Wake Turbulence Question

Funkeruski

Funkeruski

Pre-takeoff checklist
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Funkeruski
Went out and did my second solo today in the pattern. Did a couple of touch n goes with my CFI before he turned me loose. While waiting at the runway hold line for a landing jet, I asked him about wake turbulence in this situation. The way I understand it, I should not lift off the ground until I am beyond the touchdown point of the jet. I asked my CFI while we were holding, and he told me I needed to lift off before the touchdown point. I told him I was calling BS on him. Seems like if we were to do it his way, I'd be much more likely to fly right through the turbulence, whereas if we did it my way, there would be no wake turbulence as I am beyond the jet's touchdown point. Of course, may have to cruise down the runway a bit if done my way, but since its a 172, runway length is not an issue.

So, I now turn it over to the board to tell me who is right.
 
Geico266 said:
Lift off before his touch down point. The wake turbulance sinks.
Click to expand...

Think about that awhile. Yes vortecies sink, but if you lift off before the touchdown point, you will potentially fly through them on climbout. ESPECIALLY if there is a crosswind that keeps a vortex over the runway.

Actually, given enough runway, it would be best to start the takeoff roll PAST the touchdown point of the big airplane. That way it isn't an issue. And on landing, stay high and land long.
 
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Do you have a copy of the AIM? It has some good pictures in it to help you visualize it.
When taking off after a heavy has landed you wait till after his touchdown point to rotate.
You were correct.
 
Funkeruski said:
The way I understand it, I should not lift off the ground until I am beyond the touchdown point of the jet. I asked my CFI while we were holding, and he told me I needed to lift off before the touchdown point. I told him I was calling BS on him. Seems like if we were to do it his way, I'd be much more likely to fly right through the turbulence, whereas if we did it my way, there would be no wake turbulence as I am beyond the jet's touchdown point.
Click to expand...

You are entirely correct. You want to takeoff beyond the jet's touchdown point to mitigate the onset of wake turbulence. Assign your CFI a reading assignment (AIM 7-3-6).

Perhaps he was thinking about taking off beyond a preceding jet departure. In that situation you want to rotate prior to the preceding aircraft's rotation point and climb above their path.
 
The simplest way to think of it is that you want to be on the ground where the other aircraft was in the air, and in the air only when the other aircraft was on the ground.
 
The folks who are saying to liftoff after the large airplane's touchdown point are correct. The reverse is true if a large aircraft has just departed: you want to liftoff before the other aircraft became airborne and stay above its flight path. Anything below where the large aircraft was at one point airborne should be suspect for wake turbulence.

That said, in an anemic training aircraft, the best thing to do is probably to wait a few minutes. Especially if the other airplane involved is a real "heavy" (e.g., 767). I remember reading about a guy in a Baron who had an unexpected inverted reunion with terra-firma after following a large jet on final... a real shame.
 
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Think of the flight path as a parabola. The approach, landing, roll-out, take-off, and departure defines the parabola. You want to operate inside that line, as close as possible to the vertex.

Think of that parabola as the bowl and you want to stay within the bowl.
 
Something else to think about regarding takeoff behind a heavy is whether or not you can out climb the preceding departure. If not, you may find yourself looking at the horizon from a rather uncomfortable attitude! My preference is to wait 2-3 mins depending on the "heaviness" of the departing aircraft.
 
As far as sinking/drifting vortices go, the only way you'd encounter them if you took off after the heavy plane's touchdown point would be if everyone was landing and taking off downwind. :wink2:

Even so, I'd rather deal with a vortice that is settling than one that is fresh. Less energy.
 
At Boeing Field KBFI,where I trained we waited at least 3 minutes for most jets and longer for 757's or the Dream-lifter 747. I have shut down to save hobs time. Dave
 
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