shynung

I recently looked at Angel-125's DSEV mod, which has a fusion engine. The fusion engine, interestingly, doesn't start right away when I activated it though the staging system. Instead, it prints out "Charging Capacitors", and the engine sucks in EC at a constant rate while a percentage rating is displayed in the context menu, which reaches 100% when total EC fed reaches 48000. Only then does the engine actually start, ready to thrust. When the engine is on, it doesn't take in any more EC, but instead uses little amounts of fusion fuel to keep the reaction going, sucking in more as thrust levels are raised, and LqdHydrogen propellant is pumped through. http://imgur.com/gallery/oA80k Might be something interesting to learn from.

Yep, that. Also, in space vehicles, mass more expensive than volume, hence why space-going vehicles are OK with having more than 75% of their internal volume being occupied by propellant tanks. Should the space vehicles used enough hydrocarbon-based propellants to get the same dV, what they'll lose in tank size (and mass) they'll start to gain in propellant mass, due to lower Isp. Tsiolkovsky's equation would then push the propellant requirements beyond the impractical range.

@Red Iron Crown Cool links on the cars there. Makes me drool already...I only have an itty bitty scooter, mind you. On Skylon using hydrogen, I think it has to do with the fact that hydrogen carries more energy by mass compared to hydrocarbon fuels. That, and the hydrogen gets used as the coolant in the precooler system.

@Nertea Nice work on the AM factory plugin. Have a good vacation.

And as I said, those energy sources are limited in terms of power density compared to non-renewables. We can get gas from corn stalks and unused parts of plants, along with organic wastes, so we're not completely limited on that. There won't be as much gas as today when we switch to carbon-liquefaction gas, but enough can be produced to at least prop up specialized applications such as aviation. The rest can run on electricity just fine. Can we switch the topic back to flying cars?

Nothing in this universe is truly renewable, truly infinite. 5 billion years from now, our Sun will enter the Red Giant phase of its life, possibly devouring all the inner planets, including Earth. Even if humanity was able to move away before then, the Sun doesn't have enough fusion fuel to shine forever. One day, in the far future, it will die, explode in a nova, and turn into a white dwarf, ceasing to shine on the once-solar-system. Even in the shorter term, solar power (wind power comes from solar energy, so that counts) has limitations in the amount of energy it can deliver for a given space, something we don't have infinite amounts of. The only energy source left with enough power density (if you forgot, power is energy*time) to power our technologies, crossing out fossil fuels, are nuclear fission and fusion fuels. And even then, those aren't renewables, so we'll run out of them given enough time. Geothermal plants has limitations in areas that can have them, because geothermal energy can't simply be found anywhere with a reasonable amount of drilling. As does solar and wind generators; there are areas which don't provide much of either. So basically, if you want full-'renewable' energy sources (no fossil and nuclear fuels), you're on a limited energy budget. While using them to power cities and battery-electric cars may be well and good, the storage solutions for electricity (batteries) doesn't provide enough energy density for aviation applications carrying any significant amount of cargo, traveling for a significant amount of distance. Like it or not, for aviation, we're stuck with gas for now. We may have electric cars tomorrow, but flying cars need much more energy delivered at any given moment, and for longer periods of time, the energy density of alternative energy solutions just doesn't cut it. Only hydrocarbon based fuels' does.

Coal. As of today, there are technologies designed to make long-chain hydrocarbons from essentially anything containing carbon. Coal, biomass from farms, organic waste, plastics, you name it. It's still in the same class as hydrogen electrolyzers, in that it needs energy to produce the fuels, but the end products are safer, easier to handle, and has greater energy density.

Because gas works. Modern gas engines are a proven, reliable technology that has been continually improved for more than 100 years. It not only delivers respectable amounts of power, but also does it while emitting far fewer pollution than its predecessors. It also runs on a high-energy-density fuel that are relatively safe to handle, and stable enough to be stored for long periods of time. As I said earlier, electroyizing water for hydrogen is energy intensive. The process itself may release no CO2, but the power plant generating the power needed to run it may well be. And, as you said, that energy more often than not comes from a coal-burner plant. Methane steam reformers end up being cleaner, because the energy needed to run the hydrogen-forming reactions come from burning some of the methane, which burns cleaner than coal.

Most of today's hydrogen come from methane steam reformers. Natural gas, basically. And the production releases carbon dioxide pollution. Electrolized-water hydrogen is energy-intensive, and very expensive. Most car manufacturers today are betting on either hybrids or full-electric vehicles. Very few of them actually sell production-model hydrogen fuel-cell vehicles, and even then, only in limited areas. So no, hydrogen is not a step-up. At best, it's a diversion that nets us some use in specialized applications. At worst, a waste of time and resources.

And why is that? We started the discussion of automated flying cars. Why does it have to deal with hydrogen? Standard-issue fuels like gasoline, diesel, and jet fuel works well enough. Just so you know, outside rocketry applications, hydrogen isn't some wonder fuel that magically improves the performance/efficiency of anything it is fueled with. Besides difficulties in storing and handling them, it doesn't carry anywhere near the energy density. For a daily driver/flyer, it's impractical, full stop. I don't see why we should even bother. Also, @DaMachinator, I would definitely fly around in an autogyro. If I have one, that is.

I was talking about in-vehicle storage. A vehicle can't drive or fly if it left the fuel tank at home. Also, I'm sorry, but you're wrong. Hydrogen has worse energy density than gasoline or diesel fuel. A liter of gasoline contains 34.2 MJ of stored energy; that of diesel fuel is 35.8. Hydrogen, pressurized at 700 bar ( about 690 atmospheres), contains only 5.6 MJ.

Even as a gas, hydrogen still gets through the molecules of the tank. If the vehicle carrying the tank is stored in a closed, unventilated garage for a long period of time, a dangerous gas concentration may appear. When that happens, a smallish spark is enough to set off the whole shebang. Also, even if we do have tanks that are light enough, yet strong enough to contain pressurized hydrogen gas, there is no getting around the low energy density of hydrogen. Usable range would be terrible compared to hydrocarbon vehicles. Let's just face it, hydrogen as a fuel isn't much of a good idea for everyday use. Sure, rockets get better specific impulse from using it as propellant, but we don't exactly commute using rockets nowadays.

I disagree. Here's my previous take on it: That said, I do agree that airships are obsolete for most purposes. They are good for long-term loitering, though.

@James Kerman Here's the next best thing: It's basically a Glasair Sportsman light aircraft fitted with road wheels, and a second engine mounted in a pod underneath the cockpit to drive the wheels. The wings can fold rearwards for road travel.

Which is exactly my point. I think main engine gimbals are simpler to develop than vernier engines. Not only there are less chambers and nozzles to worry about, it also ends up lighter.

Hydrogen is a PITA to store. It leaks out, molecule by molecule, through almost any tank material you can think of, no matter how tight the plumbing is fastened. It burns with an invisible flame, so one never knows they are walking into a hydrogen fire until they feel the heat. It also has utterly terrible density, requiring inordinately large tanks to store any usable amounts of them (Remember the Space Shuttle External Tank? 80% of that by volume is hydrogen, but it only makes up ~16% of the propellant mass, the rest was oxygen). So no, the tanks wouldn't be simple.

I think that is to reduce the number of engines needed to be designed, to save on development costs.

The thing about VTOLs is that they have terrible fuel economy, and for a very good reason: burning fuel just to hold the craft airborne doesn't get it anywhere. That is why most of light aircrafts aren't VTOLs; it enables them to have a smaller, cheaper engine. If you want VTOL and good fuel economy, you have to provide hardware for both. That basically means a set of rotors for VTOL operations, and a set of wings and propellers for forward aerodynamic flight. One of the few vehicles that can combine both seamlessly is the V-22 Osprey, which rotates the engine nacelles and propellers upwards for VTOL, and forwards for flight. Most other designs have separate hardware systems to handle VTOL and forward flight, and they're about as complicated, if not more, than the V-22 solution. Also, if storage space (=garage/hangar) is limited, you can make parts of the vehicle fold into itself. This does introduce additional complexity, however.

It very well may be. Fully autonomous flight from apron to apron (jumbo jet parking spots) isn't here yet, much less car-parking-spot to car-parking-spot. If you want to speed it up, best thing to do is to make a usable autopilot program first (or find a usable program someone else made), attempt to apply it to a real vehicle, and develop the system from there. The ground-car equivalent would be something like Google's Self-Driving Car project. Again, if a flying car's what you want, equivalent vehicles are already available on the market, as light/ultralight aircraft. You just have to manually pilot them.

I've never said the concept was unworkable. I merely pointed out that there are still plenty of roadblocks to a mass-produced flying drone car, among them the various technical and legal obstacles, and the fact that we haven't had a production-model autopilot system that's capable of maneuvering the vehicle from parking spot to parking spot, while being easy enough to be operated by the common man. And even if it did come out, it may not look like what we think it would look like today. For all I know, the future drone car could be flying saucers, or just a common small helicopter with an autopilot module and no manual controls. EDIT: Found the flying saucer. This is a Moller Neuera, developed by the same person that made the Moller Skycar that Red Iron Crown found. Same engines, just more of them, in a different configuration.

You mean the Space Shuttle Orbiter? That thing is an entirely different beast than your average 747, designed to run on wildly-different fuels, carry different things, and to endure different environments. It's just a 747-sized reusable payload fairing with a flight deck bolted on the front, rocket engines on the back, and a big fuel tank on the underside, lofted to orbit with the help of what are essentially scaled-up fireworks skyrockets. And yes, there are already multiple designs that almost match the description of a passenger drone. The only things those designs haven't got yet is an advanced autopilot that can be instructed on where it is supposed to go, and automatically plans the flight path, contacts ATC (just like ground vehicles, airplanes have traffic regulations), and actually fly the vehicle there, avoiding any obstacles in the way. Current autopilots can fly to waypoints, can land/takeoff automatically, and can follow terrain, so we're not very far from that either. In the end, passenger drones could be a reality. Not necessarily quadcopters, but self-flying passenger-carrying vehicles nevertheless. Still going to be pretty expensive, though. This thing can't actually fly on it's own (it has to be towed by a plane), but it flies nevertheless.

@ZooNamedGames Quadcopter designs are popular for small remote-controlled vehicles because the attitude of the vehicle can be controlled entirely by changing the torque applied to individual rotors. This means the rotors don't need to change pitches, and can be made as a single piece to save production costs. This control scheme works well in electric-motor-driven rotors, but pose additional challenges when applied to larger crafts. Small helicopters (the size of an R22) typically don't have spaces for multiple engines underneath each rotor, and so gets by with having only one or two engines driving a shaft, which is connected to all rotors. This means changing torques applied to individual fixed-pitch rotors gets complicated really fast (needing clutches, transmission systems, and more), and often adds weight. This makes it cheaper to instead make the rotors themselves changes pitch, so that all rotor's RPM can simply follow the engine's, and still result in a controllable vehicle. After that, it's a matter of complexity and cost; a single large collective/cyclic-pitch-adjustable rotor (and a smaller one for the tail) is less complex than 4 smaller pitch-adjustable rotors that can produce the same lift, and are cheaper as a result. A coaxial counter-rotating pitch-adjustable rotor may be more complex, but it doesn't need long drive shafts needed to drive the individual rotors of a quadcopter, needing only one nested drive shaft next to the engine, connected by bevel gears. A bit more complicated, but it can go a bit faster than the single-main-rotor-plus-tail-rotor configuration, and there's no risk of the tail rotor striking the ground. And those are why larger helicopters have only 1 or 2 main rotors rather than 4; they're simpler and cheaper to produce. Another interesting take on flying cars is combining regular cars with paragliders. This one is called the Parajet SkyRunner. It debuted in late 2013 at a price of $119k. It's about as literal as a flying car could get. Using fuel for vertical thrust is definitely bad for fuel economy. No way of going around it, I'm afraid. That said, if I want a practical flying-car-like vehicle, the R22 is probably the first thing that comes to mind. If not that, the R44 or R66, which carries 4 and 6 people, respectively.

You need the tail rotor for countering main-rotor-induced yaw (don't know the aviation term). Otherwise, the entire helicopter rotates in the opposite direction of the main rotor, which usually results in a crash. The tail can be replaced by a fenestron or a NOTAR system. Above: Kawasaki OH-1 reconnaissance helicopter. Lower: MD Helicopters 520N. If the tail really needs to come off, using a pair of coaxial rotors is a viable design, however it requires a nested drive shaft. Above: Berkut VL.

What I think chemists working at a rocket propellant laboratory looks like whenever they found something interesting.

I don't see why we shouldn't simply install an autopilot module into a Robinson R22, and be done with it. It fits in a 9x9 m box, and can carry 2 people. Runs on gasoline (aviation-grade). Comes with leather seats.