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Captain Kevin

Thrust Reverser Question

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Tried looking through the Introduction Manual, the Flight Crew Operating Manual, and a forum search, but couldn't find anything, so here goes. Noticed that in the Boeing 747-400 with PW4056 engines, if I go full reverse, EPR is 1.44 with N1 hitting 106.3. Is that normal?

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Dunno but an excellent eye for details, brother Kevin, and I too am now curious.

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Someone asked about this before release asking if the engines will go that high in reverse based on what was observed  at 5:15

 

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Yes, I remember seeing that question asked, but it appeared as though that was based off of the General Electric engines. Not sure if the same applies to the Pratt & Whitney engines.

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Engines are engines. Granted, they're controlled by slightly different (software/hardware) methods, but in general they're all going to behave the same way: they spin (one of them spins the 'wrong' way), produce thrust when you move the throttles forward, and move the airplane.

 

Why would one of them be randomly different in terms of function?

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Engines are engines. Granted, they're controlled by slightly different (software/hardware) methods, but in general they're all going to behave the same way: they spin (one of them spins the 'wrong' way), produce thrust when you move the throttles forward, and move the airplane.

 

Why would one of them be randomly different in terms of function?

Electronic software limitation? I don't know. That's why I asked the question in the first place, because I don't know the answer.

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It's difficult to find information on reverse thrust levels in manuals. I have one GE manual which (rather) broadly states that N1 is limited to 100% during reverse thrust (with both reverser translating cowls deployed on the engine). However, another manual states:

 

"The ECU calculates the reverse thrust demand as a direct function of TLA (thrust lever angle) position. This limits reverse thrust to 90% of maximum rated thrust."

 

The RB211 and the PW4000 do not use EPR for control during reverse operations. The airflow around the EPR sensors may be disturbed during reverser operation. They use N1 control during reverser operation, but no (unambiguous) max rpm limits are given in my manuals. The PW EGT limit during reverse operation is the same as takeoff (650C). During maintenance, only 30%N1 reverse is allowed.

 

In the maintenance manual (for the RB211), the following limitation is specified:

 

"91%N1.... for more than 40 seconds".

 

The manual does not say if the FAFC controls the N1 to a value above or below this limit.

 

Of course, different engine types have to have limits according to their particular design.

 

Cheers

John H Watson

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Of course, different engine types have to have limits according to their particular design.

I figured as much. I guess I was surprised that I was able to hit 106.3% N1 with the PW4056.

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I guess I was surprised that I was able to hit 106.3% N1 with the PW4056.

 

 

All I know is that the PW N1 limit is 111.4% and the N2 limit is 105.5% during forward thrust ops. If you apply the GE 90% safety value it would give 100.26%N1 (111.4 x 90%), but it's not a GE.  

 

Has anyone found a PW reverse video on YouTube? All I could find was one labelled "Delta Boeing 747-400 Landing at New York JFK Cockpit View". I didn't notice an extra digit being added to the N1 readout.

 

Cheers

John H Watson

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