Stonebreaker

The Stonebreaker is in the mid-power category, and this will be my first true “big” rocket, with a diameter over two inches and able to use bigger motors.  It is a kit produced by Dynastar.  It also requires a hefty ¼” launch rod.  Something about the design of this rocket absolutely won me over, so I just had to get it!  I like military-styled rockets, and the black-and-white schemes appeal to me. The red and blue color bands and the big, bold lettering just adds icing to the cake. I am making no modifications to this other than to hide a small altimeter compartment in the nosecone.

Here is the rear view of the rocket showing the newly installed motor mount. I re-inforced both of the two cardboard centering rings with balsa. I purposely placed the rear reinforcements on the external side to show them off. This should look pretty cool when painted silver (or red?).

The fins were paper-covered to hide the grain and make them more streamlined. The relatively thin edges of the fins can't be covered too well, so these edges will need a balsa fillercoat and sanding.

Everything is glued to the tube and true. Glue fillets were added to contour them to the body better and make the joints stronger.



The last step in the construction of the rocket was to add a small compartment for an altimeter and accelerometer.  Since this rocket is so large, I didn't want to add another whole tube section and bulkhead for a payload, and there was a lot of free space in the nosecone.  I cut a small square out of the base of the nosecone and formed a square box out of some Lexan plastic, riveted the bottom of it and folded it up with just enough space to hold the altimeter. The tabs of the Lexan was then glued to the opening in the nosecone, and a small plastic door was riveted to the nosecone to hold the altimeter securely inside. The door was purposely sized to allow a free flow of air pressure into the altimeter compartment.

Here is the compartment installed in the nosecone without the door. The Lexan tabs were glued to the sides but were not cut off or sanded yet.  They required sanding to prevent the shock cord or parachute lines from getting snagged in them. A small piece of flexible plastic foam was inserted to act as a spring to keep the altimeter from rattling around in the box.

Here is the completed altimeter box with a small plastic door riveted to the nosecone. I decided to use a rivet because unlike a screw and bolt, I will not have to worry about it comming loose, it is lightweight aluminum, and is tight enough to resist opening on its own.  The plastic door has a hole and gaps on the sides to make sure that there will be no air pressure difference between the outside and inside.

At the last minute I decided to add a second launch lug size of 3/16" to the rocket to allow launches with a smaller rod, even though it will produce a slight drag penalty. I added it to the other side of the body strake as shown below.

The construction, balsa filler and sanding is now completed. I then cleaned and primed the entire rocket with gray primer and sanded it lightly.  A second coat of primer was sprayed on but this time it was a white primer. This allowed me to make sure not to sand the second coat too deeply, because where I do the gray primer color then shows up.  With the white primer sanded it is now ready for the final paint color.  Although the kit recommends light gray paint, I chose to paint this rocket with a high-gloss silver finish.

When the primer had days and days to dry, I then sanded it with a fine, 800 grit sandpaper, getting all the surfaces very smooth and clean. I was using some Rustoleum silver paint, and it proved to be somewhat of a disaster with the first coat.  It appeared (as it has in the past) that the Rustoleum paint was not compatible with the Rustoleum primer! Because of all the extra work it will now cost me to sand off and repaint the finish, I will never use Rustoleum again.

Here, the paint seemed to react with the primer and started bubling up immediately.

Here you can see how much the paint ran. OK, it may be my fault, but all I did was give it a single light coat, the paint seemed especially thin and runny.

My argument for the paint being runny is seen above.  On the leading edge of this fin, I had sprayed a moderate coating to cover all the white primer.  After letting it dry vertically, the thin paint did not even adhere to the bare paper covering near the leading edge of the fin, and left the white primer exposed at the top and ran down to thick drips at the trailing edge.  Spray paint that can't even adhere to normal, untreated copy paper? I'd call that too thin.

OK well the Stonebreaker will remain in the paint shop for a while now, as I will need to sand off all the bubbles and thick runny parts and try it again.  Sanding off silver paint can be very, very messy.

Here is a closeup of the sanded rocket. Most of the paint was removed, but more importantly the lumpy imperfections were removed and I can try again, this time with a very light coat while holding the spray can ridiculously far away.

I tell you, painting these things takes a lot of the fun out of rocketry.

I gave the main rocket body a good fine sanding and another light coat of silver Rustoleum.  Although the finish is far from perfect, I decided it won't get any better than it is and declare it complete.  I then painted the nozzle end gloss red, because it's a cool detail to have. I used Testors, not Rustoleum.

As for the nosecone, it was so marred from the layers of paint and sanding that I had to completely sand out the paint and primer and give it another try.  I applied the first layer of white primer, and it started crazing again, so I sanded those wrinkles down and then gave it something like 15 coats of white primer!  I then sanded that thick primer layer with coarse and then progressively finer sandpaper grades and now it is looking like a shiny, gloss white surface again.  Bad luck showed up again and the wind blew the nosecone down, nose first onto the concrete.  It cracked the nose of the cone along the molding seams.  I went ahead and continued to add primer coats, and then tried to re-glue it together with plastic cement. Here is what I have so far.  I will have to again re-prime the tip before spraying the silver color.  When completed, the very tip will have a black paint over the silver.

Just to be safe, I am going to let the primer cure for about a week before attempting another coat of silver paint.  At this point, if I get any more crazing of the paint, I will likely just throw out the rocket kit and all the Rustoleum paint.  (And NEVER buy Rustoleum again!)  I will have to buy another Dynastar Stonebreaker though, it's a really cool looking kit.

I have been letting the rocket sit for weeks to allow this tempermental paint to cure well. Although the silver finish is far from perfect, I decided it is good enough and will likely not get better. The re-paint of the nosecone started running a bit, but I gave up trying to get a contest-winning finish and just get this model airborne. I'm sure it will become beat up over time anyway!  I am going to add the (stick-on) decals, assemble this rocket using a smaller parachute and see how it flies.  The stock 32 inch parachute that came with the kit is way to large for the weight of this kit. I think Dynastar just didn't have the desire or means to produce a chute in the 24" range, so they just threw in the already-stocked 32" to save money. Just a guess.

So I have pretty much assembled the rocket using a 19" Nylon parachute.  There was no supplied shock cord and I did not add one because the Kevlar length is quite long.  The entire rocket (sans parachute) weighs in at 183.5 grams, so with a 19" parachute I expect it to descend slightly fast (apx. 5 m/sec).  That should be OK because it is a relatively light but sturdy rocket, and with the higher-powered motors it should easily surpass 1400 feet, so I would like it to return a bit fast to prevent it from getting lost.


I have added the stick-on decals.  The color bands that wrap around the body tube were not long enough to make a complete wrap - that's a big negative for me with DynaStar.  I drilled three 1/8" holes in the upper body tube to allow air pressure to equalize inside the rocket at altitude, this was needed because the altimeter is only exposed to the air pressure inside the rocket.  The larger holes should compensate for the large chamber in the body tube. (Because of its large volume, it will take a lot of air flow through the static vent ports to keep the pressure inside and outside equalized.)

One thing I could not complete was the black tip of the nosecone.  I tried to add some masking tape to spray the tip black, but the tape started grabbing the pathetic Krylon silver paint and ruin the finish.  I imagine it will take weeks before this poor paint surface is cured enough.  So anyways, weather (wind) permitting, I will attempt to fly this at this weekends launch.  I now present rocket #28: The Dynastar Stonebreaker.

FYI: The photo and distance hides a lot of sins of the paint surface. In real-life, up close, the paint is pretty ugly, inconsistent and rough.  Regardless, let's see how she flies!

I waited weeks for the silver finish of the Stonebreaker to cure and let it bake in the sun inside my car where it got up to 120 degrees F.  Apparently all that did was cause the finish under the stick-on-decals to bubble up and look uglier!  At first I placed it on a towel in the car, but in that single afternoon the paint took on the texture of the towel, so there are areas where it is all rough and wrinkly.  Another day a bit of red towel was accidentally touching a fin. Big suprise: the paint absorbed some of the red dye in the towel! Seems everything I do to this rocket just makes it uglier.
I gave up and decided to paint the black nosecone tip with gloss black paint. To avoid masking tape peeling up the finish I hand-painted the edges.  After a few minutes the black paint and silver started reacting, and the color came out gray and was getting gloppy and gooey.  As a final desperate attempt I painted on some thinner to try to even it out, but it was not working.  I now have a silvery-gray nosecone tip with lumps and runs on it. I completely give up, this rocket will never look good.

SPECIFICATIONS

Series Number: 28

Number of Stages: 1

Length: 28.81"

Payload Volume: 0.76 cubic inches (sized for Altimeter 2 only)

Diameter: 2.22"

Number of Fins: 3

Fin Circular Span: 6.72"

Stock Weight: 178.1 grams

Altimeter Compartment Additional Weight: 5.4 grams

Total Weight as built: 183.5"

Motor Range: C-E

Motor Diameter: 24mm

Motor Length: 95mm (adaptor for 70mm)

Motor Mounting Method: Spring Clip (non-stock feature)

Recovery Method: Parachute

Parachute Diameter: 19" (non-stock feature)

Parachute Material: Rip-Stop Nylon (non-stock feature)

Recovery Protection: Nomex 6"x6" (non-stock feature)

Shock Cord: Woven Kevlar, No Elastic

Altimeter Capable: Yes (non-stock feature)

Nosecone Material: Plastic

Fin Material: Balsa, Cardboard Laminated

Body Strakes: 3

Launch Lug Size(s): Dual: 1/4" and 3/16" (non-stock feature)

Completion Date: May 22, 2013

Flight Logs

2013, June 30: Indiantown Gap, light wind.

Here is the Stone, loaded and connected on the launch pad and ready for the first flight.

Note the nosecone tip has been painted before the flight.

D12-5:   This was the first flight for this rocket, so anything could have happened.  The D12 lit as it usually does, and fired this light rocket quickly off the rail at 10.8 Gs, burning for 1.8 seconds and averaging 2.5 Gs throughout the burn. This was just enough to get this rocket to 100 mph while it shot very straight upwards.

The delay was a little short, firing off at 4.6 seconds while the rocket was still going up while at the altitude of 478 feet.  This caused the upward coast to stop in the next 1/10 second at an apogee of 484 feet. (quite a bit lower than Apogee’s website shows: 639 feet, but that was probably from a computer simulation – not reality).

My custom 21” Nylon parachute caught the wind and opened up fully, bringing back the rocket slowly at 7 mph. I can only imagine what that 32” monster chute in the kit would have done!
This was a very satisfying first-flight, with a slow but steady return, not unlike the big rockets, giving all a chance to admire its glossy silver finish gleaming in the sunlight.  The duration of the flight was 50 seconds.

I could imagine myself using an E9 or E15 motor some day, but I would need an even smaller chute if I want to see it again.

2013, August 31: Fort Indiantown Gap, 6mph wind, 86 degrees.

D12-5: This is only the second flight of the newly minted Stonebreaker. Again I will use a medium power for this flight, but this time I will choose an even smaller parachute. The stock 32 inch 'chute was almost comically to large, and the first flight showed that the 21 inch 'chute was still a bit large. I prepped a 15 inch for this flight, because the winds were a bit high.

When the mighty D12 started burning, the rocket left the rod at 11.1 Gs. The motor burned for 1.8 seconds while sustaining an average of 2.7 Gs. This brought the rocket to 102 mph. It travelled straight up, then coasted for 4.4 seconds. The delay was early at only 4.4 seconds, and the parachute ejected at 491 feet, slowing the rocket in the next 3/10 seconds while gaining an additional 7 feet for an apogee of 498 feet. A full 5 second delay and this would easily have broke 500 feet. Thanks Estes.

Descent was all OK and a thing of beauty. The smaller parachute let it return at a safe 10 mph. Even at that speed, it landed about 350 feet from the launch rod. This second successful flight showed me it is ready for flights with an E9 or E20, or even a C11.

 

  2014, May 24: Fort Indiantown Gap, 5-10 mph winds, 70 degrees

 
D12-5:   I considered using a C11 motor for a low-power test, but I was looking for fun, and the D12 delivers fun.  

The Stone burst off the pad with 9.1 Gs of acceleration, burning for 1.8 seconds and averaging 2.6 Gs thru the thrust phase. It then coasted for 4.2 seconds from a top speed of 101 mph and finally topped-out at 469 feet above ground.  It then turned over and started its descent for 3/10 seconds before ejection.  The altimeter didn’t sense the ejection so I can’t say exactly what the altitude was, but it was close to apogee.

The large 21” parachute opened up but not fully since it was burned and melted shut a bit because the Nomex protection was too small to cover the entire parachute.  Rather than blame it on the Nomex I could say I didn’t fold the parachute tightly enough. It descended with a distinct wobble and spinning of the chute at 11 mph.

The flight time was 33.7 seconds, and landed in the grass about 350 feet away. Overall it was a good flight except for the burned Nylon chute.  The bright silver finish and large diameter of this rocket always makes it a joy to watch.

Here is a closer look at the parachute damage. It's still useable, but getting uglier.

2014, July 20: Gloucester College, 85 degrees F, 8 mph winds

C11-3:  For the second flight of the day, the ‘Stone rocket and motor combination was the next lowest altitude flight I could make with what I brought.   The winds made it a good opportunity to test low-power on the Stonebreaker, and flying with a new club, its size made it a somewhat more impressive model to fly today.

The motor fired loudly when it was supposed to, and the Stonebreaker slid off the over-sized 3/16” rail with an acceleration of 9.4Gs.   The burn time of 6/10 seconds shot this rocket straight up despite the winds, averaging 4.3 Gs.

It made a top speed of 61 mph and then coasted to 165 feet where an early ejection timed at only 2.3 seconds released the parachute. It stumbled up another 12 feet to reach an apogee of 177 feet before the big green Nylon parachute opened up to return the rocket with a speed of 9 mph. Flight time was only 14.8 seconds. (Compare to a 50 second flight with the D12 motor in its first flight.)

2015, November 15: Cross Keys NJ, 12-15 mph wind, gusty, 60degF

 

C11-3: Still windy, so I had to keep low, and the hefty Stonebreaker with a C11 motor is just right. This was its second low-power test flight, and as far as I can recall, the first flight in windy conditions.  I chose a light Nylon chute with a diameter of 21 inches.

The C11 motor fired up on cue, and pushed the rocket off the 3/16” launch rod with 9.6Gs of acceleration.  It burned for 7/10 seconds, propelling the rocket to a speed of 63 mph.  The average acceleration of 4.4 Gs was the strongest ever for this rocket, even better than the mighty D12s have done.

 

From there, it coasted for the next 3.1 seconds to reach an apogee of 192 feet, a good bit better than the previous C11 flight.  It did not turn much in spite of the stiff, gusty winds.

The ejection charge fired with near perfect timing, after only 2/10 seconds after the apogee and only 3/10 a perfect delay time.  With that timing it only dropped 2 feet to 190, and the bright orange Nylon parachute opened to the wind and brought the ‘stone back at 11 mph to a soft landing.

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It rested in tall grass only about 150 feet from the launch pad.  That was a good flight, making three perfect flights for the day, and a good way to wrap up and hope for calmer winds next month.

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2019, April 7: Penn Manor, 70 degrees, 10-15 mph winds, gusty

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C11-5: It was not an ideal launch situation. Although comfortably warm for this

early in the spring, it was windy, with the launch pads set up just upwind of an

electric line and a road.  There was a high risk of hanging on the wire with a

low power flight, or losing sight of the rocket completely with high power

flight, but I took the chance on low power.

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The Stonebreaker is a fine rocket, but the paint didn’t come out all that well,

and I am on the fence about making another (white or gray) one.  I needed this

flight to be low, and the Stone with a C11 will be below 200 feet.  I needed a

rocket that I could stand loosing, and yet I wanted to put up something that

would impress the 30+ college students launching this day as a school assignment.

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Also, I needed a rocket with a fast impulse to fight the wind, and the 11 of the

C11 fit the bill.  So although this was not a scheduled flight, and I had the

data for this flight, I instead used that data to give me the confidence to

launch it and expect just shy of 200 feet.

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I loaded the C11-3, and a new home-made, home-sewn bright orange Nylon parachute

with day glow yellow shroud ribbons, 17” diameter.

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It was a beautiful liftoff. Not too fast, but it did not turn much into the wind

either.  Acceleration off the pad was 11 Gs, and as it burned for 6/10 second, it

averaged 4.3 Gs.

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This got the rocket moving at 60mph. Next it coasted for 1.9 seconds, and at only

129 feet high the ejection fired.  With the big parachute tightly packed and

encased in Nomex, and connected with a long shock cord, it took a long 4/10

seconds to unfurl and continued climbing another 30 feet to peak out at 159 feet.

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It could have gone higher but the delay was only 1.5 seconds. This was the lowest

and slowest ever flight for the Stonebreaker. Not surprisingly the shortest coast

to apogee and shortest duration flight thanks to the short delay.

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In seeming slow motion the recovery system deployed, and the craft returned at a

leisurely 7 mph, landing just at the edge of the field short of the road, about

100 feet downwind after 13.3 seconds in the air.

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The flight video shows three college girls in the background watching and taking

phone video of this flight. I hope they got something cool to show.
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2019, Sept 21: Halifax PA, 80 degrees, 5 mph winds.

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E9-8:  I have some disconnect in my brain about the Stonebreaker.  While I really like this model, I was quite annoyed with how the paint job turned out, so much that I almost want to build another one.  For this reason, combined with my fear of E9 motors that have shown a history of causing a CATO and destroying other’s rockets, I didn’t really want to fly using an E8 motor, but I had three and needed to try them eventually.
 
Since I like this model so much and almost want to build another one, I decided this model is the most expendable of the E8 carrying rockets I have.  I would not be quite as upset compared to losing my other two rockets, one is a custom build, the other out of production with a company that doesn’t exist anymore, and requires whole body decals that can’t be duplicated easily.


With all that, I sent this rocket up on the single largest energy motor I ever used, and I expected about 1100 feet.  Since today was one of the few days of light winds and such a large field, this was my chance.  At least with this larger, bright silver rocket I would not likely lose sight of it, and I didn’t, even as I watched it appear to head for the tall trees so very far away in my binoculars.


The Apogee website claimed 1293 feet on an E8-6, but I knew those altitudes were too much influenced by marketing.  My estimate was about 200 feet lower, and even that was too much.  I did have some concern for using a delay 2 seconds longer than recommended, but I did at least have a strong shock cord and parachute, so I hoped it wouldn’t lead to anything more than maybe some zipper damage.

After a false start where the LCO forgot to switch on the launcher, it fired off with 9.6 Gs.  That magnitude was on par with all the other C and D flights so far.  The power of this motor lies in its burn time, and at 2.8 seconds burn it was really hauling up there.  It averaged 2.5 Gs for the entire thrust time.  This moved the rocket to a top speed of 149 mph, which was a good 50% faster than any D12 flight so far. It tied for 9th in speed with a composite motor flight of another rocket.

Slowing down from its blistering pace, it coasted up for another 4.9 seconds, achieving a record apogee of 811 feet.  That was well short of my estimated max height and seriously short of the manufacturer’s estimate.

The ‘stone turned over and began dropping for the next 2.2 seconds.  Thankfully, a short 7.1 second delay allowed it to only drop 63 feet, where at 748 feet it ejected the parachute. I chose a small 14” parachute that was sewn cloth, anticipating this possibility.  It held together, opened just fine, and brought the rocket back at a speed of 12 mph.

It was later in the day and the strong sun got the winds moving a bit by then.  As it happened, 12 mph was just enough of a descent speed to prevent it from drifting into the tall trees so far downwind where I would likely never be able to retrieve it.  It appeared to land just inches from the trees, but in fact it was still a good 80 feet from the trees.

This particular flight clocked in at 50.5 seconds, the longest flight of the Stonebreaker. 


With this big motor, all readings were records except for accelerations.  The one minimum was the parachute diameter, smaller than I ever used on this, and compared to the 32” monster included with the kit, 14” was extremely small.  As I started out on the long trek to recover this rocket, I joked “I’ll see you in about an hour.”  Scott returned with “We’ll be packed up and gone by then.”  Funny joke.


While walking back from the 500 to 1000 foot retrieval, as I got close I noticed that indeed they club was packing up, and already had six of the eight launch pads removed. Thus ends a flying day of 100% success, 0% damage in five flights.
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