trisho0

Trim question for PMDG 737NGX

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18 hours 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.

I owe you an apology.  When I learned to fly in 1974, the AIM was the basic guide to piloting.  Now it seems it is more about the aviation environment, navaids, airspace and the such.  I misdirected you.  The correct basic guild to piloting and all things airplane is their Pilot Handbook (here: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/ ).  This very comprehensive handbook covers everything a student pilot should learn about piloting basics, including Ch 6 Flight Controls and specifically in this case pg 6-8 Secondary Controls and pg 6-10 Trim Systems.  The adjustable stabililzer used by larger aircraft such as the NG is on page 6-12 but I think  it would benefit you to read the entire section on flight controls.

Again, sorry for the misdirect.  I couldn't swallow that the AIM was too technical for you so on checking I found that it simply failed to cover the pertinent material on this topic.

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4 hours ago, Ephedrin said:

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.

Many thanks Marc. So, not much to use Trim but just to control attitude (not altitude). What about controlling the tail? via trimming right? I mean, the plane takeoff and if the nose is going too high then trimming nose down a bit until the plane is on airborne. Once on airborne continue flying with stick, no need more trimming. I assume if no trimming before the plane leaves the ground runway then is the reason why I have sometimes a message "tail on strike". Hmmm ..... learning....

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47 minutes ago, downscc said:

I owe you an apology

Please Dan, no need apologize. This thread is really one of the best classroom including those handbooks from the https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/

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5 minutes ago, trisho0 said:

Many thanks Marc. So, not much to use Trim but just to control attitude (not altitude). What about controlling the tail? via trimming right? I mean, the plane takeoff and if the nose is going too high then trimming nose down a bit until the plane is on airborne. Once on airborne continue flying with stick, no need more trimming. I assume if no trimming before the plane leaves the ground runway then is the reason why I have sometimes a message "tail on strike". Hmmm ..... learning....

You are better off controlling pitch during takeoff during the initial climb below 400 AGL and forget trim until after acceleration height.  Sure, a tap on trim during this time for me might be done without thinking but primary pitch control is always with the yoke/stick.  Pitch trim changes are continuous as flaps retract and airspeed increases and your first opportunity to trim for pitch is once established in a steady attitude climbing at 250 KIAS.

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16 minutes ago, downscc said:

You are better off controlling pitch during takeoff during the initial climb below 400 AGL and forget trim until after acceleration height.  Sure, a tap on trim during this time for me might be done without thinking but primary pitch control is always with the yoke/stick.  Pitch trim changes are continuous as flaps retract and airspeed increases and your first opportunity to trim for pitch is once established in a steady attitude climbing at 250 KIAS.

This is exactly I was doing ever until this thread started. All flight I did with only joystick, no trimming. But now, as I trim the plane doesn't get "Tail On Strike" as I had sometimes before.

You say, trimming for pitch is once established  in a steady climbing. I don't see the needs to do that if the plane is already on airborne and the AP will be armed. I will check handbooks later.

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35 minutes ago, trisho0 said:

I don't see the needs to do that if the plane is already on airborne and the AP will be armed.

You should trim out any control forces prior to engaging the autopilot, technically. If you're too far out of trim, the AP won't take it, or you'll have an abrupt pitch change when you let go of the stick in order to get the AP on (as pressure on the yoke will cause the AP to kick off).

As I've mentioned to you a few times already, I'd really suggest paying attention to what people are telling you instead of pushing back with "well I'm doing this and it works." You can put your car in park without using the parking brake (if you drive an automatic car), but that actually puts a lot of strain on your transmission. Just because you can, and it "works" doesn't mean that you should.

Everyone in this thread has jumped in to help you get a better handle on things because they have experience, and knowledge where you don't (and that's not a bad thing - everyone has to learn over time). Do them the favor of listening to them after they've volunteered their time to help you out.

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2 hours ago, scandinavian13 said:

You should trim out any control forces prior to engaging the autopilot, technically. If you're too far out of trim, the AP won't take it, or you'll have an abrupt pitch change when you let go of the stick in order to get the AP on (as pressure on the yoke will cause the AP to kick off).

How far out of trim will be if before takeoff I set trim accordingly (FMC info). I use the Stick carefully on the initial climb by looking at the horizon PFD and flaps up following the Primary Flight Display. PFD is telling me when is time for flaps. I don't have AP issues yet.

2 hours ago, scandinavian13 said:

Everyone in this thread has jumped in to help you get a better handle on things because they have experience, and knowledge where you don't (and that's not a bad thing - everyone has to learn over time). Do them the favor of listening to them after they've volunteered their time to help you out.

I follow them and your help as well. It's just trimming procedures wasn't clear to me. I want to do trimming but all I see is the plane nose goes up or down as I want. Helpers ask me to take a look at handbooks and that is what I am doing to understand trimming.

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4 hours ago, trisho0 said:

How far out of trim will be if before takeoff I set trim accordingly (FMC info).

Doesn't matter. TO trim is set to allow you to rotate the aircraft effectively. Trim as appropriate after takeoff to follow the flight director without pressure on your hardware. You're approaching this too over-analytically. Trim until you don't need to hold pressure on the yoke. Done. It's really that simple.

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15 hours ago, trisho0 said:

How far out of trim will be if before takeoff I set trim accordingly (FMC info). I use the Stick carefully on the initial climb by looking at the horizon PFD and flaps up following the Primary Flight Display. PFD is telling me when is time for flaps. I don't have AP issues yet.

I follow them and your help as well. It's just trimming procedures wasn't clear to me. I want to do trimming but all I see is the plane nose goes up or down as I want. Helpers ask me to take a look at handbooks and that is what I am doing to understand trimming.

You'll set the trim from the FMC on the ground.

You'll rotate and pitch up to ~15deg and set the trim again to remove the pressure on the yoke.

At acceleration, you'll pitch to ~9deg and you'll have to trim until you're done accelerating to 250kts (or whatever your target).

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On ‎6‎/‎12‎/‎2018 at 9:25 PM, scandinavian13 said:

Doesn't matter. TO trim is set to allow you to rotate the aircraft effectively. Trim as appropriate after takeoff to follow the flight director without pressure on your hardware. You're approaching this too over-analytically. Trim until you don't need to hold pressure on the yoke. Done. It's really that simple.

I did several times this procedure and yes it worked perfectly in the Cessna C172 and found the trimming changes the attitude rapidly. Trim helps me with Cessna more than 737NGX. Rarely tried with small planes before because I like PMDG and Level-D, all more realistic. I don't need trimming the PMDG maybe because I use Logitech Extreme 3D Pro Joystick which I don't sense the pressure. I think if I get a better joystick design probably I would feel the pressure. Trimming is clear for me now. 

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On ‎6‎/‎13‎/‎2018 at 8:34 AM, Spin737 said:

You'll set the trim from the FMC on the ground.

You'll rotate and pitch up to ~15deg and set the trim again to remove the pressure on the yoke.

At acceleration, you'll pitch to ~9deg and you'll have to trim until you're done accelerating to 250kts (or whatever your target).

I understand that and Cessna did a good attitude changes but I don't realize pressure from joystick. I think your joystick is similar to Pilot Training classroom and I guess you can feel pressure from Yoke. I don't because my joystick is not that sophisticated but I can fly my birds.

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The 737 Yoke is held by a spring, nothing really that much different to a sim yoke. It moves the elevators. If the trimmer moves the stabiliser, the elevators, being hung off the back will be in line for minimum drag with the yoke centred.

In a Cessna, you trim by moving a tab at the back of the elevator. This provides an aerodynamic force that holds the elevator displaced and literally takes the force out of you holding it there. 

Different mechanical systems. Please also remember the horizontal stabiliser is by far the most powerful surface on a 737.

Now, where your issue comes is in using a toy joystick.....

If you get down to basics, you are pulling against a spring to lift the nose up. Try to move gently, to avoid tail scrapes. 2-3' per second is correct. You lift the nose, and by 8-9' you should hear a click, as the weight on wheels logic triggers the release of a relay in the overhead panel.

Now move the nose up to 15'. Hold it there. 

Do you need to push your joystick forwards or back to keep it in place?  If it's back, then you need to trim up just slightly. If down then trim forward. Just a quick tap of the button, that's all. Now relax your joystick. Is it staying put? If so, great. If not, then use the joystick to move the nose to the right pitch and hold it as required and repeat process. V2+20kts target speed. (V2 +15 for the 737-700).

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4 hours ago, MarkJHarris said:

The 737 Yoke is held by a spring, nothing really that much different to a sim yoke. It moves the elevators. If the trimmer moves the stabiliser, the elevators, being hung off the back will be in line for minimum drag with the yoke centred.

In a Cessna, you trim by moving a tab at the back of the elevator. This provides an aerodynamic force that holds the elevator displaced and literally takes the force out of you holding it there. 

Different mechanical systems. Please also remember the horizontal stabiliser is by far the most powerful surface on a 737.

Now, where your issue comes is in using a toy joystick.....

If you get down to basics, you are pulling against a spring to lift the nose up. Try to move gently, to avoid tail scrapes. 2-3' per second is correct. You lift the nose, and by 8-9' you should hear a click, as the weight on wheels logic triggers the release of a relay in the overhead panel.

Now move the nose up to 15'. Hold it there. 

Do you need to push your joystick forwards or back to keep it in place?  If it's back, then you need to trim up just slightly. If down then trim forward. Just a quick tap of the button, that's all. Now relax your joystick. Is it staying put? If so, great. If not, then use the joystick to move the nose to the right pitch and hold it as required and repeat process. V2+20kts target speed. (V2 +15 for the 737-700).

Exactly. $35M yoke or $15 joystick - you trim it for hands-off. 

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On 6/18/2018 at 1:32 PM, MarkJHarris said:

 

The 737 Yoke is held by a spring, nothing really that much different to a sim yoke.

 

It’s not a spring and much more complex than a sim yoke. The column force, provided by a computer controlled hydraulic feel unit, varies with dynamic pressure and stabiliser position. At a given flight condition it behaves like a spring but the forces are much higher than a hobbyist sim yoke or joystick. Trimming by feel is a much harder with hobby equipment because the forces are much lighter.

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47 minutes ago, kevinh said:

Trimming by feel is a much harder with hobby equipment because the forces are much lighter.

Still, a flight sim yoke comes closer to a 737 yoke than to a GA airplane‘s yoke. The 737 (as all boeings) has a center position even in flight while a GA airplane has a „zero force point“ that varies with the trim setting.

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7 hours ago, Ephedrin said:

Still, a flight sim yoke comes closer to a 737 yoke than to a GA airplane‘s yoke. The 737 (as all boeings) has a center position even in flight while a GA airplane has a „zero force point“ that varies with the trim setting.

True, but that doesn't really help with trimming a PC sim. It just means the trimming process for a GA plane (or any aircraft using elevator trim tabs) is less realistic.

As in all things, practice makes perfect and the more you fly without autopilot the easier it gets.

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9 hours ago, kevinh said:

It’s not a spring and much more complex than a sim yoke. The column force, provided by a computer controlled hydraulic feel unit, varies with dynamic pressure and stabiliser position. At a given flight condition it behaves like a spring but the forces are much higher than a hobbyist sim yoke or joystick. Trimming by feel is a much harder with hobby equipment because the forces are much lighter.

I flew a 767 -400 Level D sim at the Delta Training center years ago. I was surprised when hand flying it at the force needed to fly level, if the trim was off a little bit. Constant tweaking of the trim was needed, 

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1 hour ago, kevinh said:

True, but that doesn't really help with trimming a PC sim.

Actually I think it does: as soon as yoi have to push or pull your yoke or stick to maintain nose attitude: trim.

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1 hour ago, kevinh said:

practice makes perfect

Correct practice makes perfect 😉. Practicing the incorrect technique, however, leads to frustration.

Although the stick forces on typical consumer sim hardware are light, they are more than sufficient to provide trim cues except for the completely ham-fisted (and I admit that for all the very gifted simmers I have flown with I have certainly come across some who fall in to that category!). More of an issue, I would say, is having the base of the stick/yoke firmly secured to the desk so that the forces can be felt consistently and the stick does not go sliding all over the desk when inputs are made! However, I have successfully taught many students to trim correctly and accurately in FS over the years so it certainly is possible, and in very little time if the correct technique is utilised. A light, relaxed, fingertip grip is essential.

Worth noting that some aircraft have very light stick forces in real life as well -- I was very pleasantly surprised when I went up with a friend in a Eurostar three-axis microlight recently to find that fingertip pressure was almost too much: certainly in the cruise one barely had to breathe on the stick to produce a very effective response, far lighter than any aircraft (or hardware) I've flown in FS (rudder forces, on the other hand, were quite firm and far beyond any consumer hardware). A very good example of less very much being more when it comes to control inputs!

On a related note -- oddly enough I can remember that many, many years ago (in the days of FSW95) I had a QuickShot joystick which had 'trim' thumbwheels on both axes which, as I recall, actually mechanically moved the centre point of the joystick. And they say things have moved on in the last 20 years!

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8 hours ago, skelsey said:

Correct practice makes perfect 😉. Practicing the incorrect technique, however, leads to frustration.

Although the stick forces on typical consumer sim hardware are light, they are more than sufficient to provide trim cues except for the completely ham-fisted (and I admit that for all the very gifted simmers I have flown with I have certainly come across some who fall in to that category!). More of an issue, I would say, is having the base of the stick/yoke firmly secured to the desk so that the forces can be felt consistently and the stick does not go sliding all over the desk when inputs are made! However, I have successfully taught many students to trim correctly and accurately in FS over the years so it certainly is possible, and in very little time if the correct technique is utilised. A light, relaxed, fingertip grip is essential.

Worth noting that some aircraft have very light stick forces in real life as well -- I was very pleasantly surprised when I went up with a friend in a Eurostar three-axis microlight recently to find that fingertip pressure was almost too much: certainly in the cruise one barely had to breathe on the stick to produce a very effective response, far lighter than any aircraft (or hardware) I've flown in FS (rudder forces, on the other hand, were quite firm and far beyond any consumer hardware). A very good example of less very much being more when it comes to control inputs!

On a related note -- oddly enough I can remember that many, many years ago (in the days of FSW95) I had a QuickShot joystick which had 'trim' thumbwheels on both axes which, as I recall, actually mechanically moved the centre point of the joystick. And they say things have moved on in the last 20 years!

 

I've initially learnt to fly on an ASK13. Old, wooden/steel glider airplane, double seater, heavier than it looks. I was 14/15 and alsmost couldn't move the stick fully to the right with one hand in flight. normal "cross country" speed is 100-130km/h and the forces on the elevator were very (!) strong for an untrained 15 years old. Flying straight forward I used to put the trim lever a good cm forward. When I found a thermal and circled at ~80km/h I almost certainly pushed that trim lever back again, the forces were just too strong. though you normally fly a bit nose heavy in a thermal, at least in a K13. But flying out of trim is reaaaally exhausting. after several hours you really are happy that you actually have this little green lever. 

On the other side the DR400 I flew was extremely light on controls. I also can't say that I needed a lot of force on the HK36. Significantly less than on a C172. In the Remorqueur I sometimes simply didn't touch the trim when I knew there would be a lot of movement, for example when flying "low" (while LOW isn't possible in Germany at all, lol) 

Now at home I prefer really low forces on my yoke and I even have dismounted one of the springs inside (actually it broke off, but shhh) and lubricated the yoke's shaft. But still, as long as I have to hold it forward or back, I use the trim almost automatically. Though I still prefer flying approaches a little bit nose heavy. It (subjectivly) gives me a better feel of the airplane.And you seldomly become too slow when your attention is on your girlfriend for a second xD

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Posted (edited)
5 minutes ago, Ephedrin said:

Practicing the incorrect technique, however, leads to frustration.

I always found it completely wrong adjusting the level flight or rate of climb/decent with the elev trim. Some people who have trim tabs on their (real world) yokes even start a decent using trim. I really have problems to understand why.. a little bit too much and your nose dives down too fast and you have to counter steer and have to pull against the trim.. Doing this you have NO feel of your airplane. it's a more expensive mouse click... But very very common.

 

Edit: Okay, no idea what I did here, but actually I wanted to quote Simon and edit my previous post.. xD Cell phone issues 😃

Edited by Ephedrin
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18 hours ago, Ephedrin said:

Actually I think it does: as soon as yoi have to push or pull your yoke or stick to maintain nose attitude: trim.

Marc, I was talking about the point you had made previously, that the trimmed column position in a sim yoke doesn’t move, as in the 737. How does your reply relate to that? What you said applies to any aircraft, whether the trimmed yoke position moves or not. 

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1 hour ago, kevinh said:

Marc, I was talking about the point you had made previously, that the trimmed column position in a sim yoke doesn’t move, as in the 737. How does your reply relate to that? What you said applies to any aircraft, whether the trimmed yoke position moves or not. 

Yes I think I read your post differently from what you meant 🙈

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17 hours ago, skelsey said:

Correct practice makes perfect 😉. Practicing the incorrect technique, however, leads to frustration.

 Although the stick forces on typical consumer sim hardware are light, they are more than sufficient to provide trim cues

The only incorrect technique I know of is to fly using the trim. As long as you learn to use the trim to zero elevator control force it’s all good.

Of course. If the stick force is insufficient people wouldn’t be able to trim at all. But higher, more realistic, forces would make trimming much easier.

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On ‎6‎/‎18‎/‎2018 at 12:36 PM, Spin737 said:

Exactly. $35M yoke or $15 joystick - you trim it for hands-off.

I think Yoke is not a joystick. Yoke is for real aircraft and joystick is for sim platform. We can trim via Yoke but not via joystick because no pressure is feeling …..so, no need trimming for my birds (lol). I can't afford such sum for a Yoke but at least I learned on it works.

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