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!

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.