x-wind, landing gear stress
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x-wind, landing gear stress
hi,
forgive me if this subject has been already discussed.
i was wathcing crosswind landings of boeing and airbus on youtube.
the boeing pilots decrab after touchdown where as the airbus pilots decrab before.
i know its mentioned in the airbus FCOM to decrab before landing. but is there any reason why you cant land the airbus and then decrab?
is it anything to do with stresses on the gear?
his has been debated numerous times.
thanx
forgive me if this subject has been already discussed.
i was wathcing crosswind landings of boeing and airbus on youtube.
the boeing pilots decrab after touchdown where as the airbus pilots decrab before.
i know its mentioned in the airbus FCOM to decrab before landing. but is there any reason why you cant land the airbus and then decrab?
is it anything to do with stresses on the gear?
his has been debated numerous times.
thanx
realize this is my opinion,
just don't use the wing low method, it looks so sloppy, crab/decrab is the professional [looking] way and most of the time you can handle more of a component. and it is a natural attitude for a plane to assume---it's not something that you hold or force . it just doesn't look right to have a jet in a sideslip. and don't kick the crab--- push it out.
besides it give you an excuse to explain why planes "fly sideways"
just don't use the wing low method, it looks so sloppy, crab/decrab is the professional [looking] way and most of the time you can handle more of a component. and it is a natural attitude for a plane to assume---it's not something that you hold or force . it just doesn't look right to have a jet in a sideslip. and don't kick the crab--- push it out.
besides it give you an excuse to explain why planes "fly sideways"
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<<just don't use the wing low method, it looks so sloppy, crab/decrab is the professional [looking] way and most of the time you can handle more of a component.>>
Huh?
Hardly.
The best of the best (Lockheed L1011, of course) uses the wing down method during crosswind automatic approach/land maneuvers, and the demonstrated component is 35 knots.
More?
Yes indeed, it will do more, as many have found out.
Strike an engine pod?
Hardly possible in the 'ole TriStar, at the normal landing attitude you would drag the wing tip first.
Just sit back and watch PFM at work, and yes it still is the standard from which all others are judged...if you don't believe, ask the folks who have flown 'em.
Clearly a superior design...ahhhh, Lockheed!
PS:
A good friend of mine just retired from Continental and his last airplane was the B737-800.
'Autoland' I ask?
'An embarrassment in the 73' he says...
'Gimmie a TriStar any day of the week, a far superior airplane.'
And just imagine, the design is nearly 40 years old.
Huh?
Hardly.
The best of the best (Lockheed L1011, of course) uses the wing down method during crosswind automatic approach/land maneuvers, and the demonstrated component is 35 knots.
More?
Yes indeed, it will do more, as many have found out.
Strike an engine pod?
Hardly possible in the 'ole TriStar, at the normal landing attitude you would drag the wing tip first.
Just sit back and watch PFM at work, and yes it still is the standard from which all others are judged...if you don't believe, ask the folks who have flown 'em.
Clearly a superior design...ahhhh, Lockheed!
PS:
A good friend of mine just retired from Continental and his last airplane was the B737-800.
'Autoland' I ask?
'An embarrassment in the 73' he says...
'Gimmie a TriStar any day of the week, a far superior airplane.'
And just imagine, the design is nearly 40 years old.
Last edited by 411A; 25th Apr 2007 at 17:28.
411A, I agree with you about the L-1011, you are quite fortunate to still fly a classic with real VSI!!!, so ahead of its time indeed
I'm aware quite a few autopilots use the wing low method at some point along the approach, but for hand flown operations I'm biased about crab/ decrab method, also helps out the gear a bit when the decrab is thorough. I guess
PA
I'm aware quite a few autopilots use the wing low method at some point along the approach, but for hand flown operations I'm biased about crab/ decrab method, also helps out the gear a bit when the decrab is thorough. I guess
PA
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if you land without a side component ... there should not be any extreme stress on the grear. Good ol` fashion stick and rudder skills!
Last edited by CRMCaptain; 26th Apr 2007 at 18:42.
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Would you want to be dropped on a runway in your car at 150 miles per hour without your wheels being aligned with the runway. Why do it to your airplane? If you are good enough to do it 100% of the time during the flair with wings level and kicking it out fine, if you are like most of us and encounter a gust during flair and have the wing down into the wind you can still land uneventfully without drifting off the downwind side. I was taught this technique soloing in an Aeronca 7AC and it works well on the B767.
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X-Wind Landings
Spent most of my time on Boeing equipment...Crab - De-Crab is the preferred method of x-wind landings. Check the training manuals. This ISN"T done for looks, its done for stability during the approach and landing.
Actually 411, that Tri-Star was amazing, wasn't it? You used the 'wing low' method...I used the crab - de-crab on it...greasers! Lockheed was so far ahead of itself...I'd love to see where we'd be if they still were in the commercial market.
The trick in the de-crab method is to feed in the opposite rudder during the flare and keep those wings level...it takes practice but sure beats slamming the airplane onto the ground in a wing down/slip. Also in gusty winds at low level, the workload for a wing low approach gets high...too much going on...wings, rudder, pitch and thrust...
Safe flying, gang!
Actually 411, that Tri-Star was amazing, wasn't it? You used the 'wing low' method...I used the crab - de-crab on it...greasers! Lockheed was so far ahead of itself...I'd love to see where we'd be if they still were in the commercial market.
The trick in the de-crab method is to feed in the opposite rudder during the flare and keep those wings level...it takes practice but sure beats slamming the airplane onto the ground in a wing down/slip. Also in gusty winds at low level, the workload for a wing low approach gets high...too much going on...wings, rudder, pitch and thrust...
Safe flying, gang!
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......
thanx guys.
really appreciate the advice. if i remember right the autopilot of the airbus has a decrab mode at around 45ft.
i guess when you touchdown aligned with the runway its makes a prettier picture rather than facing the terminal.
thanx guys
really appreciate the advice. if i remember right the autopilot of the airbus has a decrab mode at around 45ft.
i guess when you touchdown aligned with the runway its makes a prettier picture rather than facing the terminal.
thanx guys
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Can't Remember...
In my old age... Anyway, I seem to remember an Airbus limit (with regard to the A320 series, anyway) there is a maximum crab angle at touchdown of five degrees. So, you'll have to come up with some method to straighten out the nose to within five degrees...whatever method you use...before touchdown.
Again, can't remember, but I'm thinking on the A320 series, you have a maximum wing down at touchdown of 18 degrees, struts extended, (16 degrees struts compressed)...before you scrape something....whatever that 'something' might be.
Ultimately, in my humble opinion, the A320 series is just another airplane. We sometimes make too much of it. It's really pretty conventional in most areas. For example, the discussion on another thread about GS Mini, A/Thr, etc. It would be nice to have GS Mini on all airplanes...it's certainly an advantage...but airplanes have been flying for quite sometime without such a feature...and have done so with few problems.
It flies nicely...well balanced and well designed in terms of aerodynamics. No real surprises that I can think of. So, whatever method you like (with compliance toward your company's SOP, of course), it'll work.
PantLoad
Again, can't remember, but I'm thinking on the A320 series, you have a maximum wing down at touchdown of 18 degrees, struts extended, (16 degrees struts compressed)...before you scrape something....whatever that 'something' might be.
Ultimately, in my humble opinion, the A320 series is just another airplane. We sometimes make too much of it. It's really pretty conventional in most areas. For example, the discussion on another thread about GS Mini, A/Thr, etc. It would be nice to have GS Mini on all airplanes...it's certainly an advantage...but airplanes have been flying for quite sometime without such a feature...and have done so with few problems.
It flies nicely...well balanced and well designed in terms of aerodynamics. No real surprises that I can think of. So, whatever method you like (with compliance toward your company's SOP, of course), it'll work.
PantLoad
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On some aircraft, ie. 747 if you have >7deg AOB you will hit one of the inner engines ... their is very little ground clearance ...
If you try and kick out the drift in the flare and float in a 36Kt X-wind (max on dry runway) you will find yourself being drifted towards the downwind grass, and nothing you can do about it ... unlike other types you could correct with into wind slip ....
So, their is an argument for landing with crab on ... In a gusting 36Kt X-wind finess is NOT the name of the game on a heavey!
If you try and kick out the drift in the flare and float in a 36Kt X-wind (max on dry runway) you will find yourself being drifted towards the downwind grass, and nothing you can do about it ... unlike other types you could correct with into wind slip ....
So, their is an argument for landing with crab on ... In a gusting 36Kt X-wind finess is NOT the name of the game on a heavey!
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westinghouse:
indeed ,the 320 FCTM specifies a max 5 deg crab at landing . The 737 can be landed crab only, at max demonstrated x-wind.
It is not recommended ,though , on a dry rwy ,due to necessary quick correction after touchdown ,in order to remain on the center line. But it can be done ,and B allowes it.
I suspect,as the bus is a bit higher ,the stress on the gear should be higher when landing in a crab.
indeed ,the 320 FCTM specifies a max 5 deg crab at landing . The 737 can be landed crab only, at max demonstrated x-wind.
It is not recommended ,though , on a dry rwy ,due to necessary quick correction after touchdown ,in order to remain on the center line. But it can be done ,and B allowes it.
I suspect,as the bus is a bit higher ,the stress on the gear should be higher when landing in a crab.
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to decrab before or after touchdown
Just my tuppence worth:
Aren't the tyres subjected to far more load when they are not tracking straight down the runway?
I would have thought the tyres would be the weakest link in the argument for landing first then decrabbing due to the immense shearing forces created. You are going to lose a lot more rubber and be at far greater risk of bursting them or shearing them right off the rim.
SB
Aren't the tyres subjected to far more load when they are not tracking straight down the runway?
I would have thought the tyres would be the weakest link in the argument for landing first then decrabbing due to the immense shearing forces created. You are going to lose a lot more rubber and be at far greater risk of bursting them or shearing them right off the rim.
SB
In the first few seconds after touchdown, while the velocity vectors are helping to straighten the aircraft roll out track, we are still mainly wing borne. This eases the side loads on the tyres as we straighten up. Besides, there will be much more tyre damage caused by going off the down wind edge of the runway, not to mention the mountain of paperwork!! 
