Serious question: If a plane runs on electricity, would it ever make sense to put solar panels on top of it to try and get extra range?
Or is the scale so off that solar panels can't meaningfully contribute?
Or is the scale so off that solar panels can't meaningfully contribute?
Another reference: https://newsline.kitplanes.com/2017/07/26/alpha-electro-an-e...
You're not likely to have shock cooling issues in an electrically powered aircraft. Shock cooling is a piston aircraft thing, and is mostly an issue on turbocharged aircraft. You're not worried about shock-cooling the engine, you're worried about shock-cooling the hot side of the turbocharger. So in the use-case of spoilers being used to keep the engine spooled up, you're right that it wouldn't be necessary here.
And as far as pulling the throttles to idle and more-or-less gliding during the descent, that's the ideal, but in the real world spoilers are used to drop more quickly all the time for non-emergency reasons. If you have favorable winds up high, you might choose to stay up high until absolutely necessary and then quickly descend to make better time. In trainer class aircraft you don't typically have spoilers to help this, so you end up cross controlling the aircraft to increase the sink rate. If I could have a big ol windmill in front of me in a 172 to do that, it'd be pretty darn nice.
When power is surplus, climb to your service ceiling. When not, descend. Utilise battery when at minimum altitude.
This was the technique used by Solar Impulse 2 on its round-the-world (though not nonstop) flight. At a cruse speed of 70 kph (43 mph).
As people already commented, it wouldn't make much difference for the usual models, but you can design a plane that benefits from it. It may have some good uses (agriculture comes to mind), but probably won't be good for transportation.
For surveillance, comms, and very small-scale payload delivery (possibly drugs, far more likely munitions), ultralight drones with battery + solar could offer loiter / time-in-air and / or modest speed longer-distance capabilities.
https://en.wikipedia.org/wiki/Solar_Impulse
:)
On the other hands, if you were to beam a few hundred kilowatts by (carefully!!) aiming at the panels with a massive laser, you could power it this way, yes.
Bonus if you are doing it from a satellite: you can power a plane even across an ocean and don't need many ground stations. On the other hand you just built an orbital death ray so expect protests from, well, everybody.
It would also provide a charging option if you have to land at an airstrip that doesn't have an electrical outlet handy.
Wing area of a Cessna 172 (representative GA aircraft) is 16 m^2.
Best-case insolation on a sunny day with no clouds at high noon is around 1000 W/m^2.
Best commercially available solar cells are the triple-junction cells used on commercial satellites, at about 30% efficient. They are horrendously expensive (around $50-100k per square meter), but we will ignore economics for now.
16 m^2 * 1000 W m^2 * 0.3 = 4.8 kW.
Powerplant for a Cessna 173 is a 160 hp piston engine, or 120 kW. So, we're about an order of magnitude and a half off. The cells also aren't massless, so they will add weight and reduce range... you'd need to do a cost/benefit there.
There are a couple solar UAVs in existence (example: https://en.wikipedia.org/wiki/Qinetiq_Zephyr) which use super lightweight materials and have very large wing areas to support solar cells. Even then, they are really on the hairy edge of where physics works in your favor.
This is one of the reasons in favor hybrid electric aircraft. The marginal hp to weigh ratio of an electric motor is about 3 hp/lb or ~5.5 kw/kg. And partial load efficiency is high. Means you potentially have a lot more hp available on take off.
For commecial passenger aircraft hybrid turbofans wouldn't have spooling up lag like straight turbofans. Turbine engines take seconds to spool up. This big big problem with jet aircraft during landing. If you hit wind shear and/or need to go around you need to apply more power and sometimes the lag is fatal.
And the great thing about flying is that it's pretty much always a sunny day when you're in cruise.