The mood strikes!

This weekend the desire to build rockets finally hit, after a hiatus of several months. That's the way I roll - the urge will strike, I will build several rockets, burn out will set in, and I will build nada for months. The reason for my rocket building flurries lies in my current techniques. Unlike my younger self, I want my rockets to fly well AND look nice; the models I built when I was 13 were lucky to have their fin edges rounded and a single coat of paint. Consequently, builds take more time than way back then. Consider the typical build sequence:

1. Seal body tube spirals
2. Sand body tubes
3. Sand balsa fin sheets
4. Cut out/remove fins
5. Sand fin leading and trailing edges
6. Build rocket according to instructions (this is the fun part!)
7. Seal balsa surfaces
8. Sand
9. Repeat 7 and 8 above until balsa grain is filled
10. Apply first coat of primer
11. Sand off most of first coat of primer
12. Apply second coat of primer
13. Sand (rocket surfaces should now be smooth as glass)
14. Apply base coat of paint
15. Light sanding
16. Apply top coat of paint
17. Apply other colors as needed
18. Apply decals

A glance at the above reveals my issue - sanding. I hate sanding. Unfortunately, if you are going to build nice-looking rockets you have no choice but to do it, unless you can bribe someone else into doing it for you (The wife of a rocketeer on one of the forums loves sanding - he's a very lucky man). It is because of this fact of life that I, a dedicated rocket nerd, eventually get sick of all the sanding, to the point I can't stomach the thought of building another rocket for months. This is very sad, and sometimes I wonder if all the care I put into the builds is worth it. After all, we all know it is the ugly rockets that hang around the longest, surviving 500 foot falls as if they had fallen off a chair, while the pretty ones will crack a fin if you merely pick them up. Nature is perverse that way.

My current builds - From left, a Rocketarium scale model of the KSR-420S

sounding rocket (cluster, of course), a clone of the Estes Bat, and the start 

of an A.S.P. scale model of the Corporal missile (Click to enlarge).

But then I remember a teen wanting so very much to be able to produce rockets like those in the Estes and Centuri catalog. He lacked some tools, and most importantly, the patience to do it right. My current self has these things, and each time I build a new rocket, I snag a little bit of that old dream, with a good dose of "job well done" thrown in. That's what makes it worth the effort.

But nothing is worth sanding all year round… No mortal can handle that.

Altimeters and flying pigs...

A couple of new products caught my attention this week:

Firstly, there are new versions of the Jolly Logic Altimeters 1 and 2. I love my Altimeter 2, as it is small, lightweight, and easy to use, and John Beans at Jolly Logic has made it even better! The new versions have

• Better displays, with new explanatory fonts - no more need to carry the manual along!
• Storage for 100 flights
• Redesigned case, with a micro USB connector rather than the old style connector on the outside of the case
• Replaceable battery and LCD

Very nice improvements, and the price stays the same! Of course, I am trembling with anticipation about the upcoming Altimeter 3, which has bluetooth wireless to beam the data sampled along the rocket flight down to my iPhone. How cool is that?

Check out the Jolly Logic page here.

The other item - which I simply HAD to have - is the long-awaited Odd'l Rockets Pigasus. This rocket, shaped like a flying pig, gives new meaning to "When pigs fly", and has been the subject  of many porcine puns since its release a few days ago. Count on this one squirming to the top of the build pile - I can't wait to see it squeal off the pad!

Odd'l Rockets Pigasus (Chris Michielssen)

Math and the Avenger video

Model rockets are more than just fun to fly - you can actually do math and science stuff with them. For example, I was wondering how high my Avenger flew yesterday. There was no altimeter in the payload section, so I had no direct measurement. But I did have a video of the flight, consisting of a couple of thousand frames taken at 30 frames per second. It occurred to me that a simple application of photogrammetry could help determine the altitude achieved by my two stage beauty. Time to do some math!

Frame 493 from the Avenger video with objects identified (click to enlarge)

Looking through the frames, I found the above frame showing the launch area about three quarters of a second before apogee. It was easy enough to locate Duane's SUV, and a Google search revealed that all models of this vehicle are 188.4 inches (15.7 feet) in length. I know the horizontal field of view of this camera is 37.8 degrees, having measured it about a year ago with a simple set up involving a couple of rulers. This should be enough to determine the altitude of the rocket at the time this frame was taken.

The relevant formulas are:

where theta is the angle subtended by the object (in this case, Duane's SUV) in radians, d is the length of the object in pixels, FoV is the field of view of the camera in degrees, and L is the horizontal width of the frame in pixels (720 for this camera). D is the actual length of the object, and H is the altitude of the rocket in the same units as D. It is easy enough to measure d, the length of the SUV in pixels with software - 21.9 pixels, according to the GraphClick program on my Mac. FoV is 37.8, and L is 720. D is the length we found from Google, 15.7 feet. Plugging in the numbers, we find

Is this reasonable?

Lacking measurements from an altimeter, the best we can do to check the above number is to look at the output of computer simulations. I constructed a CAD model of the Avenger in the Rocksim and Open Rocket software (the first is the best and costs about 100 bucks, the second is pretty good and free) and added in the camera, which I weighed at 0.5 ounces.  I like the Open Rocket interior view, which shows all the components:

Avenger CAD model in Open Rocket (click to enlarge)

Open Rocket gave a peak altitude of 789 feet, whereas Rocksim calculated an apogee of 833 feet on the C6-0/B6-4 motor combination. Rocksim usually produces altitudes that are a bit on the high side, but given the crudeness of our image analysis, the 782 foot altitude agrees very well with the computer simulations. Not bad for a little ciphering, eh?

Jethro Bodine would be proud.

The flight of the Avenger

At the TARC regional, I flew my Estes Avenger clone with a keychain camera strapped to the upper stage. I figured that the C6-0, B6-4 motor combination would get the rocket sufficiently high to produce a nice video, and I wanted to look at staging from the rocket's perspective. Speaking of the rocket's perspective, take a gander at the image below.

Yours truly from the Avenger's rocket cam

That's me in the green shirt, looking up at the Avenger. I look much better from this distance, don't you think? Anyway, here's the flight video in real time:

Rocket flights go by rather quickly. In the video above, you can briefly see the first stage falling away. The nice thing about digital video is that we can play with it - slow it down, speed it up, and extract individual frames. I converted the video to individual frames - over 2000 of them - and scanned through looking for the staging sequence, which starts in frame 391. This is the frame showing the actual separation of the stages, with fire, smoke, and much coolness (Ignore the guy in the green shirt way down below):

The moment of staging

In the next few frames (12 to be precise), you can see the booster falling away. I extracted them and created the greatly slowed animation below. This is model rocket staging, imaged at 30 frames per second - I can't help wondering what a faster camera would show.

Slow motion GIF animation of Avenger staging

Some more stills from the flight:

Leaving the pad

Shock cord and payload section before parachute opening

The launch area and cars down below

About to hit the ground

Gotta love modern technology!

The Huntsville TARC Regional

Today was a good day to fly…

At least 9 TARC teams (5 from North Alabama, 4 from Tennessee) - I might have missed one or two - converged on Bragg Farms just north of Huntsville for our annual TARC regional launch. The goal is to provide TARC teams who have not had much of a chance to fly due to lack of a field or other factors a few hours practice and a chance to qualify, and to provide local teams with a chance to get in a bit more practice and hopefully make a qualification launch or two. There is also the added bonus that each team can see what sort of rockets the others have devised and compare notes. For the past couple of years, the weather has sucked - way too windy - but today, it was great, with light and variable winds and a high, hazy cloud deck that let in some sun, but not too much. A perfect day to fly rockets!

The crowd at just past 10 AM.

Duane and I arrived at the field just before 10 AM, and there were already quite a few folks there. Chuck, Vince, and Dan were hard at work setting up the range, which consisted of a metal sawhorse converted into a pad capable of launching 3 low power Estes-style rockets, and a couple of mid power pads with the standard 6 foot, quarter inch diameter rod used in TARC. A few teams - Falcon, John Paul II, and Liberty - insisted on using their own pads, as their rockets were built to use rails. All rockets were launched from a range table using the usually reliable HARA launch system. However, today we had a bit of a problem; two of the three battery/relay boxes used to supply power to the pads turned out to have really bad off batteries, forcing us to rely on just a single battery/relay box. Only a minor inconvenience, but it did emphasize that the club needs to do some maintenance on the launch system.

Chuck watches as the Liberty team gets

their rocket ready to launch.

Today was like watching a NASCAR race. Numerous TARC rockets took to the air, with all the successes and mishaps that accompany a big launch. There were several flights that hit the duration goal spot on, turning in flight times of 48 to 50 seconds, but no one was close to the altitude mark of 825 feet. Some were too high; others too low. A couple even had trouble getting off the ground - Liberty Middle's rocket had an explosive engine event at ignition (CATO to those in the rocket trade) that set their rocket on fire. Another team had an ejection charge fire prematurely, deploying the parachutes before the rocket left the launch rod. Another team's rocket was unstable, tracing loops in the sky. And so on, throughout the afternoon. I was kept pretty busy, timing rocket flights and helping debug igniter issues. Vince, my partner in crime and NAR board member, launched the birds, timed the flights, and helped fill out the score sheets. I got to do the math, as no one had brought a calculator (yes, we had cell phones, but it was easier to bug me, as I still like to work arithmetic in my head).

It was not just TARC rockets taking to the air; there were also a few flights of rockets belonging to club members. Dan Cavender wowed the crowd by flying his gorgeous Pegasus scale model to over 3000 feet using a K motor (the only high power flight allowed today). Unfortunately, it was the mandatory sacrifice demanded by the rocket gods, who directed it into a tree for their great pleasure. Efforts were still under way to retrieve it when Duane and I left the field around 3. Elliot, our club's VP, flew the most rockets. His Estes Black Star Voyager, Cosmic Interceptor, and Interceptor E were crowd pleasers, though there was a bit of consternation when the ejection charges seemed late on the Voyager and Interceptor. They were heading down and getting uncomfortably close to the ground before the chutes deployed. He flew a couple of multi-stagers, the Estes CC Express and Comanche 3, both maxed out on the power with D and C motors. I don't know if he ever recovered the upper stages, which flew pretty much out of sight, though the CC Express did drop a spent D motor casing on the hood of Vince's car. Sometimes I think our rockets feel they need to behave like birds :/ Elliot also launched an Aerotech Astrobee semi-scale twice on G motors, which left the pad with a very satisfying roar. He ended the day with a couple of Dr. Zooch rockets - the Mercury Redstone (which suffered a melted chute, but fortunately no damage) and a Soyuz.

3 TARC rockets await launch on the mid-power pads. My Estes Pulsar Pink

crayon rocket is at left, the fins of Elliot's Comanche 3 just barely visible.

And me? I had brought seven rockets to fly, thinking that I would have some time (dumb, huh?). However, I did manage to launch three. The first, my Estes Pulsar Pink crayon rocket, drew some snickers from the crowd as it lumbered skyward on a B6-4, even falling backwards a bit before chute deployment. Can't really blame them; even I thought the thing flew like a pig. Maybe a C motor next time. My Centuri Quasar clone was next, on a C6-5. It flew beautifully, landing softly on the field about 50 yards down wind. I ended my day with a flight of my Estes Avenger clone (a 2 stager) on a C6-0, B6-4 combination; it also flew well, and I got some great video from the camera strapped to the side of the upper stage.

We closed up shop around 2:30 or so. Right now, it appears that only the Falcon Rocketeers have a set of scores that MIGHT get them to the TARC Nationals, though some teams have yet to finish all three qualification flights. Time is running out, and all scores are supposed to be at TARC HQ at month's end. It would be nice if some other team in the area also posted a good set.

A sad day

My favorite rocket company, Semroc, is closing its doors after providing outstanding products and service to the rocket community for many years. The owner recently passed away and his son was hit by a serious illness that hospitalized him with organ failure. Even though Bruce recovered - thankfully - the small Mom and Pop business could not continue. This was posted today on Ye Olde Rocket Forum:

Future of Semroc

Semroc Fans,
I am sorry to say that we will be closing the company. After my father’s death and my stay in the hospital I have realized that it will be impossible to catch up. I have decided after much thought that it would be in my best interest to close the doors. This is not an easy decision after living a 10yr plus dream with my Dad. We appreciate all the loyalty that you have all shown me and my family over the years, we are forever grateful. We will always cherish the memories and friendships we have made over the years. It has made all this worthwhile. 
All of the current inventory is up for sale but there will not be any custom parts cut and once the kits and parts are gone there will be no more. If anyone is interested in buying out current stock please drop us an email and let us know. Again thank you all for helping me and my family live the dream!

Sincerely,
The Semroc Family

I will truly miss these guys - they helped me recapture the excitement of rocketry in building the models of my youth, and there was no one who did more for their customers, even making custom parts for free or a pittance. They were, and are, the absolute best!

Atouk pooka!

(If you are wondering what the heck the title means, I am a fan of the 1981 movie Caveman. A quick read of the Google page should provide enlightenment)

TARC teams in action at the Harvest horse farm on March 9, 2014
(Click to enlarge)

Today saw more TARC flights at the horse farm. Four teams - Falcon Rocketeers, Liberty Middle 8th graders, and two from John Paul II High School - took advantage of the warm, clear and moderately breezy weather to fly their rockets for a few hours. One of the John Paul teams made two qualification flights, the first scoring a 40 (818 feet altitude, 58.25 second duration) and the second DQ'd due to two broken eggs. There were many broken eggs this day, the most I have seen in a long time, and the teams struggled to hit the altitude mark. The other John Paul II team was consistently low, and the Falcon Rocketeers were low and high. Liberty's day was cut short when their rocket did not deploy the parachutes and came in ballistic, resulting in a mess on the ground; fortunately, their altimeter was undamaged. The rocket, however, was a goner. A fast rebuild will be required in order to make the TARC regional at Bragg Farms this Saturday.

The Sun was shining, the birds were singing, but the day was cursed by the rocket gods. I should have taken a cue from the teams' experiences and not flown my rocket, but hey, what rocketeer can resist flying whenever possible?

Atouk and I before launch (Click to enlarge) 

Every year I design and build a TARC rocket for that year's contest, to get an idea of what the teams will be facing. I figure that going through the process helps make me a better mentor (This year's rocket is STILL hanging 50 feet up in a tree on the edge of the horse farm, my $70 altimeter enclosed within its innards). Atouk was a rocket I built back in 2007 in an attempt to meet that year's TARC challenge. It was a short stubby critter (kinda like me), featuring two parallel boosters which would fall away when their motors burned out. It had not flown back in 2007, and I decided that today was the day it would finally take to the air. 

During a lull in the flights, I prepped Atouk with Estes A10 motors in the side boosters and a C6-3 for the main. There would be no egg in the egg capsule, but I did load my Jolly Logic Altimeter II into the red and white payload section and taped the (mostly) reliable keychain camera - available for $6 from Ebay - to the outside below the payload section. I was hoping for spectacular footage of the boosters falling away.

The pace of rocket flights slowed considerably after Liberty's rocket augured in, so I placed Atouk on the pad, activated the camera, and gave the customary short countdown. Atouk left the pad like a bat from Hades and then began doing a few colorful cartwheels in the sky, to my great chagrin. I watched as the rocket then began the "dive of death", impacting the ground about 30 yards from where I was standing. Arriving at the scene, I found the still functioning camera near the wreckage. I switched it off and turned my attention to the altimeter, which was lying nearby. It was flashing "1825 feet" as the peak altitude, which was ridiculous, as the rocket never got higher than 75 feet or so before doing its little dance. Obviously, the impact had given the Jolly Logic an electronic concussion - I held down the button to reset the altimeter, which seemed to work (to my great relief). The payload section, egg capsule, and side boosters of the rocket were undamaged, but the top of the sustainer body was crushed. Definitely repairable.

Here is the video from the onboard camera:

What went wrong? An examination of the motor casings showed all three had ignited, so a misfire was not the problem. The video showed one booster had stayed with the rocket after its motor burned out. Its twin had fallen away, and I'm wondering if this imbalance caused the rocket to go crazy. Another possibility is that the rocket center of gravity was too close to the center of pressure without an egg in the capsule; I will have to dig out the design file from my computer archive to check this out. Until I discover the cause, Atouk will remain in the damaged box, his fate pending the outcome of my investigation.

Despite everything, I did get some nice footage of one of the boosters falling away. Here's a couple of frames:

More flights this coming Saturday - should be fun!

More TARC practice

Even though it was windy, Sunday was a nice day - a fair amount of Sun got the temperature up near 70 in the afternoon. Very comfortable for the TARC teams who converged on the Harvest horse farm to put their birds in the air. I was there too, the ever-present stop watch dangling from my neck in case any of the teams decided to go for a certification flight. I also had brought along a couple of rockets to fly - my Semroc Centurion, which would carry one of the cheap video cameras I bought off Ebay, and the Shrox Bolero, with its missile styling. Sunday would also see the first use of the Mighty D relay launch controller I had purchased last year from Balsa Machining Service.

Bill's pile of stuff for Sunday flying

Liberty Middle's 2 TARC teams and a couple of the kids from Pope John Paul II High were already at the farm when Duane and I arrived around noon. Setup in the southwest corner of the field (next to a water filled ditch that resembled the Nile river) was accomplished quickly, with more JPII TARC team members arriving to help out. The flights soon began… And they proceeded at a fast pace for TARC, with 9 launches occurring between noon and 2 PM. The wind was a problem - most flights were too low, and the one rocket that managed to launch during a lull went 35 feet too high, as the team had reduced the weight to gain altitude. Wisely, no team attempted a certification flight; it was just too darn windy.

Besides the wind, there were problems with shock cords burning through or coming loose, resulting in the sustainers (the part of the rocket containing the motor) tumbling to the ground. This is what ended Liberty's practice after 5 flights, as their two rockets were in need of shock cords with better attachment to the sustainers. JP II's rocket suffered a dinged nose cone and was plagued by some underperforming F motors. The one flight they did using a F motor from another batch flew too high. After 4 flights, they too called it a day, not wishing to waste any more motors in the blustery conditions.

Duane and Nate pow-wow as the Liberty TARC teams prep their rockets.
JP II's team is in the background, their launch pad off to the left of the pic.

I decided not to fly my Bolero - it already needed a fair amount of nose weight for stability, and I shuddered to think what the wind could do to its flight path. I did decide to fly the Centurion on a C6-3. The Mighty D controller did its job well, sending the rocket on its maiden voyage. There was a bit of consternation when the parachute failed to open fully at ejection, but soon the canopy filled with air and the rocket touched down gently on the grass. I turned off the video camera, and we loaded up the stuff into Duane's SUV for the return home. Once there, I plugged the keychain camera into my computer, and discovered there was no video! 

Would you believe that I had forgotten to load an SD card into the camera? Duh...

I will get another chance this weekend, weather permitting.

The winds of March

March sees TARC season in full swing, with the teams making their qualification flights, each hoping to post scores low enough to get them into the top 100 in the country. In addition to broken shock cords, rocket motors with slightly too much or too little thrust, tangled parachutes, and numerous other rocket issues, they must contend with the weather. There's an old expression:

March comes in like a lion, and goes out like a lamb.

And in my experience, this appears true. March - especially early March - seems plagued by gusty winds, the bane of the TARC rocketeers. High winds cause the rockets to angle into the wind, decreasing the peak altitudes, which means reducing rocket weight or shifting to a different motor. Also, the teams cannot fly in winds over 20 mph, and many days have gusts over this limit. Yet, as I said, that is my perception. Is it really true that March is the windiest month, or am I biased because I am out in the field more in March, due to the TARC teams practice/certification flights? I decided to find out, at least for Huntsville.

If you can afford it, the Mathematica software package is a great and wonderful thing. It enables you to do all sorts of wondrous mathematical and sciency things without programming, and the latest versions tap into the power of the internet to fold in tons of data - astronomical, financial, geographic, and, important for this purpose, weather. I have a copy of Mathematica at work, so I fired it up and looked at wind data for Huntsville since 1980 (it can go back farther than this - I just figured 33 years was enough to answer my question).

The first thing I did was to look at the average daily wind speed for January, February, March and April:

Mathematica defaults to metric units, so I added a column with the English counterparts. Note that March is indeed the windiest month, but not by much, which kinda surprised me. 0.5 miles per hour - the difference between March and January or April - ain't that much. So if March is a lion, the months around it are at least some sort of big cats - tigers or panthers maybe. Here, the numbers would indicate that the greater amount of time I spend outdoors in March may have indeed led me to believe the month's winds are more blustery than they actually are.

What about the going out like a lamb bit? If you look at the below plot, showing the average daily values of the wind speed (in kilometers per hour) throughout March, there seems to be a downward trend as the month wears on:

In this case, your eyes are not deceiving you; the average speed for the first week in March is 14.1 km per hour (8.8 mph), whereas the average speed for the last week is 13.6 km per hour (8.4 mph). So it does appear that the old saying has some truth behind it. On average, March gets less windy with time, with the average speed dropping by 0.4 mph over the course of the month.

Something to consider when you chase down a drifting rocket.