The alarm went off this morning at 5:15 AM, giving me just enough time to ready myself and my stuff to meet Woody, who pulled up around 6:15. The day was a wet mess, and we experienced drizzle and light rain throughout the 2 hour drive to Camp Westmoreland, which is over in the northwest corner of Alabama. The poor weather had us both convinced that we would be dealing with just a handful of kids, so imagine our surprise when we pulled into the camp and found at least a hundred milling about. Checking in with the scout leaders, we found that they were expecting at least a hundred more, very close to the 250 cub limit they had placed on this event. Woody and I exchanged glances, both of us realizing we were going to be working our rears off for the next few hours. 200+ rockets is an awful lot to launch in a morning, even in sunny weather!
Fortunately, it was not just the two of us - the leaders informed us that the U.S. Space and Rocket Center had provided someone to help with the rocket construction, which left us free to focus on the launching. We also found out that Tracy and Lee from Russellville were out at the launch area trying to assemble some launch gear. The rain had slacked off, so Woody and I moseyed over there, only to find our Russellville colleagues starting to assemble some Estes Porta Pads. I must confess that I fought down a smirk at the idea of launching over 200 scout rockets using single pads and individual launch controllers; it could be done, but it would be an unholy chaotic mess, and take much longer than the 3 hours or so we had in the launch window. Lee and Tracy were much relieved at the sight of the HARA launch equipment, and thanks to their help, we had the range set up in no time. Sometimes the presence of a well stocked rocket club is a wonderful thing!
Akela 1's motor ignites (Click to enlarge).
The candy bowl saucer starts its journey (Click to enlarge).
The selected clear area was small and surrounded by trees, but it was just big enough to accommodate the scouts' Estes Dinks on 1/2 A motors. Red barricade tape cordoned off the pad area, and we placed some more around the battery packs and cables to indicate a no walking zone. I launched my Akela 1 rocket on an A8-3; it reached about the same altitude we expected of the Dinks, and recovered comfortably within the field. Knowing I was going to be really busy very soon, I also launched the Target Halloween Bowl saucer on a C6-0. My colleagues were impressed by how straight the ungainly purple oddroc flew. After these flights, the range was declared operational around 8:50, and we settled in to await the first wave of Cub scouts, expected around 9:20.
But the rain came first...
Waiting out the drizzle (Click to enlarge).
A light rain set in, continuing for the next 40 minutes. The first group of launches would involve scouts who had built their rockets in advance; they lined up under the porch of the camp bathhouse to receive their wadding, motors, and igniters. The rain was getting less, but even so, the first rack of 15 rockets was launched in a light drizzle - umbrellas were in much use when loading the pads. Scout Wave 1 involved launching 3 racks, about 45 rockets in all. By the time rack 3 was completely launched, the rain had finally stopped; I suppose it had deemed things were sufficiently soggy and decided to move on. The rockets in this first group were well made, and there were no parts falling off or ballistic returns.
Loading the final rocket of the rack (Click to enlarge).
A full rack of Cub scout rockets (Click to enlarge).
There was a lull of a few minutes before the next wave of scouts, who were the first to build their rockets in the camp activities building this morning. We expected two more groups after that, but what actually happened is that we had a more or less continuous influx of scouts for the rest of the morning. You could tell these rockets were built in a hurry - some had fin cans that fell off and had to be re-glued, while others had shock cords that were dangling. 11 more racks of rockets would take to the air, and while most performed well, some would not survive the morning. About 3 were lost in the trees, and 5 landed on building roofs; 4 came in ballistic, a couple re-kitted themselves at ejection, and 3 caught fire on the pad when the igniters pulled loose, igniting the plastic fin units. I felt particularly bad for one determined young lady; after 3 misfires, her 4th attempt resulted in the rocket catching fire, melting the fin unit and burning the lower portion of the body tube. I gave her one of the spare Sky Duster ready-to-fly rockets I bring to these events, and we were able to get this one up into the cloudy sky, which made her happy.
This video gives good idea of the pace of the launch
We were finished right about noon, and Lee and Tracy helped pack the very wet equipment back into Woody's SUV. I didn't take many pictures, because we were constantly occupied with pad duty, loading motors, and launching; there simply wasn't time. This launch was busy, even hectic at times, but it was good fun - the scouts thoroughly enjoyed themselves, and we put a bunch of rockets into the air. This is enough to satisfy any old rocketeer, even one a bit on the damp side.
After the scout launch yesterday, Duane warned me that he might head over to Pegasus field this afternoon for a couple of practice flights with his geezer TARC rocket. When he called about 3 to let me know that the warning would become reality in an hour, I immediately started looking over the fleet to decide which rockets would make my first flights at Pegasus this season (Pegasus field has been overgrown all summer, and they finally cut the weeds a few days ago). My new black-and-yellow Big Bertha caught my eye; next to her stood Beulah, also awaiting her first launch. Inspiration hit... It was time the three B sisters - Big Betty, Big Bertha, and Beulah - had a Sunday outing. Dragging out the range box, I prepared them for flight.
A B6-4 pushes Big Betty off the pad (Click to enlarge).
Duane's Goth rocket on an Aerotech F32 (Click to enlarge).
Duane and I quickly set up his launch rail and my LPR camera tripod pad after arriving at the field; Big Betty would be up first, and she left the rod around 4:15, soaring to a couple hundred feet on a B6-4. Duane then launched his black-and-red Goth geezer TARC rocket, which had its flight recorded by a family friend from Texas. She was a complete rocket novice, having only flown water rockets in her youth, and was very interested in the goings on. It was nice seeing the enthusiasm and answering her questions - very different from the usual "rocket smack talk" normally heard at our launches. Anyway, the Goth rocket reached 815 feet and was down in about 40 seconds. Not too shabby, but Duane was determined to do better, so he started prepping for flight #2.
Bertha lifts off to an audience (Click to enlarge).
Beulah is a blur as she clears the rod (Click to enlarge).
Big Bertha was loaded with a B6-4 and placed on my pad; she reached about the same altitude as her sister and recovered very nicely on a 15" green rip stop nylon parachute. I then fit a C6-3 into Beulah's motor mount and slid a Jolly Logic Altimeter 3 into her payload bay. The Altimeter 3 uses Bluetooth to talk to a phone or tablet, and I had re-paired this one with my Kindle - Apple does Bluetooth in a funky way, and I occasionally experience problems with the Altimeter 3/iPhone 6 combination. The Kindle communicated flawlessly; recording by the altimeter was started, and I quickly loaded Beulah on the pad. Flight was straight, with a good parachute deploy and a recovery about 25 yards downwind. The altimeter data was downloaded into the tablet, which showed she had reached 321 feet. Kind of low for a C6, but Beulah is a heavy girl - basswood fins, baffle, interchangeable motor mounts, and paint, plus the weight of the altimeter.
Beulah's flight profile as reported by the Jolly Logic Altimeter 3 (Click to enlarge).
Duane ended the launch with another flight of his Goth, which overshot the target altitude, hitting 905 feet. The parachute also failed to deploy, resulting in a very quick descent; luckily, there was no damage to the rocket, or to the eggs in the payload section. I have to hand it to Duane - his molded egg protectors are the cat's meow. The loading of the SUV was accomplished almost in the blink of an eye, and I was back at the apartment by 5. Five flights in one hour, no losses... A nice Sunday outing!
I dragged myself, my range box, and four rockets outside at 6:30 AM this morning to meet Chuck and Duane in the parking lot. After loading the stuff into the back of Chuck's SUV, we headed out to the Hardees in Scottsboro, where we linked up with Woody and three Boy Scout leaders. This morning's mission - help the scouts at Camp Jackson build and fly a few rockets. Sounds pretty easy, but nothing is easy for me early on a Saturday morning.
Camp Jackson was just a short drive across the river from the Hardees; like many scout camps, it's a rather scenic place, being right on the river in the midst of some gently rolling hills. We set up the pads in a small field next to the lodge and a small picnic shelter. I immediately took note of the potential rocket hazards - a few power lines and trees ringing the field except for the river on the east side. Fortunately, there was very little wind, and, despite my expectations of hanging a few in the trees, or rocket splash downs in the water, no rockets would be lost this day. It's not often this happens.
Setting up the range at Camp Jackson (Click to enlarge).
While the scouts were assembling, I took the opportunity to fly three of the four rockets that had journeyed from Huntsville. The BMS School Rocket was up first, making its maiden flight on an Estes A8-3 - straight up, with a nice parachute deploy, and best of all, it drifted back into my outstretched hands. Definitely a good start for the day. I followed this with my Estes Snitch on a C6 motor. This rocket delighted some of the scouts, who were intrigued by its unconventional appearance; clearly they had never seen a saucer fly before. The Snitch is showing its age, being rather battered after lots of flights - one of the plastic supports for a landing leg has cracked. Repairable, but I'm afraid this rocket will not be able to handle many more launches. My final flight was the venerable Der Red Max on a B6-4. Outfitted with a keychain camera, it also put in a textbook performance and returned a not too shabby video. I particularly like the part just after landing, where you can see some scouts running up to the rocket.
Video taken from Der Red Max
The scout leaders had this event organized pretty well, with the first step being rocket assembly in the lodge. The chosen rocket was the Estes Dink, repackaged for the Boy Scouts as the "Scout Voyager". Because of the limited time available for this activity, construction was done using super glue, which got the job done, albeit with lots of sticky fingers and mess. Fortunately, the leaders had ample quantities of nail polish remover (acetone) to help clean things up. After the scouts built and prepped their rockets, they moved on to an outside station, which had some space-related crafts. The final stop was the launch pads.
Scout Voyager rocket
(Click to enlarge).
Building rockets (Click to enlarge).
We had set up three racks, each containing three pads; all were tied into the trusty HARA launch controller. Duane acted as the LCO, with Chuck, Woody, and I acting as pad managers; each scout would get to press the fire button to send his rocket on its way. Launching went smoothly, with no mishaps. Several rockets did not fully deploy a parachute or streamer, but none came in ballistic or were lost. All in all, about 30 scout rockets took to the air (three and a half sets of nine), and everyone had a most excellent time. I was approached by a couple of parents afterwards asking where they could get rocket supplies so they could fly with their kids - always a good indicator of a successful launch.
Demonstrating how to connect igniters (Click to enlarge).
Woody powers up the pads (Click to enlarge).
A Dink gets going (Click to enlarge).
Up, up, and away! (Click to enlarge)
Dink drag race (Click to enlarge).
Woody and I get to repeat this at another scout camp in Florence this coming Saturday. Since it's a bit farther away from Huntsville, I will have to get up even earlier...
Quest Aerospace is offering a pink and red version of its old Big Rage rocket for just $10! Part of the proceeds go to raising breast cancer awareness through the It's the Journey foundation. A very easy to assemble rocket that stands over 3 feet tall, plus making a contribution to the fight against cancer! What are you waiting for? Order one (or two, or three, or ...)!
This thing looks perfect for those evil Hello Kitty decals and stickers, btw.
I continued to ponder why the Perfectflite PNUT flown in Probe-18 on Saturday had ground level at -65 feet. I am not an electronics type of guy, so I did what any nerd seeking enlightenment would do - I contacted tech support:
Sir,
I experienced my first ever anomaly with a Perfectflite altimeter at this past Saturday’s launch. In brief, it seemed to think ground level was at -65 feet, and underreported the altitude by that amount (as compared to another altimeter in the same payload section). I have a post describing this on my blog:
and have attached the data file to this email. Any insight/help you can give would be greatly appreciated.
Kind regards,
Bill Cooke
Perfectflite responded in a day with this very informative post, which gives a lot of insight into the workings of the PNUT:
Hi Bill
The Pnut does not start recording at T = 0 & Alt = 0. After you turn it on and wait for the init procedure, it constantly samples pressure and fills several circular buffers. One buffer records the last 32 altitude readings (MSL, or above sea level, not ground level) to provide pre-launch data. The other buffer stores averages of the contents of the first buffer to track the ground elevation which can change due to weather variations if the rocket sits on the pad for an extended time. The averaging also minimizes the impact of sensor drift and wind gusts.
The altimeter detects launch when the current altitude reading is 100 feet higher than the averaged ground elevation (this launch detect threshold is changeable from the download software, 100' is the default). The program then copies the last 29 readings into the flight memory and continues sampling and recording data from that point. So the bottom line is that you get about 1.4 seconds of data preceding the 100 foot altitude point, which will not necessarily mean that T=0 on the graph will be at altitude = 0. If the rocket takes off quickly, you will have a number of altitude = 0 readings stored before the curve starts upward. Similarly, if the rocket has a slow ascent, the T=0 altitude will be greater than 0. With a 100 foot launch detect, as long as the rocket's average speed is above about 70 FPS you will be assured of getting data extending back to the liftoff point.
The above is just an explanation of the fact that T = 0 and altitude = 0 do not coincide (so we can record and display some pre-liftoff data), it has nothing to do with explaining your anomaly.
The second buffer averages the MSL readings from several seconds prior to the current point in time back to about 26 seconds prior to the current time. The produces the stabilized ground elevation that the altimeter later uses to convert MSL readings to AGL (above ground level) readings. Because the average is based on a "moving window" that is updated continuously, effects of sensor drift and weather variations are essentially eliminated. Because it is an averaged value based on a large number of samples, noise due to wind gusts or other anomalies is also reduced. If you just sampled the ground elevation once when the altimeter was turned on and the rocket sat on the pad for 30 minutes before launch (not uncommon...) then the sensor drift and weather issues could be quite large. If you just take a single sample every so often to update the ground elevation (without averaging), then a wind gust at that particular point can shift the ground elevation significantly, potentially leading to false launch detect and large errors in the ground elevation.
As soon as the altimeter detects launch (altitude greater than 100 feet and T=1.4 seconds) the ground elevation averaged from the period 3 seconds earlier to 26 seconds earlier is "locked in" and is never subject to change. The large ejection spike occurs well after that point, so it has nothing to do with the issue.
So something during the period of 3 seconds to 26 seconds prior to launch detect had an enormous impact on the ground elevation. If it was a brief event, the magnitude would have to be huge to shift the average of nearly 450 samples by 65 feet.
Is it possible that sunlight entered the payload bay's vent holes (i.e. are any lined up in such a way that this could be possible)? If your Pnut is one with the newer stainless steel covered pressure sensor (U3 on the bottom of the unit) then one of the sensor's holes should be covered with a small black piece of tape. If the tape has been dislodged, then the sensor will have a large degree of light sensitivity and a hit by direct sunlight could easily cause the issue you describe. If you have the older sensor with a white plastic cover, light sensitivity is not a problem.
Can you email a sharp closeup of the bottom of the altimeter?
Also, the difference in magnitude of the ejection spike is easily explained by the fact that the spike is very brief (less than 1 sample in duration) and the Pnut samples at 20 samples per second vs. the MicroPeak 10 sample per second. Unless the two devices were in perfect synchronization, they would be sampling different pressures due to the rapid change in pressure during the spike.
The paragraph highlighted in bold is what surprised me - a light-sensitive pressure sensor? I hauled out the PNUT and took a close look:
Bottom of PNUT altimeter (Click to enlarge).
Sure enough, there was no tape covering one of the holes (I have no idea which one is supposed to be covered). So that seems to be it - light entering the payload section and hitting the sensor caused ground level to be reset. Who would have thunk?
Perfectflite, being a class act, offer to repair and clean the altimeter if I return it to them, which I will do next week. Hard to turn down an offer like that. They also gave me a couple more tips, which I am posting below for those who may find them of use. Technical support (except for Apple Genius Bar) is good - a couple of emails yielded a plausible answer to my mystery.
Additional Perfectflite suggestions:
1) A large downward ejection spike is usually caused by ejection charge gas entering the payload bay because of insufficient sealing. Since the gas is corrosive, this can cause degradation of the electronics. Are there any holes or other possible leaks in the balsa coupler depicted in your drawing? Or is the balsa that porous?
Bill's note - nope, there are no holes or leaks in the coupler, which is a nice 1.5" length cylinder of good quality balsa. Has a nick in the bottom after this flight, but still AOK)
2) Your static ports don't need to be anywhere near as large as described on your drawing (four 1/8" holes). Four pinholes made with a standard pin would be more than enough, and using a pin is fast & clean. The smaller holes would also minimize sunlight effects and provide filtering of wind and turbulence for a smoother graph.
Rocket geeks like to know how high their birds fly; over the decades, we have gone from "just guesstimating" to visual tracking with theodolites and trig tables to the tiny barometric altimeters made possible by modern electronics. Most of us - with the exception of a few contest rocketeers - would agree that the trend has been towards increased accuracy and greater precision. Altimeters are now legal in contest events and the qualification scores of TARC teams are dependent on the beeps or flashes emitted by the devices. However, I am often curious as to the accuracy of the altimeters we use; I would guess about a few feet if everything goes normally, but that is a just a "guesstimate". So, being a nerd, I decided to fly 2 altimeters (Perfectflite PNUT, Altus Metrum Micropeak) in the payload bay of Probe-18 at Saturday's HARA launch. Lofting small payloads was what the rocket was designed to do, and I figured the comparison would be useful, fully expecting the altimeters to agree within several feet.
I was wrong...
First, a bit about the flight. Probe-18 was launched in light winds on a B6-4 motor. The field was a fairly flat sod farm, with no significant rises or dips in the terrain. The rocket flew straight, with only a slight of amount of turning into the wind, and looked to have achieved an altitude of a few hundred feet. The parachute fully deployed and the rocket descended slowly; the ejection charge fired on time, though it sounded loud, indicating perhaps a bit too much powder (i.e., a "shotgun" ejection charge). After recovery, the body tube near one fin was observed to have failed, and the fin was chipped at the leading edge. Further inspection revealed a deep gash in the balsa coupler at the bottom of the payload section, suggesting that it had snapped back into the rocket at ejection, hitting the top of the fin; the force of the impact caused the body tube to fail near the fin root.
Probe-18 damage (Click to enlarge).
Probe-18 payload section layout (Click to enlarge).
When the rocket was recovered, the PNUT was beeping out a peak altitude of 257 feet, which seemed a bit low, but, hey, my eyes aren't calibrated. I did not bother to check the MicroPeak until I returned home, at which point I downloaded the altitude profiles from both altimeters. Boy, was I surprised! The MicroPeak recorded a peak altitude of 322 feet, a whopping 65 feet higher than the PNUT value - what was going on?
Probe-18 altitude profile recorded by the Perfectflite PNUT (Click to enlarge).
Probe-18 altitude profile recorded by the Altus Metrum MicroPeak (Click to enlarge).
A "normal" PNUT altitude profile - that of Nemesis at the same launch (Click to enlarge).
Both profiles were similar in that they showed a huge altitude dip at ejection, characteristic of a pressure increase associated with the Estes shotgun ejection charge. That much I could explain. Looking closely at the PNUT profile, I saw that it did not start out at 0 feet at 0 seconds, which was unusual. I then checked the profile from a second PNUT that had flown aboard Nemesis at the same launch; that profile looked normal, with the rocket lifting off and landing at 0 feet. So no insight there. I copied the Probe-18 PNUT numbers into Excel, where I discovered that landing was considered to have occurred at -65 feet altitude. Hmm... 257 + 65 = 322, the number reported by the MicroPeak. Since the MicroPeak produced an expected profile, I was inclined to take it as the "truth"; I found I had to add 65 feet and +0.3 seconds to the Perfectflite PNUT data to get a match to that of the MicroPeak.
Altimeter profile comparison (Click to enlarge).
So what's the deal here? Both altimeters were in the same payload section, with adequate ventilation to the outside air. Both showed the dip in altitude at ejection, though the PNUT had it occurring 0.3 seconds earlier and the dip more severe, going right though 0 to -112 feet. In the MicroPeak data, the dip reached 25 feet, not quite to 0. Could this somehow have screwed up the Perfectflite smarts, causing it to think the ground was at -65 feet? Or did the shock of the impact with the fin give the PNUT a "concussion"? Were my holes to the outside too big? Or was there a gremlin blowing on the PNUT, trying to mess with my mind? I then remembered a similar occurrence involving the MicroPeak back in January; it too registered a ground level well below zero feet. Back then, I attributed the anomaly to not giving the altimeter enough time to sense ground level before launch, but this time the altimeter was beeping steadily (indicating ready to launch) and the Probe-18 sat on the pad for several minutes before lifting off - Couldn't be the case here. In the January flight, it was obvious that the altimeter moved in the payload section during flight. Perhaps the PNUT was a bit loose and shifted around in the Probe-18's payload section?
Whether it was a mistake on my part or not, this experience gives me a bit less confidence in electronic altimeters. By looking at the PNUT data, I was able to see something was fishy, and even derive the "correct" peak altitude by adjusting the zero point. But in evaluating a TARC flight, we are allowed to only use the altitude beeped or flashed by the altimeter when it is returned to the observer; no analysis of downloaded data can be used to adjust the score. How often do the altimeters beep out a wrong value?
It makes one want to fly a second altimeter as a check. But that adds weight.
Saturday marked the next-to-last or last club launch in Manchester for 2015; I'm betting that it will be the last, because the sod farm folks were already re-sodding the northern part of the field. Once this gets fully underway, we will be unable to launch there until March, when the grass is grown. Nonetheless, it was difficult to get my carcass out of bed at 6:30 AM, especially after a busy week at work. But I did manage to get moving and drag my stuff outside to meet Duane at 7:30. The two hour drive to the field was normal and uneventful; I was impressed by the efficiency of the Winchester Hardee's staff in handling a very large morning crowd - we got our biscuits within a couple of minutes of ordering.
A rack of rockets ready to fly (Click to enlarge).
I think the best word to describe this launch would be work. HARA had the range duty, and Chuck was already there unloading the trailer when we arrived. I did my customary setting up of the low power pads, leaving the mid and high power stuff to the others. We were a bit under staffed, so the range was not ready until 10:15, about 15 minutes behind schedule. This would not be a problem, as the crowd of attendees was about medium for a club launch; no one was in particular hurry to fly. The weather looked great, with a light wind out of the southeast - for once blowing AWAY from the trees. Chuck gave the flyers' briefing, and we were off to the races...
A successful level 2 certification flight begins (Click to enlarge).
Just a few high power rockets would take to the skies. Art flew the largest rocket with some fancy electronics to over 4000 feet on a J motor, Tracy certified Level 2 on a J, and Keith Nyman flew his Laika on an I239 Blue Thunder motor; the rest of the high power flights used H impulse. One gentleman put an H in a 38mm minimum diameter rocket, which got some air, and then stuck an H400 into the same rocket. It streaked off the pad like a bullet, and I did not see it until it landed near the road about a hundred yards away. Another H flight netted a young rocketeer a Jr. Level 1 certification. That was about it for high power.
A red and black Leviathan lifts off (Click to enlarge).
An E motor suffers a nozzle blow out
(Click to enlarge).
We had lots of mid power flights; there were several Leviathans flying on F's and G's. The Leviathan is not available from Estes any more, but it is a very popular rocket on the flight line. Duane flew his Goth Geezer TARC rocket 3 times, finally reaching an altitude of 867 feet, about 17 feet above the 850 foot goal. However, it was a good thing he substituted dummy weight instead of eggs, because the shock cord broke in each of the last two flights, perhaps cut by the end of the brass tube used in the shock cord mount. An Estes Silver Comet from the 1990's flew twice on E motors, and there were many others I cannot recall.
3 Crayon rocket drag race (Click to enlarge).
The low power pads were the most active; a 3 crayon rocket drag race and one involving 2 Estes mini motor powered ready-to-fly models delighted the crowd. The crayon drag race was especially colorful, and those crayons would individually fly several more times in the morning. Brenna Nyman flew a 3 stage mini Comanche-3, which had an issue with the upper stage, and a Red Max. Lots of other model rockets took to the air, but I was not paying much attention, being tied up with RSO (Range Safety Officer) and LCO (Launch Control Officer) duties.
Brenna's Mini Comanche-3 leaves the rod (Click to enlarge).
The first stage falls away from the Comanche-3
(Click to enlarge).
A RSO is the person who checks the rocket for stability and workmanship; he or she makes sure the rocket has the fins glued on, has a recovery device, that the motor is installed properly, and that the flight card is complete. If the rocket is not a kit, the RSO also checks the rocket's stability, visually verifying that the center of gravity is forward of the center of pressure. Finally, the RSO assigns the model a pad number. The LCO is the individual who controls the range, makes the launch announcements over the PA system, ensures the range is clear, and does the actual launching. At past launches, I have performed one or the other of these duties; I took stints as both yesterday. I actually like these roles, but it does take time away from flying and picture taking. However, range duty is a necessary evil if your club is running the launch.
My Falcon 9 blasts off on its first flight (Click to enlarge).
Nemesis' dual E12's leave behind a trail of smoke
(Click to enlarge).
The net upshot was that I only got to fly 3 of the 6 rockets I had brought to the launch. The Quest Astra, Balsa Machining School Rocket, and Beulah would have to fly another day, while the Space X Falcon 9, Nemesis, and Probe-18 made their inaugural flights. In my last post, I characterized Estes E motors as "sticks of dynamite"; that was not true at this launch, where all 3 E12's I flew performed superbly. It was probably a bit too much motor for the Falcon 9, which got way, way up there; I had a very long walk to recover that one, which gently descended under a black 18" nylon parachute. Nemesis flew to 878 feet on her 2 E12 motor cluster, proving that you can achieve this year's TARC goal by clustering Estes black powder motors. My scratch-built Probe-18 model soared to 322 feet on a B6-4; however, the payload section carrying the two altimeters snapped back into one of the fins, ripping the body tube. Notice that I did not say "knocking the fin off" - the double glue joint technique produces a very strong bond; the fin will break or the body tube will fail before the fin comes loose. I am still trying to decide whether to repair the damage (which will conserve parts) or build a new sustainer (which will probably be quicker).
Probe-18 heads into the clouds from Pad 10 (Click to enlarge).
Probe-18 altitude profile as reported by the Micropeak altimeter. The major dip is caused by the B6-4
motor's "shotgun" ejection charge (Click to enlarge).
Around 1:30, pop-up thunder storms began showing up in the local radar, and 15 minutes or so later, the sound of thunder convinced us it was time to go. Everyone pitched in to break down the range, and we had the trailer loaded by 2:15. Rain had started to fall, bringing to an end the last HARA Manchester club launch of the season. Even if there is a launch next month, it will be the Music City Missile Club's job to run the range.
