L265 assembly tips

Discussion in 'Propulsion' started by jkovac, Jul 14, 2019.

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  1. Jul 14, 2019 #1

    jkovac

    jkovac

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    First CTI reload for me. Any tips from those who have flown an L265 before greatly appreciated.

    One thing I have noticed: When I test fit the reload in the 6XL case, I can only get the tailcone retainer on 2 and 3/4 of a turn with considerable effort. It goes on 2 1/2 turns OK, then another 1/4 with effort, and that's it. The CTI instructions state that the retaining ring should go on at least three turns once the reload is in the case. The CTI instructions also say it's OK for the reload to protrude up to 1/16 of an inch at the bottom of the case, which it is, but no more than that, so from that standpoint it seems like the reload does fit the case.

    Another thing I've noticed is the forward closure just sets into the top of the liner. It fell out when I took the reload out of the bag. There is a 3/16" section of the closure that inserts into the top of the liner, but no o-ring (or groove for one.) There is about a 1/32" gap between the liner and the forward closure, so maybe that's part or all of the problem. The reason for the gap appears to be the gray disk glued onto the bottom of the forward closure. It protrudes just enough from the bottom of the forward closure that it prevents the closure from seating fully, albeit by a tiny amount.
     

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  2. Jul 14, 2019 #2

    timbucktoo

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    There are some threads here where many folks recommend gluing the foreword closure in place with 5 minute epoxy. This has been recommended for 4 grains & up to help prevent any gas blow by. Have also seen others use 2 orings on both closures. I believe CTI even mentions that in instructions.
     
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  3. Jul 14, 2019 #3

    OverTheTop

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    I have taken to gluing the top end in now also. I have never had a problem but others have seen results of possible blowby and case deformation. I think the glue if worthwhile. I use BSI 30minute epoxy.
     
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  4. Jul 14, 2019 #4

    timbucktoo

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  5. Jul 14, 2019 #5

    jd2cylman

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    The gray disc is your delay/tracking smoke element.
     
  6. Jul 14, 2019 #6

    jkovac

    jkovac

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    Ok I tried an L935 load in the same case, fit perfectly. I swapped forward closures, still fit. Discovered the difference is the length of the liner. The L265 is about 3/16” longer than the L935.
     
  7. Jul 14, 2019 #7

    manixFan

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    I have flown a number of both the L265 and the L935 CTI reloads. Great motors both. As mentioned, I have started gluing in the forward closure to prevent any issues. Here's an email I got from the motor vendor I buy my motors from:

    "The bead of epoxy is to help prevent the flame from escaping between the liner and forward closure. Most people have put the epoxy on the lip of the forward closure, but there is nothing wrong with putting it on the inside of the liner. Just make sure when you install the closure, you twist it around to make sure you have a good seal.

    You could probably use grease instead of epoxy, but this is the method that Jarvis came up with. The object here is not gluing the forward closure on, but making a good seal to prevent a blow by."

    and

    "Despite telling people the object is to make a seal, not glue. I guess using epoxy equals gluing. I've seen one failure with the epoxy method. The person epoxied the forward closure on, but did not twist the closure to get a good seal. The flame found an exit point, and there went the case. He thought he was just gluing the forward closure on, and didn't bother to do the twist."

    So the main point is to make a seal, not just glue the closure in place. The other issue I've run into, as have others, is if you are using the tail cone closure, you may get some erosion on the inside of the closure. I fly those motors in MD rockets so I use the tail cone closure and have experienced the erosion. I'm going to try a layer of JB weld on my next flight to see if the helps prevent the issue.

    It is strange that the forward closure just slides into the liner, but when the motor is assembled it is firmly pressed into place. But on the longer motors the lack of a second o-ring does seem to be an issue hence the epoxy seal. I have flown at least 3 of each with good success. My best is 23,500' at BALLS a couple of years ago with a L935, and a bit less than that with the L235.

    Good luck,


    Tony
     
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  8. Jul 14, 2019 #8

    Cameron Anderson

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    I realize it's a remedy for a different problem than what's being discussed, but is anyone gluing grains into the liners with these reloads? Or is a expoxying the forward closure the only additional step for this reload?
     
  9. Jul 14, 2019 #9

    manixFan

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    Not to take over the thread, but as I have mentioned I have flown a fair number of both of these motors. I've not heard of anyone glueing in grains in these motors, only the forward closure. And as mentioned, that's more to create a seal than retain it in place.

    The only small motor I've glued grains in is the Loki K627, which has very explicit instructions on how to assemble the motor. On larger motors, especially 75mm research motors and up, glueing in the grains is pretty common. Of course one of the main reasons grains are glued in place is to prevent the casting tube from going through the nozzle, which I've never heard of being an issue with the CTI motors.


    Tony
     
  10. Jul 14, 2019 #10

    Cameron Anderson

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    The dorward closures have 2 o-ring grooves and one o-ring...I'm curious if a second o-ring would be a better solution than epoxy.

    (Pretty sure CTI says on their website that the second groove is there in case it's needed for future designs)
     
  11. Jul 14, 2019 #11

    manixFan

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    Unlikely a second o-ring would hurt anything, and could help. But the point of sealing the shoulder of the forward closure into the liner is to prevent hot gases from ever making it to the o-ring, at least until there is a burn through of the liner (which would happen very late in the burn.) So we are talking about two different areas. The o-ring on closure helps prevent hot gases from blowing past the front of the closure and possibly igniting the ejection charge or pressurizing the area ahead of the motor. The epoxy seal helps to prevent hot gases from getting between the liner and the case in both directions, both fore an aft. Also helps prevent a case bulge or burn through at that joint. At least that's my take on it.

    If you haven't read the linked thread in Post #4 above, it has a lot of great info.


    Tony
     
  12. Jul 14, 2019 #12

    jkovac

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    Thanks for the replies, everyone. Now that I know the issue is the liner length itself, I’m wondering what people think about only being able to screw the tailcone on 2 3/4 turns. 1/4 turn short doesn’t seem like a lot. The tailcone screws on the whole way - 3 1/2 turns - both with an empty case and with an L935 load in there. So I am able to get the tailcone within 3/4 turn of being fully threaded, and with 1/4 turn of what CTI says it should be with a loaded case.

    Of course the decision to fly it or not is 100% my responsibility. I’d just like to know what you guys think.
     
  13. Jul 14, 2019 #13

    Cameron Anderson

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    I'd just sand the end of the liner down some.
     
  14. Jul 14, 2019 #14

    manixFan

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    I completely understand your concern, especially since this is your first CTI reload. I hate to admit it but I've never counted the number of turns on any of my CTI reloads - and I flew 4 just a couple weekends ago. All I've ever looked at is the amount of thread that is exposed. If it's within the CTI guidelines of 1/16" I feel I am good to go.

    Do keep in mind that if you are flying with the tail cone closure, you may see some erosion of the inner edge. A motor expert that I trust thought that the retainer was a bit too long. I haven't decided what I'm going to do to mine before I fly it again. I may have it turned down a little shorter or coat the inside with some JB Weld to try and protect it. Or maybe a sort piece of sacrificial coupler.

    Maybe the best advice is to get some help when you are at the launch. Very likely you'll be able to find flyers who have lots of experience with the CTI motors and will be able to advise you on your particular concerns.

    I like the fact that you picked the 6XL case and the L265 as your first CTI reload. It's my favorite long burn motor with that 10 second burn time. I really hope your flight goes well. Keep us posted.


    Tony
     
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