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rec.models.rockets FAQ Part 08 - Boost and Rocket Gliders


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Archive-name: model-rockets/gliders
Rec-models-rockets-archive-name: rockets-faq/part08
Posting-Frequency: monthly
Last-modified: 1996 April 26
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html

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Rec.Models.Rockets FAQ (Frequently Asked Questions): PART 08 OF 14

BOOST GLIDER AND ROCKET GLIDERS

8.1 R/C Rocket Gliders

The D-G powered R/C rocket gliders now available are presenting some new
problems to ModRoc'ers, who are more used to making balsa wings, fins, etc.,
then built-up wings.  Here is a set of tips submitted by Iskandar Taib, a long
time model plane enthusiast, and others.  There is an excellent FAQ in the
rec.models.rc news group.  It includes very good information on how to get
started into R/C flying, tips on where to buy equipment, etc.
------------------------------------------
8.1.1. Have there been any construction reviews of R/C rocket gliders?

     Aerotech Phoenix:     August, 1992, "Model Builder Magazine"
     Estes Astroblaster:   September, 1992, "Model Builder Magazine"

     Both articles are written from the perspective of experienced R/C
     aircraft modelers.  They both contain good construction and flying
     tips.
------------------------------------------
8.1.2.  I'm building the 'XXX' R/C Rocket Glider and it uses foam core wings.
    Are there any  things I should know about working with foam?

     The first thing to know is that certain paints and glues dissolve
     foam. Both the stuff made out of white beads (referred to as "bead-
     board") and the blue (Dow Styrofoam (tm) ) or pink (DuPont Foamular)
     extruded foam will behave in the same way. Once sheeted a foam wing
     can sometimes be finished in a paint that ordinarily dissolves foam
     if one is careful about not putting too much on at a time. Here is
     a list of what will dissolve styrofoam and what won't:

     Will dissolve foam:

        Nitrate and butyrate dope
        Ambroid
        "Model Airplane Cement" (you know what I mean)
        Polyester resin (sold as "fiberglass resin" at K-Mart)
        Thick and thin cyanoacrylates (excepting UFO)
        Paints from spray cans
        Dope and paint thinners
        Gasoline
        Dope thinner, acetone
        Solvent-based contact cements

     Won't dissolve foam:

        Polyurethane paints and varnishes (inc. Rustoleum)
        White or aliphatic glues (Elmer's, Titebond)
        Epoxies
        Ethanol or methanol (sometimes used to thin epoxies)
        UFO superglues
        Water-based contact cements (eg. Southern Sorghum)

     Follow the instructions provided and you won't go wrong. Most struc-
     tural building is done with white glue and epoxy is used for sheeting
     the wing and/or putting down fiberglass, graphite or kevlar cloth.
------------------------------------------
8.1.3.  Any tips for sheeting the wings on my Aerotech Phoenix?

     The Phoenix kit requires that you sheet the wing with balsa using epoxy
     as the glue. Aerotech also recommends that you vacuum-bag the wing for
     the lightest wings possible. Vacuum bagging is a fairly new technique
     that I will describe later.

     The process involves preparing the wing skins, mixing the epoxy (need-
     less to say, the 24 hour laminating variety, spreading it on the skins
     with a squeegee, scraping most of it off, applying the skins to the
     core, then assembling everything together in the core beds (the pieces
     left over after the core is cut), and putting lots of weight on top
     of the whole thing. Oh yeah.. the wing has to be kept straight so
     you'd have to do this on a very flat surface. The more pressure you
     can put on this, the better glue joint you'll have, and the less glue
     you'll have to use, which makes for a lighter wing.

     VACUUM BAGGING

     This is where the vacuum bagging comes in. The core bed/sheeting/core
     assembly is put into a large bag which is sealed on all sides. Then the
     air is pumped out of the bag. This is supposedly the equivalent of pi-
     ling hundreds of pounds of weights on the core. In fact they tell you
     to limit the vacuum to so many inches Hg otherwise the cores will crush.

     Vacuum bagging is also useful if you are going to lay up fiberglass
     on top of the balsa wing skins. Fiberglass cloth is now available in
     very light weights and people often use it in lieu of a covering film
     or fabric.

     The way it used to be done was that the cloth was laid down and a thin-
     ned (with alcohol) epoxy brushed into it. Then excess epoxy was removed
     using rolls of toilet paper (discarding layers as they became saturated).

     With vacuum bagging one lays down a sheet of drafting mylar on top of
     the wet glass cloth, then puts the assembly in core beds. The assembly
     is then vacuum-bagged. After curing the mylar sheets are removed and
     you end up with a glass-like finish that is extremely light since all
     excess epoxy has been squeezed out. This also obviates the need for
     lots of the filling and sanding usually necessary before painting.
------------------------------------------
8.1.4.  How about help with my Estes Astroblaster wings?

     The Astro Blaster kit uses contact cement for sheeting the wings. The
     cement is of the water based variety. It is applied to both skin and core
     and is allowed to dry. After this has occurred, the skins and core can
     then be brought together. This is a little trickier, since you don't get
     a second chance.. Once the core touches the skin you can't separate them
     without breaking something. The skins are just 1/32" thick so one
     has to be gentle with them.
------------------------------------------
8.1.5.  How do you repair damaged foam wings?

     Repairing foam is fairly easy. One simply hacks out the damaged piece,
     glues in a block of foam and carves and sands to shape. Carving is best
     done with a brand new utility knife (the kind that has break-off points)
     and sanding can be done with a sanding block. Sheeting is replaced in
     the same manner - cut out the damaged piece and glue on a replacement.
     A little glass cloth or carbon fiber matte over the break helps too.
------------------------------------------
8.1.6.  Some more uses of foam in rocketry...

     Foam is interesting stuff to play with. You can cut wing cores using a
     hot wire and 1/16" ply or formica templates. Parts for rockets can be
     made by simple carving and sanding.

     Even more interesting is making lightweight wings and other parts using
     foam, silkspan and thinned white glue. Someone called Ron St. Jean built
     lots of competition free flight models in this manner. The silkspan is
     applied wet over the foam, and thinned white glue is brushed on. When
     the silkspan dries it shrinks, and the result is an incredibly strong and
     stiff structures. One could conceivably use this method for nose cones
     or complex scale models. In England, foam and brown wrapping paper is
     used for complex ducted fan models (someone actually flies a seven foot
     long scale Concorde constructed like this).

     If one uses heavier paper (eg. grocery sacks) perhaps one can dissolve
     the foam once the white glue is set (use acetone or dope thinner for
     this).  For rockets imagine something shaped like a V2 made like this.
     Once the foam was dissolved you'd end up with a light weight craft paper
     tube of the proper shape, boat tail and all.
------------------------------------------
8.1.7.  I need to cut the piano wire control rods.  Bolt cutters don't work 
        well, as the metal is too hard.  Any ideas?

     From: ntaib@silver.ucs.indiana.edu (Iskandar Taib)
     What you want to do is get your hands on a reinforced cutting wheel
     like the House of Balsa Tuf-Grind. The Dremel ones tend to shatter and
     throw pieces at high speed. If you use them harden them with thin
     superglue.
------------------------------------------
8.2 Free Flight Boost and Rocket Gliders

    Copyright (c) 1996 by Robert G. Kaplow. Permission granted for non-profit
    distribution and may be reproduced by any group or individual for
    non-profit use, provided that the source and author of this document is 
    acknowledged.  The distribution and reproduction of this document for
    commercial use without permission of the author is specifically denied. 
    Any other use requires the permission of the author.
    Feedback can be sent to Robert_Kaplow@hccompare.com. 
------------------------------------------
8.2.1 What is the difference between a Boost/Glider and a Rocket/Glider?

    In a Boost/Glider (referred to as a BG in the rest of the FAQ), only a
    portion of the rocket as launched is required to come down gliding. In a
    Rocket/Glider (RG), the entire model remains in one piece, and the whole
    thing glides down. Typically, this distinction is only important in NAR
    competition, where these two classes are distinguished. An RG is a legal
    entry in BG events, but a BG is not a legal entry in RG events.

    The other thing to distinguish is a philosophical distinction between a
    BOOST/glider and a boost/GLIDER. The question is which half of the flight
    the emphasis is on. A BOOST/glider is a rocket that happens to have glide
    recovery. In reality, it probably doesn't glide that well. The Space Shuttle
    kit is a good example of this type of glider. A boost/GLIDER on the other
    hand is a high performance glider that is carried aloft by a rocket motor.
    These are the type of models typically seen in competition, and the topic of
    most of this FAQ.

    Also note that regardless of the emphasis, all of these gliders are launched
    vertically, like other model rockets. Horizontal launch and shallow climbing
    supported by wing lift doesn't work for these models, and is prohibited by
    the safety code.
------------------------------------------
8.2.2 What are some types of gliders?

    Early BGs were rear engine designs. The first was built by John Schultz and
    Vern Estes in 1961. They usually looked like delta-winged jets or X rockets.
    The old Estes Space Plane is an example of this style.
    
    In 1963 Larry Renger invented the front engine BG with the Sky Slash design
    winner. It was basically a hand launched glider with a motor pod hung on the
    front. The old Estes Falcon followed this style. A few years later, Larry
    invented the detachable "pop" pod. Almost all gliders today are front engine
    design, and pop pods are the most common of the BGs flown today. The old
    Centuri Swift and Estes Dragonfly were Pop Pod designs.

    Parasite gliders are small gliders attached to the outside of larger
    conventional model rockets. They can be as simple as a small foam glider
    hooked to an extra launch lug on the side of a standard model rocket. Many
    of the popular mass market kits fall into this category, including the Estes
    Manta, ARV Condor, Space Shuttle and the old Orbital Transport, and the
    Quest Aurora.

    Flex-wing (FW) gliders were inspired by the Rogallo wing that was intended
    as the recovery device for the Gemini program. They are basically 3 sticks
    with a lightweight plastic covering. They fold for boost inside a long
    skinny rocket, and eject like a parachute. NAR competition rules prohibit
    "flexies" as they are called in BG and RG events, and create a separate
    category for them.

    Gliders are further broken down into categories describing how they look or
    work. Some of them are fixed pod, pop pod, swing wing, slide wing, box wing,
    t-rail, slide pod, no moving parts, canard, auto-elevator, variable camber,
    flop wing, scissor wing, flying wing, swept wing, delta wing, Rogallo wing,
    etc.
------------------------------------------
8.2.3  What are all these funny names I see referenced?

    Until the 1979 Pink Book revision, different power classes were designated
    by names. For gliders, the names were of flying creatures. Here is a decoder
    table:
    
        1/4A    Gnat
        1/2A    Hornet
        A       Sparrow
        B       Swift
        C       Hawk
        D       [no official name, sometimes called Deagle or Falcon]
        E       Eagle
        F       Condor
        G       [no official name, but commonly referenced as Dragon]
------------------------------------------
8.2.4   I'm just starting. What kits or plans are available?

    Several model rocket manufacturers make glider kits. Very few make really
    good gliders. Among the non-spectacular performers are the Estes Space
    Shuttle and Tomcat, and assorted parasite and foam gliders.

    The Quest Flat Cat is an improvement on an old design that can fly
    reasonably well. QCR has several glider kits, including a good booklet on
    flex-wing gliders. Edmonds Aerospace offers several glider kits. Eclipse has
    a few glider kits as well. The Estes Trans-Wing and MRC Thermal Hawk are
    reasonable fliers. Apogee had glider kits, but I don't know what their
    status is today. NCR glider kits are gone, but plans may resurface in the
    future. 

    My favorite BG plan for the beginner is the Flanigan Flyer, designed by
    Chris Flanigan of the MIT Rocket Society. Plans for it can be found in the
    MIT Competition Notebook available from NARTS. It is suitable for A-C 18mm
    motors. Guppy's Fish & Chips (1/2A) and High Performance Sparrow (A) BG were
    some of my favorites, but are very touchy to trim (more about that later).
    Try Mark Bundick's Parksley Eagle for 13mm 1/2A & A motors, available from
    NARTS in the "NIRA Glider Plans from 'The Leading Edge'" reprint. There are
    several other glider related NIRA Reprints also available from NARTS.

    [I'm looking for a C/D BG recommendation - rgk]

    For a first RG, I recommend the Seattle Special, by George Riebesehl. Plans
    for this model are also in the "NIRA Glider Plans from 'The Leading Edge'"
    reprint. It flies on A-C 18mm motors. 

    [I'm looking for a 1/2A RG and C/D RG recommendation - rgk]


    For a FW, I recommend the QCR kit and manual. This proved good enough for
    NAR V.P. Trip Barber, a fellow FW hater, to take a first place with at
    NARAM-37, building the glider on the field. Also refer to George Gassaways
    articles in American Spacemodelling, December 1980 and September 1986.

    Many more plans are available from NARTS or NARTREK publications.
------------------------------------------
8.2.5   Why do most gliders have the rudder under the fuselage?

    This is probably more for historical rather than technical reasons. Since
    the motor is on top, a conventionally placed rudder would be in the exhaust.
    In reality, some glider tails are far enough from the exhaust that it
    doesn't matter. The real question should be "Why do airplanes have the
    rudder on top?" :-)
------------------------------------------
8.2.6  These things are very different from what I've built before. Are there
         any tips for building them?

    Lots of them. The most important things to consider are to build light,
    strong, and warp-free. Weight is the enemy of a glider. A weak glider will
    break easily. A warped glider is very difficult to make glide properly. All
    three of these problems are hard to fix later.

    In order to keep surfaces straight, I recommend the use of a building board.
    A scrap of kitchen counter, larger than the finished model is perfect for
    this purpose. All planing, sanding, cutting, and gluing is done on this work
    surface. It should have at least one straight perpendicular edge.

    The flying surfaces of a glider need to be airfoiled to work best. Unlike
    other rocket parts, a glider wing needs a non-symmetric airfoil. The standard
    fin airfoil shape, split in half, is a good place to begin. To rapidly shape
    a wing airfoil, use a device called a razor plane. Much like its big brother
    used for carpentry, this tool shaves off wood quickly. The difference is
    that it uses a razor blade or equivalent to do so. Many different types are
    available. My personal favorite is the David Combi. An inexpensive nylon one
    is available from Master Airscrew. These and many other handy tools can be
    found in model airplane catalogs. The SIG catalog in particular is an
    excellent source of many materials needed to build and fly gliders,
    including these two razor planes.

    Once roughly shaped, a sanding block is needed to get everything smooth. A
    6" piece of 1x2 is perfect to wrap 1/6 of a sheet of sandpaper around (or
    1/3 of a sheet around a 12" block). Use thumb tacks to hold the sheet in
    place. Sanding across the grain removes wood fast, sanding with the grain
    gives a nice final finish. Start with 100 grit, and work down to 400. The
    stab and rudder are similarly airfoiled, usually symmetrically.

    In order to glide, your glider will need dihedral. This is the upward
    tilting or curving of the wings. Some designs use multiple joints, trihedral
    or polyhedral. To do this, cut the wing in half (or thirds, quarters, etc.
    as per the plan). A razor saw is the best tool to do this, but a modelling
    knife and a straight egde will do. Tilt each tip up the required amount on
    your building board. Use a handy scrap or a piece of 1x2 to prop the wing
    pieces up. Now bevel the root edges using a sanding block and the edge of
    the building board so that they are once again perpendicular to your work
    surface. 

    The two edges can now be glued together. Standard wood glues can be used for
    this, either carpenters, CA, epoxy, or Amberoid or Duco. I particularly like
    Amberoid or Duco cement for gliders because it can be dissolved to remove
    parts that end up misaligned.

    The wing, stab, and rudder are now glued to the fuselage of the glider. Take
    care to align things accurately. Typically a design will call for a tilt in
    the wing or stab, in order to make the glider gently turn in flight. This
    prevents very long chases to retrieve your glider. Also designs will
    frequently include a few degrees incidence in the stab. By putting the stab
    at a slight angle to the wing, it aids in the transition of the glider from
    boost to glide, and prevents the "death dive" where the glider flys straight
    down.
------------------------------------------
8.2.7   Should I paint my glider?

    Most competition models are not painted in a normal sense. Many gliders are
    left unpainted at all. Some modelers will color the model with magic marker
    or a thin layer of model airplane dope for visibility. Others will apply a
    coat or two of clear dope to prevent warping. I personally prefer Jap Tissue
    and dope (discussed later), as it adds both strength and color to the model,
    at a very minimal weight penalty.

    Conventional finishing techniques of filler, primer, paint, and decals
    should be left to models where glide performance is not a concern.
------------------------------------------
8.2.8   Can I convert a hand launched glider (HLG) to rocket power?

    Yes. The cheap balsa "snap together" toy gliders (i.e. North Pacific) are
    *NOT* strong enough for flight conversion, however many HLG kits and plans
    are convertible. Plans for Jetex models are usually too flimsy for model
    rocket power. A wealth of HLG plans are available from the Academy of Model
    Aeronautics (AMA), National Free Flight Society (NFFS), Zaic yearbooks, and
    some of the other RC modeling magazines. I highly recommend the NFFS
    newsletter and journals as sources of free flight glider information.
    Usually, all you need to do is to add a pop pod to the HLG, and perhaps
    invert the rudder. 

    The references at the end of this part of the FAQ list several good HLG
    plans.
------------------------------------------
8.2.9   I'd like to design my own glider. How do I know if it will work? How do
        I compute the CP for a glider?

    Glider stability is similar to a rocket stability, but a bit more
    complicated. The equivalent to a rocket Center of Pressure (CP) is called
    the Neutral Point (NP) of a glider. There is an article on how to calculate
    this in the 1980 MIT Journal available from NARTS. Just as a rocket CG needs
    to be ahead of the CP, a glider CG must be ahead of its NP for it to be
    stable. 10-20% of the wing cord (the distance from the leading edge to
    trailing edge of the wing) is a good margin for free flight models. RC
    models can get by with much smaller margins.

    There are several good articles on Boost Glider Stability in old Model
    Rocketry Magazine and Model Rocketeers. Reprints of many of these are
    available from NARTS and/or NARTREK.
------------------------------------------
8.2.10   What motor should I use to fly my glider?

    Typically, you want a short delay, and a low average thrust for a glider.
    For example, a B class model would probably do better with a B4-2 than a
    B4-4 or a B6-2. Be careful of motors with large ignition spikes, like the
    A10-3 or C5-3, unless you want to re-kit your model. Core burning motors,
    including most composite motors are not usually suitable for gliders.
------------------------------------------
8.2.11   This thing looks weird sitting on the pad. How do I launch a glider?

    Since the motor is near the front of the glider. there isn't much left of a
    3' launch rod once you put a glider on the pad. Frequently the glider will
    fall off the pod while sitting on the pad. The other big problem is that
    once the motor ignites, the clips fall, and can catch in the wings or stab
    of the glider.

    The solution to all of these problems is to launch gliders from a "Power
    Tower". This is nothing more than a 3' dowel with a launch rod on the top.
    Sharpen one end of the dowel, and pound it into the ground. You can drill a
    hole for the rod, or just tape it in place. I like to bevel the end of the
    dowel at a 45 degree angle. A scrap ceramic tile with a hole drilled near an
    edge makes a good blast deflector. Make sure that the exhaust is directed
    AWAY from the glider, and not back into the wing! The pod now sits on the
    deflector, and the glider hangs below the rod, against the dowel.

    To prevent the clips from catching the tail, you can either tape the clip
    lead to the dowel, or better yet, use a second launch rod about a foot away
    as a gantry, so the clips fall away from the glider. A couple more rods are
    handy if it is a bit windy to prevent the glider from blowing off the pod,
    or twisting on the pad.

    I've gone one step farther, and made a miniature version of a Chad Pad,
    using 2 2' pieces of 1x2, a 1/4-20 carriage bolt, and a blind nut (T-nut) in
    the end of the 3' dowel. The base of the Chad Pad has extra holes in each
    "leg" for extra launch rods to hold the wing and ignition leads.
------------------------------------------
8.2.12   My glider looped and crashed into the ground. What is wrong?

    First check for a warp or misalignment in the wing or stab. These are the
    most common cause of boost problems, and the reason that accurate building
    is so critical. If anything is found, fix it.

    Most gliders will have some pitch down at ignition and early boost, and
    gradually change to a pitch up condition near burnout. This results in an
    "S" shaped flight profile. If the deviation is minor, don't worry about it.
    A slight roll during boost will keep your glider headed in the right
    direction.

    Models that have boost problems can often be helped with a longer and/or
    heavier pod. Extending the fuselage to put the motor farther in front of the
    wing also helps. A longer rod may help boost also, as will avoiding high
    winds when launching.

    If the model pitches down severely under thrust, the pylon may be too tall
    or the thrust may be misaligned. If the model pitches up under thrust, the
    pylon may be too low, or the thrust misaligned. If the model starts
    straight, then starts pitching up, the wing lift is causing the problem.
------------------------------------------
8.2.13   My glider shredded. What is wrong?

    It was either not strong enough, or the motor was too powerful. If the motor
    was too powerful, then the fix is obvious. Use a less powerful motor next
    time. Beware of cored motors, they love to shred gliders. This includes the
    ignition spike of the C5-3, A10-3, B8, and almost all composites. A few
    composites, like the AeroTech/Apogee C4, D3, and E6 are designed for
    gliders. 

    There are several things that can be done to strengthen gliders. Spruce is
    often used for the fuselage to increase its strength, but at a significant
    weight penalty. Wings can be made of thicker wood, although this increases
    the weight of the glider. When trying to maximize performance, it becomes
    important to select the density of the balsa used in your glider. Lighter
    wood (6#/ft^3) will save weight, while denser balsa (10#/ft^3) is stronger.
    Use the lighter wood for wings and stabs, the denser for fuselages, which is
    still lighter than spruce.

    You also need to consider the grain of the balsa. "A" grain wood has the
    grain running perpendicular to the surface. It is very flexible. It is not a
    good choice for wings, but is excellent for sheeting built up surfaces, or
    rolling balsa tubes. "C" grain wood has the grain running parallel to the
    surface. It has a mottled appearance, and is very stiff. It is ideal for
    wings and stabs. "B" grain is between A and C, and should be used where
    stiffness is not an issue, such as fuselages.

    The SIG catalog is an excellent reference on the subject of balsa density
    and grain.

    Higher aspect ratio wings are weaker than low aspect ratio wings. Try
    redesigning your wing or tail to lower the aspect ratio.

    An excellent way to strengthen balsa without adding much weight is to tissue
    the glider wings. This is an art in itself. You will need some "Jap" tissue
    (from SIG or Peck Polymers) and some clear dope. I have found that SIG
    Nitrate dope is less likely to warp the wings. The tissue comes in assorted
    colors to decorate your model. Use 2 colors, with a darker color on the
    bottom, for visibility in the air, and a lighter color on top for visibility
    on the ground. Green is a poor choice for the top, but Blue surprisingly
    looks pretty dark in the sky. A couple primer coats of dope are applied to
    the balsa surfaces. Another coat is used to stick the tissue down to the
    balsa. More coats over the tissue soak thru and bond the tissue to the
    balsa, and fill in the pores. 

    Two other ways to make lighter wings particularly on large gliders are built
    up construction, and foam cores. A wing can be built of balsa strips, and
    covered with tissue. This can yield a very strong but lightweight wing. Foam
    is commonly used in RC models, and can be used in some of the larger gliders
    (C-D and up) covered with fiberglass or tissue. Uncovered foam from meat
    trays can be used for some mini-motor designs. These techniques are beyond
    the scope of this FAQ.

    The leading edge of a wing is prone to nicks and dings from running into
    things. This can be reinforced with a thin strip of spruce, or a thin piece
    of nylon or Kevlar line glued along the edge.

    For the ultimate in strength and low weight, all parts of a glider can be
    reinforced with carbon fiber or Kevlar. This is applied either with Amberoid
    or an Epoxy resin.
------------------------------------------
8.2.14  The pod stuck on my boost/glider and the thing crashed. What is wrong?

    You've just been shot down by the "Red Baron". If it stuck, try sanding to
    loosen things up a bit. Check the action of the pod when deploying.
    Streamers or parachutes have a nasty habit of catching on things that you
    didn't want them to, like glider wings. Sometimes fastening the recovery
    system to the pod in a different manner will fix the problem. Some pod
    systems are specifically designed to prevent this problem, Try one of them.

    You can also have the opposite problem, where the pod falls off too soon,
    sometimes under power. First check the fit. If it is too loose, use tape to
    make it tighter. This could also happen at launch, where the glider is blown
    off the pod by wind, or just after launch due to a structural failure.
------------------------------------------
8.2.15   My glider glides like the space shuttle (or worse). What is wrong?

    Unless you are very good and very lucky, your glider will need several
    adjustments before it glides well. The process of making these adjustments
    is called trimming. The goal is to get a glider that transitions quickly and 
    flies smoothly, gently circling overhead. If you are right-handed, you will
    probably have best luck trimming your glider to circle to the LEFT. If you
    are left handed, reverse all the following references to left and right.

    All trimming is done with the model in glide configuration. For a BG, this
    means without the pod, For an RG, it means with a spent motor casing
    installed, and wing, pod, or whatever deployed as it will be in flight.

    The first step in trimming is to locate the CG at the proper position. If
    you are lucky, the instructions or plans will tell you where to locate the
    CG. If not, you will need to compute the Neutral Point (CP), or use a
    typical location like 1/3 of the wing cord from the leading edge. Gliders
    are often tail heavy. Add weight to the nose if necessary to get the glider
    to balance 10-20% of the wing cord in front of the NP.

    All the rest of the trimming should be done by controlled warping of the
    flying surfaces. Start by getting the model to glide straight, which is much
    easier if it was built without any warps. In an open area gently toss the
    glider forward, releasing it with both the wings and fuselage level. Note
    its action. If the model dives (drops its nose), warp the stab trailing edge
    UP a bit. If the model stalls (noses up, then suddenly drops, often straight
    into the ground) warp the trailing edge of the stab DOWN a bit. The best
    glide us usually right on the edge of a stall. 

    I like to warp both wing tip trailing edges up to prevent tip stalls, and the
    center portion of each wing down to increase the wing lift.

    Then add a left turn until the model has a slow flat circular glide. Some
    turn is often added during construction by tilting the wing in the direction
    of the desired turn, or tilting the stab in the OPPOSITE direction. Turn can
    be increased by warping the trailing edge of the OPPOSITE wing down a bit. I
    try to avoid warping the inner wing panel trailing edges up at all, as this
    can lead to spiral dives. Turn can also be adjusted with the rudder.

    For a left roll on boost, warp the left tip of the stab trailing edge up,
    and the right tip down. This works at high speed, but has little effect at
    glide speeds. Use wing warp, stab tilt, and a bit of rudder to increase or
    decrease the turn as needed. 

    Try a few harder throws. The glider should quickly settle down into a flat
    gentle circle. Continue adjusting the surfaces until you get this result.

    Now you are ready for a serious hand launch. This is an art form in itself.
    Throw the model up as hard as you can, at a 45 degree angle up and to
    your right, and with the wing banked at the same 45 degree angle. The model
    should slowly roll to the left, changing from a right turn to a left turn.
    If you are lucky, the model will be gently circling 30 or more feet
    overhead. If not, it probably smacked the ground, so pick it up and try
    again. Go back and check the trim with a gentle toss, and if all is OK, try
    again. You may want to vary the angles between 30-60 degrees each, until you
    find what works best for you and your model.

    Now you are ready for the first launch. Pick a reduced power motor, just
    enough to get the glider to a reasonable altitude, and launch it. Use a
    power tower as described previously. Carefully observe the boost,
    transition, and glide. Watch out for a "death dive" where the glider never
    transitions and comes straight down. This can be fixed with increased stab
    incidence or warping the trailing edge of the stab up. Also watch for
    "spiral dive" where the model turns very tightly and crashes into the
    ground. This is caused by too much turn, or a wing that isn't producing
    enough lift. Try reducing the turn or warping down the inside edge of the
    inboard wing.

    Continue to adjust the flying surfaces until you get the flight you want.
    Now move up to the desired motor size, and fly again. Soon you'll need to
    read the answer to the next question.
------------------------------------------
8.2.16   My glider never came down and flew away. What is wrong?

    If it went in a straight line, you need to re-trim the glider to circle as
    it glides. Perhaps your field was too small. Find a larger place to fly.
    
    If neither of these is the case, you probably just found a thermal. Air is
    not static. It moves around due to uneven heating and cooling. A hawk
    circling overhead, without flapping its wings is in a thermal. When air is
    heated, it rises. Whatever is in that air goes up with it, be it bird,
    rocket, or airplane. If the air is rising faster than the sink rate of your
    model, the model will rise in the air. In general, this is good, as it
    allows your model to fly much longer. It stops being good when you lose the
    model!

    This is a "good" problem. it means you've solved most of the problems you've
    encountered, and have (had?) a pretty good glider. Picking thermals is an
    art that is beyond this FAQ. Now we have to find a way to get the glider
    back. These devices are called dethermalizers (DT) because they are designed
    to get your model out of a thermal. 

    This is done by transforming a good glider into a bad glider. There are two
    parts to this transformation. The first is some sort of timer, to cause the
    action to occur when you choose. The second is an actuating device that
    de-stabilizes the glide.

    Timers come in several forms. Most common is dethermalizer fuse. This looks
    more like cotton rope, and burns very slowly, typically 1/4" per minute. By
    having this fuse burn a string or rubber band, we can actuate a device in
    flight. Be sure to use a snuffer tube with the fuse, to prevent the fuse
    from falling free and starting a grass file. Other more sophisticated timers
    are built from small spring wound motors, or a viscous fluid like STP or
    silly putty with a piston slowly moving thru the fluid.

    There are many actuating devices used. The simplest is a drop weight. Since
    we often need to add weight to the nose of a glider when trimming, this
    weight can be dropped, with a string going either to the tail or INSIDE wing
    (if you go to the outside wing, all you will do is change the glider from a
    left turn to a right turn, or vice versa). By shifting the weight, the
    glider will now severely stall (tail), or spiral (inside wing) into the
    ground.

    The "beer can" DT was popular at MIT because of its first step, empty a can
    of beer! A piece of the aluminum can is deployed as a flap from the INSIDE
    of the fuselage. This acts as a drag break, and causes the glider to slowly
    spiral down.

    Often a DT consists of a flap, either on the wing or stab, that pops up and
    alters the trim of a glider, causing it to spiral dive or stall. One problem
    with these is that if not set properly, they can mess up the trim of your
    glider, eliminating the need for a DT in the first place. 

    Another problem with many DTs, especially those that produce a stall or
    gentle spiral, is that in a strong thermal, they may be insufficient to
    recover the model. Finally, the DT action may bring the glider down so hard
    that it is damaged on landing.

    I like the pop up wing DT used on the Gold Rush (Model Aviation May 1985
    page 64). The entire wing is hinged, and pops up about 60 degrees. This
    effectively turns the entire wing into a drag break, sending the fuselage
    straight down. The model lands nose first, protecting the delicate tail from
    damage. A variation of this totally cuts the wing loose, except for a string
    that ties the wing to the tail. The fuselage falls like an arrow, nose
    first, with the wing fluttering behind. Another nice feature for the serious
    competitor is that the hinge pin can be removed, making the model very easy
    to pack for shipping.
------------------------------------------
8.2.17  References: (kits, books, publications, catalogs)

    Kits:

        Apogee          Maxima A
                        Maxima B
        Eclipse         ???
        Edmonds         Deltie
                        Deltie-C
                        Deltie Thunder
                        Ivee
                        Ivee-C
        Estes
                #2075   ARV Condor
                #2097   Manta
                #1284   Space Shuttle
                #2086   Tomcat
                #2112   TransWing
        MRC             Thermal Hawk
        QCR             Auta Sight FWs
                        Easy Slide RGs
                        Edmonds Canard RGs
                        Folded Wing RGs
                        Never Loop BGs
                        Dethermalizer kit
        Quest   #3002   Aurora
                #3006   Flat Cat

    Plans:

        Name            Number          Source
        ----            ------          ------
        Athena                          NFFS plans
        Bo Weevil                       NFFS 1973
        Catharsis       BH-151          Bill Hannah ???
        Challenger                      MA August 1985 page 67
        Flip                            SIG kit
        Gold Rush                       MA May 1985 page 64
        Pigeon                          SIG kit
        Polly           AMA #263        MA May 1979 page 50
        Roll Out        AMA #201        MA 
        Roscoe 18       AMA #509        MA May 1986 page 60
        Semi Pro        AMA #124        MA January 1976 page 22
        Stomper         AMA #510        MA May 1986 page 60
        Supersweep 22                   NFFS 1976, AAM December 1974
        Sweepette 18                    NFFS 1982
        Thermic                         Jetco kit
        Wasp VI         AMA #343        MA August 1981 page 57, NFFS 85
        Zenith          AMA #705        MA December 1991 page 61

    Books:

        "Flying Hand Launched Gliders" John Kaufmann, William Morrow 1974
        (out of print, often found in the children's section of libraries)

        "Handbook of Model Rocketry", G Harry Stine, Wiley 1994,

        "Hey, kid, ya wanna build and airplane?", Bill Hannan, Model
        Builder

        "Model Rocket Design and Construction", Tim Van Milligan, Kalmbach
        1995 email: 102374.2533@compuserve.com

        "Throw it out of sight" Lawrence Abrams

        ???, Bill Winter, 1951 

    Publications:

        NARTREK, c/o Lew Proudfoot 310 Dover Court Allen, TX 75002 e-mail
        lewis_proudfoot@comsys.rockwell.com or Dr40Lew@aol.com

        NARTS, P.O. Box 1482, Saugus, MA 01906 e-mail
        73320.1253@compuserve.com 

        NFFS digest, 19 Frederick Dr. Newport News, VA 23601 $15/year

        NFFS plans, 10115 Newbold Dr. St. Louis, MO 63137

        NFFS publications, 4858 Moorpark Ave. San Jose, CA 95129

        Zaic yearbooks, Model Aero Publications, P O Box 135, Northridge, CA
        91343

    Catalogs:

        Apogee Components Inc., 19828 North 43rd Drive, Glendale, AZ 85308
            email: 71441.1111@compuserve.com

        Eclipse Components, 570 Buckeye Dr, Colorado Springs, CO 80919 
            email: 102100.1566@compuserve.com

        Edmonds Aerospace, 13326 Preuit Place, Herndon, VA 22070
            email:  RobEdmonds@aol.com

        QCR, 7021 Forest View Drive, Springfield, VA 22150

        SIG, 401 S Front St, Montezuma, IA 50171 (800)247-5008
---------------------------------------
Copyright (c) 1996 Wolfram von Kiparski, editor. 
Refer to Part 00 for the full copyright notice. 


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