Trimming the FSX stock 737 for straight and level - endless oscillations

I can't seem to get the 737 (and quite a few of the FSX planes) properly trimmed for straight and level. If I trim up one notch, the nose goes up and I climb, and one notch down and it's the opposite.

 

I find it impossible to complete the ATPL Rod Machado lessons because of this problem - maintaining a fixed altitude requires fulltime attention.

 

Can someone tell me if I'm doing anything wrong here?

I found it pretty near impossible also! Have you ever watched the elevator trim knob while the AP is engaged? It's in constant movement trying to keep the airplane on the fixed altitude. Smack Rod upside his noggin and tell him to shut up. :p

thanks, I'm glad I'm not the only one who finds this. And Rod's jokes are awful.

Is rod telling you to use elev trim to adjust altitude? I doubt it.

Trim is for speed, not altitude.

no, he's just telling me to maintain an altitude. Are you saying that the trick is to adjust your throttle until you maintain straight and level - given that the trim setting does not appear to have small enough increments for this.

Check your settings...

Make sure the Repeat slider is full left. This reduces the amount of trim adjustment with each click.

 

The downside is that large trim adjustments can......take.....a.......long......time......

 

Even still I find that often I have to fine tune the trim with the throttle.

 

On some planes I even cheat and click on the autopilot and let it set the trim, then turn it off.

 

Also, I have edited a few plane's aircraft.cfg to lower...

 

elevator_trim_effectiveness = 1.0

 

peace,

the Bean

no, he's just telling me to maintain an altitude. Are you saying that the trick is to adjust your throttle until you maintain straight and level - given that the trim setting does not appear to have small enough increments for this.

 

Yup, to climb add thrust, and vice versa.

Trim adjusts speed. (you'll need to jiggle thrust as well then.)

 

Best way to practice is in the ultralight.In free flight.

Without yanking on the stick, climb, descend, and increase/decrease speed in that.

 

One exercise: Start the default flight (over KFHR, at 3000ft). Then climb (add thrust only.)

 

Once at 4500 ft, Level off, by reducing thrust only.

 

start to increase speed: Add thrust and push the stick forward to stay level. Then use trim and let your stick return to the centered position. (while maintaining the higher speed.)

Then do those two steps again.

Push the speed up so you are flying at 75 kts with your stick centered.

 

Then fly towards a nearby airport, and start slowing down: Reduce thrust while slowly adding more and more trim.

 

Descend by reducing thrust. Not to much. If you keep the v/s within limits, your speed won't vary much.

 

Land at 38 kts, with the stick centered. (maybe pulled just slightly back.)

 

Flying a precice altitude in a 737 is more touchy. but can be done when you carefully manipulate the throttle.

Practice a lot in the ultralight.

 

Remember: Trim for speed, thrust for climb.

 

Go-arounds have lead to crashes because a pilot pulls up to climb instead of adding power!!!

(only pulling up, leads to a stall)

 

Practice - Practice - Practice - Practice...

getting the thrust just right isn't easy either in a 737. I usually get as close as I can with the throttle on my joystick, so vs is 100 fpm or so. Then reduce it slightly with F2 to level off.

The throttle on the logitech 3D extreme is just not precise enough.

 

(Or when I'm lazy andflying a 737, I just let her keep Climbing slowly. When it's 100 fpm or less at 26.000, and you stop trying to tune it, the plane will climb slower and slower, and will level off at 28.000 or so.)

Part of the problem is the (relatively) poor resolution of the digital controls in Windows/FS. Real life (at least on non-fly-by-wire aircraft) is analog, so (theoretically) infinite adjustment levels.

 

It used to be that virtually all controls for FS used 8-bit resolution (256 steps), but some have now gone beyond that.

For example, the Thrustmaster Warthog uses 16-bit (65K) resolution on the stick and 14-bit (16K) on the throttles, so may do quite a bit better. Trouble is, it's expensive. Unfortunately I've not yet succeeded in finding that sort of spec for other joysticks/throttles, but I suspect some, at least, are noticeably better than the old 8-bits. Still, it's limited, compared to real life.

 

Also, as indicated above, trim is for speed and throttle is for altitude (in general terms -- let's not get into the jet vs. prop discussion please), though in real life they interact considerably (to a degree, in the sim also, depending on the aircraft model).

There is a way in FSUIPC to assist with the trim control. I don't remember the particulars and can't get to it at the moment. Two things to look for until I can get back to this.

A forum post related to adjusting the trim via FSUIPC. I think it was on AVSIM. The other that may help refine the search is to go into FSUIPC. Go to the button/switches tab. Select one of the buttons used for trim control, and search through the drop down list for an applicable FS action. Finding what the action is called specifically may help refine the search for the forum post I mentioned.

 

Fixing it does make a world of difference in how well the trim action works. I'm sorry I couldn't give a more definitive response. But I thought I would rather send you in the right direction today as opposed to waiting a couple of days before saying anything.

 

Best of luck

So I got the PMDG 737 and trimming for straight and level is a piece of cake. The trim 'resolution' is simply not high enough on the stock 737.

 

I challenge anyone to get the stock 737 in a non-FSUIPCd FSX flying at 250kts and 12,000 feet for more than a few seconds with your hands off the stick.

In the aircraft.cfg file, you normally find a section that looks sort of like this:

 

 

[flight_tuning]

cruise_lift_scalar = 1.0

parasite_drag_scalar = 1.0

induced_drag_scalar = 1.0

elevator_effectiveness = 1.0

aileron_effectiveness = 1.0

rudder_effectiveness = 1.0

pitch_stability = 1.0

roll_stability = 1.0

yaw_stability = 1.0

elevator_trim_effectiveness = 1.0

aileron_trim_effectiveness = 1.0

rudder_trim_effectiveness = 1.0

 

The "1.0" values are default - this section interfaces with the "xx.air" file and normally lets you adjust some of the handling sensitivity.

 

Play with the below two parameters for pitch sensitivity till you like it; one may have an effect on the other. Here is an example.

 

The "//" allows you to keep a previous value in place (for that parameter line) if you want to revert back; anything following the // is ignored.

 

I have used this technique for years. If a plane does not have this section, add it in somewhere in the aircraft.cfg file for use.

 

By the way, though it defies logic, longitudinal trim is actually trying to maintain a constant indicated airspeed (in a given configuration), not altitude; this seems counterintuitive, but it is true.