what's the primary way a jet plane slows down on the runway?

Question

Is it the brakes, the engines?

Answer 1

The PRIMARY device to slow the plane is the thrust reversers. Even though the engine is still applying forward thrust in the core part, it's that huge fan in the front that supplies a good 2/3 of overall thrust in a high bypass modern engine. It is that part of the thrust that is reversed when the rear part of outer cowling slides back and internal baffles slide up to block it's forward thrust. When this happens there are devices called "cascades" that push the thrust forward and overcome the forward thrust of the core. The speed brakes that pop up upon touchdown destroy upward lift and act as air brakes when they are armed and the pilot pulls the throttles to idle. Brakes are applied usually using an autobrake system and at a preset value on the front console in the flightdeck. To keep the brakes from skidding there is also an anti-skid system that works in conjunction with this auto-brake. And just as an add on, there is also a position on this auto-brake system called RTO (refused take off) that if the pilot has to abort the take off, the brakes are applied at maximum for much quicker braking. When the plane is slow enough, the TRs are retracted and the pilot uses the "toe brakes" (pressing the top of the rudder pedals with their toes) this disables the autobrakes and turns the control over to the pilot and first officer (co-pilot). To keep the plane going down the runway straight after the landing, the pilot has a few degrees of what is called "pedal steering". Once the plane is slow enough, he uses a "tiller" in the flight deck (just a handle to his left, or right if he's the co-pilot) that makes much larger steering movements of the nose gear. On a multiple main geared aircraft (example the 747 has four with 16 tires total) the inner (body) gears have their own steering system (body gear steering) that works with the nose gear to keep them from skidding sideways as the plane pivots around the outer (wing) gears. I've seen 747's where the body steering wasn't working and the pilot had to apply a LOT of thrust to get the plane turned.

Well, that ended up getting off subject, but what the heck... :P

Answer 2

Flaps and slats are primarily used for the approach phase prior to landing. As with any aircraft, they help increase the angle of descent without increasing airspeed by creating drag (they create lift too). This results in a slower "landing speed".
Once you are on the ground (which is what I think you are asking), a combination of things slows the (jet) airplane down.

First you will notice on the top of the wing, a bunch of panels will raise up. The # of panels varies depending on the aircraft. This is the Ground Lift Dumping system (it may have a different name depending on the airplane). These panels create drag and basically "kill" the lift produced by the wings. They automatically deploy when the aircraft is on the ground (there are sensors associated with the landing gear that can tell when you are on the ground or in the air).

Next, you will probably hear the engines get louder. This is the reverse thrust. There are several designs for this, but the principle is the same...there are "doors" that open and redirect the airflow that normally goes out the back of the engine. The air is directed forward, creating more drag (this is a very simplistic explanation, so all you pilots, A&P's, engineers, etc. take it easy on me).

These first ways are most effective at higher airspeeds.

Finally, you have the wheel brakes (just like your car). We try to use the brakes as little as possible because excessive use really makes them get hot, not to mention they cost money.

Again, this is a very simple answer, so different aircraft have variations in the way their respective systems work.
I hope this helps answer your question.

Answer 3

Actually, contrary to most answers here, the wheel brakes are the primary mode of slowing down an aircraft. On large airliners, thrust reverse only decreases landing distance by about 15%. On many smaller airplanes, brakes are the only means as they don't have have thrust reversers or beta thrust (on props).

Many airlines these days only engage thrust reverse but don't spool up the engines to save money on fuel if the runway conditions warrant this. This also reduces noise in noise sensitive areas.

Speed brakes or spoilers (on top of the wing) also cause some drag and slow the plane down, but mostly they destroy the lift right after touchdown and make sure that the weight of the airplane rests firmly on the wheels, so that the brakes can be used without the wheels skidding along the concrete.

Answer 4

Imagine you are just begin approaching the run way.
1. You down the flaps (notice the parts of wings which move up & down at that time) on the wingsand maintain a decent appraoch speed.
2. The glide slop is calculated on the basis of current height of the aircraft and length of available runway plus the wind speed.
3. Then, you touch down (Middle Set of Wheels first, then the Nose Wheel).
4. At this time, an ANTI-THRUST is applied (that is a side panel of the engine slides open and the complete pressure if bypassed---in new generation boiengs or airbuses for example. In older boeings you will find a Bucket-Shape Callipers which are slided to minimize the THRUST.
5. Subsequently, a sensor (activated upon touchdown of the nose-wheel) pops up the Air Brakes (These are flat panels in the middle of the Main Wings which are lifted up), which disturbs & stops the Aerodynamic Flow.
6. Gradually the Brakes are applied (these are located on the upper tips of the Rudder Pedals), and the Thrust Lever is Pulled Back (Pushing is for Adding Thrust) instantly to cut the fuel completely.
7. You are ready for a gradual slow down and then stop.

Easy...isn't it!

Answer 5

Using the thrust reversers does not "reverse" the engine. The engine keeps spinning in the same direction it was. It would be impossible to reverse the direction of an engine that is spinning at thousands of RPMs in the short transition between flying and landing on the runway.

The thrust reversers are small slots that open on the side of the engines diverting some of the thrust forward. This, along with flaps, airbrakes, spoilers, and finally the wheel brakes, slows the plane down to taxi speed.

Answer 6

First you need to slow the aircraft down by causing drag, resistance & friction. This is done by deploying the flaps and spoilers, air brakes etc ( your secondary flight controls). The aircraft slows- engines are reversed. The brakes are not normally applied until the aircraft is already slowing from the drag. If you were to slam the brakes on right away the aircraft could lose control. Also you could end up w/ hot brakes which could cause a fire or blow a tire.

Answer 7

There are a number of ways that an aircraft slows down on the runway. First of all, the flaps are fully deployed; this increases drag to help slow it down. Many large aircraft also have speed brakes or spoilers on the upper wing surface. This both destroys lift and increases drag, slowing the aircraft down. Many airliners have thrust reversers that redirect the engine exhaust towards the front of the aircraft helping to slow the aircraft. Finally, all aircraft have brakes on the wheels, just like a car.

Answer 8

The PRIMARY way is definitely the engines. When the pilot pulls the thrust reverser lever, "doors" (called cascade vanes) behind the engine are deployed, and those cascade vanes deflect the engine exhaust forward instead of straight back, causing the airplane to slow down. Brakes are used, but imagine slamming on the brakes in your car at 120 mph. Doesn't work so great.

Answer 9

it depends on where in the roll out you are. upon first touching down. if you get on the brakes hard you can crash the aircraft (called a ground loop) or set the brakes on fire. So they stick allot of things out in the wind to cause friction, flaps and spoilers are deployed, Allot of aircraft have speed brakes (a large flat surface that pops up into the wind stream) this friction slows the aircraft. Most have reverse thrusters on the engines, further slowing the aircraft, last but not least when the aircraft is slowed sufficiently, the brakes are applied.

Answer 10

Commercial jet aircraft on finals will be travelling at least 150 mph before a landing, typical safe landing speed with 30 degrees of flaps is 140 knots ( about 160 mph) and thats just about for all commercial Jets, they have to be travelling within altitude speed limits by aviation law anyway, so there is little likelyhood of a Jet being too fast on finals unless landing procedures have not been followed.As most Jets now "autoland" the chances of having to "Go around" and repeat the whole landing procedure are reduced".