Bank Angle required to hold drift on landing

[Capn Bloggs]

The recommended technique for my Boeing for landing in a crosswind is to kick straight early and track the centreline with aileron down to the flare; this has raised questions regarding wingtip scrape and FOQA pinging at 10°.

Does anybody know how to calculate exactly what bank angle is required to maintain a track with a certain crosswind? Eg 140KIAS Vapp, 25kts of crosswind. Bank Angle required to track the CL?

[de facto]

As you adjust the rudder to center the nose, you input your aileron so the rudder input will NOT cause the wing to rise.you will therefore land with both main at the same time,wigs level,thats a de crab technique.
In any case look outside and no maths necessary.

[Contact Approach]

de facto:

I think he was referring to the wing down method, not the de-crabbing method.

[Capn Bloggs]

Thanks CA. The method being used for my question is the Forward Slip method.

From FCOM:

At approximately 200 feet AGL, gradually change the approach crab angle to a forward slip. Control drift with aileron (the upwind wing will be lower), and use opposite rudder to maintain airplane alignment parallel with the centerline of the runway....
...Airplane may touchdown on upwind wheels first.

[bigjames]

I think 'down wing' and 'forward slip' refer to the same method.

i don't fly big planes but when i am landing in a cross wind with wing down to hold centre line, i have eyes outside, feet on the pedals and one hand on the throttles in case i need to go around.

there may be a calcualted angle specific to each aircraft but i have just learned to feel it through experience.

[framer]

I think that Bloggs probably knows how to look out the window and do it but is interested in what the actual bank angles would be in an ideal situation. Right Bloggs?
For me, I like knowing what drift I will have to kick off in degrees. ie knowing that at an approach speed of 140kts with a 20kt crosswind you only have to squeeze out 8-9 degrees of drift is useful to me. It's not that I monitor how many degrees the nose is changing by,I think it's more that I know it is not a large amount or something. Anyway, does anyone know how to work out the bank angle?

[Capn Bloggs]

I think that Bloggs probably knows how to look out the window and do it but is interested in what the actual bank angles would be in an ideal situation. Right Bloggs?

Correct framer, although some of my effos may say otherwise!

A typical scenario is: approaching the threshold with the wing down already: big gust requiring even more wingdown to stay on CL. If say 5° was being used already, then the 10° FOQA trigger will come into play if you put on another 5-6°. The question is, what would that initial 5° being used actually be?

[lederhosen]

The Boeing Flight Crew Training Manual would appear to provide clear guidance, at least in the case of the 737. The graphs show the risk of striking a nacelle or flap track fairing occurs at just below 15 degrees roll and that in strong crosswinds wing low alone is discouraged.

Sideslip only (zero crab) landings are not recommended with crosswind components in excess of 17 knots at flaps 15, 20 knots at flaps 30, or 23 knots at flaps 40. This recommendation ensures adequate ground clearance and is based on maintaining adequate control margin.

If anyone has any better ideas or I have misunderstood the question I would be happy to be corrected.

[fireflybob]

Kick off the drift

surely a better phrase is "straighten the a/c (with runway) with rudder"?

Further effect of rudder is roll so simultaneously apply into wind aileron to keep the wings level. My advice also is to err on the side of applying a tad more aileron rather than less so that if the timing of the runway alignment has been slightly early (common methinks because to most pilots it feels somewhat alien to touchdown with drift on) the upwind wheel touches marginally first.

Accomplished on limit crosswind landings require quite a lot of practice before you feel competent but generally best to aim for wings level on touchdown.

[A37575]

From FCOM:
Quote:
At approximately 200 feet AGL, gradually change the approach crab angle to a forward slip. Control drift with aileron (the upwind wing will be lower), and use opposite rudder to maintain airplane alignment parallel with the centerline of the runway....
...Airplane may touchdown on upwind wheels first.

What Boeing type are you talking about? The FCOM you quote seems to have different advice to the FCTM for the 737 for instance. It seems unusual to quote a certain height (200 ft agl) at which to transition from crab to lowering a wing. The problem with lowering a wing at that height is spoiler operation which can cause an undesirable loss of lift followed by increased rate of descent and potential for hard landing.

[rudderrudderrat]

Hi A37575,

The problem with lowering a wing at that height is spoiler operation which can cause an undesirable loss of lift followed by increased rate of descent and potential for hard landing.

Or you could raise the nose a bit - as we used to do on TriStars.
On a manual crosswind landing we "Aligned" at about 150ft and rolled in about 5° bank.

See 411A's post.
http://www.pprune.org/tech-log/37312...topilot-6.html

[DBate]

@A37575

What Boeing type are you talking about? The FCOM you quote seems to have different advice to the FCTM for the 737 for instance. It seems unusual to quote a certain height (200 ft agl) at which to transition from crab to lowering a wing. The problem with lowering a wing at that height is spoiler operation which can cause an undesirable loss of lift followed by increased rate of descent and potential for hard landing.

I don't know what type Capn Bloggs is talking about, but can tell you that the mentioned method is the standard crosswind technique for the MD11.

Of course, the additional drag from the deflected flight control surfaces requires a bit more power during the approach.

@ Capn Bloggs

As for your original question on how to calculate the bank angle... cannot tell you how to do that. What I do know, is that when flying an approach with a max CWC of 35kt a bank angle of about 5° is required to keep the aircraft (MD11 in that case) from drifting using the required landing technique.

Cheers,
DBate

[Capn Bloggs]

Thanks for the replies,especially to IGh for the links.

A37575, I'm talking about DBate's smaller brother, the "Boeing" 717. Sounds like our FCOMs are still written by MD troops.

[thermostat]

Drift Angle Correction

Fly with the necessary crab angle until over the threshold. Then do the straighten with rudder and wing down into the wind for touchdown.
The 2 methods used to determine the crab angle were
A. Divide the 90 degree crosswind component by the aircraft speed in N.M. per minute, eg: 20 kts divided by 2.3333 (140 Ktas) = 8.5 degree correction.
B. 300 divided by the TAS = degree per 5 kts of crosswind component
eg : 300 divided by 140 = 2.1 degrees per 5 kts of crosswind component.
Best to make a table with wind angles from 5 to 90 degrees down one side and the wind speed in 5 kt increments from 5 to 35 kts across the top.
eg with a wind angle 35 degrees to runway heading and 20 kts X wind, the drift correction angle would be 5 degrees.
140 kts is a ballpark approach speed for almost all jets.

[stilton]

The ghost of 411A strikes again, he would love to know he's still being quoted !

[fireflybob]

I never realised crosswind landings were so complicated!

[4dogs]

FOGA

Bloggs,

You really need to get over the FOQA triggers!

If there is a sound operational reason for them to be transgressed, so be it - they are just a monitoring tool.

Stay Alive,

[Lord Spandex Masher]

Of course, it will also vary with weight. But you all knew that right?

[Escape Path]

Thermostat

I never really understood those "final leg" calculations... too much bother when you might as well do it by just using the MkI Eyeball. If those calculations were to be made, they would teach them in flight school, they would appear in flight manuals and the whole lot.

[have another coffee]

Does anybody know how to calculate exactly what bank angle is required to maintain a track with a certain crosswind? Eg 140KIAS Vapp, 25kts of crosswind. Bank Angle required to track the CL?

No....

In the steady state situation after applying all the controls to align the aircraft (MD 11 or other MD series?) with the centerline there is a force balance. As most of the forces are somehow related to aerodynamic forces, air speed is a dominant factor. Besides there is the weight who(which) changes the lift (being banked into the wind as well).

Needs quite some modelling before a rough answer can be given. Good question though for the aero/engineer student.