# Electric (non-boogaloo) airplanes 2: supercaps **URL:** \ **Category:** Factual Questions\ **Created:** [December 6, 2020, 11:19am UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374 "2020-12-06T11:19:31Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [December 8, 2020, 9:05am UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/21 "2020-12-08T09:05:55Z")
> [@eschereal](#): > > One significant difference between batteries and supercaps is the discharge profile. Batteries discharge at a nearly flat voltage, Unless you are using a battery chemistry with a significant fixed-charge profile. Supercaps are an extreme end of the spectrum, but all batteries more-or-less exhibit the super-cap effect. Until recently, battery chemistries were deliberately chosen for flat voltage discharge. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 8, 2020, 12:05pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/22 "2020-12-08T12:05:58Z")
The discharge curve used to be a significant point against capacitors for many applications, but nowadays, with lightweight and highly efficient solid-state voltage switching devices, it’s basically irrelevant. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [December 8, 2020, 1:37pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/23 "2020-12-08T13:37:16Z")
> [@Mangetout](#): > > I can’t help wondering if we would first get to a point where it is more effective\* to use electricity to manufacture hydrocarbon fuels from scratch, then use these in conventional jet engines. Not exactly hydrocarbons but hydrogen was made at industrial scales at a few hydro power plants in the initial days. It was done using electrolysis. The hydrogen was in turn used for making Ammonia which in turn was used for fertilizers. Making hydrocarbons has always been capital cost and operating cost expensive including environmental costs. The easiest hydrocarbon fuel to make is methane which is not attractive to airplanes. The other synthetic fuel is DME (Dimethyl Ether). China makes a lot of it by first converting coal to Syngas, then syngas to methanol and then the methanol is dehydrated to make DME. I have seen DME being used in some of the chafing candles used at restaurants but not much in the US. ---
**Author:** ![Crane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crane/32/3495_2.png) [@Crane](https://boards.straightdope.com/u/Crane)\ **Post date:** [December 8, 2020, 2:17pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/24 "2020-12-08T14:17:32Z")
Good point, but with only 2.5 to 3.5 volts input, and sucking out hundred Amp currents, it’s not quite irrelevant. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [December 8, 2020, 2:48pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/25 "2020-12-08T14:48:50Z")
One of the axes is J/kg like the first plot, power density is not charted though ---
**Author:** ![3AxisCtrl](https://avatars.discourse-cdn.com/v4/letter/3/ecd19e/32.png) [@3AxisCtrl](https://boards.straightdope.com/u/3AxisCtrl)\ **Post date:** [December 8, 2020, 3:38pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/26 "2020-12-08T15:38:24Z")
A point worth noting here is that aircraft propulsion systems can efficiently consume power only over a fairly limited range. A propeller that’s efficient at cruise - delivering, say, 100hp - will be less efficient if asked to deliver 200hp, and probably incapable of 300hp. Which may mean there’s no way to make good use of the supercap’s big plus: very high power density. And you still have to haul those supercaps along during cruise, where they do little to no good. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [December 8, 2020, 8:15pm UTC](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374/27 "2020-12-08T20:15:48Z")
> [@DPRK](#): > > One of the axes is J/kg like the first plot, power density is not charted though Correction noted. Thank you. [Previous page](https://boards.straightdope.com/t/electric-non-boogaloo-airplanes-2-supercaps/927374.md?page=1)