CTI Questions

Would it be safe to say that you could fly every motor in the 38mm range with the CTI 38 starter kit and a 6XL case?

The starter kit comes with (2) spacers so you can 1-3 grain motors. In the 6 grain case you can use the (2) spacers to fly 4-6 grain reloads.

So if this is true why do they have 1, 2, 4, and 5 grain cases? My guess would be the design of the rocket and size of motor tube may not always allow the length for a size "6" motor tube.

I'm trying to determine if I should continue with AT cases or go with all CTI cases? I know AT offers several cases in each size and some cases can fly more reloads than others.

Just trying to crunch the numbers and determine what would be best? I mean anything that's 38mm and larger you will hit with HAZMAT fees so that's a wash. I guess what I need to figure out is for instance what CTI motor say a 3 grain reload represent what size in an AT reload? So for instance a 38/360 is equal or similar to what size CTI case?:confused2:

Then I could figure cost or better yet just buy a variety of both

you've hit the nail on the head, available space in the rocket. motor tube length is less important than you might believe. this past weekend I flew my stealth with a cti 3-grain motor, looked like a motor with a skirt (great flights though). AT also has a spacer system with both a 360 & 720 cases(also a seal disk) you can fly anything from a G61 to a J500. from looking at Wildman's site; a 3 grain case(the 360 is a 3 grain case) will get roughly the same impulse range motors in either brand. a while back Tim had a special AT 38mm starter set for $100 I got a 360 and 720 case w/ spacer system...have not used the 720 case, yet. mainly because my rockets were not built for a case that long. a 6 grain AT motor puts you into the small J motors.
Rex

Rex R said:

you've hit the nail on the head, available space in the rocket. motor tube length is less important than you might believe. this past weekend I flew my stealth with a cti 3-grain motor, looked like a motor with a skirt (great flights though). AT also has a spacer system with both a 360 & 720 cases(also a seal disk) you can fly anything from a G61 to a J500. from looking at Wildman's site; a 3 grain case(the 360 is a 3 grain case) will get roughly the same impulse range motors in either brand. a while back Tim had a special AT 38mm starter set for $100 I got a 360 and 720 case w/ spacer system...have not used the 720 case, yet. mainly because my rockets were not built for a case that long. a 6 grain AT motor puts you into the small J motors.
Rex

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Rex

As far as numbers how does it work out price wise? Is it more favorable to go with CTI or AT or in the long run they offer about the same?

hmm, I didn't happen to look at prices, sorry. in 29mm AT is cheaper, as I recall from the forum 38s are about even, and 54s cti is cheaper(not counting hardware costs). long run, you can fly a lot of mid power birds for the price of one J motor . if you have AT hardware you would probably do well to stay with AT in the 38s. main concern would be, what does your motor vendor carry? I get my hpr reloads at the field and skip hazmat fees.
Rex

Its probably wash either way? IDK I guess its just about getting out there and flying....

I still have a close to 2 dozen 29mm motors to fly

given your location, find out what your vender sells at the launches since nearly all 38mm motors require a hpr cert and a lot of that size rockets require a waiver. if said vender sells both...then worry about brand/price .
Rex

Which AT cases do you have?

I was in the same situation, I had a 38/360, and a 38/720, as well as the AT spacer system. When I decided to get my L2, I ended up getting the CTI starter kit and a J381 skidmark using the certification special they had at the time, the starter kit was either free, or heavily discounted. If you can afford it, having both types of hardware provides quite a bit of flexibility. The vendors that come to my launches typcially sell both AT and CTI, but CTI is become more popular in my club based on my unscientific observations. I have also grown to enjoy the simpler loading of CTI, and more importantly, the ease of clean up. I buy all my HPR loads at the field to avoid the hassle of hazmat shipping.

Both AT and CTI have case dimensions on their websites.

KurtH said:

Which AT cases do you have?

I was in the same situation, I had a 38/360, and a 38/720, as well as the AT spacer system. When I decided to get my L2, I ended up getting the CTI starter kit and a J381 skidmark using the certification special they had at the time, the starter kit was either free, or heavily discounted. If you can afford it, having both types of hardware provides quite a bit of flexibility. The vendors that come to my launches typcially sell both AT and CTI, but CTI is become more popular in my club based on my unscientific observations. I have also grown to enjoy the simpler loading of CTI, and more importantly, the ease of clean up. I buy all my HPR loads at the field to avoid the hassle of hazmat shipping.

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29/240 38/360 and the AT 29mm hobbyline case 29/40/120

The starter kits are well worth it. That's about all you need and the high case for each size

You can get by, depending upon your fleet, with the starter set and a couple of spacers. This will put you from G to J. If you really want the 6XL case to fly the entire line, then, by all means--have at it. I had the 3 and 6 grain for a long time. Then picked up a 5 grain because the 6 wouldn't fit and the 3 didn't give it QUITE enough "oomph." I picked up the 1 and 2 because... well... no real good reason, I suppose... I could have left it with the 3 and spacers, but I figured if I had more cases, I could pre-prep everything faster. I still haven't picked up a 4 grain in 38, and as far as the XL... eh... I might... but anything I'd fly it in already has a 54mm hole...


Later!

--Coop

AfterBurners said:

29/240 38/360 and the AT 29mm hobbyline case 29/40/120

The starter kits are well worth it. That's about all you need and the high case for each size

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I would get a 2g, 4g and 6g in case some rocket motor tunes are a problem.

If you want to go to the expense of a 6XL, just get a 4g or 5g 54mm case instead.

Dave A said:

I would get a 2g, 4g and 6g in case some rocket motor tunes are a problem.

If you want to go to the expense of a 6XL, just get a 4g or 5g 54mm case instead.

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But what if he doesn't have a 54mm MMT? :wink:

You are forgetting that odd half spacer for XL. I believe you need both a standard spacer and the XL spacer to go from 6xl to 6.

jimzcatz said:

You are forgetting that odd half spacer for XL. I believe you need both a standard spacer and the XL spacer to go from 6xl to 6.

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Ah, but he would have the 6 grain casing that comes with the set. No XL spacer needed.

Afterburners, both AT and CTI are represented at ROC. Great vendors and pre-orders saves money and avoids Hazmat. How many clubs have 3 vendors at almost all launches, WE are spoiled.

Exactimator said:

Ah, but he would have the 6 grain casing that comes with the set. No XL spacer needed.

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Yes, the set comes with a 6G case, but he mentioned 6GXL in first post.

Edit : Ahh, I get it now. He was going to add the XL case in addition to starter set.

Just my $0.02, Performance Hobbies (perhaps others) has a modified version of the Pro38 starter set, which provides the 4G[*]and 6GXL cases instead of 3G/6G, and also includes the two standard spacers as well as the XL spacer (though he was out of stock on the XL spacer when I ordered it in January, so I got that part from my local vendor). It's a bit more than the 3G/6G set since the cases cost a bit more plus the extra XL spacer, but it wasn't any more than the delta between each of the separate pieces. So with this I can fly any 38mm reload from 2G to 6GXL with only two cases, not 3. And the 1G Pro38 loads frankly didn't interest me since they're all G-impulse, while giving me access to the 6GXL loads which are more interesting to me (once I get my L2 and can actually fly them). Of course you do need to ensure that your rocket(s) are long enough to handle the 6GXL case, that wasn't an issue for me.

[*] I will note that the website says 6GXL and 3G, when I remarked about this Kenn said it should have been 4G since the point was to cover the 2G-6GXL range. But I think the quoted price on the website was computed for the 3G so I believe the cost difference between the 3G and 4G was added to the package price when I ordered it. I could be wrong, I'll have to dig up the receipt and see. If you do order it I'd suggest you be clear on whether you're expecting the 3G (wouldn't be able to fly any 4G loads) or the 4G (wouldn't be able to fly any of the 1G loads). Unfortunately it sounds like he has difficulty getting his web guy to actually update the pages.

I feel like I sorta blew it with the AT 38mm cases, I have a 360 and a 720 plus the RAS, but again the 38/120 and even the 38/240 loads just aren't interesting to me. I should have picked up the 480 instead of the 360, and could have even gotten by with a single spacer instead of two for everything from 38/360 to 37/720 (of course they come as a set with AT), or perhaps even just a 600 and the 720, to cover 360-600 and 720. Of course if the G/H motors are what you're looking for than the more traditional sets do the job just fine I think.

Will, I agree with everything said, and I have that set. But correct me if I'm wrong, using a 5G load in the 6XL case requires 3 spacers, and CTI only certified for 2. Yes?

I was in the same situation Afterburners was in about a year or so ago.

I've had the AT hobbyline cases for quite some time, so I was looking to get into the AT high power cases and get my cert. I had already had my rocket and it was 90% built. It was close to being finished, just never got around to it. Anyways, I'm always on the lookout for rocket deals so within a few months of looking, I scored a practically complete set of 38mm AT cases for a fraction of the new price here in the yard sale section. Then right after that I ordered a few of the smaller AT 29mm HP cases, brand new, I scored a pretty much complete set of 29mm cases along with complete sets of CTI 24mm and 29mm cases. Shortly after that I came across a CTI 38mm stater set used. So within less than a year's time, I have pretty much the gamut of all the AT & CTI cases any of my birds could possibly use. I had to force myself to stop looking! Maybe 2016 will be the year for 54mm.. lol

So basically don't worry about the price. Get both! There are tons of smoking deals out there!

Jerome

JeromeK99 said:

I was in the same situation Afterburners was in about a year or so ago.

I've had the AT hobbyline cases for quite some time, so I was looking to get into the AT high power cases and get my cert. I had already had my rocket and it was 90% built. It was close to being finished, just never got around to it. Anyways, I'm always on the lookout for rocket deals so within a few months of looking, I scored a practically complete set of 38mm AT cases for a fraction of the new price here in the yard sale section. Then right after that I ordered a few of the smaller AT 29mm HP cases, brand new, I scored a pretty much complete set of 29mm cases along with complete sets of CTI 24mm and 29mm cases. Shortly after that I came across a CTI 38mm stater set used. So within less than a year's time, I have pretty much the gamut of all the AT & CTI cases any of my birds could possibly use. I had to force myself to stop looking! Maybe 2016 will be the year for 54mm.. lol

So basically don't worry about the price. Get both! There are tons of smoking deals out there!

Jerome

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I think having the starter sets of both 29 and 38's would be a good addition.

I have the 29mm and 38mm Aerotech spacers with two different case lengths in each size.
Despite this, I will eventually have to buy shorter cases in both MM’s if I ever want to launch “H” motors in the booster and sustainer of my “Aerobee-Hi” this due to the limited length available for the motors.
The same would be true if I was using CTI.

my 2 cents if you have a onsite Loki dealer look at the the long Loki 38mm over 6xl


that advise is because in my case CTI is hard to come by at launches AT and Loki easy

jimzcatz said:

Will, I agree with everything said, and I have that set. But correct me if I'm wrong, using a 5G load in the 6XL case requires 3 spacers, and CTI only certified for 2. Yes?

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The second page of these CTI Pro38 spacer instructions show using the XL and two standard spacers to put a 5G reload in the 6GXL case, so I would take that to mean it's not against the manufacturer's recommendations. They show putting the XL spacer closest to the reload, I didn't pay attention to that detail and my first 5G-in-6GXL load I put the XL spacer at the top. In my set at least, the standard spacers have curved tops while the XL spacer doesn't. It seemed to wedge itself into the curved top of the casing a bit, was difficult to get it out afterwards. So I'll be putting it in the bottom of the stack for now on.

So it seems you're not supposed to use more than two standard spacers, but two standards + the XL seems to be okay for the Pro38 line AFAICT.

In the case of Pro38 reloads, the 1G thru 6G casings contain 1 to 6 identical standard 1G length bates grains, however the 6XL casing contains 6 longer than standard XL propellant grains. The XL casing spacer is not the length of a single XL propellant grain, but rather the difference between the length of (6) XL propellant grains and (6) standard 1G propellant grains so the conversion is from 6XL -->6G (note this is not grain number reduction, but a grain length reduction). To reduce the 6XL casing to contain (5) 1G propellant grains you need a 1G grain spacer and 1 XL conversion spacer. To convert a 6XL casing to a 4G casing you need (2) 1G grain spacers and the XL conversion spacer. So you are reducing the number of propellant grains from (6) XL grains to (5) 1G grains or (4) 1G grains for the 38 mm casing so technically it gets by.

You have to read the instructions very carefully. The XL spacer by itself does not permit you to convert a 6XL casing to a 6G casing and use (6) 1G propellant grain because it does not have a curved end to distribute the thrust force to the curved forward end of the casing. Doing this could point load the curve forward casing surface and shove the XL space out of the casing, breaking the pressure seal and catoing the motor. That's way the instruction specifically state that you insert (1) or (2) 1G spacers in to the 6XL casing first and then insert the XL casing spacer last before inserting the forward closure.

Bob

bobkrech said:

In the case of Pro38 reloads, the 1G thru 6G casings contain 1 to 6 identical standard 1G length bates grains, however the 6XL casing contains 6 longer than standard XL propellant grains. The XL casing spacer is not the length of a single XL propellant grain, but rather the difference between the length of (6) XL propellant grains and (6) standard 1G propellant grains so the conversion is from 6XL -->6G (note this is not grain number reduction, but a grain length reduction). To reduce the 6XL casing to contain (5) 1G propellant grains you need a 1G grain spacer and 1 XL conversion spacer.

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Actually that's not correct, and it's clearly shown in the PDF I linked to in my previous post (re-attached as a rotated picture below). The difference between the 6 'standard' grains and the 6 'XL' grains is the total length of one standard spacer and one XL spacer. So to fly a 6G reload in the 6GXL case you need 1 XL and 1 standard spacer. To fly the 5G reload in the 6GXL case you need 1 XL and TWO standard spacers. You couldn't get a 4G reload in the 6GXL case without using 3 standard spacers, which as I understand it would be against the rules. But the first important note on this page says "Only use an XL spacer in conjunction with a regular spacer.", and the lower picture shows a 6G reload in the 6GXL, the upper picture shows the 5G reload in the 6GXL. And this certainly matches my own experience of putting a Pro38-5G (I297SK) into my Pro38-6GXL case, I needed to use all 3 spacers as shown in the picture.



Interestingly, looking at the instructions below the notes, they're unclear if not wrong in what they say. The instructions say "Drop spacer(s) into motor case with the rounded end towards the rounded end of the motor." But this does not match the diagrams (not so clear in my picture above, but very clear if you zoom in on the PDF), which clearly show the curved ends facing AWAY from the motor (towards the rounded end of the motor case). And as I had noted above, when I accidentally put the XL spacer (which has no rounded end) at the top it did a pretty good job of jamming itself into the curved part of the case during the flight, which seems to be the main reason why they want the curved end of the spacer pointing up, and why they say to load the XL spacer after the regular spacer(s) in these instructions. I guess it's okay to not have a curved end on the XL spacer since it always has to be used with a regular spacer, it just drives putting the XL in last since it has no curved end to put at the very top of the casing.

Here's a zoomed-in picture showing the spacers in the 6GXL -> 5G example, clearly showing the curved ends.

Will, you are correct. Didn't multi-task well today.

Bob

michigander said:

my 2 cents if you have a onsite Loki dealer look at the the long Loki 38mm over 6xl

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I'd agree, but only if you're looking to max out. The CTI J530 is 1115 Ns. The AT J510W is 1162 Ns. The Loki loads for the 38/1200 are 1220Ns, 1284Ns, 1266 and the sparky is 942. (6XL skidmark is 848)

zoom zoom.


Instead of looking at the theoretical possibility to fly every motor, I'd suggest looking at which motors you really want to fly and making sure to cover those. I rushed out to buy casings to try and be able to fly everything, and found myself only wanting to fly certain motors in 38 and 54. 29 it's easy to buy motors on a whim.... when they start costing 50-150 a pop, you start planning individual flights more...and there's less need to be able to cover the entire range. At least for me there wasn't.

DizWolf said:

I'd agree, but only if you're looking to max out. The CTI J530 is 1115 Ns. The AT J510W is 1162 Ns. The Loki loads for the 38/1200 are 1220Ns, 1284Ns, 1266 and the sparky is 942. (6XL skidmark is 848)

zoom zoom.


Instead of looking at the theoretical possibility to fly every motor, I'd suggest looking at which motors you really want to fly and making sure to cover those. I rushed out to buy casings to try and be able to fly everything, and found myself only wanting to fly certain motors in 38 and 54. 29 it's easy to buy motors on a whim.... when they start costing 50-150 a pop, you start planning individual flights more...and there's less need to be able to cover the entire range. At least for me there wasn't.

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Yes, the Aerotech 29mm non hazmat are a bargain.

i have just started flying some 1 and 2 grain CTI 54mm ..have had the starter set for years but just started flying less than 4g recently.

Also had not flown CTI Pro38 until ROCstock last year . Purchased a 5g case and a I125 Long Burn ..then bought a 3g and a spacer for the H400 vMax . Like DizWolf said pick a motor then a strategy. Exactimator bought a 38 6xl in the last sale and i bought the 54 6xl.. if i share i assume he will too..

Kenny

Some thoughts with XL spacers, mark them well so you don't accidentally use it as a normal spacer.

I almost did it with a 54mm flight.. something didn't fell right so I took it apart after just loading it.
Which could have been bad, I would guess the case would have heated up in that extra missing space and boom goes the rocket!

michigander said:

my 2 cents if you have a onsite Loki dealer look at the the long Loki 38mm over 6xl


that advise is because in my case CTI is hard to come by at launches AT and Loki easy

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Good old Cali won't make it affordable for Loki to come here as of yet.