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- Nov 29, 2018
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Cool deal
thanks for the update
thanks for the update
Just wanted to say Pepe is looking beautiful and please do keep the updates coming. A couple of questions:
1. Can you post a pic of your camera mount?
2. Do I see charge wells next to the eyebolt? Would those be for a chute cannon? So 2 charges to pop the shear pins and another 2 to push out the chute?
Also, the links Jim posted on leveling no longer work. If you still have the files would you mind sharing them? I would love to read them.
Do you see a problem if the load was say 25% top, 75% bottom, or vise versa? Here is a pic of where my top of casing contacts the glued in coupler. It's about .150 from the bottom of the rocket. If I put a spacer on top of casing around .145, this will put me just shy of bottom of rocket. I will snug up the top of casing to the coupler/spacer with the threaded rod that's used for motor retention. Then I will screw on boat tail until it is snug against bottom of airframe, since the bottom of casing is about .005 from the bottom of airframe. Now both ends of motor are making contact with their push points.An N5800 will generate shear stresses of about 1,500psi in those threads. The shear strength of 6061-T6 is 30,000psi.
Controlled sharing of the load is quite hard, because of the stiffness of the motor and the tubing. You will end most likely with a flight where the vast majority of the load gets transferred via one end. It's better if you decide which end should transfer the loads.
Reinhard
Hey Nytrunner,Heck if you tighten the boattail enough you'll have tension on your MD retainer rod
I don't see a problem with either load distribution if the rocket is well constructed. The "problem" is that you will have a really hard time controlling your load distribution. Both your airframe and your motor are rather stiff. This means changing loads by a lot will only result in a rather small compression or expansion. Looking at this from the other way, very small length changes are equivalent to significant load shifts. This means if your motor is only slightly longer than you need, basically all the loads will be transferred through the forward end and vice versa. It will be tough, if not impossible to get both lengths matched up well enough. This is before you even consider the fact that your tubes have different coefficients of thermal expansion and that your motor will expand as soon as it becomes pressurized. At the end of the day, you will probably transfer 90%+ of the load via one end, so you still need to make sure that both ends can handle the full thrust.Do you see a problem if the load was say 25% top, 75% bottom, or vise versa?
I don't see a problem with either load distribution if the rocket is well constructed. The "problem" is that you will have a really hard time controlling your load distribution. Both your airframe and your motor are rather stiff. This means changing loads by a lot will only result in a rather small compression or expansion. Looking at this from the other way, very small length changes are equivalent to significant load shifts. This means if your motor is only slightly longer than you need, basically all the loads will be transferred through the forward end and vice versa. It will be tough, if not impossible to get both lengths matched up well enough. This is before you even consider the fact that your tubes have different coefficients of thermal expansion and that your motor will expand as soon as it becomes pressurized. In the end of the day, you will probably transfer 90%+ of the load via one end, so you still need to make sure that both ends can handle the full thrust.
If you really want to spread the load in a controlled manner, you'd probably need to put a spring or something equivalent in there. But that's not necessary. Both your motor and your tube will easily handle the thrust of an N5800. Just use the end that you prefer.
Reinhard
Just curious on this thought. Is the internal pressure of the motor considered since it will basically be pushing the closures apart?Edit: If I didn't mess up my calculations, the full thrust of an N5800 should compress the casing by about 0.13mm (5 thousands of an inch). So for any thou that you're off from the ideal value, the load shifts by about 20%.
This is ignoring internal pressure. If you put two identical motors on the test stand, one with forward retention and another one with aft retention, their length difference should be about 5 thou.Just curious on this thought. Is the internal pressure of the motor considered since it will basically be pushing the closures apart?
Sounds like you are on the right track!
the M2245 should make for one heck of a “shake down” flight!!!
They don't like the amount of BP I'm using for drogue or main. They think it's to small. Containment of BP has a lot to do with how energertic your ejection force will be. With the right setup, you don't need much BP. After many test firings in the back yard of both the drogue and main, I decided .4 grams is good for the drogue with .6 grams for backup, and the same for the main. When I used .8 grams in my drogue shotgun setup, the nose cone came off like a bullet traveling 75 feet before hitting the ground. The rocket was only 6 inches off the ground at the nose before firing. Yes, PePe uses 3 4-40 nylon shear pins to keep the nose from separating from the airframe.odd the 2245 flight was denied
was a reason given?
FAR?TRAPHX has a 50K standing waiver, and if all else fails you can always take it to FAR.
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