With the untimely demise of the T-2 motor. I decided to get to work on a replacement. I really liked the T-2 motor, it had proven very reliable, and was a nice mid power motor to test new propellants, as well as launch rockets at a relatively low altitude for testing. There wasn't a lot to be changed. The T-2 was destroyed on a launch attempt. I believe the problem was not enough chamber length, in other words, the grains fit in the motor casing to tight. Another problem may have been the RTV I used to seal the nozzle after the grains are in the motor. I think a thin bead of the RTV may have pushed up the casing wall as the nozzle was inserted, and with the long grains the bead of silicone actually sealed to the bottom grain. That would have increased the problem of gases not being able to get behind the grain, causing the grains to pressurize from the inside, and cracking them. The cracked grains greatly increased the burning surface area, resulting in over pressurization of the motor casing.
So two changes were made. First, the casing internal length was increased to give the grains more spacing. Second, I put an o-ring groove in the nozzle so I don't have to use RTV to seal the nozzle. I guess another change is I welded the forward closure in place, the old T-2 used screws to retain the forward bulkhead. I have been using the welded bulkhead in all my recent designs.
Above is a picture of the completed T-4 motor.
Here are some of the dimensions:
Nozzle Throat Diameter: .42"
Convergent Cone: 60 degrees
Divergent Cone: 30 degrees
Exit Cone Diameter: 1.04"
Expansion Ratio: 6.1:1
Casing Material: 1 1/2" EMT (mild steel)
Casing Thickness: .065"
Casing I.D.: 1.62"
Casing O.D.: 1.75"
Casing Length: 13.5"
Forward Bulkhead: .3" Welded Mild Steel
Nozzle Retension: (8) 10-32x3/8" Machine Screws
The T-4 has had its first static test.