I decided to build a biggest one after I started building HPR models. It is 4" in diameter, about 5 feet tall, weighs about 5 pounds and has a 38mm mount. It has not flown yet but should fly great on an I motor. The middle-sized ones are BT-70 and 3" upscales. Neither has flown and the BT-70 one will be a test vehicle for a Magnetic Apogee Detector and PerfectFlite timer and altimeter.
Following is a chart of scale information for every size of tubing I know of. It can give you the information you might need if you're trying to build your own Bertha (Big or Small).
|My Fleet||Description||BT Size (OD)||BT Length||NC Length||Scale|
My Fleet indicates the ones I have built (*) or that are under construction (^)
Description is what the tube is commonly called
Tube OD is the outside diameter of the body tube, all scale data is based on the original Big Bertha being an Estes BT-60 which has a diameter of 1.637"
BT Len. is the length of the cut body tube
NC Len. is the approximate exposed length of the nose cone
Scale is the scale factor, how many times the original size the
model will be
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