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Thrust reversers?

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michael707767 said:
actually, thats BS. Aircraft are certified for take off and landing distances without TRs, so there would be no penalty.

You'd think so, but part 25 allows for the manufacturer to demonstrate WET Runway accelerate-stop distance using Thrust Reversers if installed. So, here at CHQ, on our 2 airplanes without TRs, we do take a weight penalty (for takeoff only) with a wet runway (note that if the runway is grooved it's not really wet, so in reality we almost never actually have to apply this).

The bigger problem with these 2 pos's is the weight and balance issue. One is a "ghost" plane that circulates the system, the other is dedicated to UA with the new UAX paint scheme. The problem with these planes is twofold; they have the same MZFW as a 140, which means they really can only carry 45 adults or so. In addition, the loss of the galley supplies is more for balance issues (without TRs, the basic moment is extremely biased to the nose). As we acquire more 170s for UA we are reducing our 50-seat flying for them by 2 shells, which is supposed to relegate these 2 pos's to charter only. I can't wait.

As to the op's question, I've had a few big iron drivers ask me why we don't use our TRs. In reality we do, but our SOP is to deploy the buckets in idle reverse only, unless needed. Part of the reason the 2 aircraft without the reversers are getting better brake life is it removes the temptation for new jet drivers to spool the TRs on a 10k runway just because it "sounds cool". (And before anyone flames, when I was new to the airplane I gave into the temptation myself a time or three, maybe ;))
 
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Last time I sat in the Jumpseat of a TSA plane the capt. was explaining to me that they take a weight penalty on planes without TR's.

You think? I bet it adds a lot to your accelerate/stop dist.
 
blzr said:
You think? I bet it adds a lot to your accelerate/stop dist.

With all due respect, I believe that those figures are calculated without the use of reverse. After all, what is one of the biggest reasons you'd need to stop before V1, engine failure right? So you bag an engine and need to stop, well you've only got one reverser now anyway, AND it's probably going to be giving you some assymetrical reverse that could pose a problem if you need alot of it.

But I could be wrong. Comments or additions?
 
I have never heard of an airplane being certified with TRs. As 91,100 said, if you need to stop during takeoff, its likely to be because of an engine failure. I have never flown an aircraft that was certified with TRs, have asked the question everytime.
 
91 said:
With all due respect, I believe that those figures are calculated without the use of reverse. After all, what is one of the biggest reasons you'd need to stop before V1, engine failure right? So you bag an engine and need to stop, well you've only got one reverser now anyway, AND it's probably going to be giving you some assymetrical reverse that could pose a problem if you need alot of it.

But I could be wrong. Comments or additions?

TR's are never never never used in the calculations when it comes to stopping the aircraft.

Think of them as gravy. Nice to have to help get you stopped but not required nor used in the certification numbers.
 
The CRJ takes a takeoff penalty for a inoperative TR. Don't know why but thats the way it is.
 
In a ERJ, if you're really serious about having to stop and bury the pedals, by the time the TR's deploy and spool you're down to about 70-80 knots or less anyway. They are of little or no value in normal op's and of marginal value in a panic stop, although in that case every little bit helps.

As some have accurately stated, they are not used for Part 25 certification of the performance #'s, however there is indeed an exception for wet runway performance. If there are no TR's (not sure about deferral of one), there is a weight penalty for wet runways.

Now if we could only find a clear-cut definition of "wet runway" we'd be all set. That is for another thread...
 
TR's can be used in the calculations of take-off performance. They are never used for calculations when it comes to landings. I have found this out due to numerous amounts of research at my company. On our 145's with thrust reversers, you may defer 1, and only one thrust reverser at a time. Most who fly the airplane understand Qty inst...2, num req 1. However, we also have a s#%tload of european ones that have no thrust reversers. How is it that we can fly some of the same airplanes with no thrust reverser, but other we must have one operational. I was told that you have to account for the worst case scenario. Basically, the reason you can defer one and only one if it is installed is because if you have an egine failure before V1(accelerate stop), you will have the the operating engine AND it's reverser available too you. They did give us some guidance as far as part 25 certification, but I can't find it right now, if I do, I'll post it for you
 
The weight penalty the guy mentioned on the TSA 145s is most likely a CG issue. Most of our non TR birds are former swiss planes with a bunch of HUD equip up front (hud removed but the weight is still there) and less weight from the lack of reversers way aft. Unless we have a seriously load of bags, we often can't get 50 peeps in CG. Of course, sometimes those bags put you over gross weight.
 
91 said:
With all due respect, I believe that those figures are calculated without the use of reverse. After all, what is one of the biggest reasons you'd need to stop before V1, engine failure right? So you bag an engine and need to stop, well you've only got one reverser now anyway, AND it's probably going to be giving you some assymetrical reverse that could pose a problem if you need alot of it.

But I could be wrong. Comments or additions?

You right, you right, glad you brought that up. They are just an added bonus.
 

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