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Under Wing Engines Vs Tail Mounted Engines

Wed Feb 27, 2002 9:41 pm


Can anyone explain the advantages and disadvantages of having the engine podded under the wing or mounted in the back of the plane.


-Why do many smaller aircraft have the engines mounted in the back, does it have to do with engine clearance?
-Is there any economical or technical/performance gain in having the engine under the wing or mounted in the back?
-Does the weight of the engines mounted in the back cause any problems during flight? (I know it does in the ground with some aircraft like the MD-11)

Any more comments or information on the subject will be greatly appreciated

Regards,
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GOT
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 2:59 am

I'll try to answer:
1. It does probably as to do with the ground clearence. Wingmounted engines would need really long gears.
2. Having the engine in the rear of the a/c means that you can have a clean wing, which may give it better dynamics. However, with engines on the wing the wing can be built lighter becuase the weight of the engines work against the lift created by the wing, thus reducing weight.
3. Have no idea.

Cheers
GOT
Just like birdwatching - without having to be so damned quiet!
 
pikachu
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 3:27 am

A few general points about engine location from Handling the Big Jets.
Advantages of underwing mount:
1. Inteferenece drag is minimized
2. Intake efficiency is rarely compromised
3. Engines provide wing bending relief reducing wing structure weight
4. Wing profile is not compromised
5. Pylons tend to control spanwise flow
6. Less accoustic damage to airframe
7. Reverse thrust design uninhibited
8. Good accesibility
9. Good for a gear up landing
Disadvantages:
1. Higher yawing movement with engine failure
2. Roll freedom on the ground is limited
3. Low thrust line can have an adverse effect on longitudinal control
4. FOD ingestion
Advantages of rear fuselage mount:
1. Reduced noise in cabin
2. Low yawing movement with engine failure
3. Free to design more aerodynmic wing without engine mounts
4. Odd number of engines can be mounted
Disadvantages:
1. Passenger accomodation is reduced for a given length
2. Engines suseptible to airflow disturbances
3. Fuel lines require careful routing to the engines
4. Aft set wing to compensate for aft C of G and larger tail surface required
5. Basic structure weight must be higher
6. Higher set tail plane can lead to problems in stall qualities
 
Guest

RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 3:36 am

Thank you both for the helpful replies  Smile
 
AWspicious
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 7:44 am

Which bring me to another question: Are there any airplane manufacturers making a three engine aircraft? If not - Why? Are there disadvantages that aren't appreciated in today's market?
Why did Airbus, for example, put 4 engines on their 340 instead of three? Matter of fact, why didn't they build a three engine aircraft and call IT the A330?
2 engines = A320; 3 engines = A330; 4 engines = A340. Then, you have a your variants within each family  Smile/happy/getting dizzy
Nevermind political correctness - Envision using your turn signals!
 
AA737-823
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 11:32 am

I have no idea why they gave the A340 four engines rather than three. I do know that some airlines don't like to deal with ETOPS requirements, so they would prefer a 340 to a 330... but the 340 is not nearly as efficient as the 330 or 777, so why didn't they just give it three engines, like the MD-11??? I would (probably, depending on other variables) make the plane more efficient AND eliminate ETOPS concerns.

Randy
 
transswede
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 11:54 am

The third (center) engine is a maintenance nightmare on DC-10's, MD-11's, and L1011's. A center engine could also much more easily have its air-intake compromised in a stall/nose-up situation, making a bad day even worse.

According to the A340 history at http://www.a340.net, a 3-engine design was ruled out very early.

As for the A330 being much more efficient than an A340 - the range clearly proves otherwise. Remember that the 777 and A330 are actually *overpowered* due to being twin-engine designs.
 
Tom_EDDF
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 5:35 pm

AA737-823:

ETOPS would not affect a 3 engine A330 design, it does only apply to twinjets. ETOPS = Extended TWIN engine operations.

Tom-
 
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VapourTrails
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RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 7:15 pm

Here are some threads that may also help answer your question..

Engine positions on larger jets
http://www.airliners.net/discussions/tech_ops/read.main/19708/4/

Engine placement: does it matter?
http://www.airliners.net/discussions/tech_ops/read.main/24693/4/

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Guest

RE: Under Wing Engines Vs Tail Mounted Engines

Thu Feb 28, 2002 8:19 pm

Thank you

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