Tag Archives: vortices

If You Want Shocks, You Don’t Need Fast Jets

Every once in a while, when photographing a fast jet at transonic speeds, you might get something in the background that allows the diffraction caused by the formation of shockwaves to be visualized.  I have posted about that here.  I was in Vancouver and shooting the floatplanes taking off from the harbor (since it is a Canadian harbor, perhaps I should write harbour).  As I was looking through the images zoomed in to check on sharpness, I realized that there was a visual effect of a similar nature.  (If you think this is a Schlieren effect, it is not.  That is a technique that involves a certain type of lighting to show the density differences but should not be applied to every time you see it in the wild.)

I don’t know whether what is showing up is the result of shocks forming on the props as they spin rapidly or just the tip vortices causing a similar effect.  You can often see diffraction in trailing vortices.  Whatever the reason, as you look above the aircraft at the patterns of structures on the shoreline beyond, you can clearly see some interesting effects.  Since the props are spinning fast and there is an overlap of the wakes from each pass of a blade, the shapes are rather complex.  Now I know that this is a thing, I might be tempted to take a longer lens and see what I can get in more detail of this interesting visual effect.

Humid Approaches to SFO

AU0E6356.jpgMoisture in the air is not always what you want when you are out shooting aircraft. However, it does have its benefits if there isn’t so much of it that everything is either obscured or gray. The weather conditions over San Francisco Bay can be very localized and, as the planes come down final approach, they can go through quite a variety. I was out hunting for Air Force One a while back and I got some good examples of this.

AU0E6062.jpgThe weather at SFO was actually quite nice (although not when Air Force one departed as I have previously written about). The sun was out and the sky was pretty clear. In fact, there was quite a troubling amount of heat haze. However, once you got towards the south end of the bay, there was pretty solid cloud cover. The planes coming in were in full IMC for a good portion of their approach. Somewhere in the region between Coyote Point and the San Mateo Bridge they would break out of the cloud cover. Then, for the next mile or so, they were in the clear but still in very humid conditions.

AU0E6319.jpgThe result of this humidity was a lot of vapor forming up over the wings. The low speed and high lift configuration made the wings a good place to get cloud formations as the moist air passed over them. Additionally, the trailing vortices were showing up well as a result of the condensing moisture in them too. For quite a while, each aircraft showed similar patterns as it descended. The widebodies seemed to be better for showing this but that might just be a function of them being easier to see further away when the effect was most pronounced. The closer they got to the field, the less the effect until it was pretty much gone when they were on final approach.

AU0E6193.jpg AU0E6127.jpg