Within the very high speed flows of air in an aircraft’s exhaust, you can set up a series of shock waves and expansion fans as a result of the differences between the pressure of the flow and that of the surrounding air. When afterburner is engaged, the hot gases and the temperature changes these shocks and expansions cause, result in a diamond pattern forming in the exhaust plume. In darker conditions, these diamonds are more conspicuous but they are visible even in normal daylight.
These diamond patterns are a function of the flow being symmetrical since most engines have round exhaust nozzles. This isn’t the case for the F-22, though. It has flattened nozzles with a pointed profile top and bottom. This got me wondering what the effect is on the exhaust plume and whether the traditional diamonds are formed or whether the nozzle shape results in a different pattern of shock and expansions as they reflect within the plume. I decided to dig in to some shots to see what I could find.
I don’t have a lot of F-22 afterburner shots. While I have shot them a lot taking off, they often take off without afterburner. Since they have plenty of power and burner use dramatically increases fuel consumption (and the F-22 is not over-endowed with range as it is), there is no point using burner if it isn’t needed. Air shows are a time when they do give it plenty of burner, so that is the source of the shots.
The result of this is that there is definitely something unusual about the shock patterns. I include some shots of F-16 and F/A-18 afterburner plumes and the normal shock patterns that create the hotspots known as the diamonds are very obvious and simple in shape. For the F-22, things are very different with the patterns of hot zones being something more in line with the shape of the nozzle. The way in which the patterns repeat is more complex than for an axisymmetric nozzle. There is nothing much to conclude in these observations. It is just something that appeals to an old aero guy like me.
An early ISAP symposium included a visit to Lockheed Martin’s facility at Fort Worth. We were there to see the first F-35 test aircraft, AA-1. In addition, they had arranged to bring Glacier Girl, a P-38 Lightning, to be there too to provide two Lockheed Lightnings. However, while I was up the scissor lift that was provided for us to get an elevated view, I looked the opposite direction. There were two interesting looking airframes parked up. One was an old F-16 that had probably been used for test duties. The other was not a flyable plane but it was some sort of test rig for the STOVL configuration of the F-35 – what would become the F-35B. A couple of cool looking items that you wouldn’t normally get to see.
Ahead of an ISAP symposium many years ago, my friend Richard had arranged a visit to JRB Carswell at Fort Worth. As well as being the home of the Lockheed Martin assembly plant, it also hosts the 301st FW of the USAF Reserve with their F-16s. They were great hosts and we got to spend a bunch of time around the base. On their ramp space, we had a lot of freedom to shoot them prepping for missions and heading out.
We also got to go to the EOR and see them come in after their missions and have the jets safed prior to taxiing back to the ramp. Being close to the jets while they are doing real work is such a different experience to seeing them at an air show when things are all a bit more contrived. This was a new experience for me at the time and so I was following the example of a few of the other guys when looking to see what sort of things to get shots of. It was a great learning experience and a bunch of fun too!
The heat haze was a bit of a problem on this day so I was hoping that they would roll out a bit long to get into usable range. They couldn’t have been more obliging. It turned out to be a US Marine Corps KC-130J. They didn’t exit early for the taxiway even though they could have done so with ease but instead rolled all the way to near me before exiting and taxiing back to the ramp in the other direction. This was very kind of them. I got them close enough in to have little in the way of heat haze and to get a decent look at them.
Another day, another retro post. I am pleasantly surprised by what I find as I go through old shots since I am not able to get any new shots while we are all self-isolating. In this case it was a visit to Edwards AFB that was a pre-symposium trip ahead of an ISAP meeting. I think Richard was the one that organized it all. Anyway, the Edwards test fleet includes a bunch of F-16s. Some are from the test pilot school and some are test program assets or chase planes. There was also a Danish jet that was supporting the F-35 program.
We got to hang out on the ramp as see the jets under the shelters as well as get up close and personal as they were heading out for a mission and recovering. We later went out to shoot near the runway which was fun but not ideal from a shooting perspective because of heat haze. Who would have thought the Mojave Desert would have heat haze! Still better than a day at work of course.
Here are a bunch of shots from that day. I haven’t been through most of these for ages so it is interesting to see what upgrading them to the latest editing algorithms of Lightroom can do for the processing results. I have yet to find one that doesn’t look better with the new processes applied.
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!
The F-35 has been around for quite a while by now so I have shot them on plenty of occasions (although an F-35C is still on the wish list). My UK trip was one where I was hoping to get an RAF F-35B. It was scheduled to make an appearance at RIAT but the information did not make it sound like a display. On the first day of the show, the weather was shocking. Low cloud and rain got in the way of a lot of things displaying. Late in the day the F-35B was due in. Our initial forecast for arrival was extended as the cloud base meant an instrument approach was needed. It finally appeared and flew through the display line once. Then it powered away and a while later we were informed it had gone home.I was shooting video of that which is at the bottom of this page.
The next day had better weather so I was hoping for a little more. It did show up and we did get more than one pass. However, even then, it was a rather lackluster performance. I guess they have not worked up any form of display – not even a hovering portion – so we got some passes and a couple of configurations and that was it. I don’t think I was alone in feeling a little underwhelmed by what they put on. I guess in coming years, a more worked up display will be seen but I will have to wait a while for that.
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 apretty 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.
Speedway departures can be a mixed bag at Nellis. Flex departures with a pull over the Speedway are the best but it does depend on how high planes have got. Some climb out quite steeply and are way too high for a good shot by the time that they reach you. On my most recent Nellis trip, though, we were treated to a few departures by the locals that broke the mold. They got airborne and kept it nice and low as they accelerated towards us before breaking in to the flex departure routing.
The evening light combined with the great angles made for some good shots. It didn’t hurt that I had a lower shutter speed than usual so got some nice blur of the mountains behind the planes courtesy of them being nice and low. The Strike Eagles also gave it a go which was nice.
A USAF Lockheed Martin F-35 Lightning II flexes on departure from Nellis AFB NV.
Some late day departures after the Flag returns included F-15Es, F-35As, L159s and A-4s. You don’t know how long anyone is scheduled to be out but you find yourself hoping that they will all make it back before the sun sets so you can get some arrival shots in the nicest light available. Once they are gone, it is a case of watching the time and crossing your fingers. As it was, we got lucky. They came back in a steady stream with all of them showing up as the sun was at its best. Arriving over Cheyenne is not ideal from a sun angle perspective at this time of year but we still got some nice angles. Some turned tighter while others went wider so we got to try all sorts of angles out to see which picked up what light was remaining.
A USAF Lockheed Martin F-35A Lightning II turns on to final approach at Nellis AFB NV.
Two USAF Lockheed Martin F-35A Lightning IIs run in to the break for landing at Nellis AFB NV.
A USAF Boeing F-15E Strike Eagles turns on to final approach at Nellis AFB NV.