Trident / Tristar question

[tigercat]

I'm thinking of doing an aircraft with an engine faired into the tail like the Trident and the Tristar.

I can see where the air goes in for the middle engine I assume the jet comes out the stern of the aircraft rather than straight through in a conventional aircraft.

[JayBee]

Hi TC,

In both types the engine is mounted right at the back of the fuselage, the intake ducting in front of it has a double bend.

Jim

[Leading Observer]

I believe that the DC-10 had the engine mounted in the fin, so was staright through

[PR19_Kit]

DC10s, MD11s and all other variants had straight through air flow, it's quite obvious if you look at a direct side view of the aircraft.

The Trident, 727, Tri-Star and Falcon 50 (and maybe others...) all have an S duct to feed the air to the centre engine, as Jaybee said. Once again a direct side view shows the shape of the duct.

[rallymodeller]

Also the Tu-154, Yak-40 and Yak-42. The term "S-duct" is actually the technical name for the intake ducting. The trick with it is to get the maximum amount of airflow into the engine while losing as little air velocity as possible. While the DC-10-style has advantages in terms of design simplicity, having the #2 engine buried in the tail makes for simpler engine-out handling as well as better overall aerodynamics. With the retirement of the Convair 990s and both SST types, the Tu-154M is the fastest cruising airliner in the world.

[PR19_Kit]

While the DC-10-style has advantages in terms of design simplicity, having the #2 engine buried in the tail makes for simpler engine-out handling as well as better overall aerodynamics.

Having watched a Northwest ground crew taking the #2 engine out of a DC10, I'd say the maintenance aspects of the lower engine height in the Tri-Star would have been a positive point too. They had to use HUGE ladders and some special bracketry to swing the engine rearwards and then down to the ground.

[rallymodeller]

While the DC-10-style has advantages in terms of design simplicity, having the #2 engine buried in the tail makes for simpler engine-out handling as well as better overall aerodynamics.

Having watched a Northwest ground crew taking the #2 engine out of a DC10, I'd say the maintenance aspects of the lower engine height in the Tri-Star would have been a positive point too. They had to use HUGE ladders and some special bracketry to swing the engine rearwards and then down to the ground.

It does from a maintenance standpoint; however, once you commit to a specific engine in a buried design you are pretty much stuck with that engine for good unless you want to redesign the entire rear fuselage. Boeing ran into this issue when trying to re-engine the 727 to meed Stage III noise limits. For Stage II, it's OK to fit the aircraft with hush kits (i.e. big mufflers) but Stage III requires a quieter engine overall. B727 Super 27s with the quieter JT8D-27 engine variant can only get the quieter powerplants in the engine pods, while the tail engine remains a hush-kitted JT8D-17. The same goes for the Tristar which was only available with the Rolls-Royce RB211, while the DC-10 on the other hand has been available with several different engines over its life. This is also one of the major reason that there are no more flying Tridents; the RR Spey is LOUD (and thirsty, and dirty) and there was no economical way to fit a quieter motor (RR Tays were suggested) without basically redesigning the plane's entire empennage.