Corsair2
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Dassault Falcon Thrust Reverser

Sat Oct 21, 2006 11:24 pm

Recently I was returning from a flight and saw a Dassault Falcon 900 landing. I noticed that it only has one thrust reverser and it is on the center tail engine. It was an awesomely loud noise! Why did Dassault only use one thrust reveser in the design of this plane? If the T/R fails can one defer it through the MEL (Minimum Equipment List)?
"We have clearance Clarence. Roger, Roger. What's our vector Victor?"
 
N231YE
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RE: Dassault Falcon Thrust Reverser

Sat Oct 21, 2006 11:44 pm

Like on the Airbus A380, which only has 2 "thrust reversable engines," and the BAe 146/ Avro RJ85, which doesn't have any, thrust reversers are used as a helpful supplement and to reduce wear on the brakes, but are often not needed.
Why The Airbus A380 Has Only Two Thrust Reverser? (by 747400sp Jul 2 2006 in Tech Ops)
Thrust Reverser Importance (by Videns Dec 11 2004 in Tech Ops)
 
corey07850
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RE: Dassault Falcon Thrust Reverser

Sun Oct 22, 2006 12:16 am

Don't know how accurate this is, but I was once talk that noise of Falcons during reverse is actually compressor stall... Again, don't know how valid that is though
 
Corsair2
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RE: Dassault Falcon Thrust Reverser

Sun Oct 22, 2006 2:45 am

N231YE- That makes sense. Having more thrust reversers would also be more parts to fix when it is broken. When an airplane is on an MEL restriction (i.e. MD-80 with JT8D-219's) for one thrust reverser inop it can only be deferred for a short time period.

Corey07850- It probably is a compressor stall as the back pressure on the compressor from the T/R disrupts the airflow and cause the compression ratio to be out of synch with N1/N2 rpm.
"We have clearance Clarence. Roger, Roger. What's our vector Victor?"
 
BAE146QT
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RE: Dassault Falcon Thrust Reverser

Sun Oct 22, 2006 8:38 am

Quoting Corsair2 (Reply 3):
It probably is a compressor stall

Really? I thought that such events were generally considered a Bad Thing.

Normally that's because a stall means that either your engine is worn out or you took off with a high crosswind component.

But surely the stall itself causes damage? It's basically hot and dirty combustion gasses being blown forward into your nice shiny fan - which isn't designed for it - because of a low pressure region around the fan disk, isn't it?

To put it another way, is there realy ever a time when a compressor stall is considered a positive thing? Or even acceptable?
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Fly2HMO
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RE: Dassault Falcon Thrust Reverser

Sun Oct 22, 2006 11:15 am

I highly doubt it is from a compressor stall. The engine would spool down and die, not up. It's probably just the shear from the exhaust being sharply redirected.

JT8Ds make one hell of a racket when in reverse, and they're not stalling.

Quoting Corsair2 (Reply 3):
It probably is a compressor stall as the back pressure on the compressor from the T/R disrupts the airflow and cause the compression ratio to be out of synch with N1/N2 rpm.

I was taught in turbines class that unless you actually block the exhaust someway, the pressure ratio remains the same, therefore, T/R has no effect.
 
liedetectors
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RE: Dassault Falcon Thrust Reverser

Sun Oct 22, 2006 12:05 pm

When you design airplanes, you design it such that items such as T/Rs are considered nonessential items, that way if it should fail prior to the flight, you can still dispach. Also while it is nice to have them, landing and stoping distances are computed assuming no T/R. All the certified landing and stoping distances are determined without the T/R as well. As mentioned before, airplanes such as the A380 only have two, the BAe 146 doesnt have any, and they are locked out all together on the F100, clearly, the TR is nonessential to normal operations.

Should the T/R fail when deployed on landing, the pilots are trained to take action to stop with out them.
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G4Doc2004
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RE: Dassault Falcon Thrust Reverser

Mon Oct 23, 2006 12:15 am

I work on a 900, S/N 39. The center reverser is indeed on the MEL, but landing weights and runway lengths are more critical, as is why the flightcrew is briefed if the TR is MEL'd. The brakes on the 900 are pretty stout. As for the noise, it is merely the core air hitting the buckets.....most TR buckets are vertically oriented, so alot of the noise is directed up. These TR's are oriented horizontally, so more of the noise of the high speed core air being suddenly redirected is heard.
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N231YE
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RE: Dassault Falcon Thrust Reverser

Mon Oct 23, 2006 12:30 am

Quoting Corsair2 (Reply 3):
When an airplane is on an MEL restriction (i.e. MD-80 with JT8D-219's) for one thrust reverser inop it can only be deferred for a short time period.

I apologize about any word confusion; if the T/R is broken, then obviously, it is to be fixed, otherwise, it isn't a necessity for most landings (when it is working).

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