achutchison

747/777 yaw damper lag?

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I've noticed that at slow airspeeds both the 747 and the 777 do not stay coordinated rolling into/out of turns. Is this an accurate simulation (I've heard that there is never a need to touch the rudders except take off and landing in large airliners) or is it a bug, either on my end or yours? This problem doesn't exist on the 737.

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Hi Aidan,

Seeing exactly the same thing here. I do not have the autocoordination box ticked, I guess the same for you. And it is true the NGX is not concerned by this problem. It might be related to large aircraft, yaw dampers and FSX? I dont know...

I have also the impression the 744 behaves a little bit better than the 777 on that matter.

Happy flying

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Surprised no one has brought this up before. I guess simmers don't handfly as much as they should lol. Your using a computer to use another computer if you just let the autopilot handle everything :D

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I think it is normal for a large bank such as 30 deg. at slow speeds for the aircraft to slip a little.  My B77L was in a hold at 1500 ft 200KIAS and there was about a half bar slip in the 30 deg turns.  I assume that is equivalent to the ball being half out of the "cage," which certainly is not serious.  As Aidan mentioned, a little pressure on the rudder will center the skid/slip bar but be careful that you don't over do it and introduce a skid.  Might be better to just let it be.

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No no no... you misunderstand, holding bank angles is fine, the yaw damper catches up eventually. Its when rolling out of turns when its most problematic esp rolling out on short final and the airplane is in an slip from the turn. I guarantee that doesn't happen in the real thing. I would coordinate it myself, but i've got a twisty joystick and it doesn't feel good... besides it is a problem that needs fixing.

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15 hours ago, achutchison said:

(I've heard that there is never a need to touch the rudders except take off and landing in large airliners) or is it a bug,

That's probably because the yaw dampers take care of coordination.

 

3 hours ago, achutchison said:

I guess simmers don't handfly as much as they should lol.

.

The yaw dampers operate whenever the aircraft is in the air (and hydraulics, IRUs and ADCs are operative). It doesn't matter if the A/P is engaged or not.

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2 minutes ago, Qavion2 said:

That's probably because the yaw dampers take care of coordination.

That's the premise of my post.

 

3 minutes ago, Qavion2 said:

The yaw dampers operate whenever the aircraft is in the air (and hydraulics, IRUs and ADCs are operative). It doesn't matter if the A/P is engaged or not.

Happens with the a/p engaged too. Simmers won't notice if they're not handflying it though.

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In general, the only time you use the rudders in a heavy jet would be a crosswind takeoff or crosswind landing when taking out part of the crab on a short final, or with an engine failure, either hand flying or single autopilot operation. If you do a slow, smooth, steady turn at slow speeds, the yaw damper will tend to keep up. If you do a more abrupt or faster turn, the airplane will tend to slip slightly, usually like a 1/4 deflection, then the yaw dampers will catch up and coordinate it.

Depending on the pilot, some will add a small amount of rudder in turns referencing the slip skid indicator on the PFD, some will not and could care less. Usually the guys that add a small amount of rudder are civilian guys that were brought up in countless prop planes and are used to adding and using rudder in all kinds of situations. The guys who don't are generally military pilots with mostly countless jets that they have flown. I belong to the first camp, so I would add a little rudder in turns at slow speeds, almost unconsciously because I wanted coordinated turns and would notice the slight slip. Not a big deal either way.

Interesting thing about the 747-400 is that it was one of the first airplanes with a redesigned wing that had less sweep of the wing compared to earlier generation aircraft. The loss of a yaw damper had no restrictions of speeds or altitudes. The loss of 2 yaw dampers also had no restrictions, mach tuck tendencies were benign in this jet. The only thing that was mentioned is that with the loss of 2 yaw dampers you might get some fish tailing in turbulence at slow speeds at lower altitudes.

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3 hours ago, Captain_Al said:

The guys who don't are generally military pilots with mostly countless jets that they have flown.

Hanging around Air Force Flying Clubs for years, we ground pounders always took delight is watching a jet jockey learn about rudders.  My instructor for my commercial/MEL/Instrument license and ratings was a KC-135 pilot with 12,000 hours and he was ruthless with the less initiated. I sure enjoyed those days.

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Just did a flight in the -300. The issue wasn't as pronounced as in the -200 I guess because of the longer arm of the tail and higher approach speeds. 

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It's realistic. The yaw damper provides turn co-ordination, but it doesn't (in the 747 at least) compensate for adverse aileron roll, which is why you only notice this issue when rolling into/out of turns.

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So its realistic that the aircraft is a full bar uncoordinated for 5-10 seconds after rolling out smoothly and slowly on to final at vref+5 fully configured with no weather?

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I doubt it, but since that wasn't your question I'm not sure what response you were expecting. Nowhere else have you mentioned it was that severe (and I'm certainly not experiencing it) so suggest you drop the patronising tone and go raise a ticket.

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1 hour ago, achutchison said:

Oh here we go with the flakey avsim insults. I'll just fly the 320

No one intended to punish you by forcing you to fly an Airbus.  In my simple opinion, a movement of the slip/slide bar about half a length is not a significant amount of slip.  I would much rather see a little slip than any skid, so a little less is better than too much.  It's perfectly normal while flying a smaller plane where rudder is required to see the ball about half way out of the cage during turns, so I presume (I could be wrong) that this is equivalent to what we are seeing in the big jets.  Is it realistic?  None of the dozens of type rated pilots that tested these products objected. That is good enough for me unless you have evidence to the contrary.

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As a matter of fact, the slip is not that bad. It is there but not that bothering. And the yaw dampers are catching up pretty well.

As I said (not an expert here...), it might be some FSX limitations...

But remember, it is a 90 bucks simulation, and a wonderful one, not a full professional simulator! And even there, it is not perfect... As far as I am concerned, nothing to prevent me enjoying this great product!

En-joy

Happy flying

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John is clearly expert on the systems side of the 74', but my understanding was that turn coordination on the 747 was only available with flaps extended. Therefore, there will be some slip in turns when flaps retracted, but it is not very pronounced and generally it's not advised to use the rudders when not on takeoff/landing because if you overcook the correction, you throw the passengers' coffee all over them. In the cruise, the yaw dampers are there to prevent dutch roll, to which most swept-backed winged aircraft are prone, I believe. 

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I decided to upload a 1 min video showcasing this issue along with the ones immediately related to it: READ THE DESCRIPTION

 

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14 hours ago, achutchison said:

Oh here we go with the flakey avsim insults. I'll just fly the 320

  looks like  your not  following  advice  you  were asked  to raise a  ticket   and  next  thing  you  come  back  with this  reply  good luck  with any other  help

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In the discussion accompanying your video on Youtube, you seem to assume that your increased angle of attack is due to the slow response of the yaw damper.  It seems to me that the increased angle of attack is due to the fairly steep bank angle, which reduces lift and requires more nose-up to maintain the same altitude -- particularly large nose-up because you are flying so slowly.  Also, it looks like you are losing some speed due to the increased angle of attack.  The loss of speed requires even higher angle of attack to maintain the same altitude, until the A/T compensates. 

Mike

 

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On 4/21/2017 at 1:07 PM, alex98 said:

As a matter of fact, the slip is not that bad. It is there but not that bothering. And the yaw dampers are catching up pretty well.

As I said (not an expert here...), it might be some FSX limitations...

But remember, it is a 90 bucks simulation, and a wonderful one, not a full professional simulator! And even there, it is not perfect... As far as I am concerned, nothing to prevent me enjoying this great product!

En-joy

Happy flying

I am in your camp alex98, for $90, this piece of software is amazing and I fly, teach, and check in the 747-400 and 747-8 where it costs hundreds or thousands of dollars for an hour of time. This is nothing, at least in the PMDG 747-400, I will have to try it in the 777, but I never noticed anything that I could not live with there either.

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On 4/21/2017 at 9:27 PM, achutchison said:

I decided to upload a 1 min video showcasing this issue along with the ones immediately related to it: READ THE DESCRIPTION

In my opinion, this is a little exaggerated from what the real airplane probably does in the 777, although I will not speak for the 777. In the 747, like my post said earlier, there is some slip induced when turning (like 1/4 deflection), which some pilots will or will not correct with a small amount of rudder.

What I will say is that this is not the airplane or a 35 million dollar simulator. When I do steep turns in the PMDG 747-400, it is no where close to the correct pitch and power for the given weight and conditions (280 knots, 10,000 feet, 45 degrees of bank, mid range weight) that you will find in the jet or a Level D simulator. Instead of 4.5 degrees of pitch, I am holding 10 degrees to hold altitude, instead of 75-76% N1, I am at 85% N1.

My point is that for less than $100 you are getting a pretty well designed accurate simulation of the jet, perfect...no, but pretty darn good. Can it be more accurate, yes, and is it flawless, no. But I am sure PMDG will decide what is worth fixing and what is not. I have found a lot of small things that are not accurate to the jet, does it detract from my enjoyment of the product, no. Have I let PMDG know about some of these items, yes. Will they fix these in time, maybe, up to them. If you really feel it is an issue, submit a ticket, they will listen...

 

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Quote

 

John is clearly expert on the systems side of the 74',


 

I wish...

I wasn't aware there was any input from the flaps to the Yaw Damper System (but I stand to be corrected). My wiring diagrams and manuals don't show this.

Generally, the Yaw Damper System is designed to stop uncomfortable sideways accerations. The system does the following:

Supresses dutch roll (this can happen at any speed)

Coordinate turns (you would hope it would also do this at high speeds)

Suppress "structural modal oscillation" (the twisting of the fuselage about the wing area during turbulence). Again, you would hope it would happen at all speeds.

The YD System uses the IRUs and 4 dedicated accelerometers (two at each end of the fuselage). The system also uses Air Data Computer information. It has a maximum authority of 4 degrees of rudder (left or right), but the authority is reduced if the IRS or ADCs are faulty. As far as I know, it bypasses the Rudder Ratio system, so the YD system has to compute the effect of increasing airspeed on the rudder surfaces. I guess at higher speeds you normally wouldn't see much rudder movement due to the YD system..

The pilots will only feel the effect of the YD system through the seats of their pants (There is no feedback to the rudder pedals).

Cheers

JHW

 

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