Aircraft Braking Question
Join Date: May 2003
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Wasn't there also a similar incident/accident with a Lufthansa A320 in Warsaw some time ago to what avioniker refers to?
I'll stand corrected but wasn't there some combination of tail-wind and water logged runway which caused hydroplaning? And was it this that prevented wheel spin-up which in turn prevented spoiler deployment? This (if I'm not mistaken) had the effect of not getting the weight on the squat switches so the reversers were locked out!
Sorry if this is/was deemed to be inaccurate.
Dan
I'll stand corrected but wasn't there some combination of tail-wind and water logged runway which caused hydroplaning? And was it this that prevented wheel spin-up which in turn prevented spoiler deployment? This (if I'm not mistaken) had the effect of not getting the weight on the squat switches so the reversers were locked out!
Sorry if this is/was deemed to be inaccurate.
Dan
While travelling back from Crete on a MON A321, I noticed that the reversers made a terrific noise from inside the cabin unlike a 737. I have not been on an airbus for a long time, but was wondering weather all airbus's have to use max reverse on landing or weather it was just pilot preference at this time?
Reverse thrust cannot contribute to much of the stopping potential of a jet aircraft on landing if the landing distances are calculated without the use of reverse thrust?
Many Thanks
Dan
Reverse thrust cannot contribute to much of the stopping potential of a jet aircraft on landing if the landing distances are calculated without the use of reverse thrust?
Many Thanks
Dan
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Easy,
No aircraft "has" to use max reverse thrust on landing. Sounds like it was pilot technique. Certainly, pilots will use more reverse on a short and/or wet runway.
Reverse thrust will contribute to the stopping distance based on the retarding force. Assuming a constant reverse thrust force (not necessarily the case) then the reversers will dissipate more of the aircraft's energy if used at higher speeds, versus used at lower speeds. Hence, a 10 second use of reverse at higher speeds will mean the brakes have to absorb less enery than a 10 second use of reverse at lower speeds.
I suspect this is why it is often said "reversers are more effective at higher speeds"
Hawk
No aircraft "has" to use max reverse thrust on landing. Sounds like it was pilot technique. Certainly, pilots will use more reverse on a short and/or wet runway.
Reverse thrust will contribute to the stopping distance based on the retarding force. Assuming a constant reverse thrust force (not necessarily the case) then the reversers will dissipate more of the aircraft's energy if used at higher speeds, versus used at lower speeds. Hence, a 10 second use of reverse at higher speeds will mean the brakes have to absorb less enery than a 10 second use of reverse at lower speeds.
I suspect this is why it is often said "reversers are more effective at higher speeds"
Hawk
Oh right i see thanks for the reply. I read in an earlier post that in the airbus manual it says to use max reverse, hence why I thought this was the case with airbus aircraft.
So reverse thrust is more efficient at higher speeds - is this why the reversers are cancelled when at 60knots?
Many Thanks
Dan
So reverse thrust is more efficient at higher speeds - is this why the reversers are cancelled when at 60knots?
Many Thanks
Dan
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Dan, I haven't seen any airbus manuals, but I doubt they say to use "max" thrust for all landings.
On small jets, use of reverse thrust can poses some controllability problems, and hence those pilots are hesitant to immediately go to full reverse on landings. Typically, in these cases, the pilot concentrates on applications of brake, and steering of course. Reverse takes a much lower priority, and the usual sequence of events are to first get reverse thrust deployed at idle, and then slowly increase power in a controllable way. And often the aircraft is well decelerated by the time full, or close to full, rev thrust is attained.
And here's one to think about. With any crab on, eg for a slippery runway with a cross wind, then the added use of reverse thrust will actually pull the aircraft towards the downwind side of the runway. When this starts to happen, immediate reduction of power, among other things, can be required to keep the aircraft from drifting off the downwind edge of the runway!!
Yes, you could say rev thrust is more "efficient" at higher speeds, I prefer to think of it as the reverser dissipates more energy when used at higher speeds than at lower speeds, hence less brake wear.
The aircraft type/engines can have different speeds to be out of reverse. For example, for some, only idle thrust with reversers deployed below 60 kts, and some even allow an appreciable amout of thrust up til the time the aircraft has stopped.
Hawk
On small jets, use of reverse thrust can poses some controllability problems, and hence those pilots are hesitant to immediately go to full reverse on landings. Typically, in these cases, the pilot concentrates on applications of brake, and steering of course. Reverse takes a much lower priority, and the usual sequence of events are to first get reverse thrust deployed at idle, and then slowly increase power in a controllable way. And often the aircraft is well decelerated by the time full, or close to full, rev thrust is attained.
And here's one to think about. With any crab on, eg for a slippery runway with a cross wind, then the added use of reverse thrust will actually pull the aircraft towards the downwind side of the runway. When this starts to happen, immediate reduction of power, among other things, can be required to keep the aircraft from drifting off the downwind edge of the runway!!
Yes, you could say rev thrust is more "efficient" at higher speeds, I prefer to think of it as the reverser dissipates more energy when used at higher speeds than at lower speeds, hence less brake wear.
The aircraft type/engines can have different speeds to be out of reverse. For example, for some, only idle thrust with reversers deployed below 60 kts, and some even allow an appreciable amout of thrust up til the time the aircraft has stopped.
Hawk
Oh right i understand fully now. So when you are slowing down a large jet aircraft, does it require a large amount of concentration to keep the aircraft travelling in a straight line.
Do the large forces assosciated with applying braking and reverse thrust make the aircrafts movements more liable to become unstable?
Many Thanks
Dan
Do the large forces assosciated with applying braking and reverse thrust make the aircrafts movements more liable to become unstable?
Many Thanks
Dan
