Tag Archives: rotation

El Al 777 Overwing Vortex on Takeoff

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.

Eagle Inlets

B11I2311.jpgThe 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.

B11I5733.jpgThis 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.

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Another Go at 777-300ER Rotations

Getting repetitive here.  My never ending quest to capture and demonstrate the unusual gear articulation of the Boeing 777-300ER gets another outing.  Similar animation of some stills as before.  This time the light was good and the distortion was limited so here we go again.  I won’t bother with the technique aspects this time.  Instead, here is the animation with the rotation about the rear axle pretty easy to see.

Closest Yet on the 777-300ER Gear

AU0E9795.jpgYou might not think a really windy day was going to be a great time to head out and take photos with a long lens hand held. This certainly is not ideal but there are some advantages that a really windy day can bring. The purpose of the trip was to catch the new Virgin 787-9 service coming in to SFO on a Sunday afternoon when I didn’t have anything else planned. While the wind was very strong, the light was nice so I gave it a go. What I didn’t realize was that, while it was windy at home, it was really windy at SFO! Everything was operating on the 28s because the wind was above 30kts and gusting to well over 40kts. This also meant that departures got airborne quite quickly given that they started with over 30kts after zero takeoff roll!

AU0E9781-EditThe heavy jets were frequently airborne before the intersection of the runways and this included an Air France 777-300ER. Consequently, I was able to get a clearer view of the gear during rotation than I have managed before. Above are a still of the gear during rotation and also an animated GIF of the rotation in progress. I think I shall consider myself happy with this. It is the best I have got. Unless I get to spend some time out by the runway while one is departing, I doubt I will get a better chance than this.

Another 777-300ER Wheel Post?

AU0E2336.jpgIf you aren’t already bored with my quest for something definitive on the takeoff characteristics of the Boeing 777-300ER, here is something more on the topic. Rather than animation, this time it is a couple of still shots. The first is a 777-300ER rotating. The second is a 777F. You can clearly see that the truck is rigidly rotating on the 300ER while the freighter has all wheels firmly planted on the ground up into it gets airborne. Maybe I will call that it for now. I promise no more posts on this for a while!

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Another go at the 777-300ER wheels

I have been trying to get evidence of a feature of the Boeing 777-300ER for many years. I previously posted on my efforts to get shots that showed the effect where the main gear bogie is locked to allow the aircraft to get a higher rotation angle at take-off. I have since had another go at this. Taking pictures during the winter has helped since the heat haze is a lot less obvious. Even so, the aircraft are usually quite a distance away. This time I managed to get a sequence that seems to show the effect quite well.

AU0E9767-EditI also had a go at doing the same thing from head on.  Not quite as clear cut but you can see some of what is happening.

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Boeing 777-300ER Main Gear

AU0E5067-EditWhen Boeing launched the 777-300ER, they took the stretched fuselage of the 777-300, a model that didn’t sell particularly well and married it to the updated wing that made use of the fuel capacity of the outboard portion of the wing that had been left when the original concept of a folding wing was contemplated.  The increased the weights of the jet, added far more powerful engines and, with the increased fuel capacity, came up with a winning formula that has done a very effective job of killing off the 747.

One problem that they had to deal with during development was runway length requirements for takeoff.  Even with the bigger engines, the long fuselage limited rotation angles at takeoff and meant a higher takeoff speed was required which meant a longer runway requirement.  Boeing came up with an interesting solution (after dumping some slightly more curious ideas).  The main gear on the 777 has a triple axle bogie.  Previously this had rotated about the pin attaching it to the main gear leg.  Boeing’s solution was to lock the bogie level during takeoff.

The result of this is to have the rotation of the jet at takeoff to take place around the rear wheels of the bogie rather than the gear leg pin.  The slight aft movement of the rotation point allows the aircraft to rotate slightly more nose up and gain a greater angle of attack.  This gives slightly more lift for a given speed.  This means an earlier takeoff and a shorter runway requirement.

I have tried many times to witness this at work.  First, it happens pretty quickly.  Second, I am often in a poor position to see the rotation point.  Recently I was at SFO to pick up some people.  I was getting a few shots prior to their flight arriving and a Singapore 777-300ER was taking off.  The rotation point is quite far away (although, if you are in the terminal, you might have a good view) and the heat haze is a problem.  However, I decided to get a sequence of shots anyway.  Now, how to use them.

Heat haze is crappy on stills but less of an issue with moving images so I decided to animate the sequence.  I imported all of the shots into Photoshop as layers in a single document via Lightroom.  The hardest part was aligning them.  I started at the bottom layer and then progressively made each layer above visible.  I then changed the latest top layer blend mode to difference.  This makes aligning them a lot easier since everything is black unless it is different.  I was focused on the gear so used that as the reference as the fuselage rotated.  Once each layer was in place, I changed the blend mode back to normal and moved to the next layer up.

Once they were all aligned, I used the animation timeline to make frames from each layer (and reversed the order since every time I do this they seem to be the wrong way around).  Then I could crop in to get the overall view I was after and save the file.  A Save for Web allows the generation of the animated GIF and we are done.  The image at the top is the final result.  It does allow you to see a bit of what is going on if you look closely although it is still a bit hard given the distance, the angle to the ground and the heat haze.  I guess I will have to find a location closer next time.