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Alex Kulak

PMDG not stopping fast enough

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No, reverse thrust has more effect whilst the aircraft is at high speed, the slower you get the less effective it is.

 

In the real world at least..


Rob Prest

 

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Yes correct :) Reverse thrust saves on brake life since the Autobrakes have to do less work, also keeps the brake temps down.

 

 

Looking at it the other way round, autobrakes save on engine wear&tear and keep the noise down.


What happened to AVSIM

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Looking at it the other way round, autobrakes save on engine wear&tear and keep the noise down.

Hehe true :) Qatar airlines don't even use reverse thrust on rollout in Doha on the Airbus fleet


Rob Prest

 

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I didn't get it. Do you mean that reverse thrusts effectiveness is directly proportional to the speed on the runway ?  I thought the reverse effectiveness should be always the same from when applied to around 60 knots when disengaged.

 

Basically, when you land with autobrake armed and activate reverse, braking force created with reversers is strong enough to achieve preselected autobrake deceleration value, so little or no braking is provided by wheel brakes. As you are slowing down, braking force generated by reverser cannot achieve preselected autobrake deceleration value anymore, so wheel brakes kick in to help reversers to achieve preselected value.


[color=#a9a9a9][size=1][size=4][img]http://forum.avsim.net/public/style_images/flags/rs.png[/img][/size] Lj. Prodanovic[/size][/color]

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With carbon fibre brakes, reverse thrust will hardly be used, except for those rare circumstances when (no, I don't really know about that stuff; just following discussions :ph34r:)

 

- even carbon brakes get really hot (high weight/speed, short runway)

- short turnaround time (for brakes cooldown)

- noise abatement procedures NOT prohibiting rev thrust.


What happened to AVSIM

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Hehe true :) Qatar airlines don't even use reverse thrust on rollout in Doha on the Airbus fleet

 

At that runway they do not need to brake at all. Aircraft will stop eventually.  :lol:


[color=#a9a9a9][size=1][size=4][img]http://forum.avsim.net/public/style_images/flags/rs.png[/img][/size] Lj. Prodanovic[/size][/color]

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I have been checking this out on the internet, and there seems to be a considerable amount of disagreement regarding just how effective thrust reversers are. I am certainly no expert, but I would be surprised if the effectiveness of thrust reversers at high speeds was not significant.....or are we only talking about how much extra stopping power they provide when used with the brakes?


Christopher Low

UK2000 Beta Tester

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I have been checking this out on the internet

 

Even if that's true, I wouldn't include that in your posts.  It immediately makes me think "watch out guys, we got an internet scholar here!!!"

 

...and in this case, it proves to be true.  Details follow:

 

 

 


I am certainly no expert, but I would be surprised if the increase in stopping power at high speeds was not significant. To be honest, I have seen a LOT of landings at Manchester and Edinburgh airports over the years (the two airports that I am most familiar with), and thrust reversers appear to be used over a large percentage of the entire rollout in a large number of cases

 

The problem with reading things on the internet is that you have no idea as to what their credentials are, and, unless they specified the type of thrust system, their commentary may be invalid.  Certain thrust systems actually reverse the thrust, throwing it forward, which is where the name came from.  Others simply divert the thrust in a direction other than out of the rear of the engine to reduce thrust below idle.  Obviously, the thrust system throwing the thrust forward, and more forcefully so, will be more effective than simply diverting it away from the rear of the engine in general.  You can't categorically say they're all really effective, or not effective.  That's like saying all props are good a climbing, or all props are very effective brakes on the idle stop.

 

 

 


In my book, that does not equate with "negligible".

 

I think his quote was more aimed at the fact that the plane is going to stop in X feet on a dry runway either with TR or without.  Autobrakes, being so prevalent, set a deceleration rate and maintain that.  It will maintain that with or without TR.  The difference between its use, and lack of use is therefore negligible.


Kyle Rodgers

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It differs by company how to deal with reverse. Some use them all a long till 80kt, others only idle as SOP depending on rwy lenght and weather. 

 

John

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You responded too quickly, Kyle! I updated my post several times because I wasn't happy with what I had written.


Christopher Low

UK2000 Beta Tester

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Also, remember that the airplanes are certified to stop without reversers. The brakes are the main stopping device, the reversers only help to reduce the wear on the brakes.

 

So, don't rely on the reversers too much to help you stop.


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As discussed above, we have touched on the fact that autobrake achieves same braking distance with or without the use of reverse thrust as autobrake applies a specific deceleration rate between the different settings.

 

 

 

However and for what it’s worth; When you talk about MANUAL braking landing distance calculations with real world 737NGs, reverse thrust is not factored in to the distance used as well because its effectiveness is subject to the amount of thrust applied. That amount applied is always a unknown variable and thus cannot be considered as a factor when calculating distance.

 

Anyways, Use both however you feel fit for the situation. who really cares about the NGX's brake and engine wear, its not like any of us pay for maintenance. B) 

 

 


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I know for a fact that a 737-700 can stop in dry conditions and make a taxi way (appox 2/3s down) the runway, with no reverse. Just using brakes,  RTO and/or manual braking, and spoilers, I always pick a wing seat, to see some flap and reverser action, so I know hat is going on.

 

This was with flyglobespan, into London Stansted. EGSS. About 2006-ish

 

Sadly saving a bit of fuel on reversing didn't save the airline from going bust. :(


J u l ia n D i a m a n d i s

 

 

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Going back to the original question, how early are you starting your flair? I read the manual, but didn't like the idea of beginning my flair 10' from the ground...it just looked like I was going to slam into the ground. So, I started my flare around 50' like I do in most other turbojets, and always used up the whole runway to get the dang thing stopped. Once I finally got myself to trust the dang thing, and perform my flare at 10', I have no problems getting stopped (with, or without reverse thrust). Just a thought.

 

My suggestion is to allow the aircraft to perform a full autoland, and see what happens. Then you'll know if it's the aircraft or the pilot causing your problems. In my case, the results of that test are why I now flare at 10', lol!


Steve T. Midgley

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I read the manual, but didn't like the idea of beginning my flair 10' from the ground...

 

 

On auto land the aircraft FD seems to start its flare at 50 feet.  Even with a late flair I can still stop. I don't think it is his (posters) landing technique. Something is interfering possibly  FSX, or maybe the calibration of the thrusters.

 

I have the Saitek Yoke, and throttle.  I have had it a while, over 2 years, sometimes it seems to surge power on the ground unexpectedly, going a bit goofy sometimes.


J u l ia n D i a m a n d i s

 

 

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