### Help Support The Rocketry Forum:

#### Ccolvin968

##### Well-Known Member
So I recently purchased a kit that flies on 75mm motors...
It will be my L2 rocket, and I'm starting to wish I would have checked the cost of the reloads before buying.
Do the 75mm reload the same as every other CTI motor size? (No individual grains and the sort.)
Does CTI do the certification special on 75mm reloads?
If not, I already have plans to fly it on 54mm motors with an adapter and rarely fly it on 75mm.
I would eventually save up and drop the money on it for a "once in a while" flight.
As you can imagine, I was kind of surprised to see that a 5g casing was $380. Plus$27 per spacer. Then $44 for the wrench. Then$187-$330 per flight after that. I know it's nobody's fault but mine. I'm just exploring some of my options. So... I guess what I'm getting at is this: Should I suck it up and drop the cash now and fly it as it was built with 75mm hardware? OR... should I fly it on 54mm (already had the adapter to flip flop if I wanted) for a while until I can afford the bigger hardware and motor casing? I definitely flubbed this up a bit. Try to reserve judgement. Thanks for any guidance/constructive harassment. ;-) -C #### noffie79 ##### Well-Known Member I'd definitely fly it on 54mm reloads. No harm in that. Just be sure that you use a motor with enough thrust to safely get it off the pad. Most importantly, have fun! #### Nathan ##### ☢ TRF Supporter 54 mm may be all you ever need, it depends. What kit is it and how high do you want to fly it? #### Ccolvin968 ##### Well-Known Member Thanks Noffie. I will run sims on every flight that I intend on flying. So far, I haven't encountered an unsafe flight in the couple that I have ran sims on. #### alex_car763 ##### Well-Known Member On a $$/Ns once you get to the longer casings it's better bang for your buck to go to the next motor diameter up. That being said there is the investment in hardware that must be made. Personally I would rather spend 200 on a 3G 75 than 180 on a 6 or 6Xl 54. In answer to the other question Pro75/98 build like an Aerotech so you have individual grains to assemble. #### Ccolvin968 ##### Well-Known Member Nathan, it's a 4" Madcow Tomach. We have clearance to fly to 20,000 ft every club launch day. I wouldn't mind breaking 10k someday, but I'm thinking for my normal every month flights between 4,000 and 8,000 ft. I just like the noise and making something fly! haha #### Ccolvin968 ##### Well-Known Member Alex, thank you for the answer to that about assembly. I would need some direction before I was comfortable doing that by myself. Is it difficult? I've heard horror stories about people assembling them wrong and poof... there goes a couple hundred dollars. That's true though... I don't really have to go all out right away for the 5g casing. I didn't even think about that. Food for thought, for sure. #### alex_car763 ##### Well-Known Member My advice is at your next launch watch somebody build an Aerotech or Pro75/98 (some do need grain bonding which complicates further but still manageable). If you've done smaller Aerotech already same principle just bigger grains. I had the same concerns my first 75mm. I just had another experienced guy at the launch watch me build so give me any pointers if I missed something and help make sure it was successful. I can pretty well guarantee somebody would be willing to give you a hand. #### CzTeacherMan ##### Well-Known Member The 75mm CTI motors are not like loading 54 and smaller. I would fly 54s for now. I only ever buy hardware on special... Look for drag race deals, annual sales, etc. Watch the forum for someone selling used hardware. Heck, ask your friends and club mates to borrow hardware for those "rare" 75 flights... Just keep in mind that standard borrowing rules are: the owner goes home with clean hardware or new hardware (if you lose/break it). What kit, out of curiosity? I picked up a Drago 4XL, and I'm looking forward to finally having a rocket with a 75 mount! But it will probably fly on many 54s as well. But when you get into the long 54s, the cost per Newton is lower with short 75s. #### Ccolvin968 ##### Well-Known Member I have really helpful people at my club. I'm still the newest guy there, and I have yet to find a rude person. I have never built an Aerotech motor. So that would be a new experience for me. #### Ccolvin968 ##### Well-Known Member Cz, I bought the Madcow Tomach on sale on Black Friday for 223. Regular price is 299. I will keep those rules in mind. A guy I fly with INSISTED I fly his JL Altimeter 3 on my L1 cert flight... I was a little nervous. It went off without a hitch, but still. I thought it was a HUGE deal at the time, but it turns out... There are much more expensive electronics out there. haha! #### CzTeacherMan ##### Well-Known Member Cz, I bought the Madcow Tomach on sale on Black Friday for 223. Regular price is 299. I will keep those rules in mind. A guy I fly with INSISTED I fly his JL Altimeter 3 on my L1 cert flight... I was a little nervous. It went off without a hitch, but still. I thought it was a HUGE deal at the time, but it turns out... There are much more expensive electronics out there. haha! Nice kit! I grabbed the Drago for 200, though I should've pounced on Wildman Wednesday because it was 170 then. The Tomach will fly nice on many of the 54s. If you've got the waiver, it could be your L3 kit, too! Yeah, I've borrowed and lent things fairly often. Loaned a tracker to a friend at MWP for his L1. Had a very unfortunate nosedive deep into the ground. The tracker was pretty banged up, and he wanted to replace it, but I insisted that he not. I knew the risks. And I felt bad for him since I'm the one that recommended the motor choice and forgot to tell him to add BP... Ugh. I learned the hard way that hardware should be cleaned. I was given an EX motor to fly, free of charge, and stupid me was just handing him the dirty casing. Luckily another friend knows how socially stupid I am and gave me the tip... A little embarrassment, but now I know. #### Ccolvin968 ##### Well-Known Member It could be my L3, but I haven't been keeping enough build documentation on it to do that. This is only my second FG build ever, so I'm still very much in the learning stages of building FG rockets. I will for sure keep those rules in mind. Don't need to be that guy. I really appreciate the support for my dumb decision. I may end up getting the 3g case for those more rare flights in the future. First off will be the 54mm starter kit. #### Ccolvin968 ##### Well-Known Member On a$$$/Ns once you get to the longer casings it's better bang for your buck to go to the next motor diameter up. That being said there is the investment in hardware that must be made. Personally I would rather spend $200 on a 3G 75 than$180 on a 6 or 6Xl 54.

In answer to the other question Pro75/98 build like an Aerotech so you have individual grains to assemble.

Curious, where are you seeing a 3g 75mm casing for $200? Apogeerockets.com has them listed as$310.

#### Ccolvin968

##### Well-Known Member
Dude! That's awesome!

Even the hardware set (that I need anyway) that includes the casing is still $30 cheaper! Thanks a ton. #### Steve Shannon ##### Well-Known Member TRF Supporter If you're flying with a club ask and see if anyone has a case you can borrow. My Prefect at the time was very quick to offer cases and since I became Prefect ten years ago I've made the same offer. Also, some of the large CTI loads are cross certified so you can fly in either CTI or AT cases. Check to see if your load is. #### Ccolvin968 ##### Well-Known Member That's awesome! Thanks for the tip! #### jimzcatz ##### Boss, Carolina Rocket Mafia Not being an altitude junkie, I would never put a 3" motor in a 4" rocket. That rocket will fly fine on 38/54 mm motors, and probably some 29s. #### Dave A ##### Lifetime Supporter TRF Lifetime Supporter Curious, where are you seeing a 3g 75mm casing for$200?
Apogeerockets.com has them listed as $310. If you can find a 54/2550 snap ring case, you get get a CTI, Animal Compatible, K-1130 Blue Baboon or an L-1276 Red Rhino for$120 or others with less impulse that fit all the AMW compatible cases.
If you find a Kosdon case somewhere the agreement was it is ok as long as you use the certified forward, in this case is the AMW fwd. These reloads come with a disposable nozzle. Someone in your club probably has the hardware you can borrow or rent.
That line comes in everything from J to K, real economical price.

#### Ccolvin968

##### Well-Known Member
So... Dumb question.

I know the first number in the designation (54/2550) is the MMT size in mm.
What does the second number tell me? How do I know how many grains the casing is just from that?
If I were to go this route, it seems like after I get the compatible hardware I'll still be paying around the same ish price for compatible items as I would for the actual CTI hardware.

Do they make 75mm cross compatible hardware?

I'm on the AMW website right now.
So if I were to buy the 54/2550 what all is that actually getting me?
Can I fly all CTI 54mm reloads on that case?
Do I need other hardware to use the CTI with the AMW case?
Or is that the hubcap that was referred to before?

#### Steve Shannon

##### Well-Known Member
TRF Supporter
So... Dumb question.

I know the first number in the designation (54/2550) is the MMT size in mm.
What does the second number tell me? How do I know how many grains the casing is just from that?
If I were to go this route, it seems like after I get the compatible hardware I'll still be paying around the same ish price for compatible items as I would for the actual CTI hardware.

Do they make 75mm cross compatible hardware?

I'm on the AMW website right now.
So if I were to buy the 54/2550 what all is that actually getting me?
Can I fly all CTI 54mm reloads on that case?
Do I need other hardware to use the CTI with the AMW case?
Or is that the hubcap that was referred to before?
The second number is a rough estimate of the impulse that a reload for that motor will deliver in Newton seconds.

The 38 mm AT system is easy for me to remember. Each grain is about 120 Ns (Newton seconds, not Newtons per second although you might see people mistakenly write N/s). So the cases are 38/120, 38/240, 38/360, etc. So it's easy to see that a 38/720 is a six grain case.

With the exception of some snap ring cases, the hardware is not what's cross compatible. Reloads for CTI and Aerotech are considered cross compatible off and only if the manufacturers have submitted them to the certification agencies (TRA, NAR, and CAR) for all cases they can be flown in. That's expensive, so it really only happened between those two companies in an effort to sell reloads to people who have the other's cases. Initially CTI did it because more people had AT cases in the 98 mm sizes.
Several years back Tripoli and NAR recognized the interchangeable nature of some manufacturers' snap ring cases. That allows people with Gorilla cases and AMW cases (and some Loki cases with the right forward closures and nozzles) to use each other's cases.

I have no experience flying CTI loads in AMW cases. I have a pretty complete set of CTI cases up through 54 mm, so I've never learned about the CTI and AMW compatibility. CTI has an interest in AMW so there's no problem with it and Robert DeHate is a good guy. Give him a call. I'm sure he can explain their system far better than I can and who knows, maybe he'll have a cert special going on.

Steve Shannon

Last edited:

#### Ccolvin968

##### Well-Known Member
Is there a chart for the larger motors?
I can't seem to find an easy pattern with 54mm or 75mm for figuring designation to grains.

#### jimzcatz

##### Boss, Carolina Rocket Mafia
All 75 and 98 motors are cross certified. You can use any pro 75 load in the comparable snap ring hardware with the AMW Hubcap adapter (I have 3). These are allowed at all commercial launches. I will let Dave Alewine explain the Aerotech snap ring conversions. Also, both CTI and Aerotech have a line of motors designed for the 3" snap ring hardware.

#### Dave A

Jim is correct that the CTI 75s and 98s are cross compatible with Aerotech reloads. Instead of getting into a more in-depth of each understand that CTI hardware in 75mm line is much less expensive than the comparable-sized Aerotech (AT) hdw. For example you can get the CTI set like a 5 or 6 grain case , also use 1 or 2 spacers for many more combinations.
The 75mm CTI reloads are certified to be flown in the AMW snap ring case (along with the CTI adjustable fwd closure or hubcap as it's known), the CTI AND AT hardware. The agreement Tripoli agreed to was allow similar snap ring cases like AMW/GORILLA, KOSDON/ and some Loki. I.E., If you use a Loki reload in a compatible case you must use the Loki closures and nozzle.
Once you get certified Level 3, and club rules allow non-certified motors then you can fly more cominations.
I personally do not want to fly 75mm 1, 2 or 3 grain reloads due to cost. That's where I use my larger 54mm reloads, the AMW L-1276 has a total impulse of over 2700n.

#### Ccolvin968

##### Well-Known Member
So it's more cost effective in a sense to fly larger 54's than it is to fly a small 75mm. Got it.

That brings me back to my other question though.
How do I know the size of a casing in grains given a designation or whatever it's called such as 54/2550.
I know the 54 is the motor size, and the 2550 is the average amount of thrust in Ns expected to be produced by said reload in said casing.
It was explained earlier that in 38mm it's easy to convert to grains. because it's roughly 120 Ns per grain.
Is there an easier way to convert or is there a chart for larger and smaller motors?
Thanks!

#### Dave A

AT and CTI hdw both allow to use 1 or 2 spacers. I have 1 - 6g 75mm case and snap ring cases from 4,5 and 6 grain.
I can layout a chart for you to compare cases based on grains for 54 and 75mm hdw.
54mm CTI hdw is less expensive than AT and they are not cross compatible. I only have CTI and AMW in the 54mm line and it serves me fine. When more CTI Animal Compatible reloads are available I will get them, they will save money and time building. I built that L-1276 in about 3 minutes.

#### Ccolvin968

##### Well-Known Member
That chart would be amazing if you have the time.
I really appreciate it.