If you are talking about the smoke-system (I-key) then there's a simple way to change the color - if you've got the right effect. I'll upload a red one here (bottom of the page)...

Take a look at the aircraft.cfg of the hornet. You should find a section called [smokesystem].  Make sure you've backed-up the orig. file first then change the fx_smoke_w to fx_smoke_r and save the cfg.

Now go into the main FSX effects folder and add the downloaded file. Restart the Sim and the white smoke should be red now!

That's beyond my abilities... It came with an aircraft, sry! 

If you've got the right effects you could add them to the quoted section; messing with the first three numbers will move the contactpoint in x-, y- and z-direction... I e.g. use red (left wing) and white smoke (right wing) with my Su-47 

Open your aircraft.cfg.  If the aircraft has a smoke system already, you will see a section entitled [smokesystem], and then a line or two that looks like

smoke.0 = X.XX, X.XX, X.XX, fx_smoke_X
smoke.1 = X.XX, X.XX, X.XX, fx_smoke_Z

If the aircraft does not have a smoke system, you simply add it to you config by typing in [smokesystem] (usually, for convienience, I put it under the [lights] ) abd add the lines, starting with "smoke.0" and the co-ordinates x.xx, y.yy, z.zz, FX_effectname  where X is front to back, Y is left and right, and  is up and down from teh centerpoint of the aircraft (Usually the center of gravity, but that's not too important)

The "FX_Effectname" can be found by looking in your effects folder, and looking for "FX_smoke_X.  where "X" is some letter or number that defines the particular smoke effect.  Just enter that file name to the end of the smoke line, test, then adjust.

You should have something like:

[smokesystem]
smoke.0 = 0.00,  8.00, 0.00, FX_smoke_r
smoke.1 = 0,00, -8.00, 0.00, FX_smoke_b

(Added:  This, in theory, would give you two streams of smoke, one on the left, and one on the right.  But it could also give you a pet comet above and below your aircraft too.  Some times the co-ordinates get a little mixed up between aircraft.  Just keep playing with the numbers untill it looks right.)

That's basically all there is to it (The above is just a made up example, and may not do anything if you have no "FX_smoke_r, or FX_smoke_b)

Also, if you do a site search (at the top of the forum page) for "smoke system", I believe there is a download "kit" that has instructions and effects that you can use to install the effect files and a tutorial for adding the effects to any aircraft you want.

Can someone also tell me how the color-codes for the smokesystem works? my Hornet has now white,red,white,red,white.. but I want blue :d

So I can make red, white, blue ...

But then I have to know how I can make the smoke myself

My beachcraft does also have a smokesystem now XD

I guess FSX - at least he didn't complain about my *.fx-effects-file 

I'd like to know how to change the colors, too, btw... 

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edit: FSX! Look below his avatar... 

ok, just have a look here if you still want to know how to change the color... 

Hmm :\

How do I make black smoke?