Rattworks H and I Motor Reload Tutorial


These are the tools you might need to load a Rattworks motor.


A space for the electric matches need to be made in the preheater grain.  Shown is one method using a drill on low speed to drill a pair of holes. Alternately you could use your razor knife or pocket knife to do the same thing.  I install two electric matches to increase my chances of the preheater grain igniting, some folks only use one.  Taking the rocket off the pad and disassembling the motor is a major pain in the patoot so the second match is cheap insurance. 


Slice the preheater grain to receive the fill line. Shown is an Aerotech 38mm delay grain which is BlackJack propellant.  They're cheap and they work. The manufacturer recommends an Aerotech D White Lightning motor sliced into 3/8" chunks for this purpose but I say why ruin a perfectly good solid motor when the preheater grains work so well and it's something you often have kicking around in the range box. 


This is what the slice of propellant looks like prior to
installing the ematches.  

Select 2 electric matches with long enough leads to extend outside the combustion chamber.  Shown are homemade dipped matches made from 28 gauge telephone wire twisted with a cordless drill.


Install the electric matches so the heads are flush 
with the forward end of the preheater grain.


Insert the fill tube so about 3/4" of tube extends 
beyond the preheater grain as shown above. 


Tape the preheater grain closed.  This is about half a turn of masking tape.


Match the fill tube/ematch assembly up to the motor grain.
Mark the filler tube to indicate where the assembly will
poke out the nozzle once completely assembled. 


Wrap the assembly with teflon tape.  This is the most important trick and it guarantees that the 
motor will light at the head end and burn the fill tube off right at the injector.  If the fill tube
burns off at a place other than the injector only part of the motor grain will be burning  which
will substantially reduce the performance of the motor. 

This is something I came up with after having the tube burn off at the wrong spot resulting in the motor performing in less than nominal fashion.  Some wag named it the "Fortune Sheath" but that sounds to much like a DIY prophylactic for my taste. heh


Continue wrapping the tape to the mark you made on the filler tube.
Make sure the ematch leads are on opposite sides of the fill tube and keep 
the tape as tight as possible.  The first time is a bit difficult as all the parts
want to flop around but once you figure out a system it's not that difficult.
In lieu of teflon tape you can also use a brass tube to protect the filler line.  
Slide the tube over the assembly and butt against the preheater grain. 


Install the collar and little sleeve (called an olive) on the fill tube.



Install the assembly on the floating bulkhead.  

DO NOT TIGHTEN COLLAR AT THIS POINT !

Notice the gap between the preheater grain and the floating bulkhead?
This is not good so the tube must be trimmed to fit ........ 



........ like this.  Snip off as much filler tube as necessary to ensure the preheater 
butts up directly to the injector collar.


This is what the finished assembly should look like.


Lubricate the O-rings with a teflon (PTFE) based lubricant.   
Krytox (PTFE) grease is recommended by the manufacturer. Here I'm using a teflon spray, you can use the MCG111 grease shown in our lubrication section.


Insert a 5/16" Allen wrench into the floating bulkhead.
Make sure the filler tube seats tight to the injector.  
Tighten the collar on the injector, this crimps the litlle metal
sleeve making it unusable for future motors.  Additional
sleeves are provided in each reload kit. 


Install the graphite nozzle into the phenolic collar.  The convergent sections
faces into the grain and is indicated by having a gentler slope than the divergent 
nozzle section. 


Install the O-ring on the shoulder of the nozzle.  Lubricate with
suitable grease.   MCG111 grease, Vaseline, silicone grease or other suitable lubricant.


Inspect the grain to determine which side the preheater
fits into.  This is indicated by a deeper shoulder turned in the grain.  
You can feel the differences in depth with your finger. 


Thread the ematches and filler tube assembly through the grain.


Thread the nozzle, convergent section first, onto the filler assembly.


Insert the floating bulkhead and nozzle into the grain.


Install the grain in the motor tube.  
Lubricate the grain and tube prior to installation to make things slide and clean up easier.  
The PTFE spray works great for this. 


Here is the nozzle poking out the tube.  Be gentle with the nozzle since
graphite fractures fairly easily.  Let the aft motor tube collar do the remainder
of the tightening. 


Thread the aft collar onto the filler assembly.


Tighten the collar hand tight.


Check the forward tank end to ensure it is tight.  There should be no gap between the 
tank end and the motor tube.  This O-ring comes pre-lubricated from the manufacturer
though if disassembled it should be greased prior to reassembly.


Here is the completed motor with a dowel that is long enough
to push the floating bulkhead and grain out of the tube.  This is a 1/2" dowel and 
should be included with your flight equipment. 


To remove the motor, unscrew the forward tank end and the aft motor collar.
Insert the dowel and push the floating bulkhead out the aft end. 



This is the whole unfired assembly. 

If you have any questions feel free to drop me a line! 



 

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