Scenario: you are in a 2 seat sports plane, about 2500lbs, and about 30 seconds to touchdown when the 737 lined up on “your” runway finally starts its takeoff roll.
Tower then clears you to land.
What do you do?
Will tell you later how it played out in reality.
HBadger wrote:
What do you do?
“Going around” ?
Going around for me also, with a deviated track to avoid the wake.
But I don’t think it should have gotten to 30 seconds. With a minute still to go, if the aircraft was still lined up, I think I’d be telling the controller that I can’t continue due to wake turbulence.
Or do you mean that with just a short time to go ATC, cleared the 737 to line up for an immediate?
If that was the case I’d be going around as soon as I heard the controller clear the 737 to line up.
For wake turbulence (generated by wings not engines and stays where they are then sink), with departing heavy traffic I will land short (*) or go-around upwind…the jet blast? well this is different, it’s generated by engines not wings and travels behind? 
please tell?
(*)Behind landing heavy traffic you stay high and land further
Jet blast is totally different from wingtip vortices. Jet blast usually dissipates in seconds. The other stuff is much nastier – example.
If in doubt, go around, but avoid flying into the jet’s trajectory. Stay upwind of it, too. The vortices descend at about 300fpm.
Very bad ATC work.
I saw the situation devolving, as heard tower clear the 737 to line up relatively late, then ask them “confirm rolling”, then query them again, saying “traffic short final”. So it was a mic between tight ATC work and slower than expected 737 crew. I was cleared to land when the 737 was just about to rotate.
Since I was mentally prepared, I had two main thoughts:
1) jet blast is not the same as wake. Should dissipate faster, and especially have no (?) vortices that can flip my plane.
2) the effect would be such that my airspeed would increase, so it wouldn’t be that I fall out of the sky.
What regretfully biased my decision making was that tower was well aware of the situation and cleared me anyway, so I thought they must have some experience with that.
What I did: was mentally prepared and committed to going around (also planned on avoiding wake turbulence) in case i dont like how the plane is feeling and I also added about 5 kts to my approach speed to have more control authority.
The effect of the 30 sec old jet blast was noticeable but much weaker than what I expected. Airspeed increased temporarily by 10 kts and it was a bit turbulent, similar to a gust factor of 10 kts. A gusty crosswind would have been much more challenging to land in.
One note here: my plane has fairly high wing loading. So I expected the effect to be less pronounced than eg in a 152. If I had flown a Cessna 152 or similar, I would have gone around 100%.
Winds were calm btw, so I didn’t expect the blast to be blown away from the runway.
This time it was rather uneventful, but im still not happy with my decision making here: the conditions were such that I wasn’t fully comfortable, so I should have done a go around.
And now that I have a data point, I’m wondering what to do if a similar situation came again, because it went well in 1 out of 1 cases :)
Since I was mentally prepared, I had two main thoughts: 1) jet blast is not the same as wake. Should dissipate faster, and especially have no (?) vortices that can flip my plane. 2) the effect would be such that my airspeed would increase, so it wouldn’t be that I fall out of the sky.
Yes you are flying in laminar airflow (not furbulent one from wake), however, near the ground, I does not sound like comfortable situation to experience for the first time
Now to 1M$ questions, does jet-blast increase or decrease landing distance? can you takeoff in jet-blast?
(*)treadmill got replaced by jet-blast
The physics do get nasty when wheels are on ground even with propeller blasts
What do you do?
Same thing as with a 50 kts headwind: land.
Yes you are flying in laminar airflow
Jet exhaust isn’t anything like laminar airflow. To start with it’s very hot so will rise rapidly.
Unlike vortex on the edge of the wing you can “mathematically” and “practically” treat it as laminar flow…laminar is something to do with Reynolds numbers, the fact that is fast supersonic (Mach number) or very hot (Eckert number) does not matter that much
If Re < 1000 it’s laminar flow (this is a definition) and Bernoulli, Newton stuff will work just fine irrespective of compressibility and temperature
Most of jet engine engineering is done assuming laminar flow (otherwise those engines won’t generate trust if it becomes turbulent behind the nozzles)
