It sure eats a lot of wadding with that big BT60 tube! I installed a Nomex cloth so it will never need wadding again, and a nylon cloth parachute. I have modified this rocket with my "Iris" altimeter bay, which adds another 2.88 inches in length and 14.6 grams of weight. (Iris is named after the Greek god of the rainbow. She is a messenger of the gods, linking the gods with humanity.)
This model always seemed to weathercock a lot for me, I hoped that the extra nose-weight of the newly added payload would have helped a bit, but it just slowed it down some more, the Nomex and heavier Nylon cloth didn't help either, I just made Big Bertha into Big & Heavy Bertha. With a C6 motor his rocket has flown higher than the the Saturn V Apollo spacecraft, and the famous Spire of Dublin. But with the extra weight and drag I added, this slow flier seems to always be sensitive to the wind.
A late ejection on a B6-4 (I should have used a -2), damaged the engine mount in a high-speed impact with the mud, so this was re-built with a larger motor mount so she can fly again with D12 power. (The original stuffer-tube was removed with no apparent problems.) The added impulse should get her up in a hurry and the longer burn time should produce some really high flights, I would expect more than 600 feet at least, possibly 7 or 8 big ones. We will see...
...we did see. It has now flown higher than the Two Liberty Place Building in Philly, the US Steel Tower in Pittsburg, and the Chase Tower in Indianapolis IN.
I have flown five different models using the D12-5 motor, and of those the Bertha holds the record for highest speed, travelling upwards at 171 mph.
SPECIFICATIONS
Series Number: 19
Number of Stages: 1
Stock Length: 24"
Added Payload Length: 2.88"
Total Length: 26.88"
Diameter: 1.637"
Payload Interior Length: 3.7"
Payload Interior Diameter: 1.60"
Payload Volume: 7.44 cubic inches
Fin Span: 5.75"
Stock Empty Weight: 94.5 grams
Payload Section Additional Weight: 14.6 grams
24mm-18mm Motor Adapor Weight: 5.8 grams
Liftoff Weight Range: 140.6 - 160.9 grams
Motor Diameter: 24mm (with adaptor, 18mm)
Motor Length: 70mm
Motor Mounting Method: Clip
Altimeter Capable: Yes
Modifications: Upgrade to 24mm motor, adaptor for 18mm
Recovery Method: 15" Nylon Parachute
Typical Descent Speed: 12 mph
Recovery Protection Method: Nomex Sheet
Shock Cord Elastic Length: 31"
Shock Cord Mounting: Steel into Paper
Number of Fins: 4
Fin Material: Balsa Wood
Launch Lug Size: 1/8"
Kit Brand: Estes
Completion Date: probably 1976
FLIGHT LOGS
2010, November 13: Tanguy Soccer Field, Light to moderate wind
B6-4: This flight had strong weather-cocking, a late ejection, and 2 shrouds separated from canopy. It came down fast but it was OK.
2011, May 29: Indiantown Gap, Light wind
B6-2: This time I had a slightly early ejection and it appears to need a longer delay. Somewhere between a B6-4 and a B6-2...should have a B6-3 (if it existed). Nice flight though...as usual for this ol' 70's bird. Not much weather-cocking this time but then again there was little wind. Probably went about 175 feet or so.
2011, June 12: Penn Manor, Breezy wind
C6-3: Strong weather-cocking, C6-3 had a good delay time for this model, good flight & recovery. Considering the curve of the flight path was near 90 degrees with the weather-cocking in strong winds, I suspected an altimeter error. Only later I realized I never added vent holes for the altimeter (duh). This altitude appears to be about the same as other flights logged here for the Bertha on a C, so maybe it actually went that high - I will re-test this particular rocket-engine combination again with the Iris payload. Later I'd like to try it with an Aerotech D sized composite engine!
B6-4: Good liftoff, but added weight of the Iris payload, Nylon chute and Nomex cloth makes B-power borderline at best. This model always weathercocks on me, and today was no different. The ejection delay was way too long, came back ballisticly - almost a lawn dart. Although the altimeter read 112 feet apogee, the parachute deployed at about 30 feet and too low, tube planted in mud, on impact the engine mount pushed forward and was damaged just like my Bandit last month. The rear cardboard centering ring shredded/split and the entire engine mount will need rebuilding. Time to upgrade!2012, February 5: Penn Manor, 5-10 mph wind
C6-3: With a newly rebuilt and larger 24mm motor mount, the Bertha needed a test flight. I wanted to use a D12-5 on this, expecting 600 feet or more, but it was just too windy for that kind of altitude, so I opted for a C6-3. As usual for this model, it ended up weather-cocking quickly after launch and ended up flying horizontal into the wind after more than 2 seconds of burn. I just can't expect vertical flights with this model in any wind because of it's slow lift-off speed.
The maximum acceleration was 4.8G and averaged only 1.3G through the 2.3 second burn time. It reached a speed of 65 mph and an apogee of 428 feet (a new record for this model). The coast to apogee was 3.6 seconds (a bit longer than spec'd), and then it deployed a full nylon parachute at 187 feet and descended at 12 mph. Duration of the flight was 15.8 seconds.
Here is a cool series of pictures showing the parachute deployment:
With the firing of the ejection charge, the nosecone pops out with a puff of smoke and pulls out the parachute wrapped in a Nomex blanket to protect it from the heat. The shock cord rubber is stretched.
2012, March 18: Penn Manor, Light wind
D12-5: The best flight I ever had with the slightly Bigger Bertha. Flies great on a D12, much better than the C6! Acceleration peaked at 15.7Gs, averaging 4.7Gs for the 2.3 second burn. With little wind it sped straight up at 171 mph and coasted for 4.3 seconds. The delay was a bit short at 4.1 seconds and it ejected at 821 feet, 2/10 seconds later it apogeed at 852 feet - a record for this model. A D12-7 might be a bit better. It descended under a good chute at 9 mph. Total flight time was 1 minute and 6.1 seconds. It landed within 200 feet of the launch pad. Complete success!
2012, April 1: Penn Manor, 5-10 mph wind, gusty
C11-5: I wanted to test the C11 motor out on my Bertha with a new 24mm mount. I already knew she flew well with a D12, but wanted to see if the C11 would work better in winds if I didn't want to go up to 800 feet or so. The C6 is a bit weak for this model and allows too much weather-cocking. Also, after two failed plastic chutes in another model, I was counting on the reliable nylon parachute to appease me. While the motor worked great, the parachute did not.
The C11 burned for 7/10 seconds, peaking the acceleration at 13.5Gs and averaging 6.3 for the burn; Three times better than the C6 and almost as much as the D12. This got Bertha moving straight up at 101 mph, and then coasting for 4.3 seconds to an apogee of 378 feet. The strength of this motor prevented the winds from altering the flight path. After another 0.3 seconds and while falling only 4 feet the ejection charge fired slightly early, tossing the parachute into the airstream.
Unfortunately it did not open up for unknown reasons, and the 4+ oz. rocket fell at a very fast 31 mph to hit the ground within 50 feet of the launch rod with a sickening thud after a very short flight of 13 seconds to 378 feet and back! Another rocketeer arrived at the crash site first, stating that it looked fine. I picked it up only to find the body tube intact. I turned it over while saying "but look here at the motor mount..." only to see that it also was intact. She's one tough bird! I immediately loaded her up with another C11 and launched her again.
C11-5: Second attempt with this new motor type for Bertha. This time she flew about as well as the first time. The peak acceleration was a bit less at 12.8Gs, and averaged 6.1Gs for the burn (a little less). It reached a speed of 99 mph, also a bit less. After a 4.2 second coast she apogee'd at 361 feet (17 feet less), and dropped 8 feet in 1/2 second before the ejection fired.
This time the parachute fully opened and she descended at 12 mph to a softer landing in the grass after a 25 second flight. One shroud was caught on the shock cord knot on the swivel clip, so the canopy was a bit mis-shaped. Considering my last three flights with failed parachutes, I'll take it! Successful test flight of the C11-5 motor in gusty winds;Possibly the best motor for this model, with near-perfect delay times.
Comparing the C11 flights with the C6 which have almost the exact Newton-Seconds of total impulse, I can see that the C6 flies about 35% slower and goes about 3% higher because of the reduced drag at lower airspeeds.
2012, June 10: Halifax, near calm
C6-5: This was the eleventh and last flight of the day. I vacillated over which model to fly before choosing the venerable Big Bertha. The choice of motor was more difficult. The D12 is a great choice, although it would produce altitudes a bit too high for my comfort today, and I was saving them for another rocket to carry a camera. The C11 was the next best choice, but I didn’t have any.
I would have to use the 18-24mm adaptor and a C6-something. The -3 was a bit short on delay time, but a 5 second delay could be a disaster if this wind-cock-prone model caught a gust on liftoff and veered horizontally. It was generally calm but late in the afternoon occasional gusts would appear at random. I decided on the 5 second delay but chose to wait out any gusts and launch only in absolute calm. This decision paid off as the model accelerated off the pad with a 5.6 G peak and an average for the 1.9 second burn of 1.8 Gs. Travelling straight up, Bertha beat the wind.
It then coasted to apogee in 3.2 seconds while dissipating its energy of 73 mph. It then turned over and lost 29 feet as it descended for the next 1.3 seconds before the ejection fired early (at only 4.5 seconds). The apogee was at 277 feet (much lower than average), and the ejection was at 248 feet. The nylon parachute opened well and the model descended at 12 mph to the land in the grass about 200 feet away for a flight time of 20.1 seconds. Thus ended a great day of flying with no significant damage, loss or injury!
2012, June 30: Indiantown Gap, Erratic winds
C6-3: I needed to end on a more spectacular flight, so of course I had to bring out ol’ Bertha. I love how she flies on a D, but didn’t want the 800+ feet it would make, the winds were just getting too much. In hind-sight I should have used a C11, but I already prepped her with a C6. The choice of the C6 was risky, and a stronger, steady wind was building. The C6 normally just doesn’t have enough git-up-n-go to prevent serious weather cocking, as I learned from previous bad experiences. I had to hold the launch for a good 5 minutes before it calmed for a second.
She flew great. The C burned for 1.9 seconds and got her going to 77 mph. Acceleration peaked at 6.2 Gs and averaged 1.8 Gs for the burn. After burnout she coasted straight up another 3.5 seconds to 319 feet. The ejection was early but OK (a -5 would be way too much in these winds). I honestly don’t know why she didn’t turn in to the wind like always.
The ejection came as it was starting its turn, 6/10 second before apogee. She tumbled a bit and then peaked at 328 feet. The parachute unfurled well and she coasted down at 9 mph, landing within about 300 feet, ending a flight of 28.3 seconds. I thought that was enough for the day, but then I ended up doing one more.
2013, May 4: Halifax, 5-10 mph wind, 70 degrees
D12-7: I have only sent Bertha up on a D12 once before since it had its new motor mount installed, and it was a spectacular flight reaching over 850 feet. Today I was about to try again but use an even longer delay charge since a -5 was not enough. This was flight number 199 since I was a born-again rocketeer, and I was planning a big launch for #200 to follow.The rocket took off well and travelled fast and straight up for a beautiful high flight. The bright yellow Nylon ‘chute opened well and the rocket floated for about a minute in the sky. As it came down, it drifted West and was caught in the very top of a tall tree, about 50 feet high. The club’s longest recovery pole only reaches about 35 feet, so there was plenty of space between the tip of the pole and the rocket, with no hope of recovering it.
Big Bertha is now on permanent display 50 feet up on the 7th tree from the entrance on the West side of the field. Having a Nylon parachute with extra thick shrouds, a Kevlar “screw eye” holding the paper and wood payload compartment, it is not likely to rot and fall anytime soon. Best I can hope for is the high-quality shock cord to eventually rot and the body might fall to its death or recovery.
The $70 Altimeter Two may easily survive for years before it falls inside its thick plastic padding wrapped in painted cardboard and covered with a plastic nosecone and plywood bulkhead. If it ever does fall, I should be able to recover the flight data if a lawnmower doesn't get it first. For now though, after about 17 flights and many adventures, Rest in Space Big Bertha Iris, you will be missed.
Heartbroken, I abandoned my plans to execute flight #200, which was to be the Estes Interceptor on a Apogee D12-5 composite motor.
Three weeks later, after many rainstorms, I devised a plan to retrieve the rocket or at least the payload. The rocket body was not in the tree, the shock cord rubber broke and the body was nowhere to be found after a substantial search. The parachute was severely wrapped around a branch and so was the Kevlar leader to the payload, obviously from many windy days.
The altimeter was intact but the battery was dead, after charging I could retrieve the data. The burn was 1.8 seconds long, peaking the Gs at 14 and averaging 3.8 for the whole burn. It coasted for 5.5 seconds after reaching a top speed of 149 mph, apogee was 777 feet. Then it dropped 32 feet in the last 1.3 seconds and the ejection fired 2/10 seconds too short at 745 feet. It descended at 10 mph before hitting the tree at about 80-90 feet. Flight time was 56.3 seconds – or arguably 504 hours and, 56.3 seconds.
I shot a fishing sinker over the offending branch using a sling shot. Attached was a few hundred feet of 60 lb. fishing line. The fishing line was used to haul a heavy rope up and over the branch. Shaking and tugging would not shake loose the parachute/payload, but eventually the branch broke and it fell to the ground with the payload and parachute.
The payload section was obviously soaked during a few rainstorms, but the plastic nosecone and plywood bulkhead kept the altimeter intact and the plastic padding seemed to keep it dry. The Nylon parachute is definitely useable. Someday I may rebuild the rest of the rocket using the original nose cone, but that might have to wait until I complete another 25 kits in my to-build box.
Much thanks goes to my wife who helped me every step of the way. This terse description makes it sound simple, but it took about four hours to complete this rescue as we had unforeseen problems with every step.
Seeing how twisted up the heavy shroud lines were, it was clear there was no way the wind would have blown this out of the tree.
One more week later, I got an email from a club member, stating that a friend found “the bottom of a rocket”, and he thinks it might be mine. Don’t want to get my hopes up to whether it really is Bertha’s bottom or what condition it is in. I will get it back at the next launch late this month…so the saga continues.
I got it back and it was the uniquely colored Big Bertha. Unfortunately it sustained some water damage and had a few bugs calling it home. The body tube suffered a crumple mid-section, probably as a result of falling without a parachute. There was no shock cord or even the paper mount left. The clay rocket nozzle had completely degraded and was absent, only the casing remained. The Nomex sheet was lost also. I may not be able to get this bird flying again, but at least my record of never having lost a rocket is still alive.
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