Last-modified: 1996 April 26
See reader questions & answers on this topic! - Help others by sharing your knowledge
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: email@example.com (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: firstname.lastname@example.org "Throw it out of sight" Lawrence Abrams ???, Bill Winter, 1951 Publications: NARTREK, c/o Lew Proudfoot 310 Dover Court Allen, TX 75002 e-mail email@example.com or Dr40Lew@aol.com NARTS, P.O. Box 1482, Saugus, MA 01906 e-mail firstname.lastname@example.org 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: email@example.com Eclipse Components, 570 Buckeye Dr, Colorado Springs, CO 80919 email: firstname.lastname@example.org 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.