Tag Archives: diamond

Shock Diamonds and the F-22

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.

Diamond DA62

AU0E0676.jpgI was actually looking for something else when I headed to Livermore.  An interesting aircraft had come to the field from Denver and a friend had given me a heads up about it.  I went over to see if I could see it.  As it turned out, the tail was just visible in a hangar across the field but there was nothing much to see.  I decided to hang around for a short while before heading home.

AU0E0620.jpgAs I was wandering along the fence line, a light twin came in to land.  I got some shots as it landed and could read the DA62 logo on the aircraft.  This is Diamond’s newest product and this appears to be the first example to show up in the US.  I had just been reading the flight test on it in Flight International.  It turns out the wife of the pilot was standing nearby.  They were due to head off but we chatted for a while about their training operations and now the role of distributor for the type.

AU0E0470.jpgThe DA62 has a change for Diamond in that it can be painted in colors.  Previously, the airframes were white and all you could do was add stripes to customize them.  They have done something new with the composites and this example was in a really nice metallic gray finish.  They soon loaded up and headed out.  This is a cool plane and a comfortable seven-seater.  If you are in the market, give these guys a call!

Diamond Head Hike

Just beyond Waikiki in Honolulu rises the remains of an extinct volcano.  Diamond Head is the most obvious geological feature in the vicinity of the city and is a famous landmark.  The crater (not such to be honest whether it counts as a crater or caldera but who is keeping score?) is home to a park.  You can drive in to the park through a tunnel and then park up to climb to the top.

We took the advice of the guide books and went early in the day.  Given how hot we got, I hate to think what those who went later in the day and had the midday sun to deal with felt like.  It is quite an exertion.  I don’t consider myself an athlete but I am not too out of shape either.  This was quite a climb.  There is a trail that is well maintained and the final stages include several flights of stairs – some quite steep.

When we reached the top, we were both pretty relieved to be there.  It was worth it since the view across the city was very good.  We enjoyed it a lot and anyone who suggests that our extended viewing was an excuse to take a rest can’t prove anything.  The trip down was a lot better than the climb up!