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Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

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Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#81

Post by m463 »

mk_stjames wrote: post #79
m463 wrote: post #77

Earlier quoted context omitted.

I kind of wonder how the orders of magnitude work out for solar and wing area. Solar cells are actually quite thin and could be almost like paint on the wings of aircraft. I wonder if the energy generated vs required is even ballpark. There is plenty of sun at 30,000 feet during the day.

Man this is a middle-schooler level napkin math question. 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…

I wish I could upvote you more than once. I now realize my middle-school math studies were sub-par :)

yeah, I was thinking of the solar planes. I also didn't know that "horsepower at cruising speed" was something you could look up. obvious now, thanks!

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#82

Post by mk_stjames »

m463 wrote: post #81
mk_stjames wrote: post #79

Earlier quoted context omitted.

Man this is a middle-schooler level napkin math question. 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…

I wish I could upvote you more than once. I now realize my middle-school math studies were sub-par :) yeah, I was thinking of the solar planes. I also didn't know that "horsepower at cruising speed" was something you could look up. obvious now, thanks!

Cheers- I guess I'll add, the turbofans that all modern airliners use are almost always referred to by their 'thrust' and you ofter see a lot of published numbers of takeoff thrust and such - it is harder to find numbers at cruising seed and altitude, and then in reality what you need to know is the actual power needed to generate that thrust.... there is some complexities there but in general the turbines generate what is known as 'shaft horsepower' which is a good stand in number we're looking for to compare.

The real takeaway is that power is power and energy is energy and regardless of how it gets to do the 'pushing' of the air, if you want to use solar energy (power, at any given moment, not integrating over time) those are the numbers you are comparing. It's all just unit conversions, at least when you're attempting such napkin math. Anything more - taking into account the actual systems, losses, efficiencies, etc.. just makes it all worse, not better.

A cool exercise is - given the 777 wingspan I esitmate and the power output from solar of said size... what kind of current aircraft use piston-driven engines with similar horsepower? Assuming we had motor inverter electronics and an electric motor that was 100% efficient, you could imagine trying to build a similar weight aircraft of that size that has such a wingspan.

This is why you wind up with the only solar powered aircraft out there being superlight, high altitude craft with super high aspect wing surfaces- maximizing wing area to weight / lift capability such as: https://en.wikipedia.org/wiki/AeroVironment_Helios_Prototype (note the largest of those prototypes and the tiny amount of power output they were making. All that wing area and it would have barely been able to carry a single passenger as payload and cruise a day without battery power)

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#83

Post by arijun »

cwillu wrote: post #78
arijun wrote: post #21

Earlier quoted context omitted.

Sorry, I meant in the low speed, high acceleration regime (maybe easily confounded with takeoff?). There the engine will turn one motor to generate electricity, which will then power the second motor, like a series hybrid.

No, that's just wrong: at no point is (say) a Toyota Hybrid burning gas to generate electricity to immediately turn another motor that actually moves the wheels.

What do you imagine happens if the battery is low and the car wants to start from a stop? The engine can't shift down to first so it would just stall out if you tried to use it to drive the driveshaft directly, and there's no other source of electricity to put into the motor driving the wheels.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#84

Post by ssl-3 »

Melatonic wrote: post #70
soperj wrote: post #35

Earlier quoted context omitted.

After they land, they usually sit around for a while. Not really super important to charge the battery on decent I wouldn't think. Would be interesting to get rid of the battery entirely (or reduce the size) and have a beefed up magsafe plug that was attached during lift off, and came unplugged once it was at cruising altitude.

At that point seems like you might as well use a launch system like aircraft carriers use

That would certainly help get the aircraft up to a speed where it has usable lift and can leave the ground. That's a good headstart, and it represents a significant amount of energy.

A catapult launch can't help with the next 30,000 feet of climbing, though, while the impossible umbilical might.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#85

Post by coderenegade »

kspacewalk2 wrote: post #10
avidiax wrote: post #4

I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial aviation. This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly dur…

>This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly during cruise if needed. Isn't that exactly what hybrid cars (e.g. Prius) are? Extremely efficient gas engine for highway cruising, but insufficient for acceleration, w…

This is mostly correct. The Prius is actually a series-parallel hybrid, as it maintains a direct mechanical link between the engine and the wheels (and the engine is capable of adding power to the wheels) but it also uses two electric motors to isolate the two degrees of freedom (engine rpm and wheel speed). This second part is the series bit: the wheels and the engine are, in principle, fully independent, because the motors can absorb or add power to the crankshaft and the driveshaft to hit a target rpm without changing the rpm of the other shaft. In practice, the Prius doesn't run at a constant rpm due to sizing constraints of the motors, as the mechanical linkage means that one motor has to be able to absorb the engine power and torque of the other motor, which is impossible across all conditions.

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.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#86

Post by coderenegade »

_diyar wrote: post #41

This is very clever: instead of focusing on electric only flight, just make the existing engine fly in the most efficient window while the electric engine buffers the flight profile. Like a big-boy prius.

Cars have a wide operating band, which is why hybrids make sense. Fundamentally, hybrid cars want to run the engine at a narrow set of operating points that are most efficient, and use a reservoir to do time arbitrage on the energy generated during driving. It's more than just regen to recover energy already spent -- the motor also lets you navigate the engine map to pick your point of operation. Ideally, the engine and the wheels are fully decoupled, at which point the engine rpm would just be constant. The battery and motor just move energy around.

Planes aren't really like this, they're actually a lot closer to boats. They move from fixed operating point to fixed operating point, and the engine is optimized around this. There's a lot less fat to trim, because the engines already have a narrow operating band.

That's not to say that this won't work; Pratt obviously knows what they're doing. But it's probably not an accident they've gone for smaller turboprops. I actually think the biggest opportunity for hybrid propulsion is in smaller drones where you want high performance piston engines, because tip clearance becomes an issue for gas turbines. A turboprop might suffer similar performance challenges that would make a hybrid configuration make sense.

Edit: just saw a post below on the relevant patents. Looks like they're using hybridization to decouple the two shafts. Without the motors, they're coupled via the gas path. With the motors, you can navigate the maps of the two shafts independently. I'm guessing this lets them pick a combination of shaft states that saves fuel. Most of that is pretty uncontroversial, but I'm surprised the claimed fuel savings are that high. As I mentioned above, it's probably because it's a turboprop on a small aircraft.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#87

Post by rsynnott »

idontwantthis wrote: post #17
avidiax wrote: post #4

I think there are startups making a similar sort of engine for general aviation. It's good to see that there is development of the same idea for commercial aviation. This isn't like a hybrid car. It's a parallel hybrid, where the gas engine is just big enough for efficient cruise at altitude, and the electric motor/generator provides extra power for takeoff and ascent (or go-around power), and then charges slowly dur…

Hybrid cars are mostly parallel hybrids. Only the Chevy Volt comes to mind as a serial hybrid.

Some hybrid buses are also serial hybrids.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#88

Post by chabska »

delecti wrote: post #34
dgfl wrote: post #20

Earlier quoted context omitted.

This is a great related watch if you have some time to kill: https://youtu.be/KnUFH5GX_fI

That's such a fantastic video. I never totally grasped why hybrids were so much more efficient, because my naive assumptions about how they worked were so simplistic. The real-time graphs he showed were excellent for making his points.

One thing I really don't like about this video, is that he was specifically describing the advantages of that specific van and drivetrain, that being Toyota Sienna, and he's not wrong at that, but then he made grandiose general statement like "Hybrids are simple" and "minivans are great".

No, quite a few other hybrids are just an electrical motor tacked on to an existing ICE drivetrain, and they are actually more complicated than a regular ICE car, with horrible reliability and repair cost. And other non-hybrid minivans are either seriously underpowered, or require a seriously big engine that eats fuel.

The complaints that people have against hybrids and minivans are valid, if they're not talking about Toyota hybrids or this specific Toyota minivan.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#89

Post by cwillu »

arijun wrote: post #83
cwillu wrote: post #78

Earlier quoted context omitted.

No, that's just wrong: at no point is (say) a Toyota Hybrid burning gas to generate electricity to immediately turn another motor that actually moves the wheels.

What do you imagine happens if the battery is low and the car wants to start from a stop? The engine can't shift down to first so it would just stall out if you tried to use it to drive the driveshaft directly, and there's no other source of electricity to put into the motor driving the wheels.

It's a planetary geartrain, with electric motors on the outer and inner, and the gas on the middle. If the electric is _completely_ dead, the gas will just spin without driving the wheels at all. There is no first gear, the mechanical advantage and “clutching” all comes from the inner electrical motor driving the sun gear, while the electric boost/drive comes from the electric motor on the drift shaft (which is on the outermost gear of the planetary set).

There's a video linked elsewhere in this thread that explains how the toyota system works, it's worth watching as it clears up several common misconceptions about the system.

Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency

#90

Post by Toutouxc »

cwillu wrote: post #89
arijun wrote: post #83

Earlier quoted context omitted.

What do you imagine happens if the battery is low and the car wants to start from a stop? The engine can't shift down to first so it would just stall out if you tried to use it to drive the driveshaft directly, and there's no other source of electricity to put into the motor driving the wheels.

It's a planetary geartrain, with electric motors on the outer and inner, and the gas on the middle. If the electric is _completely_ dead, the gas will just spin without driving the wheels at all. There is no first gear, the mechanical advantage and “clutching” all comes from the inner electrical motor driving the sun gear, while the electric boost/drive comes from the electric motor on the drift shaft (which is on th…

I think what they're trying to say is that there are regimes in which the HSD actually shunts energy from one electric motor to the other (i.e. one of them is "braking" and acting like a generator and the other one driving) and a big part (maybe the majority even) of all power goes through that path. This works even if the battery is empty, because the electricity isn't coming from the outside, it's coming from the spinning ICE.
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