Saturday, December 30, 2017

More scale modeling...

Hawk missiles on their launcher (Click to enlarge).
At the December HARA meeting, Elliot Laramie gave a tech talk on the Hawk anti-aircraft missile, which was first deployed way back in 1959. Despite being nearly 60 years old, the missile system has undergone improvements over the years - the last major one being in 1995 - and is still in use by several countries, including Egypt, Israel, Saudi Arabia, Turkey, South Korea, and Greece. The U.S. phased out the Hawk in favor of the much more capable - and way more expensive - Patriot in 2002. However, the cost of the Patriot is such that many countries with Hawks are opting to go with far cheaper upgrades to their existing missiles rather than buy Patriots. This is for good reason - the Hawk has proven itself to be a decent anti-aircraft weapon over the years, with over 80 kills. Jane's gives a single shot kill probability of 85% for the 1995 Hawk. However, as any missile man could tell you, Hawks are launched in pairs or more, adding to the lethality of the system.

There have only been a few flying scale kits of the Hawk produced - Estes produced a not-even-close-looking Army Hawk from 1990 to 1992, and The Launch Pad put out a much better kit of the MIM-23A version, but this one is very hard to find with the company now out of business. However, scratch builders have better luck, as Peter Alway gives plans and tips in his "Scale Bash" booklet for constructing a Hawk in one of 4 different sizes (BT-5, BT-20, BT-50, and BT-55). This Hawk information is shown in the scanned image below.

Hawk page from Peter Alway's "Scale Bash" (Click to enlarge).
Acting on a whim, I took the dimensions from Peter's BT-55 version and entered them into Open Rocket. I found that the rocket required a lot of nose weight - 70 grams - to get a decent margin of stability with a D12 motor. This amount of weight jives pretty well with the Alway notes, which state that the CG needs to be 9.4" from the nose; my CG is 9.0" from the nose with a D12-5. I went with a 24 mm motor mount because you can always adapt down to smaller sizes, and because I liked the performance (900 feet) on the D12.
Open Rocket sim of a BT-55 based Hawk (Click to enlarge).
Open Rocket rendering of Hawk in flight (Click to enlarge).
I suppose that I must add this rocket to the build list, given that I went to the trouble of simming it in Open Rocket and also because it would make a nice addition to my collection of scale models. If you happen to be interested in building one for yourself, my Open Rocket file can be downloaded from here.

Sunday, December 3, 2017

Warm December launch at Pegasus...

(Warning - this is a long post with many pictures)
Some of the activity at Pegasus field this Saturday; the Jurassic TARC team is in the foreground (Click to enlarge).
Huntsville has been experiencing a period of warm weather with little wind of late - a phase that is projected to end this Tuesday. Yesterday's conditions were so good, they positively demanded that rockets be put in the air, forcing me and Duane to join some of our colleagues and a couple of TARC teams at the field for some flying fun. We arrived at noon, and the next couple of hours saw a lot of activity, so much so that I had a hard time keeping up with it. What follows is a brief summary of that launch, which I figured I'd better post before I forget many of the details.

Duane giving advice to some members of Jurassic TARC (Click to enlarge).
"Velocity Raptor" on the pad (Click to enlarge)."America" is launched (Click to enlarge).
The Falcons setting up their range table (Click to enlarge).
The two TARC teams turning out onto Pegasus yesterday were both familiar, being Duane's Falcon Rocketeers and Jurassic TARC from Pope John Paul II High School. Saturday saw their first practice flights, with each team getting one - and only one - flight in. Jurassic TARC launched first, and their "Velocity Raptor" rocket struggled to reach 691 feet on an Aerotech F42. Might have had something to do with the too-short 4 second delay, which also caused the shock cord to pull loose from its mount, sending Velocity Raptor back to the Mesozoic Era. The Falcon Rocketeers had their rocket - the red, white, and blue "America" - ready a few minutes later. The F42-8 motor powered it to an altitude very close to the goal - 808 feet - but the payload section pulled free of the sustainer, causing the payload to tumble to Earth. It too was out of action; hopefully these teams can overcome the bad mojo next time out.

"Fat Chance" starts its first successful flight (Click to enlarge).
Speaking of Duane, he only flew one bird. Determined to show that he could actually have a rocket land safely, he brought out "Fat Chance", equipped with a new shock cord mounting system. Fat Chance put in a beautifully straight flight to 862 feet on a F32-6, and held together at ejection. Both parts of the rocket made a gentle landing under parachute, and we congratulated Duane on breaking his curse (which seems to have transferred to his TARC teams).

Allen launches his Estes Patriot (Click to enlarge).The Mammoth leaves the rod with camera and
telemetry active (Click to enlarge).
Frame from the Mammoth's onboard HD camera (Click to enlarge).
Another frame from the Mammoth camera (Click to enlarge).
The Inductor leaves the rod, its Aerotech D10 leaving a trail of black smoke (Click to enlarge).

Allen brought a slew of rockets to fly, and their performances did not disappoint. His A10 powered Sonoma (an Estes Sequoia with adapted decals) led off, followed by his venerable semi-scale Patriot on a B6-4.  He then launched his Mammoth on an F42, which was fitted out with a Missile Works T3  tracker system and an HD video camera. The T3 worked well, and the camera recorded some decent onboard video, which you can view here. A flight of his finless induction rocket (the "Inductor") was next; the Aerotech D10 motor chuffed quite a bit before building enough thrust to loft the model, which started doing a big loop in the sky at motor burnout. 

The QCC Explorer rides the fire of a D12
(Click to enlarge).
The Fletcher clears the rod on an A10
(Click to enlarge).
Allen's Skydart II on the pad (Click to enlarge).Liftoff on the B6-4 (Click to enlarge).
The Skydart glides in for a landing (Click to enlarge).
Frame from the HD camera on the QCC Explorer (Click to enlarge).
The video camera got another workout taped to the side of Allen's Estes QCC Explorer, which went surprisingly high on a D12. However, I would have to say his most impressive flight was made by his Estes Skydart II; powered by a B6-4, the model flew arrow straight, with ejection of the power pod occurring right at apogee. The Skydart settled into shallow glide, moving in a wide lazy circle over the field for about 30 seconds. It was the best flight I have ever witnessed a Skydart make, and I congratulated Allen on his trimming skills. He also flew his Estes Fletcher (painted camouflage) on an A10, and risked his QCC Explorer on an Estes E9, but those flights - good as they were - were nowhere near as awesome as that of the Skydart.

"Purple Pink" is launched (Click to enlarge)."Starshooter" clears the pad on a B6 (Click to enlarge).
Razor's A3 motor ignites (Click to enlarge)."Shockwave" heads up into the sky (Click to enlarge).
Marc's Screaming Mimi on a D12 (Click to enlarge).Big Bertha rises majestically on a C6 (Click to enlarge).
Marc had his son and daughter along for this launch, and it was his daughter's "Purple Pink" which started his series, flying on a B6-4. That same motor pushed his son's "Starshooter" (an Estes Make It Take It) off the pad, after which Marc's scratch built orange "Razor" took to the blue on an A3-4T. Also scratch built, "Shockwave" was up next, grabbing some decent air on a B6. His last two flights were those of an Estes Screaming Mimi on a D12 (despite 4 noise makers, that rocket almost never makes any audible screams on the way up), and a very nice black Big Bertha powered by a C6-5. There were no recovery failures -  Marc and family retired from the field happy, with all models intact.

James' School Rocket lifts off (Click to enlarge).Yellow Walmart scratch build gets going
(Click to enlarge).
James' Orange Walmart rocket starts its voyage on an E9 (Click to enlarge). 
One of the JPII team members, James, had three rockets to fly. The first was that of a Balsa Machining 3" School Rocket, which lifted off on an E9-4. Unfortunately, the orange model caught the Duane curse, and the upper motor tube centering ring pulled out of the model. The nose cone drifted gently to the ground, whereas the sustainer plummeted straight down, being saved from total obliteration only due to impacting into a pile of soft mulch by the road - very lucky. James also flew a couple of similar rockets (one orange and one yellow) made from body tubes and materials bought at a local Walmart. These put in very good performances on Estes E9's, deploying their homemade parachutes for safe landings. I must say that I was surprise by the fact that there was not a single CATO out of all those E motors flown on Saturday.

Vince's Quest Starfire on a B6 (Click to enlarge).The A10 in the MoonGo ignites (Click to enlarge).
Vince gets the Enterprise ready for launch (Click to enlarge).
The Enterprise leaves the pad, with a clothespin caught in its tractor beam (Click to enlarge).
The Enterprise descends under its parachutes as Vince starts his recovery trek (Click to enlarge).
Vince also brought along a few rockets; a venerable Quest Starfire was first off the pad, riding the thrust of the popular B6-4 motor.  Next was the much anticipated flight of his Estes Starship Enterprise, the long "atmospheric probe" being painted to look like phaser beams. The Enterprise did not quite achieve warp on the C6-3, but the flight was very nice, with the parachute deploying to ensure a safe landing on the grass. An inspection of the pad showed that the motor's thrust had destroyed the clothespin used as a standoff, which I captured flying behind the model in a cell phone pic. His last flight was that of a Semroc MoonGo, which was up and gone on an A10-3T.

Methinks the rod needs adjusting, else the Airwalker
may stray far away  (Click to enlarge).
My Stellar Photon Probe looking all pretty before
launch (Click to enlarge).
Duane launches my Estes Asteroid Hunter (Click to enlarge).
And what did I fly, you may ask? I put three in the air, all powered by B6-4's - my Estes Airwalker,  my orange and white clone of the Centuri Stellar Photon Probe, and an obscure out-of-production Estes RTF - the Asteroid Hunter. Everything went well, including parachute deployments. I probably should have brought along a few more models, considering that the weather is going to be sucky cold for the foreseeable future, but I suppose that's why we have winter coats.

And that, good readers, is the short story of the two hour December 2nd launch at Pegasus field. Sunny, warm, and windless, we shall probably not see its like until Spring.

Thursday, November 30, 2017

Testing a bit of the past

There are very few 3 stage rocket kits nowadays (the Estes Comanche 3 being the best well known), and those that do exist use the 24 mm Estes C11 or D12 motors in the first stage booster. This is because the first stage motor has to loft a lot of weight fast enough to have the model stable when it leaves the rod, and the current lineup of 18 mm motors doesn't have one with enough oomph to accomplish this. But 50 years ago, things were a bit different...

Back in 1964, Estes released the B3 motor, which under the English unit nomenclature of the time meant that the motor had an average thrust of a whopping 3 pounds (13.3 newtons). The B3 was a Series II motor, which meant that a) it had high thrust and b) the manufacture required an additional step - drilling a deeper nozzle into the black powder propellant. The result was a motor with a short duration (~0.3 seconds), spike-like thrust curve with a peak thrust around 7 pounds (31 newtons) - the Estes catalog described the thrust as "like a sledge hammer blow." And it was true - the B3 could move single stage rockets so fast that poorly attached fins would rip right off, and easily had the power to loft heavy 3 stage payload carriers like the Farside-X. When I first started rocketry in '68, the motor classification system had just gone metric, so the B3 became the B14. Same characteristics, different label.

Comparison of B6 and B14 thrust curves in the 1968 Estes catalog (Click to enlarge).
We swore by the B14, as it made 18 mm 3 stagers possible. But good things cannot last, and Estes, citing safety concerns, stopped producing the B14 in 1980, when it was replaced by the B8. Also classed as a Series II motor, the B8 had a thrust curve with a sharp initial spike (up to 22 newtons), which dropped into a plateau with about the same thrust as that in the B6, except that the plateau didn't last as long. Total thrust duration was around 0.5 seconds. The B8 was a less capable motor, but it was safer to make, as the motor machine could be equipped with a pintle (think small thin nail) that could produce a deeper nozzle than that of the normal Series 1 motors. The B8 was discontinued around 1997, and we currently have no high thrust 18 mm motors. This is likely to remain the case, because spokespersons for Estes have categorically ruled out any notion of restarting their production, despite the frequent demands of geezer rocketeers.

So why this foray into rocket motor history? It's because I have recently acquired some old Centuri B14 and Estes B8 motors, and I tested a couple of them - along with a current B6 - on my motor test stand last Saturday. I measured the thrust on the 50 newton maximum scale at 50 samples per second; the resulting curves are shown below. Note that the blue B14 curve is very similar to that shown in the catalog image above - a sharp spike up to 21 newtons, followed by an impulsive event at the end of the thrust (this was a booster motor, so no delay). However, there is a bit of a puzzle, as the peak thrust should have been over 30 newtons, whereas this Centuri motor produced only two-thirds that amount. I'm at a loss to explain this, except maybe to invoke motor deterioration over the 44 years since this motor was made. The red Estes B8 (manufactured in 1980) curve shows a similar sharp rise to 23 newtons peak, and then drops down to a thrust of just over 4 newtons, similar to that of the modern B6-4 (black curve). It is spent after 0.5 seconds, with the ejection charge occurring about 5.9 seconds after burnout.

Saturday's thrust measurements (Click to enlarge).
It's kinda cool to have this data, as thrust curves for the B14 are hard to come by, with most folks referring to the figures in old Estes catalogs. This is actual data, though I am going to test another one of the precious B14's to see if that one's peak thrust is also lower than expected. Even so, the availability of those motors enables me to build unmodified Estes Farside and Centuri Arrow 300 clones, secure in the knowledge that I can get them off the pad fast enough to be stable in wind, even with altimeters in the payload sections.

2018 is gonna be a fun year!

Saturday, November 25, 2017

A short Saturday launch...

It's been over a month since I last launched a rocket - Work and travel have kept me busy and away from Pegasus field on the weekends. However, Duane and I decided that enough was enough and that we HAD to use today to get a few birds in the air. So high noon saw us pulling into Pegasus field for a couple of hours of rocket fun. The weather was perfect - temps in the low 60's, slight overcast to dim the sun a bit, and a gentle breeze out of the west. Couldn't ask for a better day to fly!

Fat Chance takes to the air on a F32
(Click to enlarge).
My Quest Thunder just before launch
(Click to enlarge).
Duane readied the first rocket - his Geezer TARC "Fat Chance" - while I was busy futzing around with my motor test stand (more on that in a later post). Duane's rockets have a rep for flying arrow straight, and Fat Chance was no exception; it rose to an altitude of 792 feet (only 8 feet shy of this year's mark) on an Aerotech F32-6. However, the curse that afflicted Duane at the Geezer TARC launch remained, as the parachute came loose from the rocket at ejection, drifting away on the winds. Fat Chance tumbled to the ground, fortunately suffering very minor damage - a tribute to Duane's "Build them like tanks" construction.

I was up next with an out-of-production ready-to-fly model - the Quest Thunder. At least that's the claim; while prepping the rocket, I discovered that the engine hook was too short, forcing some manipulations with needle nose pliers to get a proper fit over the end of the motor. The molded launch lug on the fin unit was also too thin for the 1/8" rod, resulting in me getting a little practice with a small rounded file. After some work, the model slid back and forth on the rod. You would think that all this activity would have resulted in a nice flight, but that was not the case. Powered by a B6-4, the Thunder arced over soon after leaving the pad, leaving me holding my breath until the chute deployed a few tens of feet above the ground. A bit too close for comfort...

Duane's Cherokee-D upscale on 3 E9 motors
(Click to enlarge).
My Excelsior Polar-1 Goony (Click to enlarge).
Duane's upscale Cherokee-D is always a show-stopper; powered by 3 24 mm motors, this beauty turns in the best flights and is a joy to watch. Today, Duane decided to live dangerously and loaded the rocket with 3 cato-prone Estes E9-8 motors; I must confess I had visions of the bottom part of the rocket being blown to bits as he connected the controller to the igniters. I shouldn't have worried about the launch, for the 3 E9's lit in unison, lofting the Cherokee to a very respectable altitude of 972 feet. Then the curse struck again, and the nose of the Cherokee separated from the body. Fortunately the Jolly Logic Chute Release functioned as programmed, landing one piece safely, while the other tumbled to a landing nearby. There were only a few scratches on the rocket, and I could not help noticing Duane's luck - my models would have augered straight in, exploding into pieces of cardboard and balsa and leaving nice craters in the ground. His always seem to fall horizontally.

Then Santa got a short ride up into the blue on my Excelsior Polar-1. This out-of-production (2004) Goony turned in a very nice flight on an Estes A8-3, landing just a few yards from the pad. After stashing the Polar-1 in the car, I brought out the eBay rescue Estes Sky Hook for its maiden voyage. I put a fair amount of work into getting this model flightworthy, and it rewarded my effort by shooting straight off the pad to a very respectable height. I'm glad I used an A8-3, as a B6-4 would have put it way, way up there. To be consistent with the model's heritage, I had equipped it with a vintage Estes orange and white plastic parachute for recovery. For some reason, the chute turned inside out, but the deployment was good enough to land the rocket safely. It was a good reminder of why I switched to rip-stop nylon parachutes years ago.

The B6-4 in Duane's Make-It-Take-It leaves a cloud
of smoke (Click to enlarge).
The eBay rescue Estes Sky Hook clears the rod
(Click to enlarge).
Duane's red, white, and blue Estes Make-It-Take-It followed the Sky Hook. Powered by a B6-4, the flight went fine, including the parachute recovery. Apparently, Duane's curse only affects the models he has designed, not the kits he assembled. After the Make-It-Take-It touched down, I loaded my clone of the Centuri Groove Tube on the pad. I had checked the stability of this model, making sure the CG was in the right place, and was gratified to see it turn in a flawless straight flight on a B6-4. The Groove Tube's first flight would have been absolutely perfect if it had not smacked into a mowing tractor on landing, which knocked loose one of the tube fins. Very easy repair, and the rocket is ready for its next voyage.

Ignition of the Groove Tube's B6-4
(Click to enlarge)
Duane's Mega Mosquito heads up into the blue
(Click to enlarge).
The day's last flight was that of Duane's Mega Mosquito - it lumbered off the pad on an Estes E9-4 and landed safely under parachute a few yards downwind.  I did a few motor thrust measurements for several minutes and then we packed up and headed to our respective domiciles around 2 PM. Duane and I both agreed that it had been a very good day at Pegasus - 8 rockets launched, and 8 rockets came home. A pretty good tally for 2 hours.

Tuesday, October 31, 2017

The (short) 2018 build list...

It's the end of October and time to put together a build list for the coming year. I have done pretty well this year - the Falcon Commander is done, the Gyroc is in the final coat of primer, and the Centuri Mach 10 is under construction. Should easily have the latter two finished by Christmas, which means I will have completed all 3 models on the 2017 list. It would seem that a short list is best for me, given my rocket ADD - I am too easily sidetracked to handle more. So what about this coming year?

Centuri Javelin in the 1971 Centuri catalog (Click to enlarge).
The first choice, and top of the list, is easy - 1968 marks my 50th year in rocketry, so a clone of my first rocket must be the priority. The Centuri Javelin was released in 1965, sporting a black paint decor with a set of white roll bars. It kept this appearance until 1971, when the catalog art showed a white body with a black nose cone and fins, along with orange roll bars and a Centuri logo. This is my favorite style, and I will fashion my clone in a like manner. Its maiden voyage will be powered by a 1/2 A6-2 motor, just as in my first flight almost 50 years ago. I am really looking forward to this build - which should be easy, btw. The only slightly difficult part will be creating the roll bar decal.

The last appearance of the Estes Starlight in the 1972 catalog (Click to enlarge).
The other two models on the list both made catalog appearances in 1968, but I avoided them in the past because they had too much balsa to finish. The Estes Starlight was designed by Bill See, and sported 4 huge fins with rings - the body tube is lost amidst all that fin area. It had a relatively short run - only available from 1968 to 1972 - but its looks are quite appealing. Appealing, that is, if you can get past the thought of all the filling and sanding you will have to do to get a nice looking model. However, 2018 is the year that I am going to tackle this puppy.

Estes Trident in the 1970 catalog (Click to enlarge).
The last model on the list is the Estes Trident. Designed by Gene Street, the rocket features separate nose and tail sections, joined by three tubes that duct the ejection gases up from the motor into the nose, thereby deploying the parachute. This sleek beauty is also finishing hell, possessing 3 nice size fins and 9 (!) balsa nose cones that require sanding and sealing. As a kid, the Trident scared the heck out of me - it seemed a lot of work to build, too much effort to watch it drift away from the small fields I often flew in back then. But now, older and wiser, with my days of cramming into my models the biggest motor that would fit behind me, I am going to build a Semroc version of this kit. Hopefully I can keep it within the confines of Pegasus field.

And that's the build list as it stands now... 3 models over 12 months. I wonder if I can do it 2 years in a row.