29mm to 38mm seems like a big jump

[techrat]

When all I used to was 18mm motors, 24mm seemed like a big jump, even though the difference was just 6mm wider. But then, going from 24mm to 29mm didn't seem that big a leap as it's just 5mm wider, and with the E motor, you kind of get used to the size and weight, although there are very long 29mm reloadables. However, the jump from 29mm to 38mm seems MASSIVE as it's a sudden leap of 9mm, the biggest jump in diameter (until you get into HPR, where the next size up is 54mm, and then to 98mm, which I imagine as enormous)..... Anyone else having this kind of experience? I mean, over time, you come to accept these things, but putting a 38mm next to an old 18mm motor for example, and you see how far you've come.

 

[Antares JS]

18mm: A-D
24mm: C-F
29mm: F-I (a few E's)
38mm: G-J (a few K's)

The actual diameter means less to me than what range is available in that diameter. I would argue that 24-29 is a bigger leap.

 

[rocketace]

I agree with you. Every step for me in my journey seamed big at the time, but after each step the last ones doesn't seam as big. One of my last builds can launch on an 18mm D motor up to a 38mm J (I could probably do a K if I add a spacer....) and honestly every launch with it has been a thrill!

 

[heada]

Volume of propellant is by width and length. With each increase in width you also get a increase in length. Each step in standard motor size can be significant but there is overlap between all sizes.

I put a 6mm MMX motor next to my 76mm Loki case and the difference between 1/8A to M is kinda laughable. And 75mm/76mm is a standard size step as well as 150mm.

 

[techrat]

29mm: F-I (a few E's)

I could swear I've seen some H motors that fit a 29mm case.
For example, there's someone selling motors in Yard Sale, and his 29mm loads all identify as H motors.

 

[Antares JS]

I could swear I've seen some H motors that fit a 29mm case.
For example, there's someone selling motors in Yard Sale, and his 29mm loads all identify as H motors.

F-I means F, G, H, and I

 

[techrat]

F-I means F, G, H, and I

D'oh!! I couldn't remember the alphabet. For some reason I was thinking H came *after* I <embarassed>

 

[techrat]

OK, I need more coffee....

 

[tsmith1315]

Comparing diameters only,

13 to 18 is about 38% increase
18 to 24 is about 33%
24 to 29 is about 21%
29 to 38 is about 31%
38 to 52 is about 37%
52 to 75 is about 44%, and
75 to 98 is about 31%

 

[techrat]

It is interesting that each step (18, 24, 29, 38) support 4 impluse varieties, as long as we're counting BP and composite.

 

[heada]

Comparing diameters only,

13 to 18 is about 38% increase
18 to 24 is about 33%
24 to 29 is about 21%
29 to 38 is about 31%
38 to 52 is about 37%
52 to 75 is about 44%, and
75 to 98 is about 31%

54mm and not 52mm

 

[lakeroadster]

Comparing diameters only,

13 to 18 is about 38% increase
18 to 24 is about 33%
24 to 29 is about 21%
29 to 38 is about 31%
38 to 52 is about 37%
52 to 75 is about 44%, and
75 to 98 is about 31%

Seems like using area would be a more applicable comparison?

 

[heada]

Seems like using area would be a more applicable comparison?

View attachment 532825

Volume of the cylinder is more appropriate. A 6grain 75mm vs a 1 grain 54mm is HUGE. And again, its 54mm and not 52mm

 

[tsmith1315]

54mm and not 52mm

A leftover from a previous life- 52mm was a common size for dome midranges. I make that mistake often.

And yes, looking at one motor vs another in real life 3D, volume would be the best dimensional value to compare.

Cost is even better.

 

[lakeroadster]

Volume of the cylinder is more appropriate. A 6grain 75mm vs a 1 grain 54mm is HUGE. And again, its 54mm and not 52mm

I revised the chart I posted.

Sure, but trying to list every motor volume, and every nozzle oriffice, etc. would be quite a list. But looking at areas gives us a good idea of variation, with respect to what @techrat asked in the OP.

 

[smstachwick]

It is interesting that each step (18, 24, 29, 38) support 4 impluse varieties, as long as we're counting BP and composite.

Five, actually. I spend too much time on ThrustCurve.

18: 1/2A-D

24: C-G

29: E-I

38: G-K

I don’t think that’s how it was planned, I think it just happened to work out that way with the engineering concerns and market forces and all.

Of course, not all of these ranges are commonly used in these diameters, of course. Most prefer Estes’ 13mm 1/2A3s for the better cost per flight of the mini motor over Estes’ 18mm 1/2A6-2, for example. Loki’s 38mm Ks also aren’t common here in California because they don’t have State Fire Marshal approval and thus can only be flown at FAR’s site that supports experimental motors. So most ranges are like 4-and-a-half (give or take a fraction to accommodate for any weirdos like me in your club).

But those unusual motors are out there and if you have an unusual goal in mind, knowing about those options may make or break your plans to accomplish it.

Interestingly, AeroTech plans to still manufacture 32mm (yes, 32mm) hardware and reloads sporadically, but they’re F and G loads for gliders. Every system has an oddball or two.

I did find it interesting how small the 6x26mm MicroMaxx II motors were that I received. You can read all about my response on the MMX subforum, I’m sure it won’t be hard to find.

 

[waltr]

I agree it is the Volume. Also remember that each increase by letter can be Double the Total Impulse.
I started with the microMax, upped to 13mm then 18, 24 an now fly a lot of 29mm. Still fly all sizes but just bought a 29/180 case since I have L1 so I can fly some H & I's.

 

[bjphoenix]

Back to the question- I considered it a big jump from 29mm to 38mm, but nothing to be worried about. I was using Aerotech and had the 29/40-120 case. I usually used G64 reloads in it. I bought a 38mm set including 240 and 480 tubes so I could do level 1. I typically use H and I reloads in that set. So for me I went from G to H and I, just seems like a minor jump. Of course this is a jump of double the impulse or 4 times the impulse.

 

[gdjsky01]

Not really. You need to focus on total impulse. That is the key. With every letter change the range doubles. People are like, "I am flying an E today!!!" Sure? An E12? That 7ns over a full D. I piss people off all the time when I point out their 'J' is like 10% more than a full I. THINK about it. A FULL E is 40ns. Now go look at what passes for a F. The F15? Fifty ns? Sure its an F. But its a 25% F.

Same with the my favorite goad people motor, the J350. It's a 680ns J. Just 40 ns over a full I. It is nothing like a 54mm J that might tickle 1280ns. Both are J's. But only in name only. THIS is why CTI's labeling is 100% better than Aerotech. CTI TELLS YOU, this is a xxxx NS motor. I wish NAR, CAR, and TRA would make labeling like CTIs mandatory.

 

[smstachwick]

Not really. You need to focus on total impulse. That is the key. With every letter change the range doubles. People are like, "I am flying an E today!!!" Sure? An E12? That 7ns over a full D. I piss people off all the time when I point out their 'J' is like 10% more than a full I. THINK about it. A FULL E is 40ns. Now go look at what passes for a F. The F15? Fifty ns? Sure its an F. But its a 25% F.

Same with the my favorite goad people motor, the J350. It's a 680ns J. Just 40 ns over a full I. It is nothing like a 54mm J that might tickle 1280ns. Both are J's. But only in name only. THIS is why CTI's labeling is 100% better than Aerotech. CTI TELLS YOU, this is a xxxx NS motor. I wish NAR, CAR, and TRA would make labeling like CTIs mandatory.

I don’t think NAR intended for the motor code to be the be-all end-all source of information on motor selection. Sure, that may be valid for very small rockets, but I think one of the reasonable assumptions we operate under is that by the time most people get into impulse ranges where this kind of thing is really important, they’re going digging for published data and thrust curves in addition to deciphering the codes.

I also notice that the manufacturers tend to space their products out to produce a more sensible increase from one range to the next. That Estes D12 is a 68% D and the E12 is like a 36% E. Not a perfectly symmetrical (is that the word?) spacing but you’re getting enough of a difference to put its performance into a different category.

Meanwhile, that Estes E16 is like a 67% E and the F15 is a 24% F (so, close enough). Again, a completely different performance category, even if not perfect matches. The F15 is also limited by Estes’ desire to have two of them in a rocket, such as an F15-0 to F15-8 stack, be allowable under class 1 rules, so they’re close to the 125g propellant limit for a pair (60g each).

There are some exceptions to this “spaced out” strategy, such as AeroTech putting out the matched E35 and F41 motors recently. They’re pretty close in total impulse, but they’re designed with different limitations in mind. The E35 takes full advantage of the E impulse class, while the F41 provides additional propellant, and thus thrust and impulse, but not enough to bust non-HAZMAT shipping limits.

 

[jmasterj]

Same with the my favorite goad people motor, the J350. It's a 680ns J. Just 40 ns over a full I. It is nothing like a 54mm J that might tickle 1280ns. Both are J's. But only in name only. THIS is why CTI's labeling is 100% better than Aerotech. CTI TELLS YOU, this is a xxxx NS motor. I wish NAR, CAR, and TRA would make labeling like CTIs mandatory.

Every impulse letter has a 2x range, it's not unique to J and up. There's obviously more room to spread out at a higher impulse level, but double is double when you place it in the context of the rocket it will be powering. "In name only:" isn't that what the letter is part of?

I would prefer a mix of AT and CTI labelling that included total impulse like CTI but also the propellant like AT. Both things are important to me. When looking through motors on Thrust Curve, the missing propellant type on CTI designations is actually more annoying because the total impulse gets its own column.

 

[Getmore]

38mm to 54mm was a big jump for me. I really enjoy the 54mm so there will not be a 75mm jump in my future.

 

[gdjsky01]

I simply believe, nay know, in my experience, people don't know the total impulse. Its an E! Well yes. But barely. And I said the J350 was my favorite one to list because its barely a J. And as you go across the range of I's you'll see there are almost full I's. I don't think the peeps at Estes or AT are thinking, "Well it is almost double the impulse of our X"... but maybe..
Anyway thats my story and I am sticking to it.

 

[LithosphereRocketry]

I simply believe, nay know, in my experience, people don't know the total impulse. Its an E! Well yes. But barely. And I said the J350 was my favorite one to list because its barely a J. And as you go across the range of I's you'll see there are almost full I's. I don't think the peeps at Estes or AT are thinking, "Well it is almost double the impulse of our X"... but maybe..
Anyway thats my story and I am sticking to it.

For me, that goes both ways. The J350 is one of the most common J's, so when people say J that's the size range they're thinking of. In terms of perception, the understanding gap isn't so much that a J350 is barely a J, it's that a J760 is basically a K.

It would be interesting to see what people's expectation of what a J is vs. what expectations of other motors are. I see a lot more baby H's and baby J's, but a lot more full K's and full I's.

 

[waltr]

I see this also with G motors. Not many are full G (160Ns). It does take a bit of looking (ThrustCurve is very handy for this) but then do you want to buy another case for the load.

 

[Spitfire222]

This thread made my think of a question: do any rocketeers really care about the actual newton thrust of a specific motor, and look down at "baby" motors? I'm getting that vibe from some responses here. I don't see anything wrong with someone being happy/proud that they've moved up an impulse range by using a "baby" motor versus a "full" one of the same impulse class. It's a range; a "G" is a "G", etc.

 

[heada]

This thread made my think of a question: do any rocketeers really care about the actual newton thrust of a specific motor, and look down at "baby" motors? I'm getting that vibe from some responses here. I don't see anything wrong with someone being happy/proud that they've moved up an impulse range by using a "baby" motor versus a "full" one of the same impulse class. It's a range; a "G" is a "G", etc.

The only place I ever pay attention to it is for L2 certification. Lots of people will build a L2 rocket, fly it on a J350 (baby J) and then immediately go look for a minimum diameter project that uses a full L. It is true that a baby J and a full L are in the same cert range but they take vastly different rockets and build processes. The same could be said for L1 with getting a cert on a "low and slow" rocket and H128 motor and then look for that full I but it isn't as big a difference in the L1 range. A J350 vs a J415 isn't an issue in my eyes. Same with an H128 vs a H180

I don't look for it but others do in the records area. A complex K for example, you'd want to find 2 full J motors so that you have the maximum allowed for that record. J1026 staged to a J1000 kinda thing.

 

[techrat]

I don't see anything wrong with someone being happy/proud that they've moved up an impulse range by using a "baby" motor versus a "full" one of the same impulse class. It's a range; a "G" is a "G", etc.

Exactly. I'm hearing of L1 attempts that fail because they shoot for the moon, and then wind up not being able to retrieve their rocket. Too many people think that extreme altitude is "manly", and rush to join the LDRS club before they really know what they are doing. I plan on playing it safe with a low and slow flight using the minimum motor I can get away with.

It's like when I took the class for my motorcycle license. I was told at the end of the class that everyone was now qualified to ride in circles in a parking lot. Dum-dums then buy the biggest, baddest bike they can afford and promptly wind up as a splat on the road. I bought a small scooter, and worked my way up to highway speeds with the second, larger scooter.

 

[Spitfire222]

The only place I ever pay attention to it is for L2 certification. Lots of people will build a L2 rocket, fly it on a J350 (baby J) and then immediately go look for a minimum diameter project that uses a full L. It is true that a baby J and a full L are in the same cert range but they take vastly different rockets and build processes. The same could be said for L1 with getting a cert on a "low and slow" rocket and H128 motor and then look for that full I but it isn't as big a difference in the L1 range. A J350 vs a J415 isn't an issue in my eyes. Same with an H128 vs a H180

I don't look for it but others do in the records area. A complex K for example, you'd want to find 2 full J motors so that you have the maximum allowed for that record. J1026 staged to a J1000 kinda thing.

Fair enough, and thank you for the thoughtful reply!

 

[smstachwick]

Exactly. I'm hearing of L1 attempts that fail because they shoot for the moon, and then wind up not being able to retrieve their rocket. Too many people think that extreme altitude is "manly", and rush to join the LDRS club before they really know what they are doing. I plan on playing it safe with a low and slow flight using the minimum motor I can get away with.

This is what I’d like to do, except I’d also like to keep the build light enough that I could test-fly on a G prior to certification. I’m a bit on the cautious side and a rocket like that would have a number of unknowns to begin with. If something is going to go wrong on the first flight, I’d rather have only a little bit of power, and have it not be a cert flight.