Aircraft engineers/designers,planes with engines on wings.
Discussion
Any aircraft engineers or designers on here?
If so could you care to explain what the difference in approach is when designing a wing with engines mounted on them against one without.
Obviously the wing with engine or engines will have extra vertical loads while not in flight.
I understand the principles of a wing,lift vs drag etc.
But I was more intrested in what affect the forward propelling forces have on the design.
If so could you care to explain what the difference in approach is when designing a wing with engines mounted on them against one without.
Obviously the wing with engine or engines will have extra vertical loads while not in flight.
I understand the principles of a wing,lift vs drag etc.
But I was more intrested in what affect the forward propelling forces have on the design.
It's relatively easy to put them under the wings at the wing is fully structural and pretty much on the centre of gravity. The only problem is the need to have the space underneath. The big issue with upgrading 737 is the grond cleance and the risk of ground strikes on the nacelle.
One of the upsides of rear fus mounted engines is the ability to reverse on the engines - MD83 can do this off the stand rather than needing the tug.
One of the upsides of rear fus mounted engines is the ability to reverse on the engines - MD83 can do this off the stand rather than needing the tug.
Speaking as a student aircraft engineer:
The majority of planes have engines on wings as a) as mentioned, its a pre-existing strong structure to mount them to - fuselage mounted engines are heavy because of the need for an additional reinforced bulkhead across the cabin to take the extra stresses. Also it means you dont need a t-tail, which adds more weight as the tailfin has to be reinforced all the way up , b) minimal wiring and fuel piping and other extended systems are needed to connect them to the fuel tanks in the wings, c)there is quick and easy good all-round access to the engine for servicing and repairs when it is hanging off a wing, d)engines under wing = below centre of gravity of plane, so thrust from engines pitches plane up into air. Thrust from high fuselage engines above CG pitches plane down into floor without extra corrective trimming (which adds more drag)
There are a few advantages to fuselage mounted engines, of course. firstly, as mentioned, ground clearance. this is why almost all smaller jets have them at the rear instead of on their very low wings. secondly, and related to this, is that it keeps them out of the "ingestion zone" when operating from the smaller, dustier, less well maintained airstrips that regional jets/private jets often use. Thirdly, it is a lot quieter in the cabin with the engines at the back. Th good old VC10 was renowned for being whisper quiet inside as the jet exhaust wasnt travelling down the half the plane
The majority of planes have engines on wings as a) as mentioned, its a pre-existing strong structure to mount them to - fuselage mounted engines are heavy because of the need for an additional reinforced bulkhead across the cabin to take the extra stresses. Also it means you dont need a t-tail, which adds more weight as the tailfin has to be reinforced all the way up , b) minimal wiring and fuel piping and other extended systems are needed to connect them to the fuel tanks in the wings, c)there is quick and easy good all-round access to the engine for servicing and repairs when it is hanging off a wing, d)engines under wing = below centre of gravity of plane, so thrust from engines pitches plane up into air. Thrust from high fuselage engines above CG pitches plane down into floor without extra corrective trimming (which adds more drag)
There are a few advantages to fuselage mounted engines, of course. firstly, as mentioned, ground clearance. this is why almost all smaller jets have them at the rear instead of on their very low wings. secondly, and related to this, is that it keeps them out of the "ingestion zone" when operating from the smaller, dustier, less well maintained airstrips that regional jets/private jets often use. Thirdly, it is a lot quieter in the cabin with the engines at the back. Th good old VC10 was renowned for being whisper quiet inside as the jet exhaust wasnt travelling down the half the plane
Other thoughts -
Engines on wing are further apart than engines on fuselage - so engine out gives you more yaw to cope with.
Engines are further from fuselage which might help keep debris away from passengers if you have a failure in flight, but a failure on take off is more likely to go through a wing fuel tank
Engines have an effect on the aerosynamics around the wing (especially if its a turbo-prop, where you can end up with an aircraft which has very different roll characteristics depending on which way you roll...)
Compared to a tail engined A/C, you have different apron procedures regaring self loading cargo
Different water injestion characteristics
Need to worry (more) about aeroelastic effect of a big lump of engine cantilevered forward off a relatively flexible wing structure
Engines on wing are further apart than engines on fuselage - so engine out gives you more yaw to cope with.
Engines are further from fuselage which might help keep debris away from passengers if you have a failure in flight, but a failure on take off is more likely to go through a wing fuel tank
Engines have an effect on the aerosynamics around the wing (especially if its a turbo-prop, where you can end up with an aircraft which has very different roll characteristics depending on which way you roll...)
Compared to a tail engined A/C, you have different apron procedures regaring self loading cargo
Different water injestion characteristics
Need to worry (more) about aeroelastic effect of a big lump of engine cantilevered forward off a relatively flexible wing structure
Ironically, a wing which has engines mounted on it can be lighter than one without.
Wings have a tendency to bend when in flight and a wing with engines can use those those engines as a counterweight to the bending moment.
A wing without an engine needs a stronger (and therefore heavier) wing spar to restrict that bending moment.
Wings have a tendency to bend when in flight and a wing with engines can use those those engines as a counterweight to the bending moment.
A wing without an engine needs a stronger (and therefore heavier) wing spar to restrict that bending moment.
To a degree, the whole wing is affected by the engine, because at the loads derivation stage, the engine can play a fairly significant part in forming the loading envelope. Not just in its weight, thrust and torque, but also with a multitude of failure cases which the wingbox structure must withstand.
In general - where pylon mounted high-bypass engines are concerned - to integrate one in to a wing structure requires 'heavy' wing-box ribs, and some work to accommodate the pylon beam in the leading edge structure and maybe the introduction of a heavy fitting between two ribs to carry the aft pick-up pins. The chosen internal architecture of the wingbox will have a say in what is the most practical solution. Of course there will be lots of systems work involved in routing electrics/fuel/pneumatics/hydraulics to and from the engine itself (but as a structural engineer that doesn't bother me!
). It's likely that there will also be an effect on fuel tank configuration and architecture, if your engine is somewhere else other than on the wing.
Having read some of the posts above, I think I should say that this is not a configuration decision that can be changed - you decide where your engines go, and that's where they stay. It must be understood that this is one of the major early decisions in an aircraft projects life. If you go from a T-tail or an integrated engine design to a podded design - you start again. And this would never happen after a configuration had been selected.
In general - where pylon mounted high-bypass engines are concerned - to integrate one in to a wing structure requires 'heavy' wing-box ribs, and some work to accommodate the pylon beam in the leading edge structure and maybe the introduction of a heavy fitting between two ribs to carry the aft pick-up pins. The chosen internal architecture of the wingbox will have a say in what is the most practical solution. Of course there will be lots of systems work involved in routing electrics/fuel/pneumatics/hydraulics to and from the engine itself (but as a structural engineer that doesn't bother me!
). It's likely that there will also be an effect on fuel tank configuration and architecture, if your engine is somewhere else other than on the wing.Having read some of the posts above, I think I should say that this is not a configuration decision that can be changed - you decide where your engines go, and that's where they stay. It must be understood that this is one of the major early decisions in an aircraft projects life. If you go from a T-tail or an integrated engine design to a podded design - you start again. And this would never happen after a configuration had been selected.
Edited by coanda on Wednesday 18th July 23:34
To add to coanda, its part of your integrated control system on the plane. Not just the physical immediate structural forces, but your flight control system is then designed around that decision. Whilst it is one thing to tweak it ways various during upgrades, the designs are utterly different for wing or tail engines. If for instance you put a control system into an aircraft with tail engines that was designed for a wing engined aircraft, the whole thing would be so out of wack, you could well rip the wings off as you would load the aircraft in a completely alien way to it was physically designed.
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