Engine tail/wing

Tailmounted engine aircraft have shorter rudders which leads to tougher crosswind landings (my opinion).

A disadvantage of tail mounted engines, is that the wing has to be made a lot stronger/stiffer and hence the wings are heavier.

With wing mounted engines, the weight of engines relieve the bending stresses in the wing, caused by lift. This allows for a lighter wing structure.

With tail mounted engines, the wing has to be built to withstand these bending stresses, hence are made stronger/stiffer and heavier.

A nice picture of a tail mounted engined aircraft.
http://www.airliners.net/open.file/326271/L/
Do engines on the tail also improve take off performance? Just because the MD80 and 90 had quite good TO performance!

Since nobody mentioned it … the weight of the landing gear is very much lower on a tail mount because it is much shorter. We are talking tons here.
Every configuration has its pros and cons, but basically wing mount prevails because the airlines are a bunch of conservative bean counters and don’t want to take no risk with a/c configurations. Otherwise we should see BWB in commercial air transport by now.

I am struggling to think of a typical exec jet that does not have rear mounted engine regardless of whether they have 2 (Bae 125/Citation/Learjet/Gulfstream) 3 (Falcon 50 / 900) or 4 (Jetstar)
possibly to make the cabin as quiet as possible so increasing the ‘luxury’ of being in one.

I really don’t know much about exec jets but I would imagine that a really long haul exec jet is going to benefit from an increased number of smaller powerplants in the same way as an airliner, however I guess the lack of space under the wing precludes the 4 engine option. A VC10 style quad engine layout probably just isn’t worth the development cost as current tri layouts are just fine at the moment. Perhaps the development of all these new microjet engines may change things.

do tri-engines based airframes give more from the aircraft in executive jets?

…but to answer your question properly…I have never flown an aircraft with rear engines (I tell a lie I have flown a few light aircraft with the engine at the wrong end!) however the fact that all the noise is contained in the economy section and as far as possible from my office coupled with the ease of assymetric flight would make me keen to fly one.

On the other hand you could just follow the Airbus principle and have the FBW take away all the hassle of pitch/power couples and assymetries! Incoming…

Whichever one pays the higher salary! 😀

Seriously, these days rear engines are generally found on regional aircraft (smallish airframes with not enough space under the wing to stick a high bypass turbine) so they command regional type salaries. Big aircraft generall command bigger salaries and tend to have underslung power units. I go where the money is!

Thanks wys and Paul.

And what about the pilot point of view? What are the differences in term of a/c behavior?

Originally posted by Arthur
Your wing is aerodynamically and lift-wise cleaner without engines dangling off them too.

While this was definitely the case with older aircraft I remain to be convinced with modern installations. Current pod and pylon design acts as a very effective lower surface wing fence restricting spanwise flow!

Originally posted by markkipling
Apologies, slight confusion on my part, was thinking tail mounting along the lines of 727 L1011 etc. Sorry, mustnt reply to posts before 10am

Actually Mark I think you’re taking the thread in a very associated but slightly different direction…which is good! I tend to only ever think of twins and tend to forget the tri’s.

The DC10 actually has a small ‘workshop’ built in to the rear upper fuselage to facilitate work on the number 2 engine!!! My company would only ever use reverse thrust on the center engine at home base (unless they REALLY needed it of course!) in case the reverser failed to restow and you needed an engineer.

Your wing is aerodynamically and lift-wise cleaner without engines dangling off them too.

Apologies, slight confusion on my part, was thinking tail mounting along the lines of 727 L1011 etc. Sorry, mustnt reply to posts before 10am

There are good and bad points about either arrangement and have assumed low wing aircraft rather than high wing (such as Bae 146)

wing mounted engines good points include :

easy access for maintenance & replacement
close proximity to fuel tanks so less ‘plumbing’

wing mounted engines bad points :

easy to injest stones / objects etc
higher risk of ground strikes
higher risk on damage by ramp vehicles
assymetric thrust problems if 1 fails
larger u/c needed for ground clearance so adding weight to the overall structure

Tail mounted engines good points

little assymetric effect if 1 fails
allows for a aerodynamically clean wing
less prone to fod damage
ground clearance does not need to be as high so smaller / less heavy u/c can be used.

Tail mounted engines bad points

complex ‘plumbing’ arrangements for fuel etc
deep stall risk
access difficult
concentration of weight at one end of the fuselage (CoG issues)
uncontained failure more likely to damage structure / other engine
(VC10 / Il62)

accesibilty?? how?

Just for starters, advantages of tail mounting:

1) Increased distance from runway so reduced chance of foreign object ingestion.
2) Quiet cabin (except for the area alongside the engines).
3) No risk of a pod scrape during a wing down crosswind landing.
4) The engine thrust line is about as close as you can get to the centerline of the aircraft so there will be minimal nose up/down pitch change with addition/removal of power.
5) Laterally the engines are also immediately proximate to the centerline so an engine out situation causes the minimum possible swing.
6) For non-FBW installations the thrust lever linkages have a much straighter and easier routing.
7) In my view they just look right on regional aircraft!

Disadvantages of tail mounting:

1) possible ingestion of contaminants from the top surface of the wings (eg anti-icing fluids, etc)
2) high g loadings cause greater shear forces on mounting pylons.
3) on large aircraft it can be difficult to inspect the engines during walkround.
4) this also means increased difficulty servicing the engine in situ on larger aircraft.
5) on many installations the fuselage area just inside the cabin from the engines is taken up with mounting and engine services so the fuselage ends up being longer than it would need to otherwise be. The alternative to the longer airframe is reduced cabin volume.
6) Engines are mounted higher than the tanks that feed them so in the event of total fuel pump failure there would only be the natural suction from the engines rather than gravity assisted flow.
7) Tailpanes invariably have to be relocated to the top of the fin requiring a stronger fin structure and therefore increased weight and more complication for de-icing on large aircraft. This also leeds to ‘deep stall’ tendencies.
8) Engine intakes may well suffer from bad airflow due to air passage around the fuselage or wing. They can also suffer from water spray ingestion from deflected nosewheel spray.

I believe the main advantage is accessability (if you mean wing mounted engines)?