple of hassles.
+1) They eliminate the need for launch lugs and therefore reduce drag.
+2) They keep ignition leads from fouling in glider wings.
+3) They can increase lift off velocity (see below).
+4) They recover an otherwise lost portion of the whoosh generator's
impulse.
-1) They require additional maintenance.
-2) Ignition can be a hassle.
A launch piston is usually made of cylinder of 12-18" of BT-5 or PT-13
and a fixed piston made of an old 13mm motor casing or brass tubing.
In practice, the support shaft is attached to a tripod or other launcher,
an igniter is inserted into the tubing on the top of the piston. The
bottom 1/4" of the motor in the model is friction fitted to the top of
the piston tube and lowered onto the igniter (I use 2-3 short pieces of
thin 1/4" masking tape across the joint of the piston/body tube to
reinforce the friction fit - actually I've found it easier to use a
looser fit and the masking tape than to get just the right friction fit).
The micro clips of a launch controller are attached to the bare ends of
the zip cord. When the motor ignites, exhaust gas pressurizes the
cylinder and pushes the piston down. Since the piston is fixed, the
effect is that the cylinder is pushed up. When the stop ring at the
bottom of the cylinder hits the bottom of the head, the cylinder stops
and the model pops off the cylinder.
In effect the piston has acted as the launch lug for the fist 12-18" of
motion.
Roger's Piston Theory (developed through observation and tinkering, it
is not based on a mathematical analysis):
For performance events, pistons offer an advantage over launch lugs or
towers primarily because they convert an otherwise unusable portion of
motors total impulse into motion. There is a startup time at the
beginning of the burn where the motor is not producing enough thrust
to lift the rocket - it is this portion of the burn that the piston is
making use of.
Since the piston gets the model moving before the motor generates enough
thrust to lift the model, it is possible that at the instant of
separation, the motor may no be developing sufficient thrust to keep
accelerating the model and the model may decelerate for the next few
feet after leaving the launcher. This is not a problem for PD/SD models
and most gliders - they are typically light enough that the piston has
accelerated them to a high enough speed for the fins to work properly;
however, it can be a real problem for payloaders and egglofters (I have
seen egglofters almost come to a stand still after leaving a short
piston). So for heavier models, a piston/tower combination provides
additional guidance and helps prevent tip off.
The tower is of only small advantage with SD/PD models; however, it can
help if there are other disturbing forces at separation that could cause
the model to tip.
Because they affect the gas flow during the ignition of the motor, pistons
don't work well with composite motors. My experience has been that
composites either cato or chuff when used with a piston. (If someone
has worked out using a composite on a piston, how did you get it to
work?)
Pistons are a real advantage in any performance event. For eggloft and
payload, they typically allow you to use the next longest delay. For
instance, a B6-2 is needed for a conventional eggloft model. On an 18"
piston, a B6-4 ejects at apogee. Earlier I referred to using a piston
on a Big Bertha - an A8-3 gives a marginal flight without the piston;
with the piston, ejection is at apogee.
There are a couple of variations and modifications to conventional pistons
that can further enhance their performance. The diameter of the head
(6, 13, 18 and 24mm) is one parameter to play with. Jeff Vincent and
Chuck Weiss presented a floating head piston as an R&D project at NARAM-
28 that further increased performance.
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9.5 Aside from hanging around 'old timers', how can I learn more about
competition strategies and techniques without re-inventing the wheel
many times over?
The best place to start looking would be the NAR Technical Services
(NARTS) catalog. NARTS has several documents of particular interest to
competitors. The NARTS catalog can be browsed at the NAR web site -
http://www.nar.org/
Look for the NARTS catalog, and when browsing through it, look for these titles:
US Record Setting Designs
CMASS Plan Book
MIT Competition Notebook
Journals of the MIT Rocket Society...
Proceedings of the MIT Model Rocket Conventions...
NAR Technical Reviews, Volumes 1 - 7
Boost Glider Analysis-"A Free Flight Method For Boost Glider Analysis."
Streamer Duration Optimization
Basic Design Rules for Boost and Rocket Gliders
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9.6 Tripoli Altitude Records
The following is a list of altitude records based on motor class. These
are all official Tripoli Altitude Records as determined by the Tripoli
Contest and Records Committee. Further information on Tripoli Altitude
Records and specific requirements can be found in the Altitude
Competition portion of the Tripoli Handbook.
Motor Class Altitude Name Date
------------------------------------------------------------
F 1387 meters Mark Clark 3/10/96
G 1483 meters Mark Sims 11/02/96
H 2221 meters Dave "Fritz" Katz 11/05/95
I 3997 meters Pius Morozumi 9/09/95
J 3006 meters Chet Geyer 5/18/96
K (unclaimed)
L (unclaimed)
M (unclaimed)
N 9431 meters Walter Blanca 8/14/95
O (unclaimed)
The above list of official Tripoli Altitude Records is current as of
January 20, 1997.
Robert Gormley, Chairman
Tripoli Contest and Records Committee
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9.7 NAR Competition Records
NAR competition records can be viewed using your web browser at:
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9.8 Some Unofficial High Power Altitude Attempts
Some of the high power records come by way of a posting from Chip Wuerz
(d...@engr.ucf.edu). Chip is part of the University of Central Florida's
high altitude rocketry project. Additional information has been taken from
several issues of _Tripolitan_/_High Power Rocketry_ magazine.
* * Some current records for NON-METALLIC NON-PROFESSIONAL Rockets: * *
---Top altitude holders:
Altitude: 27,576 (altitude by Adept altimeter)
Set by: Pius Morozumi
Event: Black Rock V, Black Rock Dry Lakebed
Date: July 16-18, 1993
Altitude: 24,771 feet (11.7% tracking error)
Set by: Chuck Rogers and Corey Kline
Event: Lucerne Dry Lake Bed, Lucerne, Ca.
Date: June 1989, USXRL-89
Altitude: 24,662 (tracking error unknown)
Set by: Tom Binford
Event: LDRS XI, Black Rock Dry Lake Bed, Nevada
Date: August 16, 1992
Altitude: 22,211 feet (5.3% tracking error)
Set by: University of Central Florida
Event: LDRS X, Black Rock Dry Lake Bed, Gerlach, NV.
Date: August 1991
Highest tracked flight at LDRS-X / BALLS 1.
Second all-time highest track of a non-metallic high power rocket.
University of Central Florida's research project and altitude attempt
to break the current high-power rocketry altitude record of 24,771 feet
set by the KLINE/ROGERS team in 1989. Altitude attempt had been based on
3850 NS L-engine, new Vulcan L-750 engines deliver 3,000 (now known to be
less from motor testing results) newton seconds. In an attempt to make
up power loss and to provide margin on the goal altitude of 25,000 feet,
the upper stage was delay-staged by several seconds. Altitude predictions
computer simulation program predicted 28,500 feet. Upper stage flew
substantial trajectory, reaching apogee nearly 2 miles downrange.
Rocket used microprocessors / timer-controlled staging and ejection,
on-board flight data measurement package, and a radio beacon system to
locate upper stage. Track was accomplished using red carpenters chalk.
Both stages were recovered.
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9.9 Biggest Non-metallic Rocket Flights
1) Rocket: Down Right Ignorant
Weight: 800 pounds +
Set by: Dennis Lamonthe, Chuck Sackett, and Mike Ward
BlackRock Dry Lake Bed, Gerlach, NV.
August 17, 1992, FireBALLS experimental launch
Description: Super scale based on Esoteric rocket designed by Ron Schultz
Height: 34' 7"
Diameter: 24"
Power: 1 O-class custom motor
5 Energon L1100 motors
8 ISP K1100 motors
(around 76,000 NS total impulse)
Materials: 24" fiberglass tubes for main body tube
1/8" aluminum plates for coupler bases and fin
mounting boxes
1/2" aluminum plate for motor thrust plate
2x5" oak boards for tube coupler assemblies
2x5" pine boards for body tube strengthening
plywood centering rings
3/4" birch fins
14" paper tubing for upper body tube hard resin/fiberglass
nose cone (originally a sounding rocket nose cone shroud)
Note: The definition of 'non-metallic' traditionally has meant
'no substantial metal components' as well as no structural
components being metal. DRI appears to push that definition
to its absolute limit, or a little beyond.
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9.10 Other Non-professional Flights of Note
1) Rocket: Frank Kosdon metal rocket
Date: LDRS XII
Argonia, Kansas
15 August 1993
Power: Kosdon non-certified O10000 (that's O-10,000)
Materials: All metal rocket with custom manufactured motor
Altitude: 35,407 feet AGL; closed optical track
Notes: This is a special-case flight. The rocket does not
follow the rules for high power because metallic rockets
are expressly prohibited by both the NAR and Tripoli.
It also uses a custom made motor. The motor was made
by a manufacturer with other high power motors certified
by Tripoli. It was pre-manufactured and solid propellant,
within the total NS limits of high power consumer rockets.
Tripoli does not recognize this flight, or any other flight,
for altitude record purposes unless a successful deployment
of the recovery system is observed or the rocket can be
recovered to show successful recovery system deployment.
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9.11 Some other highest verified altitudes
Robert (Bobby) Gormley has gathered the following F through Open (i.e.,
unlimited) altitudes. These are not official records, but the highest
verified altitudes of CONSUMER ROCKETS for each motor class.
From: rgor...@phoenix.Princeton.EDU (Robert Gormley)
Class By Motor(s) Altitude Launch
-----------------------------------------------------------------
O Frank Kosdon O10,000 37,978 feet Fireballs 005
M Univ. Cen. FL L750/L750 22,211 feet LDRS-X
L Pius Morozumi K550/K250 27,576 feet Black Rock V
K *Deb Schultz K250 21,659 feet LDRS-XI
J Mike Keller J125 15,062 feet LDRS-X
I Mark Clark I132 11,873 feet LDRS-X
H Mike Vaughn H125 8,435 feet Fireballs 005
* The K250 has been tested to be in the L range and I am looking for
another entry to replace it.
---------------------------------------
Copyright (c) 1996, 1997, 1998, 1999 Wolfram von Kiparski, editor.
Refer to Part 00 for the full copyright notice.
Wolfram v.Kiparski
Rec-models-rockets-archive-name: rockets-faq/part10
Posting-Frequency: monthly
Last-modified: 1997 September 12
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
Rec.Models.Rockets Frequently Asked Questions: PART 10 of 14
HIGH POWER ROCKETRY
Review: A High Power rocket is a model weighing more than 1500 grams (3.3 lb)
at liftoff, or containing more than 125 grams of propellant (total),
or containing any one motor with more than 62.5 grams of propellant.
-----------------------------------------------------------------
10.1 I'm a successful model rocketeer. What do I need to get into HPR?
When this question was posted to r.m.r a while back, these were the pre-
dominant suggestions and tips:
- Start with E/F/G kits with 29mm motor mounts from LOC or Aerotech.
These should be the easiest to build.
- Read and become familiar with the NAR and/or Tripoli High Power Safety
Code(s).
- Get familiar with and use expendable motors before jumping into
reloadable technology.
- Join a high power club if possible (local NAR section or Tripoli
prefecture).
- Be very careful of the construction differences between model and high
power rockets. You HAVE to build higher power rockets to be more sturdy
than model rockets (see the next question).
- If not already a member, join both the NAR and Tripoli (if you can
afford high power rocketry, you can afford to join and support both
these organizations).
-----------------------------------------------------------------
10.2 What are the major differences between model and high power rockets,
besides size and motors? Are they built differently?
Above and beyond all else, high power rockets are built much stronger
than standard model rockets. This is due to the higher speeds and
acceleration achieved by these models. Some of the construction
differences are:
- High power rockets have stronger, thicker body tubes.
- They have MUCH stronger engine mounts, bonded using epoxy rather
than white or yellow glue.
- Engine mount rings, adapter rings, etc., are typically made from
1/8" or thicker aircraft plywood, fiberglass, or phenolic sheet, rather
than paper or balsa.
- Fins are typically made from plywood, fiberglass, phenolic, or
waferglass, not balsa; Thick balsa fins have been used on H/I powered
models, but they have to be reinforced with fiberglass/epoxy laminate.
- Fins are often mounted into slots in the body tube with Through The Wall
(TTW) mounting. Most common and recommended method is glued TTW and
directly onto the motor tube.
- Parachutes are larger and typically made from some type of fabric
(plastic chutes are not strong enough, usually).
- Heavy elastic shock cords or bungee, tubular nylon, or Kevlar shock line
are used rather than rubber for shock cords, and these are typically
epoxied to the motor mount or a bulkhead.
- Positive motor retention systems (clips, bolts, etc.) are important,
as HPR reload casings start to get pretty expensive.
-----------------------------------------------------------------
10.3 How do I get high power certified?
There are two organizations which may certify you to purchase and use
high power rocket motors. These are the National Association of
Rocketry and the Tripoli Rocketry Association. Note that you must be
a member of the organization to certify for high power with that
organization. Once certified, both organizations recognize the
certification of the other.
As of April, 1996, new NAR certification procedures have gone into
effect.
Current NAR procedures:
- For Level 1 certification (the first step) one must fly an H or I powered
rocket successfully, and have it witnessed by two senior NAR members, one
of which must be high power certified. Fill out the proper form, have it
signed by the witnesses, and send it in to NAR HQ.
NOTE: NFPA 1127 allows an uncertified individual to purchase a single H
or I motor for certification purposes.
- For Level 2 certification (the next step up) one must take and pass a
written exam, and then successfully fly a J/K/L powered rocket.
Questions for the examination come from a pool of questions that are
available for review prior to taking the test at the NAR web site.
- The NAR does not currently certify to Level 3 (M and up).
Tripoli certification procedures are scheduled to change on 1 Sep 1996.
At that time there will be three (3) high power certification levels:
- Level 1, allowing single motor H and I flights. No clusters or staging.
- Level II, allowing up through L motors, staging, clustering and hybrids.
- Level III, unlimited, allowing M power and up.
A written test will be required for Level II certification, in addition to
the certification flight. Level III certification requirements will require
pre-flight approval and review from the Tripoli Advisory Board.
-----------------------------------------------------------------
10.4 What is a 'reloadable' motor. Are they worth the price? Are they legal?
A reloadable rocket motor is a metal cylinder with removable end pieces.
Solid propellant and time delay are purchased separately from the motor
casing, in 'reload kits'. These kits contain all of the expendable,
non-reusable materials for a single flight. The cost of the reload is
significantly less than the cost of an expendable motor (when talking
about F sizes and up). Quite a number of reloadable motors and reload
are now certified by NAR or Tripoli. Refer to the approved motor lists of
each organization to see exactly which motors are currently certified.
YOU MUST BE A CERTIFIED MEMBER OF A QUALIFIED ORGANIZATION TO PURCHASE OR
USE RELOADABLE HIGH POWER MOTORS. See section 3.1.9, below, for
information on becoming certified to use high power reloadable motors.
WARNING: IT IS HIGHLY RECOMMENDED BY r.m.r CONSENSUS THAT YOU DO NOT
ASSEMBLE AND/OR PREP A RELOADABLE-TYPE MOTOR UNTIL JUST PRIOR
TO ITS USE (I.E., ON THE FLYING FIELD). *** UNDER NO
CIRCUMSTANCES SHOULD ASSEMBLED RELOADABLE MOTORS BE STORED WITH
IGNITERS INSTALLED ***
---------------------------------------------------------------
10.5 What are these different 'types' of composite motors I hear about (White
Lightning, Black Jack, Smokey Sam, etc.)?
These are all manufacturers' names for various formulations of 'stuff'
they have added to the propellants to get specific pyrotechnic effects.
Black Jack (Aerotech): low(er) average thrust engine which produces a
dense, dark exhaust to aid in tracking. Also has a distinctive roar.
Note: BJ motors have a slow thrust buildup and long ignition time. Take
care when using this type of motor in a cluster. Also play close
attention to the manufacturer's Maximum Recommended Liftoff Weight
(MRLOW).
Blue Thunder (Aerotech): high level average thrust engines with a bright
violet-blue flame and very little visible exhaust. Designed for high
thrust, high acceleration lift-offs. Ignites quickly. Very fast thrust
build-up.
Firestarter (U.S. Rockets): low impulse composite formulation which
produces large numbers of sparks.
Hellfire (Vulcan): a high thrust motor which produces a bright red
flame.
Smokey Sam (Vulcan): produces a dark exhaust to aid in tracking.
Silver Streak (Rocketflite/MRED): produces a fine shower of white sparks
during boost (these are actually black powder motors). VERY fast
ignition and thrust buildup.
White Lightning (Aerotech): medium average thrust engine producing a
bright white flame and distinctive roar. Ignites quickly. Moderately
quick thrust buildup.
-----------------------------------------------------------------
10.6 What's an FAA waiver? Which rocket flights require one?
An FAA waiver is official permission by the Federal Aviation Administra-
tion allowing the launching of rockets exceeding a certain size. The rules
appear in FAR 101.
A document describing FAR 101 is available at the sunsite archive:
http://sunsite.unc.edu/pub/archives/rec.models.rockets/FAA/FAR101_explained
The following are the relevant sections of FAR 101, regulating the
launching of model and high power rockets.
----------------------- FAR 101 Subpart A--General --------------------
Sec. 101.1 Applicability.
(a) This part prescribes rules governing the operation in the United
States, of the following:
(3) Any unmanned rocket except:
(i) Aerial fireworks displays; and,
(ii) Model rockets:
(a) Using not more than four ounces of propellant;
(b) Using a slow-burning propellant;
(c) Made of paper, wood, or breakable plastic, containing no
substantial metal parts and weighing not more than 16 ounces,
including the propellant;
and
(d) Operated in a manner that does not create a hazard to persons,
property, or other aircraft.
[Doc. No. 1580, 28 FR 6721, June 29, 1963, as amended by Amdt. 101-1, 29 FR
46, Jan. 3, 1964; Amdt. 101-3, 35 FR 8213, May 26, 1970]
Sec. 101.3 Waivers.
No person may conduct operations that require a deviation from this part
except under a certificate of waiver issued by the Administrator.
[Doc. No. 1580, 28 FR 6721, June 29, 1963]
Sec. 101.5 Operations in prohibited or restricted areas.
No person may operate a moored balloon, kite, unmanned rocket, or unmanned
free balloon in a prohibited or restricted area unless he has permission
from the using or controlling agency, as appropriate.
[Amdt. 101-1, 29 FR 46, Jan. 3, 1964]
Sec. 101.7 Hazardous operations.
(a) No person may operate any moored balloon, kite, unmanned rocket, or
unmanned free balloon in a manner that creates a hazard to other
persons, or their property.
(b) No person operating any moored balloon, kite, unmanned rocket, or
unmanned free balloon may allow an object to be dropped therefrom,
if such action creates a hazard to other persons or their property.
(Sec. 6(c), Department of Transportation Act (49 U.S.C. 1655(c)))
[Doc. No. 12800, Amdt. 101-4, 39 FR 22252, June 21, 1974]
--------------- FAR 101, Subpart C--Unmanned Rockets ------------------
Source: Docket No. 1580, 28 FR 6722, June 29, 1963, unless otherwise noted.
Sec. 101.21 Applicability.
This subpart applies to the operation of unmanned rockets. However, a
person operating an unmanned rocket within a restricted area must comply only
with Sec. 101.23(g) and with additional limitations imposed by the using or
controlling agency, as appropriate.
Sec. 101.22 Special provisions for large model rockets.
Persons operating model rockets that use not more than 125 grams of
propellant; that are made of paper, wood, or breakable plastic; that contain
no substantial metal parts, and that weigh not more than 1,500 grams,
including the propellant, need not comply with Sec. 101.23 (b), (c), (g), and
(h), provided:
(a) That person complies with all provisions of Sec. 101.25; and
(b) The operation is not conducted within 5 miles of an airport runway or
other landing area unless the information required in Sec. 101.25
is also provided to the manager of that airport.
[Amdt. 101-6, 59 FR 50393, Oct. 3, 1994]
Sec. 101.23 Operating limitations.
No person may operate an unmanned rocket--
(a) In a manner that creates a collision hazard with other aircraft;
(b) In controlled airspace;
(c) Within five miles of the boundary of any airport;
(d) At any altitude where clouds or obscuring phenomena of more than five-
tenths coverage prevails;
(e) At any altitude where the horizontal visibility is less than five
miles;
(f) Into any cloud;
(g) Within 1,500 feet of any person or property that is not associated with
the operations; or
(h) Between sunset and sunrise.
(Sec. 6(c), Department of Transportation Act (49 U.S.C. 1655(c)))
[Doc. No. 1580, 28 FR 6722, June 29, 1963, as amended by Amdt. 101-4,
39 FR 22252, June 21, 1974]
Sec. 101.25 Notice requirements.
No person may operate an unmanned rocket unless that person gives the
following information to the FAA ATC facility nearest to the place of
intended operation no less than 24 hours prior to and no more than 48 hours
prior to beginning the operation:
(a) The names and addresses of the operators; except when there are
multiple participants at a single event, the name and address of
the person so designated as the event launch coordinator, whose
duties include coordination of the required launch data estimates
and coordinating the launch event;
(b) The estimated number of rockets to be operated;
(c) The estimated size and the estimated weight of each rocket; and
(d) The estimated highest altitude or flight level to which each rocket
will be operated.
(e) The location of the operation.
(f) The date, time, and duration of the operation.
(g) Any other pertinent information requested by the ATC facility.
[Doc. No. 1580, 28 FR 6722, June 29, 1963, as amended by Amdt. 101-6, 59 FR
50393, Oct. 3, 1994]
-----------------------------------------------------------------
10.7 OK. I want to fly some high power rockets. How do I get an FAA waiver?
A downloadable, printable copy of
Form 7711-2, Application for Certificate of Waiver, is available at:
http://www.faa.gov/avr/afs/Waiver.htm
From: js...@edison.rc.rit.edu (J A Stephen Viggiano)
I'd like to share with those interested what is involved in applying for
an FAA Waiver. It's not a particularly difficult procedure, and the
FAA personnel I have dealt with are courteous, professional, and
helpful. Don't be scared of the bureaucratic red tape, there isn't a
whole lot of it.
You can get the forms from the Flight Standards District Office (the "Fizz-
Doe") at any airport with air traffic control. Phone the tower and ask
for Flight Standards. Tell them you're interested in launching rockets,
and need an Application for Waiver, FAA Form 7711-2. They should know what
you want. While you've got them on the phone, ask for the address of the
Regional office. You will probably have to file your application with them,
so it will help to know where it has to go!
Now, you take a field trip. Get in your car, and drive to the airport. Not
the passenger terminal, the part where all the private general aviation
planes are parked. There should be a place there for pilots to pay for
fuel, buy toothbrushes and other sundry items, including section maps.
Ask them for the map which includes your launch site. If you're not near
a section boundary, it should be the same map which includes the airport.
(It will also be the most popular map there, and they may be out of
stock.)-: We're covered by the Detroit section map, for example. Never
mind that it's a few states away, and New York is closer, that's just
the way they carve things up. It costs about $3, and it's fun to look at
and try to decipher.
Locate your launch site on the section map. Are there any airports
within 5 miles? If so, you'll need a waiver of Section 101.23(c), which
addresses your proximity to an airport, in addition to waiver of Section
101.23(b), which covers controlled airspace. You type these section
numbers on line 4 of the application. Lines 1, 2, and 3 are your name,
address, telephone number, and all that David Copperfield crap, as
Salinger called it.
Line 5 asks for a detailed description of what you want to do. I usually
put something like the following:
Normal operations of Model and High Impulse Rockets
weighing more than 16 ounces (but less than 80 ounces)
in accordance with the National Association of Rocketry
Safety Codes (please see attached).
Line 6 asks for the location. If you've got the latitude and longitude
to the second, use them. Otherwise, you can refer to a copy of the portion
section map, like this:
On the grounds of and directly above the National Warplane
Museum, Geneseo, NY (please see attached portion of Detroit
section map).
You can then copy that portion of the section map, circle the launch site
in red or some other color, and write the legend, "Area of Proposed
Operations." (Remember, these folks talk in Bureaucratese.)
In either case, this is the line on which you request altitude. Again,
in FAA patois, "No operation under this waiver will exceed 5000 feet AGL"
are the magic words which have worked for us (along with "please" and
"thank you"). If you can read the altitude of the terrain on the section
map, you can add this to the requested altitude above ground level to
arrive at the altitude above Mean Sea Level (MSL), which might be
appreciated by the person processing your application.
On Line 7 you give your starting and ending dates and times, and any
rain dates. It's not necessary (nor is it desirable) to use Zulu
(Greenwich Mean) Time, but these folks use that "hundred hour" jazz
that Colonel Blake on M*A*S*H hated so much. Make sure to indicate
what time zone you're referencing, for example "1030 EDT".
Lines 8 through 14 pertain to airshows and the like, so just put an
"N/A" or two there to let them know these areas aren't blank because of
an omission. You sign on Line 15, and have an opportunity to say a
little something about how you're going to be running things. I usually
write in the following, under "Remarks":
All operations will be conducted in accordance with the NAR
Safety Codes and shall be under the control of an experienced
Range Safety / Launch Control Officer. A spotter will watch
for aircraft entering the operations area, and will temporarily
suspend operations in this contingency.
Make three copies. Keep one for yourself, send your original and two of
the copies to the Regional Office. Attach three copies of both Safety
Codes, because the Model Rocket Safety Code covers rockets which will
be under the terms of the waiver. Also attach three copies of the
germane portion of the section map, if that's how you're indicating
where you are going to fly. Include a short letter of transmittal.
After having some scares about the last two applications I sent in,
next time I plan to include a receipt postcard. I'm going to put my
address on the address side, and on the other side it will say:
Received _________________ (date) an Application for
Certificate of Waiver or Authorization, FAA Form
7711-2, at this office. For further information,
please contact ___________________ (name) at
_________________ (telephone number, extension).
Bureaucrats see these things all the time, and they know what to do with
them.
Mail off this packet to the FAA Regional Office, to the attention of
Flight Standards (I think!). You need to apply at least 30 days (the form
says 45 days, so be sure) in advance. If you don't hear back from them
in two or three weeks, give them a call. We had to do this twice; once the
form was lost, and another time it was just in the "in" basket.
If all goes according to plan, you should get back your application, all
the other stuff you sent (talk about carrying coals to Newcastle!), and
the Magic Certificate of Waiver! There will be a few strings attached.
You should be instructed to inform the nearest ATC, and possibly an
Automated Flight Information Service, a certain time before you start,
in order to "activate" your waiver. You'll probably be instructed to
contact them when you're done, too. Usually these things are not a big
deal, but sometimes you get a person who doesn't know why you're
bothering them. Just tell them that you're carrying out instructions
from the Regional Office to give a Notice to Airmen, pursuant to the
terms of your Certificate of Waiver. A little official-sounding talk
will make them feel right at home.
Of course, you have to make sure all fliers are familiar with the terms
and conditions of your waiver, because it's your butt that's on the
line, too. It is a standing MARS policy that the waiver certificate
and application are available for inspection by all fliers.
After the launch, I usually send a letter to the person who sent me
the Certificate of Waiver, thanking them for their help, and letting
them know we had a safe and enjoyable time. It helps grease the skids
for the next waiver you want, besides being common courtesy.
It's not hard to obtain a waiver if you make your application in a
professional manner, and conduct your activities likewise. There's no
fee, but there is some effort involved. Finally, keep in mind that the
people working on your application are people, and as such they
respond to being treated courteously and professionally. I hope you
find the process relatively simple and painless.
-----------------------------------------------------------------
10.8 Is high power rocketry legal in every state, if the proper forms are
obtained?
No. Even with an FAA waiver, HPR is NOT legal in every state. Check
with your local fire marshal for requirements/restrictions in your area.
The NAR and Tripoli are actively working to get state restrictions on
model and HPR removed.
-----------------------------------------------------------------
10.9 Where do I find out the proper way to use HPR rockets and motors? I'm
familiar with the NAR Model Rocketry Sporting Code. Is there an HPR
equivalent?
Both the NAR and Tripoli have HPR safety codes. The two organizations
are working together to produce a consistent safety code to be presented
to the NFPA. These codes specify minimum launch field sizes, minimum
distance to keep from launchers, etc. The NAR High Power Rocket
Safety Code has been published in Sport Rocketry, and is on their web site.
The Tripoli safety code is published in their Members handbook, which is
sent to all new Tripoli members.
EVERYONE WANTING TO GET INVOLVED IN HPR IS STRONGLY URGED TO JOIN ONE OR
BOTH OF THESE ORGANIZATIONS. There are legal restrictions to buying
high power motors. Only certified members of 'legally qualified'
organizations may purchase them. If you want to fly high power you need
to be a member of either the NAR or Tripoli.
The High Power Safety Codes for both the NAR and Tripoli are based on the
NFPA 1127 guidelines. Both organizations recognize the others safety
code, motor certifications, and HPR user certifications.
-----------------------------------------------------------------
10.10 What are some good kits to build when first getting into high power
rocketry (assuming I have all of the basic model rocketry skills)?
Popular rec.models.rockets vote:
LOC Graduator
From: c...@pdp.sw.stratus.com (C. D. Tavares)
AAA Penn. Crude
From: kapl...@hccompare.com (Bob Kaplow)
- Avoid any kit with plastic fins or internal parts.
- Avoid phenolic tubes, thick cardboard tubes are more familiar
and easy to work with
- For Large Model Rockets, try a LOC Graduator or Rocket R&D/THOY
Hornet
- For a High Power rocket try a LOC IV or EZI-65, or a Rocket R&D/THOY
Falcon
From: JCook@Epoch.C (Jim Cook):
LOC kits are a good introduction into high power - they are strong
(banging it several times for emphasis on the table).
From: buz...@netcom.com (Buzz McDermott)
If you have never flown anything bigger than an Estes or FSI D
motor, I would recommend building one or more E-G kits before
tackling H power and up. When you go for your NAR or TRA
certification, choose a rocket where G and H motors are the low
end or mid-range power options. Going with a rocket where your
chosen motor is at the high end or above the rockets recommended
power range is more likely to fail by over-stressing the design.
Bigger, slower high power rockets are less stressed and more likely to
succeed. In the case of NAR certification, this gets you a rocket
good for multiple certification levels. I like the following (any
are good NAR or TRA certification rockets):
LOC Mini Magg, 38mm mount (G-I motors)
LOC EZI-65, 54mm mount (G-I motors)
THOY (Rocket R&D) Falcon, 54mm mount (H-J motors)
From: mike_...@cjnetworks.com (Mike Forman)
I bought, built, flew and certified on a PML Io. Very nice kit. I
glassed the tube, and would bet it's as close to bulletproof as you
could get and still be legal to fly as a hpr. I posted a review of
the Io here, and you could probably go to dejanews' archive and
retrieve it. Great rocket, great flights, easy to build.
From: ma...@netins.net (Mark U.)
My favorite 4 in. rocket is the THOY/R&D Falcon. In stock configure it
easyily will handle H-J and if beefed up a K is not out of the question.
My second choice would be a PML Quasar this will fly nicely on a H-I
motors.
-----------------------------------------------------------------
10.11 When is a Federal Low Explosives Permit required?
NOTE: As of 1997, the BATF will be formally clarifying their
interpretation of what high power rocket motors require a Federal
Low Explosives Users Permit (LEUP). At the time that this is written
(Jan. 9, 1997) it appears that reloadable motor propellant segments
less than 62.5 grams in mass will require a LEUP if their intended use
is to assemble a motor that has more than 62.5 grams of propellant.
Furthermore, LEUP fees may be raised. At the time of this writing, these
changes are not yet in effect. The National Association of Rocketry and
Tripoli Rocketry Association are working together to see what can be done
to protect the interests of high power rocketry enthusiasts, and will
be keeping their members informed of the latest developments.
The following are excerpts from a joint communique issued by the
High Power Rocket Manufacturers and Dealers Association and the Tripoli
Rocketry Association to the high-power rocket community on 25 April 1994.
It was posted to CompuServe by Michael Platt, president of the HPRMDA.
----
[Based on informal clarification from the BATF, it is our belief that:]
(a) single-use model rocket motors containing no more than 62.5 grams of
propellant are exempt from Federal licensing and storage requirements;
(b) reloadable rocket motor products are also exempt from Federal licensing
and storage requirements, provided that the mass of each propellant grain
is no more than 62.5 grams, and has received a DOT shipping designation
as Explosive 1.4, but may not be made available to children;
(c) any single-use motor containing propellant mass greater than 62.5 grams,
or any reloadable rocket motor product containing a propellant grain
which weighs more than 62.5 grams, is subject to Federal licensing and
storage requirements.
Users (e.g. consumers, flyers) of high-power rocket motors and reload kits
as described in item (c) above, are subject to Federal, and possibly state
and local, permit requirements for the purchase and storage of explosives.
On the Federal level, this involves obtaining an explosive user permit from
BATF, at a cost of $20 for the first year, and $10 for each subsequent
three-year period. An important exception to the Federal requirement for a
user permit is if the user were to purchase a motor or reload kit in his
state of residence as defined by BATF, and either (a) use the motor or
reload kit at the site of purchase (e.g. a launch), or (b) transport it to
an approved storage facility located within the boundaries of said state.
Everyone--manufacturers, dealers (distributors), users--who stores (as
defined by the BATF) a high-power rocket motor or reload kit as described
in item (c) above is subject to Federal, and possibly state and local,
requirements for the storage of explosives. All storage of a high-power
rocket motor or reload kit must be in accordance with Federal explosive
storage requirements, even if a Federal license/permit is not required for
purchase. There are no exceptions to this rule.
-----
A document with questions and answers about the BATF and rocketry is
available at the sunsite archive:
http://sunsite.unc.edu/pub/archives/rec.models.rockets/BATF/batfqa.txt
Instructions for filling out a LEUP are available on the Rocket Science
web site:
http://www.scsn.net/users/rockets/LEUP_consumer.html
-----------------------------------------------------------------
10.12 How do I get an LEUP? Are there any requirements?
The following is an excerpt from the June 1994 'Tripoli Report'. Since
this deals with Federal Law and not Tripoli rules, I do not believe that
there is any violation of Tripoli by-laws in doing this.
Q: How would a person qualify for a Federal user's permit?
A: The chief, firearms and explosives licensing center, will approve a
properly completed application if the applicant:
1) Is 21 years of age or older,
2) Is not a person to whom distribution of an affected high-power
rocket commodity is prohibited under the Act (Federal law),
3) Has not willfully violated any provisions of the Act,
4) Has not knowingly withheld any information or has not made any false
or fictitious statement intended or likely to deceive concerning the
application,
5) Has storage for the class (low explosive) of an affected high-power
rocket commodity, as described on the application, unless he establishes
that his operations to be conducted will not require the storage of an
affected high-power rocket commodity.
6) Is familiar with and understands all published state laws and local
ordinances relating to affected high-power rocket communications
in which he intends to conduct operations.
ATF Form 5400.13/5400.16 must be filed to obtain a permit.
From: buz...@netcom.com (Buzz McDermott)
You may obtain a users permit with or without a storage magazine. If
your primary reason for the permit is to be able to buy HPR motors
at out of state launches, then you don't need a home storage magazine.
If you do have a home storage magazine, remember to keep the proper
records for all motors added to and removed from the magazine.
Michael Platt has indicated willingness to help anyone who has any
questions regarding the proper filling out of the permits. He may
be reached at 7023...@CompuServe.COM.
-----------------------------------------------------------------
10.13 How is thermalite affected by the ATF regulatory enforcement?
From: 7023...@CompuServe.COM (Michael Platt )
Thermalite is a brand name for igniter cord. Purchase and storage of
igniter cord is regulated by BATF. Purchase and/or storage of igniter
cord, IN ANY QUANTITY, requires an explosive license and an approved
storage facility, i.e. an explosive magazine. This includes thermalite
in any length, including the one inch lengths commonly included with
motors produced by various manufacturers. The only exception to this
would be the purchase by a user for immediate use in the state where
he/she resides.
-----------------------------------------------------------------
10.14 How can I get the Orange Book (explaining the ATF explosive laws
and regulations) and the proper LEUP forms?
Call you regional BATF office and ask for the Orange Book and an
application for a Federal Low Explosives Users Permit. Remember that you
want a Users permit (there are several other types of permits). The
regional office will mail these to you at no charge. The documentation
you receive will indicate where the filled in forms and payment should
be remitted.
-----------------------------------------------------------------
10.15 Just what is a 'hybrid' rocket motor? Who makes them?
From: kevin...@aol.com (Kevin Reed)
A hybrid motor as sold for model rocketry uses a solid fuel grain and a
liquid oxidizer -- in the case of commercial model motors, nitrous oxide.
A composite motor uses a solid oxidizer -- ammonium perchlorate -- mixed
with a rubber binder/fuel to make a unified solid grain.
I can't think of any 24mm hybrids on the market; the smallest, I think,
has an "I" rating and fits into a 54mm mount.
There are two companies currently manufacturing them commercially,
Aerotech and Hypertek. One system loads the oxidizer tank before loading
the motor in the rocket, while the other fills the tank after the rocket
is in launch position.
Hybrids have a couple of advantages over composites: one is that there is
virtually no fire hazard transporting or storing the motor: without the
oxidizer in direct contact with it, the fuel grain is almost inert. It is
also not covered by the same DOT shipping restrictions, because the tanks
are DOT certified and the fuel grain poses no environmental or fire
hazard.
[Editor's note: The Jan 1996 issue of High Power Rocketry magazine has an
excellent article comparing the Hypertek and Aerotech hybrid systems.]
---------------------------------------
Copyright (c) 1996 Wolfram von Kiparski, editor.
Wolfram v.Kiparski
Rec-models-rockets-archive-name: rockets-faq/part11
Posting-Frequency: monthly
Last-modified: 1997 January 9
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
rec.models.rockets Frequently Asked Questions: PART 11 of 14
HIGH POWER CONSTRUCTION TECHNIQUES
This section includes tips and suggestions on various topics having to do
with construction and finishing techniques for High Power rockets. Many of
the same techniques may be used with Large Model Rockets, as well.
Readers are encouraged to read the North Coast Rocketry technical reports
on HPR construction and finishing techniques (available from NARTS and
other sources).
[Note: This portion of the FAQ is maintained by Jerry Irvine
(jjir...@cyberg8t.com).
All comments and suggestions should be sent to him.]
------------------------------------------------------------
11.1 Do you have any tips for cutting and sealing fins used on HPR rockets?
From: utid...@remarque.berkeley.edu (David M.V. Utidjian):
To fill the grain in balsa fins and fill in the spirals in body tubes
use epoxy. I use HOBBYPOXY "Smooth 'n' Easy" Epoxy finishing resin.
For fins it does the trick in one coat... and sands easily... and
adds strength to the fins. I use those disposable brushes with the
metal handles and brush on a single coat after a preliminary sanding.
I then use auto body primer filler in gray and red-brown from spray
cans for the entire model. This gives very thin and even coats. I
alternate the colors of the coats to show where the low and high spots
are. My last sanding before paint is done with 400 grit wet/dry paper
and I do this wet... being careful not to get any inside the body tube.
[Another good coating-type epoxy is PIC 'Coating Poxy'...Buzz]
[NOTE: This is not for kids or the inexperienced!! This technique is
used in HPR where the added weight is not a penalty: Buzz]
From Bob Turner (NAR member, not on net):
Bob Turner (the DARS NAR section advisor) suggests using alcohol in
smoothing 'coating' type epoxies. The PIC 'Coating Poxy' instructions
suggest using your fingers to 'burnish' any surfaces (i.e., fins) filled
with the coating epoxy. Bob suggests using a VERY soft cloth which has
been dipped in alcohol to rub the fins after about 30 minutes (or
whenever the epoxy starts to set and is just slightly sticky to the
touch). [I followed Bob's suggestion and got MUCH smoother fins over
the hand/finger burnishing method...Buzz]
From: ja...@rml.com (Jack Hagerty):
When sanding fins, or any other balsa part that you want to be all
uniform, stack the parts together, even them up the best you can
(you'll be surprised at how uneven those die-cut pieces are!) on
the root edge and drive a couple of straight pins through them to
hold the stack in registration while sanding. For larger fins,
anything over about 2 sq. in, use three pins. I find that the pins
that come in shirts are just about the right size. The small holes
that are left when you remove the pins are easily filled during the
sealing/filling step.
From: kapl...@hccompare.com (Bob Kaplow)
I've found two handy tools for sanding big rockets. 3M makes these
sponge-like sanding pads. They are great for conforming to the
curves of tubes, nose cones, fillets, etc., and make quick work of
fillers. The second is a palm sander, just like Norm uses on TV. Big
rockets call for heavy duty solutions. Save the belt sander for
airfoiling the fins during construction.
Condensed thread on filleting fins; many contributors:
First, ALWAYS fillet high power fin joints, even fins mounted TTW to
the motor mount. This will add strength and improve the aerodynamics
of the model. The suggestions for filleting material include:
* 5 - 30 minute thick epoxies
* 30 minute (or longer) thin epoxy mixed with micro-balloons
until it has a thick, paste-like consistency; let it thicken
some prior to using it
* SIG Epoxilite (warning: this got very mixed reviews)
Always keep a bottle of rubbing alcohol handy when working with epoxy.
Dip your finger in the alcohol and run it along the fillet to smooth
out the bumps. It was mentioned that a pure epoxy 'topcoat' was
necessary on top of the epoxy/micro balloon mixture, although using
an alcohol-soaked finger to smooth the micro-balloons might eliminate
the topcoat requirement.
Use 30 minute epoxy with microballoons added. Let it sit for a few
minutes in the pot so it thickens, and then apply it. The microballoons
make it much less runny, so you don't have to keep watching the fillet
to make sure it's not dripping or running around the edges. Also do one
side of two fins at a time:
\ /
\ / f = fillet, ^ = really bad version of body tube
\f f/ / and \ = fins
^^^^^^
------------------------------------------------------------
11.2 How do you keep in a high power motor in its mount, but still allow
for the numerous lengths in which HPR motors are sold?
From: bi...@hpcvaac.cv.hp.com (Bill Nelson)
I make a clip similar to the ones used on model rockets - however, I do
not pierce the motor mount tube - I place the front end of the retainer
over the front of the tube. It is epoxied/taped in place, just like with
a model rocket. I do not rely on spring pressure to hold the clip over
the end of the engine. I use several turns of strapping tape - wrapped
around the engine or motor mount and the retainer clip. So far, I have
never had a problem with an ejected engine.
From: JC...@Epoch.COM (Jim Cook)
Some folks at NARAM 33 suggested drilling a small hole in the side of
the flange of the rear nozzle retaining ring [of an ISP reloadable motor
casing] to tie the casing to the model. Some might claim this to be
"modification of rocket motors not approved by the mfg." I had though I
heard Aerotech was going to start doing this themselves, but I haven't
seen anything yet.
From: ne...@boi.hp.com (Neil Pyke)
I've built #8-32 "t-nuts" into my last couple of rockets and then made
sheet metal brackets to hold the motor in. I drill two holes, 180
degrees apart, in the aft centering ring and then press and glue the
t-nut into the hole. The screw holds the bracket to the centering ring
and I bend the bracket so it hooks over the end of the motor. The t-nut
works great but I've made my brackets too wimpy. Those that saw
me wandering around just past the flight line at LDRS a couple weeks
ago, looking for my ejected motor, will know that I have not perfected
my application of this design.
From: Roger....@umich.edu (A. Roger Wilfong)
I've used a similar technique with t-nuts and had no problems - yet.
I've also tried a coarse thread sheet metal type screw (I'm not sure
what they're really called - the threading is about twice as coarse as
a regular sheet metal screw) screwed into the rear centering ring at
three locations. The centering ring needs to be plywood and you need to
carefully drill the correct sized pilot hole for the screw. After
'tapping' the screw into the hole, I took it out and ran a small amount
of thin CA into the hole for reinforcement - let the CA set before you
put the screw back in the hole or you won't get it out again. This has
worked on RMS-29 and while it is not as strong as the T-nuts, so far it
has been more reliable than masking tape.
From: soc...@vx.cis.umn.edu (Tim Harincar)
On the 2 29mm birds I've constructed, I use a clip and a thrust ring.
It works like this:
---:| |
=====:| |====== <- Centering Ring
:| |
:| | <- motor tube
:| |
:| | --:
:| | : <-Clip made from steel rod
=====:| |====== :--
:
:--
The steel rod has two opposite 90 degree bends, and is run through the
centerings and along the motor tube. The idea is to spread the force of
ejecting along the top centering ring and to the rest of the motor
mount, instead of making the clip do the work. Also, on larger tubes,
you can design this so that the clip swivels into place, instead of
using spring tension.
The clip then extends 1/4" to 1/2" beyond the end of the tube. You then
use this space for the motor thrust ring. The thrust ring is then added
to the end of motor. I just usually wind the end of my motor with a
bunch of turns of masking tape, but I've heard of people epoxying some
other type of ring to the end of the motor.
From: wa...@netcom.com (Walt Rosenberg)
You use a "thrust ring" - several wraps of masking tape on the nozzle
end of the motor. This prevents the motor from going up the mount.
Of course, if you use re-loadables (ISP, AeroTech), the nozzle enclosure
is larger than the O.D. of the motor mount - in this case, just the tape
to keep it from coming out. Of course there are several methods used to
keep the motor from kicking - screws and washers, screws and hooks,
retaining rings, etc. placed over the ridge on the nozzle end of the
motor.
From: pste...@well.sf.ca.us (Paul J. Ste. Marie)
Typically what you do is wind a ring of masking tape at the end of the
whoosh generator of the same thickness as the engine mount tube.
This serves as a block to keep the engine from sliding up into the
rocket under thrust. Typical widths of tape to use are:
.25" 1/4A-B
.5" C-E
.75" F-H
1.0" H-I
1.5" I-J
2.0" J-K
From: wa...@netcom.com (Walt Rosenberg)
[Referring to the use of different tape widths, above]
1.5" for I-J and 2.0" for J-K may be too wide. You are now going to move
the center of gravity further back. You may introduce instability. I've
never used more than 3/4" for all my high power launches (H-K).
From: kapl...@hccompare.com (Bob Kaplow)
My [retainer] hooks look like this:
----
| | <<- this end slips over lip of bottom reload
| closure
|
|
|
____| <<- this end screwed/bolted onto rear bulkhead
^hole drilled here for cap screw
The top of the hook wraps over and around the reload closure lip, and
can't push out like an Estes clip. Hooks ARE brass. I use stainless cap
screws to hold the clips in place - cap screws stay on the end of the
tool, unlike other screws. I use T-nuts installed on the back side of
the
rear centering ring, or threaded brass inserts to retro-fit older
rockets.
------------------------------------------------------------
11.3 Custom Decals for High Power Rockets
The techniques described here could also be used for model rockets. The
decals made this way tend to be large and `thick', so this info has been
included in the High Power section.
From soc...@vx.cis.umn.edu (Tim Harincar):
As a computer graphics person, I have done quite a bit of experimenting
with laser printers and making my own rocket art. I mostly stick with
clear sticky-back type stocks, they are the cheapest and most available.
I use Fasson brand, and I think its 1.5 or 2 mil. thick. It works
good for
large models but is a little thick for small scale stuff. It curls right
out of the laser while it cools. Don't worry, though. It doesn't distort.
This stuff is typically available at most quick print shops. Typically
its called Crack 'N Peel.
Toner chips very easily off of the smooth finish, so be careful and as
soon as you can, spray on an over coat of clear flat enamel or lacquer.
I tape the sheet down to cardboard then spray, Leave it for a day or so.
This also makes it lie flat.
I know that blank water transfer stock is available, but its about $3 for
an 8.5 x 11 sheet. Use same method as above to preserve the image. This
is usually available at model railroad shops.
I have never seen the dry-transfer stuff, but I know its pretty popular
with the railroad folks. (that is, the pre-printed stuff).
One other option that I have wanted to try is the heat-transfer colors.
Once you have a laser image, you lay a piece of special colored film
over the image and heat either with an iron or re-run the sheet through
the laser and let the fuser do the work. The color then attaches to the
toner.
Most of these colors are metallic, but there are some standard, non-
metallic colors as well. Letraset was the first company to market
the color transfer stuff.
------------------------------------------------------------
11.4 I've had several rocket body tubes ruined by the shock cord tearing
into the body tube at ejection and making long slits. How can I
prevent this?
Many of us have recovered our rockets only to find that shock line has
slit ('zippered') the body tube. This happens most often when a very
thin shock line is used or when the rocket is traveling very fast when the
tubes separate. The following suggestions have been offered to prevent
this from happening:
From: bar...@powder.add.itg.ti.com (Stu Barrett)
I built a LOC Caliber a year or so ago. I installed a LOC ejection
baffle at the top of the motor mount tube and that worked great.
However, I'm in the process of enhancing my model so that it uses the
"anti-zipper" technique that is described in the Mar/Apr [1993] issue
of HPRM. It combines a fool proof mechanism to eliminate the dreaded
"zipper effect" and also has a nice effect that no wadding is needed.
------------------------------------------------------------
11.5 Estes 'toilet paper' recovery wadding strikes me as a bit wrong for HPR
rockets. What are some alternatives?
From: ja...@rml.com (Jack Hagerty)
Just go down to your local building supply store and get a bale of
cellulose wall insulation. This is just shredded newspaper treated in
the same fire suppressant [as Estes recovery wadding]. A $5 bag will give
you enough wadding to last years!
From: js...@rc.rit.edu (J A Stephen Viggiano)
In order to avoid fallout, you might want to put the engine in *before*
the [cellulose] wadding, or, for smaller rockets, a sheet or two of
regular
wadding underneath the fluffy stuff.
Wayne Anthony uses cabbage leaves (you get more leaves per head [than
lettuce], and they seem to be a little tougher than lettuce), and I've
heard of people using grass.
From: buz...@netcom.com (Buzz McDermott)
I use acoustic speaker insulation. I costs #3 - $5 per bag at Radio
Shack. It's reusable, and one bag generally lasts me for dozens of
flights. [Editors note: This material is not necessarily bio-degradable
or environment friendly. Do not use this type of recovery wadding at any
field where remnants might be ingested by live animals. It will kill
them. Also, consider tethering fiberglass to shock line to prevent
loss.]
------------------------------------------------------------
11.6 What are the differences between the various HPR body tube materials
used by the most HPR manufacturers?
The most common one is that material used by Estes and later by other
suppliers such as U.S. Rockets, LOC Precision, AeroTech, Launch Pad, etc.
This material is a spiral wound virgin kraft tube. Virgin kraft is stiffer
than recycled kraft and can much more easily withstand flight stresses at a
given thickness than recycled tubes as commonly found in household goods.
This material typically has an outer wrapper of "glassine" which makes the
tube smooth and accepts paint more easily. It also covers up the thicker
tube spirals of the under layers and makes removing tube spirals with a
couple applications of sanding sealer practical.
Another common tube material is that used primarily by Public Missles. It
is a spiral wound paper with phenolic resin impregnated into it. This has
several advantages such as higher ultimate strength in aero-applications,
more waterproof out of the box and being fairly stiff. However this
material is also susceptible to cracking due to impacts and has been known
to crack during routine slow landings under over adequate parachutes.
A really good material for HPR is used only by Dynacom and U.S. Rockets and
is known as G-10 fiberglass. There are several practical variants of this
material. One can use either cloth wound or filament wound and the G-10
refers to one supplier's particular classification of a resin they use.
Even they use a dozen different resins. Among the glasses uses are
"e-glass" and "s-glass". Since one is both more expensive and stronger in
ultimate fail tests it is often used as motor casing material. However for
airframe applications, cheaper and thinner is better.
Other good but less common materials include cloth wound phenolic
impregnated, paper convolute wound phenolic impregnated, exotic composites
of kevlar, graphite, etc.
A very common material used (at one's own peril) is recycled paper style
tubes such as mailing tubes, paper towel rolls, etc. These must be over
1/8" thick to even be used for HPR at all. Even then they are easy to
damage and "unroll" on landing as they typically do not use glue except on
the edges. Rocket specific tubes are glued across the entire surface of
the superior virgin kraft material.
Plastic tubes can be used but the bonding problems of motor mounts and fins
have resulted in these having virtually no adoption among serious model or
high power rocketeers. Motor mount tubes must have an insulating element
as plastic motor tubes would quickly become the permanent owner of a motor
casing.
------------------------------------------------------------
11.7 How can I strengthen my thick paper (i.e., LOC type) body tubes?
Various composite construction techniques may be employed to strengthen
paper body tubes. These same techniques may be used to build scratch body
tubes as well. An excellent article on composite construction techniques
appeared in the XXXXXXXXXX issue of High Power Rocketry magazine. Another
article dealing with strengthening HPR rockets appeared in the XXXXXXXXX
issue.
The two most practical methods for strengthening the paper body tubes
used by LOC, THOY, etc. are 1) reinforce the tube with couplers for most
of its length and 2) wrap the tube with some type of reinforcing layer.
The first option produces a strong tube, but has the drawbacks of high
cost (at $2-4 per coupler) and high weight.
The most common material used with the second option is fiberglass cloth.
Two ounce cloth is good for use on 2.5 to 4 inch diameter tubes. Five
ounce cloth might be used for larger tubes. R.m.r posters have recommended
several techniques for applying the fiberglass. Here are two of them:
From: bmcd...@ix.netcom.com (Buzz McDermott)
1. Sand the tube with 320 grit sandpaper to slightly roughen its surface.
2. Mark a straight line down the length of the tube.
3. Lay out the fiberglass cloth on a flat, smooth surface. Use a square/
straight edge and a SINGLE EDGED RAZOR BLADE to cut the fabric to
a rectangle, allowing for at least 1" overlap around the diameter
and off each end of the tube to be covered.
4. Lay out and tape together enough wax paper on the floor of your
garage, basement, etc., to be larger than the fiberglass cloth in all
dimensions. Lay the cloth on the wax paper. Tape the wax paper to the
floor (but NOT to the glass cloth).
5. LIGHTLY spray one side of the cloth with 3M 77 adhesive. I mean
to put on a QUICK, VERY LIGHT coating of adhesive.
6. Lay the tube down on one edge of the fiberglass, using the line on the
tube as a guide to get the tube straight along the glass cloth.
7. SLOWLY roll the tube along the cloth, working out wrinkles with your
fingers. The 3M 77 should lightly tack the cloth to the body tube.
8. Once the cloth is on the tube, use thin *odorless* CA to seal the
overlap and edges along fin slots and ends of the tube. Using a
plastic
bag over one hand gently rub the CA into the cloth. Also CA any
wrinkles that are left. When the CA dries you can use the single edge
razor to trim off excess cloth at the ends, feather sand the overlap
joint (with 320 grit), cut out fin slot openings, and sand down or
slice off any wrinkles in the cloth.
9. Brush on 20 minute 'finish cure' epoxy. Bob Smith 'Coating Poxy' and
Hobby Poxy 'Smooth N Easy' are good choices. Completely cover the
entire cloth surface. Be sure and gently work the epoxy into the
cloth. You want the cloth soaked and the epoxy soaking into the
body tube.
10. About an hour after you finish, the epoxy should be getting real
'tacky'. Soak some rubbing alcohol into a clean, lint free cloth and
use that to lightly 'buff' the epoxy. This will help smooth the
coating and get rid of air bubbles.
11. After 24 hours, sand with 240 grit wet-or-dry, WET, until smooth.
You are now ready to prime.
Two additional notes:
1. With lighter cloth (3/4 up to 2 oz), I sometimes soak cyano into the
entire cloth surface. I then sand with 320 grit VERY LIGHTLY. I find
I use much less epoxy and end up with a lighter rocket. This is a
good technique when weight is critical.
2. Always wear latex gloves when working with epoxy. People do develop
nasty reactions to this stuff over time.
From wo...@netheaven.com (Wolfram v.Kiparski)
When using 3/4 oz. cloth, I find it easiest to first paint epoxy
(thinned
with a little laquer thinnner) on the body tube and then lay the cloth
onto the tube. The cloth readily "wets out" when it touches the epoxy,
and adheres to the tube without curling up. The cloth can be gently
arranged and gently brushed to smooth out the wrinkles as you wrap it
around the tube. Extra epoxy can be dabbed on as needed.
For 3/4 oz. cloth:
1. Cut the cloth to size first. Cut the cloth slightly oversize so that
it is a little longer than the tube, and will overlap if wrapped
around the tube.
2. Mix your favorite epoxy and add about 5% laquer thinner. Paint
this onto your body tube with a china bristle brush. I use a 1.5
inch brush. Thinning the epoxy makes it spread easier, and will
help keep lightweight cloth from distorting and wrinkling. It will
also cause you to use less epoxy.
3. While the epoxy is still "wet," drape one end of the cloth onto the
body tube. Use your brush to smooth the cloth out. Brushing in only
one direction will help avoid wrinkles. Roll the tube slightly as
you smooth the cloth onto the epoxy-covered tube. The cloth will
pick up enough epoxy to wet-out. If it doesn't, add a dab of epoxy
to help it along. You can free both hands by placing the body tube
over a long wooden rod like the kind used for closet hanger rods.
Support the rod at both ends kind of like a giant toilet paper
dispenser.
4. 3/4 oz. cloth will stick to the body tube and tend not to lift up
before the epoxy has cured. Be careful not to brush too vigorously
when overlaping the cloth as you finish applying it. You might
wrinkle the bottom layer of the overlap, and experience a great deal
of frustration.
5. After the epoxy has cured, lightly wet sand with 220 grit sandpaper.
Fill in any low spots with spot putty and sand smooth.
A few coats of primer will fill in the weave of 3/4 oz. cloth,
especially if you lightly wet sand with 320 grit between coats.
With a little practice, this technique is easy to do, and adhesives
other than epoxy are not required.
From da...@ddave.com ('Dangerous' Dave)
[Dave had the following comments about the above described technique.
Dave
is an expert in the use of composites, fiberglass and laminating
techniques]
When the glass is fully cured, you can sand the lap joint till it
feathers into the adjoining surface. Any irregularities can then be
filled with a polyester filler (Bondo) and spot putty to blend the
surface so that it is unnoticeable.
Don't use an adhesive to tack the glass in place. It will prevent the
resin from soaking into the fabric and will effect the physicals of
your epoxy. Cut your fabric to size allow and inch or so overlap that
you can trim off later. Wet your surface and then drape the fabric on
to it. Then stipple the resin into the fabric with a china bristle
brush. Don't use a paintbrush that is made from synthetics, i.e.:
nylon, polyester, ect.. The epoxy and/or your cleaning solvent will
dissolve your brush and it may react with the resin.
Be sure and read my Safety Document on handling composite materials
before you do any of this.
You will get your best adhesion by completely removing the glassine.
Since resin can't penetrate it and will not bond well, you must remove
it in order to take advantage of any strength gains you get from
applying glass.
Visit my web and ftp sites for some more info on laying glass.
FibreGlast at: http://www.fibreglast.com has a very good section on
composite techniques.
[Editor's note: If you're going to work with fiberglass, epoxies, or
carbon fiber, check out DDave's web page, www.ddave.com].
------------------------------------------------------------
11.8 Is there any way to retrofit my existing rockets to have some type of
positive retention system?
From bi...@PEAK.ORG (Bill Nelson):
Well, you can reinforce the aft ring a bit, then use the screw-in
threaded
connectors that are available.
From sil...@ix.netcom.com (The Silent Observer):
Drill a hole on each side, and install a Molly (R) or similar "drive
fastener" or expansion fastener -- the kind used for hollow walls and
doors. Do this with a dowel or motor casing in the motor tube, so the
little metal "legs" on the fastener don't punch through the tube; you'll
find these are about as strong as a blind nut, install from the front,
don't cost much more (if at all), accept standard threads (and come with
a screw!), and look neater. One thing to watch, though; the threads in
the fastener strip pretty readily (they're aluminum) and they're the
devil to remove if you do strip one.
From jsi...@ux1.cso.uiuc.edu (Jonathan Sivier):
I retrofitted blind nuts on a couple of my rockets using the anchor bolts
that are available at most hardware stores. These are a metal tube with
threads on the inside and slits along part of their length. You drill a
hole in your bulkhead, push the bolt unit through and tighten the bolt.
As it tightens the tube expands at the slits to push against the back of
the bulkhead. It also has a lip on the front so the anchor is firmly,
uh,
anchored. :-) With a little epoxy under the lip it becomes a very strong
mount for motor retention devices. They have different sizes for
different thicknesses of material, from 1/8" up. They may take up a bit
more room than the blind nuts, but if the rocket is already built
they are
a great way to make this improvement.
From kapl...@hccompare.com (Bob Kaplow):
Use threaded brass inserts, and a drop of thin CA to keep them in. They
don't have the large lip on the back, so it won't be as strong, but my
first 3-4 HPR models were done this way. Now I put blind nuts (also
called
T nuts) in all my larger rockets. I even use them in motor mounts
where I
have the room. DuBro makes some VERY SMALL 6-32 T-nuts that fit most
adapters that have a plywood ring. I've yet to come up with a retainer
for the heavy cardboard tube style adapters.
From: c72...@aol.com (Gary ??, C72500)
If you have already assembled the rocket, look for a "thinsert" and
installer tool. This is basically a threaded rivet -- drill a hole in
the
centering ring, put nose of tool (with insert threaded on) and squeeze -
permanently installed threaded insert! I have used this to retrofit
every
rocket I have built, and have yet to lose an insert or a motor.
Installer
and inserts are available through a company called Northern via
catalog -
runs about $13.
------------------------------------------------------------
11.9 All these high power motors are different sizes. How do I hold
them in? What do I use for a motor block and where should I put it?
From: jac...@sn3.jsc.nasa.gov (Al Jackson)
For mounting and retaining HPR motors I have this suggestion, especially
with PML models. See if you can let a good one inch of motor mount
protrude from bottom of model. Then when using a reload motor, besides
using a tape friction fit, put a wrapping of strapping tape around the
end enclosure and wrapped also around the piece of motor mount sticking
out.
From: jjir...@aol.com (Jerry Irvine)
Perhaps I'm just tired of seeing people reinvent the wheel to
non-round shapes, but I have found that:
1. There is no need for thrust rings inside rockets of any power or
weight. The application of a masking tape thrust ring on the
nozzle
end of the motor of adequate width for motor thrust is always
adequate, to the point where a fiberglass or metal one is better.
a. 1/4" wide masking tape is often used for 1/4A-F motors with
thrust levels under 40 newtons.
b. 1/2" wide masking tape is often used for 1/4A-J motors with
thrust under 200 newtons.
c. 3/4" wide masking tape is often used for F-K motors with thrust
under 600 newtons.
d. 1" up to 1000 newtons, 1.5" up to 2000 newtons, then above
that
a structural ring at the rear of the motor.
2. With the above system one can add an external motor hook with NO
protruding rear thrust block, extended out the rear the exact width
of the masking tape you most prefer. The hook should typically be
metallic and bonded to the outside with epoxy for maximum strength
and instead of protruding hooks, they can fan out to the side for
better bonding strength.
From kapl...@hccompare.com (Bob Kaplow):
You want to install blind nuts on the BACK side of the aft centering
ring,
before the mount is installed in the rocket. That way it can't pull
through.
[Epoxy a little around them]to hold them in place when not bolted in.
The
screws go into these threaded holes, and hold in whatever clip you are
using. I personally prefer cap screws and an allen wrench to machine
screws
and a flat blade screwdriver. The allen wrench holds the screw while I'm
installing it at a funny angle.
From bmcd...@ix.netcom.com (Buzz McDermott):
You can use blind nuts (also called T-nuts), available from many hobby
shops and most hardware stores. Two or three size 4-40 work fine for
up to 38mm motor mounts. For anything bigger I would use two or three
size 6-32 nuts. For three and four motor clusters that don't have a
central motor you can epoxy a balsa or spruce strip into the central
gap between the motors. Drill a 1 inch deep hole in the exposed end of
the strip appropriate for epoxying in a 2.5 inch length of 1/8" threaded
rod. Use a washer and nut to retain all three or four motors from a
central point.