Reference / Paper · 2012
Peak of Flight #327: First Class Fillets - Classic Way
Apogee Components' Peak of Flight newsletter, issue 327 (2012-12-04).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2012
Apogee Components' Peak of Flight newsletter, issue 327 (2012-12-04).
Apogee Components' Peak of Flight newsletter, issue 327 (2012-12-04).
In This Issue First Class Fillets The Classic Way Terminology of Model Rocketry - Part 2 Cover Photo: North Coast Rocketry’s SR-99 HyperSwift Rocket Kit. Get one at: www.ApogeeRockets.com/Rocket_Kits/Skill_Level_3_Kits/SR-99_HyperSwift Apogee Components, Inc. — Your Source For Rocket Supplies That Will Take You To The “Peak-of-Flight” 3355 Fillmore Ridge Heights Colorado Springs, Colorado 80907-9024 USA www.ApogeeRockets.com e-mail: [email protected] Phone: 719-535-9335 Fax: 719-534-9050 ISSUE 327 DECEMBER 4, 2012 First Class Fillets - Classic Way By Matt Steele Fillets are small glue reinforcements between a model rocket’s body and fin. They are required on almost every model that you will build. As my kids were starting to fly competition rockets, I went looking for a simple method that would give good results, time after time. Once we got the details worked out, the method worked so well that I use it for all my models to this day. The method involves masking off the area before you get any glue near the model. By masking the areas before you apply any adhesive, you avoid making a mess in areas that do not need glue, saving a lot of clean up (and aggravation). I used the upper fins of the new North Coast Lance Delta for these photos. It has two sets of fins, both a forward and an aft set, so there are twice as many fillets required as on most four-finned models. Use a “low tack” masking tape for this type of work. I like the “blue” painter’s tape, as it sticks well enough to keep epoxy from leaking under the edge, but lifts easily when you are done. Other tapes tend to lift the paper layers off the tube I begin by masking off the tube at the forward and aft edge of the fin root (see Photo 1). On models where the fins are flush with the aft edge of the tube, you do not need a piece of tape. Once the forward and aft tape is in place, lay two pieces of tape lengthwise along the fin root, about 1/8” apart for mid power rockets, and 1/16” apart for smaller rockets (see Photo 2). The width dictates how big the fillet will be. Repeat for the other fin. This method lets you do two fillets at a time, so for a four finned model, it takes four operations to complete the model. My approach lets gravity do a lot of the work, so you don’t have to fight with drips or runs. Most of the time, I use epoxy for my fillets, though I have also had good luck with wood glue. I generally use a five-minute epoxy, although for best results (when I am not in a hurry), 30-minute epoxy works best. The longer cure time of the 30-minute epoxy allows the liquid to “smooth” before curing. Photo 2: Tape is then placed along the tube and the fins, about 1/8-inch from the joint. Mix up a small batch of epoxy. The easiest way to get enough without wasting material is to run a line of each part the length of the fillet, then mix it up. I use a popsicle stick to apply a generous amount to the joint. Once the joint has epoxy the entire length, use the curved end of the popsicle stick to scrape away the excess epoxy. Be sure to fill in any areas where bubbles may have popped up. Photo 1: Mask off the tube in front and behind the fins. About this Newsletter Newsletter Staff You can subscribe to receive this e-zine FREE at the Apogee Components web site (www.ApogeeRockets.com), or by sending an e-mail to: [email protected] with “SUBSCRIBE” as the subject line of the message. Page 2 Continued on page 3 ISSUE 327 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason DECEMBER 4, 2012 Continued from page 2 First Class Fillets - The Classic Way Clean up any epoxy that may have gotten out of place. I usually dip my finger in some rubbing alcohol and then smooth the joint out, but that is not necessary for small fillets or ones that use 30-minute epoxy. Photo 3: Lay epoxy in the joint, and scrape off excess with a popsicle stick. Once you have the excess epoxy scraped away, remove the lengthwise sections of tape, starting in reverse order from the way you applied it. Photo 5: Smooth out the edges with rubbing alcohol. Then I remove the tape at the leading and trailing edges of the fin and clean up those joints, if needed. Let the model cure, rotate to the next set of joints that need filleting, and repeat until the model is finished. The same technique works for launch lugs and other joints. This has become my standard technique for model building. I hope you find it useful. Photo 4: Peel off the tape while the epoxy is still in a semi-liquid state. {Editor’s Note: I call this method shown here the classic way, because it requires you to wait until the epoxy has cured before starting the next set of fins. If you use the Fix-It Epoxy Clay (www.ApogeeRockets.com/Building_Supplies/Epoxy_Clay), you can do all the fin joints at one time, because the clay epoxy does not run like liquid epoxy. You can see the technique on the Apogee web site at: www. ApogeeRockets.com/Advanced_Construction_Videos/ Rocketry_Video_65} • Soft, flexible foam padding provides superior protection from cracking • Conforms to the egg to eliminate pressure points • TARC style places the egg horizontally in the rocket • Lightweight & reusable Made by: ISSUE 327 DECEMBER 4, 2012 www.ApogeeRockets.com Egg-Payload Protectors Page 3 Terminology Of Model Rocketry - Part 2 By Ken Kosanke {editor’s note: Ken Kosanke has released a new product called the Encyclopedic Dictionary of Pyrotechnics. To promote this new reference dictionary, Ken has allowed us to reprint a few of the entries here that pertain to model rocketry. This thing is massive, and you’ll want to get a copy for yourself. For information about this publication contact [email protected]. Also, if you’re ever thinking about writing for the Peak-of-Flight, this could be used as an idea generator. Take a topic, explain its importance, give background information and then take the subject even deeper. See Part 1 in Peak-of-Flight Newsletter, issue 321 at: www.ApogeeRockets.com/Education/Downloads/Newsletter321.pdf} gas from a burning ejection charge to travel through a maze-like path before reaching the recovery device. In the process, the temperature of the gas is reduced by its mixing with cooler air; also any large hot particles will likely be trapped within the baffle. Often an ejection baffle is merely two or more perforated disks with a separation between them (illustrated below-left). As an alternative, the ejection baffle may incorporate metal mesh or metal wool for additional gas cooling. Vieille equation (Also Vieille’s law, St. Robert’s law or burn rate equation) This was initially proposed by Paul Vieille (1854–1934), a French chemist and the inventor of a smokeless powder. The Vieille equation states that the linear burn rate (r) of a pyrotechnic material or propellant, at constant temperature, is equal to some power (n) of local pressure (P) times a constant (a): Ejection Baffle This is an assembly that eliminates the need to use disposable wadding to protect the recovery device of an amateur rocket. The ejection baffle works by forcing the r = a Pn Here, a and n are constants that depend on the nature of the pyrotechnic material. Further, n is sometimes described as the pressure exponent and a as the pressure coefficient (discussed below). Accordingly, the pressure Continued on page 5 Pro-X A better way to fly.™ • Standard Sizes Fit Your Existing Fleet • Easy Assembly, Minimal Clean-up • Casings & Propellant Available • Adjustable Ejection Delays • 9 Propellant Formulations Starter Packs Available! ApogeeRockets.com/Rocket_Motors/Cesaroni_Casings Page 4 ISSUE 327 DECEMBER 4, 2012 www.ApogeeRockets.com Kick Your Rockets Into High Gear Your Source For Everything Rocketry Cesaroni Reload Motors Continued from page 4 Terminology of Model Rocketry - Part 2 in a larger block of composition, to be raised to its ignition temperature. The result of taking less time is an increase in burn rate. exponent is the slope of the burn rate curve when burn rate is plotted against pressure in a log-log format. An example of the effect of increased pressure on a flame is shown below for a double-base, smokeless propellant. The flames are burning under pressures of 1, 2 and 3 MPa (approximately 150, 300 and 450 psi), from left to right, respectively. For Black Powder, with the burn rate in mm/s and a pressure in atmospheres, a = 12.1 and n = 0.24 (Shidlovskiy, 1964). This relationship is presented below. For some pyrotechnic compositions, this relationship holds over a wide range of pressures, but for others, it only applies over limited pressure ranges (i.e., the constants are not truly constant). The mechanism through which burn rate increases as a function of increased ambient pressure is by increasing the efficiency of thermal energy feedback. With increasing pressure, any flame produced will shrink in size to become a more concentrated source of radiated thermal energy, and it will be held closer to the burning surface. The effect of greater thermal energy feedback is to decrease the time taken for each successive thin layer of composition, Many seemingly slow-burning compositions become fast burning when strongly encased. Smokeless powders (i.e., nitrocellulose-based propellants) are especially good examples of the importance of the pressure exponent on burning behavior. A small trail of smokeless powder, such as used in small-arms ammunition, burns fairly slowly in the open. However when the same powder is ignited in the confined space of a weapon, it burns almost instantaneously. In rocketry, the Vieille equation constants (a and n) play Continued on page 6 AltimeterOne - See how high your rocket flew • Records peak altitude up to 29,000 feet (ASL). Displays in meters too! • Easy-to-read LCD display. No need to count beeps or flashes of light. AltimeterTwo - See how fast and high your rocket went • Records peak speed and acceleration using 3-axis accelerometer. • Also tells you how high the rocket flew. www.ApogeeRockets.com Penny shown for size comparison ISSUE 327 DECEMBER 4, 2012 www.ApogeeRockets.com “The one altimeter you’ll use in every rocket you fly.” Your Source For Everything Rocketry AltimeterOne Photo credit: Naminosuke Kubota Page 5 Continued from page 5 Terminology of Model Rocketry - Part 2 Pressure coefficient – The constant (a) in the Vieille equation can be easily determined experimentally. It is simply the linear burn rate at a pressure of one atmosphere. a central role in determining chamber pressure (Pc). 1 a ⋅ ρ ⋅ C* ⋅ K n 1 - n a⋅ ρ ⋅ Kn = Pc = g g ⋅ cd 1 1-n Here, ρ is the density of the propellant (in lb/cu.in.), Kn is the ratio of the burning surface area to the cross-sectional area of the nozzle, g is the gravitational constant (32.2 ft/ s2), C* is the characteristic exhaust velocity (in ft/s), and cd (in s/ft) is the discharge coefficient of the nozzle (a function of the temperature and composition of the combustion products). Note that cd is equal to 1/C*. Pressure exponent – (Also burn-rate pressure sensitivity or combustion index) – The exponent (n) placed on the pressure term in the Vieille equation can be determined experimentally. This can be accomplished by making a minimum of two, but preferably more, linear burn rate determinations at different pressures (at constant ambient temperature). This can be accomplished using a closed bomb, such as a strand burner, that has been pre-pressurized with an inert gas. A strand burner, self-pressurized by combustion gases can also be used. (As an alternative, a series of small, specially-made and instrumented test rocket motors can be used.) With the burn rate and pressure data from these tests, n (i.e., the slope of the log-log curve) can be determined by curve fitting. Need A Parachute? We’ve Got The Right One For You! Minimum Diameter Motor Retainers! Apogee is your one stop shop for your minimum diameter rockets projects! We Have: • Minimum Diameter Retainers • Fly High • Motor Extenders • Fly Fast • Threaded Forward Closures • Impress Your Friends! The pressure exponent is a property of the pyrotechnic composition and is not highly sensitive to temperature. • Adapters for Cesaroni Cases www.ApogeeRockets.com • MONSTER Nose Cones from LOC-Precision • Durable Heavy-Duty Plastic • Fits Standard LOC Tube and Blue Tube • Get That Big Project Off The Ground • Affordable! www.ApogeeRockets.com/Building_Supplies/Nose_Cones/ Page 6 ISSUE 327 DECEMBER 4, 2012 www.ApogeeRockets.com High Power Nose Cones