Iskierka

LOx/LH2 engines only produce H2O and some intermediate byproducts in any meaningful quantities - reactions with the combustion chamber and nozzle are minimal. What does happen, though, is that the reaction between these two very quickly gets so hot that it can't complete, which is the actual reason for using a higher LH2 quantity - H2 and H+ ions in the exhaust do make it lighter and travel faster, but they don't travel as fast as a H2O molecule that's had its energy released. The trouble is that H2O has to share its energy with everything else that hasn't reacted, slowing it down, so the LH2 ratio is increased to make sure that everything else is faster. The ideal exhaust from a LOx/LH2 rocket would be pure H2O, but because it burns far too hot (reaction tapers off around 3000K, theoretical temperature would be around 6200K), we instead use a mixture that produces H2O, lots of H2 and H+ ions, and some trace amounts of O2, O2- ions, and HO- ions. The excess hydrogen mostly tidies up unreacted oxygen parts, but small amounts get left in.

No, I fully understand it - but you wouldn't have the plane "controlled" by CG because of this, and you don't realise that the control surfaces are very, VERY powerful if they are attempting to control the aircraft. CG change will not overpower them to keep the nose up, only potentially cause the aircraft to completely stall out and crash if instability movements become faster than the controls can move.

The trouble is that the control surfaces were under automatic control, not just set in place to hold the descent - if you moved the cg back, the flight computer will sense the changing loads and slight movements, and automatically compensate by holding the nose down. Like I said - this is possible if the controls are in fixed position, but in the suggested case, they are not, as they are either under automatic computer control or pilot's control, both of which counteract anything passengers could do.

The problem is that moving CG out of rear limits doesn't create a problem whereby the plane will always pitch up no matter what the pilot does - the elevators are very, very powerful and can always remain in control. What happens when CG is out of limits in normal flight is that the aircraft becomes very difficult to control, as you can't just hold it in a position and have it go forwards. If you're pointing a tiny bit too high, it'll go up as you imagine, but if you're pointing a tiny bit too low, it'll pitch down just as violently. This is because an aircraft is a dynamic vehicle trying to keep control by deflecting air, not simply balancing like a see-saw as you might imagine. There are some aspects of stability that are see-saw-esque, but they're more around when you have a stable aircraft and are watching its behaviour - moving the pivot has very, very different effects, which are far more reminiscent of trying to throw a dart forwards for a stable aircraft, or backwards for an unstable aircraft. Wikipedia has an article if you're interested, though there isn't a simple-English equivalent. The better KSP/FAR plane design tutorials should also explain how it works. The end result of it though is that if the plane is being actively controlled, by a pilot or autopilot, then in theory you can put the CG extremely far back, considerably beyond aft limits - and so long as the controller is quick and precise enough in its response to movement, the plane can be kept in control, and so if you were trying to crash it, you'd be able to succeed. You can control an aircraft using CG if that's the only input, but aerodynamic input overrides CG. CG movement just causes some annoyances for aerodynamic control, which in their extreme can become lethal, when it becomes impossible for either to control the aircraft, as CG is too far back and controls don't respond fast enough.

Open-cycle does not mean the coolant is dumped without generation, and your presumptions about the desires for nuclear reactors are a bit strange. Are you assuming that this would have to be a space-based reactor? Earth-based reactors would very much prefer to be open-cycle, as it would mean a lower incoming coolant temperature (you can't cool a closed loop back to ambient). The reason they are not fully open-cycle is because of the corrosion they would face from water impurities and radiological concerns - so instead they have a closed-loop primary coolant which is re-cooled by a secondary open-loop coolant, which avoids radiation and keeps corrosives away from the reactor core. This is done after as much energy as possible is extracted from the primary coolant, and if the primary coolant was open-cycle, it would do the same thing, and then be ejected back into the sea/river that was supplying the reactor. Now, asking about high-density and high-capacity coolants for Earth reactors is a bit redundant, as water performs well and is abundant, whereas anything else is in limited supply. In space however, everything is in limited supply, so you wouldn't want open-cycle cooling due to limited coolant - but the same coolants may be very good for closed-cycle, also. In vacuum all your cooling has to be done by radiating heat, and the primary affecting factor for how fast heat is lost by a radiator is its emissive temperature - which increases power emitted to the fourth power. Doubling temperature means 16x (2^4) more cooling, so suddenly it looks quite desirable to find something other than water, which is limited to a few hundred degrees with reasonable pressures. Say that water is operating at 900 K (very high for steam), while tin could be run at 2700K. The tin coolant can therefore emit 81x (3^4) more power per radiator area, assuming the radiator reaches the same % of coolant temperature. Now, there's some other concerns, such as that you could only throttle the reactor back so far - the tin can't be allowed to re-solidify. But, if you know there's going to be enough minimum load on the reactor - or you have tricks such as partially folding the radiator, so it heats itself and keeps the tin hot - then the same question of what materials would get a high density and capacity are quite suitable for a closed-loop reactor.

From the perspective of someone fairly far into studying an Aerospace Engineering degree, Fel's understanding is incorrect - although appeal to authority would be a very bad idea here, as their misunderstanding is the same as what I normally see coming from pilots. I've seen many arguing on the internet, that think speed is somehow directly related to current lift, and that too little is an automatic stall - and to preserve that misunderstanding many seem to think stall in turn is somehow a fundamentally different phenomenon to level flight. But, this isn't particularly related to the original question. The original question can be summed up as: if the controls are left in free-floating trim or fixed position (which would be unusual for an Airbus due to its automatic controls), then it's very easy to control an aircraft using CG changes. There are many small aircraft designed to be flown this way, and many pilots of light aircraft have attested that in free-floating trim they can control their plane just by shifting in their own seat. However, if there's anything that would actively fight you, then aerodynamic control will always beat you - the most you can do is change the plane's stability margin, but if that remains positive, that only changes how twitchy the plane is to control, not whether it can be. And if the stability margin becomes negative, then there's only two possibilities - pilot remains in control with unstable aircraft, or pilot loses control and the plane tumbles out of the sky. Neither of which would save anyone, so your time would be better spent trying to talk the pilot out of it through the door.

I'm sorry, but can you cite for your calculations where the 66 tonne variant can move 120 knots with only 822 kW? (Which is already more power than you estimate being available to the 250 tonne version, I'd note) When I run the drag calculations, using an underestimated area (80ft x 160ft), using a slightly lower frontal drag coefficient than has ever been demonstrated (0.05), and assuming it can lift to far above where it likely can (I assumed air density of 0.5 kg/m^3), I still find it needs 3200 kW total power to move at 120 knots, or around 4300 hp. This is the result when I'm generous to it - it's more likely to end up well over 10,000 hp, especially when you have to factor in propulsive efficiency, motor efficiency, storage efficiency, and so on, which I've ignored. This would mean best-case equivalence in conventional aircraft engines would be an A400M turboshaft, providing around 11000 hp. It's not unlikely that it would need two, either. That would put it around 16 MW supply needed - how are you going to get that from solar? Equation you can put into google to confirm the power requirements: 80 ft * 160 ft * 0.05 * 0.5 * 0.5 kg/m^3 * (60 m/s)^3 Area -- -- -- -- Cd, --- dynamic pressure, multiplied by speed again to get power rather than force.

Someone who wants to operate a new vehicle cares what the USA says. The goodyear blimp gets special permission to operate in a small airspace away from airlanes and specifically avoids getting near housing or large buildings. Air traffic must remain above 500 ft unless on final approach, and typically is held at 2000 ft, or nearly half a mile up, and kept away from inhabited areas as much as city geometry and winds allow. Much closer to "Wait, I can transport thousands of tonnes of material from one location to another for nearly no fuel, and all I need is to slap some cheap wood/concrete and steel down between those locations?" Versus airships, "Wait, so it barely carries anything, it's goddamn enormous, I need somewhere to unload this at both ends, and it's not as fast as the planes everyone can offer already? Why would I bother?" -We've already addressed that it's not, trucks and trains can use fuel cells or electrical power, and both can do it far more effectively. Even a fully loaded truck needs only 100-200 hp to run at speed, while all air vehicles need hundreds to tens of thousands of hp to get around. A fuel cell that can provide that is too heavy for a blimp. -Not if you're going to have the vehicle usefully powerful - it very much will have emissions, and it very much will run on diesel, as the experts are actually proposing. -Which is useful why? In the general case, it isn't, unless you're going to make use of thin air at altitude to provide transport at near Mach 1 so that you can provide transport to anywhere on the planet within 24 hours, as planes do. This doesn't - it's not a big benefit outside small niches. -As above, VTOL is only applicable to flying vehicles, and flying isn't providing a big advantage. This only removes a disadvantage of flying to help small niches. -Again, a limited niche use. Unless it's something that -has- to be delivered to rough terrain, why not land? Other than the fact this thing is far too big to land, which is its own problem. Helicopters are far more stable than you think - and they won't be nearly as affected by wind as this thing. -It isn't higher payload than aircraft - the An-225 has more than exceeded the 250 tonnes you're quoting, and fits tidily in a 90m box. This is too big for regular operations at airports, but it's small enough that special arrangements can be made when there's cargo that has to make use of its large payload or internal size. Again, how are you going to land 233m of airship at a place that hasn't built a landing area? Aircraft do also have a very similar ratio of increased size versus payload - they're operating on more similar principles than you think. -Very dubious, it certainly isn't simpler to operate, needs special infrastructure, and if it wants to be FAA certified it needs to be as well maintained as any cargo aircraft. -As do aircraft, at least due to the denser air. If we were still talking about your PV suggestion, this would be totally false for the airship, as it'd be getting a fraction of the sunlight it's designed for. -Again, false. You can't land a 233m long vehicle just anywhere, especially if you want to unload. Maybe you could on African plains that are hard ground that trucks could deal with, but you're dealing with a lot of payload that needs to transfer to something else that can reach it. Anywhere making big use of it needs proper landing sites, and nearby - and you won't find this much space anywhere near a city. -Former is false, what use is the latter? For sea-based wind farms, perhaps, as an extension of what we've all suggested, but this provides no advantage there - a simple barge can carry the parts for several turbines, and float around using far less energy than this. -Entirely false, as mentioned - it's using huge amounts of not-cheap material. And it won't reach high production, given how niche it is. -So, like helicopters and aircraft are when supplemented by simple trucks, only much less practical? -Again, false, as the fuel cell idea won't work for any kind of large-ish aircraft. It'll be just as range-limited as anything else. -In what way? There's nothing to suggest it would be more reliable than rail, ship, or air. Maybe truck, as they can be affected a lot by bad traffic, but trucks are serving a different part of the transport market to begin with. -So slower than any reasonable helicopter, and all planes, for a relatively meagre payload advantage, and massive payload disadvantage to trains and ships that keep a reasonable fraction of that speed? No advantage here. -What? -Not an advantage if it's free-floating anyway. That would just make it harder to control while moving. Small reduction in fuel use in movement if it's a heavier-than-air airship, but then it can't float for no energy, as you're suggesting it would. That's pretty much every point either false or fairly negligible. This is a potentially very useful vehicle for very small niches, it is not useful for general transport. Did you read that part? He's saying that even choosing now, for the future, it's more desirable to build expensive new infrastructure that would provide more trains and ships that will be cheaper, and more nodes that transition to trucks to minimise the length of the more costly leg - which airships couldn't cover anyway, due to their immense size making them so impractical for last-leg transport.

It's a niche market, but it would potentially be enough to fund this thing - many wind turbines are built in rather poor locations for actual wind strength, as no road or other suitable transport infrastructure goes there. And even if it does, for large, highly effective wind turbines, you need a fairly high capacity road to fit it down, which is going to be very expensive to assemble even over a short distance. This would reduce ground transport to assembly crew, who can get to good, high-wind locations by offroad trucks, and until the parts needed to be put in position, the craft could be anchored and left while the crew leaves, such as if problems arise. This vehicle is extremely good at this one task, and I won't be surprised at all if we see it developed solely to do this - but I'll be quite surprised if we see it doing too much else, given its low capacity, low speed relative to aircraft, and very large, impractical size.

Airports could not support this vehicle. You quote the "standard" 250 tonne capacity as being 233 m long - airports have no capacity for any vehicle larger than 80 metres. Special arrangements have to be made for visits by the An-225, which is only around 86 m. Yet this thing is three times that size. This would require specialised landing sites with specialised infrastructure, at least if it was to ever carry significant payload mass.

A plane with free-floating controls, or controls fixed to neutral, can be controlled quite easily by small changes in CG. However, CG change only results in a gentle control moment - what it does quite a lot of is reduce or increase aircraft stability margins. If someone actively pushed the nose down and everyone moved to the back of the plane, all that would happen is the plane would become rather more twitchy as it was forced to the ground, if the pilot was truly determined - or if just pushing down gently, and not trying to keep the plane under control, then you might overpower the controls, but you would then very quickly push the aircraft into a stall and lose control altogether.

Fuel cells would likely work out more efficient for this vehicle than batteries due to weight, but they would not work out more efficient than simply directly using the power. Which then results in being limited to maybe 1/4 of a hp per m^2 surface, at the best times of the year - then meaning you'd need huge PV layers to get any useful thrust, when there's plenty of lightweight turboprop engines that will happily get you lots of power, efficiently, for less weight than that much panelling. I'd also note that 40 km/h somewhat under-exaggerates the speed of freight trains running in the open. Yes, they may go quite slow near inhabited areas, and some awkward locations put 30 mph or so limits on them to survive the slope and turns, but often they'll idle around highway speed once they can, especially if going long-distance. Beyond that, 400 tonne-mpg is the practical average actually being achieved - when put to the test of what's possible, quite a few modern trains will happily pull at over 1000 tonne-mpg, so if rail was used more and ideal loading was therefore easier to achieve, they could do even better. Trains are actually a really good transport system - it's just that it would be really expensive to have enough rail routes to make them as universally useful as road and air, so they remain "good" rather than "fantastic" in terms of efficiency.

Train is the most efficient method of transport in terms of distance and mass per fuel. Ships work out cheaper due to fewer restrictions in paths, timing, infrastructure maintenance, and similar problems trains run into. Airliners are not as inefficient as often made out to be, and are very attractive because they are effective for time-sensitive cargo, being able to make deliveries to almost anywhere on the globe in under 24 hours in many cases, 36 covering the vast majority of more difficult locales. Trucks and vans are attractive because of flexibility of paths and ability to get all the way to their destination. This thing ... doesn't win in terms of efficiency, is slow, can only deliver to limited locations. About the only thing this is useful for is delivering relatively light, but possibly bulky payloads to remote locations where there is insufficient road development to allow a truck to get there. I recall a suggestion that this kind of thing would be useful for allowing wind farms to be built in better locations, with heavier winds and further from inhabited locations, as no road infrastructure needs to be built to the location - technicians can come in offroad cars and trucks while this delivers the huge components, and it seems quite likely that this may be useful for that - but it's going to be little use for anything else.

To ensure that the vehicle entered service, BA and AF had special contracts that their initial orders could be to purchase the aircraft for a value of just £1 each (possibly 1 frank for AF, but BA paid £1). BAe and Aerospatiale, the manufacturers, most definitely did not make a profit - though governments funding the development mean they didn't specifically lose money on the project, just broke even. Also, it was just the lobbying of US manufacturers. Most people didn't think Concorde would be loud enough to be a problem initially, and indeed it was quieter than many aircraft of the time. Why did people start complaining? Because US manufacturers lobbied, and made overblown PSAs, and did everything they could to make people think there was a problem that didn't particularly exist, so that the US government had to cave and give the bans they requested. The knock-on effects of this is that the rest of the world found out what was going on, heard things about "supersonic aircraft are loud", assumed that the truth was being told and the aircraft were as loud as claimed at the time (again, they weren't), and so very few countries in the world lack a ban on supersonic flight - those that do likely lack any rules around flight. If a US manufacturer had successfully developed an SST, then you can be absolutely certain, supersonic overland flight would've been legal for at least decades longer, as they'd've done everything in their power to do the exact opposite of what they used everything in their power to do initially. And yes, all the techniques for reducing sonic booms are technically purely experimental. This is purely because there is no vehicle, in flight or in development, able to use them - military aircraft have much greater freedom so do not need reduced sonic boom unless it also provides greater efficiency with no other losses, and there are no commercial vehicles that would have significantly gained from the techniques. If you could somehow convince someone to develop an SST now, it would be incredibly quiet, especially compared with military aircraft that is most people's only idea of sonic booms - but no-one thinks that's the case, and because of that you can't fly most of the useful SST routes, and so no airline is interested in an SST, and so no manufacturer is interested in developing an SST, and so these technologies remain ideas in a lab. Sometimes they get applied to UAVs and proven, but largely they remain ideas in a lab. All because the US threw a hissy fit over losing the SST race four decades ago.

While there's a couple other errors I see, the main one is that you assume full coverage of a planet is possible with three satellites. Without ionospheric effects and similar, it's not - there will always be points at the poles that are just out of their line of sight. The minimum number of satellites for full planetary coverage is four, in a very irregular arrangement known as Draim's Tetrahedron. The minimum practical number of satellites in circular orbits, to provide consistent view resolution/communications delay/etc. is six.

It may surprise you, but that is not a particularly bad list, even for a fleet of just 20 aircraft. Most of those are very minor issues that other aircraft won't experience particularly less often, barring components unique to supersonic engines. It also looks like a large fraction were related to tyre failures, which were a relatively common problem for all airliners prior to its 2000 crash - following that incident, new tyres were developed that are totally burst-proof, meaning both that Concorde would be far more reliable and that all other modern aircraft also are, as the new tyres perform so much better that every single airliner has switched over.

This vehicle doesn't look supersonic at all. It has no supersonic intake design, and the low-speed electric fans don't appear to be able to be closed off to reduce drag at high speed. Additionally, its wings are very wide and narrow, clearly more designed for high-subsonic speed. It could be quite an efficient fast transport with relatively good STOL performance, but supersonic is quite doubtful for that design, even if there's some rumours that it may be. That was its original definition, but variance depending on the meridian and location used caused disagreement, so it was defined as a specific average. It's close enough that you can reliably call it 1 min of arc, but that's not the definition. Suborbital travel isn't going to be a thing any time soon - even Skylon is only targeting the possibility of around $100,000 per seat, which only the very richest will pay for 55 minutes-to-anywhere flights. $10,000 should be the target price for first-class travel, no matter how fast, which is achievable for supersonic or hypersonic, but not suborbital. $100,000 is only justifiable for people if you're talking about somewhere totally unique, like actually getting to orbit - SS2 selling zero-g flights at $200,000 proves that, but you're not going to get many repeat passengers, so regular travel flights won't go for that.

Electrolysis is able to exceed 100% efficiency in a similar way that air-conditioning can be used as a heater with greater than 100% efficiency. Both, rather than trying to do the whole job themselves, are taking additional energy from surrounding systems, and are using their input energy to manipulate that, rather than to provide energy directly. Thermodynamics only say that energy cannot be created - but that's never what we measure with efficiency of some useful device, we measure the energy we are required to provide directly compared with the energy resulting. If we have some nice trick where some ambient energy gets added alongside input energy, then that's a helpful thing we'll take and is entirely capable of putting measured efficiency above 100%. Thinking of another thing - how efficient is wind propulsion? It requires some energy to manipulate and hold sails, but one human is enough to control and move a several-tonne boat at potentially speeds of over 10 m/s. That boat is receiving at least dozens of kW of propulsive energy, possibly hundreds in some cases, yet the only "input" to the system, from the human perspective of what we need to put in, is less than 100 W or so. That's somewhere between a hundred thousand percent to possibly tens millions of percent efficient. Because we can steal ambient energy from the wind, but that's not our energy, so we don't need to consider it as part of the propulsive efficiency. And then if you simply tie the sails off, and stop actively sailing, you can genuinely make it infinitely efficient. So if we've had the capability to make infinitely efficient systems for thousands of years, perhaps we should stop asserting that a system of 120% is impossible? It's perfectly acceptable to question how, and I did initially think "is that possible?" on reading it, but I continued reading, and saw what was meant, where excess heat from other systems can be used to allow reduced direct input. Any claim of efficiency >100% should be questioned, but don't automatically assert it's impossible when infinity is possible.

I see one misconception throughout this thread that Concorde was somehow unprofitable - this actually isn't true, as while yes, it cost more to operate, they did get a significant number of extra passengers who wanted specifically to fly on Concorde, who, now that is no longer an option, simply go elsewhere, flying with Lufthansa or such rather than BA or AF. Modern re-evaluations of Concorde's economics say it certainly made significant profit compared to what happened after, as many rich first-class passengers were lost. The main reason Concorde actually got shut down was because of Airbus, who were done with maintaining what was effectively their first aircraft and now out-of-production, and instead used the opportunity to massively raise maintenance costs and push their newer aircraft that they could make much more of a profit from. Additionally, costs were naturally higher because of a few mistakes made, as BA for some reason actually laid off a lot of Concorde's maintenance crew during the downtime, so when it came back they didn't have experienced crew to work on it. Of course, the shutdown can actually be blamed on AF, as BA were happy to continue operating Concorde after the incident - they saw that it likely seemed to be some outside interference, so felt there was no issue to continue flying while the investigation went on, as the planes themselves were safe. It was only after lobbying from AF that BA cancelled operations - which then massively harmed public image of the plane, as people started to think it may be unsafe if there was a total shutdown on flights (entirely false, as seen by its perfect safety record aside from one incident caused by another aircraft's poor maintenance). Although, while the economic argument is not a strong a reason for Concorde's shutdown as people believe, Concorde was notably less economical than it could have been. What everyone is familiar with is actually the Concorde A model, and following commercial introduction of the A model, the original plan had been to make a slightly enlarged B model, with much quieter and more economic engines, improved aerodynamic performance, potentially higher speed, and overall being an all-round better vehicle. Which is saying a lot, as Concorde A was a fairly impressive vehicle. This plan was unfortunately shut down when America threw a temper tantrum, and decided to get overland supersonic flight banned despite there being little evidence for it actually causing problems, simply because all their companies had failed to develop anything comparable while two tiny Euro nations had beaten them. The overland flight ban then massively reduced interest in the plane, and various other US-centralised lobbying against the Concorde meant that only AF and BA were willing to buy and fly them, resulting in it being, from the standpoint of selling the vehicle itself, a commercial failure that did not warrant Concorde B's development. In short, if you want to know why we don't have any supersonic airliners, it's because America was bad at making them then threw a hissy fit so no-one else could. That's genuinely the main reason for it, and then one badly-handled incident of the only one that succeeded got it taken out of the sky when it was perfectly fine to continue operating.

Given that the coefficient of friction of a wheel is largely independent of its rotational velocity, there is no velocity at which you could draw the conveyor belt such as to pull the plane back as hard as its engines pulled it forwards, given reasonable assumptions that the brakes are not being applied. Thus, the only case where the belt's own movement directly prevents an aircraft's takeoff is not possible. On the other hand, there's mechanical limits to how fast those wheels could rotate before breaking off. If you determine those limits, you may find a point at which a conveyor belt would prevent takeoff by breaking the plane - but the belt cannot prevent takeoff simply by pulling a plane back, only by causing physical destruction of required components. Moving the belt does not actually provide noticeably more mechanical resistance than the plane rolling forward under its own power on a runway, so the fringe condition people are suggesting, where the belt is moving fast enough to pull back on the plane, is a non-existant condition. In fact, the belt would sooner help the plane takeoff, as its movement would pull air along with it, and if it is moving contrary to the attempted takeoff direction, then that is simply increasing air velocity over the wings, meaning a lower ground-relative velocity is needed, even if the conveyor-relative velocity is considerably higher.

That would be a higher pressure tankage line for hydrogen - 35 MPa vs 70 MPa, different safety factors and tank masses. Additionally, not marked on that table but something to consider is that metal hydride storage can be used to carry hydrogen at an efficiency somewhat worse than the basic hydrogen compressed storage, but with significantly lower odds of leakage and still far superior performance to regular batteries. As all of these are functionally identical systems of storing an energy supply for the vehicle's independent use, and because batteries are not, as seems to be commonly believed here, 100% efficient storage, the result is that while batteries are simpler and require less tech, they very obviously do not perform as well as a hydrogen system. Most good batteries have about 80% charging efficiency, which is the kind of ballpark you'll be looking at with graphene-based fuel cell, especially if an additional heat engine is used on wastage. Current hybrid fuel cells are already around 85% efficient at generation, and if a claim I saw earlier in this thread is true that electrolysis is around 95% efficient, that puts current hydrogen storage almost exactly on-par with batteries for charging efficiency. Charge retainment is something to consider, but considering most batteries do drain rather quickly in relative terms, that may not be particularly different either. Unless battery density hugely increases in the next few years, hydrogen may be very interesting for cars simply as a lighter and smaller energy storage medium, and the vehicle may still be charged from electricity, meaning no additional infrastructure required.

Trying to blow a sail with a fan fails because you're pushing against the direction you're trying to make the sail push you. The props on a plane push air back while a wing pushes air down to push the plane up, and additional airspeed from a prop does help with this - it's a well-observed effect that props consistently have slightly lower takeoff speed than jets, and there's various experimental features like blown flaps to try exploit such effects in various ways. So no, they're not crazy for getting more lift by using lots of props, that's a known and well documented effect. Whether it'll help more than they lose from all the interactions between having so many separate propellers ... that's another question that remains to be answered.

Helicopters have their main and tail rotors mechanically linked, allowing them to retain yaw control through auto-rotation. Can you explain how exactly a single rotor with no correcting torque would avoid spinning the capsule?

Do bear in mind also that there are a number of metals which cannot be usefully printed - particularly as they may have properties that emerge from the way they are machined. Cold-rolled, hot-rolled, cast, forged, and all sorts of other variations on steel all have different material properties, and 3D printing will only be able to produce its particular property set (which will likely be most similar to cast). Milling and other machining techniques then perform work hardening on the material, in various different ways, meaning the 3D printing won't be the be-all end-all to manufacturing metal components - for many, it will still be more desirable to cast in a mould and then perform milling as it would have traditionally been done. Also, maximum mechanical strength in a metal can't be achieved by this method. It's not enough of an advantage to actually be bothered with in most alloys, but with inconel it certainly is, and this has to be achieved by careful cooling of molten inconel in a mould over the course of around a week, forcing the metal structure to develop as a single crystal. The resulting components are then worked as needed to produce the final properties required. None of this process can be done by 3D printing, except for mould creation, which is already done in its most common application, the manufacture of jet turbine blades. 3D printing is interesting, but won't produce a flawless crystal structure in the metal, which can be achieved with moulds.

Gasoline/petrol actually detonates near-instantly in regular engines, diesel is the one that burns and expands. RP-1 is actually extremely similar to petrol, as is Jet A1 and its local variations - but all of them are, as mentioned, extremely refined to remove some problematic compounds that will tend to gunk up in these engines. Rockets are actually the more sensitive to this issue though, as they use their fuel for cooling where jet engines do not - fuel's first interaction with significant heat and air in a jet engine is combustion, and modern engines consistently have near-total combustion leaving very little residue. Jets can, entirely feasibly, run on petrol, and quite often will be demonstrated doing so - rockets are too sensitive to risk to a problematic fuel, and so performance-driven that you'd rather have something you can be absolutely sure of the performance and behaviour of.