This will be last update before Balls. Fortunately, RCS came through and deliverd my much delayed order from April. The backup plan was to cannibalize a 38mm Blue Thunder propellant reload for the preheater grain. Thankfully, I received a delivery last week that included everything I ordered except for the 98mm casting tubes. These are not needed since I came up with the 3d printed grain.
Preparing the forward closure is the same as the 54 mm, except the preheater grain is larger and longer. In addition, instead of using a cut-down fiberglass motor casing, I was able to use the pre-cut delay grain insulator part # 03081 from RCS. I was not able to cut out an insulator for the forward end of the delay grain so instead I ordered some 38mm DMS baffle disc, part # 05404-1, which is the same fiber material as the regular insulators and is made of fish paper. After the launch, I can draw some up and use a laser cutter for the correct size. The diameter of the washer is slightly larger than the ID of the delay insulator, so I slightly sanded the OD of the washer until it fit in the insulator. This also allows the insulator to sit flush with the closure so you dont have to trim it.
Blue Thunder 38mm pre-heater grain with a 7/16 core.
The standard injector for the 98mm is a 4-hole plate with each orifice measuring 0.125. Thanks to Leland Dexter, I have a 7-hole injector plate that I am using to provide more flow since the original used boosted white lightning grains. The extra nitrous flow will make up for the lack of ammonium perchlorate in the grain. The center stem is omitted, and there are seven holes with a diameter of 0.105.
I was going to use the three grain configuration, but due to a miscalculation on my part, the assembly was too long to fit into the booster section of the rocket and seat the avionics bay completely so I have to go with the two grain version.
54mm top, 2 grain center, 3 grain bottom.
3 grain installed does not allow seating of avionics bay.
There will be two launches at Balls, the 54mm will have the paraffin / mache grain that resembles black oatmeal, while the 98mm will have the poured grain with the ABS support matrix.
Although this was supposed to be published before we left for Balls, I did not get it done in time. I’ll post the launch report and photos soon.
