CFI Pop Quiz #126 - Vortices

Chris Burgess

GYRO-CFI
Joined
Oct 30, 2004
Messages
821
Location
Winter Garden FL 34787
Aircraft
Many makes and models, prefer open frame, Sold my SnoBird Tandem
Total Flight Time
3400+
What effect would a crosswind of 5 knots or less have on the wingtip vortices generated by a large aircraft that had just taken off?

A) A light crosswind would rapidly dissipate the strength of both vortices.
B) The upwind vortex would tend to remain on the runway longer than the downwind vortex.
C) Both vortices would move downwind at a greater rate than if the surface wind was directly down the landing runway.
 
Iam going to use comon sence . I feel the crosswind will psuh both wake turbulance in the same path of the wind.

ChuckP
 
Oh by the way Chris remeber you told me of the tendency to roll on a foward slip. I did push the limits and TO in a 25 gusting to 30 cross wind almost flip it to the right and it hover over the fence for 1/2 minute finally manage to get back to the runawy and hover it to land.

Lesson learn, if the book said max xwind componet is 25 dont push it.

chucP
 
Lets all B Happy!
Vortices spread out a at a speed of about 5 KT. A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus, a light wind of 5 KT could result in the upwind vortex remaining in the touchdown zone for a period of time or hasten the drift of the down wind vortex toward another runway.
 
"B" is correct. Paul gave us the correct reference, the AIM (Aeronautical Information Manual. 7-3-4 b. actually contains the answer. Brandon pretty much explained the situation well.

Hey chuckP. Stay away from that strong right crosswind especially. The TwinStar will flip. Glad you got out of it safe. Remember that lesson.!!! Don't try it again, Please.
 
Also remember that heavy aircraft that generate wake turbulence only do so in flight-- so take-off earlier on the runway than they did and land farther down the runway than they did -- and best idea-- wait 3 minutes.
 
Hi Chris,

Without looking it seemed B was best.

I am unable to use the net for any activity outside of work at the moment. I will let the explanation go at that for the moment.

Jim
 
~ nice
While the vortices have less strengh for an aircraft close to the ground (within 1/2 a wingspan) low speed, high lift operation will add to it. The vortices will trail an aircraft many miles, as can be seen here.
 

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Just to confuse things, I've never sen tests done on rotor wash from heavy helicopters: CH-47 and larger with a full load. From my ATC experiences, disturbed air seems to just sit at point of take-off for about 3 minutes. Even a heavy UH-60 can cause problems for airplanes the size of a Cessna 182 that rolls through the rotorwash long after the helicopter is gone. I've also seen a CH-47 blow a Cessna 172 over backwards before the rotors even started turning. The best advice I can offer when operating around any heavy aircraft: Be cafeful! Even ATC may miss vortice and rotorwash hazards. They are kind of tough to spot.
A friend of mike in the ROK Air Force, also a controller, used to caution the Korean pilots about "air dragons". I think he was on to something.
 
And if you are....

And if you are....

If you are following a heavier, larger, aircraft always stay above and land beyond its touch down point.

Question I was asked on my check ride...

Jonathan
 
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