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All-engine-operative asymetrical power landing

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All-engine-operative asymetrical power landing

Old 4th Jan 2009, 07:40
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Question All-engine-operative asymetrical power landing

Hello,

Is there (or "should I try") a way to prevent excessive crabbing in strong crosswind landings/approaches through the use of asymetrical power in multiengine airplanes? If so, crossed controls technique still applies, right?

In a way it doesn't seem right to me because if you decompose the thrust vectors you still HAVE to have some component of thrust going against the crosswind (or, if you wish, normal to the runway). But then again, how is that normal vector created in a crossed-controls-only technique where the plane's heading is the same as the runway - which implies the engines are exactly lined up with the runway (even if one is higher than the other)?

Thank you for your input!


3-minutes-after-posting edit: --regarding the second part, I figure that the decomposed LIFT vector is the one responsible for contradicting the wind's effect, because of the airplane's bank against the wind with opposite rudder.
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Old 4th Jan 2009, 08:17
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RF
You are either a sim pilot or are having a go at a wind up. If you're the former....try it and see how you go., it doesn't matter if you crash a PC. If you're the latter then may I suggest you be more subtle, a little less obvious.
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Old 4th Jan 2009, 08:20
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........??
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Old 4th Jan 2009, 09:19
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I've just had a look at some of your previous posts and it seems that you are in fact a CPL flying twin engined a/c.
With that being the case I would suggest that you do not try it. The wind is changing all the way down the approach anyway. just crab the thing, let it point way off into wind and just concentrate on tracking the centerline, shortly after starting the flare squeeeeze on enough rudder to bring the nose around, eeeaaase on enough aileron to stop the drift and bobs your uncle. Thats how I was taught anyway and it's seen me through a fair few crosswinds. If your instructor has told you something slightly different then do that.
I wouldn't go mucking around with these sorts of experiments if I were you, winds swing and change, engines fail, flaps deploy assymetrically etc etc etc. It sounds like an accident report written before the accident . All of this is over and above the fact that it won't help you anyway. When you close the taps in the flare you'll be back to square one and all you will have accomplished is a dangerous approach followed by a juggling act.
Regards, Framer
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Old 4th Jan 2009, 09:31
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Is there (or "should I try") a way to prevent excessive crabbing in strong crosswind landings/approaches through the use of asymetrical power in multiengine airplanes? If so, crossed controls technique still applies, right?
You probably shouldn't try, and yes, assymetrical thrust can be used in cases where the limit or aerodynamic control has been reached. It's not an appropriate practice or technique for most types of operations, and one that will certainly bite you in the backside if you're not extremely careful and on top of things.

I've used it in restricted operations in which wind conditions and locale left little other choice, and few if any runway or landing options existed. I've done it in light twins and in large four engine piston powered airplanes. It's not something I advocate or teach, and don't care to expand on it as a practice here for concern that the original poster or someone else may elect to do so.

Yes, it can be done, and no, you probably shouldn't do it.
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Old 4th Jan 2009, 09:34
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Excessive crabbing?

either that means excessive crosswind

otherwise there's no such thing, at once liberated from the effects of the ground an aircraft does not feel the wind!!!

it's the decrab that's the challenge of crosswind

My technique is to keep the crab until established ground effect straighten the nose to help in the decrab while using windward aileron to enter a gentle side slip in order to keep a true track

don't worry too much about touching down on one main it's OK

except if the wing needs to be disturbingly low perhaps a GA is in order---but only you can decide that-not me

a crab is natural and it tells a lot about the actual ground condition perhaps on those days when twr wind seem a little conservative

use the asymmetric thrust to taxi


PA

Last edited by Pugilistic Animus; 4th Jan 2009 at 09:41. Reason: said soo wrong
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Old 4th Jan 2009, 09:56
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framer, that's how I do it as well (ideally, at least!)

SNS3Guppy, believe me, I'm really not very interested in trying, since it's said to be dangerous! I'm a lot more interested in the physical/aerodynamical explanation of how and why it works (albeit in a potentially unstabilizing way towards the flare/idle part).

Pugilistic Animus, maybe my wording was a bit confounding. Certainly, "excessive" crabbing denotes "excessive" crosswind. What I meant was a "what if" you, for some reason (even an academic one), don't wish to crab (or in a limited fashion) and your maximum angle of sideslip is a shallow one (due to a low wing/engine, let's say), what could you do to land safely in strong crosswinds? (Other than the obvious G.A. in case of danger! )


Thank you all for your inputs, more are welcome.
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Old 4th Jan 2009, 10:10
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Well in many bigger planes like Boeings one can touchdown with a certain amount of crab and with a limited bank angle as recommended like 10 deg crab with 5 degree bank angle or any combination of the two that limits---but still no thrust asymmetry but you can't usually leave the crab in a smaller far 23 or 25 airplane

although I I find 20-25 crosswind knot in most small planes on a dry paved rwy about what I can take 28-30- knots SFC winds stop all GA operations for me I don't need unnecessary stress

depends not on the make or model but on the N-number

although two-niner papa is a a tough ol' heiffer

Last edited by Pugilistic Animus; 4th Jan 2009 at 11:39. Reason: emboldened
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Old 4th Jan 2009, 10:21
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You may already be familiar with this!

YouTube - Cross wind landings boeing 777

I couldn't find one with out the music

Go -Around Thrust - Go-Around Attitude
Go- Around Flap-Check Airspeed
Gear Up!
Whooo Baby

YouTube - DC-8 Freighter in Nasty Crosswind

Last edited by Pugilistic Animus; 4th Jan 2009 at 11:46.
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Old 4th Jan 2009, 12:18
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Any minute now, wait for it, wait for it.....
ROTFLOL! It's Tri-something alright
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Old 4th Jan 2009, 12:25
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Pugilistic Animus, I've seen those videos before, they are great! The Boeing crosswind certification flights (off-topic, regarding certifications: I love this one). It's a bit weird that the first 777 in the first video is crabbing with contrary sideslip.. why is that?

Thanks for the links!
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Old 4th Jan 2009, 12:43
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I've done it, many years ago in a Metro 2.
They have a 20kt demostrated crosswind limit, and at 20kts you're pretty much out of rudder and you need a fair bit of wing-down to keep it all under control. I had to land a few times in 30kts of crosswind, and I found that if I cut the downwind engine back to flight idle it'd pull the aeroplane around straight with the runway, good enough to land off. I still needed so much wing-down that I thought it was close to hitting the ground though! (Never did)
The really tricky part was not doing all that, but keeping it straight after touchdown. Still needed a heap of asymmetric reverse and a touch of brakes.

I highly do not recommend it.
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Old 4th Jan 2009, 14:47
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Same experience here as 18 Wheeler and Guppy.

It can be done, but it's something to "ease into" as you get more and more comfortable in the airplane.

Highly recommend using all of the *primary* flight controls FIRST and then resorting to differential thrust/reverse as needed...

...but here's the kicker...

...you need to practice this a little before you really need it.

And I guess that's the most important point: You should only be using this technique if you're routinely flying in conditions that require it.

If you're just using this technique to be fancy, don't bother.

The aerodynamics are pretty straight forward but there's the potential for confusion when using differential reverse due to thrust lever position.
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Old 4th Jan 2009, 19:19
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twotter

or twin otter properly termed-

the way i was shown to deal with extreme crosswinds in the out stations in alaska, by a former fighter pilot from one of the scandy countries then displaced into the far north, was to use assymetric power on the engines, and the use the rudder and aileron to compensate.

he told me to do it soon enough in the approach to get an idea whether you could track the runway or not--if not--then don't land that way.

at other times, he would simply, slow it down into the the high power-low airspeed high pitch reverse side of the power curve and land across the runway.

i don't do that in the 738 of course, at least intentionally.

there is more than one way to skin a cat, but if anything goes wrong, there is only one captain that takes the blame.

and in this day and age of more solicitors/lawyers on the ground than passengers on your aircraft, you had better follow the aircraft manufacturer's and your company's procedures!

as for the reverse bit, he said to simply keep the same split in the power levers. and at least on the twotter, it worked with me at the controls as well.
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Old 4th Jan 2009, 19:23
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Does the Twin Beech 18, ring anyone's bell? In a strong crosswind, once the tailwheel touched down and the rudders blanked out.

GF
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Old 4th Jan 2009, 20:53
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and in this day and age of more solicitors/lawyers on the ground than passengers on your aircraft, you had better follow the aircraft manufacturer's and your company's procedures!

Such an asymmetric thrust technique is not part of the routine certification process.

While there arises the rare occasion where a crew is caught out badly while doing all the sensible things and necessity becomes the mother of invention .. the above thought ought to provide wise counsel as to why one ought not to be too adventurous in handling techniques not endorsed by the TC holder.

This does not preclude having a look at such things in the sim .. while acknowledging that the model may not be correct ?
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Old 5th Jan 2009, 08:48
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While there arises the rare occasion where a crew is caught out badly while doing all the sensible things and necessity becomes the mother of invention
Quite true.
The technique was sometimes required in old straight-pipe powered B707's, whilst landing in very strong crosswinds.
A Captains only maneuver, generally...and must be done with absolute care.
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Old 5th Jan 2009, 19:48
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In the context of this thread, what does "crabbing" mean?

Dick

Last edited by Dick Whittingham; 5th Jan 2009 at 20:37. Reason: typo
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Old 5th Jan 2009, 19:58
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It means flying a wings level ball in the centre approach in a crosswind.

If the R/W was 180 and the wind from 090 the aircraft heading would have to be 170 or some such angle less than 180 in order to track the R/W centreline. This would make it appear the aircraft was 'crabbing' across the ground.
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Old 5th Jan 2009, 20:48
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JF

Which is as I thought. I've never flown anything bigger than an HS125, and on that I used this crabbing technique to fly down to the flare, then put the a/c straight with rudder, using aileron to keep the into-wind wing down and plonk it on. I don't see any sideslip or rudder limitation there except as transients in the flare. Do I have that right?

Dick
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