A small twin is not going to get a lot of attention from the local photographers at Paine Field on a busy day with lots of traffic. However, it was still relatively early in the day and the air still had a fair bit of moisture in it. I took a guess that this might result in some prop vortices so decided to shoot it anyway. Sure enough, some swirls of moisture showed themselves. Not a dramatic look to them but still what I was after and there wasn’t anything else to do anyway!
Boeing was supposed to be making the first flight of the fourth 777X one Saturday, so I headed up to Paine Field to see it. The weather was not great with low clouds and rain and it was below minima for the flight, so we didn’t get to see the 777X. However, an American Airlines 787 was doing a test flight and it took off in the damp conditions.
As they powered up the jet, the moisture on the surface of the runway got sucked up in the vortex that forms between the inlet and the ground at high power and low forward speed. A dull day makes it easier to see this as well, so I was able to get a few shots of it. The lack of flying that day was a disappointment but this meant the days wasn’t a total bust.
Damp days can make for great prop vortices on takeoff. However, I have been feeling less than satisfied with my results recently. As I was going through some shots, I made a discovery that should probably have been something I worked out before. I like to have a good amount of prop blur so drop the shutter speed down when I can. I go with a high frame rate with the aim of getting a good sharp shot amongst the more blurry examples.
As I go through the shots, the sharp ones have okay prop vortices but not great. Then I will come across some really nice vortices but the shot is otherwise not sharp. It seems that, in panning with the plane to get a sharp shot, the trailing vortex gets blurred out. If I am not panning well, the vortex can be the thing I have tracked better and it shows up well. I have seen shots from others with the props almost frozen with a high shutter speed and the vortices easily seen.
Consequently, I am going to have to make a decision in future. How much prop blur do I want versus the ability to see the vortices well. A little trial and error will be involved. At least it is fall/winter so the Pacific Northwest will probably provide me plenty of damp days on which to experiment!
With a sharp LERX, the F-16 regularly pulls a nice vortex on each side as it maneuvers hard. Getting a shot of that is not a surprise. However, I have recently been slowly making my way through shots from RIAT (months after the event) and I was working through some shots of the Belgian F-16 display. I came across a shot of the jet pulling and rolling, taken from astern of the aircraft. I noticed a second, smaller vortex trailing from the tail plane. It appears that, with differential tail for the roll, there is a vortex coming from the tail plane – possibly at the route. This pleases the old aero guy within!
Departure day at RIAT was a bit overcast, much like the majority of the show. The damp atmosphere did have the positive effect of meaning many of the more powerful prop aircraft were pulling vortices from the tips of their propellers. This was most obvious earlier in their take off runs but you could get a pretty good view of it even head on from where I was sitting in the FRIAT stand. Here is one of the Hercs that was beating the air into submission.
Damp and cloudy days are not always ideal for aviation photography but they can provide some interesting options. One weekend I was up at Everett when they were approaching from the south. The jets broke out of the cloud at quite low level but there was some light from the side coming under the clouds. The damp air meant that the jets were pulling some conspicuous vortices as they flared for landing. They were a long way off but it was possible to get some shots of them. The 747 produced vortices that were easier to see but the 787s didn’t do too badly either.
San Francisco Bay tends to provide a bit of moisture in the air that shows up as vapor clouds in the trailing vortices of approaching airliners. Before the planes reach Coyote Point, they are often trailing these streamers but, as they get closer to the airport, something about the conditions must change as they do seem to peter out. However, on some occasions, the moisture content must have been higher as the streamers lasted longer.
Engine nacelles are optimized for cruise performance. At high angles of attack, their shape results in some rather awkward flow properties which can influence the wing performance above and behind them. In order to control things, you will see small vanes attached to one or both sides of the nacelle that generate a vortex that stabilizes the flow somewhat. As an aircraft rotates at takeoff, the strength of this vortex increases and it will often become visible as moisture in the air condenses within in. This vortex will stream back up and over the leading edge of the wing.
When you are inside the aircraft, this is pretty easy to see provided the conditions are right. From head on or aft they are also quite conspicuous. It isn’t often that you get a good view from above. When I was flying over LAX in the helicopter, the aircraft departing from the north complex had better light on them. However, the runways are offset so the rotation point is further west and beyond the area in which we are allowed to fly. However, you can get a view from above and behind as the jets get airborne. An El Al 777 took off while I was up and I managed to get some shots of it as it rotated and climbed away and the vortices were clear to see as the angle of attack increased.
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.
Moisture 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.
The 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.
The 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.