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Guest HepburnUGA

Autobrakes disarm question

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From the PMDG manual (and verified in Bill Bulfer's 737NG manuals)...---------------(1) AUTO BRAKE DISARM Light Illuminated (amber)

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I would assume everybody else sees this behaviour, since it is a subject that has been frequently discussed before. I remember that even before SU1 was released there was a very lengthy discussion about it, in which some one from the PMDG team participated, but alas, it hasn't been changed. Below one part of my part in the discussion."I dug up these pieces of trivia in my Lufthansa manual today:- if you set the autobrake to RTO it will self-test, as indicated by the DISARM light illuminating for 2 seconds (as modeled in the DF737, BTW)- if you LAND with the selector still in RTO it won't function, the DISARM light will go on after 2 minutes, not seconds as previously mentioned- the autobrake is actually armed for take-off when anti-skid switch on, autobrake RTO, airplane on ground, wheel speed less than 60 kts and both throttles in idle- if throttles are retarded between 60 and 90 kts the system will disarm and the DISARM light will come on- autobraking on take-off will only occur with wheel speed greater than 90 kts and both throttles in idle- they may be deactivated by moving the speedbrake handle from position beyond armed to down, by depressing brake pedal after 2 seconds of RTO mode activation or 3 seconds after autobrake activation, by advancing throttles after touchdown for GAThe manual is for the 3/4/5, but I don't think much has been changed for the NG. Enjoy."As it turned out there were a few differences. The self-test only lasts 1,2 seconds, I believe, and after landing if the selector is in RTO it will only show DISARM for 2 seconds, if I remember Ian Riddell's input correctly.While I understand that some details may not be implemented, I do hope that at least for the 800/900 the sim will reflect its own manual in this respect :-)Leo Bakker

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Correcting A/B behaviour was considered during the SU-2 beta, Leo. However, initial attempts introduced some unexpected complications which appeared to be too hard to fix. Last I heard, the modifications were removed (I had to quit the beta team for personal reasons, so I didn't get to see what modifications stayed and which were removed).Jeff, the (real) 737NG Autobrake switch cannot move by itself. There are no electromagnetic latches as found on other Boeings (It's just a simple multi-position rotary switch). Only the light will give you any indication of the status of the Autobrake system. I'm not sure if this light is working correctly or not in PMDG (I am unable to download SU-2 at the moment).Hope this helps.Cheers.Ian.

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Thanks for the response Ian. Insightful and informative as always. I hope you are able to pick back up testing the 800/900 series.Thanks! Jeff

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Leo,- There is no anti-skid switch in the NG- Landing with the switch in RTO will cause disarm after 2 SECONDS indeed! (It does not show it for two seconds)Regarding this behavior, there's the problem in FS that you cannot apply more or less brakes, it's just brakes ON or OFF. One pretty big flaw if you ask me.

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It would be a flaw if that's how it worked. Actually, you can apply measured amounts of braking by using an axis input. I can map an axis on my PFC throttle quad to one/both brakes and apply variable braking that way...and the new PFC pedals with variable differential braking work the same way.The PMDG autobrakes, BTW, do not just apply full "on" braking...if you monitor the internal braking offsets during autobraking you will see that the panel clearly is modulating the amount of brake input at levels below the max threshold. Otherwise, why provide varying levels of A/B?RegardsBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, D.C.

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Ah yes, but you're talking about modulating brakes. I recall that 767PIC simply used the method that a microwave oven uses. When powering at 50%, it just goes 1 second on, 1 second off, and that was the same way the different auto brake settings were simulated. You won't really notice the difference if it's done quickly.I didn't know FS2004 (and FS2002?) supported analog braking inputs.

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Iz; Writing a 2-byte value to FSUIPC offsets 0BC4 and 0BC6 (0-16383) will set a variable brake setting for each MLG. Believe it worked the same way in FS2002. PIC767 (which was written for FS2000) does cycle the brakes, utilizing the damped rise/fall of the FS braking effectiveness to give a variable braking effort. Pretty ingenius, but no longer needed...CheersBob ScottATP IMEL Gulfstream II-III-IV-V L-300Washington, D.C.

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