ERJ Question

[g-code]

I was riding XJet from IAH-BHM last week on one of their E-145s (great crew, great seats) and I noticed while at cruise the aircraft would never stay straight and level.

The aircraft would actually roll 2-4 degrees left, then do the same to the right all the way through the flight. What causes this?

I asked the captain and F/O but they both gave me diff. answers so I wanted to ask you guys as the planes I fly don't have A/P at all.

 

[Flying Illini]

We had this problem for a while in one of the Falcon 10's and one of the Falcon 20's I used to fly. In the 20 it was an aileron servo that was going bad. In the 10 they never really nailed it down though they were thinking there was something wrong with the yaw damp.

 

[mokitty]

From my experience, if you didn't properly trim the rudder, the yoke would rock back and forth while on the autopilot. Since the ERJ doesn't keep the yaw damp on the whole flight, the best technique I was taught, and seemed to work the best, was to trim the rudder with the yaw damp off, re-engage it then engage the autopilot. The plane would usually stop oscillating.

 

[Avi8tor2000]

The AP is garbage on the ERJ. Even with it perfectly trimmed it will continue to roll like that. It over-corrects then does the same in the other direction.

 

[rjacobs]

Its called dutch roll. The ERJ is very bad about it. The airplanes get a bit bent, not trimmed right, XR model is really bad about it because of the strakes, lots of other reasons. I think it is bad about it because of the short wing. What ever the reason, its dutch roll. If you put a bit of aileron trim in one way or the other it can usually calm it down pretty well. I think its actually pretty good to rock you to sleep.

 

[littleagnes99]

.............

 

[siucavflight]

Yep, dutch roll. The YD is engaged the whole flight, dont know what mokitty is talking about. AP on this plane is garbage, but you get use to it.

 

[another cfii]

And i thought the CA and the FO were doing something naughty up front...

 

[mokitty]

Yep, dutch roll. The YD is engaged the whole flight, dont know what mokitty is talking about. AP on this plane is garbage, but you get use to it.

Maybe I worded my post a little poorly. I don't know where you flew/fly the ERJ, however, where I did, the YD was not engaged on departure until accelleration alt., and was the last item on the before landing checklist to .... disengage. So, yes, YD on for MOST of the flight, however, not the whole flight (like I stated earlier). For comparison, the 737 YD is on the entire time.

Anyway, the problem is dutch roll. Can't speak for the XR (never flew it), however, on the LR if the rudder is trimmed properly with the YD disengaged and then re-engaged, oscillations created by the YD counteracting dutch roll are minimized. I used to get a kick out of guys giving me an airplane and saying "good plane... but it is one of those where the yolk moves back and forth. Oh well, good flight". We would get in the air, play with the trim (YD off then back on) and get the plane to not rock. Your mileage may vary, but I'm calling it like I saw if for 4000+ hrs in the ERJ.

 

[g-code]

Its called dutch roll. The ERJ is very bad about it. The airplanes get a bit bent, not trimmed right, XR model is really bad about it because of the strakes, lots of other reasons. I think it is bad about it because of the short wing. What ever the reason, its dutch roll. If you put a bit of aileron trim in one way or the other it can usually calm it down pretty well. I think its actually pretty good to rock you to sleep.

I would have thought so too, but I had a head cold so all I got when I closed my eyes was the leans and having flash-backs to unusual atttitudes on my checkride

 

[andym037]

I'm not entirely sure that the rolling is caused by an aerodynamic issue. Just as an experiment, when I've flown airplanes that "rock" badly I've clicked off the AP and handflown the thing (YD on) for a while. Sure enough, the rocking stops. For this reason, I'm convinced its purely an autopilot problem (servo? software?), and not aerodynamic in nature. Just my $.02 Anyone else try this?

 

[BigShotXJTdrvr]

Bad (or going bad) autopilot servos.

No one likes to write it up because it is more of an annoyance than a safety issue. And if you do write it up, they'll just MEL the AP and that's a lot more work than just sitting there watching the plane tip left and right.

 

[huncowboy]

I flew one a few months ago that would do that in NAV mode. In HDG mode it was fine so it was not a dutch roll. Extremely annoying sitting on it all day long.

 

[Texanflyboy]

It's the freakin' auto pilot......our Citation Bravos do the same thing. We have the Honeywell Primus 1000. For us it's more noticable when we're setting up for an approach. After setting in the LOC freq. and switching back to FMS/NAV, the software seems confused rolling oppsite direction then quickly back the correct way. There are ways to minimize it however, it still does it.

 

[Stifler's Mom]

Probably having lunch during the flight. Cheeseburger in one hand and a drink in the other. Only thing left to do is fly with your knees. It's challenging, but once you get the hang of it....