speedrestriction

Howdy folks,

Last week, on the way across the LTMA a Blue Islands ATR42 passed overhead at FL170. We were in a thin layer a few thousand feet below, ISA+7.

It was interesting to see a thin but clear wintip vortex extending aft from each wingtip for about three wingspan lengths. The AC was straight and level. Is this a usual phenomenon on ATRs? I've only noticed it before on aircraft manoeuvering agressively (high AoA) and flaps/wingtips of aircraft on approach (high AoA) in humid conditions, never at cruising speeds.

1jz

Any phase of Flt, if there's enough moisture to get caught up in the vortex (low pressure) n low enough temp to condense it. Wingtip trailing vortices would be visible.

mustafagander

I have been lucky enough to feel and hear the vortices land on me.

I was walking into Narita village from the airport hotels and the path through the rice fields is directly under the flight path. With wind calm, it was not uncommon for the vortices to fall on us as we walked along the pathway.

John Farley

Speedrestrction

Just to confirm the earlier post by 1jz I agree that with any wing that is developing lift there will be atmospheric circumstances where the wing tip votex will become visible.

Granted the circumstances for them to be visible are more common when the wing is close to Cl max and so the wingtip vortex is at its strongest.

speedrestriction

Thank you for the replies. By my reckoning that would be a SAT of -12c. Super cooled droplets then in the vortices?

mustafagander

Just take a look at the vortices shed from the B737 flaps during an approach on a cold dampish day. Quite impressive!

1jz

Vortices visibility isn't only cause of very low temperatures or super cooled water vapor. It depends on the air reaching it's dewpoint ( air cooled to a temperature where it's moisture content becomes visible ), the air that passes above the wing moves inward because lowest pressure point are close to wing root [top surface] n similarly the one passing below the wing moves outward as it tries to ride the wing tip n thus both flows spill n form a vortex. So the greater the CL the greater the pressure differential - low presure vortces n low temp- n more chances of visible vortex.

speedrestriction

Thank you for all your replies. I understand the mechanism for formation but am more interested the phenomenon of visible vortices in sub zero atmospheric conditions and at low AoA.

1jz

Though it won't generally happen at fl170 but, u sure they were not contrails? Which offcourse are improbable on a turboprop.

speedrestriction

No, certainly not contrails, as I said: very thin vapour trails extending to about three span lenghts aft of the wingtip.

Incidentally I have seen Saab 2000s, Q400s and a Dornier 328 TP all generate contrails.

Sir Niall Dementia

1jz;

Take a look at some of the 1940's pictures of B17s over Europe and the contrails they generated. Any aircraft will generate a trail if the conditions are right.

SND

1jz

Thanks for the pic references, I never said impossible but generally improbable.