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Under Wing Engines Vs Tail Mounted Engines  
User currently offlineQatar From , joined Dec 1969, posts, RR:
Posted (12 years 8 months 3 days 2 hours ago) and read 14067 times:


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,
Qatar

9 replies: All unread, jump to last
 
User currently offlineGOT From Sweden, joined Dec 2000, 1912 posts, RR: 1
Reply 1, posted (12 years 8 months 2 days 21 hours ago) and read 14021 times:

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!
User currently offlinePikachu From Bhutan, joined Feb 2002, 89 posts, RR: 0
Reply 2, posted (12 years 8 months 2 days 20 hours ago) and read 13999 times:

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


User currently offlineQatar From , joined Dec 1969, posts, RR:
Reply 3, posted (12 years 8 months 2 days 20 hours ago) and read 13976 times:

Thank you both for the helpful replies  Smile

User currently offlineAWspicious From , joined Dec 1969, posts, RR:
Reply 4, posted (12 years 8 months 2 days 16 hours ago) and read 13922 times:

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


User currently offlineAA737-823 From United States of America, joined Mar 2000, 5873 posts, RR: 11
Reply 5, posted (12 years 8 months 2 days 12 hours ago) and read 13897 times:

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


User currently offlineTransSwede From United States of America, joined Sep 2001, 1000 posts, RR: 0
Reply 6, posted (12 years 8 months 2 days 12 hours ago) and read 13882 times:

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.


User currently offlineTom_EDDF From Germany, joined Apr 2000, 452 posts, RR: 0
Reply 7, posted (12 years 8 months 2 days 6 hours ago) and read 13838 times:

AA737-823:

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

Tom-


User currently offlineVapourTrails From Australia, joined Aug 2001, 1258 posts, RR: 1
Reply 8, posted (12 years 8 months 2 days 5 hours ago) and read 13823 times:
Support Airliners.net - become a First Class Member!

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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Photo © Ben Pritchard



Click for large version
Click here for full size photo!

Photo © Ben Pritchard



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Photo © Glenn Alderton






"I've never known an industry that can get into people's blood the way aviation does" -- Robert Six.
User currently offlineQatar From , joined Dec 1969, posts, RR:
Reply 9, posted (12 years 8 months 2 days 4 hours ago) and read 13797 times:

Thank you

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