Thrust vectoring on commercial jets

Fabrizio Mazzoni
  • Thrust vectoring on commercial jets Fabrizio Mazzoni

    Is there a particular reason for which thrust vectoring is not used in airliners as with military aircraft besides weight and complexity factors?

    I understand that on military aircraft maneuverability is a core component but, by implementing this technique also on commercial airliners, wouldn't there be any benefit? For example one thing that comes into my mind would be reduction of stress on the tail of an aircraft at high speed/high altitude turns, thus reducing maybe maintenance.

    Another option would be increased safety, whereas if maneuverability would be compromised by loss of the tail of the plane (for example American Airlines 587), you would still have some sort of control, even though reduced, on the plane with directional thrust.

  • Thrust vectoring is for flying outside the "normal" envelope (which is characterized by attached flow). Airliners should really never leave this envelope, so they are perfectly fine with regular control surfaces.

    If you want to add thrust vectoring, it would make most sense if the engines are at the back of the airplane. On most airliners, it is really better to put them on and ahead of the wings, because in this location they help both with flutter damping (mass ahead of the elastic line helps) and bending relief. Putting the engine mass right where lift is created is better than carrying stresses all around the airframe, which would be the case with rear-mounted engines.

    The redundancy point is valid, but it would be more helpful to have redundant control surfaces, and this is exactly what airliners have. At some point, every airplane has to come down for a landing, which requires to throttle the engines. No thrust, no control!

    Most extreme case: If one tail surface breaks off, I wonder if thrust vectoring would be up to the job of trimming the aircraft even with cruise thrust. Not only have the raw forces to be sufficient, the reaction time to control setting changes has to be quick enough to suppress oscillations. I am sure, however, that thrust vectoring will certainly not suffice in all flight phases.

    Thrust vectoring is perfect for situations at high angle of attack where you quickly want to point the nose of your aircraft at your adversary, so you get lock-on first. This is quite different from what an airliner has to do.

  • Thrust vectoring enables extreme maneuverability, airliners don't need that. Personally I don't want to be subjected to 9 Gs on the redeye from JFK to LHR! It's also very expensive technology to build and maintain, so your airfare would go up substantially. You also need a huge amount of power to make it work, so you'd have to fit afterburning engines to your commercial aircraft, which isn't workable.

    Anyway, differential thrust is already an option on airliners and other aircraft which have engines outboard on the wings. A B-52H lost its tail in the 1960s and made it back, the pilots made good use of differential thrust. UA232 used differential thrust after they lost hydraulics.

    So it's a technology that is expensive to implement, and isn't going to help prevent an accident.

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