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.
Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
41–50 of 104 posts
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#42Earlier quoted context omitted.
> I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
Time to invent regenerative air brakes, like fold-out windmills.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#43Earlier quoted context omitted.
> you're carrying all that dead weight for the rest of the flight 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 requ…
> I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
So, for a Dash 8-100, at 13,000 kg, disregarding drag, engine efficiency, etc, to take-off and climb to 1000m and accelerate to 150 knots (77 m/s), you will need:
- 13000 * 9.81 * 1000 = 127.5 MJ, to reach your altitude
- 0.5 * 13000 * (77)^2 = 38.5 MJ, to accelerate to your climbing speed.
Total: 127 + 38.5 = 166 MJ, or about 46.11 kWh
For a go around, re-accelerating from 1.3 * stall speed (85 knots / 44 m/s) to your climbing speed, and going to your missed approach altitude of 1000 m, you will need:
- 13000 * 9.81 * 1000 = 127.5 MJ, to reach your altitude
- 0.5 * 13000 * (77^2 - 44^2) = 26 MJ to accelerate back to your climbing speed.
Total: 127 + 26 = 153 MJ, or about 42.5 kWh
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#441300 HP electric engine power, now that's an achievement. I do wonder if prop engines can act as "windmills" (similar to turbine engines, which often in accidents still have been found to provide a bit of hydraulic power), which means regenerative braking could be used instead of speedbrakes.
There would never be a reason to use windmilling props in flight for electrical generation. Even when descending, airliners like the Dash 8 need at least some forward thrust in order to maintain control and stay on the glide slope. They only use reverse thrust for a few seconds during the landing roll.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#45I 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…
The fuel burn of take-off and climb substantially lightens the aircraft for cruise. Electric batteries have no such effect, you're carrying all that dead weight for the rest of the flight. This reduces the passenger or cargo capacity of the aircraft, which reduces potential revenue. And what if you need two go-arounds?
"And what if you need two go-arounds?"
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.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#46I wonder if during descent instead of cutting power alot to control speed it can instead use the energy to charge the batteries.
I'm not sure how that would help. If you're descending it's probably to land, and then you can recharge the batteries with electricity from the ground. That would be more efficient (and cheaper) than burning fuel to charge them.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#47Earlier quoted context omitted.
> I assume that a go-around requires less sustained power output than a full climb from takeoff, No. Source 1: PE = mgh Source 2: am pilot
So, for a Dash 8-100, at 13,000 kg, disregarding drag, engine efficiency, etc, to take-off and climb to 1000m and accelerate to 150 knots (77 m/s), you will need: - 13000 * 9.81 * 1000 = 127.5 MJ, to reach your altitude - 0.5 * 13000 * (77)^2 = 38.5 MJ, to accelerate to your climbing speed. Total: 127 + 38.5 = 166 MJ, or about 46.11 kWh For a go around, re-accelerating from 1.3 * stall speed (85 knots / 44 m/s) to yo…
Nice to see some numbers. So for the peak load situations, a Dash 8-100 would not require a battery bigger than that a short range BEV ("city", though in reality the short range BEV use case is more for the rural equivalent of stuff that would be walkable in a city setting). And that's even before considering the energy contributed by the fossil fuel engine.
"13000 * 9.81 * 1000 = 127.5 MJ, to reach your altitude"
Presumably quite a bit of that would be harvested back during the descent that follows. The conventional engine would still need some excess power (relative to cruise load) to fill the gap left by drag and imperfect circle efficiency of the electric motor/generator, but mass x altitude is stored energy, not lost. (I'm still talking about the "what if we need a second abort" of the root post)
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#48Earlier 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.
TC is filled with these sorts of videos. If you have time to burn then they are basically all this quality. His interests are also just wildly all over the place. From Christmas lights to dishwashers to coffee machines you just don't know what the next video will be.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#49anything that gets rid of leaded fuel on prop aircraft is a win even if 0% efficiency improvement
This is about replacing a turboprop with a slightly smaller turboprop and electric motor/generator+battery. The turboprop burns Jet-A, not leaded aviation gasoline.
Re: Hybrid-Electric Aicraft Engine Targeting 30% Fuel Efficiency
#50I 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.
The BMW i3.