01-06-2019, 12:49 PM
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BAR 13790
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Join Date: May 2008
Location: Johnson City, NY
Posts: 524
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Quote:
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Originally Posted by LeeR
Les,
I think you might want to hollow the nose cone. It would allow gases to get passed the end of the motor tube and “wrap back around” to get to the ducts you have to cut, assuming you are committed to ducting the ejection gases.
The other option is to not use motor ejection. This means no complicated cuts for ducting, greater strength in the structure, and more reliable timing of ejection by using electronics to blow the chute out. You are going to need a very robust joint at each junction of ducting tube to the upper and lower body tubes.
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That was actually my next question/issue. The pods are about 1.22 diameter x 36 long. For all 3 pods that is 126 cubic inches. The Passenger pod is about 2.25 diameter x 17.87 for an additional 71 cubic inches. Total is about 200 cubic inches. For now I have excluded the motor pod (not a lot of spare space in there) and any detrimental effects of static pressure passing through the ports. For even just 12psi that will require slightly over 1.2grams of BP. I believe this is more that what is normally provided in a commercial motor (I normally use CTI)....
One option would be to block off 1 or 2 of the tubes. If only one has ducting than that reduces that volume to 42(ish) cubic inches. Adding back in the passenger pod of 71 and we are at 113 which reduces the ejection charge to 0.7grams.
BUT - for the pod connection I can lengthen the cutout but I can't make it wider - there are still two circular tubes meeting tangentially. Do I now risk blowing up the motor compartment with having only one vent to get the pressure up to the passenger compartment?????
I built the Hawks Hobby upscale and it added some balsa pieces along the tube interfaces to strengthen the bond, but it is only about a 1.4 upscale, not a 2.25
Are there any other beta testers out there? What did you do??? Did you stay with ducted tubes or go to electronic deployment?
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