Engine locations
Engine locations
(OP)
Hi
Many new large aircraft (Boeing, Airbus...) have the engines located under the wings.
I don't know if they are around anymore, but I remember the planes with two or three engines located at the tail of the plane.
What are the main benefits of installing the engines at the back? Is the balance and flight characteristics affected much?
Many new large aircraft (Boeing, Airbus...) have the engines located under the wings.
I don't know if they are around anymore, but I remember the planes with two or three engines located at the tail of the plane.
What are the main benefits of installing the engines at the back? Is the balance and flight characteristics affected much?





RE: Engine locations
Other reasons include a lower ground stance for the smaller business size jets, and being higher they are less likely to injest rocks or anything else that might come off the runway. (like concord tires)
The main reason for putting the engines under and forward of the wing is because they generate the least possible amount of drag there, and they also help by being near the center of gravity. There is also a drag penalty caused by the air flowing between the engines and the fuselage on rear-mounted aircraft like the ones you mention.
aerodynamics and weight considerations aside, it's also much easier to work on an engine that is hanging right in front of your face instead of having to use a lift to obtain access to the engines
RE: Engine locations
RE: Engine locations
and then there are dynamic effects from landing
both of these are quite a bit less significant for fuselage mounted engines
RE: Engine locations
RE: Engine locations
i know this is the new honda-jet, a similar configuration was tried in the 70s/80s, the VFW614 i think; i guess it's a way to improve the ground clearance issues (of an under wing installation) i wonder ('cause i'm not smart enough to know) about the aerodynamic effects (is there a shock on the wing? (probably not) how does the the higher velocity airflow affect things ? (airflow above the wing is faster (locally) than below the wing)
there is also the option of submerging the engines in the wing root (a la comet, nimrod). this style has gone out of fashion, i guess because of the structural weight, manufacturing complexity, servicing/maintenance access issues.
RE: Engine locations
RE: Engine locations
RE: Engine locations
RE: Engine locations
debodine
RE: Engine locations
RE: Engine locations
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Regards
Fernando
RE: Engine locations
Regards
Dave
RE: Engine locations
Today jet engines are still frequently mounted below the wing as it is a structurally convenient location to do so. In addition to all the info in the above messages, the spar and skin of the wings are already "beefy" to take the shears and bending moments of flight, so not much additional thickening is required to react the loads of a wing-mounted engine. Aft fuselages without an aft-mounted engine tend to be fairly light, but placing engines in this area introduces significant additional structure (and thus weight) in order to take the loads. This is offset, to some extent, by the opportunity of using a shorter, lighter landing gear as in this case there is no protuberance beneath the wing to worry about.
This is made less straight-forward by rotation angles and runway clearances. When taking-off with a long fuselage, it is easier to get a tail strike on rotation, so to counteract that, longer 'planes tend to have longer gear. So if you have a long aircraft, you may as well use a wing-mounted, under-slung engine as you are stuck with using a tall, heavy landing gear anyway, and the wing is a good place to mount the engine. If you have a short aircraft and you can get away with a shorter, lighter landing gear and still achieve adequate runway clearance on rotation, then go for an aft-mounted engine and retain the short, light gear. Just beware of adding too much additional structure in the aft fuse to carry the engine.
There are many exceptions. The originally short DC-9 with aft-mounted engines was eventually stretched into the long MD-90 (although they tried hard to do most of the stretching forward of the landing gear to reduce the tail strike issue, I think), and the A320 with its under-slung engines and long gear was shrunk to the short A318. However, that these derivatives both are a long-way removed from their original concepts and they inherited their configurations. And there is also the case of high-wing aircraft, like the C-141, but they have to have different requirements compared the usual Airbuses & Boeings.
I recall that Dan Raymer's "Aircraft Conceptual Design" has a nice summary of engine-mounting options.
FastMouse
RE: Engine locations
Thanks, FastMouse
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Bring back the HP-15
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RE: Engine locations
Steven Fahey, CET
RE: Engine locations
Bombardier's C-series, currently existing on paper only, departs from their traditional aft fuse-mounted engines in that it has wing-mounted engines. (As an aside, it will be interesting to see how it performs in the market compared to Embraer's 170-195 family. Does Bombardier have the investment grunt required to make the C-series significantly better than the Embraer products and overcome their first-mover advantage and established product? Time will tell... Ah, it'll all come down to a subsidy shouting match anyway!)
Just for fun, I listed Embraer's & Bombardier's current commercial jets and sorted them by length. The data came from the companies' websites. I was vaguely hoping to see a definite fuselage length, on one side of which all the aircraft had fuselage-mounted engines, and on the other side of which all the aircraft had wing-mounted engines. However, this is what I got:
Manufacturer Aircraft Length (m) Engine Mounting
======== ===== ======= ==========
Embraer 135 26.33 fuselage
Bombardier CRJ 200 26.77 fuselage
Embraer 140 28.45 fuselage
Embraer 145 & 145 XR 29.87 fuselage
Embraer 170 29.90 wing
Embraer 175 31.68 wing
Bombardier CRJ 700 32.51 fuselage
Bombardier C110 35.56 wing
Embraer 190 36.24 wing
Bombardier CRJ 900 36.40 fuselage
Embraer 195 38.65 wing
Bombardier C130 38.76 wing
While the general trend is in-line with the previous post (short 'planes have aft fuse-mounted engines, and long 'planes have wing-mounted engines), the cross-over point is not distinct. This analysis is courageously simplistic, but it just goes to show that while you can forecast the trends, the constraints of design & tooling cost, time to market, etc, mean that it is hard to predict exactly what configuration will be chosen be the design team. I mean, what were the criteria that lead each manufacturer to acknowledge that its existing aircraft configuration had been fully exploited and a new configuration was needed?
It would be nice to include additional data from other manufacturers in the above list, and do some sort of correlation with range, manufacturer and product family. One could maybe even do a rough wing loading and high-lift analysis and guess how much growth potential Bombardier & Embraer have built into their initial designs for the C-Series & 170-195 family. Hmmm, well off topic now.
FastMouse
RE: Engine locations
Concorde had underwing engines and tall landing gear, yet still needed a "wheelie bar" to prevent tail strikes:
RE: Engine locations
1. Engine below wing:
Some Advantages
Less engine noise
Inertial relief (lighter wing structure weight)
Easy alternative to solve wing flutter problems by shifting the engine mass enough forward
Easy access for engine repair and overhaul
Undisturbed inlet flow for the engine inlet
Might be safer in case of engine fire
Some Disadvantages
May require longer landing gear
More chances of ingestion of debris from the runway during Take Off.
2. Engine above wing:
Some Advantages
Less engine noise
Inertial relief (lighter wing structure weight)
Easy alternative to solve wing flutter problems by shifting the engine mass enough forward
Less long landing gear required
Can have a positive influence on maximum lift capability in short take off runs (shorter TO distances)
Some Disadvantages
Less chances of ingestion of debris from the runway during Take Off
Disturbed air flow (shock waves possible and also possible wing boundary layer ingestion) to the inlet possible especially at high angles of attack
Less accessible for engine repair and overhaul
3. Engine at aft fuselage or tail:
Some Advantages
Less long landing gear required
Less chances of ingestion of runway debris during Take Off
Looks more esthetical
Some Disadvantages
Disturbed air flow to the inlet possible especially at high angles of attack
More engine noise
Maybe smaller aircraft W-CG limits constraints
No structure weight saving due to inertial relief
Usually requires a T-tail which is heavier in construction and has the potential for dangerous stall characteristics (deep stall)
OneMoreChance
RE: Engine locations
Less chances of ingestion of debris from the runway during Take Off
Should be in the Advantages-list.
OneMoreChance