zachlog

Reverse Thrust

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Is reverse thrust just for sound effect or does it actually impact braking ?

Thanks,

Zachlog

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Yes it does provide forces to stop the plane. I think PMDG modeled that quite accurately. 

However, if you use autobrake 1, 2 or 3, the effect of reverse thrust on landing distance is minimal. This is because autobrake system maintains a specific deceleration depending on your setting (1/2/3). Therefore, even if you use full reverse thrust the plane will sense a strong deceleration and will brake less harder. In fact, I heard some real world pilots does not use autobrake 1 because the reverse thrust is strong enough that the brakes will toggle between on and off during the landing roll, which isn't ideal.

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Cascade type TRs like those installed on the CFM-56 only divert the fan airflow and as a consequence aren't very effective as you begin to slow below 100kts to being basically neutral at 80 knots...

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Hi Zachlog

 

Seeing that you go backwards when you select reverse thrust in PMDG I'd say it's modeled rather well. (not recommended :happy:)

 

From an operational point of view Jetstream96 is absolutely right, the autobrake maintains a specific rate of deceleration and the stopping distance doesn't chance but just to point out this is on a DRY runway. On a dry runway the stopping distance when calculating landing distance required would be exactly the same whether you used full reverse or idle reverse.

 

Here is an example from the OPT onto a generic runway

 

DRY RWY, NIL WIND, OAT 15C, F30

(All Reversere Thrust) - AUTO BRAKE 3 = 1756M

(NO Reverse Thrust) - AUTO BRAKE 3 = 1756M

 

As soon as you land on a WET runway reverse thrust has more of an impact on stopping performance as the wheel brakes become less effective although the distance is negligible. 

 

WET RWY, NIL WIND, OAT 15C, F30

(All Reverse Thrust) - AUTO BRAKE 3 = 2022M

(NO Reverse Thrust) - AUTO BRAKE 3 = 2036M

 

Reverse thrust has a much more significant impact to stopping distance when landing on a contaminated runway, one with standing water/snow/ice etc

 

BRAKING ACTION MEDIUM, NIL WIND, OAT15C, F30

(All Reverse Thrust) - AUTO BRAKE 3 = 2219M

(NO Reverse Thrust) - AUTO BRAKE 3 = 2647M

 

You may ask why use revere thrust at all on a dry runway if performance is the same! One reason could be a quick turnaround! Using Reverse Thrust means the wheel brakes will not have to be used as much so Brake Cooling doesn't become an issue. We have to wait for a certain amount of time for the brakes to cool before dispatch.

 

I know this expanded on your actual query but it's something you might find interesting!

 

Have a good weekend! 

 

 

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