Why are jet engines attached to wings?

Question

some planes may have engines in different locations like the rear, but for most planes, the engines are hanging down the wings. why is this so??

Answer 1

It allows for symmetry, and thus stability, but mostly it leaves more room in the fuselage. It tends to be passenger and cargo jets that have wing mounted engines. Single and two seat fighters often have the engines in the fuselage.

Answer 2

It allows for more space in the fuselage, and keeps the noise away from the interior.

Answer 3

Noise, stability, and aerodynamics. It reduces cabin noise dramatically when the engines are placed on the wings, it also lowers the center of gravity significantly, and it reduces interference drag with the airframe.

Answer 4

Because the vast amount of air that is forced through them would make it unpractical to have them on the fuselage.

Answer 5

Everything in an aircraft is about compromise. The best place to put an engine is away from the airplane; but without wings it would not fly very well, and without the fuselage, it would not carry much.

Engines located under the wing has a few advantages over being placed at the rear. Firstly, the weight of the engines is already subtracted from the lift by the time the load reaches the aircraft center-line; it may not be much but this load alleviation helps to make the structure a bit lighter. Second, the engines see a realtively undisturbed airflow coming in (as compared with engines mounted on the rear fuselage), especially if the airplane is operating on the ground in cross wind, or sideslipping in flight (in such conditions, the airflow is distrubed by the fuselage and there is what we call "inlet distortion" that reduce engine efficiency). Third: engine thrust reverser also operate in a cleaner environment; aft mounted engines will have to deflect the reversed flow up and down, and the down flow may lead to re-ingestion after striking the ground; again this leads to reduced efficiency but also may blow foreing objects from the ground that could get ingested by the engine; an unlikely event, but why take chance?

Fourth:  engines located on the wing are easier to access for maintenance operation.

Fifth: the underwing placement reduces the percieved engine noise inside the aircrat cabin (although this is a marginal effect, as most modern aircraft have adequate sound proofing material in place).

Six: under the wing, the engines inlet are located in front of the main landing gear, and any foreing object tossed about by the wheels (and that includes water spray when a runway is wet) is thus less likely to get in the engine.

So if it is so good; why are engines not always located under the wing?

Well, putting the engines under the wings mean they have to clear the ground, and that implies slightly taller landing gear (and gears are *heavy*, as they have to support the whole plane). Also, the engines are located further from the center line, and if an engine fails the rudder needs to compensate for the lateral imbalance, and that means larger rudder surface (the rudder has to be designed to balance for one engine failing).

In general, putting the engines aft is perhaps a better compromise for smaller plane. When you move to the big ones, under the wing seems the way to go.

Edit: now who is the ignorant who keeps down thumbing expert answers? You got 27 years in the business and a master dregee in the field, perhaps?

Answer 6

Stability and noise.  Not an issue on fighters etc (in fact, the less stable they are - the more manouevrable they are), passenger safety is the main one here.

Answer 7

stabilitly, weight distrobution. Engines on the back of the aircraft are a bad design as the tail of the aircraft is above them and contain the elevator section (up and down movment called pitch). Should the aircraft get into a stall, it is very difficult to get out in this combonation of engine and wings as the thrust hits the tail forcing it into a greater stall. Thats a reason to put them on the wings. Also it is closer to the fuel and saves weight.

Answer 8

Safety,. In the event of an engine fire, the fire is kept away from the wings ( and the fuel tanks)

Also, maintenance.  An engine can be  replaced  in a short amount of time with 2 mechanics and a towmotor seperate from the wing.

Answer 9

stability. short and siimple

Answer 10

the engines are on the wings, especially for propeller and larger commercial planes, because the lack of propulsion for the prop planes and the added weight of comm. planes requires greater stability than can be provided by a back engine.  normally, the only planes with a rear mounted engine are jets that are designed to fly at incredibly high speeds.  this prevents the wings from getting damaged or destroyed by the intense pressure being pushed against them constantly due to the power of the engines on those types of planes.

Answer 11

It is for balance and stability, however not all aircraft have jets attached to their wings, look at the Boeing 727 for instance.

It has jet engine attached near the tail of the aircraft.

Answer 12

i wouldnt think people on here would know the answer to that. you should try asking someone in the travel business.

Answer 13

were they not attached, they'd leave without the airplane. seriously, most answers are fairly good but, moment of inertia causing the nose to pitch up? don't think so. could never get that aircraft certificated under far part 25. all transport category aircraft engines are mounted, tail or wing, with an aft downward can't so as when nearing a stall, added power will pitch the nose down. in fact this lowered pitch must be counteracted with back pressure on the yoke during wind shear escape maneuvers to arrest the sink rate.

regarding the comment on aft mounted engines being a bad design? rediculous. the 727 and gulfstream aircraft are among the most aerodynamically efficient swept wing aircraft ever designed. shut em all down in a 727 and then do it in a 737 and tell me which glides the furthest from 35,000 feet. bad desgn my A$$.

Answer 14

Balance.  It is easier to get the balance correct if the engines are attached near the center of gravity.

Answer 15

Easier to access for maintainence. Produces alot of drag though.

Answer 16

The location the engines are mounted to requires a very strong structure to withstand the strains of holding the engine. If the engine is in the tail, the entire real fuselage has to be reinforced to take this strain. But the wings are already very strong to hold the aircraft up in the air. So it doesn't take as much reinforcement to put an engine there, saving weight over all.

Also, with the engines in the tail all the control linkages and such are in very close proximity to a very hot engine. And the underwing location makes easy access to the engines or service.

Answer 17

is it the noise?

Answer 18

The weight of the engines give stability to the structure of the light wing design. Especially when fuel is stored in the wings, as the fuel drains the stability is maintained with engine weight.

This stops the wings flapping

Answer 19

One of the main reasons is historical.

The DeHavilland Comet (the first western jet passenger aircraft in commercial service)had it's engines within the wing, close to the root, in pairs on either side years before Boeing built a passenger aeroplane.  The basis of this design was to counter asymmetric thrust as much as possible owing to relatively poor reliability in early turbojets.  

Boeing opted for the underwing arrangement on it's aircraft (the B-47, and later B-707 and B-52) because, at least in part, it added a safety measure to the aircraft in case of engine fire.  Engines in the wings led to more complexity as well, and do not bring about the effect known as 'wing bending relief', a factor in how strong the wing needs to be (and concommitant weight considerations), and can be noisier, mor difficult to swap and more difficult to service.

Answer 20

Most answers are ok, but one important point has been missed.

Mounting an engine in a pod beneath the wing means that a 'moment of inertia' is added to the thrust of the engine, in as much as it helps to lift the nose of the aircraft especially al lower flight speeds.

Another lesser point is that as the engines are below the main fuel tanks, gravity helps with fuel flow should main pumps fail.

Answer 21

It's for balance, nothing more nothing less. You'll notice that there's never an engine on one side when there isn't one on the other, they always come in pairs. If there's two on the right, there's two on the left.

Aside from weight balance, having two or even four engines on the wings rather than one at the tail (am assuming those with just the one in the tail are small ones) helps prevent accidents. The chances of one engine failing due to a technical fault are minimal, the chances of all four engines failing due to technical faults are close to nil.

Hope that helps

Answer 22

One reason must be ease of maintenance. If they are below the wings, then they are more accessible.