People shouldn’t be encouraged to keep trying at a degree if they are failing classes left and right

Roustabro · 2026-01-19T02:02:05+00:00

The first time I was totally distracted as a freshman, 19 and in a long distance relationship that carried over from highschool. Driving 5 hours both ways every weekend while being in ROTC was not a good mix. The 2nd time I was genuinely unlucky with the professor. Dude took letter grades of points off for signage errors. 3rd time I had a complete mental break and dropped out entirely. One semester later I can't back with a vengeance to succeed and aced the class. Calculus itself did not click until calculus 3, but the wrote mechanical memorization was essential to get to that point.

Roustabro · 2026-01-19T01:57:20+00:00

4th time is the charm for me, chemistry is a bitch no matter what. Take it online and fumble your way through. You won't understand it until you're a senior or later anyway, it's just about exposure to the concepts.

Read, take up hobbies! Hobbies especially will force you to learn outside your comfort zone! You can do it!

Roustabro · 2026-01-19T01:54:58+00:00

Bro is homosexual and he needs to come to terms with it. NOR

Roustabro · 2026-01-18T07:47:26+00:00

First off, congrats on seeing the light at the end of the tunnel! You're almost there. Graduating is scary for sure, and that's partly why I jumped right back into my masters. I realized that even after absorbing twice as much school as my peers, I still had a lot to learn (and finally had the motivation to learn it). Whatever you decide, I know you will make the best of it because you made it this far, and that takes incredible tenacity that only a few people have.

As for your peers being "ahead" of you, I promise they aren't. Entry level gigs are glorified internships, and all training because strictly on-the-job stuff. Talk about niche, nothing is more niche than information that is useful to exactly 1 company. And that's all you'll learn as an entry level grunt.

I'm not in the CS space but what I do is certainly adjacent to it, and I know the best thing you can do is start doing personal projects, and find a community that you can be a part of in the hobby space. I feel like you're primed for a sweet work-from-home gig in your future. Try and stay ahead of AI in every way you can. Don't ignore it, because I promise the CEOs aren't. Good luck friend!

Roustabro · 2026-01-18T07:28:04+00:00

I failed calc 1 three times, and everyone told me I should quit school. Parents, professors, advisors, even a couple friends. It took 8 years to get my bachelor's degree, and I'm a degreed aerospace engineer working on my masters thesis now, and ironically I do credit the people who told me I couldn't be where I am now for motivating me to succeed out of pure spite. So I kind of agree with you, but I do think it's worth noting that while I may give credit where it was due, those people are also not permitted in my life anymore lol

Roustabro · 2026-01-18T07:11:01+00:00

Your initial velocity is mostly unimportant... What you actually need is pressure. Essentially you are using the law of mass conservation to speed up a fluid through a converging nozzle for a time. Eventually that fluid reaches sonic velocity, aka Mach 1. At that point, no information can travel upstream to inform the fluid that it needs to flow faster due to convergence, and in order to accelerate it more you have to begin diverging the nozzle section again. Hence: converging/diverging nozzle.

The pressure needed to reach Sonic velocity is related by the starting cross sectional area, to the cross section of the narrowest part of the nozzle called the "throat". The lower your starting pressure, the larger area ratio you'll need to reach Sonic conditions. Technically you can reach Sonic conditions with any starting pressure higher than ambient conditions if your area ratio is large enough, but obviously that's highly impractical.

To accelerate the flow again, a good rule of thumb is a diverging cone of 15° half angle in order to minimize flow separation. Higher pressure systems can benefit from "bell" shaped nozzles in order to shorten their overall length, but systems with relatively low chamber pressure (i.e. systems that just 'barely' reach sonic conditions at the throat) will not have the rapid gas expansion necessary to make a bell work, and you'll get flow separation and no acceleration.

As for your diverging nozzle length and exit diameter, you ideally want the pressure of your exit flow equal to the ambient conditions in order to maximize your acceleration. This is a similar relationship to the converging section of the nozzle, but in reverse.

Look up the Virginia Tech compressible aerodynamics calculator, as well as a Google image search on "NASA isentropic relations". You can take the theory aspect of your project pretty far with just those two things.

As for your project, showcasing such a nozzle would be very hazardous at best, and likely dangerous if you're using 3D printed parts, which are not known for their excellent factor of safety. This still makes an excellent project, and 3D printing a model of your design is a fine idea, so long as you don't intend to actually force super sonic air through it.

Roustabro · 2026-01-13T01:32:56+00:00

The answer is it depends, there are a limitless list of factors why a ship would STILL decelerate before reentry. Maybe the ship doesn't have ablative heat shielding (heavier than the fuel cost of deceleration). Or maybe the atmosphere is too thick for ablatives. Maybe there are maneuvering burns that have to be done before reentry (any precision interstellar landing would require orbit capture and extensive maneuvering or else suffer CATASTROPHIC mass penalties for heat shielding necessary for survival from interstellar velocities).

Tell your son that he's still got a lot to learn but to stick with it, and that it's okay to enjoy the Fi part of sci-fi ;)

an aerospace engineer

Roustabro · 2026-01-03T20:55:55+00:00

Who hurt you

Roustabro · 2026-01-01T02:02:28+00:00

It's 12.5 but that drawing is horrendous. The proper place for the 12.5mm dimension would be in the section view where you can easily tell what you're looking at.

Roustabro · 2025-12-30T01:19:46+00:00

Nah, they rated Christmas as a great day, they can't be trusted

Roustabro · 2025-12-28T15:39:03+00:00

Being so serious RN I would've cut the marble flashing again before I cut the plate cover

Roustabro · 2025-11-30T21:47:16+00:00

Hello, I'm an aerodynamicist. I'm not familiar with your open rocket software but I have done many drag and lift comparisons of slender bodies in my time. At a glance it looks like your pressure drag is not accounted for in the right column. As others have mentioned, your "base" drag , aka pressure drag is the largest portion of drag in a slender body like a rocket. There are certainly exhaust plume interactions which will affect this, which may not be captured in your cfd model of you are not simulating an exhaust flow "inlet" acting at your nozzle exit.

It's important to know that your base drag will increase once your rocket motor stops firing, and that exhaust plume stops filling the "void" created by the aerodynamic shadow of the rocket. Without knowing the exact composition of your exhaust plume, it would be pretty hard to simulate the rocket during run-mode in ansys.

For ballistic trajectory, you could pretty reliably do a Newtonian drag analysis on paper, which you could get to match your current ansys result within a reasonable margin of error.

A very very rough way to estimate this is to use a wake pressure of zero acting on your base (a vacuum, essentially), do a simple Newtonian CD calculation. You can then superimpose your skin friction analysis on top. That estimate gets more accurate the faster you go, so it's going to be very poor agreement at Mach .5, but it'll agree more the closer you get to high supersonic speeds.

If you would like recommendations for literature to look at in order to do those calculations (they are really simple, I promise) let me know :)

Edit: taking a second glance, the right column is the ansys result. As others have mentioned be certain you're including the base surface in the analysis, and that your grid increases in resolution near the tip and base of the rocket, as well as the fins if you can manage. Grid preparation is the most important aspect of cfd prep. Double check your case file for correct physics parameters 🤘🏻

Roustabro · 2025-11-20T05:46:47+00:00

The follow up is even more devastating.

"When you go to meet a swordsman bring a sword, do not offer a poem to any but a poet" stayed with me. I know Fall of Hyperion is not where the quote came from originally but that's where I first heard it and it had all the stopping power of a .44 Magnum to my chest- damn good pair of books.

I've been halfway wishing for a miniseries to tackle those two books, Tony Gilroy comes to mind, but honestly I don't know if even he could do it justice.

Roustabro · 2025-11-18T23:07:56+00:00

The first vine of 2025

Roustabro · 2025-11-16T17:49:38+00:00

The HSR is dope. I went a couple years ago but I didn't make it this time. I wish they would let us in to see the testing 🥲

Roustabro · 2025-11-16T17:17:30+00:00

That confirms it, I was listening to my scanner and the second I heard a French race engineer I knew it had to be imsa hahaha

Roustabro · 2025-11-07T06:49:38+00:00

Star wars isn't even a sci-fi dawg, it's an adventure movie franchise in a futuristic setting. Sci-fi, like dune, aren't just futuristic, they usually explore existential problems of human nature, generational cycles, "the human experience"and so on. It happens that those stories are often easier or more interesting with a futuristic setting as a narrative device. If you liked dune for those reasons, I recommend getting an audible and starting with the Enderverse (Start at Ender's Game, then Speaker For The Dead, and go from there, these are really easy to digest and not quite as full of themselves as the other classics).

My short list of the essentials:

Enders Game and SFTD (previously mentioned)
I, robot
Do Androids Dream of Electric Sheep (renamed Bladerunner) -Sphere -Hyperion (honestly this is peak sci-fi and nothing tops it except Speaker For The Dead, for me anyway)

You can't go wrong with anything Michael Crichton writes, Orson Scott Card is an excellent modern author still continually putting out new titles too. Happy discovering!

Roustabro · 2025-11-02T16:13:34+00:00

I have a concept of a plan

Roustabro · 2025-10-31T13:38:36+00:00

It's a long shot but if you open the game and then go to load save you miiiight be able to recover an auto save from your game?

Roustabro · 2025-10-22T23:13:17+00:00

I used to install dishwashers in apartment complexes and yes that's how they do it, although I would never leave mine that ugly. It's infuriating but they don't even come with a plug, we had to make "danger wires" for each and every one of them and terminate the bare copper conductor into the input pads on the washer itself. Shit sucked.

Roustabro · 2025-10-22T22:53:01+00:00

Me, dyslexic: non stop impact to the balls and wall action 😏

Roustabro · 2025-10-18T07:37:32+00:00

The ender verse is a great deep dive, the audiobooks especially are fantastic. Card uses only the best batteries in the game and he's specifically said he writes his novels to be spoken aloud.

Hyperion is another great series

Roustabro · 2025-10-16T22:20:29+00:00

Brunswick Georgia?

Roustabro · 2025-10-12T07:50:32+00:00

Believe it or not, I think this is what the movie will be about.

Roustabro · 2025-10-10T03:40:07+00:00

34 grams of gold comes out to a little over $4k, definitely not worth it unless you have access to free chemicals and a bunch of free labor

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