2
$\begingroup$

Most civil multiengine jets and some civil multiengine propeller aircraft have engines mounted in nacelles on the ends of pylons extending some distance away from the wing or fuselage. Wing-mounted engine pylons generally extend vertically from the lower (or occasionally upper) surface of the wing; in contrast, fuselage-mounted engine pylons tend to stick out horizontally from the (almost always aft) fuselage.

In some cases, this horizontal pylon surface can get quite large:

Embraer concept drawing with turboprops on long tail-mounted pylons

(Image by Arjan Meijer at Twitter, showing a propliner under development by Embraer with turboprops on empennage-mounted nacelles, necessitating quite long pylons to allow the propellers to clear the fuselage.)

Additionally, at least one airliner had control surfaces mounted on the engine pylons, although these were only used as a stall-recovery aid.

On aircraft with horizontal engine pylons, are the pylons usually shaped to produce lift (either up or down)?

$\endgroup$
1
0
$\begingroup$

Like a flat plate, the horizontal pylons will generate lift at higher Angle of Attack, with little matter as to how they are shaped. Aerodynamic optimisation of the pylons and the nacelles during the design phase are listed in Torenbeek section 6.5.2 as follows:

  1. Avoiding drag problems due to boundary layer separation in the divergent portion of the convergent-divergent channel formed by the nacelle, the pylon and the adjacent fuselage wall.
  2. Configuring the nacelle behind and above the wing to create an effective Whitcomb-body effect, and increase the drag-critical Mach number of the aeroplane.
  3. Since the nacelles are located behind the aerodynamic center of the wing, they will cause the aerodynamic center to move backwards. This stabilizing effect is partly compensated by an increment in the downwash at the horizontal tailplane due to the low effective aspect ratio of the nacelle/pylon combination.

  4. At large angles of attack, particularly when the airflow over the wing has separated, the wake created by the nacelles and the pylons may greatly reduce the effectiveness of the horizontal tailplane. For this reason the location of the engines will be a factor in connection with the deep stall problem (cf. Section 2.4.2.).

(3. and 4. are direct citations.) The low aspect ratio of the pylon/nacelle combination creates problems, unlike the stabilons of the Beech 1900-D which alleviate problems with deep stall.

enter image description hereCropped photo from Airliners.net

So the pylons are aerodynamically optimised, and lift generation is part of the optimisation process. And as mentioned in this answer: deflected thrust counts as lift as well.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.