5" Motor Page 1

Click Here for Page Two.
 

Our 5 inch two grain motor is coming together! The bulkhead has a well for a tracking smoke grain. We had to cut the nozzle washer from a sheet of 6061 aluminum using hole saws (5" and 3.5") and cleaned it up on the lathe. The nozzle is from the threaded base of a very big electrode, it is pictured with 38 MM and 75 MM nozzles for scale. The 1.25" x 11" Delrin mandrels are cut and polished and the casting bases are made.

As soon as our orders for snap-rings get here we will  test fire it! It sims at 6500 N-sec, M1300 with a 5 second burn. More photos and static fire/launch reports coming soon.
     

We did not have any cap plugs and the right sized ones are not listed in their catalog, so we cut disks with the circle cutter from some 1" plastic to the OD size of the casting tube. Then drilled the 1 1/4" hole for the mandrel. Chucked them in the lathe and cut a 1/8" step in the top edge so the casting tube just slips on, maybe able to cut it by readjusting the circle cutter and making the step without the lathe.
 

To use them we cut the casting tubes to length, slip them over the step and tape together with masking tape. It works great, the grains have a 1/8" of casting tube sticking out on one end so they are self spacing.
 

 
The motor parts and it loaded from both ends. We added a recovery ring to the bulkhead and the bulkhead insulating disks are made from Formica sheet (like used on counter tops) works great.
 
It simed to a M1400, 6100 N-sec, 4.3 sec. burn. Shortly after ignition the nozzle broke (in the air in the first photo) and it burned for about 5.5 seconds. We believe there were two failures;

First the case was cut for a steel nozzle holder with a 3" graphite nozzle and we found a cheep source for big graphite so we made a very deeply stepped nozzle that failed.

Second we failed to take the Iron Oxide raising the thrust and pressures into account, leading to over pressurizing.   

We are having two 3 grain cases cut and we have a 4 and 5 grain cases, so all is not lost, we can't give up we have rockets built to fly on them! ... :-)