Reference / Paper · 2011
Peak of Flight #286: How to Achieve Extreme Altitude Deployment
Apogee Components' Peak of Flight newsletter, issue 286 (2011-05-10).
- peak-of-flight
- apogee-components
- model-rocketry
Reference / Paper · 2011
Apogee Components' Peak of Flight newsletter, issue 286 (2011-05-10).
Apogee Components' Peak of Flight newsletter, issue 286 (2011-05-10).
In This Issue How to Achieve Extreme Altitude Deployment Cover Photor:Two version of Mad Cow Rocketry’s Black Brant rockets. Get your own kit at: www.ApogeeRockets.com/Madcow_4in_Black_Brant_FG.asp 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] ISSUE 286 M AY 1 0 , 2 0 1 1 How to Achieve Extreme Altitude Deployment By Joel Schiff & Martin Aspell When a rocket is launched on low- or medium-power motors, little consideration is given to the effectiveness of black powder to blow the rocket apart and deploy its parachute(s). This is because at the altitudes reached by these rockets, the atmosphere has enough oxygen molecules for the black powder to detonate properly. But this is not the case as we go increasingly higher into the atmosphere with high-power motors. As Table 1 and Figure 1 (altitude in feet, pressure in pounds per square inch) indicate, the air pressure at 20,000 ft is less than half that at ground level. This means that there is less than half the necessary air available for heat conduction between the burning BP particles in your ejection canisters. This can lead to incomplete combustion with some of the BP left unburnt, with a consequent Table 1: The left-column shows altitude in feet, and the right side shows the atmospheric pressure as measured in pounds per square inch. Figure 1: The atmospheric pressure drops off dramatically as the altitude increases. About this Newsletter From Table 1, it is clear that as one goes ever higher, the air pressure is going ever lower, until at 100,000 ft the air pressure is virtually nil — actually 0.16 psi vs 14.7 psi at sea level. Recently, the authors have been working on a carbon fiber, unmodified, Mongoose 98 and after preliminary test flights with a K458 and then L952, we wanted to go for broke (almost literally) and purchased an Aerotech N1000. With its whopping 14,000 N-s total impulse it would according to RockSim models, boost the rocket to about 33,000 ft AGL. As others had succeeded in reaching over 40,000 ft with some modifications to the Mongoose 98, we used this altitude as our ‘best case’ scenario. At 40,000 ft however, the atmospheric pressure is 19% that at sea level (2.73 psi) and therefore there is too little air available for conduction to Figure 2: The ejection canister set-up simply use our for the K and L flights with no conaluminum ejec- sideration given to diminishing air tion canisters as density. These are at the bottom end in the successful of the avionics bay for deployment of K and L flights. the drogue chute at apogee. A tapered Something en- red plastic plug with paper wadding tirely new would retains the 1.2 g of BP. (An aluminum have to be done unpainted ejection canister has been to ensure the added to the original kit as a safety complete burn- backup). 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 loss of pressure to blow the chute at apogee — either drogue or main, whatever is being deployed. ISSUE 286 Writer: Tim Van Milligan Layout / Cover Artist: Tim Van Milligan Proofreader: Michelle Mason M AY 1 0 , 2 0 1 1 Continued from page 2 Achieving Extreme Altitude Deployment fact, aren’t the ejection canisters a form of non-expanding bladder? Well, yes they are. Since we had the canisters already installed, perhaps we could still use them and save a lot of hassle. But clearly our red plastic plugs were not going to be sufficient on their own as the air pressure differential would soon have them popping off, rendering each canister useless in conditions of 2.73 psi. ing of the 1.2 grams of 4F black powder to eject our drogue chute at apogee. Moreover, the Quest Q2 igniters (www. ApogeeRockets.com/igniters.asp) had to do their job as well in the same environment. Another important consideration here is that the combustion of the BP is not instantaneous and therefore the vessel containing it must hold the explosion intact for complete combustion to occur. The solution was indeed obvious — seal in 1 atmosphere of air pressure in each canister so that the tapered end plugs did not blow out until we blasted them out with black powder at apogee! This was achieved as follows. What should we do new to compensate for the lack of air at 40,000 ft? We did a search on the internet on how to overcome the combustion problem at high altitude and one of the solutions was replacing each existing ejection canister with a bladder made of surgical rubber. The bladder idea is based on the notion that it would contain the black powder long enough for complete combustion to occur while at the same time sealing in the 1 atmosphere from ground level. Now, New Zealand (where I live) is not a place where surgical rubber can be bought right off the shelf. But as we had a vacuum pump, we were able to test various alternatives and ‘take them up’ to 40,000 ft and check their suitability. We did have a latex glove and proceeded to cut out one of the fingers to use as a bladder. It swelled up like a balloon and eventually ruptured explosively. We tried various fingers, including the thumb, as they were of different sizes, but all with the same result. We definitely did not want latex. Even two layers was useless. For one thing, the back end of the ejection canisters are Figure 3: An ejection canister threaded and come with ignition wires entering with tight fitting black the bottom of the canister with several turns of teflon tape wrap- plastic caps. The wires to the ignitping. A glue gun is at the ready to seal the black cap and seal up ers go through a tiny hole in the bottom of the hole. So the bladder idea was starting to look too hard and we began thinking, did we even want a bladder at all? In Continued on page 4 • Standard Sizes Fit Your Existing Fleet • Easy Assembly, Minimal Clean-up • Casings & Propellant Available • Adjustable Ejection Delays • 9 Propellant Formulations 29mm Starter Pack Available ISSUE 286 M AY 1 0 , 2 0 1 1 Pro-X A better way to fly.™ www.ApogeeRockets.com Kick Your Rockets Into High Gear Your Source For Everything Rocketry Cesaroni Reload Motors Page 3 Continued from page 3 Achieving Extreme Altitude Deployment around the cap itself, as shown in Figure 4. each canister, then several wraps of commonly used teflon plumber’s tape are placed around the threads. (Both of the apogee ejection canisters were treated identically although only one is depicted in Figure 3). By the end of this process, we were quite confident that not a single molecule could escape the back end of the ejection canister before it had gasified. Now the top end has to be secured similarly and this was achieved by putting a few wraps of teflon tape onto the tapered red plastic plug used on previous launches, as shown in Figure 5. Before the cap is put in place, the bottom of the canister is doused with a glue gun so that when the cap is put on firmly, some of the glue goes into the hole and seals it as well. Covering the black cap is a plastic tie wound tightly Again, with only 2.73 psi in mind, the inserted red plug was sealed with a single wrap of Scotch aluminum foil backed tape that is carefully folded down over the top as seen in Figure 6 on the next page. The ejection canister now had 1 atmosphere sealed in and was ready for testing. This was done using a vacuum pump and placFigure 5: The top end of the ing the loaded ejection canister into a metal pipe ejection canister with teflon tightly sealed at both ends tape covering the red plug so that we could pump out about to be inserted. Figure 4: The bottom sealed end of the ejection canister with the black cap covering the wires and teflon tape, and finally sealed tightly with a plastic tie. 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. ���� Penny shown for size comparison Page 4 • Also tells you how high the rocket flew. www.ApogeeRockets.com/AltimeterOne.asp ISSUE 286 M AY 1 0 , 2 0 1 1 www.ApogeeRockets.com “The one altimeter you’ll use in every rocket you fly.” Your Source For Everything Rocketry AltimeterOne Continued on page 5 Continued from page 4 Achieving Extreme Altitude Deployment Figure 6: The final seal over the top of the canister is a single wrap of Scotch aluminum foil backed tape folded over the top. the air and simulate the conditions of the upper atmosphere. To be on the safe side, rather than just going up to 40,000 ft, we decided to err on the conservative side and took the interior of the pipe up to 100,000 ft — essentially a complete vacuum! was made of the canister and pipe confirming that all the BP had completely combusted. The testing phase now over, it was time to give our new knowledge a reality check. The N1000 motor burned for what seemed like an eternity with the rocket reaching apogee of 33,701 ft after 43 seconds. Deployment of the drogue at apogee occurred just like we knew it would. Once the vacuum took us up to the top of the atmosphere (note the dial is maxed out in Figure 7), we placed a heavy blanket over the blue pipe installation to contain the explosion of more than 1 gram of black powder. And detonate it did! An inspection Figure 7: Here is the vacuum pump used in our atmospheric simulation with the loaded ejection canister inside the blue pipe ready for ignition. Figure 8: The launch of the Mongoose 98 to an altitude of 33,701 ft with a drogue ejection at apogee. We’re Paying Cash For Great Articles for This Newsletter Are you a writer looking for some serious pocket change? We’re paying up to $350 for good how-to articles for this newsletter. If you’re interested, see our submission guidelines on the Apogee web site. www.ApogeeRockets.com/Newsletter_Guidelines.asp ISSUE 286 M AY 1 0 , 2 0 1 1 Page 5