As we drove across Bainbridge Island, we took a road that passed by a very attractive inlet. This was Eagle Harbor. At the time, I only appreciated it at the last moment and we were already passed. However, we did come back along the same road so, this time I slowed down and found a place to pull in and look around. It was a tranquil spot to hang out for a few minutes. However, we were heading to other places so I didn’t stay to appreciate it for long.
More shots from a fun shoot a while back. If the wind is coming from the west, evening departures from O’Hare provide plenty of opportunity to get some shots. The heavy departures to Europe leave later in the afternoon and in to the early evening and, as the sun drops down things are getting better and better. The nice thing about this day was that we got a combination of good conditions. Earlier in the afternoon, while the light wasn’t as good, a storm had not long passed through and there was plenty of moisture in the air.
The result was a lot of vapor in the inlets of the jets as they climbed out at high thrust settings. Some of them had clouds sitting in the inlets for long periods of time. Others would just pulse with the vapor as they climbed away. They would also puff up little clouds over the upper surfaces of the wing as they fought to gain height. As the afternoon wore on, the air dried out a bit and the vapor went away. However, the light was then getting better so no reason to go just yet!
The F-15 came onto the scene in the 1970s and it has been a major force ever since. As a kid growing up fascinated with planes, the F-15 and F-14 were two of my favorites. They each had features I loved. One of the cool things about the F-15 for me was the inlets. Big ramp inlets were in vogue at that time. They combined an angled profile with complex ramps and doors to take flows from above Mach 2 down to subsonic speeds to feed the engines. (Interestingly the F-16 went with a simple pitot inlet and could still just about make Mach 2. It used the fuselage to redirect the air into the inlet rather than raking it.) The F-14 inlets were very sharply angled. The F-15 didn’t have such a sharp angle but instead took a different approach. The inlets rotated down towards the approaching air.
This always struck me as a cool feature and whenever I see F-15s now, I am always looking at the angle of the inlets. Since they are often at lower speeds when I get to shoot them, they are at higher angles of attack and this means the inlets are rotated down. McAir’s engineers did a great job of the joint so the top surface doesn’t look too discontinuous. I include a shot of a parked jet to show the difference. Even after all these years, I still get a kick out of this.
There are some aerodynamic effects that always catch my eye when I am going through images and one of these is vapor forming in engine inlets. The combination of lower airspeed with high thrust settings and moisture can result in puffs of vapor forming in the inlet, either continuously or, more often, as little flashes of cloud. The F-16 can often demonstrate this phenomenon when taking off although the formation is a little way back in the inlet.
On a recent Red Flag, the F-16s were out in force and, since it wasn’t the hottest and driest day that Nellis can provide, they were getting a bit of vapor to show up. Here are a few of the jets squeezing the moisture out of the air (even though it is the opposite of squeezing that makes it happen!).