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  1. #1
    Join Date
    10th February 2013
    Fremont, CA

    Cracked phenolic liner in I59WN

    Assembling an Aerotech I59 long burn motor last night I realized, after I had epoxied the big grain into the phenolic liner per instructions, that the liner was cracked through about 2" beginning at the nozzle end. I went ahead and finished the assembly making sure to liberally grease the outside of the liner as it slide into the 38/480 case.

    What are the likely ramifications if I launch tomorrow given an 8 second burn. Does this deserve a green, yellow or red flag?


  2. #2
    Join Date
    9th July 2014
    Phoenix, AZ
    RED ALERT! Even hairline cracks can cause a cato. If the crack is as large as it sounds, I wouldn't even think about putting it in a case, let alone a rocket.

  3. #3
    Join Date
    18th March 2009
    Do not fly this motor! Either contact the dealer or Aerotech directly for a replacement reload.

    Sent from my iPhone using Rocketry Forum
    Mark Koelsch
    Tripoli 6155 L3
    Owner of
    Editor of
    Member of the Tripoli Motor Test Committee, and keeper of the motor file

  4. #4
    Join Date
    22nd September 2017
    The liner is the thermal protection system for the aluminum casing containing the pressure. The engineers did not design it overbuilt for a liner crack fault. The system has a safety factor for the metal casing, but the thermal liner is not designed in that way as it is a disposable item. When a crack is in the liner it exposes the raw 6061T6 casing wall to a tremendous heat loading at a single concentrated spot then the material fails at the crack point in liner when the casing pressurizes. This isn't your daddy's air compressor. It's got 800-1000 psi and enough thermal loads to melt a lot of lesser materials. Even aluminum 6061T6 aircraft grade alloy is less strong at higher thermal loads. That is why the liners need to be flawless.

    Do not fly until liner is replaced. Inspect the fuel grains for cracking. Check nozzle for defects too. Contact Aerotech.

  5. #5
    Join Date
    22nd September 2017
    I also noticed apogee was selling a different forward closure specifically for the I-59WN reload. Make sure you have the correct closure too. Improper inspection, assembly, fuel grain or liner defects, ignition position ,and hardware configurations will all cause CATOS.

    The advantage of the Aerotech system is you had the chance to spot the defect vs CTI sealed reloads.

  6. #6
    Join Date
    26th November 2009
    Ditto, Contact the vendor although they might argue you did it from rough handling me suspects they'll give you the benefit of the doubt and replace it for good will.
    Don't fly it until you get a new liner. Kurt

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