Reverse Thruster

[hopskip 253]

FSX does not require the engine to be at ground idle, FSX doesn't even know about flight and ground idle.  All it looks at is the thrust lever position.  Anyway I'm sure PMDG modelled approach idle properly in their custom engine model, not by fiddling with FSX thrust lever position.

Here's an interesting little experiment. Fly the NGX on an approach, and put your gear down on glideslope capture, go flap 15 and slow down to Flap 15 green dot speed.

 

Now as the aircraft starts decending and trying to slow down at the same time, the engines will roll down to approach idle. - let them stabilize a little at approach idle.

 

Now press and hold down F1. - the engines will go below approach idle N1.

 

Now release F1 and the N1 will increase back to approach idle.

 

For whatever reason FSX sees the NGX's "Approach Idle" setting as "not idle enough to engage reverse thrust" once you touch down.

[kevinh 409]

Here's an interesting little experiment. Fly the NGX on an approach, and put your gear down on glideslope capture, go flap 15 and slow down to Flap 15 green dot speed.

 

Now as the aircraft starts decending and trying to slow down at the same time, the engines will roll down to approach idle. - let them stabilize a little at approach idle.

 

Now press and hold down F1. - the engines will go below approach idle N1.

 

Now release F1 and the N1 will increase back to approach idle.

 

For whatever reason FSX sees the NGX's "Approach Idle" setting as "not idle enough to engage reverse thrust" once you touch down.

I had to approach really fast to force the NGX to spend time slowing down.  However, yes it's true if you force the engine to idle by holding F1 the rpm will drop lower (it doesn't go to ground idle, mine went to 29% N1).  So there is some interaction there in how PMDG implemented flight idle which should ideally be cleaned up in SP2.  In simulating this, idle RPM should be treated as the minimum rpm the engine will run at in a given condition, not the RPM set by the thrust lever at idle (which should always be below ground idle).  If PMDG put that in their custom engine simulation approach idle would never be an issue like this.

 

If you think about it, because you can override approach idle by using F1 in the air, you certainly should be able to do so on ground.  But I never use F1 on touchdown, I just hold F2 down.  FSX has two rates of thrust increase and decrease from keyboard inputs and as long as F2 is assigned to the fast thrust decrease control there should be no problems.  FSX certainly doesn't know what idle N1 should be, all it cares about is throttle position to determine forward or reverse thrust.

 

However none of this has any bearing on the fact that in my NGX (fully up to date) I observe thrust reverser operation immediately after touchdown, both in terms of engine indications and external animation. The only difference between my set up and anyone else's will be how their throttle hardware is calibrated and what control they might have F2 assigned to.

[dts 0]

Kevin,

 

My work around is for Saitek Thrust levers, or other joystick thrust levers, if you press F2 it works 100% of the time, but for thrust levers especially saitek it doesnt, so this is the work aorund

[Christopher Low 5,331]

I guess it must be because I don't have auto anything on when I am flying the NGX, but the thrust reversers work great. In addition, because I do not have autobrakes active, I can let the thrust reversers and spoilers slow the plane down to the cutoff point, and then manual brakes to bring the aircraft to a stop. That gives me a much better rollout, because applying the brakes just after touchdown results in the aircraft slowing down way too quickly. This is probably due to the lack of weight (I do not carry any passengers).

[Fabo 213]

Autobrakes are deceleration automats, that is, they will achieve a desired rate of losing speed. They will not apply any braking if you achieve selected rate by spoilers and reverse thrust alone.

[Christopher Low 5,331]

Thanks for that information. I wasn't aware of that, but it makes sense.

[kevinh 409]

Kevin,

 

My work around is for Saitek Thrust levers, or other joystick thrust levers, if you press F2 it works 100% of the time, but for thrust levers especially saitek it doesnt, so this is the work aorund

Your post was 100% clear and helpful, but other comments in the thread confused the issue both for your workaround and F2 use.  There isn't a problem inherent in the NGX, there isn't an FSX limitation. However PMDG could improve things if they changed how they modelled approach idle to be more like how the real aircraft does it.  If they did that it might help those who have VNAV descent idle problems too

[Fabo 213]

 

 There isn't a problem inherent in the NGX, there isn't an FSX limitation.

 

Well, there kind of is. FSX is not prepared for different idles in different flight state. It is of course possible to make some workarounds, PMDG are using some. In this case, I believe due to observed behaviour, it is made so that the lowest idle, ground idle, is set as "FSX idle". PMDG has then coded some logic, that will never allow the thrust to reach FSX idle when a higher idle is actually required.

 

Now, this would mean that until PMDG sets idle to actual ground idle, FSX will not believe the thrust lever to be at idle and will therefore not allow reverser deployment. This can be overriden by repeated F1 or F2 pushing/holding, as noted several times in this topic.

 

In any case, this is not a trivial fix, as you make it to sound like.

[kevinh 409]

Well, there kind of is. FSX is not prepared for different idles in different flight state. It is of course possible to make some workarounds, PMDG are using some. In this case, I believe due to observed behaviour, it is made so that the lowest idle, ground idle, is set as "FSX idle". PMDG has then coded some logic, that will never allow the thrust to reach FSX idle when a higher idle is actually required.

 

Now, this would mean that until PMDG sets idle to actual ground idle, FSX will not believe the thrust lever to be at idle and will therefore not allow reverser deployment. This can be overriden by repeated F1 or F2 pushing/holding, as noted several times in this topic.

 

In any case, this is not a trivial fix, as you make it to sound like.

FSX does not need to know what idle thrust is to allow reverse thrust to operate.  You can go from full forward thrust straight into reverse.  RPM never gets anywhere near idle.

 

And I do know how trivial it is, as I've designed propulsion systems simulations for full flight simulators.  If PMDG have a custom engine simulation then it really is straightforward to do properly.  If they have designed it from observed behaviour in the simulator then they may have unnecessarily complicated things.  If they are using parts of the FSX engine fuel control model then that will complicate things.

[Greg Hollen 27]

Automatic reversion to ground idle after landing (what happens in the real aircraft) does not work right in the PMDG NGX 737; never has and apparently never will.      I've long since given up ever trying to map reverse thrust to a joystick axis and now just press F1 on the keyboard after landing to manually spool the engines down to ground idle.     Honesty, there are so many additional things like this wrong with the NGX sim that I really hate even messing with it anymore.     Ground effect is messed up too and never works reliably.    

 

Maybe if/when PMDG build things for the Xplane platform, the Frankenstein approach to programming required by the prehistoric FSX engine will be a thing of the past.    Trying to fit a complex sim add-on into the FSX or P3D is like trying to drive a square peg in a round hole.      FSX and P3D are essentially general aviation simulators, and trying to Rube Goldberg these outdated and under-designed platforms with sophisticated add-ons is always an exercise in 'acceptable' compromise.

 

The code of Omerta between developers and their customers when issues like this arise is standard fare:   just don't talk about it and hope the software users will simply accept things the way they are, or even better, be beat down in the forum by loyal f_a_n_b_o_y_s until they become too frustrated to attempt further resolution.    

[Fabo 213]

I will get back to the last post that happened to be quoting me... for nostalgic reasons I guess... but what a way to bring up an old thread  :wacko:

 

 

 

FSX does not need to know what idle thrust is to allow reverse thrust to operate.  You can go from full forward thrust straight into reverse.  RPM never gets anywhere near idle.

 

Yes, but the FSX throttle "axis" needs to go to idle and then into reverse, as far as I can tell. Of course if executed properly spooldown will not allow the engine to reach idle.

 

 

 

 If they are using parts of the FSX engine fuel control model then that will complicate things.

 

I think that is part of the reason. It might still be easier to work around the existing model than to code a completely new one and figure out how to tie it in. For a jet anyway.

[kevinh 409]

Yes, but the FSX throttle "axis" needs to go to idle and then into reverse, as far as I can tell. Of course if executed properly spooldown will not allow the engine to reach idle.

No, from what I can observe all the throttle has to do is go into reverse, just like the real aircraft. It doesn't need to be at idle first, but clearly it must pass through idle on the way. I've tried setting full throttle and then just using F2. This runs the throttles rapidly into full reverse and the reversers operate just fine. It isn't necessary to hit F1 first, then F2.  However doing can be faster.

 

I think that is part of the reason. It might still be easier to work around the existing model than to code a completely new one and figure out how to tie it in. For a jet anyway.

As I said earlier in the thread it is really easy to get approach idle to work if you have a custom engine model, which I always assumed PMDG had.  However despite that, it does appear they have modelled those flight idle settings by messing around with thrust lever angle rather than do it properly (which would be so much easier to achieve).  If they want to know how it's done they only have to ask.

 

It only appears to be a problem for those who have assigned thrust lever axes via FSUIPC and attempted to set up idle and reverse detent positions.  Simmers who, like me, are using a simple throttle axis don't notice the problem because they don't have a physical reverse thrust lever position to control, so they always use the keyboard shortcuts.  However, as with the toe brake axis, there must be a way to set the hardware up so it works satisfactorily with the NGX.

 

If only PMDG sorted out the engine fuel control design this would cease to be a problem.

[Christopher Low 5,331]

I don't have a problem with the PMDG 737NGX thrust reversers. I use a CH Flightstick Pro joystick to fly the plane, and I have Button 2 set up as the thrust reverser activation. I cut the power to idle when I flare, and then press the button (and hold it down for two or three seconds if I want maximum reverse thrust) to activate the reversers. This has never failed to work for me. I then "flick" the throttle lever forward a touch, and then back to disengage the reversers.

 

For the record, the PMDG 737NGX has the best simulation of reverse thrust (activation, sound, and effect) of any aircraft that I have used in FSX.

[Fabo 213]

This is not much of a problem if you want max reverse, yes. I have a Saitek yoke with their TQ - in it, you can actually pull the levers a bit under the idle detent - there a button is pushed. I have it set up so that button mimicks F2. So for full reverse, I just throw lever down, and off I go.

 

But I like to use idle reverse... which is a bit of a problem - as I have to first use F1 to set idle, then F2 to open reverse, and maybe repeat again if at first I didn't catch...

[mounty 13]

Hi,

 

Thought I'd put in a comment.  I use the Saitek Throttles through FSUIPC and have them set with the offsets for each Reverse Thrust, as follows.

 

Custom Offset 70312 = engine # 1

Custom Offset 70313 = engine # 2

 

Parameter is 20000000 for both offsets

Check "Control to he repeated while held"

 

Action - Throttle 1 Cut

Action - Throttle 2 Cut

 

It doesn't matter what your throttle settings are or whether you are actually on the runway.  I have had the engines spooled up to 60% on approach and gradually reduceds it to 40% just before touchdown and then apply reverse thrust on touchdown when the engines are at about 30%.  I get full reverse thrust up to around 40% - 50% (can't remember which) as soon as I pull the throttles into the reverse position.  The Saitek throttles have a switch for reversers, so it's just a matter of assigning the switches to the offsets etc.  I find that this is a more realistic way of using reverse thrust.

 

Rob