Rolls Royce Sets Electric Records

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12notes

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Could electric aircraft eventually beat the piston powered record ?
It´s not a question of if, it´s a question of when, really. The motor isn´t an issue, high power electric ones exist which are much lighter than the equivalent piston motor, and also do not need air intakes and exhaust for the engine. It will need cooling for the battery/motors, but this can be closed off with non-recirculating liquid cooling used for a record run. Essentially, you theoretically have a smooth plane with no openings vs. one that needs at least two. With identical power on identical designs, generally the one with no openings will have less drag than one that has two more, one of which is throwing exhaust pulses over the airframe.

Is this possible now? Current record holder Rare Bear's engine (Wright R-3550) weighs about 2,700 lbs dry. I don't know the exact power of Rare Bear, so I used 2,000kW because it's in the range for the engine and I like round numbers. This also assumes a nutso pilot willing to do a record run followed by a dead stick landing. Using numbers that are possible with current commercially available products, a 2,000 lb (909kg) battery at 225Wh/kg for the entire pack should have 204kWh of energy while leaving 700 lbs (317 kg) for a 2,000kW (~2,700hp) electric motor/controller. That's enough juice for a 3 minute climb at 1,000 kW (1350hp) with 4.5 minutes of full throttle for the record attempt. There are a lot of other factors that would increase this, accounting for the weight of gasoline would allow for more battery, lower drag with less openings, etc. For simplicity and roundness I'm going to call it "about 5 minutes of climb and about 5 minutes full throttle". With all the unknowns, it's a decent estimate of what flight time is possible if you just swapped the drive system of the current record holding plane for a similar power electric system. It's realistically optimistic, assuming a best case but still practical scenario for electric. The accuracy is "-ish".

Whether about 5 minutes of climb and about 5 minutes of full power on a plane with a little less drag are enough to set a record is not a question I have enough experience or data to answer. I do not know if batteries/controllers exist that can discharge at the rate required. An airframe optimized for the electric drive system would result in a faster plane than swapping one into Rare Bear. Batteries will continue their slow increase in power density, and the time available for full power on a record flight will increase until, eventually, someone will design and fly an electric plane just for this record. Could happen tomorrow if about a 10 minute flight is enough time to get there, could take 5, 10, 20, or 30 years, but eventually someone will do it.

I'd appreciate it if someone more knowledgeable than I on these things do a rough calculation to get a ballpark on how fast a Rare Bear type plane would get on a theoretical 5 minute 50% throttle climb, 5 minute full throttle run, or a 1 minute climb, 7 minute full throttle run, or whichever combination works out the best. I just don't know enough about record run acceleration or flight profiles to set the calculation up.
 
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