Lagger: Plaster City 1/1/11 Launch Report

The coolness of the date of this launch was exceeded only by the complete lack of wind and excellent flying conditions all day. The primary reason for this delayed report is that I was trying to improve the video I shot that day to no avail. My pictures sucked too so that's awesome.

Fiberglass Nike Smoke 4" - This is the kit mis padres purchased for me for Xmas (bah humbug :). It's designed like a tank with a weight to match -- 81 oz dry!! I purchased a Pro54 4-grain 1597K400 Green^3 reload from Jack. The liftoff was slower than I'd expected but, like all Nike Smokes, the thing flew straight as an arrow. I trimmed the delay to 11 seconds and ejection was about 1 second after apogee. I used a 48" parachute and the descent seemed slow until it got nearer the ground then it seemed speedier than I'd like. In any event it landed at the edge of the 'bowl' free of damage.

I think this kit needs some serious thrust so I purchased another 4-grain motor, the 1633K940 White Thunder, for its next flight. At the same time Jack offered me a mystery 4-grain motor for half-price. Others reportedly shied away earlier in the day but I wasn't skerd and bought it anyway. When I got it home I opened the package to find "VM" written on the ejection cap so I'm forced to assume it's the 1408K2045 Vmax. Score!! So I'll reserve that for the third flight of my new Smoke and it should be scootin'.

.38 Spatial - I last flew this minimum diameter, carbon-fiber-over-phenolic design on an I284 to ~9100'. The next logical step on the way to the insane 1115J530 was the J350 I've had sitting in my motor box for many years now. As always these minimum diameter flights take way too long to prep and there never seems to be enough internal room to fit everything despite previous successes there. Once on the pad I had trouble locating the Raven's arm button so I pulled the rocket, slightly rotated the electronics board, and tried again. The second time was sort of a charm. I was able to arm the Raven but, upon 'ignition', the motor pressured up very slowly as old motors will. After a sizable chuff the thing lifted off but was marginally stable. This is about the 10th photo of a 5 fps sequence and the motor took about 5-6 seconds to pressure up:

The resultant wiggle sent it NW and way out there. I had a radio tracker signal the whole time and figured everything was intact. After walking out toward the wash for over half an hour and circling about I finally found the transmitter.... just the friggin' transmitter!! It looked like someone had wrenched the thing off the shock cord, left it there, and kept the rocket; or so I initially thought. I ventured out on the original line and asked a camp of moto dudes if they'd seen anything. One fella seemingly sketchily answered "With a green 'chute?" Yes I answered to which he replied "Oh it's back from where you came about a quarter mile out." His answer didn't sit right with me but what was I gonna do? Ask to search their motor home? I bit my tongue and walked back toward the launch site only to find the rocket about 30 feet east of where I'd found the transmitter. I immediately felt guilty about my suspicions so I need to offer the benefit of the doubt in the future.n Here's roughly where I found it:

OK so the payload section and booster were still mated but the nosecone was off and the Kevlar™ cord had ripped through the payload tube about 1.5". Man that aramid fiber is tough!!

As I walked I pondered failure analysis... The apogee charge had blown but the motor and delay had already burned up so the delay hole in the motor must have vented too much of the gas and failed to pop the payload section off. As the rocket came in ballistic the main popped but I had only loosly knotted the 'chute lines the shock cord (no knot on the cord itself). So the parachute, mounted above the taped-on radio beacon transmitter, slipped up the cord, stripped off the transmitter, zippered the payload section, then promptly shredded off. As I walked back I even found the 'chute!:

I'm constantly destroying those TopFlight 'chutes at every single launch. The Raven survived and here's the flight graph:

Despite the serious flight arc I still attained about 8100' so I'm convinced it would have exceeded 10k were it straight. Also the velocity wasn't too bad at roughly mach 1.5. You can also see the blip after apogee where the charge failed to eject and then where the main ejected at ~800'. I wanted to swap nosecones with an extended design anyway so .38 Spatial will fly again soon. Lessons learned:

• Burn those motors soon after you buy them! Chuffing (motor pressure surge before actual ignition) is dangerous. In the early 80s motors employed progressive thrust curves and weren't nearly as reliable as today's motors. I saw a few rockets chuff, pop off the launch rod, then fire off horizontally into the desert. If a motor is older and you still choose to fly it always use a long launch rod/rail as an insurance policy against chuffing.
• RockSim's CP calculation is way too aggressive hence the metastable liftoff. I'm now relying more on OpenRocket's CP calculation as it's typically between RockSim and Barrowman.
• [Just added] Plug those forward closures!! I'm certain I would have attained apogee ejection were it not for the unintended pressure vent offered by the motor itself.
• In the unlikely event of a similar failure in the future place the transmitter above the parachute connection point or, even better, always tie a knot in the shock cord for parachute attachment. That way if the parachute strips off it won't take anything with it.
• Offer the benefit of the doubt to those sharing the desert with us. I have a bad history with this so I have some trauma to overcome. When I was a kid I flew a Composite Dynamics 29mm F45 motor in my prized AeroRoc. It was a high flight on a windy day and the rocket landed on the side of the highway in the bay area. I ran toward it only to see someone pull over and drive away with it when I still had a quarter mile to run. Damn them! Epic recovery FAIL.

Building three simultaneously = efficiency!

I'm taking advantage of my two-week break from work to complete construction on:

1. 4" Extreme DarkStar - This was my gift to myself this year after seeing KO's success with the all-fiberglass kit. I've decided to break this one in with the pink M1676 Pro75 motor.
2. Madcow Rocketry 4" fiberglass Nike Smoke - Thanks to the kind generosity of my parents who bought this kit for me for Xmas I plan to select motors with reckless abandon on this one.
3. 3" Vertical Ass... - This is my abbreviated kit bash of the Vertical Assault parts from Giant Leap Rocketry.

Those are the second and third all-fiberglass rockets I've built and they seem to go together quite nicely. Here are the first two in my studio for scale:

And here's the build progress on the Vertical Ass... I took this opportunity to neatly cut exact diamond shapes from the 3" tube to perfectly fit the fin can shape:

Here's the clamping setup while the epoxy cures:

And I'm very pleased with the final cured form of the assembly:

Further analysis for DRM II's first flight

I was chatting with my aerospace buddy Chris at work today and, having seen the blog entry and data below, he was as confused as I about the barometric altitude curve shape. I normally plot barometric altitude as that's accepted as the official peak. Accelerometer-based altitudes can suffer from integration errors caused by wobble, spin, coning or other undesirable flight behavior. Chris asked if it might have been caused by a Mach transition effect but I only hit Mach 0.58 so I was nowhere near the transonic region (0.8-1.2). I continued to ponder this irregularity and think I can explain the difference. In this alternate plot from the Raven you can see that the accelerometer-based altitude is shaped as one would expect with air-starts (slight slope increase when they kicked in):

I remembered that the aluminum tube that connects the electronics bay to the motor area was not plugged. When I pulled the camera it had a bit of smoke residue on it and the electronics board smelled sooty. This 7.5" rocket produces a great deal of base drag that I think forms a vacuum. I think that's why the barometric curve is steeper than the accelerometer curve and why there's an inflection point after the air-starts burned out. Then base drag decreased at that point which might have increased the pressure in the electronics bay just enough to flatten out the barometric curve in that weird region. In any event the rocket turned only once and otherwise flew straight up so I'm going believe the accelerometer curve in this particular case. Let me know if you have other thoughts. I'll definitely plug up the conduit with clay next time to reduce this pressure tomfoolery.

Der Red Mix mark II... For The Win!

Last weekend I flew DRM mark II for the first time on a central L730 Classic and 2 x I345 White Thunder air-starts 1 second after the L burned out. I couldn't be more pleased with the outcome. First off there was pretty much zero wind all day at Plaster City though that came at the cost of a persistent cloud ceiling at roughly 6-7k feet. I had prepped a bit the night before and mounted the Flip MinoHD video camera and altimeters/battery holders on the board and also assembled the recovery system. On the drive out I decided I didn't want to char the innards of DRM II with black powder and so committed to investing in the Rouse Tech CD3 Jupiter ejection kit with 28 and 35g CO2 cartridges. This added about 45 minutes to the prep once purchased and built so I flew at noon. Thanks KO for shooting some prep shots:

[Note to self: stop talking whilst being photographed.] I got out to the pad and realized it's pretty difficult to get that 6+ foot long, 26 pound thing on the rail myself. Luckily a few folks helped. Here's my buddy Frank reminding us where ALL of his flights land:

I was confident that I'd fixed all the problems from last time with this build and prep so all that remained was to push that button. The liftoff was much faster than I'd anticipated and I'd estimate that flame to be 6 feet long:

The ascent was beautifully straight and essentially rotation-free. It appeared to me that the 2 x I345 White Thunder air-starts kicked in before the L730 Classic had burned out. The video and altimeter data would prove me wrong, however:

Note the single rotation over the mile of ascent! I'm very pleased indeed. Watch full-screen on YouTube in 720p HD for best effect. Here also is the unabridged version of the video from liftoff to shut-off (~5.5 mins). Here's a recovery shot and altimeter data from both the Parrot2 and Raven:

The average barometric peak of the two altimeters was 5,550'. Also note the clear velocity decrease after the L730 burned out and then the spike as the I345s kicked in. Yay, data. Next time I plan to fly 5 motors (1 on the ground then 2 in the air then 2 more in the air). I'll shoot for Lucerne on January 8th to get some different video scenery. Great success!! Oh and here are some other shots from that day as well.

Plaster Blaster 2010: A new personal record of 21,915'!!

This last weekend's Plaster Blaster 9 launch featured amazing weather, many cool projects, more spectators than I've ever seen at Plaster City, and my parents even drove out from AZ to visit. Nice!

As always I'd planned more flights than I'm capable of completing on this three-day weekend. At a minimum I had hoped to fly Der Red Mix II (K635 Red Thunder, air-starting 2 x I345 White Thunder), my Nike Smoke on a pink M1675, and Em-Sem-Fity with a CTI M795 in a drag race with Frank Hermes and Art and Tom Just from AZ. Jack didn't have the K635 in stock and I was too tired to prep the Nike Smoke on Sunday so the only flight I completed was for the drag race.

I started prepping the segmented M795 moonburner from CTI late on Friday night so it could cure for Saturday morning. Despite arising early on Saturday I was still tardy for our agreed flight time of 10AM. Art and Tom had their M650 rocket sitting on the pad for awhile then Frank headed out about 10:15AM. I was finally done prepping by about 10:30AM but, when I headed out there, Frank had just dropped a rail guide. He was confident that he could quickly a) swap boosters and b) increase the black powder load in his CD3 system. I set up Em-Sem-Fity on the pad, armed the electronics, and loaded the igniter. Astonishingly Frank was done with everything in about 15 minutes!! We were a bit concerned about the thin, uniform cloud veil right above us but we agreed everything should be fine. Upon ignition Frank's rocket leapt off the pad at astonishing speed and smoked both Art/Tom and I thus winning the first-to-1000' portion of the informal contest (Thanks to mom for shooting this sequence :)

Then our two remaining rockets lifted off almost simultaneously:

KO captured this video of the liftoff with her Flip MinoHD video camera (watch full-screen in HD on YouTube for best effect):

Upon liftoff my rocket appeared to be a bit overstable and coned some on initial boost. This is strange because this motor weighs almost the same as last year's M750 and that lifted off straight without even a wobble so I'm confoosed. The flight path was several degrees toward the southeast, it punched through the cloud layer, and I heard it burn for another 6-7 seconds!! Unfortunately Art/Tom's rocket failed under boost and they're not yet sure what happened. Those dudes are super nice and they say they'll come back next year with a 20k attempt.

So I have my CSI radio beacon installed and I get a nice clean signal boost when the thing blows out of the carbon fiber tubing. Having heard that I told our RSO, Ken Sparks, that I had attained apogee safely and started following the signal with my Yagi antenna. I walked for several minutes with a nice clean heading NE toward the prison then... nothing. Static. Normally static means you've crashed the transmitter but, in this case, I knew it had been falling for about the expected amount of time under streamer/'chute. Undaunted I continued to pursue that last line toward the NE. During this long walk I thought I heard a periodic blip in the static and redirected to see if its strength increased. After about an hour of meandering I decided that I had to scale the highest 'local' feature and walked up to the abandoned quarry to the east. I removed my sandals and climbed the loose gravel to the top of the 40' mound, turned on my receiver and... I had my signal back!! It was pointing me north right toward where it had earlier so I should have simply stuck to that line. As I continued walking the signal would strengthen and fade as a function of elevation. Keep in mind this was on 'long range' so this thing still had to be far away or in a really deep ravine. At one point I feared that it had landed on prison grounds or in one of trees hiding the prison from view. Finally I found the thing laying on the ground about 0.2 miles north of the prison:

I used Google Earth to map the landing destination. The red straight line is roughly 3.2 miles as the crow flies and the yellow, meandering path is my best guess on my walk of ~4.9 miles:

I was in almost constant phone contact with Frank who had just recovered his 22,176' flight 6.8 miles north of the launch site. He was kind enough to trek out to pick me up. I didn't notice my exhaustion until after I'd found Em-Sem-Fity but I was pooped. Frank took this photo as I approached:

I downloaded the altimeter data and here's the ARTS2 summary and graph with a barometric peak of 22,080':

And the Raven summary and graph showing 21,749' for an average of 21,915':

I also plugged the flight info into the ARTS2 software and here's the motor analysis:

Now allow me to be very clear: I am not taking anything away from Frank's second victory on peak altitude here!! However, none of those motor attributes match those on the ThrustCurve site. Who knows how accurate this analysis is but, again, I'm left wondering if reload aging impacted performance. One of these days I'll need to buy a pristine motor and eliminate this aging variable for my peace of mind.

This was a great launch and I'm grateful to all the club volunteers who made it happen! The spectators, including my folks, were really stoked so I consider Plaster Blaster 2010 to be a great success. I posted the rest of my pictures here if you're interested. Thanks for reading this saga and cheers to a great PB 2k11!

Lesson learned: Inspect thoroughly then comment

At Plaster Blaster 2010 this last weekend I was asked to inspect the connections in a friend's electronics bay. I immediately noticed that the stripped portion of the e-match wires were too long and likely to short out. I requested the fix then didn't dig much deeper due to other distractions. In seeing that high-level issue I had failed to notice that the e-matches on both altimeters were connected to the wrong positions. Luckily the rocket managed to save itself after failing to eject the main 'chute at apogee and landed safely and without issue. From now on, whenever I'm asked to inspect a prepped rocket, I'll record all my comments with pen and paper then submit the sum total as a group to prevent this error. Duh!!!

Finally! Great sanding success!!

On the way home today I decided to stop off at Home Depot and buy some form of different hand sander than the two B&D 'Mice' I have now. I surveyed all their sanding wares and, in the end, I selected the Rigid R2501 sander for $50. It has a vacuum function with an enclosed cloth bag and claims to retain 90% of the dust generated. BIG... FRIGGIN'... FAN!!

The raised handle on this sander absorbs most of the vibrations and the vacuum bag actually works and retains most dust. Also the coarsest grit sandpaper included was only 120 but I decided to take it for a whirl on the second, properly cross-linked layer of UV Smooth Prime anyway. I was still done in about 1/2 the time it took with the big Mouse using 60 grit sandpaper!! The efficiency of this thing has already significantly reduced my hatred of finishing. If you've struggled with sanding in the past as I have I suggest you pick one up.

As time is running short for Plaster Blaster I'm considering applying a layer or two of Kilz spray primer and again leaving Der Red Mix mark II unfinished for the maiden flight. It's a bit of a cop-out but there just aren't enough hours in the day recently. The flight should still rock. I decided to keep it RED and will fly a central 1994K635 Red Thunder on the ground but air-start the 2 x I345 White Thunder motors. After I finish the paint and decals then I'll fly the central L730 and air-start 2 x H399 White Thunder (perhaps at RocStock XXXII the weekend after).

UV Smooth Prime aging... fail.

For the second time I'm reminded that the yellow cross-linker included with the UV Smooth Prime product has a maximum shelf life of only a few months. On Friday I opened the little jar to find a rubbery solid therein. The white primer itself seemed fine so I rolled the dice and slathered it on Der Red Mix mark II anyway. Over the course of sanding for an hour today I noticed several spots where the dried primer was flaking out of the tube seams. I'd never seen this before with cross-linked primer so lesson learned: Use that $51 can of product quickly!!

They really should sell the cross-linker separately because of the aging difference of the two parts. In order to finish this rocket by Thursday I'll need to drive up to Aircraft Spruce in Corona tomorrow to buy another can. Hopefully they'll sell me a spare jar of yellow failure. Good... traffic... times.

Improvement via iteration...

I hate crashing expensive, time-consuming rockets but there is one advantage: the same design turns out WAY better the second time. I wasn't very happy with the carbon fiber fin reinforcement on Der Red Mix last time because the fabric texture was pronounced, I had to pry the fins apart after they'd cured, and, of course, the carbon/kevlar hybrid was impossible to sand.

While 1/4" plywood is pretty rigid I still wanted to add some cloth reinforcement because the fins are high profile and I don't want them shredding or breaking off during flight or recovery impact. Last time I used a mix of carbon fiber cloth and remnants of carbon/kevlar cloth. I also used a material-efficient stack while laminating but it's that configuration that caused the fabric bumping and layer separation difficulty:

For this mark II build I decided that carbon fiber was overkill so I reverted to 6 oz fiberglass. I also added 3/8" ply layers between the fin layups to force a smoother surface and to completely segregate each stack for easy separation ('CF fabric' below should read 'Fiberglass cloth'):

This layup worked much better although the surface still isn't as smooth as I'd like so, again, priming/sanding is the best!! Here are some pix of the layup:

Oh and I completed the motor assembly/e-bay, cut all the slots and doors, epoxied the goodies together, and this baby is ready for fins:

Build progress update

Der Red Mix mark II suffers only from a lack of motivation. I am making progress and the build is far smoother the second time but, honestly, I should have been done by now. Here's the upper portion of the motor tube assembly with the e-bay door. I propped it upside-down in the airframe tube whilst it cured:

I'm also making marginal progress on the >2000MPH rocket. I completed the carbon fiber reinforcement of the coupler and grafted 12" of BlueTube 2.0 on the booster to fit the payload coupler and recovery system:

Yes I SHOULD have just used one continuous 48" length of 75mm BlueTube but I had committed the Slimline motor retainer to the 36" phenolic some time ago. I'm gonna wrap the whole thing with three layers of 6 oz carbon fiber so I think it'll be strong enough for an M3700 [shivers].