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Assymetrical Thrust proper tech in x-wind?

Old 08-08-2009, 04:42 PM
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Default Assymetrical Thrust proper tech in x-wind?

Question for the masses: Is the use of assymetrical thrust a valid technique for control about the vertical axis in a crosswind in any jet, large-light? Go...

For the record, I am of the school that it is not but flew with someone who swore by it and looked at me as if I were crazy for not subscribing to it. Not that I am an expert, but this is something I've never seen taught and I'm sure there are aerodynamic consequences that make it unadvisable. However, I havn't yet put much thought into it so I thought I'd lob it out there.
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Old 08-08-2009, 05:05 PM
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not for takeoff.

performance is based on all engines at takeoff (or flex) thrust until V1, then a loss of one engine at V1 and takeoff continued, for instance.

if you reduce thrust on one engine, and have not calculated the increase in acceleration distance required to reach V1,

"oh-oh!"
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Old 08-08-2009, 05:08 PM
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I've used asymetrical thrust in a light twin for landing, but never in a turbine airplane.

Anybody who would use it for takeoff is the definition of careless and reckless, IMO...
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Old 08-08-2009, 05:09 PM
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Assuming you mean on landing, the answer is no. Some aircraft like DC-8 and B747 have roll limits to protect outboard engines which necessitate landing in a crab. My preferred technique is to hold the crab down to the last foot or so, then kick it out just as the wheels touch--paying particular attention to getting the aircraft on the ground and tracking straight down the runway before it starts drifting. Others actually land in the crab, but as spoilers and reverse don't always operate symetrically you could find yourself fighting the aircraft all the way down the runway, especially if it's slick. Plus, that's awfully hard on the landing gear. You won't need asymetrical thrust to help with any crosswind up to the demonstrated limit, and you'd also need to think about a go-around with half your power alreadly spooled up and the other half a little behind. Now that could get exciting!

As for using it on takeoff, never. That's what rudders and ailerons are for.
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Old 08-08-2009, 05:14 PM
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Originally Posted by SmoothOnTop View Post
no.

performance is based on all engines at takeoff (or flex) thrust until V1, then a loss of one engine at V1 and takeoff continued, for instance.

if you reduce thrust on one engine, and have not calculated the increase in acceleration distance required to reach V1,

"oh-oh!"

I'd be willing to bet money he's talking about landings....

and while not a great deal of time is spent teaching the principle in most flight school license mills.... if you had a real instructor (read that as an instructor who was doing more than teaching to build time to take a shiney jet job), they would have introduced you to the principle during your multiengine training. The problem with trying to teach it in light twins is that it really is a skill that isn't required in that type of airplane... actually, short of meeting or exceeding demonstrated crosswind limitations most aircraft don't need this method.
Fast forward to larger jets with poor engine ground clearance issues and the wing low method can be fairly expensive and hard on engines and wing tips... (have you ever seen the old Hong Kong 747 videos?) you will often see a crab carried into the flare followed by a "kick over" for allignment... in this case you may find some old school guys also adding differential power. It can be an effective tool if used correctly, much as the souix city crash/incident was as successfull as it was based primarilly upon the use of differential power.
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Old 08-08-2009, 05:21 PM
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nevermind, ought to read what i write before i post it...

Last edited by btwissel; 08-08-2009 at 05:29 PM. Reason: rambling crap
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Old 08-08-2009, 05:23 PM
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Originally Posted by btwissel
if you lose the spooled down engine on approach, the resulting torque will be greater than a v1 cut.
How do ya figure that one?
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Old 08-08-2009, 05:25 PM
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I have never used asymmetrical thrust in a turbine and have never been in a situation where I even considered it, but I have talked to a bunch of B1900 pilots who claimed that during extreme crosswind landings it was definitely a good technique that helped get the airplane down on the ground and through the rollout safely.

Maybe any B1900 pilots can contribute?
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Old 08-08-2009, 05:41 PM
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Originally Posted by DWS1 View Post
Question for the masses: Is the use of assymetrical thrust a valid technique for control about the vertical axis in a crosswind in any jet, large-light? Go...

For the record, I am of the school that it is not but flew with someone who swore by it and looked at me as if I were crazy for not subscribing to it. Not that I am an expert, but this is something I've never seen taught and I'm sure there are aerodynamic consequences that make it unadvisable. However, I havn't yet put much thought into it so I thought I'd lob it out there.

And you probably will never see it taught.....
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Old 08-08-2009, 05:49 PM
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Originally Posted by seven6 View Post
I have never used asymmetrical thrust in a turbine and have never been in a situation where I even considered it, but I have talked to a bunch of B1900 pilots who claimed that during extreme crosswind landings it was definitely a good technique that helped get the airplane down on the ground and through the rollout safely.

Maybe any B1900 pilots can contribute?
I've got over 3000 hours in the B1900 and have only had to use it a few times. It is a very extreme case that calls for it. It does work though.
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