Repulsors and forward motion

[Visionist]

In the films and other media, we usually see any sort of repulsor supported craft with turbine engines for forward motion. However buzz droids and the like float and move without any visible means of propelling themselves through the air. Ships capable of planetary landings also float on repulsors and move by engaging their main engines (the Acclamators at the battle of Geonosis were only pictured from the front however, so this is unclear. Their low speed suggest their engines were off and their repulsors alone were responsible for movement).

The use of main engines in atmosphere doesn't seem to carry any radioactive sickness issues for organic beings; Jyn was literally blasted off her feet by the shuttle's exhaust in Rogue One and seemed to be fine, although Spoiler

she's killed shortly afterwards anyway, so any sickness may not have manifested yet.

The ending of AOTC shows Acclamators firing up their main engines whilst lifting off. Although the Clones were well protected from any ill effects in their suits, the Chancellor and his aides were only a few thousand feet away.

Many smaller spacecraft have wings and engines with front intakes. In the ICS these are retro thrusters or radiators, but the possibility of also opening up and acting as a direct atmospheric intake, utilizing the engine merely to generate heat and provide "clean thrust" whilst aerodynamic lift from the wings negates the need for repulsors, presents several advantages; power not needed for the repulsor can be shunted to shields & weapons, and "clean thrust" would provide no tell-tale exhaust emissions save infrared heat, as well as being more environmentally friendly as for instance the Naboo are said to be. The quadjumper from TFA is the only ship officially possessing a dual cycle/hybrid engine setup as per the ICS, but the X wings would surely benefit.

Is there anything in the literature that explains why droids can move as well as float on repulsors, but vehicles need turbines?

[Esquire]

Obvious counter-argument: No Star Wars spacecraft is sufficiently aerodynamic to fly without some kind of repulsor-like device.

I think, rather, that basic repulsor functionality (i.e. 'can hover') is quite cheap from a volume and power-consumption standpoint, especially relative to spacegoing ion thrusters. You can use directional thrust from the main engines at vastly reduced power for actually moving about, as gravity is counteracted by the small, inexpensive repulsorlift engines.

[fractalsponge1]

The use of main engines in atmosphere doesn't seem to carry any radioactive sickness issues for organic beings; Jyn was literally blasted off her feet by the shuttle's exhaust in Rogue One and seemed to be fine, although Spoiler

she's killed shortly afterwards anyway, so any sickness may not have manifested yet.

The ending of AOTC shows Acclamators firing up their main engines whilst lifting off. Although the Clones were well protected from any ill effects in their suits, the Chancellor and his aides were only a few thousand feet away.

Someone somewhere had the theory that ion drive really pushes against hyperspace for the most part, rather than actually firing out relativistic ions in realspace. So the flare is visible in realspace, but most of the work is by conversion of the complex mass fuel into something that interacts with hyperspace. Would neatly explain away why interactions with ships and planets are so mild, both by exhaust and fueled ships hitting ground (core ship crashing in AOTC) - otherwise the amount of mass involved would have to lead to fairly bad local effects. I don't think this has any published canon basis though.

[Esquire]

That's ingenious - helps 'rationalize' the power-to-weight ratios we observe, too.

[Visionist]

That is a very clever solution and neatly allows ships and characters to interact without ill effects. Some drive thrusters are different colours, red for the Executor and blue for the common Victory, and white for the blockade runner. The temperature difference is interesting. Efficiency is surely higher the hotter an engine burns but a subspace/hyperspace dynamic complicates that. It's unclear if the ion drives could then be used as a sort of "reaction control system" in Hyperspace mid jump; it would make sense although it's never been seen in the films or other media as far as I know.

Some craft would be more suited to aerodynamic flight than others. The best would be the A wing with its smooth lifting body and vertical stabilizers, but an N1 would probably fly almost as well, ditto the Naboo Queen's various starships.

Come to think of it, I remember reading somewhere (maybe on Saxton's page) that repulsors likely expend no energy so long as their altitude remains constant, which explains Luke's landspeeder being parked in a "hover". The Snowspeeders on Hoth have no obvious forward drive system, and interestingly have pop-up control surfaces/air brakes, and so seem to break both general rules.

[DesertFly]

That is a very clever solution and neatly allows ships and characters to interact without ill effects. Some drive thrusters are different colours, red for the Executor and blue for the common Victory, and white for the blockade runner. The temperature difference is interesting. Efficiency is surely higher the hotter an engine burns but a subspace/hyperspace dynamic complicates that. It's unclear if the ion drives could then be used as a sort of "reaction control system" in Hyperspace mid jump; it would make sense although it's never been seen in the films or other media as far as I know.

Some craft would be more suited to aerodynamic flight than others. The best would be the A wing with its smooth lifting body and vertical stabilizers, but an N1 would probably fly almost as well, ditto the Naboo Queen's various starships.

Come to think of it, I remember reading somewhere (maybe on Saxton's page) that repulsors likely expend no energy so long as their altitude remains constant, which explains Luke's landspeeder being parked in a "hover". The Snowspeeders on Hoth have no obvious forward drive system, and interestingly have pop-up control surfaces/air brakes, and so seem to break both general rules.

I can't find better pictures quickly , but the snowspeeders seem to have some sort of jet-like exhaust outputs:

It appears there is some sort of power generator between each large blaster and the engine on the back. I believe the ICS had it labeled as such, although that's of dubious canonicity nowadays. The body of the airspeeder itself may have some lifting ability, although I don't have the expertise to say for certain one way or the other.

[Batman]

There's no fucking way that thing can fly on aerodynamic lift, leave alone at the speeds we see in the movie. And where the hell do you see jet exhausts?

[fractalsponge1]

Repulsorlifts might be able to "crawl" by continuously pulling in sequence against the planet. But it might be inefficient for large bodies compared to more straightforward reaction thrust, with the repulsorlift just maintaining vehicle altitude.

[Batman]

Repulsors don't seem to work by merely 'negating' gravity but 'actively pushing against it'. Maybe by angling this effect it can be used for lateral movement?
No, I don't really believe this works either, but I don't see how we can avoid having to involve a second drive system otherwise

[fractalsponge1]

Is it active though in the sense of requiring continuous power as opposed to just initial power to set a fixed distance from centers of mass? A lot of things in SW float like Coruscant platforms and such (presumably repulsorlift) - seems very inefficient if they constantly had to be powered.

[Patroklos]

I always just assumed the repulsor lifts were just pushing against mass, and they would be more effective depending on how much mass was within their area of influence. So you can near effortlessly hover over the ground. If you want to fly you have to use more effort because either the ground is further away not as effectively utilized, or for lateral movement you only have the mass of the atmosphere to push against.

[Visionist]

It's a shame that the ICS are so hazily canon/non canon, since there's a wealth of interesting technical solutions depicted. The Coruscant air taxis have "lateral repulsors" which prevent parking bumps. This means a repulsor is likely operating in a fixed direction, usually down to allow a vehicle to float, and so might not be able to angle its "field" in another direction. The fact remains that a lot of droids float and move though. R2's controversial thrusters might not have the strength to lift him alone, and are probably for working outside a ship in microgravity. He uses them on Geonosis probably out of sheer necessity; in ROTS they don't quite lift him any more I think, could be wrong though. They're probably fudged and out of warranty by the OT.

We shouldn't forget that the snowspeeders were modified; the big cannons and their support brackets were added by the Alliance (though I can't find any pictures online of a cannon-less speeder). Without them the smooth airfoil hull would be a lot more slippery, but looking at the craft it's unlikely it would fly well without support regardless. The structure on the back is given as a radiator, which had to be insulated against over efficiency in Hoth's frigid air. The craft's systems are described as getting extremely hot usually, pointing perhaps to a combined float/drive repulsor outfit.

Zam's airspeeder had a version of the "Caterpillar" drive from Hunt For Red October; energizing and magnetizing the air around the craft's mandibles and using powerful- and toxic- fields to push that air backwards. Dooku's solar sailer is powered by some "mysterious arcane energy". I always just assumed he used the Force to push against the sail whilst meditating and let his droid pilot do the navigating.

[NecronLord]

Some ships are definitively reactionless.

[Patroklos]

I am not seeing anything reaction less on there. They say distributed, which leads me to believe they have many small trust points they can direct their propulsion reaction through around their hull vice one big bank of exhausts like the back side of an ISD

[PhoenixKnig]

Or like DS