Tag Archives: military

Shock Diamonds and the F-22

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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.

Fisher P-75A Eagle

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While researching some old images of mine from the experimental hangar at the USAF Museum in Dayton OH (the collection of which has since been moved into a new, custom build display hangar which is far more spacious), I saw some shots of something which, to be honest, I had no idea what it was.  I took a look at the website of the museum to try and identify the type.  It is a Fisher P-75A Eagle.

I did not knew Fisher existed and discovered it was part of General Motors.  The configuration of the aircraft is quite unusual.  The engine is mounted in the middle of the aircraft driving a contra-rotating propeller.  The cockpit is further forward that on other single-engined fighters of the era since there was no space allocated to the engine up front.  The underside includes a pair of inlets.  The airframe is finished in polished metal rather than paint.  Overall, it looks quite impressive.  From what I read, another type was not deemed as necessary so development was terminated and they used the airframes for engine development work.  Funny how I saw it on the visit and took photos and then promptly forgot about it.

Back to Coupeville for a Day Off

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NOLF Coupeville was scheduled for FCLP training and strong winds from the Southeast were forecast which suggested the right runway would be in use.  I also had a day off scheduled.  While the rest of the weather was potentially not ideal, I figured I would make the trip.  Why. Not?  They were due to be flying from late morning but, as seems to be usual, it was just after noon by the time things started to look active.

I was worried about the low cloud base but it was actually not a problem.  The wind was really strong gusting 20-30 kts.  This was giving them some interesting flying.  Early on, there was a hint of sun sometimes which really helped the photos.  As they climbed out after each touchdown, the skies behind made from interesting backgrounds and showed off the heat haze from the exhausts as well as the streaming tip vortices courtesy of the damp conditions.

After a while, I got a visit from the Navy Police.  The young lad informed me I wasn’t allowed to photograph the jets. I pointed out I could be he was most insistent that I couldn’t.  Rather than have trouble I decided the stop shooting.  As it happened, the conditions got a bit worse anyway so I had got the best of what was on offer.  I just watched the rest of the flying which included quite a few bolsters and some sketchy touchdowns as the wind got stronger.

More of the RAF’s Poseidon Test Flying

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In this recent post, I had an RAF Poseidon flying over the house.  A little while later, I was at Boeing Field when the same jet came back from a test flight.  Here are some shots of it as it rolled out after landing.  It wasn’t long after this that the jet was delivered to the RAF and made the trip to its new home in Lossiemouth.

Coast Guard MH-60

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While at Boeing Field on a sunny day, I was pleased to see a Coast Guard MH-60 Jayhawk flying along the runway.  MH-65s are the local Coast Guard helicopters so a Jayhawk is a nice change.  Having seen the MH-65s doing a fly through before, I was hoping that we would get the same but they actually pulled up and turned in the the FBO.  However, once on the ramp, the kept rotors running so I knew they would be out again soon.

When they did come out, they actually back taxied to the far end of the field.  I would have been a lot happier with them making an intersection departure closer to me but that wasn’t to be for some reason.  Consequently, they had gained a fair bit of altitude by the time they came level with me.  A belly shot was not what I was after but never mind.  The underside view gives a good view on the three external tanks that the Jayhawk can carry.  That gives some serious range when heading far offshore to rescue someone in need.

Blue Angels Legacy Hornet Retirement

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Recently, the Blue Angels made their last formation flight with the F/A-18 Hornet.  The team is transitioning to the Super Hornet ahead of 2021 and they have started working up with the new jets.  It has been a while since I last saw the Blue Angels demonstration so I thought a few shots with their aging legacy Hornets was in order.   They always got the oldest jets in the fleet so I hope they are happy to have some slightly newer airframes to work with.

Royal Air Force P-8

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The RAF has been taking delivery of its new maritime patrol aircraft.  The retirement of the Nimrods left the RAF without a maritime aircraft for about a decade which is a strange choice to make.  Finally, the P-8 Poseidon was ordered to reinstate that capability.  They started coming off the line here in Seattle a while back.  The fourth aircraft has been undergoing testing ahead of its delivery.  It was returning from a test flight and was coming straight for our house.  It is not unusual for planes heading to Boeing Field to come our way so I grabbed the camera and got a couple of shots as it flew by.  It even turned slightly giving a slightly wing down view in one shot.

Pegasus Heading Out and Back

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Boeing seems to have addressed a lot of the problems with the KC-46 Pegasus program (but not all of them yet) and so the Air Force is taking delivery of jets at a regular rate.  Since plenty have been built, there are enough to deliver.  I was at Paine Field a while back when one of the jets was heading out on a test flight.  I ended up being there for both the departure and the arrival since the flight was not that long.  The good summer light that Seattle gets but we don’t like people to know about meant I got some reasonable shots of it.

This Is A Real Warship

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My friend Bob alerted me to an unusual warship visiting Everett’s naval base.  The USS Michael Monsoor is the second of the Zumwalt class of destroyer.  Only three of these ships are going to be built so it is an unusual thing to see.  They have a shape unlike almost any other ship with a stealthy profile.  I had seen pictures of them and figured I would try to catch it at some point.  I was hoping to see it shortly after Bob mentioned it but then saw it had already sailed for some local exercises.

As with aircraft, there are ship tracking websites available so I waited to see if it was heading back.  It wasn’t coming in that day.  Nor the next or the one after that.  Instead it was going to and fro off port Angeles at a low speed.

Then, as I got up one morning, I happened to check the tracker and I saw it was heading back.  The weather was pretty grim but was forecast to clear up a bit.  I grabbed my stuff and headed for Mukilteo.  They would come passed the point en route to Everett and it should provide the best opportunity to get a shot.  There followed quite a bit of trouble as they first appeared to not be coming my way and then made a 180 and did indeed come towards me.  I will spare the details of this.  Meanwhile, the sun had made an appearance.

I initially spotted them a long way south.  The odd profile of the ship was conspicuous, even at a distance.  As it got closer, the unusual shape seemed strangely unreal.  Pictures do make it look strange but seeing it in person it is somehow stranger.  The sun was appearing and disappearing behind the clouds but I was able to get some nicely lit shots.  The details of the structure were interesting with the bridge seemingly buried in the structure, the guns on the upper rear decks looking like something out of a sci-fi movie and the side door open with the ladder lowered, presumably for the pilot.

After it had gone, I was tied up on a call for a while but I did drive back along the shoreline towards Everett to get a look at it tied up alongside in the base.  Head on you get a clear idea of how different it is from the rest of the ships of the fleet.