The Big Bertha: Is a very old model built in the 1970s by my brother. Very popular model, you probably have this or one of its many derivatives yourself. This rocket is the classic '70s kit. It is big, fat, slow flier with a retro look. This one isn't retro-"looking" though; it's the real retro thing. It is painted in the original mid-70’s catalog scheme, but with a lighter - more 50's style - cream yellow. I would prefer the newer all-black look Estes is showing now, or maybe some red/white/blue patriotic scheme.
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.) 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.
| Flight Date: | 2012-04-01 |
| Rocket Name: | Big Bertha |
| Kit Name: | Estes - Big Bertha {Kit} (1948, 23, 7007) |
| Flyer's Name: | Rich DeAngelis |
| Motors: | C11-5 |
| Launch Site: | Penn Manor School Lancaster PA |
| Actual Altitude: | 361 Feet |
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!
Succesful 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.
| Stage | Motor(s) |
|---|---|
| 1 | Estes C11-5 |
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