Autobrakes on 11.41 (1.21)

[jeffrds]

Hello everyone.

Is there a way to increase the deceleration rate of the autobrakes? They feel kinda "weak", even o MAX setting.

Is this a known bug?

Cheers.

[ktomais]

I haven't experienced something similar. Have you checked if they have not disarmed? Like described below for instance (see: link). In the case of rudder pedals, over-sensitivity or calibration of the toe-brake can be a cause.

I also believe that for the autobrake to engage, your spoilers should be armed before touchdown. To confirm that they are engaged you should see a green light on the location highlighted on the attached image.

Unsure also if the autobrake and spoilers will not engage if the landing is too soft. Is there a wanted ft/m or a minimum limit @Litjan ?

http://www.flaps2approach.com/journal/2015/2/17/autobrake-system-review-and-procedures.html
The autobrake can be disengaged by turning it to OFF, by activating the toe brakes, or by advancing the throttles; which deactivation method used depends upon the circumstances and pilot discretion.  Furthermore, the deceleration level can be changed prior to, or after touchdown by moving the autobrake selector knob to any setting other than OFF.  During the landing, the pressure applied to the brakes will alter depending upon other controls employed to assist in deceleration, such as thrust reversers and spoilers.

Edited May 12, 2020 by ktomais

[jeffrds]

Hello ktomais, thank you for your reply.

All landing checks and procedures are being done correctly.

Since I don't have rudder/brake pedals, I brake using my joystick trigger, so no pedal spikes disarming the A/B unintendedly.

Everything is calibrated correctly.

I have recorded a small video to show you what I mean.

Conditions:

Airplane is light (44 tons), all set for landing, Speedbrake is armed and A/B is set to max.

Try not to focus too much on the airmanship and overall switches, the main ones are set correctly.

Even on MAX, the airplane behaves like no wheel brakes are being applied whatsoever. The 737-300 should be able to stop with plenty of runway to spare, even on SBRJ's short runway with a light aircraft.

Best regards.

[Litjan]

Hi Jeff,

The real autobrake at MAX will decelerate at about 8kts per second (http://www.b737.org.uk/landinggear.htm). Judging from your video I would say you get about only 4 kts per second.

Here is how I analyze your video: You pass the threshold at 5:10 and touch down at 5:16. That is 6 seconds at 130kts (65m/s) = 210m past the threshhold. That is a good, short touchdown. I would recommend using flaps 40 on a runway that short, but this is not the issue here.

You have about 1100m runway available after touchdown (total runway 1320m). To stop within that runway, you would need to decelerate with roughly 4kts (2m/s²).

Now I just tested the autobrake on my version of the IXEG 737 and I get about 4kts/second at setting "3" (roughly 0.14 brake application value) and about 8kts/second at setting "MAX" (about 0.22 brake application value). So that is very close to the specification quoted above.

You can output the brake value applied by X-Plane on screen by going to the DATA OUT tab and select field 14 and click the field "show in cockpit".

So - while Santos Dumont is certainly a VERY challenging airport to fly the 737 into - it should have been possible for you to stop with the selected values. Double check if your runway state is not set to "wet" or if other plugins (fly with lua, for example) are interfering with the stopping effort.

From my experience it is possible for an average pilot (me ;-) to reliably make the center taxiway at EDDW Bremen (1000m past the threshhold) with a normal weighted 737.

Cheers, Jan

[jeffrds]

Thanks for the reply, Jan.

The 737 is and has always a been a frequent visitor at Santos Dummont airport, despite its short runway the airplane can operate there safely without problems.

I can confirm that the runway state is set to DRY, this is Xplane's CLEAR conditions, I only added a 5kt headwind.

As for Lua scripts, I only use a tiny lua that sets the QNH/QNE with a keypress, nothing else.

Indeed, flaps 40 is recommended, I tested it with the same result, unfortunately. 

If I land with A/B OFF and apply brakes manually, the airplane stops normally, even using "Regular Brake Effort" for the toebrakes, so I am at a loss here.

Anyways, thanks for you input. If you guys could take a quick check on a/b braking action it would be great.

[ktomais]

Hey @jeffrds that seems so weird. Have you noticed the same behavior at other airports? Is it the default? I'm thinking wildly here that this may be a case where the wrong surface is defined so the brakes don't work as expected? 

Edit: I also just tested Corfu FlyTampa (shooort runway) and the autobrake seems to be working normally, not even using reversers. 

A video of my quick and dirty demonstration  https://youtu.be/80gTgnH0ftE

Soft landing A/B 3  https://youtu.be/LZV942sev-o

Edited May 12, 2020 by ktomais

[Litjan]

Now that ktomais mentions it - I vaguely remember another report about unusual ground behaviour (I think it was a payware Bergen airport in Norway). So it is definitely worth checking if this happens at other airports, too.

Did you output and check the brake values applied by X-Plane?

Cheers, Jan

 

[jeffrds]

1 hour ago, ktomais said:

Hey @jeffrds that seems so weird. Have you noticed the same behavior at other airports? Is it the default? I'm thinking wildly here that this may be a case where the wrong surface is defined so the brakes don't work as expected? 

Edit: I also just tested Corfu FlyTampa (shooort runway) and the autobrake seems to be working normally, not even using reversers. Below the aforementioned rough video. 

https://youtu.be/80gTgnH0ftE

Ok, now this is triggering me hahah!

Your A/B is behaving as expected, see the decel rate? That is what I'm looking for.

Just to confirm, the A/B behavior happens on any airport, so no, it is not some bizarre scenery bug.

[jeffrds]

Ok, @Litjan and @ktomais, I may have found the culprit, not sure.

A while ago I was having problems taxiing the IXEG on sharp, tight turns, the airplane would come to a halt, and the power required for turning would be in excess of 70%n1 or more.

Right here on the forums, I found a "fix" using planemaker, where we would set a value to zero and voilá, I could taxi normally again.

Question: Did I break my autobrakes with this "fix"? 

Forum links for reference:

Taxi turns stall

[Merged]Steering and differential braking

 

Edited May 12, 2020 by jeffrds
URL's

[Litjan]

Hmm, I would never say never...but I would like to ask you again to output the brake values as applied by X-Plane and see if they are aound 0.22 for autobrake MAX.

The next version of our plane (1.3) is really not far away now, and that one will incorporate the fix that you applied manually. I have been using 1.3 in my above test, so I am hopeful that it will fix this for you as well.

But again - lets see how much brake pressure X-Plane applies on your system and go from there.

Jan

 

[ktomais]

I also just added a video with soft A/B 3 landing as POC of different conditions. As for the "fix" that you mention I'm not sure if it would break the IXEG.

I believe that the above behaviour happens, and correct me if I'm wrong @Litjan, due to XPlane applying differential braking when using the yaw axis. @jeffrds If you switch the axis of your choosing to Nosewheel Tiller instead, you will not notice the braking behaviour while taxiing. Then return the values to default.

At least that's what I noticed on my system.

I would also suggest this lua for your manual braking: https://forums.x-plane.org/index.php?/files/file/37662-differential-and-progressive-brakes-for-x-plane-11/

Edited May 12, 2020 by ktomais

[jeffrds]

@LitjanAs you suspected, after landing, A/B set to max, no brake input whatsoever, 0.000.

When I press "B" the input goes to 0.284 or something, so yeah, A/B is not working.

[jeffrds]

@ktomaisI will try your suggestion, thank you.

Would you mind opening the b733.acf on planemaker -> Standard -> Landing Gear -> Gear Data and post a screenshot of your default values for 1.21?

Edited May 12, 2020 by jeffrds

[ktomais]

22 minutes ago, jeffrds said:

@ktomaisI will try your suggestion, thank you.

Would you mind opening the b733.acf on planemaker -> Standard -> Landing Gear -> Gear Data and post a screenshot of your default values for 1.21?

 

[Litjan]

1 hour ago, jeffrds said:

@LitjanAs you suspected, after landing, A/B set to max, no brake input whatsoever, 0.000.

When I press "B" the input goes to 0.284 or something, so yeah, A/B is not working.

Ok, so at least we know its not working...

There are a few requisites to it "triggering" - one of them is "thrust lever at idle". Just as a hunch - could you make sure that you really have thrust at idle when touching down? I am not sure how "forgiveful" the X-Plane logic is. We trigger the AUTOBRAKE DISARM light if the autobrake gets cancelled due to braking, but we cant (dont) catch the thrust not being idle, I think.

So please verify the thrust levers are fully at the stop when you touch down.

Cheers, Jan

 

[ktomais]

So @jeffrds did it work?  

[Litjan]

2 hours ago, ktomais said:

So @jeffrds did it work?  

Yeah, always a bit frustrating to try and help someone with a lot of time and effort, and then the last thing you hear is "ok, I will try that". I always try to console myself that the advice has worked and the user is happy now.

Cheers, Jan

 

[jeffrds]

Hello guys @Litjan and @ktomais, been a busy couple of days, sorry for the lack of feedback.

So, Reinstalled everything.

I can confirm that RTO works normally if I abort the takeoff roll.

On landings, I managed to get my A/B to work if I change my own piloting, as in I now wait a little longer to engage reversers, usually after nose gear touchdown.

But with a default *.acf, the problems with the steering comes back. @ktomaissuggestion for a nosewheel tiler doesnt work well for me, since I dont have an axis for that, and I DO like my steering synced to my yaw axis, (joystick with twist rudder on Z axis).

So, yeah. It's a quirk of the aircraft that I'll have to adapt myself around.

On a side note, fully default installation, no lua scripts whatsoever are active, I notice my pedestal floodlights and Dome Lights arent working, or at least are very dim. panel integral backlighting and background floodlighs, including fluorescent panel flood is working normally. Is this correct?

Cheers,

[ktomais]

30 minutes ago, jeffrds said:

Hello guys @Litjan and @ktomais, been a busy couple of days, sorry for the lack of feedback.

So, Reinstalled everything.

I can confirm that RTO works normally if I abort the takeoff roll.

On landings, I managed to get my A/B to work if I change my own piloting, as in I now wait a little longer to engage reversers, usually after nose gear touchdown.

But with a default *.acf, the problems with the steering comes back. @ktomaissuggestion for a nosewheel tiler doesnt work well for me, since I dont have an axis for that, and I DO like my steering synced to my yaw axis, (joystick with twist rudder on Z axis).

So, yeah. It's a quirk of the aircraft that I'll have to adapt myself around.

On a side note, fully default installation, no lua scripts whatsoever are active, I notice my pedestal floodlights and Dome Lights arent working, or at least are very dim. panel integral backlighting and background floodlighs, including fluorescent panel flood is working normally. Is this correct?

Cheers,

Good to know it works at least in some form for you! Hopefully the upcoming update will resolve any issue you face. For the last part I'm afraid my knowledge stops here.  

[Litjan]

Well, if you have the brakes helping with turns I could imagine they would disengage the autobrake. But with an extra axis for the yaw this should not be necessary (even with a twisty stick).

Maybe wait for 1.3 and see if that works out better for you.

Cheers, Jan