Engine attachment system for aircraft and method for attaching an engine
An engine attachment system includes a strut box. The strut box includes a longitudinal axis, a forward portion that extends along the longitudinal axis, and an aft portion that extends from the forward portion along the longitudinal axis. The engine attachment system includes a forward attachment apparatus that is coupled to the forward portion of the strut box and that is coupleable to a forward spar of the wing. The engine attachment system includes an aft attachment apparatus that is coupled to the aft portion of the strut box and that is coupleable to an aft spar of the wing. When the strut box is coupled to the wing by the forward attachment apparatus and the aft attachment apparatus, the aft portion of the strut box is positioned under the wing. The strut box is coupleable to an engine.
1. An engine attachment system for attaching an engine to a wing of an aircraft, the engine attachment system comprising:
a strut box comprising a longitudinal axis, a forward portion extending along the longitudinal axis, and an aft portion extending from the forward portion along the longitudinal axis;
a forward attachment apparatus comprising:
an inboard forward fitting and an outboard forward fitting coupled to the forward portion of the strut box and coupleable to a forward spar of the wing;
a central forward fitting coupleable to the forward spar of the wing;
a central forward-fitting link coupled to the central forward fitting and to the forward portion of the strut box and comprising a catcher; and
a forward catcher fitting coupleable to the forward spar of the wing and comprising a catcher opening that receives the catcher of the central forward-fitting link; and
an aft attachment apparatus coupled to the aft portion of the strut box and coupleable to an aft spar of the wing,
wherein:
when the strut box is coupled to the wing by the forward attachment apparatus and the aft attachment apparatus, the aft portion of the strut box is positioned under the wing; and
the strut box is coupleable to the engine.
2. The engine attachment system of claim 1 , wherein, when the strut box is coupled to the wing by the forward attachment apparatus and the aft attachment apparatus, the aft portion of the strut box transverses a spanwise axis of the wing.
3. The engine attachment system of claim 1 , wherein:
the strut box further comprises:
a forward end and an aft end opposite the forward end along the longitudinal axis; and
an inboard side and an outboard side; and
when the strut box is coupled to the wing by the forward attachment apparatus and the aft attachment apparatus, the aft end of the strut box is located proximate to the aft spar of the wing.
4. The engine attachment system of claim 3 , wherein:
the inboard forward fitting is coupleable to the forward spar of the wing and is coupled to the forward portion of the strut box at the inboard side of the strut box;
the outboard forward fitting is coupleable to the forward spar of the wing and is coupled to the forward portion of the strut box at the outboard side of the strut box; and
the central forward fitting is coupleable to the forward spar of the wing and is coupled to the forward portion of the strut box between the inboard side and the outboard side of the strut box.
5. The engine attachment system of claim 4 , wherein:
the inboard forward fitting is coupled to the forward portion of the strut box by an inboard forward pin connection;
the outboard forward fitting is coupled to the forward portion of the strut box by an outboard forward pin connection;
the central forward fitting is coupled to the forward portion of the strut box between the inboard side and the outboard side of the strut box by a central forward pin connection; and
the aft fitting is coupled to the aft end of the strut box by an aft pin connection.
6. The engine attachment system of claim 5 , wherein:
the inboard forward fitting and the outboard forward fitting are configured to react to an X-directional force applied to the strut box;
the central forward fitting is configured to react to a Y-directional force applied to the strut box;
the inboard forward fitting, the outboard forward fitting, and the aft fitting are configured to react to a Z-directional force applied to the strut box;
the inboard forward fitting and the outboard forward fitting are configured to react to an X-directional moment applied to the strut box;
the inboard forward fitting, the outboard forward fitting, and the aft fitting are configured to react to a Y-directional moment applied to the strut box; and
the inboard forward fitting and the outboard forward fitting are configured to react to a Z-directional moment applied to the strut box.
7. The engine attachment system of claim 5 , wherein:
the inboard forward pin connection comprises an inboard double shear connection between the inboard forward fitting and the forward portion of the strut box;
the outboard forward pin connection comprises an outboard double shear connection between the outboard forward fitting and the forward portion of the strut box;
the central forward pin connection comprises:
a first central double shear connection between the central forward fitting and the central forward-fitting link; and
a second central double shear connection between the central forward-fitting link and the forward portion of the strut box; and
the aft pin connection comprises:
an aft-fitting link;
a first aft double shear connection between the aft fitting and the aft-fitting link; and
a second aft double shear connection between the aft-fitting link and the aft end of the strut box.
8. The engine attachment system of claim 7 , wherein:
the aft fitting is coupled to the aft end of the strut box proximate the inboard side of the strut box; and
the aft attachment apparatus further comprises a second aft fitting that is coupleable to the aft spar of the wing and that is coupled to the aft end of the strut box proximate the outboard side of the strut box.
9. The engine attachment system of claim 8 , wherein the second aft fitting is coupled to the aft end of the strut box by a second aft pin connection.
10. The engine attachment system of claim 9 , wherein:
the inboard forward fitting and the outboard forward fitting are configured to react to an X-directional force applied to the strut box;
the central forward fitting, the aft fitting, and the second aft fitting are configured to react to a Y-directional force applied to the strut box;
the inboard forward fitting, the outboard forward fitting, the aft fitting, and the second aft fitting are configured to react to a Z-directional force applied to the strut box;
the inboard forward fitting, the outboard forward fitting, the aft fitting, and the second aft fitting are configured to react to an X-directional moment applied to the strut box;
the inboard forward fitting, the outboard forward fitting, the aft fitting, and the second aft fitting are configured to react to a Y-directional moment applied to the strut box; and
the inboard forward fitting and the outboard forward fitting are configured to react to a Z-directional moment applied to the strut box.
11. The engine attachment system of claim 10 , wherein at least one of the inboard forward fitting, the outboard forward fitting, the central forward fitting, the catcher fitting, the aft fitting, and the second aft fitting provide an alternate failsafe load path upon a failure of another one of the inboard forward fitting, the outboard forward fitting, the central forward fitting, the aft fitting, and the second aft fitting.
12. The engine attachment system of claim 10 , wherein:
one of the aft fitting and the second aft fitting is configured to provide a failsafe load path to react to the Y-directional force and the Z-directional force to the strut box upon a failure of another one of the aft fitting and the second aft fitting; and
the inboard forward fitting, the outboard forward fitting, and the one of the aft fitting and the second aft fitting provide a redundant load path to react to the Y-directional moment and the Z-directional moment applied to the strut box upon the failure of the another one of the aft fitting and the second aft fitting.
13. The engine attachment system of claim 10 , wherein:
the catcher fitting is configured to provide a failsafe load path to react to the Z-directional force and the X-directional moment applied to the strut box upon a failure of one of the inboard forward fitting and the outboard forward fitting;
the aft fitting, the second aft fitting, and another one of the inboard forward fitting and the outboard forward fitting provide a redundant load path to react to the Y-directional moment applied to the strut box upon the failure of the one of the inboard forward fitting and the outboard forward fitting; and
the another one of the inboard forward fitting and the outboard forward fitting provides a redundant load path to react to the Z-directional moment applied to the strut box upon the failure of the one of the inboard forward fitting and the outboard forward fitting.
14. The engine attachment system of claim 9 , wherein the second aft pin connection comprises:
a second aft-fitting link;
a third aft double shear connection between the second aft fitting and the second aft-fitting link; and
a fourth aft double shear connection between the second aft-fitting link and the aft end of the strut box.
15. The engine attachment system of claim 1 , wherein:
the aft portion of the strut box has an aft-portion length; and
the aft-portion length is selected for a predetermined vibrational frequency of the strut box.
16. The engine attachment system of claim 1 , wherein:
the aft portion of the strut box has a first aft-portion width and a second aft-portion width;
the first aft-portion width and the second aft-portion width are different; and
the first aft-portion width and the second aft-portion width are selected for a predetermined vibrational frequency of the strut box.
17. The engine attachment system of claim 1 , wherein:
the aft portion of the strut box has a first aft-portion height and a second aft-portion height;
the first aft-portion height and the second aft-portion height are different; and
the first aft-portion height and the second aft-portion height are selected for a predetermined vibrational frequency of the strut box.
18. An aircraft comprising:
a fuselage;
a wing coupled to and extending from the fuselage, wherein the wing comprises a midline spanwise axis, a forward spar forward of the midline spanwise axis, and an aft spar rearward of the midline spanwise axis;
a strut box comprising a longitudinal axis, a forward portion extending along the longitudinal axis, and an aft portion extending from the forward portion along the longitudinal axis, positioned under the wing, and transversing the midline spanwise axis of the wing;
a forward attachment apparatus coupled to the forward portion of the strut box and coupled to the forward spar of the wing; and
an aft attachment apparatus coupled to the aft portion of the strut box and coupled to the aft spar of the wing; and
an engine coupled to the strut box.
19. A method for attaching an engine to a wing of an aircraft, the method comprising steps of:
positioning a strut box relative to the wing such that an aft portion of the strut box is positioned under the wing and transverses a midline spanwise axis of the wing;
coupling the strut box to a forward spar of the wing using a forward attachment apparatus at a position forward of the midline spanwise axis;
coupling the strut box to an aft spar of the wing using an aft attachment apparatus at a position rearward of the midline spanwise axis; and
coupling the engine to the strut box.
20. The aircraft of claim 18 , wherein the forward attachment apparatus comprises:
an inboard forward fitting coupled to the forward portion of the strut box and to the forward spar of the wing;
an outboard forward fitting coupled to the forward portion of the strut box and to the forward spar of the wing;
a central forward fitting coupled to the forward spar of the wing;
a central forward-fitting link coupled to the central forward fitting and to the forward portion of the strut box and comprising a catcher; and
a forward catcher fitting coupled to the forward spar of the wing and comprising a catcher opening that receives the catcher of the central forward-fitting link.