how are air intakes different?

[kurja]

There's really no in-game information on how the various air intake parts work and the few numbers that are given seem similar. Circular, shock cone, ram... What difference does it make which I put on a jet?

Edited May 22, 2015 by kurja

[Geschosskopf]

Of all the visible stats for intakes, the only one of real importance is intake area. The bigger this is, the faster the intake accumulates the IntakeAir resource, so it collects more IntakeAir out of thinner atmospheres in a given amount of time. Thus, intake area affects how high you can fly before flameout.

The amount of IntakeAir resource per intake isn't really important. In effect, intakes are like fuel tanks that grow their own contents. Because jet engines consume IntakeAir just the same as they do LF, you need a "tank" of IntakeAir somewhere in the plane for them to draw from. So this number just shows how big the intake's "tank" is. But it really doesn't matter because the engine is consuming it while the intake is adding more to the "tank", and it's the relative rate of production vs. consumption that determines if the engine will keep running.

The other important stat for intakes is drag, which you can't see unless you look at its cfg file. Drag is now an important thing and IMHO makes it a wash between the slightly bigger area of the ram intake vs. the lower drag of the shock cone. In my experience, both work equally well on the same spaceplane so it's more aesthetics than anything else.

The circular intake doesn't have much area so isn't suited to high-altitude flight. It goes with the similarly low-altitude Basic Jet engine. If you're making a spaceplane or high-altitude jet with Turborams or RAPIERS, use the shock cone or the ram.

The radial intakes and fuselage pieces with intakes just add a little more intake area at the expense of drag. Most of them are only useful these days on low, slow planes, perhaps as their only intakes. For spaceplanes, they're not desirable anymore because high-altitude engines run out of power these days before they run out of air, so no need to spam intakes on them. All you really get from them now is unnecessary drag. The only exception to this general rule is the new "precooler" part, which really does no cooling and is just another fuel tank with an intake on it. Pairing one of these with each shock cone or ram intake on a spaceplane gets you more altitude before flameout than you get without, and they don't seem as draggy as the radial "structural" intake.

[Slam_Jones]

I think the main variables at play are:

Intake Amount (how much air it can take in)

Drag produced (some produce more drag than others)

Mass (how much it weighs)

Cost ($$$)

The wiki has a comparison chart, but I can't say 100% if it's updated for 1.x (I noticed the pictures for the circular and RAM intakes are using the old 0.90 models)

Edit: Ninja'd

Edited May 21, 2015 by Slam_Jones
Grammar, etc.

[kurja]

thanks, that answers it.

[NathanKell]

Shock cone intake also has lower heat increase from convection, per its cfg.