Hi there,

 

everytime I flew in real live the landing roll and brake time was pretty high whereas in fsx it looked to be pretty short. Thought it's only my imagination.

 

But I bought the pmdg 777 and also the wonderful aerologic pilotseye dvd. Now I got some good videos to catch the time.

 

Here are my findings of the pilotseye real landings(all Flap 30. Time catched from time of reverser deployment until 80kts and manual braking):

 

1st landing: 159kts (Vref+10) Autobrake 3: 23,5seconds

2nd landing: 150kts Autobrake 2: 24seconds

3rd landing: 151kts Autobrake 2: 24seconds but the FO disconnected ab at over 100kts so no exact value here

 

Unfortunately the 1st and 2nd landings were outside/inside mixed landings and I am not sure if there were a cut which lengthened the time.

 

So today I did a flight eddp->phnl and got a vref of 137kts (final speed 147kts) with ab2. I reached 80kts after 8seconds with idle reverse.

 

I took a look in the manuals but didn't found a deceleration value. So I looked inside md11 sys manual and got 2 values: 6,5ft/s² and 9ft/s².

 

Some math:

final speed on touchdown: 150kts (=253ft/s) down to 80 kts (=135ft/s) so 118ft/s to decelerate

v = a * t so t = v / a

t = 118 / 6,5 and 118 / 9

t = 13seconds and 18seconds

 

 

Now my question is if the friction within fsx is much too high or if i am really wrong and it's only my imagination? Also I thought weight doesn't matter because of fixed deceleration rates or am I wrong here?

 

What do you think? My findings are that you reach your taxi speed much too fast but could also be only imagination. Also imperial system isn't my foreign system so my calculations can be wrong here also.

hi Stefan, see this topic here

 

http://forum.avsim.net/topic/432311-777-stops-in-a-dime-is-this-realistic/

 

It got sidetracked in the end though.

Yes I followed your topic. But when you do a full brake action the fsx friction is not the highest number I think. As said... I will by no means say pmdg did something wrong. The fast deceleration is on every modell and as the ground handling with idle thrust etc. isn't perfect either I THINK it could be because of the friction model. I posted here on support forums because the 777 is the only plane where I got some video material to catch the time and I have a damn good simulation. So this thread is more a question with some calculations and observations I wrote.

 

Wanna know whether I (or my calc's) am completely wrong or if there is some thruth within.

 

Edit: I do not know the reported brake efficiency on all those landings. 1st landing was with clear weather on a dry day, 2nd and 3rd landings on wet runway. PHNL had good weather but FSX only simulates dry runway I think.

As long as autobrake system can maintain the deceleration rate required, wind, runway friction, etc. do not matter. Your best bet is to film a video after landing using just autobrake and measure actual deceleration. Then compare to autobrake deceleration speeds.