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>The underlying reason that I believe electric aircraft can break the sound barrier is that electric motors can deliver far higher power-to-weight ratios than p
by scottlocklin 6y ago
>The underlying reason that I believe electric aircraft can break the sound barrier is that electric motors can deliver far higher power-to-weight ratios than piston engines, jets, or turbines.
That's a completely worthless figure of merit (I assume he means thrust to weight; because electric helicopters have abysmal power to weight ratio -shit like this matters) and no reason to believe in this nonsense. By the same reasoning, one could build a piston engined supersonic aircraft because there are piston engined helicopters. Another thing that has a high thrust to weight ratio; those water rockets I used to play with as a kid.[0] Pretty sure you can't go supersonic with those either unless you fire them out of a howitzer.
Electric airplanes are a terrible idea without battery technology comparable to hydrocarbon power to weight ratios. Even then, they're a terrible idea unless the motivating technology is lighter than a jet engine and tanks for reasons that should be obvious to anyone with high school physics educations.
[0] https://en.wikipedia.org/wiki/Water_rocket https://en.wikipedia.org/wiki/Water_rocket
- jeffreyrogers 6y agoThis guy has a physics PhD from CalTech, so his sloppy reasoning is doubly shocking.
- scottlocklin 6y agoSo much for my CalTech fanboyism: https://news.ycombinator.com/item?id=25118150 https://news.ycombinator.com/item?id=25118150 Cipolla was right Law 1: Always and inevitably everyone underestimates the number of stupid individuals in circulation.
- FlyMoreRockets 6y ago> By the same reasoning, one could build a piston engined supersonic aircraft... Now that's a thought provoking engineering problem! Assume a supersonic propeller is required. Using the Thunderscreech as a baseline, which admittedly didn't quit go supersonic, but it gets us close. Its powerplant produced nearly 6,000 horsepower. That is certainly doable with a piston engine, top fuel dragster engines produce roughly 10,000 horsepower. For about ten seconds. If this plane burned nitromethane, it wouldn't even need much atmospheric oxygen, nitromethane required roughly one tenth the amount of oxygen per mass of jet fuel. Of course, this means it has to carry a lot more fuel https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech#Specifications https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech... https://en.wikipedia.org/wiki/Top_Fuel#Performance https://en.wikipedia.org/wiki/Top_Fuel#Performance
- jasonwatkinspdx 6y agoBurt Rutan was interested in going after it with the Pond Racer, but they didn't get past their test program before one of the engines threw a rod and ended the project. Apparently the math said it'd have been capable of just barely going supersonic when level.