Giant oneStatic test of 110mm motor (N class)

[QHarryQ]

First of all,I'd like to apologize for my humble English.I am new here and would like to introduce myself at first.I'm a high school student from China and have great interest in rocketry.Since the first time in 2011 I had flown a small rocket powered by black powder motor,I have designed and built many motors and rockets,and some of them work really well.One of my largest motor（L-DX 2139） is 75mm in diameter and provides a impulse of 4080N·s（categorized as mid L class）.The L-DX 2139 is designed as the first stage motor of my rocket(Super-QH),which is expected to reach an apogee of more than 6km(20000 feet).This rocket will be launched in July this year.

The motor I introduce today is a giant one ,which is 110 mm in diameter and 1.5m in legth,and is one of the most powerful solid amatuer motor built in China.My friends,all of them are students in high school and colledge,built it in 2012.This motor is supposed to power a rocket 3m long,and the apogee is predicted 4.6km(15300 feet).I am told that the rocket will lauch soon,maybe in a couple of weeks.

More details of this motor----

inner diameter 110 mm
chamber length 1400 mm
nozzle diameter 24 mm
propellent RNX with 3% DOS
propellent mass 17.25 kg(39.57lb)
total impulse 14837.02 N·s
thrust time 7.5s
average thrust 1978 N(444.5lb)
maximum thrust 3977 N(894.9lb)
specific impulse 94.66 s
max chamber P 7.072 MPa
material 40Cr steel

The 40Cr is a very common material in market with a low price and pretty good qualities.It is more safe to build a rocket with 40Cr rather than 45# or A3 steel.Compared with 6061,it can stand more pressure but much heavier.This rocket is designed to stand much higher pressure(70 Mpa in fact,about 10 times of the predicted pressure 7MPa) for safe.
View attachment 118066

Details about propellent grains---

exposed area core and ends
core type Pseudo-Finocyl
number of segments 6

This type of core is kind of special and not usually used in amateur motor for it is difficult to handle at home.With the help of CNC,my handle it pretty well.Compared with the ordinary round shape core,the
Pseudo-Finocyl type provides a much bigger burning surface and is suitable for low-burn-rate propellent like RNX.
View attachment 118067


THE STATIC TEST
The static test stand used for the motor static test is supposed to record the thrust and chamber pressure with respect to time precisely.The maximun designed thrust is 750kg,and any thrust above 750kg may cause damage to the weak electronic component.

The picture of the same static test stand used in test of 75mm RNX motor---


Link of the static test video!!!---
https://v.youku.com/v_show/id_XNDI0ODY4MzQ0.html

Screenshots of the static test video-


PERFORMENCE
The following picture shows a plot of the measured thrust and chanber pressure with respect to time.


class N
propellent mass 17.25 kg(39.57lb)
total impulse 14837.02 N·s
thrust time 7.5s
average thrust 1978 N(444.5lb)
maximum thrust 3977 N(894.9lb)
specific impulse 94.66 s
max chamber P 7.072 MPa