I ask my second question.
She chuckles. “Actually, yes, I did know. She told me herself, a while before they started… Well, you know.” She gestures at the space between us, a smile on her face. “With some of the antics she’s described during their planning meetings, I daresay she’s the only reason they haven’t sent anypony to the hospital.”
I blink. “Wasn’t Twilight doing that?”
She nods. “Oh yes, she does- some. You see, Twilight has a bit of a fixation on learning… Lyra described it to me, once. She said, Twilight would, let’s see… ‘smash a glass jar to find out if it’s breakable’. With some of the experiments she said Twilight suggested…” She shudders. “I, for one, am glad she never got to test how much water the average rooftop could deflect before collapsing.”
It’s a lab day. That’s the only way I can describe it; I’m not into the science of the world very much.
It all started around a week ago, when Twilight had wondered idly, during a rainstorm, how much water the roof could handle before it broke. Three days ago, I caught the budding scientist with a testing plan that might well have flooded the city, and almost certainly would destroy a few rooftops. Unfortunately, I’m not a scientist- or engineer. So I used a few choice words to get her to discuss with the rest of us before she started testing. She’d done that, later that day- and just like I had, Lyra had balked at Twilight’s methodology.
That had been my goal: Get the plan in front of Lyra before it could do any damage. The engineer has been a bit of a killjoy in our group, despite being the leader- but for good reason. I’ve lost count of the times she’s saved our flanks by pointing out what could- and probably would- go wrong with any given plan we came up with. Once, when we did something without her, she found us before the authorities- and managed to not only pull myself and Blue out of Glamour and Twilight’s sleds’ paths, but fast-talk our way out of a trespassing violation. Something about Twilight owning the violated land, if I remember right. Ever since then, she’s been involved with every single activity we do. If she’s not available, we wait until she is.
Twilight is still working on that.
Anyways, Lyra had done her thing. I hadn’t understood any of it, and I’m still not sure how pouring a couple gallons of water over a set of model rooftops at faster and faster speeds until they break is going to help. If I remember right, even ever-studying Twilight had difficulty understanding the methodology until she’d explained it three times.
I adjust the valve, opening it slightly; the model didn’t break yet. I look up at Blue, who is helping me and Glamour set up our ‘test rig’, I believe she called it, for the next test. Twilight and Lyra are busy discussing the numbers- though it sounds more like Lyra is explaining them to Twilight. Who isn’t getting them.
“So…” I begin. “Do you have any clue how the time it takes to drain the tub onto a model will tell her how much water a real rooftop can withstand?” I ask.
Blue shrugs.
“How about why she’s using inches to describe water?” Glamour asks.
I shake my head. “No clue.”
Lyra trots back up, right on schedule. Twilight, following her, still looks confused. I open my mouth to ask- but she beats me to it.
“Aaaand, Twilight just asked the same thing,” she states, before looking at the named pony. “Again.”
Twilight smiles sheepishly.
“Alright,” I state, Blue and Glamour lining up on either side.
Lyra smiles, and makes a show of clearing her throat. “A-hem, class is now in session,” she states, as Twilight joins us. “I’ve been trying to start with the house rooftop and go down, in previous explanations, but that doesn’t seem to be working. So this time, I’ll start with the decisions I made, why they matter, and go from there.
“First, we have the models. Ten different model roofs, of three different structures. It’s a small sample size, but these three structures are found in over ninety-five percent of Canterlot’s structures- including, I understand, Canterlot Castle itself. We’re using multiple to allow for errors in construction; this sample size allows us to estimate for the ‘average rooftop’.” She smiles. “The number of each structure in our models is proportionally similar to the number of each structure in Canterlot, according to the construction records, so our results should be representative of Canterlot as a whole. Make sense?”
She’s met by a round of nods.
“Right then. As for why it’s five gallons… it’s just an arbitrary volume. Not so large that it takes forever to filter down or reset, yet not so small that it might not be enough to break our models. Everypony probably already knows why we’ve got this after the valves, right?” She touches her hoof to the little contraption she’d called the ‘rain manifold’.
Everypony nods.
“To simulate a genuine rainfall,” Twilight states. “Prevent an unrealistic point load.”
“Exactly. We’re only timing four gallons because that makes it easier- and more accurate. Everything gets up to speed during the first gallon, then runs at a pretty constant rate until it runs out.
“Now we get to why rate is important.” She points a hoof at the roof above our heads. “Everpony here is in agreement that ten thousand gallons would crush that roof, right?”
Nod.
She nods as well. “Me too- though of course, it depends on how that water is poured on it. If it takes you ten thousand hours to pour all that water on it through fluffy little rainclouds, it’s never going to break it. If you dump that water on top of it as a brick- like we’d upturned a bucket- it’ll smash right through it and probably destroy a few homes around us, as well. Right?”
A few nods, and confused scowls.
She sighs. “This is where physics comes in. It’s a topic Magic Kindergarten hasn’t covered, and one I would have expected Twilight to have looked up. When you pour water on a rooftop, it flows right back off of it. That creates the aforementioned break-or-not-to-break problem- and is why the exact amount of water we’re using is unimportant, Instead, it’s the rate at which we pour the water that matters- how much water is hitting the rooftop over a specific period of time. That little example had rates of a gallon an hour… and somewhere around ten thousand gallons per second. Wildly different rates, wildly different results. Good so far?”
More nods.
“Good. Our models are what we call scale models- and in this case, they’re all exactly one twenty-fifth size of a real roof. Their strengths are all scaled down accordingly- so pouring one gallon on this model is equivalent to pouring roughly sixteen thousand- twenty five cubed- gallons on a similar rooftop somewhere in Canterlot.
“Then we get to the problem of area. Bigger roofs can withstand more water than smaller roofs, given that it’s distributed. That’s why our number can’t be a clean gallons per hour value- the same amount of water that would smash through the roof of the shed would probably bounce right off of the house roof. That’s why our final number is in inches per hour- one gallon, per one point six square feet, is one inch. That’s a square about fifteen inches on a side.
“This way, ten gallons per second on a ten square foot shed rooftop has the same rate as a thousand gallons on a thousand square foot house rooftop… both of which would probably collapse, because a gallon per second is a lot of water. Still good?”
Nod.
“Now. The reason we’re measuring time, rather than water, is fairly simple. We know how much water we have, we just want to know how long it’s taking. Four gallons, divided by however long it took, gives us a gallons per second number.”
A couple heads tilt.
“That’s where the rain manifold comes in. It doesn’t just distribute the water to simulate a rainfall- no, it has a known size, as well: thirty inches on a side, just like our models. Thus, four gallons per second going through it is exactly equivalent to one inch per second. Which becomes a scale twenty five inches per second. Which is a lot of water, and virtually guaranteed to smash through just about any roof in Canterlot, aside from drowning everypony and washing the city off the mountain.
“We’re calculating our times down to the thousandths of a second so we can have very precise measurements- and calculate an accurate inches per hour measurement. After all, I’ve seen monsoons that don’t reach a single inch per second.” She takes a deep breath. “That all make sense?”
Slow nod. “I think,” I state.
“Oh… OH!” Twilight states. “Oh! Now I understand! Thank you!”
“So then. Twilight Sparkle, Lyra Heartstrings, Vinyl Scratch, Glamour Strings, and Blue Chime. Collectively, the Cutie Mark Crusaders. If I am to understand this correctly, you teamed up on your own time to perform a series of experiments related to rooftop durabilities?”
“Yes Ma’am,” Lyra states. As the leader, she usually takes the lead- even if I am our ‘mascot’, the princess of the party. I still have the false wings and the crown; that is to say, they’re stored in our clubhouse for my use. We’re facing our Magic Kindergarten teacher right now, after school; on my suggestion, we extended the original experiment by a couple weeks, eventually compiling and submitting a paper. We finished last week.
“... Then you tested various structures, identified the design elements that contributed most to their strength, and designed the strongest one you could.”
“Yes ma’am,” Lyra states. “As I recall, our design is approximately thirty-eight point seven times stronger than the average Canterlot rooftop, for minimal additional materials, a negligible difference in construction labor, and absolutely no difference in exterior appearance.”
“So it is,” she states. “Who was it that came up with it?”
She shrugs. “We did, all together.” The rest of us nod. Vinyl, Glamour, and Blue were all enjoying themselves for much of the experiment, once Lyra explained everything.
“Ahh… So, we’ll just credit it to the Cutie Mark Crusaders, then?”
I raise my eyebrows. As expected, Lyra speaks first.
“Credit?” she asks. “Something happen?”
She smiles. “Actually, yes. I have a friend that happens to be an architect… and he agrees with your deductions.” She chuckles. “If the Canterlot Building Society accepts it, there’ll even be royalties.”
I blink. Royalties? Like, Princesses? I… I don’t understand. Lyra seems to.
“Ahh,” she states. “We… uh, the Crusaders, that is, are not a legal entity, so… Does it work to put it in the name of all five of us at once?”
She blinks. “Yes, we can do that. Have a good afternoon!”
We leave the room, and start walking home. It’s rather fortunate all our homes are close to each other- and in the same direction from school.
“What did she mean by royalties…?” I ask.
“Money,” Lyra states. “In short, if they take it, none of us will ever have to work a day of our lives… that is, once we grow up.”
“Sounds boring,” Glamour states.
She nods instantly. “Very.”
“So…” I mutter.
“You’ll find it in one of the financial law books,” she tells me.
I scowl at her. “There’s thirty of those and-!”
“Thirty two,” she states.
I huff. “Alright, thirty two of those, and I’ve still got eighteen physics books on my nightstand!”
She snorts. “Speaking of which, any luck?”
I let out a sigh; this is not going very well. “You know what… You know who I am, right?”
She nods.
“So… Can I go about it, um, candidly, and expect answers?”
She shrugs. “For the most part, yes.”
“Ahh. Then, I’ll cut straight to the point. Are you aware that, um…” I sigh again. “That, as of last Monday, your daughter- along with the rest of the Crusaders- have income?”
She blinks. “Income?” she asks. “What from?”
“Royalties on a new roof design,” I inform her. “Valued at almost a million bits just this morning.”
She blinks. “You mean to tell me she hasn’t even graduated Magic Kindergarten yet and she’s already a millionaire?”
I tilt my head. “Eh, in a manner of speaking. None of them will have access to their funds- it’s being split evenly across the five- until they hit age sixteen or enroll in a higher education institution, whichever comes first.” I sigh. “In all honesty, we’re expecting the value to be close to a half a billion bits, or more, by the time that happens.”
“So, she set herself up to be rich… on, what was it again? Roof designs?”
I nod. “It seems they did perform that experiment… many times over, with scale models. The Building Society loves their pattern.” I sigh. “The fillies have not and will not be informed directly, until such time as they gain access to their funds. You may break it to them now, if you so desire.”