Musings on Certification Cutoffs and L motors

[yvanthesaxophonist]

When I first got into rocketry, it struck me as weird that L1 was the only certification level with two letters in it, while the others each had three. Now, it feels weird to me that the others have three.

I realize that all cutoffs are in some way arbitrary, what separates a 1% J from a 100% I is measurement error, but from my (not fully inclusive) experience, H&I motors are indeed pretty similar, even the baby Hs to the full Is, and J&K motors are also similar. But L motors don't "feel" like they fit with the J&K motors. I think a lot of this has to do with that most L motors are 75mm motors. Rockets that I and others have built that are good for L motors tend to be pretty good for M motors, and the lowest they'll go is very very thrusty Ks. Similarly, the gap between a baby M and a full O, or even something like the N5800, feels much larger than between even small Ls and big Ms. I personally feel like L1 of H&I, L2 of J&K, L3 of L&M, and L4 of N&O, just makes more sense. I don't think this is a necessary change, nor do I think how we do it is unsafe. It works, it's good, people get their certs and generally speaking fly rockets they're capable of flying. Just had some thoughts and wanted to share.

 

[tsmith1315]

When I first got into rocketry, it struck me as weird that L1 was the only certification level with two letters in it, while the others each had three. Now, it feels weird to me that the others have three.

Keep in mind that early on, there were no levels at all, only HPR requiring a single confirmation flight. You could do your confirmation flight on a baby H and then purchase any motor you wanted.

 

[Art Upton]

Keep in mind that early on, there were no levels at all, only HPR requiring a single confirmation flight. You could do your confirmation flight on a baby H and then purchase any motor you wanted.

Got mine in 1989 on an H70 single use motor as TRA #492

 

[yvanthesaxophonist]

Keep in mind that early on, there were no levels at all, only HPR requiring a single confirmation flight. You could do your confirmation flight on a baby H and then purchase any motor you wanted.

Well, we seem to have decided that that was not the best idea. Very interesting to see where we've come from.

 

[Art Upton]

Well, we seem to have decided that that was not the best idea. Very interesting to see where we've come from.

At the Danville Dare in 1990 or1991, they already were talking about how to do "cert levels" in the motel bar that was next to the flying field. I mentioned to Frank who became Public Missiles some sort of simple test like they do in ham radio could be used.

I'm sure I was Not the first to have that idea, but I had it.

Jerry [you know who] was also at that launch and landed his rocket in the Prison at the very very far end of the launch field. It and a few others were held hostage until the lady that owned the Motel and field made a few phone calls... [that's a whole other story]

 

[cls]

There's something to what you say. Watching the launches at BALLS this year, we mused that basically O motors suck. Necessarily stuck in airframes with large frontal area, 6", 8", etc, and not really much more N-s than a full 4" N... They just don't get the altitude, 20k, 30k...

Might as well get a P if you're paying for drag of a 6" airframe.

Privately, I think most N motors aren't worth it, because the poor mass fraction vs the weight of empty case & closures etc.

However, big advantage of wide heavy rockets, watching and hearing the motor burn from closer!

 

[Art Upton]

I remember and still true today you can SOLO at a AMA flying field on a 40 size RC airplane, and then go and buy a giant scale. But at least at our local club someone experienced in Giant Scale will check it out for you and also stand by and spot for you as you fly it for the first few times.

 

[cls]

Thinking back a little, I've burned more Ls than Ms recently. L motors offer: good practice for a new rocket before committing to the big M/N, lower flight, watch the entire flight, closer recovery, cheaper. Horses for courses.

 

[yvanthesaxophonist]

There's something to what you say. Watching the launches at BALLS this year, we mused that basically O motors suck. Necessarily stuck in airframes with large frontal area, 6", 8", etc, and not really much more N-s than a full 4" N... They just don't get the altitude, 20k, 30k...

Might as well get a P if you're paying for drag of a 6" airframe.

Privately, I think most N motors aren't worth it, because the poor mass fraction vs the weight of empty case & closures etc.

However, big advantage of wide heavy rockets, watching and hearing the motor burn from closer!

Not so sure I agree with you on the N motors, but certainly O motors. It strikes me as odd that 5" motors never became popular, I think you'd get a lot of good N and O motors in there for big but not huge rockets, and be much more worthwhile than something like the O8000.

 

[Steve Shannon]

Just had some thoughts and wanted to share.

Thanks for sharing!

 

[yvanthesaxophonist]

Thinking back a little, I've burned more Ls than Ms recently. L motors offer: good practice for a new rocket before committing to the big M/N, lower flight, watch the entire flight, closer recovery, cheaper. Horses for courses.

The L1350 is one of my absolute favorite motors of all time. I do think L motors are one of two great sweet spots (imo) in the hobby for motors, the other being the top end of 38mm motors, those mid Js.

 

[Wayco]

I'm also a big fan of L motors, most of my research loads in the 54/2550 come out in that range, and I usually fly one at every launch. Close enough to get the "feel" of a big motor and visually more impressive.
My all time favorite L is the L1365 Metalstorm. Hard to believe that Aerotech doesn't make it anymore.

 

[AlexBruccoleri]

Just had some thoughts and wanted to share.

I second @Steve Shannon in thanking you for sharing. What you are saying makes sense given there are 8 letters of HPR motors. A friend recommended all certification flights be some impulse greater than the bare minimum for each class. In other words no baby H, J or Ms. I am guilty of doing my cert 3 on a baby M since I was worried about landing off the field. None-the-less I agree with the sentiment. This all being said, I agree the rules are just fine with certification and no need to change.

 

[John Kemker]

Certified at the tail-end of the single-level certification process. When I certified, Tim Eisner said, "Now you get to spend the big money!"

 

[DAllen]

At the Danville Dare in 1990 or1991, they already were talking about how to do "cert levels" in the motel bar that was next to the flying field. I mentioned to Frank who became Public Missiles some sort of simple test like they do in ham radio could be used.

I'm sure I was Not the first to have that idea, but I had it.

Jerry [you know who] was also at that launch and landed his rocket in the Prison at the very very far end of the launch field. It and a few others were held hostage until the lady that owned the Motel and field made a few phone calls... [that's a whole other story]

Oh man...I do love me some good Danville stories. Those are the best. Wish I was in rocketry back then.

 

[GalantVR41062]

I was amazed flying my L1 and L2. As a BAR I just became aware of composite motors, and my first one was a F44w econojet in a scratch built bt60 rocket.
Shortly after I found my L1 rocket on clearance at the hobby store. I flew the G40w that morning as a test flight before the sparky H115 at the high power range. I only had 2 H flights after that before my L2 on the Loki J320r in my redundant dual deploy Dx3.
I have flown both on the upper end of the motors that fit in each rocket, a CTI H160 and CTI J530IMAX.
I have said before with my knowledge at the time of certifying I don't think I was ready to fly the larger motors for each level.
Now after being L2 for a while I jumped from the large J motors to a small L in my scratch built 1/4 scale Viking 7 sounding rocket and now has flown on the 75mm Aerotech L1365M and the next flight will be the AT L1500T.
This is a interesting rocket as I look at my simulation file for the AT L2200G and AT M1350w flight profiles. L3 someday possibly, for now I will keep going down the EX motors and flying what I have.

 

[ZEDL1]

Keep in mind that early on, there were no levels at all, only HPR requiring a single confirmation flight. You could do your confirmation flight on a baby H and then purchase any motor you wanted.

Perfectly correct.
Jim

 

[Lawndart]

Certified at the tail-end of the single-level certification process. When I certified, Tim Eisner said, "Now you get to spend the big money!"

And then waved a bigger motor under your nose. “Want to fly this one?” Ross Dunton wanted to sell me an Energon L750 after my cert flight.

 

[John Kemker]

And then waved a bigger motor under your nose. “Want to fly this one?” Ross Dunton wanted to sell me an Energon L750 after my cert flight.

Yes, indeed, he did!

Energon. There's a name I hadn't heard in awhile. A part of the ill-fated MRED consortium.

 

[jimzcatz]

And then waved a bigger motor under your nose. “Want to fly this one?” Ross Dunton wanted to sell me an Energon L750 after my cert flight.

Are you sure that wasn't a Vulcan L750? Flew a few of those myself?

 

[John Kemker]

Are you sure that wasn't a Vulcan L750? Flew a few of those myself?

He might have meant an Energon L1100. You're right, Vulcan had the L750 while Energon had the L1100.

 

[Antares JS]

I realize that all cutoffs are in some way arbitrary, what separates a 1% J from a 100% I is measurement error, but from my (not fully inclusive) experience, H&I motors are indeed pretty similar, even the baby Hs to the full Is, and J&K motors are also similar. (...) Similarly, the gap between a baby M and a full O, or even something like the N5800, feels much larger than between even small Ls and big Ms.

It doesn't just "feel" this way, it IS this way. It's a consequence of each letter range being twice the size of the one before it.

-A baby H is around 180 N-s, and a full I is 640 N-s.
-A baby M is around 5200 N-s total impulse, and a full O is around 40,000 N-s.
-A small L is around 2600 N-s, and a big M is around 10,000 N-s.

 

[ThirstyBarbarian]

One question I have is, what would be the requirement for the hypothetical L4? What additional testing or skills beyond the L3 requirements would be added for L4?

I’m not looking for any changes to the certification process, but with the way the motor impulse classification works, doubling in impulse each time, motors get big FAST as you go up the letter scale. So I agree, there is a big difference between a baby J and a maximum L.

One of the things I don't personally like to see is when someone or some group attends a launch to certify two levels in a day or a weekend. I’ve seen a few examples of university rocket teams where they want everyone on the team to be L2, so they each build exactly the same L2-capable kit at some kind of supervised group build party, study the L2 written exam, then they show up at a launch together, all fly the same L1 motor, take the L2 written exam, then all fly the same L2 motor. At the end of the process, they've built exactly 1 rocket under supervision, they’ve flown only 2 flights, and they can now go buy and fly an L motor. Basically, they’ve checked the formal boxes, but they haven’t gained the experience. I don’t like that.

Generally, I think it’s a good idea to work your way up through motor classes without skipping letters. Obviously it would be an administrative nightmare to enforce a rule like that, so I don’t see it as a practical requirement, but I do think it’s a good practice.

 

[yvanthesaxophonist]

One question I have is, what would be the requirement for the hypothetical L4? What additional testing or skills beyond the L3 requirements would be added for L4?

I’m not looking for any changes to the certification process, but with the way the motor impulse classification works, doubling in impulse each time, motors get big FAST as you go up the letter scale. So I agree, there is a big difference between a baby J and a maximum L.

One of the things I don't personally like to see is when someone or some group attends a launch to certify two levels in a day or a weekend. I’ve seen a few examples of university rocket teams where they want everyone on the team to be L2, so they each build exactly the same L2-capable kit at some kind of supervised group build party, study the L2 written exam, then they show up at a launch together, all fly the same L1 motor, take the L2 written exam, then all fly the same L2 motor. At the end of the process, they've built exactly 1 rocket under supervision, they’ve flown only 2 flights, and they can now go buy and fly an L motor. Basically, they’ve checked the formal boxes, but they haven’t gained the experience. I don’t like that.

Generally, I think it’s a good idea to work your way up through motor classes without skipping letters. Obviously it would be an administrative nightmare to enforce a rule like that, so I don’t see it as a practical requirement, but I do think it’s a good practice.

That's a good question. I think the primary requirement for any certification is the flight, and anything else is just extra insurance as the motors get big. You could probably simplify the L3 report requirements for the new L-M L3, same general idea but just with fewer details, and maybe not needing pre-approval. Maybe single TAP approval instead of double TAP. Overall, slightly less than current L3, but not much. Then, you take the current L3 requirements and you add just a tiny heft to them for L4. Some people can keep them really low, but by and large N-O motors go really high, so you could contemplate dual deployment being a requirement, not just redundant electronics. Perhaps a requirement for a tracker of some kind. I haven't given this a whole ton of thought, so I am just spitballing, but generally the new L3 is slightly less stringent than the current L3, and the new L4 is slightly more stringent.

 

[yvanthesaxophonist]

It doesn't just "feel" this way, it IS this way. It's a consequence of each letter range being twice the size of the one before it.

-A baby H is around 180 N-s, and a full I is 640 N-s.
-A baby M is around 5200 N-s total impulse, and a full O is around 40,000 N-s.
-A small L is around 2600 N-s, and a big M is around 10,000 N-s.

Exactly, the exponential scaling is pretty aggressive. I still feel like motors on one letter away feel fairly similar, save for some spicy propellents Hs and Is fly about the same. But imagine if L1 was H-J, I think that might be a little much.

 

[Art Upton]

Are you sure that wasn't a Vulcan L750? Flew a few of those myself?

I saw a cluster of 3 of them at Danville. It was awesome.

Edit: It sounded like a freight train roaring

 

[Lawndart]

He might have meant an Energon L1100. You're right, Vulcan had the L750 while Energon had the L1100.

Yep, meant the L1100. After flying one Vulcan H100 Smokey for my cert flight, decided to turn down the L and went for another Vulcan H motor (thinking it was an H245 HF). Still have the AAA Magnum Pennsylvanian Crude rocket and some Vulcan motors.

Followed up that flight with the Estes Pro Patriot w/4 D12s. One motor lit on the paid with the other three coming online just as the model went sideways, cruising across the field about ten feet up. Made it under the irrigation equipment. Then watched Tim Eisner put a two stage bird into the forest surrounding the field, starting a fire. Made me feel a little bit better. No one was hurt by either flight.

Should say, I like the cert levels as they are now. My L3 rocket (Smokin Rockets Nike Smoke) was easier to construct and fly then some of my H/I powered birds.

 

[Tom Flint]

I'm sure the motor manufacturers would love such a change. Before there were levels of certification, M rockets were rare birds, but certification levels gave people goals to shoot for. Sales of L and N motors would, shall we say, skyrocket?

 

[cbrarick]

Thirsty is on to something, but perhaps a minimum number of flights at the previous level? say......
for L1, 5 G powered flights
for L2, 5 L1 flights
L3 is a different story because it's a much more supervised process......

 

[tsmith1315]

Thirsty is on to something, but perhaps a minimum number of flights at the previous level? say......
for L1, 5 G powered flights
for L2, 5 L1 flights
L3 is a different story because it's a much more supervised process......

Would that require witness sign-off for the 5 qualifying flights?