PMRJ Trim Indicatior

[Tim]

Does anyone know what value the PMRJ trim indicator is representing?

Adjusting pitch trim shows +1, +2, -1, -2. Does this represent a value in degrees or just a generic numeric value?

As an example, if takeoff trim is supposed to be set at +15 degrees, how is that set with 1, 2, 3 type values?

Thanks.

[Tomlin]

Tim, I wish I could tell you. Maybe someone from PM can jump in and say, but Ive found with my LJ45 that it needs to be around 4 or so. I have seen other posts regarding this for builders of the 737NG and it seems that someone found a way for the trim level in PMBGC to coincide with the FMC value...not quite sure though.

Best of luck

[Michael Carter]

Trim is usually expressed as "units of trim" based on a percentage of mean aerodynamic chord. This is usually read from a chart in the POH after W&B is figured and the percentage of MAC is found.

For example, after W&B is figured the book says the MAC is 24.5% MAC. In the table this equates to 5.2 units of nose-up trim.

[Tim]

Ok, good info. Thanks guys.

Is PMRJ is based on a Collins avionics unit? If so, I'm sure it is used in many different types of aircraft. Each would have different CG requirements and each aircraft's POH could show different values. Taking Mike's point, three notches of trim in one aircraft might not be the same for another.

So how do we get the PMRJ to reflect the correct trim value for the aircraft we are flying? I don't recall seeing that in the PM aircraft.txt file. I use the PMRJ with a Dash 8-Q300. Eric, you use it with a Lear, correct?

This is a dangerous issue, if I can use that term in flight simulation. We have a piece of software that is allowing us to develope a bad habit. I have no idea what the values indicate and normally turn the trim wheel until the Flight Control Page displays +3. Is that correct for my aircraft and it's weight and balance? I don't know.

I'll add this to the Consolidated PMRJ Issues post and wait to see what happens.

[Michael Carter]

Tim, I failed to explain that the figures I quoted above were for the 727. Any other aircraft will be different. Sorry I left that out.

An aircraft handbook is invaluable for performance information even for simulator pilots if the model is true to life.

[PaulEMB]

Hi Tim,
The Pm manual for creating an aircraft type file says:


TrimMin=6
TrimMax=16
TrimScaleMin=40
TrimScaleMax=40
Min/Max values for trim value (for takeoff) and maximum/minimum value of trim scale.

My type file (ERJ 145 LR.txt) has this entry for trim scaling:


TrimMin=6
TrimMax=16
TrimScaleMax=5 ;Not real world numbers - set to these values for proper
display.
TrimScaleMin=5 ;Not real world numbers - set to these values for proper
display.

These values show more realistic trim values in PMRJ EICAS (for the ERJ 145) - its a question of playing with the values until the display shows OK.

You can also check with FSUIPC calibration, depending on what device you are using to set trim - pot, or switch.

Hope this helps - as usual, a little trial and error is needed.

[Tim]

Hi Paul,

Ok, even in red letters I over-looked it.

Any idea what those values indicate? Percent or just a subjective number?

Thanks.

[Tomlin]

Paul, thanks! I think then what you're saying is that we can fiddle with the numbers to make the trim value display a bit closer to our aircraft's needs, right?

[PaulEMB]

I'm sure Thomas can give a more educated answer, but given that you have to choose between 5 and 40, its only a question of time....:roll:

I used the Feelthere 145 to give me the "real values" on the EICAS - ie + 5-7 for T/O, flew the T/O to see if it worked, then fiddled with the aircraft type.txt file to get the display right. Then its a question of messing with the calibration - in my case I am using the Trim buttons FSUIPC Button (Elevator trim/ Aileron trim) on the yoke, so its press, press, press, leaving time for PM RJ to react - note there is sometimes a few seconds delay depending on your network setup.

Imagine the factor is a "zoom" between the display and MSFS - you need to get it right so the display moves in line with the trim.

A look at the PM published type files will give you some ideas of the variations in that section of the type.txt file.

[Thomas Richter]

Hi

It is easy but also very complicate!!
FS has a range / value for trim from -16383 to +16383 where 0 is Center.
In Aircraft.cfg (FS) you can set the sensitivity for trim that reflacts to the trim value.
The displayed value in pmRJ is just -20 to +20 and reflects to trim Value (-16383 to +16383), but the setting in Type file don't have any effect to this (different to Boeing- / Airbus GC).