Underslung Engines
Underslung Engines
Joined: Jan 2003
Posts: 516
Likes: 0
From: Northampton
If there is a severe engine fire, there are weak points that allow the engine to simply drop off if I remember correctly, or was that just an old wive's tale?
Plus, the nacelles aid in the prevention of spanwise airflow from root to tip on the underside of the wing.
Cheers, Jack.
Plus, the nacelles aid in the prevention of spanwise airflow from root to tip on the underside of the wing.
Cheers, Jack.
Joined: Oct 2003
Posts: 76
Likes: 0
From: California (Highway Patrol)
There are a few main benefits for having a podded engine,....
The engine and auxiliary equipment are podded, facilitating engine change - a lot easier to get at with no aircraft structure round it (most engines can be accesses by engineers on the ground, with no "cherry picker" or scaffolds needed (some turn arounds require a top up of oil, or something may need to be checked)..... this saves time and money. A podded engine also makes a complete engine change easier,.......
A podded engine will result in a lighter structure - burying the engines in the wing like the nimrod is aerodynamically more efficient as there is less flow distrubance, but the extra beefing up of the structure required is a downside. A podded engine will create much flow disturbance on the upper surface at high angles of attack, lowering the CLmax (increasing stall speed), and the nacelle strakes you se either side of some engines are there to create a vortex which promotes flow attachment until a higher alpha.
(Its been a while) The fact that the engines are podded makes the vibrational analysis (modes of vibration) a bit simpler to do - I was sat beside the Nimrod boys as they were carrying out this study and it was a nightmare,.... especially as the gear was also connected to the structure around the Nimrod engine.
In the event of an uncontained failure, there is less of a risk of the blade piercing vital control lines,..... even though redundancy is built in with this design case in mind.
Podded engines also allow for quieter cabins,..... obviously depends on where your sat and the aircraft concerned, but you get my drift,......
Another downside is due to the fact that the thrust line is well below the aerodynamic centre,.... means that when you add power, there is a large pitch up moment which needs to be counter acted with nose down (unless you fly the Airbus!),....
Hope this helps!
FP
The engine and auxiliary equipment are podded, facilitating engine change - a lot easier to get at with no aircraft structure round it (most engines can be accesses by engineers on the ground, with no "cherry picker" or scaffolds needed (some turn arounds require a top up of oil, or something may need to be checked)..... this saves time and money. A podded engine also makes a complete engine change easier,.......
A podded engine will result in a lighter structure - burying the engines in the wing like the nimrod is aerodynamically more efficient as there is less flow distrubance, but the extra beefing up of the structure required is a downside. A podded engine will create much flow disturbance on the upper surface at high angles of attack, lowering the CLmax (increasing stall speed), and the nacelle strakes you se either side of some engines are there to create a vortex which promotes flow attachment until a higher alpha.
(Its been a while) The fact that the engines are podded makes the vibrational analysis (modes of vibration) a bit simpler to do - I was sat beside the Nimrod boys as they were carrying out this study and it was a nightmare,.... especially as the gear was also connected to the structure around the Nimrod engine.
In the event of an uncontained failure, there is less of a risk of the blade piercing vital control lines,..... even though redundancy is built in with this design case in mind.
Podded engines also allow for quieter cabins,..... obviously depends on where your sat and the aircraft concerned, but you get my drift,......
Another downside is due to the fact that the thrust line is well below the aerodynamic centre,.... means that when you add power, there is a large pitch up moment which needs to be counter acted with nose down (unless you fly the Airbus!),....
Hope this helps!
FP
Joined: May 2006
Posts: 2,042
Likes: 0
From: 2 m South of Radstock VRP
Advantages:
more available wing area for generating lift
more available wing leading edge/trailing for flaps/slats
places the engine weight on the wing and provides a degree of bending relief
on 4 engine types, the greater engine spacing provides less chance of an uncontained engine failure damaging the adjacent unit or the airframe
in the event of an engine fire, the wing has some degree of protection
easier/quicker engine changes and maintenance
Disadvantages:
the offset thrust line creates a bending moment on the wing at high thrust
the offset thrust line creates a pitch-up moment at high thrust
the additional distance from the centreline creates a significant yaw moment in the event of an engine power loss
the ground clearance is reduced increasing the chances of FOD
when subject to high G loads, the moment created by the mounting pylon may distort the wing; as similarly, heavy landings
the nacelle and pylon create additional drag
more available wing area for generating lift
more available wing leading edge/trailing for flaps/slats
places the engine weight on the wing and provides a degree of bending relief
on 4 engine types, the greater engine spacing provides less chance of an uncontained engine failure damaging the adjacent unit or the airframe
in the event of an engine fire, the wing has some degree of protection
easier/quicker engine changes and maintenance
Disadvantages:
the offset thrust line creates a bending moment on the wing at high thrust
the offset thrust line creates a pitch-up moment at high thrust
the additional distance from the centreline creates a significant yaw moment in the event of an engine power loss
the ground clearance is reduced increasing the chances of FOD
when subject to high G loads, the moment created by the mounting pylon may distort the wing; as similarly, heavy landings
the nacelle and pylon create additional drag
Thread Starter
Joined: Dec 2000
Posts: 84
Likes: 0
From: Beds
Thanks Guys
not sure how the wings would be protected with an underslung engine, especially one that's on fire with wing tanks ?
Somebody mentioned to me about "twisting moment " related to this matter, any clues
sp
not sure how the wings would be protected with an underslung engine, especially one that's on fire with wing tanks ?
Somebody mentioned to me about "twisting moment " related to this matter, any clues
sp
Joined: Aug 2005
Posts: 216
Likes: 0
From: SEA (or better PAE)
You can check Joe Sutter's book ("Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation" ISBN 0060882417) on how they developed 737 and 747.
It gives a good explanation how did they come to the underwing engine position which will help you with the answer you're looking for.
Cheers
It gives a good explanation how did they come to the underwing engine position which will help you with the answer you're looking for.
Cheers
