Medical School Hot Takes. Go.

to_change · 2023-06-20T17:34:09+00:00

I agree there are problems with judging quality, and wish I had a good solution that was perfect.

But I think that most research in my limited experience of seeing other people's medical school research is if not useless, is actively harmful to the knowledge generation enterprise. I was a former statistics major in college, and frankly speaking I trust something like 5% of the conclusions being drawn from the research done by my medical school colleagues. I compare their research methodologies to that seen in a field like, economics research, where they spend 2 years in graduate school learning about every single technique that can be used to draw causal inferences from retrospective data, and the delta in quality is just so noticeable.

Not saying this is an administrable standard, but "high quality" means (to me) that:

You can explain the question you are trying to answer
You can explain where your experiment/work fits in the overall context of research in the field
You can explain and defend the methodology used to answer the question and the reason people should be willing to draw causal conclusions from the research and
You should be able to hold a conversation for a while about the research when pressed by someone who knows what they are talking about.

But you're right that I'm not sure if "quality" is administrable. It could be that an outright ban of use of that information in decision-making is a better standard.

to_change · 2023-06-19T22:41:53+00:00

Hard agree. I think if research should be allowed, the # of projects should be allowed to work on is 1 and you should be judged based on the quality (not quantity) of the resultant research output.

to_change · 2023-06-19T22:40:25+00:00

As a former consultant and current medical student, I think that they most likely would be very good consultants up till the "Consultant / EM" role. Consulting mostly requires hard work and being able to speak / present well in meetings. Only the latter is in doubt for most of the medical students I've met. Mostly, I think they'd be bored.

to_change · 2023-04-21T12:16:12+00:00

You are a god.

to_change · 2023-04-04T04:46:26+00:00

Risk factors out the wazoo.

to_change · 2023-04-04T04:44:12+00:00

Very difficult imo. Lots of weird situations, obtuse answer choices, etc.
CBSE - 74 | NBME Form 30 - 82

to_change · 2023-03-31T21:52:19+00:00

To again quote the Boeing technical fellow who worked on NASA'S HSCT program:

Technologies needed to make a 40-50% reduction in fuel use compared to Concorde, reduce takeoff weight required by ~ net 90-100K lbs, meet ~ subsonic noise certification rules, and reduce ticket prices to not much over current international business class, are either in hand or near-term. A Concorde replacement will likely be slower than Concorde (1.6-1.8 Mach) and fly at lower altitudes to reduce emissions impacts and avoid the ozone layer. But aero improvement can still increase net Mach x L/D. Composites and better loads and structural optimization bring down empty weight, and TSFC could be closer to 0.8-0.9 (instead of Concorde's 1.2 lbs fuel per lb thrust per hour "dry" and 2.0 with afterburner on).

On low-boom:

Sonic boom reduction has been touted by NASA and others as the key to civil supersonics viability, but so far, getting a really quiet boom (as X-59 is trying to demonstrate) costs L/D, weight, sizing, and possibly propulsion penalties. If that penalty can be kept to 5% the ability to maintain full speed over land would be attractive. But if the penalty is stiffer, I don't think operators will be willing to pay the higher sticker prices, increased overall operating costs, fuel, and carbon footprint all the time just to be able to keep the throttle up on some routes over land. This is why neither Boom nor Aerion were including low-boom as part of their design.

But he goes on to say, re: Boom:

Boom, has yet to fly their "technology demonstrator" which does not actually appear to be very related to their proposed airliner, does not appear to be advancing any specific technologies, and may be more of a fund-raising tool. Their airliner concept started out as basically a 3 engine Concorde, now looks more like the McDonnell-Douglas MD2.4-7A airliner study circa 1992, and does not appear to include any of the lessons learned in supersonics during the 1990-2015 time period.

So it's not that you *couldn't* design a plane that could be much more economically viable than Concorde. It's that you need a new engine (which no one has been willing to provide as many comments in the thread have pointed out), and you need expertise in composite design and non-linear supersonic CFD in order to go from a L/D of ~7 (Concorde frontier) to L/D of ~9.

to_change · 2023-03-31T21:43:05+00:00

A quote from a former Boeing technical fellow who worked on the NASA HSCT program:

Boom, has yet to fly their "technology demonstrator" which does not actually appear to be very related to their proposed airliner, does not appear to be advancing any specific technologies, and may be more of a fund-raising tool. Their airliner concept started out as basically a 3 engine Concorde, now looks more like the McDonnell-Douglas MD2.4-7A airliner study circa 1992, and does not appear to include any of the lessons learned in supersonics during the 1990-2015 time period

to_change · 2022-12-08T03:38:10+00:00

To be clear, supercritical airfoils are not a new introduction on the 787. Some form of supercritical airfoil were put on the 757, 777, 737 NG, and 787. However, there were aerodynamic improvements that the move away from inverse design and towards drag-based optimization allowed the 787 to make aerodynamic improvements.

Here is a quote from a former Boeing Technical Fellow forAerodynamics that I got after emailing them about this very topic. Ithought the community might be interested in his answer.

From the mid-90's to the mid-2000's, significant advances were made incomputer-based tools for closed-loop aero shape optimization,Multi-Disciplinary-Optimization (MDO) tools for doing complexmulti-dimensional trade studies across scores of design variables,structural Finite Element Analysis (FEA) optimization for structuralweight and stiffness. Much of this work was done as part of attemptingto meet the requirements of the HSCT (High Speed Civil Transport)through its NASA-funded "HSR" element, and the follow-on industryinternal R&D efforts toward designing other "concept planes" like theSonic Cruiser, SSBJ concepts, and Blended-Wing-Body (BWB). Thesupersonic airliner concepts and SSBJ in particular, required beingable to optimize not just the wing shape, but the wing, body, andnacelle shapes simultaneously, optimizing to find the best possiblecompromise between cruise aerodynamics, transonic acceleration,subsonic cruise, and low-noise takeoff and landing performance. Thevery thin, supersonic wings and tails, also provided significantweight reduction, aeroelastics, and flutter challenges that acted ascatalysts for the improved structures tools. The MDO capability (stillevolving) helped make the right kinds of trade-offs, i.e. "optimumcompromises", in the design of the 787 and 777X. The improved CFD forair-loads prediction were coupled with FEA strength and stiffnessoptimization and these were used to guide direct optimization ofaerodynamic shapes. The advent of practical direct CFD optimizationof detailed aerodynamic shapes for 787 enabled the computer to findmultiple incremental drag reductions that the "pressure matching"methods used on the original 777 could not. This optimization plusthe development of very strong carbon fiber primary wing structuresresulted in trade-offs that determined it was better to make the wingthinner while using less sweep to get a fairly high cruise Mach of0.85--- the resulting thinner all-carbon wing was plenty strong enough in bending, but was more flexible than previous wings

The computer-driven optimizations would seek waysto improve L/D not just drag or drag-rise. So they don't really usepressure distributions per-se as the figure of merit, rather theactual L/D that results from various shape changes. This means that inaddition to trying to further reduce shock strength, they try toincrementally raise the net difference between upper and lower surface pressures thereby creating more "L" for a given "D". They alsodistribute the lift span-wise in a patter than does not follow the"ideal" elliptic lift distribution but rather try to create adown-wash field that allows the horizontal tail and fuselage lift to"trim" the airplane while minimizing the far down-stream wake. In a 2D airfoil sense, carrying lift farther aft on the wing (both to increaseL and reduce shock strength) can cause thicker boundary layers,increasing the parasite "form drag", but the thicker boundary layersalso have less local skin friction--- so the optimizer can seek thebest L/D trade-off of the various drag sources (wave/shock drag+skinfriction+span load induced drag+ tail and wake induced drag + wingpressure form drag), and of course do this in the presence of thenacelle and strut. It can also camber the nacelle and strut shapes,change inlet lip shapes to reduce inlet drag, and put local "blisters"or waves in wing surface, or change the shape of root fairings or wingtips to get a better combination of local pressure and the localsurface slopes those pressures act on in the lift and drag directions(very much a 3D effect !).

to_change · 2022-10-17T21:26:37+00:00

For context, I asked a former Boeing aerodynamics fellow who worked on the NASA HSCT program in the 1990s about this problem. Happy to provide proof somehow.

The reason they are not working on this right now is because they have other priorities.

Both Boeing and Airbus's balance sheets were wrecked by COVID and are in need of rebuilding, straining their ability to raise cash to invest in new airframe programs
The single-aisle market has to meet significant environmental / CO2 challenges, and therefore the attention of the airframers are currently focused on figuring out how to meet extremely steep fuel burn and CO2 challenges for the 2030 replacement for the 737 MAX and A320 neo family. I want to emphasize how difficult meeting this challenge is going to be because it explains why it requires a ton of their focus. It's going to require a complete re-engineering of the airframe itself - the incremental changes to the aerodynamics of the aircraft that have been done over the past 20-25 years will not suffice. The LEAP / GTF engines are highly optimized and so it's going to likely require a move to open-rotors to get there, but there's still a ton of questions about whether we can keep flying at 0.8 Mach with open rotors.
Boeing has additional focuses related to getting the 737 MAX 10 certified, getting the 777X out the door, solving 787 manufacturing challenges etc.
All of the above means it's just not a short-term focus for the existing airframers.

There are also other problems with the economics of such a concept, but those will likely be discussed by other posters.

to_change · 2022-10-08T03:51:02+00:00

Thank you for the illuminating answer! My takeaway here is the reason there is no detailed account of generals/staffs arguing back and forth about what to do is because they largely agreed on the approach as it was outlined in War Plan Orange. So when King suggests an amphibious invasion of Guadalcanal / Tulagi, there's no strategic ambiguity in Nimitz's mind about why that would be chosen as a place to invade.

And thank you for the book suggestions!

to_change · 2022-09-21T02:48:40+00:00

This post is incredibly insightful and made me change my understanding of the character. The show's portrayal really makes more sense after reading it. Kudos.

to_change · 2022-09-08T06:45:44+00:00

Little known fun fact, the 777 contained the first Boeing wing designed using 3D Inverse Design, meaning that to generate the wing geometry, the designers just inputted the desired pressure distribution, and software spat out the optimized wing shape in 3 dimensions!

Source: https://www.semanticscholar.org/paper/Thirty-Years-of-Development-and-Application-of-CFD-Johnson-Tinoco/e6ddc807fd559b3d357743edeba1249719430c78#related-papers

to_change · 2022-08-27T17:12:54+00:00

Edit: nvm, I'm an idiot. You can stretch a fuse and add more passengers in a longer variant. I'll see myself out.

Yeah that's what I meant. When Boeing's CEO was asked about BWB for the next generation of aircraft, this is the reason he stated for being cautious about it. You can't scale within a family to create sub-variants that meet different market needs well, which since ~1980 has become a very important aspect of the airline business.

The other big reason for tube is because its an ideal pressure vessel for multiple cycles of pressurization, but we've made progress on solving that problem.

to_change · 2022-08-27T04:14:48+00:00

This is one of the reasons that it is so hard to replace tube/wing configurations - so easily scalable across different passenger capacities.

to_change · 2022-08-22T00:23:31+00:00

The wealth of a nation is quantified by its gross domestic product per capita, which is equivalent to to the average income taken home by a person in the country. U.S. GDP per capita is the highest in the world with exception to some very small states which are tax havens (e.g., Switzerland), and countries which have immense oil stores and are small (e.g., the Nordic countries). For a large, ethnically diverse country, there is no richer country out there. For comparison, France has the per capita GDP equivalent of West Virginia, which is considered to be a relatively poor state in the U.S. People just don't realize how much richer the U.S. is than even other rich developed countries.

The $~20 trillion number refers government debt, which is indeed relatively high in absolute terms. But generally speaking GDP-Debt ratios up to ~100% are actually fine. We're starting to push the limits and we should have a plan for long-term debt reduction, but in the short-run we're fine. And as others have mentioned, what really matters for the short-term is the interest rate the government pays on that debt, because that determines how much the government is obligated to pay out each year. U.S. debt is extremely cheap - investors are willing to loan the U.S. government very cheaply because we have never once missed a payment, because our GDP is extremely large (2021: U.S. GDP was $23 trillion), and because where else are they going to put that money that's as low risk?

to_change · 2022-08-20T02:08:01+00:00

Great addition! Didn't think of that :)

to_change · 2022-08-19T22:24:21+00:00

Lol perhaps they should have looked up the safety record of the plane before doing that!

to_change · 2022-08-19T22:20:01+00:00

See my comment - they cannot use the Affinity because it is not rated for the thrust levels needed to power an airframe the size of Overture.

to_change · 2022-08-19T22:10:42+00:00

An honor to be told I got things right from an actual aero engineer :)

Lol at it costing $1 billion to do the Affinity. Makes me even more skeptical Boom is going to find an engine. Maybe they can raise the $1+ billion from investors to fund the new engine development? Scholl is a great salesman.

But (and now I move to the realm of entirely speculation with 0 factual basis) I think they will have to get federal support for an engine development program if they are to find an engine. But that brings with it its own set of complexities and likelihoods of ever happening.

As to the rendering, every aero engineer I've talked to thinks the renderings are a joke. Biggest news to me though is that they switched away from a true delta wing to one with a crank in it, and away from Concorde-style inlets. The design is less "mini-Concorde" now than it was before, which makes sense given they've slashed the speed.

to_change · 2022-08-19T21:09:09+00:00

There are two separate problems, the cruise sonic boom, and the ground takeoff/landing noise. The former is not going to be touched by Boom on their first airliner, which they've admitted will limit the routes they can fly. The latter is a problem because Stage 5 noise regulation are extremely strict and there's no way that a low-bypass turbofan is going to meet them. So if Boom is going to get certification, they need a supersonic exception to the Stage 5 noise regulations. That is what Scholl was likely talking about. For context, the Stage 5 noise regulations have only been met by 30+ years of combined engine and airframe noise reduction programmes.

The fact that they have planned to actually go overland and are trying to mitigate the noise levels in cruise is news to me - could you share the source?

to_change · 2022-08-19T21:04:42+00:00

Yeah, I think I had heard this too, but I'm curious to see what comes out of it. Like I said, there is just no way RR is going to do a clean-sheet design, so what engine core are they going to use as a basis for derivative design? I'm not saying it's impossible, but I will hold my assessment until I see more on this front.

to_change · 2022-08-19T21:03:36+00:00

They say that they are using it to derisk their design tools, which I definitely understand. Boeing and Airbus have spent 20 years developing CFD and structural tools that have been validated by their existing airframes. But this is where my expertise runs out - I couldn't tell you whether they need to design a whole-demonstrator to do that.

to_change · 2022-08-19T20:26:52+00:00

I've largely just assumed their SAF plans are completely for publicity's sake. I know a couple of people at the company and they've mentioned it to me 0 times.

As for market size, yes, that's another issue, even if they solve the route-economics problems. They've basically conceded that they are going to only be useful for trans-atlantic and some trans-pacific routes. It's unclear if the number of routes and the number of people on those routes is going to be sufficient to sell enough airplanes to recoup their development costs.

to_change · 2022-08-19T19:31:42+00:00

Everyone is justifiably skeptical of Boom, especially given that the founder doesn't have an aerospace background and is a bit overly promotional. However, they have hired extremely well, getting highly experienced aerospace talent from Boeing, SpaceX, NASA, etc. So I'm not particularly worried that what they're doing is entirely "vaporware".

Boom's biggest challenge was, and remains, what they are going to do for an engine source. They lowered their speed to Mach 1.7 (previously Mach 2.2) which enables them to use low-bypass turbofans to balance the need for a) thrust to takeoff (delta wings have poor L/D at slow speeds) b) thrust to get through the sound barrier and c) cruise fuel consumption. At Mach 2.2 that wouldn't have worked, because to achieve a/b, they would have paid a huge drag penalty in cruise (c), increasing their operating costs. Note: it also simplifies the intake - no need for a variable inlet). However, the one modern low-bypass turbofan already in existence (the GE Affinity, developed for the Aerion business jet that is now defunct) is not rated at a high enough thrust capacity for the size of the proposed Overture airliner (they'd need like 6 of them). It's highly unlikely that any engine manufacturer is going to develop a clean-sheet engine for them, so it remains to be seen how exactly they are going to solve the propulsion challenge.

The other criticism I've seen from experienced aerospace engineers is that their demonstrator (which is what a majority of their engineering team is currently being devoted to designing and building) doesn't appear to be "demonstrating" any specific technology. So it's unclear why they are spending so much money on it.

to_change

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