We've seen more and more discussion on HBA about battery-powered aircraft and hybrids. I've been arguing that it's fundamentally impossible to get range up enough for a practical airframe to be solely powered by batteries, necessitating hybrid aircraft powered by chemical means (piston generator, fuel cell).

This video neatly sums up the fundamental limits:

Current aircraft-rated battery systems do about 100 Wh/kg. That is the whole system weight, so BMS, insulation, packing structure etc.

Let's talk numbers. 100 Wh/kg is 360 kJ/kg. Specific height is the amount of altitude you can gain by using all the energy to climb. This is about 36 kilometers for such a battery. If we factor in drag, propulsive efficiency and prop efficiency, we see that existing planes (Antares 20, FES) obtain about half that rate.

Of course, a plane can't have 100% of it's take-off mass in batteries. If we look at the best possible today, say the Binder EB29 and we assume 50% of it's take-off mass is batteries, it can climb to about 9 km of altitude, for an equivalent mission range of 450 km (assuming a climb to 2 km altitude).

100 ft of span and 50% batteries might not be terribly practical. If we assume an SR22-like airframe with 30% battery mass and cruising at 80 kts or so, range gets down to 41 km, or about the length of a marathon.

Even with the currently non-existing Li-O batteries, that SR22-like airframe would only have a range of 235 km, or about 145 miles. While the Binder EB29 with half it's TOW in batteries would do a mighty 2200 km (1380 miles), that would be a flight of over 24 hours, cruising at a comfy 50 mph if there is no wind.

Bottomline; for range hybrids will be the future

This video neatly sums up the fundamental limits:

Current aircraft-rated battery systems do about 100 Wh/kg. That is the whole system weight, so BMS, insulation, packing structure etc.

Let's talk numbers. 100 Wh/kg is 360 kJ/kg. Specific height is the amount of altitude you can gain by using all the energy to climb. This is about 36 kilometers for such a battery. If we factor in drag, propulsive efficiency and prop efficiency, we see that existing planes (Antares 20, FES) obtain about half that rate.

Of course, a plane can't have 100% of it's take-off mass in batteries. If we look at the best possible today, say the Binder EB29 and we assume 50% of it's take-off mass is batteries, it can climb to about 9 km of altitude, for an equivalent mission range of 450 km (assuming a climb to 2 km altitude).

100 ft of span and 50% batteries might not be terribly practical. If we assume an SR22-like airframe with 30% battery mass and cruising at 80 kts or so, range gets down to 41 km, or about the length of a marathon.

Even with the currently non-existing Li-O batteries, that SR22-like airframe would only have a range of 235 km, or about 145 miles. While the Binder EB29 with half it's TOW in batteries would do a mighty 2200 km (1380 miles), that would be a flight of over 24 hours, cruising at a comfy 50 mph if there is no wind.

Bottomline; for range hybrids will be the future

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