Supersocnic electric aircraft

Somewhere between little to none

Currently there is no battery or source of electrical power that is both easy to work with, light enough, relatively safe, and matches the energy density of conventional jet fuels.

Turbojets are a great tool for the SST job, though they are noisy. They may be thirsty in the slow-speed low-altitude regimes but up high and cooking they are quite efficient. See pic related

Prove this is actually the case.
But batteries make electricity which can be converted to mechanical work at efficiencies above 90%

That's a fucking stupid idea, if you are just going straight to heat first you are not going to beat hydrocarbons.

en.wikipedia.org/wiki/Energy_density

Jet-A/Kerosene: 40.491 MJ/kg (33 MJ/L, assuming std weight of 6.8 lb/gal or 0.814 kg/L)

Lithium-Ion (non-rechargable): 1.8 MJ/kg (highest value I could find for any battery)

That proves nothing, only that jet fuel has a higher energy density than lithium ion batteries.

In addition the only way we can produce mechanical energy from jet fuel is using a heat engine. Heat engines do not have very good efficiencies. For a jet engine we might get 25% efficiency.

Now even if our electric supersonic transit has less range than batteries it might still be practical, if we can reduce the noise, to short intercontinental hops.

We can also get almost unlimited energy density if we can beam power to our aircraft using lasers or what not

>For a jet engine we might get 25% efficiency.
2/10, apply yourself:

Propulsive efficiency and thermal efficiency aren't the same thing.

The advantages of the jet engine far outweigh the mechanical inefficiency.

Weight is key in aviation. Electric motors and batteries are heavy, and cannot generate the necessary power for long enough to make electricity a viable fuel for an aircraft, let alone a supersonic aircraft. This is where the energy density is important: more energy per kilogram of fuel means less weight will have to be carried in fuel.

The efficiency advantage of a turbojet engine presents itself in the high-speed flight regimes for one main reason: ram effect. The more air you can force through a turbojet engine the better. Ram effect works by using the pressure rise at the engine inlet at high dynamic pressures to supplement the compressor section. This exceeds the compressor section's normal compression ratio and provides more air for the production of power. The faster it goes, the more efficient it gets, so long as inlet temperature limits are not exceeded. Electric motors are not combustion engines, so ram effect doesn't work, and would only result in a fantastic drag rise near and above Mach 1

>unlimited energy density if we can beam power to our aircraft using lasers and what not
What?

intuition tells me a hair dryer doesn't make for an efficient jet engine

>> electric motors and batteries cannot generate necessary power for long enough to be viable
Prove it from first principles.

If we keep using combustion powered aircraft, it is going to be very difficult to meet CO2 emissions targets. We either need to stop flying or find some other way to fly.

>> ram effect
and with a motor, the efficiency is always ~90%. You don't even need to compress the air in the first place.

Why would it eliminate IR tracking? A jet engine works by compressing and heating air. Fuel burning or not it's going to be hot.
And even if it wasn't, a supersonic aircraft would still experience friction heating.

I have proven it by comparing the energy densities of batteries and Jet-A/kerosene. Current batteries do not have the capability to store the required energy to run a conventional propeller for a respectable duration of time, let alone a reaction-type engine.

You see, high-bypass turbofans also cannot go supersonic. The fan is essentially a large-faced propeller. Turbofans rely on this surface area to run efficiently, accelerating a large air mass by a small amount, rather than a small air mass by a large amount (which is what a turbojet does). This is a disadvantage when it comes to supersonic operation though. When the aircraft approaches Mach 1, that large surface area incurs an incredible amount of parasite drag during the onset of a normal shockwave, which requires exponentially more thrust to overcome. Even if it were to somehow overcome the massive amount of drag, the fan blades would stall because there is no buffer between the relative wind and the blades, and the blades cannot function in compressible flow.

Even a turbojet cannot cope with compressible flow. They rely on carefully designed inlets to generate standing shockwaves, trading air velocity for pressure. So even if you were to make an electric reaction-type engine like the one you posted, it couldn't go supersonic.

And yes, you do need to compress the air. Reaction-type engines (those that generate a reactionary force, thrust, through the propulsion of a gas parallel and opposite to the direction of desired motion) require a pressure differential, which requires compression.

>>Current batteries do not have the capability to store the required energy to run a conventional propeller for a respectable duration of time, let alone a reaction-type engine.
Run time does not equal viability. For example, if we ban combustion then a combustion driven aircraft is not viable.

Of course OP did say electric, so this does not exclude using hydrogen fuel cells. Hydrogen(compressed at 700 bar) has a higher energy density 142 MJ/kg than jet fuel. And with fuel cells 40 -60% efficiency(83% theoretical max) and the high efficiency of electric motors, so a fuel cell powered airplane is 100% viable.

What I meant by no compressor was no need for a high pressure ratio compressor in a jet turbine. Yes, obviously we need to use an inlet to make the flow subsonic so a ducted fan can be used.

>What?
We use shine a high power laser on our aircraft either to power solar cells or supply heat for a heat engine. Pic related. For solar cells, we can get pretty high conversion efficiency for just one wavelength of light like our laser emits.

Of course we can only get line of sight, so we either need a bunch of lasers everywhere or a couple of geostationary satellites. Using geostationary satellites isn't too ridiculous as it is possible to make a laser spot smaller than a concorde's wing span from geostationary orbit.(Optical distortion from the atmosphere is a problem though)

>for example if we ban combustion
Get real. Also, with respect to commercial aviation, run time is most definitely a factor. But the issue it isn't even the run time, it's the energy storage capacity, which isn't acceptable for the job.

>Hydrogen fuel cell
The fuel then becomes hydrogen instead of kerosene, which is expensive to produce in volume, leaks easily due to it's small molecular size, and causes metals to become brittle. Kerosene also has 4 times the energy density per unit volume (33 MJ/L) compared to liquid hydrogen (8.4 MJ/L) and does not need to be stored under high pressure. It will also require insulation to keep the hydrogen from expanding during flight. When comparing fuels, the energy densities can either be compared in weight or volume, but with liquid hydrogen being so light (1 kg = 14.13L) volume must be considered due to volume restrictions. While it can be pressurized, this makes it more hazardous to work with and takes longer to fuel. Why don't you find me a working example of a hydrogen fuel cell-powered aircraft. There are reasons aircraft are not powered by hydrogen fuel cells.

>no need for a compressor
What do you think does all the work in the supersonic flight regimes?

>high powered laser for power transmission
The efficiency will depend on the atmospheric quality and the elevation angle of the beam. A lower elevation angle means more atmosphere the beam has to travel through, and thus more scattering, not to mention the aircraft will be cruising about 6 miles above the surface. Also, consider weather limitations.

>geostationary satellites
Yeah a typical geostationary satellite sits at an orbital altitude of around 35,000km. Even if you could transmit the kind of power you're referring to over that distance via a laser, the beamwidth would be too wide and atmospheric scattering would ruin it altogether.

>>it's the energy storage capacity, which isn't acceptable for the job.

Prove it. You have not proven that this level of energy storage is unacceptable, only that hydrocarbons have a higher energy density.

>>get real
well if we want to get real about fighting climate change we need to stop burning fossil fuels.

>>Why don't you find me a working example of a hydrogen fuel cell-powered aircraft.
first thing that came up on google
newatlas.com/hy4-hydrogen-fuel-cell-passenger-plane-test-flight/45687/

I don't know the energy consumption rate for a large theoretical electric reaction-type engine, which at this point is an Elon Musk napkin-drawing, but I'd imagine it's pretty astronomical.

>if we want to get real about fighting climate change we need to stop burning fossil fuels
Not gonna happen. You'd have much better luck going after manufacturing or perhaps the coal industry, but aviation will be on kerosene-based fuels for the foreseeable future. Nothing we have nowadays can match the power, abundance, ease of handling, and capability of jet fuel.

>HY4 Hydrogen Fuel-Cell powered plane
I'm not flying across the Pacific at 90 mph. Nor is my 300,000 lbs of cargo that couldn't be in LA soon enough. Its a neat concept, but it is a glorified motor glider, not a passenger aircraft.

>>the beamwidth would be too wide
for a distance of 36,212 km, and a wavelength of 1000 nm, using an aperture of 2 m, we get a beam diameter of 44 m, about twice the wingspan of a concorde.

If we use a larger aperture size, say 4 meters, we can get spot size down to 22 meters, which should fit within the wingspan of a concorde

>>but aviation will be on kerosene-based fuels for the foreseeable future
well then, if we can't do it, then we'll just have to get rid of flying altogether.

>>I'm not flying
So you would be willing to not fly then? Good, so the above solution is acceptable.

Although OP did specify a 50 year timeframe, that's a long fucking time.

That would be best-case scenario, meaning the aircraft were directly below it at the equator. The majority of flights (transatlantic, transpacific, and over Europe) would be at a greater distance due to the slant range.

Again, this is barring atmospheric scattering and weather considerations. Also, how do you plan on obtaining that kind of power with a satellite? There are literally thousands of flights a day.

>get rid of flying
Heh that's a good one

>so you would be willing to not fly then?
Nah man, I'm a pilot.

>The civil aircraft fleet average for speed and cruise altitude is not expected to increase significantly beyond 500 knots and 13 km over the next 50 years, as a result of physical and cost limitations.
ipcc.ch/ipccreports/sres/aviation/index.php?idp=92

ION LIFTERS

ion lifters are a fucking joke. Motors attached to propellers or ducted fans are more efficient

>If we keep using combustion powered aircraft, it is going to be very difficult to meet CO2 emissions targets. We either need to stop flying or find some other way to fly.
No. It's sufficient to produce the fuel in a carbon neutral way, by e.g. using renewable energy in a power-to-liquid process.

>and with a motor, the efficiency is always ~90%.
90% of the energy content of a battery is way less than 25% of the energy content of kerosene of the same weight as the battery.
Plus an aircraft that uses fuel gets lighter over the course of a flight. A battery always weighs the same.

tfw no nuclear powered aircraft

power to liquid is not very efficient and will not be very efficient.

I know. But it's the most efficient way of carbon neutral flight without compromising current range, speed and weight achievements. Efficiency gains come when a technology gets used regularly and not just in a lab.

Except when there are physical principles in the way of efficiency gains.

do you have anything particular in mind?

Aero engineer here.

Electric aircraft we will definitely see. There is a lot of work that is being done on this issue at the moment, though nearly all on the transonic/subsonic regime.

Even if the energy density problems mentioned by some anons (which are all very valid concerns) are somehow overcome by a leap in battery technology, there still exist a wide range of problems with specifically supersonic aircraft. Mainly, a large diameter high bypass fan design is an efficient design for transonic/subsonic Mach numbers. As the freestream Mach number increases, a potential electric fan's ability to create a pressure differential will decrease (i.e. the pressure ratio across the fan will decrease). This can be readily observed by noting that at a constant power addition to the fluid provided by the fan and the static pressure past the inlet:

[math] \dot{W}_{fan}=c_p*\Delta T [/math]
[math] T_{inlet}=T_a*(1+0.5(\gamma-1)M_\inf^2) [/math]
Neglecting losses at the fan,
[math] T_{fan}=\frac{\dot{W}_{fan}}{c_p}+T_a*(1+0.5(\gamma-1)M_\inf^2) [/math]

As you can see, the influence of the fan work input decreases on the temperature prior to the outlet as Mach no increases. Note that this as this temperature increases, the thrust increases by a power law of (gamma)/(gamma-1). Hence, the fan becomes less and less capable of counteracting the huge drag increases that occur as the supersonic flight regime is reached.

I forgot to add that the way turbofans overcome this problem is via simply removing/reducing the bypass and providing thrust instead by combustion in the engine core, which is not possible for an electric aircraft.

what does this mean? i don't know anything about stealth. pls explain

>Hydrogen
>A good aviation fuel

It means that whoever posted it has barely any knowledge of aviation or RF, and is very possibly what is lovingly referred to as a "vatnik."

>Land electric plane
>Please stay seated while we take 3 hours to recharge our batteries for another 500 mile leg of our journey

Not him but this is well known in RADAR tech.

Basically stealth is about reducing radar cross section by absorption and/or careful reflection, not totally eliminating. The limiting factor in a modern radar system is the clock jitter og phase noise. This is improved steadily with time and with time you will "see" stealth aircrafts again, or the air currents caused by the aircraft moving.

This is why civilian radars now can see F-117.

Using solar power, then amplifying and turning it into AC power in combination with a Tesla Turbine. Also utilizing magnets, instead of ball bearings, to provide for faster turbine spin.

Jet fuel is 20+ times more energy dense than the best battery.
>That proves nothing

Go away you're too stupid for this board.

>removing/reducing the bypass and providing thrust instead by combustion in the engine core

Like the SR-71?

>Radar seeing air currents

batter powered light aircraft (1 person) is already a thing, as are small military drones.

But supersonic? Maybe if we get enough reactor technology. Fission unlikely because of politics.

The F-117 is 40 years old.

The best alternate way of fueling an aircraft is as follows:
>Make air cooled reactor
>Mount on aircraft
>Get aircraft going with other motors
>Open intakes and start reactor
>Use reactor heat to compress air and propel aircraft to SANICK SPEEEED while spewing radiation out the back
-t. USAF

What is weather radar?

What about emdrives in atmosphere?

>The F-117 is 40 years old.
I knew it was old. Most people here would have known that. Didn't you, user? Didn't you?

Here's a hint: It doesn't sense wind

i mean of the actual engine. The batteries themselves would be fuckhuge and weigh astronomical amounts.

Superconducting motors
Lidar can see air currents and stealth aircraft:
photonics.com/Article.aspx?AID=54603

Although a more practical method is using ambient radio signals:
g2mil.com/foil-stealth.htm

Lidar != radar
Lidar isn't commonly used in an AA role.

>Ambient radio signals
FIRST OFF:
>g2mil
That page pulls numbers out of its ass. That being said, if their system works exactly the way they say it does, which is a very big if, it ignores EW and assumes that the aircraft will always be flying in a way that is intercepted by the cell towers, which is completely unrealistic anywhere besides a chicom CMANO simulation.

Another thing:
If you're expecting a visit from any modern airforce, you really don't want to be constantly radiating because you're going to attract the attention of some guys who just love radio installations.

When you work in the THz range the difference between radio and optics gets blurred. You can use lenses for THz signals.

As for g2mil that appears to be about bi- or multistatic radars which has been a real thing for a while. Last I heard they can now even use GPS signals for illumination. Hobbyists have made bistatic radars using cheap SDR receivers.

There are also more exotic technologies like gravity gradient detectors.

>well if we want to get real about fighting climate change we need to stop burning fossil fuels.

Correct me if I'm wrong, but I'm pretty sure that's not the point of the thread.
OP wanted to know about the viability of a certain type of plane, and how it stacks up compared to other planes, not whether or not we should ban fossil fuels.

Fucking africa has cell service now.

>>Lidar isn't commonly used in an AA role.
not yet, but we're probably going to need it to detect small drones

Not before we discover portable fusion reactors.

>electric
Practically zero.

A battery contains bot the oxidizer and the fuel where as conventional jet fuel is just that: fuel alone. The oxygen is extracted from the air itself. That means fuel will always have an advantage over batteries.

You would alternatively need to find a completely different way of generating electricity in an aircraft with all the restrictions on weight and volume that means and no such technology is on the horizon today.