Re: LOC Precision EZI-65 for level 1 cert motor choice

The "180" in 29/180 is the total impulse.
The "238" in H238T is the average impulse, in Newtons. The total impulse of
the motor is 178 Ns.
An H112J has 280 Ns of impulse and is a three grain motor for the 360 N
case.

A great, free performance calculator for rockets is wRASP
http://www.wrasp.com. Use it to simulate the launch before you fly on an
unknown configuration. Watch the "Launch Rod Velocity". If it is below 30
MPH, you do not have enough thrust to safely fly the rocket.

The 4-29ss at 29 ounces should leave a 6 foot rod at 39 MPH. If both motors
lit, then your rocket was either significantly heavier than the 29 ounces,
or it was sticking to the launch rod. Even at 50 ounces, it should have
been fine at 29 mph.



"lizardqueen" <googlwatson@xxxxxxxxx> wrote in message
news:1156881704.581425.130530@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Thank you Will,
Great answer!
Knowing the meaning of the impulse number clarifies much. I did notice
an apparent discrepancy. On the page below, an H-238T is recommended
for a 29/180 case. Am I missing something? Does it have to do with
total impulse as opposed to average thrust?

http://www.drrocket.com/sizematters.asp
Also why would I want to put a H-112J into 38/360 as recommended on the
same webpage?
I appreciate your help in this. When visiting Illinois, I recently
fired what I believe to be an underpowered loc precision 4-29ss using
two F20-4Ws, which was a little scary and embarrassing - not to mention
costly! (lost airframe tube, and transolve beeper) No one was harmed;
the crowd enjoyed it, but... I will NOT repeat it! I needed to do the
math :-(
BTW, I took a look at your page, spaceflightsoftware.com. I'm located
near Berkeley, and will be checking out lunar.org, which seems to be
the only rocketry club in the area.
Anyway-Thanks-Laura



Will Marchant, NAR 13356, Tripoli 10125 L3
kc6rol@xxxxxxxxx http://www.spaceflightsoftware.com/will/



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