Thunderbird whoopsie!
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Thunderbird whoopsie!
Not sure that it was necessarily that close to a mid air, but certainly a bit of moment:
As a secondary question can wake turbulence be influenced by the weather? Can turbulence get blown into the path of an aircraft by wind?
Winds can certainly affect wake turbulence. I witnessed this often airdropping paratroopers.
in large formations of C-141’s. Above a certain wind speed and angle we actually adjusted our formation position to avoid Wake turbulence. For example the #2 ac in a standard formation was usually to the right of lead, but above a certain wind speed and direction the #2 jet would transition to the left side of lead to avoid Wake turbulence among the aircraft as well as for the paratroopers.
in large formations of C-141’s. Above a certain wind speed and angle we actually adjusted our formation position to avoid Wake turbulence. For example the #2 ac in a standard formation was usually to the right of lead, but above a certain wind speed and direction the #2 jet would transition to the left side of lead to avoid Wake turbulence among the aircraft as well as for the paratroopers.
Moderator
Can turbulence get blown into the path of an aircraft by wind?
Simply put, we are trained to avoid flying into wake turbulence. Because it is nearly never visible, avoidance is either by time or position. We wait [minutes] for it to dissipate, or we carefully, and with good consideration, fly a path where it should not be. Certainly if I'm behind an airplane on departure or approach, I'll be hugging the upwind side of that plane/s path, knowing that the wake turbulence will be blown downwind - so far so good doing that. Once I flew out of position in a Cessna, formation with two other Cessnas. I was amazed at how forceful the wake of a same size airplane was! It was not good, and pretty well stood me on my wingtip. Happily, I had enough separation already that it did not create a collision risk.
But, when the airplane creating the turbulence is fast passing you, you have much less opportunity to maneuver to avoid his turbulence. If you were maneuvering a powerboat to pass another, you'd consider the effect of your wake on that boat, this is not much different.
Dang! have a look at the shadow on the guy that was upset. #3 left wing looks like it has the shadow of the RH stab of #1 on it, that was quite close. The solo bird sure added some excitement. Not sure that a manoeuvre that mimics something that shows up in a cinema with Mr Cruise's visage under a lid is really that great an idea. Assume the debrief was interesting.
Winds can certainly affect wake turbulence. I witnessed this often airdropping paratroopers.
in large formations of C-141’s. Above a certain wind speed and angle we actually adjusted our formation position to avoid Wake turbulence. For example the #2 ac in a standard formation was usually to the right of lead, but above a certain wind speed and direction the #2 jet would transition to the left side of lead to avoid Wake turbulence among the aircraft as well as for the paratroopers.
in large formations of C-141’s. Above a certain wind speed and angle we actually adjusted our formation position to avoid Wake turbulence. For example the #2 ac in a standard formation was usually to the right of lead, but above a certain wind speed and direction the #2 jet would transition to the left side of lead to avoid Wake turbulence among the aircraft as well as for the paratroopers.
Moderator
can you explain why wind will affect them relative to each other? Aerodynamically the aircraft do not "know" there is any wind.
If all of the planes are in the same formation, they should experience the same air mass, and resultant effects. Wake turbulence could still be a factor, but generally the formation does not have a formed up plane well aft in the wake turbulence zone of a forward plane. If the formed up plane is in a wake turbulence zone, it would be more constant, than an "event". When sending off jumpers while in formation, the jumpers would be leaving the formation, thus transitioning to another air mass, and subject to the effects of wake turbulence of another aircraft in the jump run formation (though not from the airplane that they're jumping from).
In the case of the video, the airplanes were not in the same formation, the fast one made wake turbulence which was not a part of the formation collective air mass, which the wind would carry [into the path of the other slower plane].
For this case, the solo aircraft is flying at a lower AOA than the others, it is still developing a vortex sheet roll-up off the wing TE that entrains towards the tip vortices, with a mixing flow in the center from the engine exhaust that is relatively irrotational, but with buckets of turbulence all of its lonesome. The #3 aircraft when they pull the data will find that most of the motion will follow the pilot's inputs; it is going to be a PIO related to the perturbation in a tight tracking task. That's not a criticism of the pilot, the lag in detection, and cognition/recognition response will lead to an opportunity to have a gain and phase issue to the aircraft state. I think the guy actually did well. The error here is to do the Tom Cruise bit, particularly without the music etc. The initial upset is not a large perturbation, the plane follows the controls, which is what the debrief should note, and then avoid such a maneuver.
The tip vortex development over time is pretty well understood, the guys below the fast mover's flight path were quite likely to have a wake encounter, it is just a matter of time. Given more time, the loss of rotational velocity of the vortex results eventually in a point of instability that will cause precession of the vortex, and it kind of does a series of gyroscopic wild rides, stepping out of line laterally, then vertically, describing a square loop, until it finally bursts. Before that, self-excitation in the form of crow instability will occur on aircraft without a centerline jet wake, although if AOA is high enough the jet wake is below the tip vortex and instability can be seen.
The manoeuver is a good way to end up with one pilot becoming a near ace in the one flight without firing a shot.
The tip vortex development over time is pretty well understood, the guys below the fast mover's flight path were quite likely to have a wake encounter, it is just a matter of time. Given more time, the loss of rotational velocity of the vortex results eventually in a point of instability that will cause precession of the vortex, and it kind of does a series of gyroscopic wild rides, stepping out of line laterally, then vertically, describing a square loop, until it finally bursts. Before that, self-excitation in the form of crow instability will occur on aircraft without a centerline jet wake, although if AOA is high enough the jet wake is below the tip vortex and instability can be seen.
The manoeuver is a good way to end up with one pilot becoming a near ace in the one flight without firing a shot.
Pilot DAR, I think your comments are aligned with my thinking/understanding, and I was not referring to this incident either, but to Chiefttp's comments about switching sides in a formation because of wind effects.
212man,
There’s an easy explanation, and I should have explained It better. We were not in the same airmass as the other jets. We were airdropping 130 paratroopers from C-141’s, a large 4 engine jet transport. Our formations were not your standard fingertip spacing. We needed space between the jets to avoid the paratroopers hitting each other, and to distribute them over a larger area. Standard formation spacing for a VFR drop was 500 ft in trail of lead, and slightly displaced from his wingtip laterally. With that much spacing, the vortices of the lead aircraft would, and did, flow, depending on the winds, into the track of the trailing jets. We also dropped in IFR, with 2000 ft in-Itrail and 500 ft lateral spacing, utilizing an instrument based system to maintain formation integrity in IFR conditions. Think flying an ILS for hours! Hope this helps explain my post. Also an important consideration regarding wake turbulence, was how the effect a descending wake affected the parachutes of the jumpers. Remember, we were dropping these soldiers from a jet bigger than a 707 and at only 800 feet AGL.
There’s an easy explanation, and I should have explained It better. We were not in the same airmass as the other jets. We were airdropping 130 paratroopers from C-141’s, a large 4 engine jet transport. Our formations were not your standard fingertip spacing. We needed space between the jets to avoid the paratroopers hitting each other, and to distribute them over a larger area. Standard formation spacing for a VFR drop was 500 ft in trail of lead, and slightly displaced from his wingtip laterally. With that much spacing, the vortices of the lead aircraft would, and did, flow, depending on the winds, into the track of the trailing jets. We also dropped in IFR, with 2000 ft in-Itrail and 500 ft lateral spacing, utilizing an instrument based system to maintain formation integrity in IFR conditions. Think flying an ILS for hours! Hope this helps explain my post. Also an important consideration regarding wake turbulence, was how the effect a descending wake affected the parachutes of the jumpers. Remember, we were dropping these soldiers from a jet bigger than a 707 and at only 800 feet AGL.
