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  1. #31
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    Quote Originally Posted by DavidMcCann View Post
    I find it hilarious when people say something is "military grade" or the "military uses it" like thats some kind of proof it's a good idea. Haven't spent much time working for the gov't, have you?
    I wasn't saying it was proof that it's a good idea. I was saying that hobby rocketry had no say in the design. CTI made it that way for someone with deeper pockets and much larger orders. IF the military contract decides to change the design, I'd bet that the hobby ones would (strangely enough) follow suit. And yes, I've worked for the gov't and have seen exactly what you're implying.
    -Ken


  2. #32
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    Quote Originally Posted by Handeman View Post
    Didn't Myth Busters have an episode where they used Tomahawk booster rocket motors to test stopping a run away trailer. If I remember right, it was a huge failure.

    It might have been the Rocket Battles(?) that used a pair of Tomahawk booster to launch Mini Coopers up a ramp and tried to drop them on a target. That didn't work so well either.
    I think they strapped on a couple JATOs to the roof of the car.

    Edit: Found it! Fun episode.


    Last edited by mccordmw; 13th October 2017 at 03:40 PM.
    Mark
    NAR#: 100890 / TRA#: 16580
    L1 - Binder Design Excel Plus 38 - CTI I242 2,540'
    L2 - Binder Design Excel Plus 38 - CTI J330 3,672'
    L3 - Scratch built 8" PAC-3 MSE Patriot - Loki M1969 (ETA MWP 15)

  3. #33
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    Smash Lab did the motors on a run away trailer. Motors made by Jerry Irvine. Scroll down on website: http://www.usrockets.com/
    _______________________
    Jeff - NAR #76531 -L2

  4. #34
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    I've found on my cti motors that it is good/wise to pull the forward delay element off, remove the paper cap and be sure the powder is loose and fresh and there is no clogging of the delay hole, I've had a failure where there was some rubbery material that blocked the hole so that the delay didn't ignite the powder, even though powder was loose. I've also found where powder was all caked together. I think it's a good idea to check the rear o-ring as well before flying.

  5. #35
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    SEDS group had a H123W Skidmark CATO. Group member forgot to replace an O-ring. Plastic f-ing retainer by CTI we hate. We've also used AT 38/480 hardware. The casing closures on AT motor are both aluminum 6061T6 and are threaded, none of the thin plastic toy feeling too it. I went with Aerotech 38/480 for my L-1 cert and never looked back, cleaning is a pain compared to CTI, assembly a few steps longer, and more O-rings, and a seal disk, but build quality is more robust. I'd highly recommend any 38mm Aerotech casing over a CTI one. CTI offers way better 29mm reload selection than AT in my opinion, but the 38 selection from AT with a beefier casing outweighs CTI options.

    There's a 38/720 AT casing I'm eying for an L-2 build. I wouldn't call that CATO proof, but if you do your part it'll function, do what the manual tells you to do on assembly, take your time, and its just beefier than CTI stuff. It's like with an aerotech casing you take your time versus a CTI you slap the core into it then cuss when it explodes. Lol.

  6. #36
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    Quote Originally Posted by new2hpr View Post
    I wasn't saying it was proof that it's a good idea. I was saying that hobby rocketry had no say in the design. CTI made it that way for someone with deeper pockets and much larger orders. IF the military contract decides to change the design, I'd bet that the hobby ones would (strangely enough) follow suit. And yes, I've worked for the gov't and have seen exactly what you're implying.
    -Ken
    fair enough. Personally I just avoid them.
    David McCann
    Dave's Rockets | My Flights
    URRG |URRF 4| Level 2 | TRA# 14210

  7. #37
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    I will also say that I've never had a cti reload that was simple push out and put a new one in, they all left sticky very tough to remove goo from the burned through liners that I had to use a stick to get out, but I've only flown moonburners....I'm just saying there was no advantage for cleanup for me in the loads I've flown compared to aerotech. However Aerotech didn't offer a load in that range so that's why I went with it.

  8. #38
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    Quote Originally Posted by burkefj View Post
    I will also say that I've never had a cti reload that was simple push out and put a new one in, they all left sticky very tough to remove goo from the burned through liners that I had to use a stick to get out, but I've only flown moonburners....I'm just saying there was no advantage for cleanup for me in the loads I've flown compared to aerotech. However Aerotech didn't offer a load in that range so that's why I went with it.
    on a 29mm 3 grain case, I flew two motors one day, an H54R, and an H133BS. The H54R is a moon burner, and stuck a bit. the H133BS slid right out. Not a bad system in 29mm, I liked it. I did sell my cases eventually, the price on AT and the ability to ship without hazmat trumped the slick design and variety of the CTI. I also prefer AT greens.

    David McCann
    Dave's Rockets | My Flights
    URRG |URRF 4| Level 2 | TRA# 14210

  9. #39
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    22nd September 2017
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    The forward seal disc on the CTI is easier to remove and dispose in 29mm line than say cleaning the AT 38MM forward closure which has a delay grain separately inserted behind a seal disc rubber then another forward seal disc behind that with a thicker o-ring then the propellant grains inside a liner followed by a big o-ring, sometimes a rubber buffer, a nozzle, and a metal closure. You only need an AT delay tool if you aren't happy with the timing of the factory fuse. If you really need to time an AT, seal the forward closure and electronically time a hotter 1299N-P WARP 9 load or any other N-P type variant load with a separate deployment charge you make yourself. The pressures seem way higher than CTI and the casing design reflects that. I would not want to install a forward seal disc backwards on a AT casing or forget an O-ring. In cold weather loosen the closures before flight while storing say overnight, then tighten before flight to protect O-rings. Nearly every o-ring in AT gets lubed and don't lube the delay grain unless its a plugged motor reload. Helps to lube outer liner for removal. You also manually add you deploy charge and tape the forward closure shut on an AT, its not auto contained like some CTI motors are.

    Sorry if I whine about AT, its not hard to use, but more thought than a CTI. Loki also offers very nice motors similar to AT casing design with reuseable nozzles vs. AT single use nozzles/O-rings contained in reload kits, but their prices are even higher. Prices were more expensive with AT so I see why there is attraction to CTI, plus CTI has a lot of variety even though a lot of propellants seem milder.
    Last edited by Andrew_ASC; 13th October 2017 at 10:20 PM. Reason: Memory fault.

  10. #40
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    umm, in AT cases you stick the forward seal on the top of the liner before you install the liner in the case. If it falls off, you tried to do it backwards (it's impossible to mess up this way)
    David McCann
    Dave's Rockets | My Flights
    URRG |URRF 4| Level 2 | TRA# 14210

  11. #41
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    Quote Originally Posted by DavidMcCann View Post
    The behavior on the left reflects what I saw in an H118 four grainer go wrong and also an H123. One of the H118's that worked had a visible "indented" ring about an inch lower than the forward closure area. The Aerotech liners never exhibited that behavior that these CTI liners do. The aerotech liner removes without any indentions post flight, every time. Two tested no problems. What we disliked about CTI was out of four reloads two had problems.

  12. #42
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    Quote Originally Posted by DavidMcCann View Post
    umm, in AT cases you stick the forward seal on the top of the liner before you install the liner in the case. If it falls off, you tried to do it backwards (it's impossible to mess up this way)
    Yeah the liner catches the lip of the forward closure through an extension and diameter reduction designed into the forward seal disc and seals with o-ring included in reload kit.

    I haven't tried to install one backwards yet. I edited my post. I guess if one real dense knucklehead forgot the real thick aft o-ring that would give enough room to install the forward seal disc backwards, but it would be very very hard to do on accident without pieces falling everywhere. Just speculating a bit. That's the only flaw I can think of about an AT where in a CTI is wasn't as many separate pieces.

  13. #43
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    Quote Originally Posted by Andrew_ASC View Post
    SEDS group had a H123W Skidmark CATO. Group member forgot to replace an O-ring. Plastic f-ing retainer by CTI we hate. We've also used AT 38/480 hardware. The casing closures on AT motor are both aluminum 6061T6 and are threaded, none of the thin plastic toy feeling too it. I went with Aerotech 38/480 for my L-1 cert and never looked back, cleaning is a pain compared to CTI, assembly a few steps longer, and more O-rings, and a seal disk, but build quality is more robust. I'd highly recommend any 38mm Aerotech casing over a CTI one. CTI offers way better 29mm reload selection than AT in my opinion, but the 38 selection from AT with a beefier casing outweighs CTI options.

    There's a 38/720 AT casing I'm eying for an L-2 build. I wouldn't call that CATO proof, but if you do your part it'll function, do what the manual tells you to do on assembly, take your time, and its just beefier than CTI stuff. It's like with an aerotech casing you take your time versus a CTI you slap the core into it then cuss when it explodes. Lol.
    I would guess I have flew at least 100 CTI 38mm reloads and I think maybe I have had 2-4 failures. Jeron from CTI bless is soul told me years ago almost all the liner shrinkage happens well after motor burn out from the heat build up.
    TRA 2225
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  14. #44
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    I find it amusing (and bothersome, sometimes) how many AT vs. CTI threads there are in the history of TRF. That is not to mention the occasional other vendors thrown into the pot. The thing we ALL need to remember is that we live in a very tiny marketplace of motor vendors. Everyone may have their preferences, but dogpiling on a vendor, especially one that may be having temporary setbacks, threatens the availablity of motors for everyone. Some can remember the Aerotech fire, the exit of Ellis, AMW (the original, not AMW-ProX), etc. When some had issues, others stepped in to fill the gap.

    For convenience, buy what your on-site vendor offers. Helps with CATO claims too. If I could, I'd fly every vendor. As is, I've got a pretty even mix of AT and CTI from 24-54mm. I choose the motor for the best flight profile fit, regardless of brand. Exceptions are when I need critical ignition, I'll use AT Blue Thunder or any CTI with the ignition pellet.

    Moral of the story, show your failure, get ideas what happened, get help from your vendor on resolution, fly again. Don't bash or we risk losing selection. If we only had one manufacturer, can you imagine how much they could charge?
    -Ken

  15. #45
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    Quote Originally Posted by new2hpr View Post
    Moral of the story, show your failure, get ideas what happened, get help from your vendor on resolution, fly again. Don't bash or we risk losing selection. If we only had one manufacturer, can you imagine how much they could charge?
    -Ken
    Well, as history has also shown, when one goes down, others step in. I don't think we'd ever have one option for long.

    Open discussion of flaws helps everyone. I'd bet 99% of CTI rear closure failures are user generated. So discussion of that can help reduce some. AT has issues too. The G1338T is the proverbial 5 pounds of manure in a 4 pound bag.

    As for liners and the condition they come out in...well they're a sacrificial part for a reason. all my AT liners in the 29 40-120 case cook through one side (they're slot burners, duh) The convolute in the larger motors obviously does better, but I don't see issues with CTI's liners other than a little clean up...which all motors need. They protect the case during burn, mission accomplished.
    David McCann
    Dave's Rockets | My Flights
    URRG |URRF 4| Level 2 | TRA# 14210

  16. #46
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    Since I pretty much only fly 29mm anymore, none of this matters to me. I like both and fly both. The CTI 29mm motors are a lot of fun and I have burned a heck of a lot of them over the years and plan to keep it up. Just not a fan of the 38's although the I212 is a great motor for my Minnie Magg.
    Jarrett Dorough

    Most people are average

  17. #47
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    .. double post
    Last edited by Len B; 14th October 2017 at 07:22 AM.
    Len Bryan
    CAR-ACF S620 L3, NAR 98782 L2, Tripoli 10220 L2

  18. #48
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    Quote Originally Posted by Nytrunner View Post
    Really? Which type of cruise missiles? I believe Tomahawk boosters are substantially larger than 6"
    Well, I can see it on their website. www.cesaronitech.com/solidrocket.php
    Name:  solidrocket1.jpg
Views: 194
Size:  25.3 KB
    This could actually be the image and that jives with their story about the affordable weapon system.
    Click image for larger version. 

Name:	ORD_Affordable_Weapon_Missile_Boost_lg.jpg 
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ID:	330021
    Len Bryan
    CAR-ACF S620 L3, NAR 98782 L2, Tripoli 10220 L2

  19. #49
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    I don't know what planet you folks live on, but on my planet the CTI 38 load almost never fail. I have flown HUNDREDS of them, I sold them for Giant Leap for over 5 years and sold THOUSANDS of them. The number of CATOS you can count on one hand. Everytime someone post something about a pro 38, the same sorry souls chime in with this bad design crap. Give me a break. If you don't like them, don't buy them. I fly Aerotech, Loki and CTI. I like them all. They all have good and bad points, but flying is the name of the game. My advise to you folks is to sell your CTI stuff and buy something that will make you happy. Because if you are not having fun, you need a new hobby. Alot of new folks read this crap and if they did not know better would think CTI is junk. That is not fair to CTI, the DR. himself, and all the fine folks who work their tails off supplying this hobby from up north. End of rant.... Tim Thomas L3

  20. #50
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    Quote Originally Posted by cerving View Post
    I'd be willing to bet that the military wasn't reusing the casings, either... they probably treated it as a on-time use motor. Given their likely use, they probably didn't expect to get it back in one piece.
    My thoughts exactly. The military is not reusing them- treated as a small, single use type of deal.

    I think reengineering them with a metal rear closure would be a fine idea.


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    Mark Koelsch
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  21. #51
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    Quote Originally Posted by lawndartman View Post
    I don't know what planet you folks live on, but on my planet the CTI 38 load almost never fail. I have flown HUNDREDS of them, I sold them for Giant Leap for over 5 years and sold THOUSANDS of them. The number of CATOS you can count on one hand. Everytime someone post something about a pro 38, the same sorry souls chime in with this bad design crap. Give me a break. If you don't like them, don't buy them. I fly Aerotech, Loki and CTI. I like them all. They all have good and bad points, but flying is the name of the game. My advise to you folks is to sell your CTI stuff and buy something that will make you happy. Because if you are not having fun, you need a new hobby. Alot of new folks read this crap and if they did not know better would think CTI is junk. That is not fair to CTI, the DR. himself, and all the fine folks who work their tails off supplying this hobby from up north. End of rant.... Tim Thomas L3
    Tim
    At the last WOOSH launch a guy was going for his L2. Complete motor failure right off the rail. Motor case was found burn in half. It was a AT motor guess what he forgot to use this tube that comes with the reload kit the liner. He thought it was just for protecting the grain in shipment. I to have only seen a very few Pro38 failures and not very many at all of case failures.
    TRA 2225
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  22. #52
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    Quote Originally Posted by markkoelsch View Post
    My thoughts exactly. The military is not reusing them- treated as a small, single use type of deal.

    I think reengineering them with a metal rear closure would be a fine idea.


    Sent from my iPhone using Rocketry Forum
    The point is (again): The military won't pay for a reengineered metal closure. The military likely buys far more of them than the hobby rocketry community. They decide. You get to live with their choice or fly something else.

  23. #53
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    Quote Originally Posted by lawndartman View Post
    I don't know what planet you folks live on, but on my planet the CTI 38 load almost never fail. I have flown HUNDREDS of them, I sold them for Giant Leap for over 5 years and sold THOUSANDS of them. The number of CATOS you can count on one hand. Everytime someone post something about a pro 38, the same sorry souls chime in with this bad design crap. Give me a break. If you don't like them, don't buy them. I fly Aerotech, Loki and CTI. I like them all. They all have good and bad points, but flying is the name of the game. My advise to you folks is to sell your CTI stuff and buy something that will make you happy. Because if you are not having fun, you need a new hobby. Alot of new folks read this crap and if they did not know better would think CTI is junk. That is not fair to CTI, the DR. himself, and all the fine folks who work their tails off supplying this hobby from up north. End of rant.... Tim Thomas L3
    Amen, Tim!

  24. #54
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    Quote Originally Posted by lawndartman View Post
    I don't know what planet you folks live on, but on my planet the CTI 38 load almost never fail. I have flown HUNDREDS of them, I sold them for Giant Leap for over 5 years and sold THOUSANDS of them. The number of CATOS you can count on one hand. Everytime someone post something about a pro 38, the same sorry souls chime in with this bad design crap. Give me a break. If you don't like them, don't buy them. I fly Aerotech, Loki and CTI. I like them all. They all have good and bad points, but flying is the name of the game. My advise to you folks is to sell your CTI stuff and buy something that will make you happy. Because if you are not having fun, you need a new hobby. Alot of new folks read this crap and if they did not know better would think CTI is junk. That is not fair to CTI, the DR. himself, and all the fine folks who work their tails off supplying this hobby from up north. End of rant.... Tim Thomas L3
    Tim, what an over the top rant. All manufacturers have had issues including CTI. I have seen a bunch of 38mm CTI motors pop the forward closure- sure it is a known issue, but a real issue nonetheless. I have seen other issues as well. That does not mean I am saying do not buy or fly CTI. They make some really nice motors.

    That said, I really would prefer a metal rear closure. Metal on metal threads are better than metal on plastic.


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    Mark Koelsch
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    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Keeper of the motor files

  25. #55
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    Quote Originally Posted by gfunk View Post
    These will be a bittersweet consolation prize at next week's elk hunting camp fire.

    The partially burned blue streak fuel grain disposal was just as good as I'd hoped!

    TRA 17281
    L1: 9/16/17, 4" Blue Angels Super DX3 - I345

  26. #56
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    Quote Originally Posted by DavidMcCann View Post
    threading plastic into metal is just a bad design. seen it many times, some day multiple times in a day. There's a reason they moved to a metal closure when they made the 29's. No idea why they didn't fix the 38's back then too.

    Loki and AT make nice 38's.
    I'd say that either the plastic material was not strong enough to support the load with the smaller area available, or that it was cheaper to produce.


    Quote Originally Posted by markkoelsch View Post
    Tim, what an over the top rant. All manufacturers have had issues including CTI. I have seen a bunch of 38mm CTI motors pop the forward closure- sure it is a known issue, but a real issue nonetheless. I have seen other issues as well. That does not mean I am saying do not buy or fly CTI. They make some really nice motors.

    That said, I really would prefer a metal rear closure. Metal on metal threads are better than metal on plastic.


    Sent from my iPhone using Rocketry Forum

    I'm not sure where this idea of plastic threads being bad comes from? It seems all the failures mentioned so far are due to either the forward closure issue (that was a material supply problem according to CTI) or from rear seal failing which then burns through the closure. If the o-ring fails it does not matter if the retainer is plastic or metal, it's highly likely it will fail during the burn. The plastic is a weaker material naturally, however it is replaced every use. Metal retainers are used every time you use the case. To the mentions of cross threads, yes that takes the one reload off the table (which hopefully the vendor or CTI would help with if informed), however if you cross threaded a metal retainer it's more than likely you would destroy the retainer and the case. A quick napkin math check gives the shear strength of a plastic thread that size as well above the pressures you would expect in a motor, I'm not sure what advantage a metal thread would have?

    Given the loose fit I've seen on metal to metal threads in most hobby size motors I'm not sure metal threads would actually offer any sort of advantage, they would fail well below the theoretical load for the size due to the excessive clearance.

    Serious question, does anyone have any in flight failures that are 100% attributable to the plastic threads failing, with no sign of o-ring failure first or incorrect assembly? And is that number significantly higher than the number of motors that have blown out metal retainers?

  27. #57
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    Plastic threads are quite easy to cross thread. Metal ones, you know basically immediately what's going on.

    Sure, it's user error if you try to drive the liner in by screwing the thing together. But I've seen it happen often enough to be worth mentioning. Properly assembled, it's a fine design. But it's much much much more prone to user error/assembly error. Whatever you want to call it. It's not "omg pull the certs" bad. But it's worth mentioning, and not the greatest idea in my opinion.

    For an idiot proof design, it's sure got a giant Darwin Award.


    And yea, sometime like this case, crap happens to anyone.
    David McCann
    Dave's Rockets | My Flights
    URRG |URRF 4| Level 2 | TRA# 14210

  28. #58
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    This is true, the problem seems to be the difference in the one piece nozzle - other sizes you push everything in and can screw the retainer most of the way before it starts to load up. With the threads being on the nozzle/closure itself often it is used to push the liner and grains in so if they are tight you're placing a large load on less than a full thread of engagement, which has the potential to go wrong no matter what material you use.

    The careful use of a spacer to slide the liner a little further can help, but since that isn't in the official instructions I agree that is a drawback to the design. Maybe the delay drill tool should also come with a small plastic tool to seat the liner and grains before the closure is screwed in?


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