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All-engine-operative asymetrical power landing

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All-engine-operative asymetrical power landing

Old 5th Jan 2009, 21:31
  #21 (permalink)  
 
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There is just one aircraft automatically that could do what Razor is trying, and that would be the Lockeed Tristar-500
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Old 6th Jan 2009, 00:23
  #22 (permalink)  
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crabbing?

maybe?...

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Old 6th Jan 2009, 01:19
  #23 (permalink)  
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tristar-500

I didn't know the Tristar could do that (automatically)! That's nice. How would it do that? If it detected a yaw in the opposite direction of a full rudder position?
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Old 6th Jan 2009, 01:40
  #24 (permalink)  
 
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why captains only?

how do the captains ever learn to do it?

simply watch until they were upgraded then suddenly they had to be able to do it? but somebody had to be the first somewhere along the line. and it would be like re-inventing the wheel over and over again.

i suppose what he saw me do in normal conditions gave him enough confidence to let me try it myself and i suppose he watched carefully enough to take over if needed, but he didn't ever have to.

makes more sense to have a try or two while in the right seat before becoming captain and then trying it for the first time alone.

learned a lot of things from him, that made perfect practical sense even though they were definitely outside the box!
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Old 6th Jan 2009, 04:18
  #25 (permalink)  
 
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Can't speak to the L-1011, but the C-5 autoland system described it this in the AFM. Paraphrasing, at the flare command, rudder will be applied to line the nose with the selected ILS final course. It was really that simple, but the limits were 10 knots.
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Old 6th Jan 2009, 07:36
  #26 (permalink)  
 
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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.
A few Beech 18's were fitted with a crosswind landing gear, which allowed landing without aligning the aircraft with the runway.
And yes, Lockheed, too.
One specific model of the 749 Constellation also was equipped with a crosswind gear.

And, just so a few here will not be disappointed, all models of the Lockheed TriStar can indeed perform an automatic approach/land maneuver with a direct crosswind of 35 knots.
Personally done several, in both standard body and short body models, a couple on wet runways.
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Old 8th Jan 2009, 01:24
  #27 (permalink)  
ftp
 
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Ok, I'll bite.

RazorFoundation,

Here's how I see the aerodynamics.

On Final:
Say you have a crosswind from the right. You could fly with more thrust on the downwind engine (left engine), this would mean you would be using left rudder to keep the longitudinal axis lined up with the runway. This would give a right lateral force off the rudder that would counteract drift. It's been a while since I've played with this and don't see any practical application. Are you or your passengers any more comfortable flying uncoordinated than flying in a crab? Absolutely not.

In the Flare:
There is a method using differential thrust to help come out of the crab and line the longitudinal axis up with the runway when reaching rudder limits. If you are proficient on your aircraft I don't see the harm on reducing power differentially on a minor crosswind day. But in my experience, you are less likely to screw something up just using 'normal' technique. Also, I really don't think most of us should be in situations where we need to be doing this. I'm in an aircraft that has a modest 35kt demonstrated crosswind limit. I know if I could not stay lined up over the runway with full rudder travel it would be time to go-around and find a more suitable runway.

ftp
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Old 8th Jan 2009, 02:41
  #28 (permalink)  
 
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Devil

I personnaly would not recommend such procedure.
Power UP on upwind side, for short final/flare...
Or all engines equal, and flare with power reduction on downwind side.
Sure... can be done, if you are a good "stick" and highly experienced on that aircraft.
I have done it a few times, but can be potential for an accident.
I rather use more conservative crosswind standard procedures.
And I never trained "my troops" to play that game. Not in my book.
Sure, was discussed with the boys over a beer debriefing.
xxx
The only suggestion regarding this is (747) for 2 engines-OUT approach/landing.
Subject to 90 crosswind, request landing with wind coming from side of operating engines.
xxx

Happy contrails
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Old 8th Jan 2009, 04:42
  #29 (permalink)  
 
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Originally Posted by ftp
RazorFoundation,

Here's how I see the aerodynamics.

On Final:
Say you have a crosswind from the right. You could fly with more thrust on the downwind engine (left engine), this would mean you would be using left rudder to keep the longitudinal axis lined up with the runway. This would give a right lateral force off the rudder that would counteract drift. It's been a while since I've played with this and don't see any practical application. Are you or your passengers any more comfortable flying uncoordinated than flying in a crab? Absolutely not.

In the Flare:
There is a method using differential thrust to help come out of the crab and line the longitudinal axis up with the runway when reaching rudder limits. If you are proficient on your aircraft I don't see the harm on reducing power differentially on a minor crosswind day. But in my experience, you are less likely to screw something up just using 'normal' technique. Also, I really don't think most of us should be in situations where we need to be doing this. I'm in an aircraft that has a modest 35kt demonstrated crosswind limit. I know if I could not stay lined up over the runway with full rudder travel it would be time to go-around and find a more suitable runway.

ftp
Just my opinion, but I think uncoordinated flight is very uncomfortable and a good way to induce vertigo, in fact!

If the ball is not centered you will experience a certain pressure in the seat of your pants--and I hate it when that happens! Please don't do that when I'm on board.

Ciao for now.

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Old 9th Jan 2009, 19:02
  #30 (permalink)  
 
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You know, a long time ago I got a flight-review from a crusty ex-bush pilot instructor who advocated this technique. Played around with it in an Aztec in some 25-30+ knot winds that day, and it did indeed work to help straighten the nose out when rudder control was nearly maxed out.

But.

Looking back on it, I think we were both pretty stupid to launch willingly that day, and I probably wouldn't do it again now. Reason being, if you MUST throttle up the upwind engine to swing the nose straight with the runway, you are probably landing WAY beyond the demonstrated / limiting crosswind for your aircraft. Which is probably not something to intentionally do if you are, like me, a run-of-the-mill airline / commuter / corporate / GA pilot.

I will admit, it is definitely a cool thing to throw in the old bag of tricks for emergencies such as rapidly changing weather / winds or control jams in heavy crosswinds. However, where I fly now we see 35 knot winds fairly regularly, and 45 or more at least a couple of times a year operating into short, crosswind, terrain-surrounded runways. If I find myself with the rudder to the floor, intuitively going for the throttle split on final, the conditioned response is now "Going Around, Set Power, Flaps 5" followed by a diversion to somewhere more favorable.

Different airplanes and different types of operations may dictate otherwise in certain situations, but being primarily a Dash-8 guy these days I can't speak for them.
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Old 9th Jan 2009, 21:26
  #31 (permalink)  
 
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I think some of you are missing the point here that was highlighted earlier. The setting of the assymetric thrust should, if the practice is to be condoned, be applied late in the approach, but significantly before the touch down. Once aligned, and at the appropriate moment for thrust reduction, the levers should be retarded simultaneously while maintaining the same differential.

This means that any corrections that may be required at touch down, or during the roll out, are made by use of rudder in the normal sense, and the possibility of aggavating the situation by addition of more or less assymetric thrust are less likely to let thigs get out of shape.
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Old 9th Jan 2009, 22:10
  #32 (permalink)  
 
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Understood. One would maintain the same differential throughout the landing rollout. However, in a normal line-flying type operation if we are not able to maintain crosswind correction through the use of aerodynamic controls alone (specific aircraft and operator procedures may make some exceptions), the condition is probably pushing the limit.

To take that further (though admittedly this mainly applies mainly to short-haul flights that turn around relatively quickly), if we REQUIRE differential throttle to land due to full or nearly-full use of rudder, logic would dictate that we then would need similar differential throttle to take off again in the same condition. I don't know of any accelerate-stop or balanced-field calculations / takeoff power setting charts / FCOMs / airport analysis manuals / SOPs etc. that would allow for this.

Just a thought from a regular short-haul line guy who flies in a lot of crosswinds, so take it for what it's worth. All operations and aircraft are obviously not the same, so other rules, procedures, and techniques may apply in different places.
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Old 9th Jan 2009, 23:16
  #33 (permalink)  
 
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If you even need to consider assymetric thrust for take off in a crosswind, you shouldn't even be considering going flying! If rudder deflection or nws is not sufficient to keep you straight at the start of the take off roll, how would you propose keeping straight in the event of a rejected take off? Start ADDING power on one side, while braking?
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Old 10th Jan 2009, 01:46
  #34 (permalink)  
 
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If you even need to consider assymetric thrust for take off in a crosswind, you shouldn't even be considering going flying! If rudder deflection or nws is not sufficient to keep you straight at the start of the take off roll, how would you propose keeping straight in the event of a rejected take off? Start ADDING power on one side, while braking?
I've done a lot of flights in which I don't know the destination, or the time, at which I'll be landing. Only the duration of my fuel. Among those flights have been a lot of firefighting missions. The fires are typically wind-driven, often with developing thunderstorms throughout the day. We wouldn't fly if it weren't for the winds and the fire. We don't know where we'll be landing, and often we don't even know where we're going when we take off...we may be told to head north, for example, and we will get the coordinates enroute.

When coming off the fire, we may be told to load and return from somewhere other than our point of departure. Winds may be excessive; sometimes they are. I've experienced this before.

I've also experienced flights in areas where the wind is simply that strong all the time. If you're going to fly, you're going to deal with it, period.

Don't make assumptions simply because the type of operation may be outside your realm of experience.
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Old 10th Jan 2009, 12:04
  #35 (permalink)  
 
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Don't make assumptions simply because the type of operation may be outside your realm of experience.
I'm sorry Guppy, but what was the assumption that you believe I was making?

You stated being faced with the possibility of LANDING at unknown destinations in weather that could not be forecast in advance of your departure. I accept the point you are making, but....

My last post advised against TAKING OFF if the crosswind was of sufficient strength that only assymetric thrust would prevent weathercocking. I'm sure that you can appreciate the folly of this, unless of course your vast wealth of experience enables you to determine that one of the engines will certainly not quit on that particular day.
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Old 10th Jan 2009, 18:46
  #36 (permalink)  
 
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My last post advised against TAKING OFF if the crosswind was of sufficient strength that only assymetric thrust would prevent weathercocking. I'm sure that you can appreciate the folly of this, unless of course your vast wealth of experience enables you to determine that one of the engines will certainly not quit on that particular day
Au contraire. My experience suggests strongly that the potential is ALWAYS there that the engines won't last the day. However, if one were to base one's actions strictly on the merits of engine failure, then one would scarcely ever fly, and certainly never attempt a takeoff in a single engine airplane!

Yes, you broached the subject of taking off, but you may recall the title of the thread is landing...

All-engine-operative asymetrical power landing
In the example previously given, when I depart for a fire, winds may be very, very strong. I may be arriving at a field where assymetrical thrust may be required or in the least useful for the approach and landing...every bit as much as I've frequently used assymetrical reverse on the rollout to aid in directional control,too.

With the concept in mind that the flight can be made safely, that the retardant is needed over the fire and yes, we know it's windy, takeoffs are also often conducted in strong winds which may require special techniques to improve controllability or even to effect the takeoff.

Over the years I've used techniques ranging from angling across a runway to to reduce crosswind component to departing and landing on taxiways and roads. I've used assymetrical thrust, assymetrical reverse, kept flaps up until ready for rotation and rotated late while applying flaps, dumped flaps upon gear touchdown, and other techniques which are appropriate and useful for the conditions, for that type of operation, and are not uncommon in certain types of utility operations.

You may assume that these techniques are inappropriate, but if so...then this is a matter of inexperience with such operations...not an indictment on the techniques themselves.

I'm sorry Guppy, but what was the assumption that you believe I was making?
Specifically? I believe you stated...

If you even need to consider assymetric thrust for take off in a crosswind, you shouldn't even be considering going flying!
Perhaps you shouldn't consider going. Hence my reason for stating previously that such techniques as assymetrical thrust in multi engine airplanes are advanced, not part of most normal operations, and something I wouldn't provide in detail or teach, for the same reasons. As you stated "you shouldn't even be considering going flying," as a statement to the general masses, and I'm among those masses, let me be the first to correct that statement by suggesting that while perhaps *some* shouldn't considering going flying, and *you* shouldn't consider going flying, some types of operations do lend themselves to techniques which are available to address unusual and demanding flying conditions. Strong crosswinds are one such condition.

Such operations are certainly not applicable, or in many cases even acceptable to a typical airline daily flying situation, and are out of the realm of experience for most pilots. If indeed this is you, and you find this a surprising and unacceptable practice, then little surprise...if you haven't encountered it or the need to make it happen, then your view isn't in the least surprising. That lack of experience, however, shouldn't serve to condemn the proper application of the technique by those who do have the experience, and the operational need, to apply it.
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Old 10th Jan 2009, 20:24
  #37 (permalink)  
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It's true Guppy, it started out as landing only, but that doesn't mean it can't be expanded at any time...

Anyway, thank you for your contribution and everybody's so far!
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Old 11th Jan 2009, 03:33
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I used to fly ambulance & scheduled ops in the Shetland Islands. METARS & TAFs aren't available for any of the outer isle airstrips. Strong winds, even gale & storm force, were the norm and sometimes they weren't there before departure. In some conditions the aircraft just couldn't be yawed straight fast enough to get the wheels aligned & on the ground before drift began. Wing down can cope with a lot of xwind in a high wing aircraft but the limit is rudder authority to prevent yaw towards the low wing.

Yawing straight from a crabbed approach just before the wheels touch has the problem that as soon as the yawing begins the aircraft starts to drift. At the yaw rate the rudder to could provide I'd alread be near the edge of the narrow runways (with no run-off areas & some with obstacles) before getting aligned. Even using a combination with full rudder deflection just prior to touchdown & then sufficient wing down just short of yawing towards the low wing.

Lots of times I've used differential power reduction to speed yawing straight just prior to landing to compensate. Like others have written it's not something I'd recommend unless you were very familiar with the aircraft.

Last edited by Tinstaafl; 11th Jan 2009 at 03:45.
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Old 11th Jan 2009, 16:25
  #39 (permalink)  
 
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I'll bite too..

Guppy,

First, just a minor correction...

You stated:

Yes, you broached the subject of taking off, but you may recall the title of the thread is landing...
No I didn't, Hikoushi broached the subject. I merely responded with a statement that I still believe is true, and thus far you have failed, in my humble opinion, to illustrate why it is prudent for anyone (including those with your abilities) to attempt a take off if the crosswind prohibits maintaining directional control with rudder and nws.

You attempt to persuade us that it is acceptable for those with your skill set by stating...

... when I depart for a fire, winds may be very, very strong. I may be arriving at a field where assymetrical thrust may be required or in the least useful for the approach and landing...every bit as much as I've frequently used assymetrical reverse on the rollout to aid in directional control,too.
Very very strong when taking off, huh? Yes, but does the crosswind during take off prohibit you from maintaining directional control with rudder and nws?

we know it's windy, takeoffs are also often conducted in strong winds which may require special techniques to improve controllability or even to effect the takeoff.
And your special techniques are?

"Angling" and use of roads and taxiways"
- common sense really, and not so unusual.

"Kept flaps up until ready for rotation and rotated late while applying flaps."
I don't see how this aids directional contol. Not really sure of it's merit either if you've used no flap V1 and VR take off data, but okay, as you wish, and no further explanation requested.

"I've used assymetrical thrust...and other techniques which are appropriate and useful for the conditions..."
Which brings us back to square one!

You didn't specify your other useful techniques, but clearly you believe that with your skills it is acceptable to use assymetric thrust to aid directional control during a take off roll.

Let's forget the fact that even you do not have charts available from which to determine the take off data, and get back to the point I made. How do you propose to deal with a failure of the upwind powerplant while it is your ONLY other means of maintaining directional control during an out of limit crosswind take off?

It strikes me as being obvious that if the additional thrust one one side is required to keep straight while accelerating, you are sure gonna need it while de-accelerating if you are required to abort due to the loss of your upwind powerplant.

If you can explain to me just why such practice is not a compromise of safety - and eactly how one can be assured of staying on the runway (or road or taxiway) if the upwind donk stops while conducting a take off that is reliant on the use of assymetric thrust, I promise to shut up and never post on the topic again!
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Old 11th Jan 2009, 16:32
  #40 (permalink)  
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Pleasure fly out of an air attack base in NorCal. Guppy's comments don't align with local procedures. S2T's (hot rods). (to my knowledge, standing by). AF
 

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