Reference / Paper · 2014
Peak of Flight #365: Making an Ablative Nose Cone For Supersonic Flight
Apogee Components' Peak of Flight newsletter, issue 365 (2014-05-20).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2014
Apogee Components' Peak of Flight newsletter, issue 365 (2014-05-20).
Apogee Components' Peak of Flight newsletter, issue 365 (2014-05-20).
In This Issue Making an Ablative Nose Cone for Supersonic flights Cover Photo: When Pigs Fly... The Pigasus rocket kit at lift-off. Get your own at: www.ApogeeRockets.com/Rocket_Kits/Skill_Level_3_Kits/Pigasus 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 I S S U E 3 6 5 M AY 2 0 , 2 0 1 4 Thermal Ablative Experiments for the Sugar Shot Nose Cone By Vicente Alvero Zambrano This report describes experimentation that was performed to test potential ablative materials (“ablator”) for use as the tip of the Extreme Sugar Shot (ESS) nosecone. The ESS vehicle will reach hypersonic velocity while it traverses through the upper atmosphere on its way to Space. Aerodynamic heating of the nosecone tip will require it to be made of suitable heat-resistant material. at elevated temperature. Besides the aforementioned basic requirements, three specific requirements of a practical ablative are being sought: The goal of the Sugar Shot to Space rocket is to reach 62 miles with sugar propellant (see: sugarshot.org) It has been calculated, that at an altitude of 13,000 meters the ESS rocket will have reached a speed of Mach 5, causing a temperature of stagnation on the tip of the nosecone of over 927 °C (1700 °F, over 4 times the oven temperature that we normally have in our homes. n Provide effective protection against severe thermal loading. In other words, the part being protected must be kept below a certain maximum temperature. n Be readily moldable, machineable and possessing good bonding characteristics. It is envisioned that an ablative material would be applied to the part requiring protection, perhaps with the aid of a mould, then machined to a final thickness or desired profile. n Resistance to “flow deformation” under a combination of exposure to heating and high velocity gas. To this end, it was felt that a filler material may be beneficial, integrated into a resin matrix. At this is a frightening temperature, it is vitally important to have a thermal shield on the rocket nosecone. Introduction This report describes an experiment that was performed on various ablator to ascertain their effectiveness in providing thermal protection of rocket motor components. An “ablative material” is a polymer with inherently low thermal conductivity which slowly pyrolyzes (decomposes through heating to a high temperature) layer-by-layer when its surface is intensely heated, leaving a heat-resisting layer of charred material. The intention of studying various materials was to come up with a simple, readily available and inexpensive ablative for use in amateur rocket motors. The immediate need is for an ablative that will serve to insulate a newly-designed nozzle and bulkhead, such that the temperature is kept sufficiently low to minimize heating of a composite motor casing under development. More so than metal casings, composites are susceptible to loss of strength and stiffness About this Newsletter All numbers shown in Table 1 are percentages RE = epoxy resin; RP = polyester resin MF = phenolic microballoons; FV = glass fibre (strands) x= 5% titanium dioxide , X = 10% titanium dioxide Continued on page 3 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 Table 1: Ablative Materials Tested ISSUE 365 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason M AY 2 0 , 2 0 1 4 Continued from page 2 Conducting Themal Ablative Experiments Photo 1: The slurry of ablative material before it was applied to the aluminum test sheet. Photo 2: The ablative material was formed into a sheet of 2.4mm thickness Preparation of specimens All specimens were prepared in an identical manner. The ablative has joined an aluminum sheet 10 cm x 10 cm. To help adhesion, the surface is left rough with 400 grit sandpaper and then cleaned with alcohol and a BB gun. To help ensure a uniform thickness of the ablative layer, the substrate was defined by a frame made with wooden oral depressants (see Photo 2). The resulting size of the sample of ablative was 6 cm x 6 cm. The different samples were prepared by carefully weighing the components, mixing thoroughly and then applying to the substrate using a spatula. All samples were degassed in a vacuum chamber at a pressure of -1 bar for at least 10 minutes. After curing for 24 hours at room temperature, the samples were post-cured in an oven at a temperature of 70 ° C for one hour. Then, the surface was sanded to leave a smooth and constant thickness of about 2.4 mm. The thickness of each specimen was carefully measured with a caliper and scored. Test setup and procedure A conventional cooking butane torch was used to heat the samples. The samples are attached vertically to a base plate, which also had a support for the torch nozzle, arranged such that the distance between the nozzle tip and the sample was consistently 75 mm. The heating time for each sample was 11.5 seconds, which was controlled by LabQuest, to which is also connected a K-type thermocouple for temperature readings, with a sampling rate of 3 samples/sec. The test setup is shown in Photo 3. Continued on page 4 • Big Kits with Classic Styling and Bold Graphics • All Rockets Feature Laser-Cut Plywood Fins and Rings • Easy-to-Build. Durable. Exciting, and a Real Joy to Fly! ISSUE 365 M AY 2 0 , 2 0 1 4 www.ApogeeRockets.com Mid & High Power Rocket Kits! Everything Rocketry North Coast Rocketry Page 3 Continued from page 3 Conducting Themal Ablative Experiments Photo 3: The material was heated with a Butane torch for 11.5 seconds. The test procedure was as follows: Results Table 2: Raw data after the flame test for the different ablative materials. • Turning on the torch. • Placing the torch flame directed to the center of the sample and start of data collection by the LabQuest. • At the end of 11.5 seconds, quickly remove the torch and cool the sample with a spray. • Cooling of the thermocouple by a fan until reaching room temperature. After the samples had cooled, the appearance of the burnt area registration was photographed. Then the burned material was scraped carefully and the thickness of the remaining ablator was again measured and recorded. Besides ablator samples, the same procedure was repeated with a sample of bare aluminum in order to provide data for estimating the rate of heating. Table 3: The higher the F value (see Conclusion), the better the ablative material. Conclusion A function of F = (1 / (t * v)), the 3 best results are for samples with phenolic microspheres (85% and 15% resin Continued on page 5 • Unique ‘transforming’ rocket - looks like a normal rocket, but then rotor blades pop out at ejection • Competition efficiency: high flights and long descent time • Features curved rotor blades and free-spinning hub, just like those used in international competitions • Versatile: can use any 18mm diameter motor • Comes with video instructions for error-free assembly Page 4 ISSUE 365 M AY 2 0 , 2 0 1 4 www.ApogeeRockets.com Gyro Chaser Helicopter Rocket Continued from page 4 Conducting Themal Ablative Experiments Graph 1: Temperature rise of the aluminum base plate during the 11.5 second test. phenolic microspheres) SS2S + x (65% resin, 15% phenolic microspheres, 20% glass fiber plus “x”) and SS2S + X (65% resin, 15% phenolic microspheres, 20% glass fiber and “X”). When choosing our best candidate, we opted for the last 2 options, because for a more rigorous analysis, we should have taken into account the density of each sample. But if you look at the 85% resin concentration in the first case and 65% in the second and third cases, the density of the two samples will be considerably smaller. About the Author: Vicente Alvero Zambrano is a Student of physical science and lives in Santa Marta de los Barros ( BadajozSpain). His goal in model rocketry is to make space more accessible. He also enjoys cycling, robotics, electronics, chemistry, physics, and geology. • Won’t Shatter Like Brittle Phenolic Tubes! • Super Smooth Surface With Tight Spirals • Standard LOC Diameters Up To 6 inches • Cut and Slot With Standard Tools • No Fiberglass Wrap Needed • Sands and Paints Easily • Cheaper than Fiberglass Blue Tube From Always Ready Rocketry www.ApogeeRockets.com High Power Tubes & Couplers www.ApogeeRockets.com/Building_Supplies/Body_Tubes/Blue_Tubes ISSUE 365 M AY 2 0 , 2 0 1 4 Page 5