Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

Both the engine and motors are used at all speeds. Particularly during highway acceleration the entire assembly rotates in the same direction.

> Isn't that exactly what hybrid cars (e.g. Prius) are? Extremely efficient gas engine for highway cruising, but insufficient for acceleration, which is aided by electric motors?

Well, it kinda depends. Where Hybrids get the biggest MPG boost is in city driving. The stop and go traffic lets you use Regen braking and go quite some time without the engine kicking back on while still moving forward.

I still don't understand Honda's system enough to speak well on it, but I can speak to THS because it seems to be the cheapest to do and is most proven on the road.

The general parameters for a THS type system on a Toyota Prius or Rav4, or a Ford Maverick/Fusion/Escape is a 2.0L or 2.5L (at least in modern US examples) engine paired to a simple planetary gearset containing a power split device. It is a single speed (At least in the cheap configurations, however that simplicity is possibly close enough to be viable for air usage vs a reduction gear.) That's part of why they tend to have fairly large engines, the valve timing magic gives them at least a bit more HP to not be too bad on the highway.

> but insufficient for acceleration

Going back to the modern cases, the engine is typically sized large enough to give some acceleration even on the highway. Not always great but usually enough.

At least as far as the non-plug-in hybrids, the 0-35MPH can be surprisingly peppy.

The bigger magic (again, at least as far as THS) is it makes it easy to just run the engine at the 'most optimal RPM' for certain tasks, excess energy gets piped to the battery or back out through the system, this does also help reliability tho, because you can then design the reliability of the engine around certain RPM ranges...

Most hybrids are actually parallel or series-parallel. Series hybrids are comparatively rare because the traction motor has to be sized for the full operational range of the vehicle. Their primary advantages are mechanical simplicity and packaging; even though the power electronics and motors are bigger, the lack of mechanical coupling means you can put them wherever is convenient.

On an airplane, most of the energy in cruise is spent overcoming parasitic drag, not induced drag. It’s spent pushing the airmass out of the way as it moves forward, not creating lift to stay aloft.

For that reason, a change in weight does not significantly change cruise fuel usage.

Weight is still precious, but that’s because airplanes’ load are more often weight constrained than volume constrained, and capital and operating costs are such that you want to maximize the load.

If you're recharging the batteries for extra go-arounds during landing, they are as dead weight as the fuel you would otherwise reserve for that purpose. And if you have 30% more efficient engines, meaning less fuel and smaller engines, it's possible you could come out ahead, weight-wise.

> what if you need two go-arounds

I assume that a go-around requires less sustained power output than a full climb from takeoff, so you will probably get more than one go-around anyway, and we don't know how much over-capacity they're designing for. In any case, any design will require tradeoffs in safety, and having more engine-out capabilities might improve safety enough to overcome the higher risk with go-arounds.

Not saying this project is will work out or that you're even wrong necessarily (this could be the equivalent of a concept car for Pratt & Whitney).

Easy: you don't try the second landing approach before the battery is sufficiently recharged to contain enough energy for the second abort. Chances are this does not take any longer than going through the pattern anyways.

The saving is not just the dead weight of the bigger engine you'd need to do take-off, climb and abort without electric assist, it's also the fuel saved during cruise from running an engine that is completely designed for efficiency at cruise load instead of for some compromise between cruise efficiency and sufficient peak power for start and abort.

A plane doesn’t have this luxury and needs predictable output. The fossil fuel engine either needs a sacrificial “overboost” mode for emergencies (at the cost of wear/long-term longevity), or has to be sized for full power at the ultimate cost of efficiency.

Perhaps it's not all negative: the electric portion could give a pilot a bit more glide than the gas portion dies.

There's an economy of scale with turbofans to some degree. Large high bypass turbofans are extremely efficient, particularly at their cruising mode.

Smaller regional aircraft have more of their fuel consumption dominated by takeoff - the cruising altitude portion of the flight is smaller in proportion.

When doing something experimental, do it on something small to start with. Then scale up when you've got it working.

Take a Boeing 777, it has a wingspan of about 60 meters, and I'll ballpark an average upper wing chord of about 7 meters, for a total upper flat area of about 420 square meters.

High quality modern but standard single sided solar panels can do about 220 watts per square meter is full sunlight (around 22% efficiency tested at a 1000w/m^2 irradiance).

So that is 92,400 watts at full power.

92kW is less than the peak power of a Nissan Leaf. 92kW is 123 horsepower.

The two GE turbofans of a 777 are generating something like 40-50 MW of shaft power during cruise. MW.... megawatts. 50-60,000 horsepower.

Plastering the wing surface of a commercial plane with solar panels would make up less than a quarter of a percent of the total power it uses to produce thrust at cruise, at best case with them fully-lit.

Fully solar sailplanes do exist (NASA's Helios prototypes are an example) but that isn't anything close to a 'normal' aircraft with any appreciable payload/passengers.

So, no need to wonder.

Or maybe you keep your downsized turbine motor running closer to peak efficiency even during landing and increase the mechanical energy harvesting to your APU or alternator thing or whatever to control speed and use that to charge a small supercapacitor. In the event of an aborted landing the supercapacitor could provide a boost of thrust to your electric motors. This would keep wear on the battery lower and also allow it to dump energy at its peak efficiency

Sorry but what the hell are you talking about? Airliners are heavy, very aerodynamic, very easy to overspeed and they regularly actively brake on descent!

Unless there are other constraints on the approach, the point of the entire descent phase is to have the engines IDLING the whole time. The FMC actually calculates the descent profile backwards, starting from the earliest known constraint (e.g. a certain point at 5000 ft) and extending that back into the air accounting for the expected weight and drag of the plane. The descent phase often begins more than a hundred kilometers from the destination. Remember how they tell you in the cabin that the plane is starting to descent and you should put your laptop away etc? That's when the engines go to idle and if everything goes right, they won't spool up again until just dozens of second before touchdown. The goal of the entire industry is to have that happen as often as possible, on as many airports as possible.

If the plane is a bit heavier or less draggy than expected, or if the approach requires a steeper descent at some point, the airplane will calculate all that (in advance!) and let the pilot know (e.g. a DRAG REQUIRED message) and will require spoiler deployment. This is very common.

Also I swear there was a company replacing a push pull type plane with a hybrid ?

There are SOME planes where you want to avoid the "no thrust" situation because their implementation of "no thrust" can lead to weird aerodynamics or prop pitch behavior, or can stress the engine.