Dog barf and adequate ejection pressure/volume in larger airframes...
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shreadvector
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Follow the instructions I posted several times in the past.
Follow them for all sized models (except absurdly short models).
Your only concern then will be using an appropriate motor for the size (volume) rocket. Bigger motors have bigger ejection charges. Much bigger.
Follow them for all sized models (except absurdly short models).
Your only concern then will be using an appropriate motor for the size (volume) rocket. Bigger motors have bigger ejection charges. Much bigger.
GregGleason
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What is the diameter and length of the airframe that needs to be presurized?
If you are concerned, you may want to do a ground test or two.
Greg
If you are concerned, you may want to do a ground test or two.
Greg
My experience is that dog barf acts like a baffle. I've had many 3" & 4" rockets that return with all of the dog barf in place. It is scorched on the bottom, but it stays in place when the motor charge goes off, if the rocket is nose up when the charge ignites.
Remember, the ejection charge does not push recovery gear out of the BT, it pressurizes the BT so the nose cone pops off. If your recovery gear is large enough to act as a piston, you will get some push from the ejection charge, but don't count on it.
Remember, the ejection charge does not push recovery gear out of the BT, it pressurizes the BT so the nose cone pops off. If your recovery gear is large enough to act as a piston, you will get some push from the ejection charge, but don't count on it.
My experience with dog barf is the same as Handeman's. Adding more in an effort to decrease the volume of space would not be my first choice. Calculating the amount of black powder needed to pressurize the volume of space for a given rocket would be the way to go. There are Apps for that on IOS and probably Android as well; plug in the diameter and length and out comes a number representing grams of BP needed in the ejection charge. Vern Knowles web site is a commonly used reference and I'm sure there are others.
https://www.vernk.net/EjectionChargeSizing.htm
https://www.vernk.net/EjectionChargeSizing.htm
shreadvector
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You need to first install regular Estes or Quest wadding - a square or a couple of squares to cover the tube and form a cup shape as you insert it. Then you install the cellulose insulation wadding above the "cup".
The ejection charge can blow through the middle of the fluffy cellulose insulation, but the layer or two of regular wadding on the bottom keeps it functioning like a piston.
jahall4
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That certainly makes sense, but I think because we where using a parachute protector it repressed that tendency. Interestingly there was still quite a bit of barf left in then tube. I was expecting it all to be blown out, particularly with the force of the ejection which was surprising. I was convinced just for a second that the ejection charge failed to push the cone out because the rocket was well on the way down, but when it finally (seemed like forever) did it was out in an instant.
My observation would suggest the the ejection charges on Composites are substantially more force full than BP motor. Anyone else conclude or know the same?
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shreadvector
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I do not agree. A 29 mm Estes F15 ejection charge or a 27mm FSI F80(100) ejection charge is just as strong as an Aerotech 29mm composite motor ejection charge. All are like a shotgun blast.
RKeller
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what motor are you using? what size rocket? I know an Estes Partizon is borderline with an AT single use 29mm motor. I watched one pop the nose but not pull the chute out. it survived the fall and next flight I pulled the red plug and added 0.3g of FFFF to the charge. It had a perfect deployment with the extra powder.
