blueflyer From United States of America, joined Jan 2006, 2523 posts, RR: 1 Posted (4 months 1 week 4 days 13 hours ago) and read 2928 times:
I was just wondering whether there is a formula taking into account wind speed and direction to figure out the angle of offset from centerline when an aircraft is coming in crabbed to land, or is it all about skills and experience?
tdscanuck From Canada, joined Jan 2006, 11033 posts, RR: 72 Reply 1, posted (4 months 1 week 4 days 13 hours ago) and read 2915 times:
Quoting blueflyer (Thread starter):
I was just wondering whether there is a formula taking into account wind speed and direction to figure out the angle of offset from centerline when an aircraft is coming in crabbed to land
For the case of a crosswind landing, the desired course is the runway heading and the airspeed is your approach speed. The wind correction angle is the crab angle...the amount to adjust your heading to fly the desired course.
If you're doing a visual approach you can do it all by eye and experience. I don't think anybody actually does a wind correction angle calculation to do a crosswind landing; there's too much else going on at the same time. If your aircraft has a flight director it will do it for you if you're in track mode.
rfields5421 From United States of America, joined Jul 2007, 4871 posts, RR: 21 Reply 2, posted (4 months 1 week 4 days 12 hours ago) and read 2910 times:
As hard as it sounds - it is something pretty easy to pick-up in flight training.
What looks crazy and ackward in videos and in simulator games is much easier to do and much more natural in an aircraft. True, I've never flown big aircraft and the only crosswinds I fly in are pretty light - but the little plane I get to fly gets blown around much easier than a big fast plane.
rwessel From United States of America, joined Jan 2007, 1614 posts, RR: 2 Reply 3, posted (4 months 1 week 4 days 8 hours ago) and read 2815 times:
Quoting rfields5421 (Reply 2): As hard as it sounds - it is something pretty easy to pick-up in flight training.
I'll second that. If you keep the wings level, the ball* centered, and stay on the line defined by the runway, it happens automatically. If you drift one way, you turn a bit the other way to compensate, when everything stops moving sideways, you're all set. Sure, it takes a bit of practice, and most people are (at least at first) far to shy about feeding in enough crab or slip when there's a substantial crosswind, and get spooked when the runway starts appears in odd places in the windshield**, but actually calculate it on final? Never. Now in cruise, it *is* appropriate to calculate the correction angle, since the external reference are just not there, and you've got lots of time on your hands.
*If you're going to insist on flying an aircraft without a proper coordination instrument like a yaw string (glider pilot humor, deal with it)
**A brisk crosswind where you end up high on final in a sailplane (a particularly easy situation to get into if the wind is mostly left to right across the active runway, which will cause a fast downwind, and *very* fast base), can lead to a combination of full airbrake (which requires substantial pitch down), and a full slip (for more drag) plus a bunch of crab for your course. And if you decide to slip and crab in the same direction (the usual), you'll be looking at the runway out the top and side of the windshield, and the view out the front is all green and going sideways. Not actually a problem, but boy does it look wrong.
26point2 From United States of America, joined Mar 2010, 490 posts, RR: 0 Reply 4, posted (4 months 1 week 4 days 5 hours ago) and read 2748 times:
When flying an approach in IMC with a substantial crosswind it's good practice to anticipate where the runway will appear relative to your wind correction angle. You don't have the outside visual cues of the crab.
Considered bad form to be looking for the runway approach lights straight ahead when they suddenly appear well off to one side of the windshield.
JRadier From Netherlands, joined Sep 2004, 4533 posts, RR: 53 Reply 5, posted (4 months 1 week 3 days 22 hours ago) and read 2578 times:
Quoting rwessel (Reply 3): And if you decide to slip and crab in the same direction (the usual), you'll be looking at the runway out the top and side of the windshield, and the view out the front is all green and going sideways.
When I was taught sideslipping I was specifically told to sideslip with the low wing into the wind, or the complete opposite from what you are saying above. Not saying that either one of them is wrong (I really don't have near enough experience for that), but is there a specific reason you'd want to sideslip with the nose into wind?
For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and ther
CosmicCruiser From United States of America, joined Feb 2005, 2045 posts, RR: 18 Reply 7, posted (4 months 1 week 3 days 11 hours ago) and read 2368 times:
Quoting JRadier (Reply 5): but is there a specific reason you'd want to sideslip with the nose into wind?
to lose altitude if you're a little high. Great for small planes; never used with big jets.
FredT From United Kingdom, joined Feb 2002, 2180 posts, RR: 29 Reply 10, posted (4 months 1 week 2 days 22 hours ago) and read 2081 times:
It makes sense to sideslip in the direction where you don't have a control reversal as you go from the slip into the flare. That obviously means low wing into the wind.
I thought I was doing good trying to avoid those airport hotels... and look at me now.
pilotpip From United States of America, joined Sep 2003, 3015 posts, RR: 13 Reply 11, posted (4 months 1 week 2 days 21 hours ago) and read 2060 times:
Quoting JRadier (Reply 8): And as far as I know sideslipping was used with the gimli glider.
Given the fact that they had one option and one chance to make the runway, they did what they had to. Going around and trying again wasn't an option.
When my options are that limited, I might consider a slip. Until then I'll go around and get it right.
JRadier From Netherlands, joined Sep 2004, 4533 posts, RR: 53 Reply 12, posted (4 months 1 week 2 days 20 hours ago) and read 2038 times:
Quoting FredT (Reply 10): It makes sense to sideslip in the direction where you don't have a control reversal as you go from the slip into the flare. That obviously means low wing into the wind.
That's how it was explained to me (plus having the bonus that the crosswind eliminates some of the slip angle), so that's why I wondered why you would want to sideslip nose into the wind...
For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and ther
Pretty much skills & experience. Not difficult to learn during training.
Besides depending what you are flying, your instruments will indicate the proper correction.
If you still want to get some quick rough numbers to X-check your instruments during the approach, divide crosswind component by the NM x Min the aeroplane is doing and presto. That's your drift angle.
Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
titanmiller From United States of America, joined exactly 6 years ago today! , 71 posts, RR: 0 Reply 14, posted (4 months 1 week 17 hours ago) and read 1580 times:
Quoting rfields5421 (Reply 2): I don't think anybody actually does a wind correction angle calculation to do a crosswind landing
With the possible exception of the B-52 since it performs a wings level, crabbed crosswind landing technique with the landing gear swiveled to match the ground track.
Here is an excellent video that demonstrates this capability.
UAL747 From , joined Dec 1969, posts, RR: Reply 15, posted (4 months 3 days 10 hours ago) and read 1277 times:
You would use A^2 + B^2 = C^2 to find the distances of the imaginary triangle you are making, the use SOH-CAH-TOA to find the crab angle.
Of course, it's a little more complicated than that due to speed and changing wind speeds, but that's a general drift of it. At least that's the basic trigonometry of it, I believe. But I think most pilots probably just eye it, and it isn't as creepy as people think. I asked my dad, who flies a Cessna 335 about it once, and he said it wasn't that hard, just have to line up the forward motion of the plane, and pay attention how things are moving on the horizon. He said it only really gets hairy when you are trying to correct the crab just before touchdown. Not all planes were built to crab like a 747.
JRadier From Netherlands, joined Sep 2004, 4533 posts, RR: 53 Reply 16, posted (4 months 3 days 8 hours ago) and read 1256 times:
Quoting UAL747 (Reply 15): he said it wasn't that hard, just have to line up the forward motion of the plane, and pay attention how things are moving on the horizon.
That's it basically, I don't do any calculations, I just point the nose in a direction that feels about right, and if the runway moves to the right in my windscreen I adjust to the right, and vice versa. It doesn't result in a nice straight final the first few times, but it gets you there and you get better at it over time. For me it is just like the rest of flying, don't over think it, just fly.
For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and ther
DualQual From United States of America, joined Mar 2006, 552 posts, RR: 1 Reply 18, posted (4 months 3 days 1 hour ago) and read 1172 times:
Quoting tdscanuck (Reply 1): If your aircraft has a flight director it will do it for you if you're in track mode.
If you're still looking at the flight director into the flare and landing it better be an autoland or the crab angle is going to be the least of your concerns.
The whole point is track centerline and as you approach the flare add rudder to the extent needed to align the nose down the runway. At the same time roll opposite aileron to counter the drift. You may need to add some power to account for the additional drag introduced.
It is purely a visual maneuver. Some airplanes have a limit and are actually landed in a crab in certain crosswinds. The 737NG is an example.
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Airbus_A340 From Hong Kong, joined Mar 2000, 1552 posts, RR: 24 Reply 19, posted (4 months 3 days 1 hour ago) and read 1161 times:
In the posts above, it is entirely correct that when you begin flying that it's about "feel". However, when you start flying IFR and in larger planes where you must fly in more challenging visibilities, it can be handy to know what drift to expect.
As B747FE correctly pointed out:
Quoting B747FE (Reply 13):
If you still want to get some quick rough numbers to X-check your instruments during the approach, divide crosswind component by the NM x Min the aeroplane is doing and presto. That's your drift angle.
The above is a handy rule of thumb to work out approximately the amount of drift.
Ground Nautical Miles per minute (GNM/min) into the Crosswind component. (i.e. x-wind / GNM/min)
Lets use A330 figures, for example.
150-160kts on approach is approximately 2.5GNM/min
Crosswind of 10 kts:
2.5 into 10 is 4. Therefore 4 degrees of drift.
Crosswind of 15 kts:
2.5 into 15 is 6. Therefore 6 degrees of drift.
Lets say you are now flying 130kts, this is closer to 2GNM/min
Crosswind of 10kts:
2.0 into 10 is 5. Therefore 5 degrees of drift.
Crosswind of 20 kts:
2.0 into 20 is 10. therefore 10 degrees of drift.
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