Question re deceleration when an aircraft lands.

Comhrá

I'm not a pilot but I'm curious when watching airliners landing, how much of the deceleration after touch-down comes from (a) the brakes (b) reverse thrust and (c) spoiler deployment.

I'm guessing brakes 60%, reverse thrust 30% and spoilers 10% but I have been known to be wildly wrong about this sort of thing before

Thanks for any enlightenment!

folbotcar

Actually this question would be good for the ' Ask an airline pilot thread'.

Not sure of the proportions myself but the brakes do provide most of the stopping power. Landing distances are worked out without reverse thrust. In fact some airports ban the use of TRs.

The spoilers main job would be to cut lift even though it would have a retarding effect.

So it's mainly the brakes in fact.

martinsvi

state of the runway plays a huge role, wet runway with some standing water or ice means brakes are less effective over reversers account for about 70% (30% reverse thrust) of braking power, whereas in dry sometimes reversers are not used at all as their efficiency is close to 0

http://flightsafety.org/files/alar_bn8-5-wetrwy.pdf

basill

And to see why not selecting even idle reverse is a big no no on an Airbus see the attached.

http://www.iasa-intl.com/folders/belfast/Congonhas/A320-throttles.htm

cerastes

Hmm, Id always thought reverse thrust was about 70% of braking
Ive never experienced a landing where you couldnt either see or feel the reverse thrust in effect and the brakes applied after at the end or in some cases seemingly not at all, either in the dry or in moderate wet, never really been in anymore extreme conditions.

folbotcar

Yes it's counterintuitive isn't it? But brakes are the primary stopping mechanism. All the sound and fury of the reversers gives the impression of massive braking. But they work best at higher airspeeds.

Also remember when operating on long runways not much braking may be needed anyway after the reversers are stowed. Avoiding use of the brakes also saves money.

My boss is always telling me not to use the brakes to save him more money for his other interests.:mad: Maybe he should retrofit reversers!

andy_g

Varies hugely down to Rwy conditions brakes depending on the airline will be used at 80kts and below other airlines 60kts or below.

cerastes

folbotcar wrote: »

Yes it's counterintuitive isn't it? But brakes are the primary stopping mechanism. All the sound and fury of the reversers gives the impression of massive braking. But they work best at higher airspeeds.

Also remember when operating on long runways not much braking may be needed anyway after the reversers are stowed. Avoiding use of the brakes also saves money.

My boss is always telling me not to use the brakes to save him more money for his other interests.:mad: Maybe he should retrofit reversers!

Counterintuitive? I dont know, I appreciate its at higher speed thrust reverse does its work, its where higher forces would act on the brakes if they were applied, increasing heat, wear and reducing life, hence the use of thrust reversers? maybe even allow for brakes to be smaller, lighter, although Im sure they have some limit there in the event wheel braking has to be applied in an emergency where thrust reverse isnt available? maybe braking to destruction?
I wasnt aware runway conditions were so significant for the effectiveness of reverse thrust? Id thought this was a big reason for them, due too reduced effectiveness of wheel brakes, to aid limit skidding and help get the weight of the aircraft on the ground killing lift over the root of the wing?

*Kol*

andy_g wrote: »

Varies hugely down to Rwy conditions brakes depending on the airline will be used at 80kts and below other airlines 60kts or below.

That doesn't sound correct. You would be a long way down the runway if you waited until 80 knots to use the brakes. Auto braking starts immediately at touchdown. Reversers are deployed straight away after touchdown if required and will be stowed by 60 knots.

Stovepipe

Auto braking is effectively ABS and is selectively applied by the braking computer. Apart from that, look at 146s and turboprops. No reverse on the 146 and most turbos don't use reverse pitch except on the shortest runways.......@folbotcar, next time your boss says that, ask him how expensive tidying up after a crash would be.

eatmyshorts

Stovepipe wrote: »

Auto braking is effectively ABS .

Anti-skid is the ABS-like function.

Autobrake is manually selectable to achieve a desired deceleration rate. Therefore, using more reverse will result in lesser wheel braking in order to maintain the desired rate.
A contaminated or wet runway will use more braking than a dry one for the same given selected autobrake setting.

Then there's Brake-To-Vacate which is more complicated!

Our SOP is to always use full reverse unless idle is enough for the performance required.
At least idle reverse must always be selected.

folbotcar

Stovepipe wrote: »

Auto braking is effectively ABS and is selectively applied by the braking computer. Apart from that, look at 146s and turboprops. No reverse on the 146 and most turbos don't use reverse pitch except on the shortest runways.......@folbotcar, next time your boss says that, ask him how expensive tidying up after a crash would be.

I ignore him, it's my licence after all. :mad:

smurfjed

That doesn't sound correct. You would be a long way down the runway if you waited until 80 knots to use the brakes.

Depending on the runway, thats what we do, it aids in quick turn arounds

maybe even allow for brakes to be smaller, lighter, although Im sure they have some limit there in the event wheel braking has to be applied in an emergency where thrust reverse isnt available? maybe braking to destruction?

Remember that the brakes must be capable of stopping you after a takeoff rejection.

And this is done without the use of reverse thrust.

*Kol*

smurfjed wrote: »

Depending on the runway, thats what we do, it aids in quick turn arounds

So you would not arm the auto brake in that case? Would you deploy the reversers?

smurfjed

We don't have auto brakes, and we can use reversers down to a walking speed.

*Kol*

What type of aircraft is that? It's unusual to use reversers below 60 kts.

smurfjed

Have you ever noticed Gulfstreams taxing around with the thrust reversers popped open?

sjb25

smurfjed wrote: »

Have you ever noticed Gulfstreams taxing around with the thrust reversers popped open?

Not till now http://m.youtube.com/watch?v=K5OUHL3mrgE

andy_g

*Kol* wrote: »

What type of aircraft is that? It's unusual to use reversers below 60 kts.

That was with First air and on the 732 also it can be done in certain airlines on the 738 depending on the sop's

Stovepipe

It's common to cycle the reversers on some aircraft as part of the pretakeoff checks. It's also be known to use the reversers to assist turning but it's not generally recommended as it can blow FOD into the engine or cowling.

smurfjed

It's also be known to use the reversers to assist turning

Interesting, what aircraft type are you talking about?

Turbulent Bill

smurfjed wrote: »

Interesting, what aircraft type are you talking about?

I vaguely remember that the C-17 has some party trick with its reversers which gives it a very tight turning circle.

*Kol*

Stovepipe wrote: »

It's common to cycle the reversers on some aircraft as part of the pretakeoff checks. It's also be known to use the reversers to assist turning but it's not generally recommended as it can blow FOD into the engine or cowling.

It can also reverse you off the taxiway as it did to a B737 in Hoedspruit.

Simon Gruber Says

Apparently this was a common sight in Detroit with the DC9. I guess the engines being mounted on the fuselage reduced the risk of ingesting FOD. Still doesn't seem like the best idea.

Growler!!!

Simon Gruber Says wrote: »

Apparently this was a common sight in Detroit with the DC9. I guess the engines being mounted on the fuselage reduced the risk of ingesting FOD. Still doesn't seem like the best.

The type my crowd uses is certified to "power back" from stand. It's practiced in the sim but never used as the airport authorities frown upon it.

If you forget what you're doing and use the wheel brakes she'll end up on her tail:o

Stovepipe

I saw a certain airline's 737-200s doing it, more than once, when taxying on the ramp. I saw it often enough to query it with a friend who flew them and he confirmed it.....with regard to turbos reversing back with reverse pitch, I saw a particular type almost touch it's tail bumper because the handling pilot did what Growler said and touched the brakes and the aircraft pitched up enough to lift the nosewheel off the ground.

regards
Stovepipe

Jimmy444

basill wrote: »

And to see why not selecting even idle reverse is a big no no on an Airbus see the attached.

http://www.iasa-intl.com/folders/belfast/Congonhas/A320-throttles.htm

If you can get to a TV this afternoon at 15:50, this accident is the subject of the Mayday episode on RTE 1.

Farting Turkeys

The Russians love deploying their thrust rebersers befor they hit the tarmac.

Can't post a link, not enough posts.

Type in TU-154 thrust reverse in the air on YouTube

Stovepipe

some aircraft have an override that allows pre-landing arming and occasional deployment on finals.It's when they inadvertantly deploy that it's a problem.One foreign operator of the casa 235 managed to telescope his by activating them in flight just before touchdown.

smurfjed

some aircraft have an override that allows pre-landing arming and occasional deployment on finals

I believe the Trident cloud use reverse thrust on the centre engine during flight, and the DC8 on the in-boards. https://en.wikipedia.org/wiki/Japan_Airlines_Flight_350

As for the CASA235, its a turboprop, therefore it doesnt have reverse thrust as such, but it changes the blade angle, rather than deploy.

https://en.wikipedia.org/wiki/Lauda_Air_Flight_004 This is one of the problems when they occur inflight, even on an aircraft with tail mounted engines, the deployment of thrust reversers is a B1tch.

phonypony

A little of the original topic but let's not forget NASA's Gulfstream II Shuttle trainer. The only way they could get enough drag for the ~20 degree approaches was to drop the main gear and use the reversers with 90% thrust from FL280 all the way to the runway.

Stovepipe

The Casa I mentioned was of the Gabon air force and the aircraft went into reverse pitch at about 50 feet and was telescoped when it hit the ground. My former colleagues saw it being rebuilt in Seville and got the story from the training staff.