Nytrunner
Pop lugs, not drugs
That's a lot of holes
Hmm, even after all these years, I still get over-excited and do dumb things. I bought four (expenses) aluminum charge wells with 8g capacity; however, I had not actually calculated the charge size for the booster.
88" total - 29" from top CR - 8" AV bay intrusion = 51"
51" X 7.75" ID @ 12 psi would require a charge size of a whopping 14.9 grams!
Now, I know the motor will consume a good bit of space, and 12 psi might be too much. My Formula 200 has 18" of volume in the booster, not including motor displacement, and I am good with a charge force of 6.4 psi. That would bring the Performer 200 booster charge back to a measly 7.95 grams.
I guess I will ground test with 8g and see where it goes. If I need more than that, I guess I may have a couple of nice 8g aluminum charge wells to sell on the cheap.
Would you mind showing your numbers? What psi? I use three #8 shear pins on my big rockets. What shear strength are you using?If your compartment is 51" long and 7.75" ID I work out around 4.5g of BP as what I would use as a starting point. Your 8g canisters might be ok I think.
Good luck with the project. I lit an O3400 recently and it was a nice feeling .
That's a lot of holes
Two for the 3/4" switches and three for vents, as I described in my post. I don't understand what is confusing about that?sure is. What's up with that?
Would you mind showing your numbers? What psi? I use three #8 shear pins on my big rockets. What shear strength are you using?
Thanks for the read. My sim shows the stability margin as pretty big with the O motor. I don't know if you read the whole thread, but the motor will be a six-foot long 98mm job. Because the motor is so long, its weight is spread out almost to the middle of the rocket. I would be more nervous with 6" O, which is why I'm not going in that direction.Be sure you read Robert Galen’s article What Barrowman Left Out. https://argoshpr.ch/joomla1/articles/pdf/sentinel39-galejs.pdf
You might have a longneck rocket there that might be butt heavy with an O motor.
The gist of the article is a longneck rocket requires the CG to be a bit further forward
for stable flight. I built a longneck Wildman rocket and had a bit forward CG as suggested and had
a bit of concern with the “smallish” fins and long length. A Loki L1400 pushed it to 10k and it went like
a bat out of Hades as straight up as can be.
As it turns out, the sustainer is so long that it could hold a 54mm Loki M, the CG is still acceptable but there
is no place nearby where it wouldn’t bust the waiver. Best of luck with your project. If you’ve already read the article, my apologies for my presumptiveness. Kurt
Only one glitch: he slotted the booster instead of the cut-off piece of payload.
If the parts were unusable, no doubt. But I just moved the extension from the front to the back, and after thinking about it some, I like it better this way.With that amount of cash outlay, Ken & Curtis would have been immediately informed of the error and replacement parts would have been requested, on their dime !
Dave F.
If the parts were unusable, no doubt. But I just moved the extension from the front to the back, and after thinking about it some, I like it better this way.
Thanks for the read. My sim shows the stability margin as pretty big with the O motor. I don't know if you read the whole thread, but the motor will be a six-foot long 98mm job. Because the motor is so long, its weight is spread out almost to the middle of the rocket. I would be more nervous with 6" O, which is why I'm not going in that direction.
Thanks. Those are good ideas. I have room in my stability margin, and the little bit of extra weight in the rear shouldn't be a problem.30" should be perfectly fine for a 4" motor in a fiberglass rocket. My understanding is there is not much, if any, torsional forces on the casing. It is almost entirely vertical, unless the nozzle is misaligned or if there is a CATO, which the length of the motor mount would not help with. A longer motor tube will also just add a lot of mass in the rear, which could cause more problems with tail weight. Then again, the motor is pretty heavy. Thrust Curve says an O3400 is 37 pounds, and this isn't an altitude bird so some support might be a good idea for the sake of overbuilding.
Maybe you could make another short motor support up higher (around 12" long is what I am thinking) with two centering rings if you want extra support for the motor case, this would save a bit of mass from the extended motor tube but provide the leveraged support on both sides of the motor cases Cg. It provides the same amount of support as a longer tube but saves weight.
Disclaimer: I in no way mean to pretend to say I am in any way near as experienced as you or have ever attempted an O motor build, this is just what comes to my mind when I think about lengthening the motor mount.
Yeah, it was a toss-up. Another, even bigger consideration was that with the 30" MMT, I could not reach far enough into the booster to connect/disconnect the quick links for the drogue harness. I considered just attaching the Y harness while building and then never removing it, but with the 48" MMT I can connect and disconnect with ease. This is going to work best for me, I think.I'm still unconvinced that 10 more inches of mmt is value-added from a structural standpoint (especially considering how solid you build). Through the wall fiberglass is very strong
If your compartment is 51" long and 7.75" ID I work out around 4.5g of BP as what I would use as a starting point. Your 8g canisters might be ok I think.
[EDIT] Just rechecked my numbers with the correct formula. 18g would be my starting position. Sorry for the confusion.
Good luck with the project. I lit an O3400 recently and it was a nice feeling .
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