# Can we see evidence of "crabbing" when viewing contrails?

Can we see evidence of "crabbing" when viewing an aircraft leaving a contrail?

Such as, in the form of an angular misalignment between the longitudinal axis of the aircraft (i.e. the aircraft centerline) and the contrail?

Or any other way?

If not, why not? Do aircraft flying up at the contrail altitudes simply avoid crabbing?

Yes, you can see evidence, but it isn't the angular misalignment you are picturing...

The aircraft does not crab relative to the airmass, it crabs relative to the earth. So, you will never see the contrail angled away from the aircraft's longitudinal axis. What you will see instead is the contrail drifting.

Observe the time lapse video linked below. You will see several aircraft starting at the top of the screen, traveling towards the bottom. The "wind" in this case is coming from the left, and the contrails drift off to the right.

Each airplane is following the same ground track, and is crabbing some amount to the left in order to maintain the centerline of what is probably an airway. However, the contrails remain aligned with their fuselage and path through the airmass as they drift.

Crabbing is the misalignment of the aircraft's longitudinal axis with the direction of travel over ground, caused by crosswind.

The crabbing cannot be seen by looking at the angle at which the contrail is trailing behind the aircraft; both the aircraft and the contrail are offset by the wind by the same amount.

• I'm being a little pedantic, but if an aircraft has an issue, such as loss of an engine on one side, then it will tend not to fly straight, and this will, in theory mean that there will be an angle between the plane and the contrails. Commented Apr 5, 2023 at 9:04
• @MikeB but that's not called crabbing, that's called a sideslip. Commented Apr 5, 2023 at 9:31

The crabbing is evidenced by the drift of the contrail as the plane passes. Think about it.

Imagine you are crossing a river. Because of the current, you point upstream to track straight across. Your wake trails out straight behind you. If you're a crayfish sitting on the bottom, you look up and see a boat pointed upstream but actually traveling straight across the river. The boat's wake will drift downstream as you watch it. Same thing, except moving air instead of water.

• @JohnK I took the liberty to include your comment into the answer, in the hope that this answer will finally disappear of our mod-dashboard ;-) Commented Apr 10, 2023 at 18:58
• I've had experienced rivermen tell me that the reason they point the bow sideways to the current when "ferrying" across is so that the current will push the boat across the river, i.e. exert a force on the up-current side of the boat. Is there no end to the ways that humans can be deceived? Commented Apr 11, 2023 at 2:20
• The boat is basically gliding on a water "thermal" going sideways down a trench, instead of up. Commented Apr 11, 2023 at 5:01
• I feel this answer can be improved with references linking crabs and crayfish as crustaceans, thereby enhancing our understanding of the ground track concept. Commented Apr 11, 2023 at 11:37
• @RobertDiGiovanni ROFL Commented Apr 11, 2023 at 12:28