Engine spool-up after reverse problem

[hamoody]

I'm having an issue, and I'm sure it's just something I'm doing wrong (I checked the manual and could not find anything helpful). After landing, I reduce the power all the way to provide full reverse thrust. When I advance the throttles again, however, it seems that they do not deliver any thrust for about 5-10 seconds, making it so that I frequently come to a stop on the runway. Am I doing something incorrectly?

[gpb500]

Same problem...doesn't seem normal.

[JGregory]

You sure about that 5-10 seconds?  There is a delay while the prop pitch changes, but I don't think it takes that long.

[gpb500]

It's enough that the plane feels like all tires are flat and you have to push the throttle far past beta to get any kind of inertia to come back into beta.  I've just learned to get out of reverse super fast...but it doesn't seem right when you're stuck on the runway trying to move and it won't.  That's my experience...i know the turbines are not direct coupled but it's not as if the props have stopped.  

 

EDIT:  You caught me in the middle of a flight...noted when landing...reverse on rollout until 70Kts...then neutral...plane continues to slow to 30kts and then as it slows further I push the throttle forward and no reaction.  I push further, then I'm out of beta, plane is now practically stopped while I'm on the runway which is unsettling (well...IRL it would be).  Love the plane...as most everyone does.  

One other nit is I can engage the AP with the standard XP button map, but the switch doesn't move and there's no beep for disengage.  I probably shouldn't be doing that...right?   Thanks!

Edited March 14, 2016 by gpb500
Added details

[mmerelles]

it happened to me as well. i reported it a long time ago (almost a year) but i was said the aircraft operates just right. This is not correct, i have been many times on a 340 cockpit, a family member is a 340 captain.

 

My workaround is to move the CLs to MIN during braking/reverse, it makes the aircraft get thrust in beta mode after landing. Otherwise the aircraft seems to get stuck on the runway.

 

This problem only happens after reverse/landing. No issues during initial roll when leaving the gate in beta mode.

Edited March 14, 2016 by mmerelles

[WR269]

A family member is also an SF34 captain and he said it does occur but only on the A model, not the B or the B+

Sent from my iPhone using Tapatalk

[JGregory]

1 hour ago, gpb500 said:

One other nit is I can engage the AP with the standard XP button map, but the switch doesn't move and there's no beep for disengage.  I probably shouldn't be doing that...right?   Thanks!

You should assign your button to the Saab AP command.

[breadwild]

12 hours ago, JGregory said:

You should assign your button to the Saab AP command.

@jgregory,  is there any documentation on how to do this? Thanks in advance.

[hamoody]

Thank you all for the replies. I just landed after a flight and the same thing occurred, only this time it seemed that normal power only got restored a minute or two after landing, no matter how much I juggled the throttles. Before takeoff, the Saab on the ground is very fast and can creep up to 30kts+ if I'm not careful, but this time after landing it wouldn't get over 13kts (power levers at flt idle, conditions at MAX). Flight was 100% normal otherwise. 

13 hours ago, WR269 said:

A family member is also an SF34 captain and he said it does occur but only on the A model, not the B or the B+

Sent from my iPhone using Tapatalk

 

Interesting! +1 to LES for realism. Could you ask them what the procedure was to smoothly transition from reverse to normal taxi thrust without stopping? There must be a way as I highly doubt the A models just hang out on the runway after landing. 

 

13 hours ago, mmerelles said:

My workaround is to move the CLs to MIN during braking/reverse, it makes the aircraft get thrust in beta mode after landing. Otherwise the aircraft seems to get stuck on the runway.

Do you then move them back to MAX for the rest of the taxi after you leave the runway and are in beta?

[JGregory]

41 minutes ago, breadwild said:

@jgregory,  is there any documentation on how to do this? Thanks in advance.

Settings > Joystick & Equipment > Buttons: Adv  (click box in upper right corner for custom commands)

[mmerelles]

52 minutes ago, hamoody said:

Do you then move them back to MAX for the rest of the taxi after you leave the runway and are in beta?

 

i move them to min and leave them there, this is a workaround i found to get consistent thrust in beta mode after reverse. In the real thing it doesn't matter. You can taxi having them in max or min because you are in beta mode.

 

turboprops per their engine nature have several seconds lag to respond to throttle adjustment changes (5-6 secs aprox). this make them very inconvenient for taxing and general ground operations.

 

in response, engineers creates beta mode, the throttle range goes from GROUND IDLE to MAX GROUND IDLE (just before you enter FLIGHT IDLE)

 

under beta mode, the engines are held constant by around 1100 rpm by electronics (do not remember the exact value) and moving the throttles within the beta range you are actually only controlling the blade pitch 0 to +10 degree. Being in GND IDLE you have a 0 degree blade pitch no air gets pushed, moving it forward you add blade pitch and air gets pushed. Blade pitch changes are almost instant and rpms are held constant by the electronics watching fuel flow. Thus you get a predictable thrust for ground operations.

 

note: Condition levers MIN to MAX position allow you to set your desired engine RPM for torque vs speed at different passes of flight while the throttles are in the flight range (FLIGHT IDLE and forward)

[JGregory]

3 hours ago, mmerelles said:

i move them to min and leave them there, this is a workaround i found to get consistent thrust in beta mode after reverse. In the real thing it doesn't matter. You can taxi having them in max or min because you are in beta mode.

This is exactly how we programmed the Saab.  It does NOT matter what position the Condition Levers are in, as long as they are between MIN and MAX, when the Power Levers are in BETA.  The prop pitch is controlled by the Power Levers while in beta and the "computer" will attempt to maintain prop rpm at a constant speed.  You should not see any difference in ground handling with the Condition Levers at MIN or MAX.

[mmerelles]

39 minutes ago, JGregory said:

This is exactly how we programmed the Saab.  It does NOT matter what position the Condition Levers are in, as long as they are between MIN and MAX, when the Power Levers are in BETA.  The prop pitch is controlled by the Power Levers while in beta and the "computer" will attempt to maintain prop rpm at a constant speed.  You should not see any difference in ground handling with the Condition Levers at MIN or MAX.

Yes i know, that was my whole point when i reported this bahaviour

when landing the condition levers are set to max, just to have torque under a potential go around

once you landed you apply reeverse and braking, then you clear the runway in beta mode. As you said, It shouldnt matter you leave the cl at max.

well, the weird behaviour is you leave them on max and the aircraft may get stuck on the runway for more than 15 seconds while you try getting thrust moving the power levers wirhin beta wirh no luck

i found that moving the condition levers to min after landing makes this weird behaviour go away

this only happens after reverse/landing

ground operatio  prior to takeoff works flawlesly

The real thing does not have this issue

 

 

 

 

[JGregory]

My point was that you shouldn't need a "workaround".  If this is a wide-spread issue we will certainly look into it.

[gpb500]

Here's an example I found of a 340 on touchdown.  Warning...turn volume down, it's only music, no cockpit sounds.  And that's Steve-o flying right side...for those that follow his youtube channel.  

 

@JGregory thanks for the comments...but are you saying you've never had this happen?  To me it feels like having flat tires...or maybe it takes 10 seconds to back out of reverse?  Because the plane won't go backwards using reverse...we wouldn't know.  What exactly is the prop pitch transition time?  Just seems odd...but if it happens in real life...wow.  Thx again.

 

 

[mmerelles]

Thanks for sharing, this video shows the aircraft -as said- has no such behavior, and when put out of reverse mode to ground idle it keep rolling freely and nicely.

These are my observations on this video.

1. at 1:02 CLs goes to max as part of landing checklist, just in case of a go-around is required maximum torque is available.

2. at 2:22 power lever goes to reverse mode following touchdown, left & right beta mode engages.

3. at 2:33 power levers goes back to ground idle as per the procedure (speed). the aircraft rolls nicely and captain is required to control final exit speed via braking.

4. clearing the runway at 2:54 they perfom after landing checklist and CLs goes to MIN as part of the procedure (this is not required by the aircraft to taxi)

5. at 2:58 while making 2 hard turns to the right the captain adds a bit of beta power lever to complete the turn, the aircraft keeps rolling nicely.

 

on the sim however, this aircraft sometimes tends to get stuck on the runway no matter you moved the power levers out of reverse mode 10 seconds away, increasing power levers on beta mode doesn't help either. It takes abnormal amount of time to regain thrust again. Following the Argentina's sol real procedures i found putting the CLs to MIN restores thrust immediately by coincidence but it shouldn't work that way.

This is not a big deal for me i can live with that, but seen others may have this behavior as well i will try to spend some time testing if i can get a repeatable and reproducible behavior for providing better evidence.

[hamoody]

21 minutes ago, mmerelles said:

Following the Argentina's sol real procedures i found putting the CLs to MIN restores thrust immediately by coincidence but it shouldn't work that way.

I actually tried this, and although the aircraft remained rolling I could still tell that power was not restored completely. I had trouble maintaining taxi speeds and the engines sounded abnormal to me as well.

[mmerelles]

3 minutes ago, hamoody said:

I actually tried this, and although the aircraft remained rolling I could still tell that power was not restored completely. I had trouble maintaining taxi speeds and the engines sounded abnormal to me as well.

glad it is getting better for you as well. I do not want to post much more and keep speculating on this. I will try to spend some time next week when able to come back on this and see if i can figure out what is going on for providing the developers better evidence about this

in the meantime enjoy this bird, is one of the very best available for xplane.

[hamoody]

1 hour ago, mmerelles said:

in the meantime enjoy this bird, is one of the very best available for xplane.

Absolutely. The Saab 340 is my favorite plane in real life, and I actually bought XP10 just to use this addon. I can't believe how detailed the Saab is, just like the Majestic Q400 or PMDG NGX for FSX (maybe even more so), and as a platform XPlane is superb. I love the 'feel' I get, like I'm actually driving a large metal machine through a fluid medium. I'm having enormous fun recreating Northwest Airlink Saab flights out of DTW I'd take as a kid, and actually haven't fired up P3D in days. Good luck figuring out this little quirk, but until then I can deal with all the phone numbers I'll get from ATC for clogging up their runways  

Edited March 16, 2016 by hamoody

[hamoody]

I'd like to add another thing I noticed. On a flight I finished just now, I still could not get the power up as normal even if I never put the levers into reverse. It didn't seem as bad as when I use reverse thrust, but I still could not get past a crawl (max 13kts g/s with the throttles well past the flight detent) until a minute or so after landing. Nothing changed when I moved my condition levers to min. 

[gpb500]

Well that IS interesting...thanks for posting.  Could it be flaps?  Wonder if retracting flaps early would make a difference.  Also wondering if XP itself (ground handling) isn't somehow the problem here.

[mmerelles]

i have a vague idea that yes, landing without applying reverse also has the issue but not sure.

maybe an issue with hydraulics? braking getting stuck?

can you try to land on a long runway applying reverse but not braking now? and then trying to taxi...

i do not think it is xplane ground issue, because when leaving the gate prior to takeoff the aircraft taxies out clean and crisp, it is very responsive to power lever beta input. Any time i have seen this issue was taxing power after landing.

I need to get back to home to open all datarefs make lot of testing and compare taxi parameters (engine, torque, blades, thrust, rpm, fuel, hydraulics, etc,) prior to takeoff against after-landing.

[JGregory]

Goran and I have both tested this, with hardware and with just the mouse and keyboard.  Neither of us have any problem taxiing after landing, whether we used reverse or not.  However, this was done with the latest dev version, which is not out to the public yet.  My guess is that this issue has been resolved as part of some of the other updates/fixes we have done.  I'm not inclined to consider this a problem (bug) until you guys have the next update and can try it.  No release date yet... stay tuned.

[-VETTE]

1 hour ago, JGregory said:

Goran and I have both tested this, with hardware and with just the mouse and keyboard.  Neither of us have any problem taxiing after landing, whether we used reverse or not.  However, this was done with the latest dev version, which is not out to the public yet.  My guess is that this issue has been resolved as part of some of the other updates/fixes we have done.  I'm not inclined to consider this a problem (bug) until you guys have the next update and can try it.  No release date yet... stay tuned.

Awww, after reading this thread I was kind of hoping it wouldn't be "fixed." I find it awesome that you guys did this, I'd much rather have a quirky and realistic plane than a bland and simple to fly one

[JGregory]

8 hours ago, -VETTE said:

Awww, after reading this thread I was kind of hoping it wouldn't be "fixed." I find it awesome that you guys did this, I'd much rather have a quirky and realistic plane than a bland and simple to fly one

Wait!     You were hoping we wouldn't fix it, but you think it is awesome that we did?  Am I reading that right?