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steamengine

Calibrating 737NGX Reverse Thrust

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I have just installed an FSC TQ semi pro with no motors.   It all works nicely but for the first time I cannot get enough reverse thrust.  The maximum digital value that the the TQ gives out for the reversers is -4096.  This produces a PMDG 738NGX reverse thrust N1 of about 62/63%.   The real aircraft gets at least 82% N1 and there are various reports of sometimes more with other aircraft of the range. Countless videos show the same being achieved in the PMDG 738.

My previous means of getting reverse were 'F2' and a built-in switch operated by a Saitek throttle quadrant at the idle end of the throttle arc (an extra little pull) and bingo lots of reverse thrust.  A test today with 'F2', once again, gives 82/83% N1.  Bearing in mind that the relationship between N1 and thrust (reversed or not) means that 83% is about 2.5 times more thrust than 62%, fluid dynamics being what it is.

I have searched all day looking for possibly a .config or .ini file that might have a setting for how much reverse N1 is reached for the TQ command of -4096. No luck!  There is a suggestion in this forum, but no more, that such a setting is hiding somewhere.

Can anyone assist me in this as I seem to have got rather less for my very expensive FSC TQ than you get from 'F2' or a Saitek throttle.

Regards

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Milton

FSUIPC cannot see the TQ.   It has it's own way of interfacing with the sim.  Counter intuitively however FSUIPC5 (P3D V4) must be running or it won't work.

You have to start the sim with FSUIPC and once it is all up, you launch the TQ app which shows you what the axes are outputting.  It works all right but FSUIPC still sees nothing.  I can remember other switch panel add-ons that did the same thing.  I never liked them.

Thanks for your reply

S

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I think it is either full reverse thrust or nothing at all. In my GoFlight TQ-6 throttle quadrant I pull on the reverse levers which act really as buttons for on off reverse thrust. I haven't looked at the percent N1 on reverse though I will come back with that.

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I have decide to substitute a Leo Bodnar board to read the 6 pots and 5 switches and have ordered the bits.  This will mean that the TQ is visible to the sim as a game controller and to FSUIPC5 for calibration.  I believe my problems will be solved by this.  Will report after installation.

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If your goal is to have variable reverse thrust I am afraid you will be disappointed as this on/off only from buttons assigned is an FSX limitation. Therefore you will only have full reverse thrust but I still don't know what the N1 percentage is. Whatever this will be an FSX limitation and not PMDG NGX.

EDITED TO ADD: Just tried on off reverse thrust using the reversers on the Go Flight throttle quadrant and calibrated as buttons with their software. max reverse thrust was 63.5% N1 on both engines and took a good while to get it. I think that you will have more unrealistic behavior from the autobrakes setting. If you set it at three or max you will really stop the plane in a hurry.

 

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Conversion of FSC TQ with Leo Bodnar board complete.  The project is a success.

It is possible to assign an analogue axis to the reversers but the problem of only 63% N1 trust is what you get; same as the FSC TQ product except you get no say in where it goes or how it's processed.

With the BU0836A Bodnar board I assigned an axis each to the engine 1 and engine 2 reverser pots, but got FSUIPC5 to process them as digital two state controls .  In the lower part of the digital range (7500) and lower, the FSUIPC5 assignment is to sent command 'Throttle 1 decrease' repeatedly.  This is the equivalent of using F2 but only to engine 1   When the reverser lever is lowered and the count goes above 7500, it sends 'Throttle 1 set 1000'; once at the transition.  This sets an idle RPM for the engine.

The same treatment is applied to the Engine 2 reverser and it all works beautifully.  Now the achieved reverse thrust N1 is the same as with F2  but separate control for each engine, around 83% N1.

We also get the proper blue arc in the engine gauge to indicate mismatch between auto-throttle commanded position and the actual position.  This essential tell-tale had disappeared with the standard TQ product electronics.

As for auto-brake settings plus reversers, the real aircraft expects to achieve an auto-brake 2 equivalent deceleration performance when the reversers are used.  If auto-brake 2 is set and the autopilot sees that the reversers are managing setting 2 deceleration it does not put the brakes on. If auto brake 3 is set it puts on some brake to achieve the level 3 deceleration on top of what the reverse thrust can manage.  This is the essence of saving your brake temperatures in quick turn-rounds; reduced use of brakes.  I do not know if the PMDG does this but it seems to be right so far.  More landings to do!

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