V_Terranova_Jr

4 mesi fadiscuss

There is an element of truth to this. It's also true that the U.S. government is a terrible customer, especially for bespoke or expensive military goods. However, you can see my other comment https://news.ycombinator.com/item?id=47652717 for what is likely the greater contributing factor. Different outcomes require acquisition leaders that prioritize doing the right thing for the public, even if that pits them against their internal government "customers".

V_Terranova_Jr

4 mesi fadiscuss

The highest priority in U.S. government acquisitions is to respect the business "rights" of suppliers and potential suppliers. It's hard to understand how tightly this is wound into the very foundations of USG acquisition until you've seen the inside of the process. There are a lot of pragmatic things the government ought to be able to do to best represent the public's interests, but the corporate supplier base's business interests almost always trump the public's interests. The exceptions are when acquisition officials buck the system, lay out expectations for technical data up-front, negotiate hard, and are willing to risk the supplier walking away.

The deference to corporate interests is deeply entrenched in how the U.S. government works. In my opinion and experience, it is also why the U.S. government fails so badly at so many things it does.

Imagine you are the end-user of the thing being acquired (e.g., a military service). You know the acquisition is system is slow, ponderous, and subject to a lot of high-level interference. You care less about the public's long-term interests than about getting the thing, especially when there's a strong risk you may never get the thing due to acquisition system failures. When you feel that sense of desperation, you let the acquisition process give away a lot to the supplier if it substantially improves the likelihood you get the thing, or the (real or perceived) timelines to get the thing.

V_Terranova_Jr

2 anni fadiscuss

I'm sorry, but this is basically incorrect on every point other than the limited tenure. Source: I work in this sector.

PMs often come directly from industry. Once they do, there is a period over which they are not allowed to make direct decisions that affect their previous company, but the previous company is free to bid on that PM's programs and speak with that PM. When these conflict of interest situations arise, the office appoints a delegate PM to make decisions associated with that company.

There are absolutely varying qualities of PM, but the majority of them would be considered a domain expert or subject matter expert in some technical area. Standard practice is for a new DARPA PM to inherit existing programs that are already executing as the old PM finishes their tenure. When a PM leaves, the office tries to hand the executing programs to a new PM who knows something about that field (or is an expert). That doesn't always happen, for various reasons, but they do try to do it that way.

There is a large contractor staff that does a lot of heavy lifting on both technical and programmatic fronts. The PM is the decision-maker, but the contractor staff are integral. These contractor jobs can pay quite well for senior staff or technical experts. Maybe not FAMANG software developer salaries, but particularly for topics in the physical domain, the salaries can be significantly higher than the equivalent role in industry.

V_Terranova_Jr

2 anni fadiscuss

Replying to finish a discussion no one will probably see, but...

> That the original comment I replied to is false: "Good luck designing crash resilient structures without simulating it on FEM based software."

In refuting the original casually-worded blanket statement, yes, you're right. You can indeed design crash resilient structures without FEA. Especially if they are terrestrial (i.e., civil engineering).

In high-performance applications like aerospace vehicles (excluding general aviation) or automobiles, you will not achieve the required performance on any kind of acceptable timeline or budget without FEA. In these kinds of high-performance applications, the original statement is valid.

> FEM raises the quality floor of engineering output overall, and more rarely the ceiling. But, excessive reliance on computer simulation often incentivizes complex, fragile, and expensive designs.

Do you have any experience in aerospace applications? Because quite often, we reliably achieve structural efficiencies, at prescribed levels of robustness, that we would not achieve sans FEA. It's a matter of making the performance bar, not a matter of simple vs. complex solutions.

> I agree with his main point. It's an essential tool for combatting certifications and reviews in the world of increasing regulatory and policy based governance.

That was one of his points, not the main one. The idea that its primary value is pandering to paper-pushing regulatory bodies and "policy based governance" is specious. Does it help with your certification case? Of course. But the real value is that analyses from these tools are the substantiation we use to determine the if the (expensive) design will meet requirements and survive all its stressing load cases before we approve building it. We then have a high likelihood of what we build, assuming it conforms to design intent, performing as expected.

V_Terranova_Jr

2 anni fadiscuss

What is your actual assertion? That tools like FEA are needless frippery or that they just dumb down practitioners who could have otherwise accomplished the same things with hand methods? Something else? You're replying to a practicing mechanical engineer whose experience rings true to this aerospace engineer.

Things like modern automotive structural safety or passenger aircraft safety are leagues better today than even as recently as the 1980s because engineers can perform many high-fidelity simulations long before they get to integrated system test. When integrated system test is so expensive, you're not going to explore a lot of new ideas that way.

The argument that computational tools are eroding deep engineering understanding is long-standing, and has aspects of both truth and falsity. Yep, they designed the SR-71 without FEA, but you would never do that today because for the same inflation-adjusted budget, we'd expect a lot more out of the design. Tools like FEA are what help engineers fulfill those expectations today.

V_Terranova_Jr

2 anni fadiscuss

I don't know about full-on nationalization, but we have plenty of evidence to show the incentives for publicly-owned for-profit companies whose primary customer is the Government are strongly misaligned with the non-economic interests of the public.

I don't have a pat solution to this, but for example, Boeing, Lockheed Martin, Northrop Grumman, and Raytheon have little reason to improve when they have a captive customer. Raytheon recently agreed to pay ~$1B in penalties for illegal exploitation of their position and the market doesn't care: https://www.justice.gov/opa/pr/raytheon-company-pay-over-950...

Pure capitalism for these kinds of uniquely critical products and services doesn't seem like the right answer.

V_Terranova_Jr

2 anni fadiscuss

This is a poor example of "Government innovation". It's more an example of legislative overreach / "pork barrel" politics, and bad acquisition practices.

The Government is certainly capable of doing a shitty job, but that tends to happen more when the Government contracts things vs. actually doing real work in-house. At least in my field, I've seen some incredible innovation done within the U.S. Government.

V_Terranova_Jr

3 anni fadiscuss

We probably won't get much further going back and forth on this. For what it's worth, you seem very reasonable, I've appreciated your comments for a long time, and I'm sure we'd get along fine if we were to work together.

I think you could let Linus off the hook by trying to find the kernel of truth as you suggest, and that seems to be the way key Rust team members work. There's been plenty of needless rancor in HN comments about Rust and you can see people like @pcwalton just not engage with the emotional content while still continuing to engage with the technical points. I'm personally impressed by this, but wouldn't be surprised if it contributed to the burnout.

Should we all aspire to be like that? Doing so seems like the human communication equivalent of Postel's Robustness Principle, which sounds great but in practice leads to shitty implementations getting away with being shitty because of the "robustness" on the other side. Maybe the better play here, especially with asynchronous communication, is to expect people come back to their message draft when they are not so pissed/emotionally triggered and then snip out tangential emotional crap. Especially the ragey condescending stuff.

V_Terranova_Jr

3 anni fadiscuss

There's more to the Linus-style jerk phenomenon than just telling entitled people to piss off (I would be reluctant to call that being a jerk if that's all it was). See https://news.ycombinator.com/item?id=33058906 for an example thread and associated comments. If you're just ranting or passing off subjective POVs as truth and obvious and those disagreeing with you as doing so out of incompetence or malfeasance, that isn't being direct, honest, or straight to the point. It's being a dick.

I've seen brilliant colleagues for whom I have the utmost technical admiration completely fail to improve bad designs implemented by others, because the brilliant person was so dickish about how they communicated to others.

V_Terranova_Jr

3 anni fadiscuss

> ... the idea that Musk hasn’t considered oil panning and should’ve just asked an engineer is ludicrous. The author assumes Musk must be an idiot despite all of the evidence to the contrary.

I don't see anything ludicrous in the author's article, even if it sneers at times. Though unquestionably successful overall, since Elon has a history of bad technical or PR/appearance-driven moves, I'm not sure what's wrong with mocking him for some of those things. He is successful despite doing some idiotic things, it's not that everything he does is brilliant and correct.

The article doesn't provide any internal Tesla evidence as to whether Elon considered it and disregarded oil canning (for whatever reason), or if people on his team told him about this likely issue and he blew them off, thinking he could just keep demanding his team bring him solutions instead of telling him about problems with his vision. Under the circumstances, either could validly be criticized as idiotic, in which case mocking him seems like fair game. This would hardly be the first such issue ("Falcon Wing" doors, display screens on the Model S, the incredibly ill-advised 'Full Self-Driving' labeling, etc.).

V_Terranova_Jr

3 anni fadiscuss

Elon is well-known for firing or sidelining technical staff with whom his intuition disagrees, regardless of his own technical depth in any of those matters. His companies have a lot of success for reasons other than his making the wisest technical and programmatic decisions. He sets his own standard for what he considers acceptable, even if those standards fly in the face of existing norms. That's not unalloyed awesomeness - there are sacrifices.

The author, in an admittedly ranty way, levels basic criticisms that are hard to individually disqualify. With the truck, it seems like Elon did Elon things, and his team is struggling to make his vision real in a mass-producible design with acceptable quality.

V_Terranova_Jr

3 anni fadiscuss

> I wonder what the situation will be in terms of fuel efficiency. Obviously it will take more energy per second to push through the atmosphere, but that may be defrayed by not having to hold the airplane up as long.

The relevant metric is mass of fuel burned per passenger seat-distance. In American units, this would be (lbs. fuel)/(pax-seat mi.). This measure allows direct comparison of differently sized airplanes with different design ranges and cruise speeds.

Take a look at Figure 1.2.7 in this study a Boeing-led team performed for NASA: https://ntrs.nasa.gov/citations/20100030607 . There were plenty of study contracts awarded under this project - Lockheed Martin did a good study as well, but the Boeing one was the first I found.

The dual/tri class band includes the (lbs. fuel)/(pax-seat mi.) for a high-efficiency large subsonic transport. Call it about ~0.1 for this aircraft type. Note the target of the study, which requires state-of-the-art technology or beyond, is 0.3 for a low-boom supersonic cruiser.

Even taking credit for efficiencies beyond Concorde technology levels, and cruising slower than Concorde, it's still ~3X the fuel burn per pax seat-mile compared to a modern high-efficiency subsonic transport. So reduced flight time is more than offset by the energy expended to fly fast and carrying fewer people in a given flight. The picture will be uglier still for supersonics compared to target efficiencies for next-generation subsonics.

V_Terranova_Jr

3 anni fadiscuss

> Give more funding to proper engineers, not physicists/chemists

Materials science departments are often called "Materials Science and Engineering". How do they fall in your categorization?

Without disrespect intended, your words sound like those of someone who has never spent any time in graduate school in a engineering program in physical disciplines. The lines can be blurry.

V_Terranova_Jr

3 anni fadiscuss

> So it makes sense that most researchers are looking for higher efficiency.

It makes sense that researchers should be considering metrics other than efficiency as well for new materials or architectures, and there's no reason why this is a uniquely industrial pursuit.

Grandparent's comment resonates - efficiency claims seem to be the only ones generating press releases.

V_Terranova_Jr

3 anni fadiscuss

I've previously written a few relevant comments that hopefully answer in parts:

[1] https://news.ycombinator.com/item?id=27386119

[2] https://news.ycombinator.com/item?id=35124271

[3] https://news.ycombinator.com/item?id=35126733

Relative to say Concorde, acquisition costs and direct operating costs need to decrease and # of revenue-generating flights/time need to increase for viability. All of these point to slower speeds. If the perceived boom noise of the "quiet" supersonic designs is low enough, supersonic overland flight could potentially be permitted (NASA is trying to make this possible via this X-plane), with vastly more addressible market. Low boom limits the Mach number.

V_Terranova_Jr

3 anni fadiscuss

If commercial supersonic flight has any hope of being economically viable, one of the prerequisites will be cruising below Mach 2.

V_Terranova_Jr

3 anni fadiscuss

> I do wonder how much modern design can overcome, in materials, engines, aerodynamics, and flight controls.

The basic physics are arrayed against you. Higher speed cruise flight already means you already fly at higher altitudes or the thermal and structural loads would be intolerable. Stall departure resistance isn't the issue. Get high enough, and you're no longer talking about cruising flight, you're talking about hypersonic glide that has been accelerated to hypervelocity by rockets (this is called point-to-point boost-glide). It has been looked at, and people are continuing to look at it. There is a whole loose industry coalition in the U.S. called "FastForward" that is interested in this topic.

V_Terranova_Jr

3 anni fadiscuss

Carrier catapults violently accelerate aircraft to the point they are going fast enough to lift their own weight, within the takeoff length on the deck.

You could likely lessen fuel burn of a supersonic aircraft taking off (as you could with a subsonic aircraft) by accelerating it via a catapult of sorts, but you have to do so at acceleration levels tolerable to all passengers, which would make for a long, unwieldy catapult. Release speed is also obviously going to be very subsonic.

V_Terranova_Jr

3 anni fadiscuss

> then they realized the fuel economy of supersonic aircraft peaks around Mach 3

As I noted in a below comment, there isn't a way for this statement to be accurate without a lot more qualifications. For "equivalent technology level", Mach 2 cruise will beat Mach 3 cruise in passenger seat-miles per unit fuel burn, and below Mach 2 will be better still.

The extremely questionable economics of supersonic commercial flight were realized by technical people far before the 1960s US programs were terminated. Two excellent sources on this topic are by aviation historian Richard K. Smith,

https://www.jstor.org/stable/26802349 , with text freely available at: https://www.thefreelibrary.com/THE+SUPERSONIC+AIRLINER+FIASC...

and the book "High Speed Dreams" which also covers the 1990s HSCT era: https://press.jhu.edu/books/title/8516/high-speed-dreams

There's significantly more to the problem than just managing heat and "solving" takeoff.

V_Terranova_Jr

3 anni fadiscuss

> No, it's exceptionally bad to fly close to Mach 1 and you do better if you fly faster up to Mach 3 or so.

Where do you get this from? I suspect you are talking about the Breguet range parameter, which is (M / SFC * L / D), where M is the cruise Mach number, SFC is fuel consumption per unit thrust, and L/D is aerodynamic efficiency.

Cruise L/D drops monotonically with Mach number until it asymptotes out to hypersonic waverider type figures (the well-known Kuchemann curve fit for supersonic L/D and the asymptoting to waverider values is illustrated at: https://aerospaceweb.org/design/waverider/design.shtml ).

SFC for gas turbines is extremely sensitive to cycle parameters and internal temperature limits, but generally well-designed gas turbine propulsion systems are going to beat ramjets until they hit thermal limits. Today's gas turbine technology is far more capable than the J-58 technology of the the A-12/SR-71 era. That said, SFC is still going to increase monotonically with cruise Mach number until you asymptote out to flatter slopes of ramjet and scramjet curves. (Edit: see the Isp illustration at: https://en.wikipedia.org/wiki/Specific_impulse ; Isp is the inverse of SFC).

So you are banking on the increase in M more than offsetting the increases in SFC and decreases of L/D. This is not going to support the case for increased efficiency in high supersonic (M >= 3) cruise. You could make the argument going full-on hypersonic waverider could "make sense" since the range cost functions plateau out, but that is still going to have a strictly lower overall range parameter than a supersonic vehicle. Kuchemann addresses this topic in his well-known text, "The Aerodynamic Design of Aircraft".

A naive Breguet range parameter perspective also fails to consider airframe mass penalties associated with flying faster (roughly, aircraft acquisition costs trend with aircraft unfueled weight), or that high aerodynamic efficiency is often at extreme odds with volumetric suitability for passenger & cargo carriage. Mass penalties will come from variable geometry, thermal management, Cg management, degree of compromise in structural efficiency for aerodynamic efficiency, etc. Let's say you manage to keep Breguet range parameter really high and fuel burn per seat-mile is acceptable. All the complexity and increased airframe mass of the faster aircraft is still going to make recurring costs to operate & maintain the aircraft really high.

The above also neglects boom, which you ideally want to minimize to maximize overland flight potential for your supersonic aircraft.

As per a previous comment I made: https://news.ycombinator.com/item?id=27386119 , if you're going to go in on supersonic civil flight, you likely want to be below Mach 2. Mach 1.4 - 1.8 might be the sweet spot when you consider all factors, assuming it makes any sense at all economically.

For the majority of air travel, we would be better served by making the airport experience much more streamlined and less shitty. And I say this as one who loves and works in high-speed flight.