The Bullpup 12D Iris

The Bullpup 12D Iris is a sport-scale model of a 30-some year old air-launched guided missile. It is an Estes kit. The real thing came in several varieties that outwardly appear different, the 12D is just one of those types. The real thing was guided by a "pilot" who remotely steered this missile onto the target.

I name this rocket with the Iris suffix because it has been modified to carry a small altimeter/accelerometer. Iris was a mythical figure, she was the messenger between humanity and the Greek gods. I feel this is a suitable name because the Iris payload makes this rocket somewhat of a messenger from above, reporting the speed and altitude of the rocket's flight. The Iris payload makes it a bit longer and a bit heavier than a "Stock" kit, so direct comparisons to the performance of other Bullpup kits will show differences.

I made several modifications. I added my own motor clip after mounting the motor a bit further aft to allow clearance from the molded plastic boat tail.  Normally I would scrap the Estes paper-fold shock cord mount idea and attach some Kevlar to an ejection baffle, but for this rocket I attached a small loop of Kevlar string tightly glued to the inside body tube.

I am using a much longer (3 or 4 feet) shock cord rubber to prevent the inevitable dings and gouges when the nosecone springs back. I cover the balsa fins with plain paper secured with photo-mount adhesive.

I also added a short 2" section of payload tube to the top of the rocket, the usual Iris payload.  I did screw up a bit here though. In my haste to get the rocket built, I glued the forward fins onto the main body tube end, and not further up on the payload end where I wanted to, so my rocket will not have the front fins quite as forward as the real missile appears. Eh, it was only sport-scale anyways.

Another modification I made was to split the launch lug in half and spread the lugs apart on the body tube a few inches or more fore and aft. This makes the model stay straighter on the launch rod while thrusting off the pad.  It is pretty small, about “Alpha” sized, but my model is a bit heavy with a wider tube and a heavy paint & clear coat.  I’m only expecting 4 to 500 feet with a C motor.

I did not bother to photograph this rocket being built, but here she is all finished and ready for flying.

This model is one of six rockets that has flown with the B6-2 motor.  This one holds the record for speed, reaching 66 mph.

Additionally, it is one of ten models I have flown with a C6-3, and it holds the record for speed, clocked at 101 mph. A different flight holds the record for altitude with the C6-3, reaching an apogee of 473 feet.

SPECIFICATIONS

Serial number: 27

Number of Stages: 1

Stock Length: 15.63"

Iris Payload Length: 2"

Tip-to-Tail Length with payload: 17.63"

Diameter: 1.33"

Fin Circular Span: 4.705"

Mass: 92.8 grams

Liftoff Weight Range: 116.4 to 123.9 grams

Motor Diameter: 18mm

Motor Length: 70mm

Payload Interior Length: 2.3"

Payload Interior Diameter: 1.28"

Payload Volume: 2.96 cubic inches

Recovery Method: 12" Plastic Parachute

Recovery Protection: Wadding

Shock Cord Elastic Length: 36"

Shock Cord Mount: Kevlar

Noseweight Mass: 13.7 grams

Fins: 4+4, Paper-covered Balsa

Start Construction: July 12,2012

End Construction: August 19, 2012

FLIGHT LOG

2012, Sept 1: Indiantown Gap, 12mph winds

B6-4 : This was the first ever flight of this rocket. When I completed it, I was surprised it was so small yet weighed so much. I suppose I was in denial just how heavy it was and how much that would affect performance.   Still, to be on the safe side, I skipped the recommended A8-3 and moved up to the B6-4. I’m glad I did.

The motor lit right up, and the rocket went nowhere, maybe 4 inches up the rod. The motor clip caught on the clothespin used to hold the rocket above the blast deflector.  After about 5 seconds, the chute popped and the whole thing was over. Such a waste of a good B6 motor. Failed flight.  That was the 13^th launch of the day for the club. Just sayin’.

B6-4: Retry on the maiden flight. This time I made sure to not let the clothespin snag the rocket and hold it down on the rod.   The motor lit and burned for 8/10 second, with a peak acceleration of 8.8 Gs – wow.   It averaged 3.3 Gs for the burn, but only reached a speed of 55 mph, turning moderately into the wind. It then coasted for 2.3 seconds to an apogee of 124 feet.   Then it descended for another 1-1/2 seconds, dropping 37 feet before the ejection fired a little early.

At 87 feet the parachute deployed and the rocket safely descended to the ground at 9 mph, landing about 70 feet from the pad.  Flight time 10.2 seconds. Good flight, but I was disappointed the B6 couldn’t lift it higher.  With only  124 feet on a B, I would never dare fly it on an A8 motor. I think a B6-2 would be better unless it is calm.

C6-5: It was windy, but knowing how little altitude I got with a B6, I knew a C6 would not get lost.  This time the motor burned for 2.2 seconds, quite a long time, only peaking in acceleration at 5.7 Gs, and averaged 1.7 Gs for the 2.2 seconds. This motor was a slow burner, pushing the Bullpup to 83 mph.  Like the B6 it turned into the wind, but more so as it was a longer burn.  Then it coasted for 2.9 seconds and reached apogee of 300 feet even.   The delay burned slow also, for 5.9 seconds.  In those last three seconds it dropped 118 feet and was picking up a lot of speed.

When the parachute finally saw the air, it tore completely off the shrouds.  The rocket then fell at 24 mph and landed 300 feet upwind, but no damage other than the parachute, which floated down a minute later.  Total air time was 12.9 seconds. While the engine choice had too much delay, other factors in this flight’s failure was the long-burning delay of this particular Estes motor, and the very thin shroud lines which more easily cut through the plastic parachute.   This rocket needs a C6-3 for sure.

2012, November 23: Penn Manor, moderately strong wind, no gusts

C6-3: After the near-disastrous flight last time, I now know to fly this rocket with a -3 delay. I had removed most of the kit-recommended nose weight, because I had almost the exact weight added already, in the form of the payload modification, so the extra weight was only hurting the Bullpup’s performance.

The C6 fired up and burned for two seconds, accelerating the rocket to 101 mph.  This time it accelerated with a peak over 4 Gs higher, reaching 10.1 Gs, and averaging 2.3 Gs for the burn.  The removed clay nose weight allowed for a much better acceleration, which was a lot quicker this time.

At 410 feet the ejection fired too quickly after only 2.3 seconds.  The Bullpup continued up for another 20 feet to reach an apogee of 430 feet – the best on record so far, much better than the previous 300 feet.

The parachute shrouds, shock cord and Nomex protection had quickly tangled up severely, causing the rocket to fall at 17 mph. Flight time was only 20.5 seconds.  It did survive unharmed though by landing in the grass about 100 feet from the launcher.

B6-2:   Now that I know it is safely able to fly with the C6, I wanted to try the B6 this time.  On this flight the motor burned for one full second, accelerating the rocket off the pad at 8.3 Gs.  The average acceleration was 3.2 Gs, and this rapid speed increase made this motor OK to fly in windy weather.  Still, the wind proved to be even too much for this rocket, and it weather-cocked a lot.

The Bullpup reached 66 mph, and turned over at its apogee of 102 feet after a coasting time of 1.6 seconds.  So while the C6 motor showed noticeable improvement with the lighter rocket, the B6 did not.  It only dropped three feet in the next ½ second when the ejection fired on time at 99 feet.

Again the parachute tangled or something, and the rocket fell fast at 16mph.  As it turned in a bad direction, the tangle may have saved this rocket from trees or a school rooftop. As you can see in this picture, it wasn't really tangled, but for some reason failed to open up even though it had plenty of time. I have seen too many times already that the Quest parachutes seem to fail to open at random.

At 7.4 seconds into the flight it struck the hard pavement of the school parking lot, and bent the motor hook on the rocket’s rear, that was a lucky strike as the metal clip absorbed most of the energy of the fall.

The nosecone cracked open at the tip.   Again I suppose this was lucky, as a lot of energy was absorbed in breaking this rather solid plastic tip. A fin tip is also slightly scraped and chewed up.  I don’t know why this rocket seems to not want to recover properly. For the most part it has been nothing but disappointment.

The nosecone was repaired with CA glue, and the motor clip was cut short and filed smooth. The crinkly plastic Quest brand parachute was scrapped, and replaced with a much softer plastic parachute with longer shroud lines (a homemade version).

2013, January 13: Penn Manor, 5 mph wind, drizzly and damp

C6-3:   The Bullpup seems to be plagued with problems with both altitude and recovery, so I wasn’t expecting much out of this flight.  I selected the C6-3 as it seems to be the best engine for this model and yet it hasn't flown very high.  Being a small, white rocket, I didn’t want it to go too far up in the air on this foggy afternoon.  The dreary light convinced me not to bother with photographs of this flight.

After a good ignition, the rocket accelerated off the rail at 8.1 Gs, averaging 2 Gs for the 2.2 second burn time.  This got the rocket moving at a respectable 95 mph, followed by a 3.3 second coast time.  Although this particular motor delayed 3/10 second too long, it was still not long enough as the ejection fired at 462 feet while still coasting up, causing the Bullpup to come to a stop 2/10 seconds later at a record height of 473 feet.  While historically the Bullpup has worked better on the C6-3, today it could have used the C6-5 for more altitude advantage, even though I didn't want that in the foggy atmosphere.

The parachute deployed into the wind while unseen far into the clouds above, but again for unknown reasons it didn’t fully open and as it fell it spun very fast and became extremely twisted up into a plastic wad, perhaps 100 or so turns on the shroud lines.  It did fall at a slow 10 mph though and was not damaged.  It landed about 250 feet downwind.  The 35.6 second flight was a duration record for this rocket, as it had a terrible history with recovery in the past. 

Murphy’s law: I wanted this to be a low flight, and it went ahead and busted its own altitude record!  Out of five successful launches, I only ever had one successful parachute recovery with this ornery rocket. Maybe I should use a streamer?  A deployed streamer has to be at least as good as an undeployed parachute!

Now with three different rockets producing three failed parachutes, it was time to call it a day.

2015, November 15: Cross Keys NJ, 12-15 mph wind, gusty, 60degF, 35%RH


B6-4:  First time out in a while, and it was borderline too windy and gusty, but clear skies all around.  I wanted to send the Bullpup up with a B6-2, but I didn’t have any left.  In the past the -4 was maybe too much delay for the expected altitude, and with the predicted wind-cocking it could mean trouble.

Furthermore, I had a history of parachute problems with this rocket, so I wasn’t expecting a lot of success, but I did use for the first time a heavier 12-inch Nylon ‘chute I sewed myself, with very strong ribbon shrouds, so there was hope.



The Bullpup’s first B6 flight hung on the rod, and another had a bad chute, but I did have one good B6 flight for this rocket, so this was a re-test flight.  Bad luck appeared again, but very minor.  I forgot to re-arm the safety launch enable switch at the pad.  A flip of the switch solved that problem.

This time she took off right away, though with only 7.5Gs it was not the fastest B6 flight.  I did get a good 9/10 second burn, averaging 2.7Gs which was low for this motor & rocket.  That was enough to get the rocket moving to 54 mph – also slow.


After burnout it coasted for 2 seconds which was ok, and reached a peak apogee of 107 feet.  Good enough and 5 feet more than I expected.  During that time it wind-cocked into the wind considerably.

After apogee, it coasted upwind for another 1.1 seconds and then deployed it’s parachute.  At that instant it descended 16 feet to 91 feet above ground.  The too-short delay of only 3.1 seconds helped the flight for sure.

Then to my surprise and delight, I saw a good parachute and it returned at a comfortable 12 mph, landing upwind only about 50 feet after a flight time of 9.4 seconds.  I was happy, after seven flights this was only my second successful flight of the Bullpup 12D Iris!

 



C6-3: Pleased with the last flight, I wanted to send this up again but with a bigger motor, since 107 feet was not all that impressive.  So I chose the C6.  I have flown this with a C6 three times, and each flight was met with a total parachute failure.

The first C6 flight with a -5 delay likely lead to the stock Estes ‘chute to be torn off completely, all six shrouds separated from the plastic.  So this was also a re-do test flight.  This time I again used a home-sewn and thicker 12” Nylon chute with heavy ribbon shrouds, and it stood up to the last flight just fine.

So off it went with an acceleration of 7.6 Gs off the pad.  The C motor burned for 2.1 seconds and pushed this rocket to a record setting 103 mph.  The average acceleration of 2.3 Gs was also a record high.

The delay was a little short, popping at 2.8 seconds while the rocket was still ascending and at 508 feet up.  For 3/10 seconds longer it rose to its record altitude of 542 feet.  So far so good, but it still has to come back.

All twelve inches of that tough chute unfurled into the wind, and brought the Bullpup back safely at 10mph, while traveling very far downwind.

Combined with a bit of drifting with the wind on the way up, and it landed about 500 feet downwind in thick, dry and dead grass.  The total flight duration was 38.8 seconds, a record flight duration for the rocket.  Zero problems.  Can’t ask for anything better than that.

2016, September 3: Fort Indiantown Gap,

73 degrees, 10 mph wind, gusty.

This was not a flight.  It was supposed to be.  The rocket was prepared, flight card
filled out and turned in, altimeter armed, ignitor installed.  I put the rocket down on
a table to take a quick picture of a high-powered launch and a big gust came along.
Pix taken, I stepped back and reached for the rocket, but it wasn’t there. At that same
instant I heard a familiar crunch sound under my foot. Fortunately I didn’t put all my
weight on it. What I heard was the crunch of balsa wood, and my heel crunched on the
Bullpup's rear fin.


Fortunately I didn’t step on the body tube, which would have essentially destroyed it.
This poor rocket has taken a lot of physical abuse, and the next two B and C flights
were scrubbed while I fix the single rear fin that broke right at the root.  I could
have used some CA or epoxy, but I wanted to do a more careful, better job on it. I had
plenty of other rockets to launch this day.

Of course I repaired the Bullpup.  And then I flew it.


2018, Nov 4: Penn Manor Field, 7 mph winds, 57 degrees F


C6-3: I wanted a better flight from this Bullpup, after too many fouled chutes, I put on the most rugged home-sewn parachute I had with nearly un-tangleable ribbon shrouds.  This was the first of two flights with the C and B motors.


The C6-3 motor came alive, with a typical energy that pushed it up with 8.9 Gs of acceleration. It burned for a typical 2.1 seconds, getting the rocket to a speed of 98 mph. The burn averaged 2.2 Gs. With a 2.5 second delay time, it ejected a bit early at 461 feet up, and stopped 24 feet and 3/10 seconds higher at 485 feet apogee.

It really should fly better with a -5 delay, so I have no answer about why I used a -3 delay. I suppose because when I did once long ago, it turned over with a very late delay and tore off all the shroud lines!  That was a windy day and combined with a long delay was a recipe for disaster.


But this flight was just fine! The parachute opened well and then it all came back at 9mph for a soft grass landing after a 37.6 second flight.  It broke no records, but was a fine flight.

 

B6-4: This is the second of two flights for this rocket so I can put the flight testing to bed.  This was the last of six good flights today, and now the Bullpup has good test flight data, and is flight ready if a bit scarred from its sordid history.

Another attempt at getting a good picture of the Bullpup 12D flying.
Usually, the very white color ends up being washed out because cameras want to expose for average light, not bright white.  Here, my other camera almost blocked the shot.
Murphy was a rocket scientist, or at least could have been a very good one.

 

This motor fired with more energy than any motor in the Bullpup.  It tore off the pad with 10.2 Gs of acceleration, then burned for 9/10 seconds. A previous motor burned quicker, so this motor only averaged 3.2 Gs for its burn, but still plenty fast. This got the pup going to 59 mph, bested only by a slow burning B6-2 once.

Two good flights with the Bullpup 12D today!
Considering its history, I could get used to this!

After flying straight and true, a coast time of 3 seconds had it reach its apogee of 183 feet, the best altitude record for a B6 on this rocket.  It then turned a bit and continued for another 4/10 seconds while it descended only 5 feet and the ejection charge fired at 178 feet.

The super-heavy duty 12” chute opened, and it came back at 12 mph to a soft grass landing about 100 feet downwind.  The flight lasted 14.1 seconds.



This is seen more dramatically in a video, but it looked at first like this was going to be a sideways-turning flight from the wind, as can be seen in the first frame.  But Bully corrected itself, as seen a split second later in the second frame, and continued straight up, with a few wiggles here and there like it wanted to dance.

This B6 flight had all the highest numbers except for average burn time. The altitude, speed, peak acceleration, burn time, total flight time, ejection altitude, and even the coast to apogee were as high as any B6 flight.  All in all, a good flight – two of them today – and enough data to call this bird fully sport-flight ready.  With six good flights today, it was time to pack up and go.


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