Why has placement of jet engines changed?
Nov 18, 2019 | 10:37 am
#1
Original Poster
Join Date: Nov 2008
Location: South Yorkshire, UK
Programs: VS Silver
Posts: 2,478
Why has placement of jet engines changed?
I was watching the new series of the Crown and it struck me that commercial jetliners used to have jet engines positioned either on the sides of the fuselage or in the tail fin. These days jet engines are pretty much exclusively mounted under the wings. Can anyone give me a technical explanation of why this would be the case? Google isn't forthcoming.
Nov 18, 2019 | 12:20 pm
#3
Join Date: Jul 2009
Programs: none
Posts: 1,680
The main reason for this engine placement relates to aerodynamics (airflow). Newer engines are more efficient, but they're larger in diameter. In short, they won't fit well on the rear of the fuselage. They are more efficient when located out on the wing where the airflow doesn't interact with the flow on the fuselage and tail.
(This is a simple explanation that doesn't consider things like center of thrust, engines pushing on the body vs. the wings pulling, ground clearance, maintenance, high- vs low-wing, cost, etc)
(This is a simple explanation that doesn't consider things like center of thrust, engines pushing on the body vs. the wings pulling, ground clearance, maintenance, high- vs low-wing, cost, etc)
Nov 18, 2019 | 2:08 pm
#5
FlyerTalk Evangelist
Join Date: Nov 1999
Programs: FB PLT again afater a decade as plebian
Posts: 22,942
The main reason for this engine placement relates to aerodynamics (airflow). Newer engines are more efficient, but they're larger in diameter. In short, they won't fit well on the rear of the fuselage. They are more efficient when located out on the wing where the airflow doesn't interact with the flow on the fuselage and tail.
(This is a simple explanation that doesn't consider things like center of thrust, engines pushing on the body vs. the wings pulling, ground clearance, maintenance, high- vs low-wing, cost, etc)
(This is a simple explanation that doesn't consider things like center of thrust, engines pushing on the body vs. the wings pulling, ground clearance, maintenance, high- vs low-wing, cost, etc)
Some designs also obstructed air flow to engine and made the a/c more prone to stalling and harder to recover, in certain situations.
Nov 18, 2019 | 3:50 pm
#6
FlyerTalk Evangelist
Join Date: Jul 2005
Location: The Sunshine State
Programs: Deltaworst Peon Level, TSA "Layer 21 Club", NW WP RIP
Posts: 11,372
The wing lifts everything. Placing weight on the wings is better, as placing it elsewhere means a stronger (heavier) fuselage is needed to support it. A flying wing is a great shape, for cargo, not so for passengers. No window seats.
Something else to consider. The fuel tanks are in the wings. With rear mounted engines, there is a fuel pipe the size of your arm running under your feet back to the engines. Want that to break in a belly landing? (Assuming you don't always fly J and sometimes sit in the high number rows.)
Something else to consider. The fuel tanks are in the wings. With rear mounted engines, there is a fuel pipe the size of your arm running under your feet back to the engines. Want that to break in a belly landing? (Assuming you don't always fly J and sometimes sit in the high number rows.)
Nov 18, 2019 | 5:43 pm
#7
FlyerTalk Evangelist
Join Date: Nov 1999
Programs: FB PLT again afater a decade as plebian
Posts: 22,942
Something else to consider. The fuel tanks are in the wings. With rear mounted engines, there is a fuel pipe the size of your arm running under your feet back to the engines. Want that to break in a belly landing? (Assuming you don't always fly J and sometimes sit in the high number rows.)
Nov 18, 2019 | 11:50 pm
#8
Join Date: Oct 2016
Location: PDX
Programs: AS DL
Posts: 9,038
Less commonly seen:
Engine is at the wing, not in a pod. Example, Boeing 737-100, Boeing 737-200
Engine is above the wing. Example, VFW-Fokker 614
Engine is buried in the wing. Example, deHavilland Comet
Pair of engines on each side of the rear fuselage. Example, Vickers VC-10
Pair of engines side by side. Example, BAe Aerospatiale Concorde
Engine within the vertical stabilizer. Example, McDonnell Douglas MD-11
Engine in the rear fuselage with intake above the fuselage. Example, Boeing 727-200, Lockheed L-1011 Tristar
What is common is engine is under and forward of the wing or under the wing.
Engine is at the wing, not in a pod. Example, Boeing 737-100, Boeing 737-200
Engine is above the wing. Example, VFW-Fokker 614
Engine is buried in the wing. Example, deHavilland Comet
Pair of engines on each side of the rear fuselage. Example, Vickers VC-10
Pair of engines side by side. Example, BAe Aerospatiale Concorde
Engine within the vertical stabilizer. Example, McDonnell Douglas MD-11
Engine in the rear fuselage with intake above the fuselage. Example, Boeing 727-200, Lockheed L-1011 Tristar
What is common is engine is under and forward of the wing or under the wing.
Nov 18, 2019 | 11:56 pm
#9
Join Date: Oct 2016
Location: PDX
Programs: AS DL
Posts: 9,038
What about high wings, like in a BAe 146? Wings protrude in to the cabin, reducing space. Some say it's worse in a water landing but those are rare. Others say engine noise is greater in the cabin. What did you say?
Nov 19, 2019 | 1:49 am
#10
Join Date: Apr 2007
Location: Australia
Programs: NZ Elite
Posts: 6,518
Engines buried in the wing root (ala Comet) are harder to access for maintenance, and MUCH harder to remove and replace. The Nimrod ( Maritime patrol/AEW variant of Comet IV) flew on successfully for decades its true... but maintenance is less of a concern time/manpower wise for Air forces.
Nov 19, 2019 | 5:18 am
#11
FlyerTalk Evangelist
Join Date: Jan 2009
Location: London & Sonoma CA
Programs: UA Plat, MM *G for life, AY Plat, BA Silver
Posts: 10,553
I read somewhere that part of the root cause of the 737MAX issues is that the engines for this variant of the 737 are placed much further forward than previously. This is because they are too big to fit under the wing, without stretching the landing gear.
Nov 19, 2019 | 10:29 am
#12
FlyerTalk Evangelist
Join Date: Nov 2002
Location: ORD
Posts: 14,773
Yes, that's what I'd seen too. Earlier 737 models had smaller engines but modern high-bypass turbofans on the 737 Max require larger air inlet diameter. So, they put the engines in front of the wing in order to be able to elevate them a bit, which induces instability that Boeing countered with the MCAS system that occasionally went haywire and crashed the plane.
Nov 19, 2019 | 6:49 pm
#13
FlyerTalk Evangelist
Join Date: Jan 2014
Location: San Diego, CA
Programs: GE, Marriott Platinum
Posts: 15,744
The HondaJet is a modern example of this.
In short, it depends on engineering tradeoffs. It happens that the configuration that's the most profitable for commercial airline operators tends to be the under-wing configuration more often than not.
In short, it depends on engineering tradeoffs. It happens that the configuration that's the most profitable for commercial airline operators tends to be the under-wing configuration more often than not.
