http://www.youtube.com/watch?v=8nKFGQCAg3c&feature
I'm too use to landing my small Cessna using a side slip in a xwind. It makes me nervous to see that crab angle maintained all the way to the ground. I guess the long wings and relatively short landing gear struts make landing in a side slip too dangerous for a big jet.
Most passengers get a little upset when the pilot side-slips an airliner. They freak out as it is when they see the runway coming towards them through a SIDE window.
Makes for a smooth ride...................and because of the deflection at the tips, no need for winglets. Note: Images are public domain. Image Unavailable, Please Login Image Unavailable, Please Login
For sure. I've seen those pics in the past but figured that that amount of wing flex was simply normal for the ultimate stress test. I didn't realize that the wing was designed to flex that much during normal ops. While we all know it's safe due to the testing involved and Boeing's reputation for design, I'm curious what joe blow is going to think once this aircraft gets pressed into daily service?
The wings won't flex as much in service as shown in the pictures but an illustration of how far they will go before failure. They are thin and designed to flex much more than the typical aluminum wing.
I apologize if I wasn't clear there Spasso. What I meant by referring to "...flex that much in normal ops" was the wing flex we see in the video. While that is safe, and designed for of course, has Boeing considered what the flying public is going to think? As it is obvious to anyone that there is quite a bit of flex there (more so than typical aluminum wings as you pointed out). This question is prompted by a friend whom I watched the video with commenting and questioning the safety of the flex in the wing. I had to reassure her that it was ok and safe.
It looks like he rudders it around a bit during the latter part of the flare. With all of that mass a large jet will not start to drift right away after the crab is taken out. Even with a Cessna there is a delay and it can be landed wings level in a crosswind. Airliner's often use all three techniques combined in a strong crosswind. . . sideslip (minimal bank), crab, and rudder just prior to touchdown. If you watch his flaperons you can see he (she) is adding a lot of upwind aileron in the flare as he feeds in the rudder and immediatly after touchdown goes to full deflection and holds it for the roll out. Even though the jet is not wing low it is a cross-crontrolled touchdown (as in a sideslip.) Dave
True, but a side slip keeps the jet perfectly aligned with the runway centerline whereas a strong crab would allow the passengers to see the approaching runway. dave Edit: Unless you are talking about what some call a forward slip, which is used to increase sink rate in an airplane without flaps. That would definetely freak out the passengers!
I've never used a sideslip for landing a jet in a crosswind. Typically (the 787 may be an exception to this) the wingtip clearance is minimal and won't allow for much of a bank angle at touchdown.
Every Jet is different. On the 727 the wing flap would hit first. On the Boeing twins the engine pods are the contact point. In crosswinds below 20 kts in these airplanes most pilots I have flown with use a side-slip (wing low) touchdown. However, bank angles must be kept less than 10 degrees at touchdown. Dave
He definitely kicked out the rudder just before touchdown, just like we would do in a fighter. Wing low and crab combined work well on fighters, both of which were taken out just before touchdown, but not with those big commercial aircraft with engine nacelles hanging down and all that wing out there. Plus they are designed to land crabbed, fighters really are not. Not sure how all that dihedral affects a wing low approach, either, especially in a crab. Not much dihedral in fighters. Anyone notice the drogue on the vertical stabilizer? Wonder if that had a video camera in it or was there for some other purpose? Taz Terry Phillips
My thought when I noticed it was one of two things, either a slip indicator of some sort, or more likely an indicator of votices off the tail?
David- Entirely possible. It was really dancing around back there for a while. Sort of a big tuft like the ones they glued all over aircraft in the past or the yaw/slip indicator on sailplanes possibly. Taz Terry Phillips
That drogue is an air data pick up---true airspeed, etc. When it is deployed well behind the aircraft it is free of any accelerated or turbulent flow from the airplane shape.
Bob- Thanks. Sure does not look like clean air back there when she is pulling some AoA. Taz Terry Phillips
I was relating to my experiences in a light plane in which It would be what you call a "forward slip", to loose altitude without flaps. It's a weird angle and the drop is pronounced. Kind alarming to the un-itiated
Don't worry about side loads on Boeing landing gears. They are well designed with very strong side struts that react the side loads through heavy structural members in the wing and fuselage. The inner cylinder, truck forks, and trucks are designed to take extreme torque loads due to crabbed landings and the outer cylinder is designed to resist spiral fractures that could occur from twisting of the inner cylinder. I've worked on all the big jets and they have never had a failure. Switches.
The drogue out the top of the vertical fin is an extendable static port. Its used for calibrating the static ports on the airplane. It goes out about a 1/4 mile when extended for getting static pressure in free air unaffected by the airplane. Its just used for flight testing. Its too much trouble to remove so its just there along for the ride in this case. Keflavik is great for crosswind landing certification. It has two runways at 90 degrees to each other. Boeing is just using the runaway that is cross to the one the regular flights are using. Both runways are ILS equipped as well which helps testing the automated landing system in a stiff cross wind. Not only are they doing 25-30 knot crosswind landings.. they are doing them in all the non-normal ways... engine out, flaps up, etc. http://maps.google.com/maps?hl=en&ie=UTF8&hq&ll=63.979049,-22.616901&spn=0.044808,0.149345&t=h&z=13