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jgoggi

777 decelerating too quickly at landing

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Hi, the PMDG 777 stops too quickly on the runway after landing. I don't need autobrakes at all, the airplane stops before half runway even without them. With the autobrakes, even at 1, my house garden would be enough to make it stop. Are you sure the braking model is correct?

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Not sure why your simulation is so slippery.  If I don't use autobrakes (or manual braking) mine will simply cruise right off the end of the runway. Are you sure you don't have something creating this issue?

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Absolutely nothing. I just need the reverse at idle and the plane will stop within a short distance, without the use of autobrakes.

By the way, I see that back in 2014 the issue had already been reported:

http://www.avsim.com/topic/445601-77l-autobrake-she-stops-in-a-dime/page-1?hl=+dime

 

So you are actually helping the aircraft slow down by using reverse thrusts? it not as if your not doing anything to help it slow down to clarify?

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Yes, I mean, if I only use reverse and no autobrakes, the airplane already reaches a taxi speed very quickly. If I also use the autobrakes at 1, it comes to a complete stop before mid runway... 

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Yes, I mean, if I only use reverse and no autobrakes, the airplane already reaches a taxi speed very quickly. If I also use the autobrakes at 1, it comes to a complete stop before mid runway... 

if you look in the FCOM you will see that the dry runway landing distance for a -200LR at 220,000 Kg landing weight, flap 30, autobrake 1, is 2205m. So it doesn't sound like your mid runway stop is too far wrong, depending on how long the runway is. 

 

Autobrake 1, 2, 3 and 4 set a demanded deceleration rate. So even if the simulated brakes were too effective the autobrake system would reduce the braking effort to achieve the required deceleration rate. Because FSX has rather excessive friction levels, depending on the runway surface, this can mean that the sim decelerates too fast for the autobrake setting even with brakes released which makes it stop sooner than data.

 

This post gives a more complete explanation:

 

http://www.avsim.com/topic/456988-question-for-rob-robson-777simmer/page-2#entry3137864

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Hi, the PMDG 777 stops too quickly on the runway after landing. I don't need autobrakes at all, the airplane stops before half runway even without them. With the autobrakes, even at 1, my house garden would be enough to make it stop. Are you sure the braking model is correct?

 

Based on the title, one would assume that you have many years of experience flying the 777. Is this the case, or are you just basing it off of what "feels" right?

 

We have a tech team for all of our products. They all either fly, have flown, or maintain the aircraft in question. As such, when it comes to what they say, and what the books say, that's what we go with, because that's reality.

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if you look in the FCOM you will see that the dry runway landing distance for a -200LR at 220,000 Kg landing weight, flap 30, autobrake 1, is 2205m. So it doesn't sound like your mid runway stop is too far wrong, depending on how long the runway is. 

 

 

The runway is 3900 m, so with autobrake 1 the 777 stops in about 1500-1800 m... Anyway I use P3D v3.4, I don't know if it behaves like FSX concerning ground friction.

 

Based on the title, one would assume that you have many years of experience flying the 777. Is this the case, or are you just basing it off of what "feels" right?

 

We have a tech team for all of our products. They all either fly, have flown, or maintain the aircraft in question. As such, when it comes to what they say, and what the books say, that's what we go with, because that's reality.

 

I don't have experience on the real 777, but I have seen lots of cockpit landing videos and it takes quite more time to decelerate. Anyway in FSX the ground friction is a known bug, I don't know if it's the same in P3D. When I use the 737, it looks like it takes more time to decelerate than the 777...

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The runway is 3900 m, so with autobrake 1 the 777 stops in about 1500-1800 m... Anyway I use P3D v3.4, I don't know if it behaves like FSX concerning ground friction.

 

 

I don't have experience on the real 777, but I have seen lots of cockpit landing videos and it takes quite more time to decelerate. Anyway in FSX the ground friction is a known bug, I don't know if it's the same in P3D. When I use the 737, it looks like it takes more time to decelerate than the 777...

Did you read RSR's comments on the same subject in the other thread I linked too? If so why are you still questioning the fact that PMDG have gone to great pains to get this right. You could easily see from the change logs whether LM have addressed the friction issue. I'm not going to do that search for you.

 

With respect you can't tell from cockpit videos where the aircraft stops on the runway, nor how hard the crew are braking when they take over from autobrake.

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Are you sure the braking model is correct?

I believe your question is answered by Keven Hall's reply and the posts above your post in this thread. The braking distance is as correct as can be when considering the FSX limitations that the T7 operates in.

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Landing distance depends on a number of factors including Autobrake setting, landing weight, outside air temperature, runway condition, using or not using thrust reversers and many other factors. 

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outside air temperature, runway condition and many other factors. 

 

I doubt these factors are taken into account in P3D/FSX...

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I doubt these factors are taken into account in P3D/FSX...

The ones quoted are certainly factors that affect aircraft performance in FSX/P3D. Not correctly in the case of runway conditions but that can be fixed.

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Maybe the reason for you thinking the 777 is decelerating to quickly is caused by the lack off peripheral vision?

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What is your VREF on landing?

AB1 has a decel rate of 4 ft/sec.

So at 140 it's, that's around 2100 m. Add it 300 mtrs from threshold actual touchdown, total landing distance is around 2400 mts from threshold.

 

And idle thrust should add too much decel at all. FUll reverse gives more decel then AB1 but not sure exactly. So the autobrakes after full reverse is applied shouldn't really be in use due to the decel being greater then the force aplied.

 

So it sounds like for some reason it may be stopped far too quick.

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