Jump to content

Trouble Trimming stock 737-800 FSX STD Edition


Recommended Posts

Hello there

I'm relatively new to fsx and still trying to get a hang on level flying( i don't want to use autopilot). I only fly short hauls and enjoy doing all procedures(takeoff, cruise, approach & landing) manually. This worked well with cessna 172. Recently l switched to stock boeing 737-800 and i found to my dismay that no matter how much I trim & adjust power for level flight the plane goes into oscillations(up, down) and eventually gets into a climb or decent. I set up autopilot to hold level and was surprised to find that as long as it is in autopilot it holds altitude and the moment I take it out it slowly (after a minute or so) gains or looses altitude. I switched to cessna... it holds altitude rock steady after proper trimming but 737-800 doesn't. I tried playing with a) settings-controls-joystick sensitivity b) trim effectiveness in aircraft cfg file but without any result.


Any ideas/suggestions?

Link to comment
Share on other sites

There are some .air fie settings that will reduce the bounce at higher altitude.


Now, ask me what they are! Go ahead, I dare ya...

Darned if I recall. I am pretty sure the settings were in the R1101 section of the .air file, but just what I can't drag out of my pea-brain atm. I'll have to try to review what I was doing to get that fixed. I'll get back soon as I can, presuming someone else doesn't beat me totally to the punch.




Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

Link to comment
Share on other sites

IIRC the setting in section 1101 of the air file changes the amount of trim per click, but I think its tied to 1024 bits. If one uses the VC or 2D trim wheel by using the mouse one can usually set trim finer. A lot also depends on the model creator's use of the Cl & Cd vs AoA graphs, as well as setting the C of G.


Link to comment
Share on other sites

I'm relatively new to fsx and still trying to get a hang on level flying..


Big airliners are always harder to trim than smaller planes because of all that mass/velocity/inertia stuff.

For example if the airspeed starts creeping up, the nose will go up too resulting in a loss of airspeed, so when you trim the nose back down, the airspeed will increase again and so on, and you'll be forever trimming up and down to match the fluctuating airspeed.

Pro pilots call it "chasing the dials" and warn against overdoing it.

Or maybe the FSX 737 is just harder to trim than other airliners, I don't know.

Link to comment
Share on other sites

Here's the EASY thing to do! Do a flight and use Autopilot. Now since the plane is being flown for you, sit there and watch the elevator pitch control go like gangbusters to keep the plane level. Ya still want to hand fly it??:rolleyes:;)

Still thinking about a new flightsim only computer!  ✈️

Link to comment
Share on other sites

(When handflying)

In aircraft adjusting trim adjusts the speed. ( more trim is lower speed)


Adjusting power controls climb/descent/altitude.



"trim for speed"


"power for climb"




To trim for speed takes a lot of 'feel' for the aircraft.

If you only trim up. the plane wants to climb. but then slows down. and drops back down as well.


To trim to reduce speed whille maintaining altitude you will need to reduce thrust slightly, while trimming up slightly.

Then wait for the plane to settle, and if necessary do it again.

Takes time.

The plane is heavy, so it takes a long time to react to a change in power.

Trim effect is almost instantaneous.

It takes good timing to combine the two.



To climb to a specific altitude, first get your speed correct.

Then make very small power changes, increasing bit by bit as you climb further.

Reduce thrust slightly when altitude is reached, but gently!

When you have a steady altitude that's pretty much correct, keep it there.

Don't try to reduce altititude by only a small amount, like 500 ft or something.



(Trim also used for countering the pitch effect when adding flaps. But that's a very different chapter)

Link to comment
Share on other sites

I..enjoy doing all procedures(takeoff, cruise, approach & landing) manually.


Me too, we don't need no steenkin autopilot and stuff!

You haven't lived til you've landed an FSX Jumbo bush-pilot style totally manually by the seat of your pants!

If manual control was good enough for Neil, it's good enough for us..:)


From a website- "During the automatic descent to the moon, Mission Control kept giving a constant stream of updates to Armstrong and Aldrin, but in the final stages Armstrong took manual control and Mission Control fell silent, and for the next three minutes the only voice you hear on the tape is Armstrong's.

There's a reason Mission Control is silent. They know nothing they can say or do will help him because Armstrong- and Armstrong alone- is in sole control of the Lunar Module as it descends."

Link to comment
Share on other sites

Hey thank you all for taking time to reply to my query. Appreciate it. I wanted to see the pitch and trim tab rotations done by autopilot as per Mr.Zippy's suggestion. I also made a crude digital display for pitch and trim(using rudimentary digital gauge, xml and modifying panel.cfg - xx.xx format - 4 digits.). I let the auto pilot level my flight for a certain altitude and speed. I have some interesting observations. The granularity the auto pilot has over Trim, Pitch & N1 is not available through keyboard nor joystick nor virtual cockpit controls. For example N1 setting was reduced from 49.6 to 49.5 when I reduced the airspeed from 175 kts to 170kts. It is nearly impossible to reduce/increase by hand N1 setting by 0.1 using joystick slider or keyboard keys(f2/f3).

Similarly the trim value increases/decreases by. 01 when auto pilot adjusts the trim - whereas if adjust the trim using keyboard/virtual cockpit trim wheel the minimum granularity I get is 0.06

Hence the aircraft never really settles down., either it has little bit more power or teeny weeny more trim.... and chasing the dial begins...

If that kinda of finite control is available then I hope it might be possible to do perfect trim adjustments.

Is there a way to get that finite control by modifying aircraft. cfg or. Air file....

My understanding might be completely wrong.

Experts your valuable suggestions please



Code for Digital Trim Display


Yes(A:CIRCUIT GENERAL PANEL ON, bool)T:%((A:Elevator Trim Position,degrees))%!2.2f!

Link to comment
Share on other sites

Just wanted to add one more thing...I tried the Airbus A321 which does auto trim( all you have to do is point the nose where you want and fly by wire does the trim for ya, of course you need to do necessary power adjustments for the desired alt and speed - read it in this forum..forgot to note down the link). I tried it and same case here too... the plane never really finds the sweet spot to just hang in there....for few seconds it seems to do level flying and after that it was all seesaw motions...
Link to comment
Share on other sites

You could try stopping all the passengers & crew from running up & down the aisles!!! (hide)

To get a more stable aircraft one would need to balance the Cl vs AoA & the Cm vs AoA graphs by changing the slope of the former around the zero to 4° AoA area, & doing the same for the Cm graph.

A bit more simple might be to reduce the amount of trim available in the .cfg file, but one might then run out of range when the flaps & gear are down. Or increasing the pitch stability value in the flight tuning section.

'Chasing the dials' also known as a PIO (Pilot induced oscillation)


Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...