Quick answer
Assemble the AeroTech L900DM-PS reload kit by carefully installing the forward seal disc, stacking propellant grains, and verifying delay grain fit. This guide walks through each step for the RMS-75/5120 system.
Why the forward seal disc matters
The L900DM-PS reload requires installing a forward seal disc (75FSD) during assembly. This disc prevents hot gases from bypassing the propellant and damaging the motor case. Forgetting or misaligning it can lead to case failure. Take your time to seat it squarely against the forward closure.
Grain stacking order
The reload uses a specific grain stacking order to achieve the L900DM-PS burn profile. The 'DM' designation indicates a dual-thrust motor with a fast initial burn followed by a sustained phase. Stack grains exactly as shown in the included instructions—reversing or skipping a grain changes thrust timing and may cause unstable flight.
Delay grain fit check
The delay grain must slide freely into the delay housing without binding. If it fits too tightly, lightly sand the outer surface with fine grit paper. A stuck delay grain can cause early or late ejection, risking parachute deployment issues. Always test fit before final assembly.
Step-by-step assembly
- Inspect hardware: Check the RMS-75/5120 motor case, forward closure, aft closure, and nozzle for any cracks, burrs, or debris. Clean threads with a nylon brush. Never assemble with damaged hardware—replace any suspect parts.
- Install forward seal disc: Place the 75FSD seal disc into the forward end of the motor case, flat side toward the forward closure. Ensure it seats evenly against the case wall. A tilted seal disc can cause gas blow-by. Verify it sits flush before proceeding.
- Stack propellant grains: Insert propellant grains in the order specified in the reload instructions. Use the supplied spacers between grains if called for. Do not force grains—they should slide in with light hand pressure. Reversing grain order alters thrust curve. Double-check the sequence against the data sheet.
- Install delay grain and ejection charge: Slide the delay grain into the delay housing. Confirm it moves freely. Add the ejection charge (black powder) as specified. Attach the forward closure. A tight delay grain may need light sanding. Test fit before adding ejection charge.
- Torque closures: Use a torque wrench to tighten the forward and aft closures to the manufacturer's specification (typically 15-20 ft-lb for 75mm hardware). Do not overtighten. Overtightening can strip threads or distort the case. Follow the torque spec exactly.
- Perform continuity check: With a multimeter, verify continuity across the igniter leads. Install the igniter into the nozzle and secure with the provided retention clip. No continuity means a bad igniter or poor connection—do not fly until resolved.
Product facts
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AeroTech L900DM-PS RMS-75/5120 Reload Kit (1 Pack) - 12900P: The AeroTech Reloadable Motor System RMS is an aluminum cased reusable motor in kit form that is assembled by the user. You will need AeroTech RMS-75/5120 motor hardware to build and complete the motor. This reload kit is not a standalone motor—you must already own or purchase the RMS-75/5120 hardware set to use it. Plan your budget accordingly.
AeroTech L900DM-PS RMS-75/5120 Reload Kit (1 Pack) - 12900P
