This is my preferred assembly method for the micro hybrid.
1) If using a paper fuel grain ensure that it fits into the motor casing, some paper fuel grains require either a wrap removing or sanding.
2) Wrap the ISI Nitrous Oxide bulb with masking tape to make it a snug fit inside the motor casing.
3) Grease the two large O’Rings with a Nitrous safe grease such as Krytox.
4) Prepare the Piercing unit / injector and injector housing as follows:
a) Place a pre-heater grain in the pre-heater well (the shallow but larger diameter well) this can be an Aerotech D24 fuel grain with the outer paper pealed off and inserted into the pre-heater well and then trimmed flush with the top of the well. Ensure the slot in the fuel grain extends over the hole through the center of the housing, if it does not then drill a hole through the center of the pre-heater; this is best done from the front of the housing.
b) Into the piercing unit well of the injector housing insert a burst disk followed by small O’ring and the injector, the injector should be positioned with the flat side against the O’ring and the point facing out.
5) Assembly is started at the forward end of the motor by inserting the forward inner circlip.
6) Put in the T-nut with the threaded section forwards and the flat to the rear (inside).
7) Insert the ISI nitrous bulb rounded end forward, do not push all the way in leave the neck of the bulb protruding for the moment.
8) Holding the casing vertically forward uppermost at all times until instructed otherwise (or you may move the injector / piercing unit. Place the prepared injector housing under the ISI nitrous bulb and gently insert it in to the rear end of the motor housing. Be very careful not to dislodge or move the injector on its O’ring.
9) Insert one of the pre greased O rings into the rear of the motor housing so it is against the injector housing.
10) Insert the fuel grain and slide all of the way in, until the T-nut is against the forward circlip keeping it pressed in place you can now turn the whole assembly over.
11) Insert the second large O’ring into the motor housing and place it against the end of the fuel grain
12) Insert the nozzle so that the O’ring will seat into the grove in the forward face of the nozzle.
13) Insert the rear circlip ensuring it is properly seated in the groove.
14) Lastly insert the outer circlip into the grove at the rear of the motor housing.
15) Insert an igniter through the nozzle so that it touches the pre-heater grain and secure in place.
Just before you are ready to launch your rocket arm the Nitrous by tightening the arming bolt, there may be a slight his as the bulb seals over the injector, the his should stop as you finalise tightening the bolt, do not over tighten the bolt or you may damage the O’rings.
If you have a miss fire then holding the motor at arms length (wear suitable gloves for handling Nitrous) loosen the arming screw slightly until the Nitrous start to escape from the front of the motor casing.
After Firing the motor be careful as the motor casing and internal components
may be hot.
The Micro Hybrid is the smallest available hybrid motor, it is classified as an experimental motor as it has not been put forward for certification by NAR or CAR. The Microhybrid uses 8g cream whipper nitrous oxide chargers as the source of oxidiser and a solid tubular safe fuel grain of varying materials from paper through different plastics and composites...
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