Tinkering with the Shuttle, I've been somewhat disappointed by the options we have to render exhaust flames. While the particle system is good for large rocket flames, it doesn't render an AB exhaust nearly fast enough so that particles separate, and it has issues with thruster flames pointing perpendicular to spacecraft motion.
Most other solutions I've seen are textured cylinders/cones which simply have too sharp a boundary to be completely satisfactory. I've tried a solution stacking a series of billboarded transparent textures, which gives a nice impression, but no sense of any motion or force.
So I've taken an hour to do a procedural shader based solution to the problem. The effect simply attacks the problem by brute force and integrates over a 3d distribution of glowing stuff with a density distribution defined as a function of coordinates inside a bounding box - noise can be added at will and motion comes from bringing osg_SimulationTime into the fray translating the noise.
This still has some quirks, but the proof of concept does what it's supposed to do - provide the visuals of a 3-dim flame.
Here's a proof of concept pic - one Space Shuttle engine rigged with the procedural flame, the lower two use adapted AB flames (I think originally from the F-14b) - note that this isn't how the flame ultimately should look like for the Shuttle, just an illustration of how different it is.
Since (unless you want to code GLSL for your aircraft) this relies on calling pre-defined functions for the density distribution, I think this would be a good time to discuss feature requests - what things do you need for AB flames etc? How should they look like? What should they do? What needs to be configurable?