S-foils were made famous by Star Wars' X-Wing star fighter.

X-Wing schematic showing s-foils closed and deployed

But why were they needed in-universe aside from "Lock S-foils in attack position" sounding cool?

S-foil Wookieepedia has this to say:

Historically, S-foils had been developed to address overheating issues on wing-based starfighters. Because of the proximity of engines and weapons systems to narrow wiring that fit inside the thin wings, an excess of heat could cause mechanical meltdowns that would be devastating to the capacity of the fighters to function. S-foils like those seen on a number of Republic starfighter models during the Clone Wars held radiator panels that dispersed heat and cooled the interior mechanisms of the ships. S-foils were used when stress was being put on a ship's systems, usually when it was traveling at high speeds or locked in a dogfight. This idea would eventually evolve into the radiator panels of the Galactic Empire's TIE series.

Q1: Where exactly in canon is there such an explanation? ("radiator panels")? Wookieepedia isn't providing a cite.

Q2: Since when do the small radiator panels work in vacuum? They typically need to be pretty large (see discussion here for ISS/shuttles), due to lack of air serving as heat transfer agent; and S-foils on a small starfighter don't seem to add all that much extra size.

Was this somehow ever retconned in canon to conform to "reasonable" physics? (even fictional)?


3 Answers 3


A radiator's size is determined by the rate at which it needs to remove heat. If the X-wing doesn't need to remove that much heat, then it's perfectly reasonable that it doesn't need massive radiators. And while the radiators on the ISS are large, they're actually quite small compared to the wing surfaces of the X-wing relative to the vessel's total size.

The way radiators remove heat in a vacuum is through thermal radiation. All objects above absolute zero give off thermal radiation, which gets rid of thermal energy regardless of whether conduction and convection occur. For example, human beings actually lose a lot of heat via thermal radiation through our skin because of the high emissivity of human skin. The only reason this isn't a problem most of the time because of the heat we regain through conduction as well as thermal radiation from other objects (including that reflected off of walls and other surfaces).

In deep space, there's no conduction and few warm objects that radiate heat back towards a spacecraft. So radiators can still be very effective. The radiators can be made even more effective by running them incredibly hot, increasing the rate at which they radiate waste heat. E.g. using a Peltier cooler or other heat pump that drives waste heat into the wing surfaces.

Depending on the heat rejection capacity of the X-wing's radiators (which is unknown), the size of its radiators could be completely adequate, completely inadequate, or complete overkill.

Why the S-foils need to open up is obvious. If they stay closed, then the direct contact between two opposing radiator surfaces would just trap heat in between them, only allowing heat to radiate out from one side of each S-foil. Opening up the wings allows heat to radiate from both sides, effectively doubling the heat rejection capacity of the system.

The real problem is that opening the S-foils only partially means that a lot of the radiative heat would just be recaptured by the opposing wing surface.


To answer Question 1, I couldn't find sources that say the X-wing S-foils are used for cooling, but Revenge of the Sith: Incredible Cross-Sections indicates that the wings on the ARC-170, the V-wing, and the Eta-2 (aka Jedi interceptor) were used for cooling. For the V-wing, it says that the "Radiator panels [on the wings] aid heat disposal during intense activity". For the Eta-2, it says:

Compacting a fighter's intense power into a tiny hull made overheating a challenge—which was met by an extensive system of heat sinks, pumps, and radiator wings.

I don't know whether a similar purpose has been established for X-wing S-foils or not. However, if you continue reading the Wookieepedia article, it seems to indicate that the primary purpose of the S-foils on the X-wing (as well as the B-wing) was increased weapons spread. This would be consistent with the line "Lock S-foils in attack position".


Heat radiators are absolutely necessary on ANY space warship or high powered space craft. Even a small reactor or laser weapon will generate a colossal amount of waste heat due to a combination of electrical resistance and other inefficiencies. If you set the efficiency at 80% (remember current laser technology is only around 10% efficient) then even the 20% left over from any reasonable laser weapon or engine powerful enough to perform high acceleration burns will be enough to quickly heat the craft to uncomfortable temperatures and then begin to melt the more fragile components. In the vacuum of space there is NO convection or conduction to remove heat so it must all be done by radiation. An efficient-enough heat radiator will allow this energy to be emitted at more or less the same rate as it is produced. Larger radiators are better but even small ones are helpful if the radiator can shift enough energy per square metre per second. I personally don't take Star Wars canon as being of high value when considering spaceship design.

As for the X-Wing, the radiator would be best on the outside of the wings; if they were on the inside then most of the heat would be radiated from one radiator straight into another. Some will escape off at an angle but it would be a really bad way to do it. The best reason for such S-foil wings would be to have thrusters pods at each tip, as seen in Babylon 5 Starfuries, that would make for large torques being possible with minimum thrust. Alas in Star Wars no one ever takes advantage of the things that a starship can physically do which aircraft cannot.

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