Config flaps warning when reverser fully deployed

[HKoeck 2]

I wonder if this is normal for the CRJ. After touchdown when reversers are fully deployed and N1 Rev is above 75 (little blue arrow), I get a config flaps warning. 

TCA Throttle is correctly calibrated and works well. 

[HKoeck 2]

And I would like to add that the plane is not moving backwards when reversers are deployed unless N1 above 75 (blue arrow). Always thought idle reverse is enough to move the plane backwards.

[JRBarrett 675]

1 hour ago, HKoeck said:

And I would like to add that the plane is not moving backwards when reversers are deployed unless N1 above 75 (blue arrow). Always thought idle reverse is enough to move the plane backwards.

 

 

The CRJ is not designed or approved to back up using reverse thrust. Idle reverse would not be sufficent - it would probably take almost full engine power to get the aircraft to move backwards, and using max reverse while standing still would quickly cause severe damage to the fan blades and engine inlet.

 

The CRJ and all modern jet airliners use bypass reversers. These do not actually “reverse” the engine thrust at all. When the reversers are deployed, blocker doors inside the engine bypass duct close. This stops all forward thrust being produced by the main engine fan, (The fan is the source of most of the engine’s forward thrust). When the blocker doors are closed, the air from the fan is redirected sideways out of vents in the cowl. 
 

When the fan air path is blocked while the aircraft is moving forward, it causes the fan blades to produce an enormous  amount of drag and resistance to air entering the engine inlet. It is that resistance which causes  the aircraft to decelerate.
 

The only true “thrust” reversers were found on old low bypass engines like the JT8D used on the DC9, 727, 737-200 and MD80. Those used clamshell doors which were deployed to block and redirect the main jet exhaust flow from the back of the engines. Only aircraft using that kind of engine and reverser can back up using reverse thrust. 

Now in a simulator like MSFS, the aircraft might move backwards with a high reverse thrust setting. I do not know how well or accurately the actual aerodynamics of a modern bypass reverser are modeled in the sim. The reverse effect is probably simplified.

 

[JRBarrett 675]

2 hours ago, HKoeck said:

I wonder if this is normal for the CRJ. After touchdown when reversers are fully deployed and N1 Rev is above 75 (little blue arrow), I get a config flaps warning. 

TCA Throttle is correctly calibrated and works well. 

You shouldn’t get a config flaps warning unless the aircraft “thinks” it is in takeoff mode. Are you landing with flaps all the way down at 45 degrees? 

[HKoeck 2]

yes I do but  I only get the warning when reversers are fully deployed, not in idle, strange.

But thanks for you great explanation, much appreciated.

[HKoeck 2]

Problem solved, I had 'Toggle Reverser' in stead of 'Hold Reverser' assigned to my TCA, no it works.

[metzgergva 210]

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