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Calculation And Application Of Reverse Thrust  
User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Posted (7 years 9 months 4 days 4 hours ago) and read 7701 times:

Simply what the title states. i know that landing distances are calculated without the use of R/T and r/t is just an extra, but since it is used more often then not, how does the PilotFlying calculate how much to use? i.e. anything from idle reverse to max reverse?

also, once the reversers are unlocked, can the setting can be change once applied: for example, if the PF wants to turn off on a certain taxiway but knows that he is slowing too gradually, can he apply more reverse in the middle of reversing already?

i know reverse is actaully like a re-direction of the exhaust, but at full reverse, do the fans actually speed up?

do i make any sense?

one last thing- obviously as far as i know the more you pull back on boeing reversers, the more reverse thrust is applied?


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same for airbus A320 series- only the more you push the throttles down?


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Am i right about the actual use of the throttle quadrant for reverse?

i know i can count on you a.nutters!!

thanks,
highflyer

[Edited 2006-10-25 03:06:33]


121
22 replies: All unread, jump to last
 
User currently offlineZeke From Hong Kong, joined Dec 2006, 8861 posts, RR: 75
Reply 1, posted (7 years 9 months 4 days 4 hours ago) and read 7699 times:

Quoting HighFlyer9790 (Thread starter):
Simply what the title states. i know that landing distances are calculated without the use of R/T and r/t is just an extra, but since it is used more often then not, how does the PilotFlying calculate how much to use? i.e. anything from idle reverse to max reverse?

It is a bonus, can land no problems with no reverse, brakes get hotter, and you save some fuel.

Quoting HighFlyer9790 (Thread starter):
also, once the reversers are unlocked, can the setting can be change once applied: for example, if the PF wants to turn off on a certain taxiway but knows that he is slowing too gradually, can he apply more reverse in the middle of reversing already?

Just apply more brake, reverse is not very effective at slower speeds.

Quoting HighFlyer9790 (Thread starter):
i know reverse is actaully like a re-direction of the exhaust, but at full reverse, do the fans actually speed up?

Yes they do spool up a little, that is why when you have a reverser locked out, you have to be careful not to use it as it will increase thrust on the side the reverser is locked out on.

Quoting HighFlyer9790 (Thread starter):
same for airbus A320 series- only the more you push the throttles down?

Incorrect, very similar to the boeing, little levers at the front of the throttles that lift up to let the thrust levers to enter the reverse range.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 2, posted (7 years 9 months 4 days 3 hours ago) and read 7695 times:

Quoting Zeke (Reply 1):
Yes they do spool up a little

So, do you actually advance the throttles on a boeing once the reversers are unlocked?

Quoting Zeke (Reply 1):

thats actually what i meant, the further down in the reverse range you go the more powerful the reverse.



121
User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 3, posted (7 years 9 months 4 days 3 hours ago) and read 7688 times:

Thrust reversers provide additional deceleration to assist during landings and rejected takeoffs. They may also be used at times during taxi as a speed control device.

Quoting HighFlyer9790 (Thread starter):
once the reversers are unlocked, can the setting can be change once applied

With modern jet aircraft, once the reversers are deployed, the Pilot Flying (PF) may increase thrust on the engine up to about 70% for maximum aerodynamic deceleration. At a predetermined airspeed (should the PF continue to select maximum reversing) the FADEC (full authority digital electronic control) will reduce the amount of thrust to 50% or so. This is done primarily to prevent FOD from getting picked up and sucked into the engine and as you slow down, thrust reverser effectivity diminishes. (Note: early model jet engines without FADEC require the pilots to more closely monitor the amount of engine acceleration during reversing in order not to exceed design limitations).

Quoting HighFlyer9790 (Thread starter):
at full reverse, do the fans actually speed up

There are two basic types of thrust reversers, some have a pivoting door which when deployed, the upper and lower doors pivot to redirect exhaust gases over the top and bottom of the nacelle. The other type is a clam shell doors which close behind the jet pipe also redirecting the exhaust to create additional drag for deceleration. Yes, if the PF commands more thrust reverser effect the fans will speed up to apply more deflected exhaust to decelerate.

Quoting HighFlyer9790 (Thread starter):
do i make any sense

I must defer to your accountant on this particular matter. 

[Edited 2006-10-25 04:10:08]


"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 4, posted (7 years 9 months 4 days 3 hours ago) and read 7686 times:
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The Falcon 50's single thrust reverser has some very specific limitations:

The maximum duration of reverse thrust is 30 seconds except in an emergency. Allow 4.5 minutes between reverser cycles. Reduce reverse thrust N1 by 5% when operating in crosswinds when the aircraft speed is less than 10 to 15 knots.



2H4





Intentionally Left Blank
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 9 months 3 days 20 hours ago) and read 7655 times:

Quoting FlyMatt2Bermud (Reply 3):
They may also be used at times during taxi as a speed control device.

On the 744, reverse thrust during taxi is prohibited. In fact, most new generation Boeings, you can't use reverse thrust during taxi.


User currently offlineF14D4ever From United States of America, joined May 2005, 319 posts, RR: 4
Reply 6, posted (7 years 9 months 3 days 17 hours ago) and read 7623 times:

Quoting PhilSquares (Reply 5):
On the 744, reverse thrust during taxi is prohibited.

Prohibited how? By the rule book, by the FADEC, or by the flight management computer? Functionally, is there an airspeed threshold below which r/t is disabled?



"He is risen, as He said."
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 7, posted (7 years 9 months 3 days 17 hours ago) and read 7618 times:

Quoting F14D4ever (Reply 6):
Prohibited how? By the rule book, by the FADEC, or by the flight management computer? Functionally, is there an airspeed threshold below which r/t is disabled?

Well, first of all in the limitations there is a specific prohibition against using thrust reverse on the ground.

• icing conditions
• standing water or slush on runway
Note: Continuous ignition is automatically provided when nacelle anti–ice is on.
Reverse Thrust
Intentional selection of reverse thrust in flight is prohibited.
Use of reverse thrust while taxiing is prohibited.
Backing the airplane with use of reverse thrust is prohibited.

(Copied from our Vol 1.)

In addition, our SOPs require us to be out of reverse by 60 KIAS.


User currently offlineMD11Fanatic From United States of America, joined Oct 2006, 81 posts, RR: 0
Reply 8, posted (7 years 9 months 3 days 10 hours ago) and read 7552 times:

How does one actually increase thrust during reversing? Do you pull the reversers back (towards the rear) to spool the engines, or do you pull the reverse levers and move the throttles forward?

User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 9, posted (7 years 9 months 3 days 9 hours ago) and read 7546 times:

Quoting MD11Fanatic (Reply 8):
How does one actually increase thrust during reversing? Do you pull the reversers back (towards the rear) to spool the engines, or do you pull the reverse levers and move the throttles forward?

It varies, but most throttle quadrants have a position which will deploy the reversers and once fully deployed, you usually pull the throttles (or in some cases reversing levers) aft thereby commanding the engines to spool up, increasing drag effect and slowing the aircraft.



"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 10, posted (7 years 9 months 3 days 5 hours ago) and read 7508 times:

Quoting FlyMatt2Bermud (Reply 9):
It varies, but most throttle quadrants have a position which will deploy the reversers and once fully deployed, you usually pull the throttles (or in some cases reversing levers) aft thereby commanding the engines to spool up, increasing drag effect and slowing the aircraft.

primarily on airbus which has the reverse range? boeing do not have a reverse range to be pulled aft, do they?

Quoting FlyMatt2Bermud (Reply 3):
With modern jet aircraft, once the reversers are deployed, the Pilot Flying (PF) may increase thrust on the engine up to about 70% for maximum aerodynamic deceleration. At a predetermined airspeed (should the PF continue to select maximum reversing) the FADEC (full authority digital electronic control) will reduce the amount of thrust to 50% or so. This is done primarily to prevent FOD from getting picked up and sucked into the engine and as you slow down, thrust reverser effectivity diminishes. (Note: early model jet engines without FADEC require the pilots to more closely monitor the amount of engine acceleration during reversing in order not to exceed design limitations).

70% sounds like a lot of thrust...so obviously, there must be some kind of ratio for the air being sucked in vs. out? im not to technical but does N2 and the compressor have something to do with that?


thanks for your responces!!
highflyer



121
User currently offlineMD11Fanatic From United States of America, joined Oct 2006, 81 posts, RR: 0
Reply 11, posted (7 years 9 months 3 days 4 hours ago) and read 7488 times:

What about on the MD-11? I suspect pulling the reverse levers farther rear spools the engine.

User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 12, posted (7 years 9 months 3 days 3 hours ago) and read 7475 times:

Quoting MD11Fanatic (Reply 11):
What about on the MD-11? I suspect pulling the reverse levers farther rear spools the engine.

let me just see if im getting this. for boeing style throttles with no reverse range aft of the idle position, the mini levers are brought up the the throttles are advanced in the direction of T/O (forward) to spool up the engines to produce reverse thrust. same with and MD/DC aircraft?


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the only commerical aircraft series i know of having a reverse "range" is the A318/19/20/21. little levers are pulled up only instead of advancing the throttles, you can actually bring them back further aft of the idle position to the red reverse range.


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am i somewhat right?

i also checked www.flightlevel350.com but i didnt find any worthwhile footage from the cockpit showing the reverse process. if anyone can find one that would be great!

highflyer  wave 



121
User currently offlineCurmudgeon From Australia, joined Oct 2006, 695 posts, RR: 22
Reply 13, posted (7 years 9 months 2 days 17 hours ago) and read 7434 times:

No. The thrust levers are retarded on landing and they stay retarded. The reverse thrust levers are raised to the vertical position and then treated as throttles...the available reverse thrust is much less than typical forward thrust owing to the lower rpm and the partial and imperfect redirection of the engine airflow.

When the thrust reverse levers are raised, the reverser sleeves are unlocked and the forward thrust levers are prevented from moving from the idle position.

This scheme is true for all western built jets and may in fact be universal.



Jets are for kids
User currently offlineAirfoilsguy From , joined Dec 1969, posts, RR:
Reply 14, posted (7 years 9 months 2 days 9 hours ago) and read 7395 times:

Is there anything that locks out the reverse thrust levers during flight? Also, is this proper landing procedure for this aircraft? I have never seen any other type aircraft us reversers when the wheels are off the ground.


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User currently offlineVikkyvik From United States of America, joined Jul 2003, 9770 posts, RR: 27
Reply 15, posted (7 years 9 months 2 days 9 hours ago) and read 7389 times:
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Quoting HighFlyer9790 (Reply 10):
70% sounds like a lot of thrust...so obviously, there must be some kind of ratio for the air being sucked in vs. out? im not to technical but does N2 and the compressor have something to do with that?

Even though the engines may spool up to 70% (N1 or EPR, I assume), you will not be getting 70% max thrust as a braking force, for two main reasons:

1.) Reversers do not redirect the flow directly forward; rather, the flow is typically directed forward and outward from the engine at some angle. So you'd take the cosine of that angle times the total thrust in order to get the forward thrust.

2.) Most high-bypass turbofans on today's commercial airliners only reverse the bypass flow. So you'll still have the core flow going out the back, which will be providing forward thrust rather than reverse.

Notable exceptions to #2 include the engines on 737-200s, DC-9s/MD-80s, and probably some others of which I'm not aware.

~Vik



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 16, posted (7 years 9 months 2 days 4 hours ago) and read 7351 times:

Quoting Curmudgeon (Reply 13):
The thrust levers are retarded on landing and they stay retarded. The reverse thrust levers are raised to the vertical position and then treated as throttles...

So the little throttles are then moved forward after having been raised to the vertical position?



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User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 17, posted (7 years 9 months 2 days 4 hours ago) and read 7350 times:

Quoting HighFlyer9790 (Reply 16):
So the little throttles are then moved forward after having been raised to the vertical position?

Can't remember about the 320, but for all the Boeings I've flown the reverse thrust levers are at full reverse when they're vertical. To open the reversers, you simply lift up on the reverse thrust levers, when the thrust levers are at the stop. You will feel the reversers engage and is seems that's just above the horizontal position. From that point on it's just a matter of using the amount of reverse thrust you want to use.

On Wed morning (3am local) I arrived in BLR, our landing weight was 296.5 tons, and we used full reverse thrust to help in stopping. However we still had to roll to the end and backtrack as the taxiway at the end of 09 is unuseable for the 744.


User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 18, posted (7 years 9 months 2 days 3 hours ago) and read 7342 times:

Quoting PhilSquares (Reply 17):
for all the Boeings I've flown the reverse thrust levers are at full reverse when they're vertical. To open the reversers, you simply lift up on the reverse thrust levers, when the thrust levers are at the stop. You will feel the reversers engage and is seems that's just above the horizontal position. From that point on it's just a matter of using the amount of reverse thrust you want to use.

I can always count on you philsquares!! so essentialy, the farther back you pull the R/T levers, (towards the thrust levers) the more reverse thrust is being engaged...?




highflyer



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User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 19, posted (7 years 9 months 2 days 3 hours ago) and read 7335 times:

Quoting HighFlyer9790 (Reply 18):
I can always count on you philsquares!! so essentialy, the farther back you pull the R/T levers, (towards the thrust levers) the more reverse thrust is being engaged...?

You got it! On the 744s and the 757s I've flown the 12 O'clock position is max reverse. It will generally be just over 70%N1. It's limited by the FADEC/EEC.


User currently offlineHighFlyer9790 From United States of America, joined Jul 2005, 1241 posts, RR: 0
Reply 20, posted (7 years 9 months 2 days 3 hours ago) and read 7333 times:

Quoting PhilSquares (Reply 19):
12 O'clock position is max reverse

Theres the answer i was looking for! thanks everyone!

highflyer



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User currently offlineMD11Fanatic From United States of America, joined Oct 2006, 81 posts, RR: 0
Reply 21, posted (7 years 9 months 2 days 2 hours ago) and read 7324 times:

Nice thread everyone, good information.

At reverse idle, are the engine really idle or are they spooled up a little bit?


User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 22, posted (7 years 9 months 2 days 1 hour ago) and read 7317 times:

Quoting MD11Fanatic (Reply 21):
At reverse idle, are the engine really idle or are they spooled up a little bit?

On every jet type I have flown, when the reversers initially deploy the thrust does not change, or not noticeably.



"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
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