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Subject: rec.models.rockets FAQ Part 05 - Model Rockets

This article was archived around: 07 May 2002 12:02:25 GMT

All FAQs in Directory: model-rockets
All FAQs posted in: rec.models.rockets
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Archive-name: model-rockets/model-rockets Rec-models-rockets-archive-name: rockets-faq/part05 Posting-Frequency: monthly Last-modified: 1998 November 16 URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
Rec.Models.Rockets Frequently Asked Questions: PART 5 OF 14 MODEL ROCKETRY ---------------------------------------------------------- 5.1 Can I legally fly model rockets in my state? What are the restrictions? Several states still require some type of permit to fly model rockets. The requirements vary greatly between the states. Also, local municipalities are free to impose additional restrictions beyond those defined in NFPA 1122 and any state laws. Check with your local fire marshal for restrictions in your area. For example, the states of Rhode Island, and California have stricter regulations than NFPA 1122. ---------------------------------------------------------- 5.2 When do I need to notify the FAA before flying a large model rocket? Large Model Rocket (LMR) is an FAA designation for a model rocket that is between 454 grams (16 ounces) and 1500 grams of mass, including propellant, -OR- contains more than 113 grams (4 ounces) but less than 125 grams of propellant (all motors). Please note that this definition is different from the definitions of a model rocket found in NFPA 1122 and 1127-94. Some rockets may be defined as LMR by the FAA, but are actually HPR according to the NFPA. If you are planning to fly a Large Model Rocket as defined by the FAA, you must notify the "FAA ATC facility nearest to the place of intended operation" 24-48 hours before launch. FAA notification requirements appear in FAR 101, and all of the pertinent regulations appear in Part 10 of this FAQ. A sample FAA notification form is available at the sunsite archive at: http://sunsite.unc.edu/pub/archives/rec.models.rockets/FAA/FAR101.22.notice From Bob Kaplow (robert_kaplow@hccompare.com) "you need to find the right FAA office to notify. If you don't know where they are, call 1-800-WX-BRIEF, and ask a briefer for the proper place to call. Get an FAA map of your area. From that you can get latitude/longitude, and radial/distance from your launch site to a nearby VOR. Call 24-48 hours before the launch and give them the information. I usually write a letter and mail/fax it to the folks first. That way they have everything in writing. As a courtesy, I also call the closest flight service station (FSS - ask the folks at 1-800-WX-BRIEF where they are) and ask them to issue a locak NOTAM. Get the "L" number as proof that you called." ---------------------------------------------------------- 5.3 I have a son/daughter that is (less than 9) years old. Is this too young for model rocketry? If not, are there any tips for helping to keep their interest in the hobby? Model rocket manufacturers all recommend adult supervision for young children (usually, those under 12). Many parents have had great success introducing these children to model rocketry. Here are a few of the tips and suggestions posted to r.m.r: From cdt@rocket.sw.stratus.com (C. D. Tavares): Children under 10 or 11 do best in the hobby when a parent participates actively with them. Introduce them to simple, skill-level-1 kits with plastic fin units. Build yourself a rocket at the same time, then go out and fly them together. From jack@rml.com (Jack Hagerty): My own experience with my son (now 5 1/2, we've been flying since he turned 4) is not to expect too much sustained interest at a time. Even though my son has a longer-than-normal attention span for his age (he'll watch a whole two hour movie!) and loves the whole idea of building and flying rockets, after 4 or 5 flights (approx. 1/2 hour) he'd rather go play on the monkey bars at the adjacent school. This is magnified if there are any kids his own age around (such as his cousins that sometimes come with us). From dwade@jarthur.Claremont.EDU: Watching they should enjoy. Pressing the button they should enjoy. Prepping with serious supervision. Building simple kits with some supervision and a pre-launch check. There's a huge difference in responsibility between kids. One thing to stress is that a lot of very careful kids will get bored or get pressured by bored friends to do stupid things when you're not around. I might not let kids have any access to motors when unsupervised -- and there's no real reason why that should cause them any trouble. It is possible to make safety fun, you know. I think that's something that a lot of people miss -- if you present things that way, it seems to work out. I don't have kids, but I've got rocket launching friends who do. From J.COOK@ens.prime.com (Jim Cook): I've successfully built an Athena and an America with a 7 year old. The body tube is pre-painted, the decals are self-adhesive, and they like the gold or silver chrome nose cone. You can build it in an hour or two - just let them run around and call them over to help periodic- ally - "glue here", "cut here", "hold this". They feel it's still their rocket and that they helped. Estes new E2X series may also be similarly suitable, but I haven't tried, yet [ed. note: the E2X series go together with plastic model cement, such as Testors, not white glue]. Estes' new E2X series is similar in construction to the Athena and America - they can be built in an hour or two with kids. Demo a range of motors. Go from 1/2A to A to B with a model to show kids the difference. Kids will invariably talk about launching them out of sight or sticking a fireworks in them. Answer with, "yeah, but I wouldn't want to wreck my model that I spent so much time building." Making the kid answer forces him [or her] to think and teaches him [her] to value his [her] possessions. From bmcdermo@ix.netcom.com (Buzz McDermott): When my 10 year old son and I started building rockets together about 2 1/2 years ago, we started with some of the level 1 Estes kits with plastic fin units and nose cones, such as the Athena and Alpha III. He has also built a couple of the Estes E2X series, which requires use of plastic cement. He also likes the Quest Falcon (plastic fins) and Estes Big Bertha (balsa fins) because they are both big enough to use C motors and not loose the models. My 7 year old daughter and I started building rockets about a year ago. She prefers the Quest models with the colored parts. She also finds the Quest parachutes, with their large adhesive connections for shroud lines, easier to build. The Quest Falcon is a large, easy to build model. Now she likes building some of the Level 1 kits with balsa fins. She has built the Estes Alpha and Quest Sprint. From jstewart@software.mitel.com (John Stewart): My daughter loves rocketry. She started when she was 3. Get colorful rockets, build them yourself (e.g. the plastic Alpha III), and don't fly them too high. (50-100' is more than fine) Let the child count to 5 (or try to!!) and push the button. Let them recover the rockets. Have say, 5 to 10 rockets loaded, ready to go when heading out. Launch them, and untangle/fix them either at the field, or at home later, depending on the child's mood. My 4-3/4 year old daughter is looking forward to launching, possibly this weekend. We spent a year in New Zealand, but she still knew all about the rockets, the parachutes, the streamers... From rbs@cyclops.micr.Virginia.EDU (Robert Sisk): People interested in easy to build model rocket kits for the younger crowd should check out QUEST models. Some of the parts are color coded (centering rings, engine blocks, engine mount tube) and the fins of some models are plastic. Some of the fins are supplied as a single unit that you glue into place. Fast, easy, and with little or no sanding! From wayne@pen.k12.va.us (Tony Wayne): I reconstructed my launcher so that me 2.5 year can launch the rocket. The launcher is homemade and uses a shorted out 1/8 mini plug for the safety key. For my son, I attached an 8 foot loop of wire with each end attached to the poles of the mini plug. In the middle of the wire loop is a film canister with a push button. To launch the rocket I have to push the button on the launcher and my son has to push his button too! (When connecting the igniter to the launcher, I carry his launch button with me.) He practicing counting by leading the countdown. (Q: Is "bi-leven" greater than or less than 4?) He checks the airspace as well. ("Look boss! De'plane.") Also when we go to the field, my rockets are ready launch. For about 20 minutes things happen fast. When we are done there are rockets littering the field. We then fetch them. (He "flies" a few of them back to the pad.) His mom has to come too as diversion after fetching so I can prep and go again. ---------------------------------------------------------- 5.4 Is there any way I can buy model rocket kits, parts and engines at less than full retail? Three mail order houses have been recommended several times by posters to r.m.r. They are Belleville Wholesale Hobby, Magnum Rockets Hobbies and More, Commonwealth Displays, and Discount Rocketry. Belleville sells MRC at 40% off list, Custom Rockets at 35% off list, and Estes at 30% off list. There is a minimum order requirement. Magnum and Mountainside sell most all of the major model and high power rocket lines. Both Estes and Aerotech model rocket motors and reloads are sold. They both advertise Estes at 28-33% off of list. Magnum will also discount educational sales (such as to schools, Scouts, YMCA, etc.) at up to 40% off of list. Another potential source for a large discount, if you are buying several hundred dollars worth of parts at one time, is America's Hobby Center. They offer discounts of up to $160 off of Estes' list price on orders of over $400. There are several other mail order sources that sell at discount. Some of the smaller manufacturers/suppliers of model rocketry kits and supplies are a substantial bargain. For the addresses of the sources listed above, and addition sources, refer to the 'Names and Addresses' section of this FAQ (PART 2). Shop around. There are bargains to be found. If you do a fair amount of flying, Estes sells a 24-pack of engines called the Flight Pack. It comes with 6 A8-3, 6 B6-4, 6 C6-5, 6 C6-7, recovery wadding and igniters. It generally retails between $32-36, which is less than the list price of the materials included. This can also be purchased at an additional discount from some mail order houses. Estes also sells 'bulk packs' of 24 A8-3 or B6-4 or C6-5 motors. Quest motors have been recommended by several r.m.r posters. At the present time, they retail at less than the Estes equivalents. They can also be purchased direct from Quest 'bagged' in quantities of 10 or more. 'A' motors can get to less than $1 ea. when bought 50 or more at a time. 'C' motors get down to around $1.25. You might also investigate your local NAR section, if one is located convenient to you. Clubs such as NAR sections often arrange discounts with local hobby merchants. Several of the clubs also have at least one member selling parts and supplies at discount, mostly to the club members. ---------------------------------------------------------- 5.5 I've had a large number of motors CATO recently. The engines are only about 2 years old. I've had them stored in my (attic/garage/basement). From J.COOK@ens.prime.com (Jim Cook): Black powder motors tend to suffer catos when they are temperature cycled. If you expose them to heat, be it storing them in the attic, on your car's dashboard, or in your metal range box in the hot sun on the launch field, you may have problems. The engine expands with the heat, but when it cools, the propellant separates from the casing inside This causes the propellant to burn faster due to burning on the side generating more pressure than was designed for, and ...boom... Storing black powder motors in a damp basement can cause the compressed clay nozzles to soften and also blow out. If you must store your motors in a damp/humid area, put them in a zip lock plastic bag. [Note: There is an excellent article by Matt Steele in the May/June 1992 issue of Sport Rocketry. This article goes into the theoretical reasons why black powder model rocket motors fail] ---------------------------------------------------------- 5.6 Is it safe to use my old rocket engines from <nn> years ago? From J.COOK@ens.prime.com (Jim Cook): I've had properly stored engines from 1972 and 1975 work just fine. If you suspect a motor, fire it by burying it in the ground with just the nozzle showing, pointing up and use your launch system to ignite it as usual. [Note: be sure and stand at least 15-20 feet away from the motor when you fire it: Buzz] ---------------------------------------------------------- 5.7 What's a good way to find other rocket enthusiasts in my area? How can I found out about local rocket clubs? Post a message on r.m.r. You might find someone there who lives close to you, or knows someone who does. Check out Part 03 of this FAQ. A list of NAR sections (clubs) is kept at the NAR web site: www.nar.org The NAR sends a complete list of its local sections (NAR sanctioned clubs) with each new member's information packet. If there isn't a sanction near you, they can send members a list of other NAR members in your area, so that you can form your own section. ---------------------------------------------------------- 5.8 Are the Aerotech composite motors the same size as Estes/MRC/Quest motors? Aerotech makes the following 'standard' retail motors in -4 and -7 second delays. The first two motors are the same size as Estes A-C motors. The next two are the same size as Estes D motors. There are some other 24mm motors that are available from Aerotech that are longer than Estes D motors. Some of these 'non-standard' Aerotech 24mm motors are listed after the four 'standard' ones. The F and G motors may be obtained from some dealers and mail order sources, but are not packaged for retail sale. Motor Size Power Same Size As D21 18x70mm 20NS Estes/Quest/MRC A-C E25 18x70mm 22NS Estes/Quest/MRC A-C E15 24x70mm 40NS Estes D motor E30 24x70mm 40NS Estes D motor F32 24x124mm 80NS Non-standard size F44 24x101mm 70NS Non-standard size G42 24x144mm 90NS Non-standard size G55 24x177mm 125NS Non-standard size Aerotech makes and sells reloadable motor casings and reloads in 18, 24 and 29 mm sizes. The 18mm is the size of an Estes C motor. The 24mm is the size of an Estes D or Aerotech E motor. The 29mm is the size of an Aerotech G motor. Aerotech High Power, formerly ISP Consumer Rocketry division, makes a 60NS F and 100NS G casing, both 29mm in diameter. ---------------------------------------------------------- 5.9 Can I use Aerotech or other composite motors in my Estes rockets? Yes and no. They are the same size. Composite motors have 2 to 3 times the power of comparably size BP motors. Balsa-finned 18mm powered models tend to loose body parts in quantity when launched with a D21 or E25. The ejection charges seem to be hotter, as well (IMHO). The same holds true for Aerotech 24mm motors. Care should be taken before launching a 24mm-based model on an E15, let alone an E30. I have an old MegaSize that I fly on E15-10's. Works great. The Estes Saturn V flies well on E15's, too. E30's tend to shred all but the strongest D models, though. E30's also tend to relocate motor mounts to someplace OUTSIDE of the rockets, as well. If I plan to use E's in an Estes model I make it a point to reinforce the motor mount, especially for EM-2060, EM-2070 and EM-5080 mounts. You also want to use an engine block (a 2050 adapter ring works great) in addition to the metal clip. IMO, I would also reinforce fin/body tube joints. Five minute epoxy fillets work great. Generous cyano fillets also seem to work well. White glued fins don't seem to survive E15/E30 launches with any consistent success (i.e., the failure rate tends to be > 50% :-). Many modelers also recommend that stronger 24mm motor tubing, such as that from LOC or Aerotech, be used for models flying with composite motors. The stronger tubing holds up better to the ejection charges of the composites. There are now several D and E reloads available for the 18 and 24 mm casings that might not over power 'standard' model rockets. The RMS motors have a variety of reloads available, some with fairly low average impulse. ---------------------------------------------------------- 5.10 Will my Estes launch system work with Aerotech composite motors? The classic Estes, Quest and MRC 6 volt launch systems will not reliably ignite the Copperhead (TM) igniters that come with Aerotech motors, and Estes Solar Igniters (TM) will not ignite a composite. These motors need 12 volt systems for reliable ignition. ---------------------------------------------------------- 5.11 Can I use Aerotech composite motors as boosters in my multi-stage rockets? Basically, NO. Black powder booster motors will not ignite composite motors. Therefore, you cannot use a composite upper stage in a traditional multi-stage, black powder rocket. Also, there are no composite booster motors currently in production. They all have delays (4 seconds being the shortest current delay from Aerotech, for example) or are plugged. Typically, you cannot (and should not) use these as boosters in standard black-powder multi-staged rockets. If you want to use composite motors in multi-stage models then you have to use other methods of igniting the upper stage (whether black powder or composite) than are used with black-powder-only rockets. One method is to electronically ignite the upper stage motor using a mercury switch to complete an electrical connection to a capacitor at first stage burn-out. This, in turn, sets off a flash bulb/thermalite fuse combo which ignites the upper stage motor. Another method is to ignite lengths of thermalite fuse at the time the booster is ignited. The length of fuse determines the delay before the upper stage is ignited. Refer to the 'Other Sources of Information' section in Part 1 of the FAQ. The NCR High Power technical reports on staging composite motors is applicable to multi-staged, composite motor powered model rockets as well. Bob Weisbe uploaded plans for a mercury switch-based staging system that he used in a converted Estes Terrier-Sandhawk kit. The URL for these plans is: http://sunsite.unc.edu/pub/archives/rec.models.rockets/PLANS/terrier_sandhawk.ps ---------------------------------------------------------- 5.12 How can I tell the age of my Estes motors? Estes uses a date code on their rocket motors. It's of the form XXYZZ (example, 25T9) where the first number is the day of the month of manufacture, the letter is a code indicating year of manufacture, and the last number is the month (1 = January, 12 = December). Date codes run progressively through the alphabet, as follows: T 1989 U 1990 V 1991 W 1992 X 1993 Y 1994 Z 1995 A 1996 - Estes cycled back to the beginning of the alphabet In the early 70's, Estes motors had the actual date stamped on them. ---------------------------------------------------------- 5.13 Are reloadable model rocket motors shippable the same as disposable model rocket motors? The Aerotech RMS line of model rocket reload kits (of B through G power levels) has been certified by the DOT for shipment as Class C Flammable Solids. This means that the reload kits may be shipped the same as other model rocket motors, such as those made by Estes and Quest. There are no shipping restrictions of any kind on the motor casings and closures. ---------------------------------------------------------- 5.14 My flying field is so small I keep losing my rockets. What can I do? DON'T GET DISCOURAGED. Everyone loses rockets. It's part of the hobby. There are ways to minimize this when you're forced to fly in smaller fields, though. The following is a consolidation of tips posted to r.m.r by numerous individuals: Recovery Modifications: 1. For smaller rockets, use a streamer instead of a parachute. This can be done with rockets of up to BT-50 body tube size and up to 18" long. Be sure and check rocket weight, though. If the model uses heavy plastic fins you might still want to use a parachute. 2. Reef the chute lines to reduce the effective surface area. Tie or tape the shroud lines together 1/3 of the way from their end. This reduces the shroud lines to 2/3 of their original length and prevents the chute from fully opening. The rocket will come down faster and drift less. 3. Cut out the Estes or Quest logo from the center of the chute. This lets more air spill through the chute and reduces its drag. Be careful to cut out the whole logo. Cutting only a small whole (say, less than 2" in diameter) can improve the chute's stability and actually make it lift better and drift further. 4. Use a smaller chute. Try cutting down an 18" chute to a 15" chute, or a 12" chute to a 10" chute. 5. Use longer ejection delays. If a B6-4 ejects the parachute right at apogee, use a B6-6 to let the rocket come down a little before popping the chute. Less time chute is open equals less drift. Take care in making the chutes and recovery attachments extra strong, though, as the descending model will put more strain on the recovery system than if it were to deploy at apogee. Other Suggestions: 1. Find a different field. If you fly alone, try and find a local rocket club. The odds are the club will have found a better field in which to fly. 2. Fly larger rockets. A Big Bertha on a B6-2 will drift a lot less than a Sky Hook or other small model on a B6-4 or B6-6. Larger models have more impressive liftoffs, as well. Larger diameter rockets don't fly as high and come down faster than the really small ones. The big ones are also easier to spot in high grass, weeds, trees, etc. 3. Use smaller motors. If the recommended motors for a rocket are, for example, A8-3, B6-4 and C6-5 or C6-7, try it on A8-3's first. If the model lands well within the recovery area you can then decide if the larger motors will allow the model to be retrieved. 4. Launch rockets at a slight angle into the wind. The rockets will weathercock and deploy recovery systems upwind. If all goes well, they will land closer to the launch site. ---------------------------------------------------------- 5.15 Are Jetex engines still available? Where can I get them? Although, technically, jetex type products are NOT model rocket motors and do not fall under NAR/NFPA guidelines and safety codes, a number of questions do pop up about these on r.m.r. The following sources have been quoted on r.m.r as selling Jetex products: Peck Polymers P.O. Box 2498 La Mesa, CA 92041 Doylejet P.O. Box 60311 Houston, Texas 77205 (713) 443-3409 ---------------------------------------------------------- 5.16 BT-20, BT-50, BT-55. What the heck do the numbers mean on Estes body tubes? Is their any special meaning in these numbers? From: PeteAlway@aol.com (Peter Alway) Estes tube numbering seems to have progressed like the numbering of steps in a BASIC program. The very first Estes Catalog had numbers unlike the BT-20..BT-50... etc. system they use now. Sometime in the early 60's they gave numbers 10, 20, 30, 40, 50 to their tubes in order of size. 10, 20, and 30 were almost identical in diameter (though 10 could be coaxed to fit into 30) All were meant to hold 18 mm rocket engines. BT-10 was an ultra-light spiral-wound mylar, BT-20 was essentially as it is today, and BT-30 was a parallel wound heavy-duty tube. BT-40 was also a parallel wound heavy tube that fit over BT-20. (rather like Quest T-20, but thicker and parallel wound.) BT-50 was as it is today, as was BT-60. BT-5 came along later, I believe created for the top of the Aerobee 300, and numbered halfway between 0 and 10. BT-55 came along after BT-60 and was numbered to fit in. PST-65 egg tubing came after the much larger BT-70 (originally used just for the Sprite tail ring) BT-100 and BT-101 first appeared in the 1/70 scale Saturn IB. BT-80 was created for the Saturn V. It is interesting to note that two standard HPR diameters, 2.6" and 4" began as scale model components. Estes also created BT-3 for the Saturn IB, and BT-51 for the tanks. BT-52 was produced for the BT-60 Semi-Scale Saturn V, and this tube still appears as a hook-retaining sleeve on some Estes D engine mounts. The sleeves are still correct for a 1/242 Saturn V. Many BT-5 clone kits still use the length for an Aerobee 300. ---------------------------------------------------------- 5.17 I've seen mention of all kinds of rocket motor types and sizes. Could you give a brief history and summary of the main marketing names for model rocket motors? From: msjohnso@WichitaKS.NCR.COM (Mark Johnson) The original hand-loaded motors made by Orville Carlisle and sent to Harry Stine in about 1956 were 0.5 in dia. (13mm) x 2.25 long (55 mm). These were used in early testing up until the time Model Missiles Inc (Stine's company) began to produce commercial product in sufficient quantities that Carlisle could no longer make motors fast enough. These had total impulse roughly from today's 1/2A to about the middle of the B range. Stine contracted with Brown Fireworks Co. of Missouri in 1958 to make mass-produced motors. Brown could have made them in the same size as the Carlisle motors, but it would have meant costly new tooling. Mr. Brown offered to produce a low-cost motor for MMI using his "Buzz Bomb" case size - 0.7 x 2.75 in (18 x 70 mm) - the Buzz Bomb had a small aluminum blade on one side of the case and a nozzle drilled into the side of the case opposite, where a fuse was inserted. Strictly a fireworks piece. In about 1959 or 1960, Vern Estes entered the picture, having offered to produce motors for less than whatever price MMI was paying Brown. G. Harry took him up on the offer, and Vern began making motors in the now-standard 18 x 70 mm size. He quickly automated production with the first of several "Mabel" machines and was able to make far more motors than MMI needed. That's when Estes entered the model rocket business himself. The short motors were 1/4A and 1/2A motors which came about in around 1963 or 64 when somebody at Estes realized that the upper 1" of the casing had nothing in it, and was just dead weight. So Estes started producing the "S" series, with a case size of 18 x 45 mm (0.7 x 1.75 in). These continued in production until 1970 or so. In about 1970 or 1971, Stine (whose MMI had gone out of business somewhere around 1962) reentered the hobby as a paid consultant to Model Products Co. (MPC), which later spun off its rocketry business as AVI (Aerospace Vehicles Inc). Stine persuaded Mike Bergenske that there was a market for the "classic" 13 x 55 rocket motors as a high-performance motor, in sizes from 1/4A to B. These were the Mini-Jet motors, which quickly resulted in rewriting the NAR altitude record books. Estes followed suit with its mini- motor line, originally trademarked "Mini-Brutes" with the 13mm diameter but choosing to go with a length compatible with the old "S" series at 45 mm (so they could use the old "S" series engine hooks, I presume). Centuri's "M" motor series, in sizes from 1/4A to B, were released at about the same time. These were 13 x 50 mm (0.5 x 2 in) The other "standard" motor type which emerged about this time was the Estes "D" motor, which was sized to fit easily in the BT-50 or 25mm tube, while keeping the 70 mm length constant (save the engine hook tooling again, I guess). These first hit the marketplace about 1969; I still have the original announcement flyer somewhere in all my old files. The 24 mm diameter has become the "small high power" standard for D, E, F, and even a few G motors, mainly from AeroTech. Estes chose to keep the existing standard diameter and extend the length on their new E15, introduced during 1993. The 29 mm standard motor emerged from the Enerjets. The original Enerjet-8, a fiberglass-cased motor developed and produced by Rocket Development Corp. of Indiana (RDC, later acquired by Centuri as Enerjet, Inc) was an external-delay, 29 mm diameter motor with about 35 N-sec of total impulse (8 lb-sec). The Enerjet-8's external delay was too cumbersome for unsophisticated users, and was replaced by a conventional internal delay when the Enerjet E24, F52, and F67 were introduced in 1973 by Enerjet and Centuri, its parent. The F67 was the first full 80 N-sec F motor produced in the US. FSI is a bit of a cipher in all this. They chose to go with a 21 x 70 mm motor for A, B, C, and small D motors, beginning in about 1966 or so. Their full D and small E motors are in 21 x 95 mm cases. (D18, D20, and E5). The larger FSI motors are in 27mm cases of various lengths. The E60 is about 95 or 100 mm long, and the F7 and F100 are 125 mm. FSI started producing 18 x 70 mm A, B, and C motors in about 1985 or so. ---------------------------------------------------------- 5.18 Why don't I just make my own model rocket motors? Shouldn't I be able to custom-make better, more powerful motors, at a cheaper price? This subject has been hotly debated on r.m.r. It is one of those 'emotional' subjects that find people either firmly for or against. The following post from Lawrence Smith probably says it all best. From: thesmiths@mv.mv.com (Lawrence Smith) In our pre-made, factory-produced society there is a bit of nostalgia for doing things the "old-fashioned" way - "home made" carries with it the feeling of being somehow "better". It could be tastier, more durable, easier to maintain, or cheaper, it is some quality that we don't find in mass-produced items. It is therefore natural for fans of rocketry to look at the prices of the ingredients of an engine and think to themselves that such engines really can't be all that difficult to make - and that "home made" might be not only cheaper, but just as good as factory engines in other ways. There is a grain of truth here - _just_ a grain - but that is enough to make the idea pretty dangerous. Most readers of this will not be old enough to remember the "Basement Bomber" headlines from the late fifties and early sixties. Making solid-fuel rocket engines _is_ a pretty dangerous proceeding, unless you do it _right_. And even if you do it _right_, you must be _consistant_ in following the safety precautions. It really won't matter whether it is the first or the fiftieth engine that blows your hand off in the long run. It is the need to watch the safety precautions that is your first "hidden cost", something that most people dreaming of home-made engines seldom add to the calculation. You need _room_, you can't do it in your basement, nor, indeed, in your house at all. Nor in your apartment, nor in your school chem lab, nor anywhere else there is something you don't want blown up. You must _assume_ the engine _will_ blow up, and ask yourself where it would be okay. Maybe an outbuilding on your property, maybe out in some field. You need _space_ to build engines. You either need to own that space or have the permission of people who do, too. In most places in the country, you need some sort of _license_. Rocket engines are first cousins to pipe bombs, and there are few municipalities that would care to have you building those. On the other hand, there are many municipalities that don't care if you reload spent shotgun shells, even without a license. You need to know and understand the local regulations. You are not building a class "C" toy propellant device. Even if you _think_ you are. That is a legal name, not a descriptive one. You _can't_ reuse Estes or other maker engine casings. Spent casings have undergone considerable stress, they can no longer be guaranteed to hold if reloaded and fired again. Yes, they have a fairly consider- able safety margin. It isn't enough to reload them. You _can't_ use the same stuff Estes uses, nor can you easily obtain composite fuel. Estes uses black powder - gunpowder - but they are using a special formulation, not just mixing the usual ingredients. In fact, it's pretty dumb to use any powder at all. Powder must be rammed to make it solid enough for "solid fuel" - that means you have to pour the powder into the casing and then take a stiff rod and ram it up and down, like one of those old-time muskets. Ramming will compress the powder - which is the objective - and will also heat it, which will also make it more shock-sensitive, not to mention the heat from the friction of the rod itself moving up and down in the casing. It can also raise dust, which is also more easily ignited than a solid slug. A fellow by the name of Jim Flis posted a commentary on creating such engines, I recall. If anyone saved that post, I'd like to see to see it inserted here. Even if you manage to pull off all the above, the engine may not perform like you expect. Your ingredients may not be up to snuff, or maybe you didn't ram enough, or maybe something else got mixed in by mistake, or maybe you forgot to add the final layer to the casing - whatever. There is a real good chance any home-made engine is going to do serious damage to your rocket, even if it didn't do any to you. One of the things you pay for from Estes and Quest is _quality_control_. And even with professionals with years of experience with A, B, and C engines, Estes has problems with D and E engines. Can you really do better? Estes, Quest, and the others have _time_, they have _equipment_, they have _space_, they have _quality_control_ and lastly, they have _liability insurance_ for when something happens with one of their engines. _That_ is what you are paying for, not just a couple teaspoons of black powder and a bit of clay and cardboard. As you can see, there is more than meets the eye in an Estes or Quest engine. The fact of the matter is this: a premade, off-the-shelf engine _is_ cheaper, more reliable, and far, far less effort to obtain. There is really no reason to try to duplicate a standard engine. That said, there will remain a small core of people who still want to roll their own. Maybe they need a non-standard size, or they just are more interested in the engine than in the rocket. Before you proceed, you will need a copy of "Rocket Manual for Amateurs" by Bertrand R. Brinley, Capt. It's out of print, so you'll have to do some looking. If you aren't patient enough to track down a copy then you aren't patient enough to build engines. Take the hint. Brinley gives a good overview of propellant technology up to the mid- sixties or so, which is good enough for you, since the advances have mostly been in the realm of "real" rockets with incredibly exotic chemistry. He concludes that amateurs should stick to zinc and sulfur. Zinc and sulfur can send rockets high enough to need an FAA waiver, so this is really not limiting. Also, though zinc and sulfur can be ram- med, they can also be mixed with acetone or alcohol to form a putty that can be inserted into a casing and cast into shape. This he terms "micrograin". I won't go into detail on proportions or other infor- mation, you'll have to find the book. _I_ not telling you how to build an engine, _I_ won't do it, and I don't think _you_ should, but if you are anyway I want you to be aware of what you need to do to succeed, for if you fail the consequences will be horrible. While Brinley is helpful for fuel, he is more valuable for the kinds of safety precautions you need to take. You are going to need sand- bags. Take the hint. One thing Brinley assumes, though, is using metal cases, including CO2 cases for small engines. This will _definitely_ make your rocket require an FAA waiver, and the metal content will make it easy to spot your rocket on radar, so you better not try to mickey-mouse it. Of course, the FAA will _not_ be forthcoming with a waiver for an experimental free-flight rocket, unless you are launching from someplace in the southwest desert area, and maybe not even then. In a way, this is an advantage. A metal-encased engine will fragment when it explodes, and is far more dangerous that one in fiberglass or carbon fiber. Also, metal is far more likely to cause a spark somehow than are non-metallic components, and so are safer to handle. This limits the size and materials you can use. You will need to improvise on Brinley and develop a fiberglass or carbon-fiber casing and clay or other material nozzle. I have an ulterior motive for mentioning this, and I admit it freely. Making a casing like that is not trivial to begin with, and you will find it's pretty expensive, both monetarily and in terms of time. If that still does not deter, at least you will be encouraged to make your engines _small_ - which will make the process safer, for there will be less to explode. I have no idea how thick the casing needs to be, nor would I say if I did. Again, you need to do your home- work. If you take the advice in this post to heart, you will not make a rocket engine. If you take only some of it, you will build a much smaller engine, in a casing less likely to become deadly shrapnel (not _un_likely, just _less_ likely), and with techniques less likely to cause an explosion. You will be doing it with the advice of a professional (Capt. Brinley, not me) and hopefully will succeed, and then either give it up or go legit and start a career with Morton Thiokol. Who are, of course, the makers of the shuttle SRB's used on the last flight of the Challenger, just in case you thought being a professional meant that you had everything figured out. --------------------------------------- Copyright (c) 1996, 2000 Wolfram von Kiparski, editor. Refer to Part 00 for the full copyright notice.