Dash 8 Q400 rudder trim

[pinepix62 63]

I am learning the Majestic Q400 and I really enjoy flying it on short hops as I do not enjoy extended flights that much. Got most of the issues sorted.

There is one thing that I am wondering about. When engaging the AP the plane seems to be in a constant slip with a wing low. I noticed in the Sample flight that they mention that you can should use rudder trim to trim the aircraft in order to align the slip/skid indicator and trimming a few degrees right does bring the wings level as well. My question is, is this normal behavior for the Q400. I would have thought that the AP would automatically trim the aircraft correctly.

[SAS443 1,716]

Yes completely normal. The YD has very limited authority and the the engines are very torque-happy. Just one of the quirks with the Q400. Others being ALT SEL button and dual HDG select rotaries for example. 🙄

[DaveCT2003 1,820]

1 hour ago, pinepix62 said:

is this normal behavior for the Q400.

In fact, it's normal behavior for most any aircraft, but the Majestic Dash 8 is the only aircraft in FSX/P3D Dash uses complex external flight dynamics engine (developed by NASA) so you'll notice things that you may not notice in other aircraft models. 

Note:  Someone is bound to jump in and say that other aircraft like the FSLabs A320 also use an external flight dynamics engine, however I've spoken directly with the developer and other developers whom people believe use and external flight dynamics engine and they are mistaken, they simply misunderstand what the developer said (at least in the case of the FS Labs A320).  Can't argue with the developer who actually wrote the software.

 

[pinepix62 63]

Thanks for the feedback, I am used to stepping on the ball with smaller GA aircraft like the A2A implementations but I never needed to really apply rudder trim. If this is the way the real plane flies I will have to watch out for that in order to keep my passengers comfortable.

A great plane and really fun to fly with just the right amount of hands on required to keep you on your toes.

[regis9 4,004]

As a general rule, i use 12 units right for take off, 8 for climb, and then adjust as needed from there.  Makes a huge difference on takeoff.

[DaveCT2003 1,820]

4 hours ago, regis9 said:

As a general rule, i use 12 units right for take off, 8 for climb, and then adjust as needed from there.  Makes a huge difference on takeoff.

Whoa!  That is definitely not advisable.  Take off Rudder and Aileron trim should also be zero.  My time in the Dash is likely in the top three of all people who have it (I've flown her for the past 7.5 years) and I've never found it necessary to apply trim for take off.  Just run up the engines and use slight rudder input and off you go.

 

 

[sidfadc 1,341]

I may be mistaken but I think in the documentation it suggests 7 or 8 units of right rudder trim on takeoff, that's what I always do anyway...

[rdtv91 73]

That's correct, it's recommended by a UK airline who operates the Q400 for right rudder trim during takeoff, it's in both FCOM and SOPs for the dash

[DaveCT2003 1,820]

20 minutes ago, sidfadc said:

I may be mistaken but I think in the documentation it suggests 7 or 8 units of right rudder trim on takeoff, that's what I always do anyway...

I was fairly certain the manuals don't say that (at least as far as the last time I reviewed them prior to release) but I just checked them all including the ones that customers don't have access to and none of them say that and the checklist has trims set at zero just as one would do in any aircraft.

You might be mistaking the part of the manual that was the rudder input can move the nose wheel up to 8 degrees (we use the rudder input to adjust the nose wheel on the take off roll).

After take off you use the Rudder Trim to align the slip indicator (which of course is zeroed on the ground), but generally this isn't done right away as whatever winds you experience on take off will change as soon as you turn the aircraft.

One of the reasons you don't use Rudder Trim on takeoff is that you will automatically limit the rudder input in the opposite direction, which is something you don't want to do until you get higher.

We used an external flight model so that the aircraft flies like a true aircraft (unlike other aircraft models).

 

Best wishes.

 

 

 

 

[DaveCT2003 1,820]

Something else about this.  There is absolutely no way that someone could operate three controls at the same time (Yoke, Power and Rudder Trim) without having their hands on the yoke and feet on the rudder pedals.  One person doing two of them and the PNF adjusting rudder trim isn't going to work either as no matter how seasoned two people are working together there is nobody who can adjust rudder trim to compensate for any power reduction after take off or wind changes unless they can feel their effects on the aircraft which requires hands and feet on the pedals.  However adjusting rudder trim with the autopilot engaged can be done.

I'm not familiar with all airline SOPs (though I'd love to see them if anyone has them), but generally speaking setting rudder trim for take off goes against all my training, even for turboprops that don't use counter rotating props. Using Rudder input rather than rudder trim to adjust for torque is how I was always taught, and there are more reasons for that other than limiting rudder authority in the opposite direction.  Winds are never, ever constant and because they change constantly during take off and initial climb it's best to have your rudder trim zeroed.  It's something I don't use until I'm on a straight course.

[vgbaron 3,508]

It really is on an aircraft by aircraft basis. Single engine high performance, for example a P51 - if you don't dial in about 5 degrees right rudder on takeoff - you may have a fun time. Most of the multi engine's that I have flown however, I agree, they are usually set at 0 to give the pilot maximum rudder and aileron authority at t/o.

Vic

[ckyliu 1,749]

2 hours ago, DaveCT2003 said:

Whoa!  That is definitely not advisable.  Take off Rudder and Aileron trim should also be zero.  My time in the Dash is likely in the top three of all people who have it (I've flown her for the past 7.5 years)

It is permissible for the Q400 to have up to one needle width of right rudder trim upon takeoff (approx 14 units), and indeed most pilots will do this as it means there's less to fight with; it is not a typical prop having 5000 shp on each wing spinning in the same direction! Rudder trim is gradually backed off as the aircraft accelerates and should be fully neutral by cruise.

[regis9 4,004]

I'm pretty sure I read the take off rudder trim bit on these forums some time ago and the reference was the airline2sim training program...I could be wrong though as I've never used the airline2sim stuff myself.