Airframes
Benevolens Magister
Looks fine Geo. The stain would depend on how much oil and fumes were blowing around inside the cowling. I've seen it vary from feint to very heavy.
If you can get a fine enough tip on a ladies eye brow pencil, or a 'Chinagraph' pencil, they're ideal for exhaust, oil and gun smoke stains, especially as they're available in black, brown and often grey (for gun smoke trails).
Lightly draw in the line to the desired shaped curve, but only about a third of the required length,then 'smudge' it rearward with the tip of a finger. Repeat the line if required.
It'll leave a very convincing 'transparent' stain and, if overdone, or not to your liking, it can be cleaned off with a damp cloth or tissue.
If you can get a fine enough tip on a ladies eye brow pencil, or a 'Chinagraph' pencil, they're ideal for exhaust, oil and gun smoke stains, especially as they're available in black, brown and often grey (for gun smoke trails).
Lightly draw in the line to the desired shaped curve, but only about a third of the required length,then 'smudge' it rearward with the tip of a finger. Repeat the line if required.
It'll leave a very convincing 'transparent' stain and, if overdone, or not to your liking, it can be cleaned off with a damp cloth or tissue.