Patent Application
20130001356
The present invention relates to the rear fuselage of an aircraft with propeller engines and more particularly to a reinforced fuselage for withstanding impacts and damages due to failure events of the propeller engines.
There are known commercial aircrafts (CBA vector 123, SARA, AVANTI, 7J7) powered with propeller engines located in the rear part of the aircraft supported by the fuselage by means of pylons.
One of the problems raised by this aircraft configuration is related to failure events such as a PBR (“Propeller Blade Release”) event, i.e. an event where a blade of one of the propeller engines comes off and hits the fuselage, an UERF (“Uncontained Engine Rotor Failure”) event, i.e. an event where a part of the rotor of the engine brakes, it is released and hits the fuselage, an ice shedding event where ice shedding created in the tips of the blades can be thrown at high speed over the fuselage, or any other “Large Damage” event.
The design of said rear fuselage shall therefore take into account such events and guarantee its capability for maintaining stability and proceed to a safe landing, i.e. shall be an impact resistant and damage tolerant fuselage.
As a consequence of the failure in the engine one of the blades of the propeller engine or any other engine component can be detached and impact against the rear fuselage at high speed, sectioning it. In this emergency condition, the aircraft operates with only one engine generating a forward thrust outside the plane of symmetry of the airplane. This thrust causes a yawing moment which must be balanced with a side aerodynamic force caused by the vertical tail plane of the empennage, so that the aircraft can continue navigating stably. As the vertical tail plane is located above the rear fuselage, this side aerodynamic force generates a torsion along the rear fuselage. If the blade impacts against the fuselage and sections it, the torsional strength of the fuselage is considerably reduced because the torsional rigidity of a closed section is proportional to the total area enclosed by the section, whereas the torsional rigidity of an open section is proportional to the material area of the section.
Propeller engines may also be located in the wing such that the detachment of a propeller blade can impact the central fuselage in front of the wing. In this area of the fuselage, the torsion that the mentioned fuselage must support is relatively low, and do not involve a critical emergency condition. However, this condition changes when the propeller engines are located at the rear part of the aircraft in front of the empennage, because then the torque generated by the empennage due to the failure of an engine is very high and can cause a catastrophic situation for the aircraft which must be prevented.
WO 2009/068638 discloses an impact resistant fuselage made with composite materials comprising an outer skin and an inner skin, both skins being joined by means of radial elements configuring then a multi-cell structure providing the required torsional strength in the rear part of said aircrafts.
The present invention is also addressed to attend the aeronautical industry demand related to rear fuselages subjected to said failure events and propose a different solution than WO 2009/068638.
It is an object of the present invention to provide an aircraft having attached a propulsion system to the rear fuselage by means of upstream pylons highly resistant to the torsional loads produced in case of a failure event such as a PBR event or an UERF event.
It is another object of the present invention to provide an aircraft having attached to the rear fuselage a propulsion system by means of upstream pylons having an impact resistant structure to withstand a failure event such as a PBR event, a UERF event or an ice shedding event.
It is another object of the present invention to provide an aircraft having attached to the rear fuselage a propulsion system by means of upstream pylons having a damage tolerant structure to withstand a failure event such as a PBR event, a UERF or an ice shedding event.
These and other objects are met by an aircraft having attached to the rear fuselage a propulsion system by means of upstream pylons; the aircraft comprising a vertical tail plane attached to the rear fuselage; the rear fuselage extending from a rear pressure bulkhead to the aircraft tail, comprising a skin and a plurality of frames arranged perpendicularly to a central longitudinal axis and having a curved shape with at least a vertical symmetry plan; the vertical tail plane comprising a torsion box with left and right skins, frontal and rear spars and a plurality of ribs, also comprising a resistant structure connecting said vertical tail plane with the rear fuselage that acts as a redundant load path in failure events of the propulsion system that can produce damages in the rear fuselage (such as a PBR event, an UERF event and an ice shedding event).
In embodiments of the present invention, said resistant structure is a beam and the aircraft also comprises a non-resistant fairing shaped as a dorsal fin covering said beam. Hereby it is achieved an aircraft better prepared for facing said events because it provides an additional load path external to the fuselage without aerodynamical detrimental effects.
In embodiments of the present invention, said resistant structure comprises a beam and a resistant fairing shaped as a dorsal fin covering said beam. Hereby it is achieved an aircraft with a dual protection for facing said events.
In embodiments of the present invention said beam is connected, on one side, to the closer frame to the rear pressure bulkhead and, on the other side, to a junction of a rib with the frontal spar of the vertical tail plane. Therefore the connection points of the beam with the rear fuselage and the vertical tail plane are outside of the main area affected by said failure events.
In embodiments of the present invention, the angle between the longitudinal axis of said beam and an horizontal plane is comprised between 10° and 30°. In that position the beam covers a significant proportion of the risks associated a said failure events.
In embodiments of the present invention, said beam has one or more intermediate supports on the rear fuselage to prevent buckling. These intermediate supports can be easily placed inside the fairing that covers the beam so that they do not have any aerodynamical detrimental effect.
In embodiments of the present invention the transversal section of said beam is a closed-shaped section (preferably a tubular shape). The beam is therefore suitable shaped for withstanding tensile stresses.
In embodiments of the present invention with a resistant fairing, the fairing comprise a resistant skin and reinforcing elements suitable dimensioned for withstanding the loads foreseen for each type of fairing.
In embodiments of the present invention, the fairings can be single parts attached to the vertical tail plane and to the rear fuselage or extensions of the vertical tail plane.
Other characteristics and advantages of the present invention will be clear from the following detailed description of embodiments illustrative of its object in relation to the attached figures.
a and 1b show, respectively, lateral and plan schematic views of the rear part of an aircraft with propeller engines.
a and 2b are, respectively, cross section and perspective schematic views of the rear fuselage of an aircraft according to the present invention.
In the aircraft shown in
The vertical tail plane 21, attached to the rear fuselage 31, comprise a leading edge, a torsion box, a trailing edge, a root joint, and a tip. The torsion box comprise spars 51, 53, ribs 55 and left and right skins stiffened by stringers. The left and right skins are joined to the leading edge and to the trailing edge panels forming its aerodynamic contour.
The main structural elements of the rear fuselage 31, as in a typical aircraft fuselage, are the skin 35, the frames 37 and the stringers (not shown). The skin 35 is stiffened longitudinally with stringers to reduce the skin thickness, making it more competitive in terms of weight, while the frames 37 avoid the overall instability of the fuselage and can be subjected to the introduction of local loads.
Therefore, in the attaching areas of the vertical tail plane 21 and the pylons 17 the structural elements of the rear fuselage 31 and particularly the frames 37 are suitable designed for withstanding the loads introduced by them.
On the other hand, the rear fuselage 31 may also comprise other structural elements to provide the high torsional strength needed to deal with an event of a detachment of a propeller blade 15 from an engine of the propulsion system 13 causing on one side a torsion over the fuselage due to the yawing moment generated by the stop of the engine and the torque generated by the empennage to balance said yawing moment, and causing on the other side damages to the fuselage if the detached blade impacts on it that, obviously, reduce its torsional strength.
In this context, the basic idea of the present invention is adding a resistant structure connecting the vertical tail plane 21 with the rear fuselage 31 that acts as a redundant load path in said failure events.
In embodiments of the invention (see particularly
In embodiments of the invention the fuselage zone 45 to which the beam 41 is connected is a zone located over the closer frame 37 to the rear pressure bulkhead 27 so that the load of the beam 41 can be translated directly to said frame 37. The attachment between the beam 41 and the frame 37 can be made using suitable fittings.
Similarly the zone 49 of the torsion box of the vertical tail plane 21 to which the beam 41 is connected is located over the junction of a rib 55 with the frontal spar 51 and the attachment between said elements can be made using suitable fittings.
Taking into account the above-mentioned requirements for the beam connection zones 45, 49 it is considered that the angle between the longitudinal axis of the beam 41 and an horizontal plane (i.e. a perpendicular plane to the symmetry plane A-A) is comprised between 10° and 30°.
In preferred embodiments said beam 41 has a closed-shaped transversal section and particularly a tubular shaped transversal section.
In embodiments of the invention (see particularly
As shown in
In embodiments of the invention (see particularly
In embodiments of the invention (see particularly
Said fairings 63, 63, 67 will be preferably arranged as single parts attached to the vertical tail plane 21 as illustrated in
In addition to said new load path, the resistant structure according to this invention produce the following technical effects:
Increases the bending stiffness and strength of the rear fuselage 31 to achieve a damage tolerant structure capable to cope with the damages caused by the impact of a propeller blade 15 detached from an engine 13.
Increases the sideforce of the vertical tail plane 21 and the stall angle.
Provides a shield against the noise caused by the propulsion system 13.
Provides a shield for ice shedding events.
Although the present invention has been fully described in connection with preferred embodiments, it is evident that modifications may be introduced within the scope thereof, not considering this as limited by these embodiments, but by the contents of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201131120 | Jul 2011 | ES | national |
