Starship From South Africa, joined Nov 1999, 1098 posts, RR: 13 Posted (16 years 5 months 3 weeks 2 days 2 hours ago) and read 1698 times:
I've discovered an entertaining website www.aviationpics.de/ which amongst other things shows some spectacular approaches. The caption to one set of pics states that a 747 has been designed to withstand a 45 degree crab angle landing and certainly the pics appear to back this up. My neighbour is a first officer on a 747 and when I asked him if this was true, he said it was highly unlikely and they rarely do anything more than 5 degrees or the pax scream and shout.
Can a 747 withstand a 45 degree crab angle landing without ripping off the undercarriage?
Buzz From United States of America, joined Nov 1999, 697 posts, RR: 20
Reply 1, posted (16 years 5 months 3 weeks 1 day 23 hours ago) and read 1598 times:
Hi Starship, Buzz here. I'm a Line Mechanic , and aspiring (perspiring?) taildragger pilot on classic airplanes.
45 degrees worth or crab at touchdown? Well the Lump's landing gear looks beefy enough to do it once.... I'd have to ask how it was on the prototype 747 that's stored at BFI (Boeing Field, Seattle)
Consider: all that momentum being applied when the rubber meets the runway. When it happens at work (UAL) we get to speen a few hours doing a "high sideload inspection", which doesn not cause good feelings between Mechanics, and the guys who brought the hurt airplane to them.
Consider #2: the rubber dosen't feel like staying on the rims (all 16 of them) when you put that much sideload on the landing gear. Most stations don't keep a plethora of tires on hand..... and once again consider the Wrench Benders who will spend the next few hours jacking up the axles (one at a time for safety) and replacing the rubber.
Consider #3: when i fly a 1946 Aeronca Champ and touch down a bit crooked, i get a good look at the edges of the runway. She flew down final approach nicely enough crabbed over to compensate for the wind, but once the wheels meet the runway you've introduced another force that isn't planned on. SO the airplane darts to one side or another. (with an Aeronca, we can land on the grass too) Similar idea in airliners, and it looks so much more professional when you make a smooth arrival.
Conclusion: Yes, it might withstand a severe crab once or twice, but it WILL cost you.
Buzz Fuselsausage: Line Mechanic by night, DC-3 crew chief by choice.
367-80 From United States of America, joined Jul 1999, 51 posts, RR: 0
Reply 2, posted (16 years 5 months 3 weeks 1 day 22 hours ago) and read 1599 times:
Though I don't know much about this topic (I'm not a pilot), I've read of the difficulties pilots face when landing any four-engined aircraft in a sizeable cross wind. For a typical cross wind landing, pilots are instructed to lower the upwind wing to compensate for the cross draft while using the rudder to align the aircraft with the runway centerline. In other words, rather than using the rudder and ailerons together as you would to turn the aircraft, you use them in opposition to compensate for cross winds.
Unfortunately, this technique is not an option on four-engined aircraft for obvious reasons--you'd drag your outboard engine on the concrete if you lower your upwind wing. As a consequence, pilots of these aircraft must compensate with rudder only, which results in the odd off-alignment landings you saw at aviationpics.de. Of course, 45 degrees off alignment is excessive as Buzz noted. I would guess that pilots would attempt such a radical landing at airports with only one runway alignment, such as the old Kai Tak (where I believe the pictures you saw were taken.) Some noise abatement procedures mandate, however, heavy cross wind landings. See the following picture of a QF B747-400 at SYD RWY 07.
Cricri From France, joined Oct 1999, 581 posts, RR: 6
Reply 3, posted (16 years 5 months 3 weeks 1 day 21 hours ago) and read 1590 times:
I know this picture very well since I took it as wallpaper on my computer! A friend of mine, pilot on A340 for AF told me that it is indeed possible to land a 747 with an angle of 30 to 35 ° as you can see this on another picture of the same mentionned website with a 747 landing on runway 13 at Kaitak. Regarding the picture you're talking about, it seems to me that the plane has to be damaged with such a landing angle ; if not then I hope that the pilot bought a ticket at the american lotery on the same day (sure he won) so he could retire himself without being fired!
Dash8 From New Zealand, joined Aug 2005, 16 posts, RR: 0
Reply 4, posted (16 years 5 months 3 weeks 1 day 20 hours ago) and read 1577 times:
The 747-400 has a maximum crosswind component of 30 knots. With apprach speeds in the 140 knot range would yield not more that 20 degrees crab. So even if it could it would not be allowed to be performed.
Even so, the 747 landing technique still calls for upwind wing down landing although it can on;y be performed to a certain extent. At 8 degrees you won't be only greasing your tires, but also one of those outboards.