trisho0

Trim question for PMDG 737NGX

Recommended Posts

Posted (edited)
1 hour ago, trisho0 said:

3. Keep hands off and start trimming accordingly to stabilize the plan

Am I wrong?

Sounds like it.  Unless I'm misunderstanding what you are saying you do.

After you pull back on the yoke/joystick to raise the nose and begin your takeoff climb, you don't "let go" of the yoke and "start trimming" to stabilize the plane.  That is exactly the WRONG thing to do.  The autopilot is still disengaged, so YOU need to keep your hands on the controls and manually keep flying the airplane.  You NEVER, NEVER use the trim wheel/button to try to get the airplane in a particular pitch attitude.  NEVER.  You HAND FLY the airplane to the pitch attitude you want to be in.  Then, IF THERE IS ANY PRESSURE YOU HAVE TO HOLD AGAINST THE YOKE to maintain that pitch attitude, you use the TRIM to RELIEVE THE PRESSURE you have to hold on the yoke.  Never, NEVER try to "fly the airplane" by using trim adjustments to do it.  You will only end up chasing the nose up and down that way and your attitude achievement would just be "guessing what trim setting to use".  Get into the attitude you want FIRST by hand-flying the airplane, THEN only use the trim to relieve the pressure you have to hold against the yoke to maintain the attitude.  THEN you can "let go of the controls" and turn on the autopilot, etc.  You would NEVER do what you said in your #3 above.  Never let go fo the yoke first, then try to "fly the airplane" using trim adjustments.  That is totally backwards.

And to answer one other question you asked about WHY you would even want to use the correct trim setting.....

In some aircraft the autopilot will NOT engage if the aircraft is "out of trim balance" to begin with.  This is even correctly modeled in some of the PMDG aircraft (I think the 777...not sure about the 747).  So if you are fighting the yoke by having to hold excessive pressure on it to maintain the nose attitude you want, you might not be able to even ENGAGE the autopilot until you set the trim correctly to relieve the pressure on the yoke.  This is a SAFETY FEATURE built into the airplane's autopilot to prevent a lazy or distracted pilot from engaging the autopilot in a way out of trimmed aircraft configuration the autopilot would have to "fight" as soon as it was engaged.

Hand flying an aircraft while using trim correctly is a BASIC requirement every pilot should be thoroughly familiar with.  There is nothing that would indicate the LACK of knowledge and piloting skills of a pilot more than if they used TRIM to try to FLY the airplane, instead of the way it is supposed to be used.

EDIT/ADD:  Having said all of the above, the issue with our flight sims is that if we are not using a force feedback joystick or yoke, we may never feel the "out of trim" back pressures holding the joystick/yoke (it can depend on the centering qualities of the joystick/yoke, or how big of a "null zone" you may have set for your joystick/yoke, etc).  And even some force feedback joysticks don't simulate it realistically.  So in our sims we need to be more "visually aware" of an out of trim situation.  If I "let go of my joystick" for a second, does the airplane change pitch attitude?  Then the trim is not set correctly and needs to be adjusted.  If the airplane maintains the attitude, then the trim is already set correctly.  But if the airplane's attitude DOES change when I let go of the joystick, I don't then try to "make things right" using trim adjustments alone.  I re-hold the joystick/yoke to manually fly/readjust the pitch attitude back to where I want it, then re-adjust the trim in the proper direction while still holding the joystick/yoke.  You'll get the hang of it after some practice, but it is actually MORE DIFFICULT doing it in the sim without having the "pressure on the yoke/joystick feedback" you would feel in a real airplane.

 

Edited by FalconAF

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

14 hours ago, trisho0 said:

That is what ephedrine said

Not exactly. I was trying to explain in the simplest way possible why it is necessary to set trim correctly for takeoff. Marc went into aerodynamic detail which is useful knowledge but isn’t the central point. That’s more about trimming in general, not takeoff in particular.

Share this post


Link to post
Share on other sites
14 hours ago, FalconAF said:

Never, NEVER try to "fly the airplane" by using trim adjustments to do it. 

Never shouldn't be used very often.  A good example is hand flying straight and level minor pitch adjustments are routinely made with pitch trim only.  I literally fly  with my thumb on the pitch switch or wheel... I prefer the wheel.  You can also use trim for a smooth transition from level flight to descent... in fact that's the only way I'd be doing it... cannot imagine pushing on the yoke to start descent unless I was in a hurry to get down.

Share this post


Link to post
Share on other sites
Posted (edited)

We're arguing semantics.  It's the same as the old discussion about "elevator controls altitude and throttle controls airspeed".  That will always confuse some student pilots until they grasp the "WHY" it is that way.  And even then, some experienced pilots will still say, "Well, not ALL the time...".  But that doesn't mean a flight instructor will ever teach it the other way around while maintaining any credibility. 

Trim is used to relieve pressure the pilot may need to use on the yoke or stick to maintain a given attitude.  You never use trim to "fly" the airplane from one attitude to another.  It just doesn't work that way, and would never be taught that way by any credible instructor or flight school. 

Edited by FalconAF

Share this post


Link to post
Share on other sites
21 hours ago, FalconAF said:

Sounds like it.  Unless I'm misunderstanding what you are saying you do.

After you pull back on the yoke/joystick to raise the nose and begin your takeoff climb, you don't "let go" of the yoke and "start trimming" to stabilize the plane.  That is exactly the WRONG thing to do.  The autopilot is still disengaged, so YOU need to keep your hands on the controls and manually keep flying the airplane.  You NEVER, NEVER use the trim wheel/button to try to get the airplane in a particular pitch attitude.  NEVER.  You HAND FLY the airplane to the pitch attitude you want to be in.  Then, IF THERE IS ANY PRESSURE YOU HAVE TO HOLD AGAINST THE YOKE to maintain that pitch attitude, you use the TRIM to RELIEVE THE PRESSURE you have to hold on the yoke.  Never, NEVER try to "fly the airplane" by using trim adjustments to do it.  You will only end up chasing the nose up and down that way and your attitude achievement would just be "guessing what trim setting to use".  Get into the attitude you want FIRST by hand-flying the airplane, THEN only use the trim to relieve the pressure you have to hold against the yoke to maintain the attitude.  THEN you can "let go of the controls" and turn on the autopilot, etc.  You would NEVER do what you said in your #3 above.  Never let go fo the yoke first, then try to "fly the airplane" using trim adjustments.  That is totally backwards.

And to answer one other question you asked about WHY you would even want to use the correct trim setting.....

In some aircraft the autopilot will NOT engage if the aircraft is "out of trim balance" to begin with.  This is even correctly modeled in some of the PMDG aircraft (I think the 777...not sure about the 747).  So if you are fighting the yoke by having to hold excessive pressure on it to maintain the nose attitude you want, you might not be able to even ENGAGE the autopilot until you set the trim correctly to relieve the pressure on the yoke.  This is a SAFETY FEATURE built into the airplane's autopilot to prevent a lazy or distracted pilot from engaging the autopilot in a way out of trimmed aircraft configuration the autopilot would have to "fight" as soon as it was engaged.

Hand flying an aircraft while using trim correctly is a BASIC requirement every pilot should be thoroughly familiar with.  There is nothing that would indicate the LACK of knowledge and piloting skills of a pilot more than if they used TRIM to try to FLY the airplane, instead of the way it is supposed to be used.

EDIT/ADD:  Having said all of the above, the issue with our flight sims is that if we are not using a force feedback joystick or yoke, we may never feel the "out of trim" back pressures holding the joystick/yoke (it can depend on the centering qualities of the joystick/yoke, or how big of a "null zone" you may have set for your joystick/yoke, etc).  And even some force feedback joysticks don't simulate it realistically.  So in our sims we need to be more "visually aware" of an out of trim situation.  If I "let go of my joystick" for a second, does the airplane change pitch attitude?  Then the trim is not set correctly and needs to be adjusted.  If the airplane maintains the attitude, then the trim is already set correctly.  But if the airplane's attitude DOES change when I let go of the joystick, I don't then try to "make things right" using trim adjustments alone.  I re-hold the joystick/yoke to manually fly/readjust the pitch attitude back to where I want it, then re-adjust the trim in the proper direction while still holding the joystick/yoke.  You'll get the hang of it after some practice, but it is actually MORE DIFFICULT doing it in the sim without having the "pressure on the yoke/joystick feedback" you would feel in a real airplane.

 

OK so,

1. Adjust Trim before takeoff

2. Hands on Yoke until near Altitude and arm Autopilot

This is what I was doing in the past months. After found Trim matters in AVSIM is when I started this thread to find out some info and answers.

Share this post


Link to post
Share on other sites
29 minutes ago, FalconAF said:

Trim is used to relieve pressure the pilot may need to use on the yoke or stick to maintain a given attitude.

In my flights I don't see/feel trim pressure so, am I lucky? I think is because I use Logitech Joystick and it is well adjusted via control panel from Windows 10.

Share this post


Link to post
Share on other sites

Think about this, too: If you're applying pressure to the yoke for pitch, you're not flying the tail as cleanly as you could. More pressure = more drag.

 

Interesting aside regarding trim:

I was in the sim (full-motion) a few days ago doing my recurrent and the instructor had us doing stall recoveries. The scenario was an auto-throttle malfunction on an ILS approach on final. The auto-throttle idled the engines and we're supposed to ignore the warnings until buffet/shaker.

I get the shaker and pushed the nose over and then added power. The nose came up to a good attitude, but wouldn't stop raising even with the yoke full forward!

So, I pulled the power back to maybe 80% while I was working on getting the trim set. My officer, doing his job of calling out any omissions, asked if I would like more power. NO! (I may have said it a little too harshly. Sorry, JP.)

The underslung engines were providing more of a pitch moment than the elevator could control, so initially I had to reduce power so we didn't end up in an upset. Once I got the trim set, all was okay and we cleaned up and it was my FO's turn.

Share this post


Link to post
Share on other sites
On ‎6‎/‎9‎/‎2018 at 3:38 PM, FalconAF said:

It's the same as the old discussion about "elevator controls altitude and throttle controls airspeed".   

Amazing.  The above is why I DO make "information correction" type posts in forums.

It's been over 24 hours since I posted the above.  And not ONE PERSON has questioned it.

The quoted part is "erroneous information" (that's what an Instructor (teacher) would call information that is FALSE).

The correct information concerning flying an aircraft is "elevator controls AIRSPEED and throttle controls ALTITUDE".  And that confuses the heck out of most new student pilots because it is totally backwards from what you use the "throttle" (gas pedal) in a car to do...increase or decrease speed.

And nobody here questioned it.

Amazing

 

Share this post


Link to post
Share on other sites

1.  A previous explanation said we trim for pitch attitude, not airspeed.  This isn't really true.  An airplane trimmed for a particular airspeed will pitch up or down as necessary to maintain that airspeed, so I've always found it easier as a teaching method to say that we DO trim for airspeed.  Try this: in any airplane from a Cessna to a 737, trim for level flight at cruise power, then pull the power to idle.  What you'll see is the plane pitch down and start to descend, roughly at the same airspeed you trimmed it for (I say roughly because with underslung wing mounted engines like the 737, every power change somewhat changes the speed you're "trimmed out" for unless you adjust the trim again.)

2.  In real life, elevator trim is definitely not "optional".  It's impossible to fly smoothly and accurately while needing to hold constant pressure on the controls.  In large aircraft (this includes the 737), if you're far enough out of trim it's almost physically impossible to use enough force to counter the situation.  In the sense that there's nothing realistic about how we control a computer simulation / game, sure it's optional.  We're all here for enjoyment so do what makes you happy (I mean that sincerely, not sarcastically).  But if we're interested in how things work for real, elevator trim is practically a primary flight control.  No pilot advances in even primary flight training until they can trim an airplane up.  Definitely not optional in reality. 

 

Share this post


Link to post
Share on other sites
5 hours ago, FalconAF said:

Amazing.  The above is why I DO make "information correction" type posts in forums.

It's been over 24 hours since I posted the above.  And not ONE PERSON has questioned it.

The quoted part is "erroneous information" (that's what an Instructor (teacher) would call information that is FALSE).

The correct information concerning flying an aircraft is "elevator controls AIRSPEED and throttle controls ALTITUDE".  And that confuses the heck out of most new student pilots because it is totally backwards from what you use the "throttle" (gas pedal) in a car to do...increase or decrease speed.

And nobody here questioned it.

Amazing

I'll question it if it makes you feel better... Because your definitive statement about power for altitude and pitch for airspeed isn't really true either ;-). 

That's pounded into the heads of primary students regarding slow flight and approaches (when you're flying at a higher AoA and towards the backside of the power curve), but isn't applicable in all or even most situations even in light airplanes.  For instance, if you're at cruise power and speed and find you're 50ft low, you aren't going to add power, you're simply going to raise the nose a bit and get that 50ft back.  Sure, you will have traded a bit of airspeed for it, but when you level you'll get it back. 

 In large airplanes like the 737, it's not even true on approach.  You use pitch to stay on glidepath and power to control airspeed.  There's not really a circumstance in the entire normal envelope of an airliner where power is for altitude and pitch is for airspeed, possibly excepting a balloon or bounce landing recovery. 

All of this requires understanding that, in any airplane or circumstance, a long - term change to one parameter will require a corresponding change to the other. They're pretty inextricably linked.  But for small, short term adjustments, this is how large aircraft are flown - power for speed, pitch for altitude. 

Share this post


Link to post
Share on other sites
Posted (edited)

Hi Andrew,

13 hours ago, Stearmandriver said:

1.  A previous explanation said we trim for pitch attitude, not airspeed.  This isn't really true.  An airplane trimmed for a particular airspeed will pitch up or down as necessary to maintain that airspeed, so I've always found it easier as a teaching method to say that we DO trim for airspeed.  Try this: in any airplane from a Cessna to a 737, trim for level flight at cruise power, then pull the power to idle.  What you'll see is the plane pitch down and start to descend, roughly at the same airspeed you trimmed it for (I say roughly because with underslung wing mounted engines like the 737, every power change somewhat changes the speed you're "trimmed out" for unless you adjust the trim again.)

You are indeed aerodynamically correct, and if it works for you I'm certainly not going to contradict you :). However, I find it is usually easier for students (FS) to get their head around the idea that they are looking for a particular "picture" out of the windscreen in any given situation.

Thus, when we level off from a climb we select and hold the level flight attitude -- reduce power to the normal cruising setting -- and trim to hold that picture. Power + attitude = performance, thus if we have set the correct power and the correct attitude the airspeed must by definition come along to join the party.

Likewise any other manoeuvre (powered descent/glide descent/climb etc) and or/airspeed will have an associated pitch attitude and power setting. Again, P-A-T rules -- select the power required, select the desired pitch attitude and trim out the control forces.

As I say, I personally find that an easier concept to get across and it gets the stude's eyes outside rather than overly staring at the ASI. However, as I say you are absolutely right from an aerodynamic point of view and this is why I always say people over-think the B777 trim system -- all Boeing did was program a computer to replicate how a conventional aircraft feels.

13 hours ago, FalconAF said:

Amazing.  The above is why I DO make "information correction" type posts in forums.

It's been over 24 hours since I posted the above.  And not ONE PERSON has questioned it.

The quoted part is "erroneous information" (that's what an Instructor (teacher) would call information that is FALSE).

The correct information concerning flying an aircraft is "elevator controls AIRSPEED and throttle controls ALTITUDE".  And that confuses the heck out of most new student pilots because it is totally backwards from what you use the "throttle" (gas pedal) in a car to do...increase or decrease speed.

Andrew has covered this -- but as you (I am sure) know, power for height/pitch for airspeed is drummed in at PPL level because you really, really don't want Bloggs in his small, draggy, low-inertia spam-can to respond to getting low on approach by yanking back on the stick. My general rule of thumb in the cruise is that for altitude changes of less than about 100-150 ft leave the power alone -- any more than that is likely to require a power change.

However, as Andrew says, when it comes to instrument flying, and particularly large slippery jets with slow thrust response, big thrust-pitch couples and lots of inertia, it is both much more effective and a lot easier to pitch for the glidepath and use thrust for airspeed - with the caveat, as already mentioned, that in the long term an adjustment to the other will likely be required also.

Edited by skelsey

Share this post


Link to post
Share on other sites
13 hours ago, FalconAF said:

And nobody here questioned it.

Amazing

 

THAT particular battle is a very old one and many (most) of us know of it.

Share this post


Link to post
Share on other sites
Posted (edited)
15 hours ago, FalconAF said:

Amazing.  The above is why I DO make "information correction" type posts in forums.

It's been over 24 hours since I posted the above.  And not ONE PERSON has questioned it.

The quoted part is "erroneous information" (that's what an Instructor (teacher) would call information that is FALSE).

The correct information concerning flying an aircraft is "elevator controls AIRSPEED and throttle controls ALTITUDE".  And that confuses the heck out of most new student pilots because it is totally backwards from what you use the "throttle" (gas pedal) in a car to do...increase or decrease speed.

And nobody here questioned it.

Amazing

 

Rick,

What is amazing is that you deliberately posted misleading information to see who noticed it. It might be a useful rhetorical trick in a classroom situation, but it's not at all helpful in a forum. Some might read it and take it as definitive. Some might have read what they expected to see, not what you actually wrote. I only noticed the post when you quoted yourself to prove an empty point.

Edited by kevinh

Share this post


Link to post
Share on other sites
Posted (edited)

It's not an empty point, Kevin.  And yes...I did it on purpose.  Because when someone asks a question in a forum like this, if ANYBODY is going to try to answer the question, the forum DOES become "a classroom" where learning can hopefully take place.

It sure did expand the number and type of replies to the original question...didn't it?  And addressed it in the many different ways it might be answered, which was one of the things I mentioned in my original post about different pilots having different opinions about it.

NOW, the original OP has a much more in-depth understanding (or capability to understand) the answer(s) to their question.

Press on.

Edited by FalconAF

Share this post


Link to post
Share on other sites
Posted (edited)

K. Zip it back up guys...before I ship you all copies of Stick and Rudder and Nerf bats...

...and lock this thread.

Edited by scandinavian13
  • Like 1

Share this post


Link to post
Share on other sites

Sick and Rudder, meh.  Let's all get "Conquest of Lines and Symmetry" and debate the relative merits of leading pulls, bottom rudder on roll entries etc ;-). 

Share this post


Link to post
Share on other sites
Posted (edited)
6 hours ago, kevinh said:

dRick,

What is amazing is that you deliberately posted misleading information to see who noticed it. It might be a useful rhetorical trick in a classroom situation, but it's not at all helpful in a forum. Some might read it and take it as definitive. Some might have read what they expected to see, not what you actually wrote. I only noticed the post when you quoted yourself to prove an empty point.

Easy to be confused as I am still learning about Trim. At the moment I figured the Elevator is the stick from my Joystick and it controls the airspeed and the Throttle controls the Altitude. I think if I am not wrong, trimming is very much similar as Throttle applying power for altitude. Any corrections for me?

Edited by trisho0
corrections added

Share this post


Link to post
Share on other sites
6 hours ago, scandinavian13 said:

K. Zip it back up guys...before I ship you all copies of Stick and Rudder and Nerf bats...

...and lock this thread.

Please, don't lock this thread is very interesting and sure somebody else is learning as I am doing here. I don't see Trimming lessons from the PMDG manual.

Share this post


Link to post
Share on other sites
5 minutes ago, trisho0 said:

Easy to be confused as I am still learning about Trim. At the moment I figure the Elevator is the stick from my Joystick and controls the airspeed and the Throttle controls the Altitude. I think if I am not wrong, trimming is very much similar as Throttle applying power for altitude. Any corrections for me?

There are many good sources of aviation basics available.  If you find the AIM too technical then I'm not sure where you are in terms of education and background.  The AIM is a very basic document orientated towards the student pilot studying for a private pilots license.  Give it a look.

Share this post


Link to post
Share on other sites
6 minutes ago, trisho0 said:

trimming is very much similar as Throttle applying power for altitude. Any corrections for me?

No. I think you're getting very confused :).

Did you try the exercise I suggested in my earlier post?

Share this post


Link to post
Share on other sites
1 minute ago, downscc said:

There are many good sources of aviation basics available.  If you find the AIM too technical then I'm not sure where you are in terms of education and background.  The AIM is a very basic document orientated towards the student pilot studying for a private pilots license.  Give it a look.

I visited AIM and saved a copy to read on it. When I started reading from I found so technical for me. I am not a Pilot. I have technical studies not related with flying but for work. I am still learning with PMDG planes. I will take another look at the AIM saved info. 

Share this post


Link to post
Share on other sites
Posted (edited)
1 hour ago, skelsey said:

No. I think you're getting very confused :).

Did you try the exercise I suggested in my earlier post?

I did what Ephedrin said and I was be able to trim the 737NGX plane right after takeoff. Instead of holding the stick from Joystick I was trimming and yes, noticed the nose was controllable up and down following the PFD line. So, when the plane was in about 1K lower than the programmed altitude is when I armed autopilot. From then the flight was fine until landed.

Also, learned trim is for attitude and stick is for altitude. You say trim for pitch attitude.

Edited by trisho0
correcftions done

Share this post


Link to post
Share on other sites
2 hours ago, Stearmandriver said:

Sick and Rudder, meh.  Let's all get "Conquest of Lines and Symmetry" and debate the relative merits of leading pulls, bottom rudder on roll entries etc ;-). 

Any day that I'm upside down is a bad one in my book. lol

Share this post


Link to post
Share on other sites
1 hour ago, trisho0 said:

I did what Ephedrin said and I was be able to trim the 737NGX plane right after takeoff. Instead of holding the stick from Joystick I was trimming and yes, noticed the nose was controllable up and down following the PFD line. So, when the plane was in about 1K lower than the programmed altitude is when I armed autopilot. From then the flight was fine until landed.

Also, learned trim is for attitude and stick is for altitude. You say trim for pitch attitude.

Well... That's not quite it. Stick is for attitude, and attitude controls altitude (in conjunction with power). Trim is to hold the desired attitude without needing to hold constant stick pressure. 

All of what I just said is a concise explanation, but probably not real useful since you have no frame of reference.  You're at the point where you need a full lesson combining all these bits and pieces we're discussing into a cohesive whole. 

There are plenty of good books available... The official FAA handbook is available online, free. For this discussion, you probably want chapter 3, Basic Flight Maneuvers. 

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/

Also, it will be a lot easier to understand these concepts in a smaller airplane than a 737.  In FSX, the stock Cessna 172 will work just fine. 

Share this post


Link to post
Share on other sites

Trim is ONLY used to take forces off the controls. NOTHING else. That's the sense of it. Early airplanes in WW1 didn't have any trim tabs and the pilots had to hold the stick back or forth to hold the nose where it should be. this is possible of course but incredibly exhausting. So they invented the elevator trim. as soon as you have to hold the stick back or forth to keep the nose up or down, use the elevator trim, stabilizer trim, what ever it is called on the airplane you fly, and you can release the pressure. I really don't understand what's so difficult about it... When you have constant pressure on the controls, use the trim to release it. that's so logical, easy, even at the simulator... Don't think too much.. just do it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now