Monolithic lipskin and method of fabrication

A method of forming a monolithic lipskin for an aircraft nacelle, the method comprising the steps of:

• forming an annular plate of metal onto a mandrel, the annular plate having inner and outer edges, an inner mold line (IML) surface, and an outer mold line (OML) surface opposite the IML surface, wherein the forming deforms the annular plate into an annular three-dimensionally curved surface having an apex between the inner and outer edges;
• selectively removing material from the IML surface, forming a plurality of protrusions for attachment or structural stiffening of the monolithic lipskin;
• and
• dividing the annular plate into two or more segments after the step of forming, wherein the protrusions include joint flanges formed at edges of the segments of the annular plate during the step of selectively removing material, wherein the joint flanges have holes formed therethrough, the method further comprising a step of mechanically attaching the segments of the annular plate back together by inserting mechanical fasteners through the holes in the joint flanges.

A method of forming an aircraft nacelle with a monolithic lipskin, the method comprising the steps of:

• spin-forming an annular plate of metal onto a spinning mandrel, the annular plate having inner and outer edges, an inner mold line (IML) surface, and an outer mold line (OML) surface opposite the IML surface, wherein the spin-forming deforms the annular plate into an annular three-dimensionally curved surface having an apex between the inner and outer edges;
• machining or chemically milling the IML surface into a plurality of protrusions for attachment or structural stiffening of the monolithic lipskin, wherein the protrusions include a plurality of stiffeners and an attachment flange, wherein the stiffeners have a circular or a spiral configuration and are sized and oriented in accordance with a finite element analysis model of the aircraft nacelle, wherein the stiffeners are continuous or segmented into a plurality of stiffener segments forming the circumferential or spiral configuration, wherein the machining or chemical milling step occurs prior to the step of spin-forming, and the spinning mandrel includes a plurality of grooves or indentions formed therein, the grooves or indentions having a size, configuration, and spacing corresponding to the plurality of protrusions, such that the plurality of protrusions nest within the grooves or indentions when the annular plate is spin-formed onto the spinning mandrel;
• mechanically attaching a bulkhead to the attachment flange proximate an outer edge of the bulkhead;
• mechanically attaching a flange of the bulkhead to the monolithic lipskin at the inner edge of the annular plate, wherein the flange is located at an inner edge of the bulkhead, opposite the outer edge of the bulkhead;
• and
• mechanically attaching the flange of the bulkhead to a fan cowl having a front edge abutting the inner edge of the annular plate.

A method of forming an aircraft nacelle with a monolithic lipskin, the method comprising the steps of:

• spin-forming an annular plate of metal onto a spinning mandrel, the annular plate having inner and outer edges, an inner mold line (IML) surface, and an outer mold line (OML) surface opposite the IML surface, wherein the spin-forming deforms the annular plate into an annular three-dimensionally curved surface having an apex between the inner and outer edges;
• machining or chemically milling the IML surface into a plurality of protrusions for attachment or structural stiffening of the monolithic lipskin, wherein the protrusions include a plurality of stiffeners and an attachment flange, wherein the stiffeners have a circular or a spiral configuration and are sized and oriented in accordance with a finite element analysis model of the aircraft nacelle, wherein the stiffeners are continuous or segmented into a plurality of stiffener segments forming the circumferential or spiral configuration;
• mechanically attaching a bulkhead to the attachment flange proximate an outer edge of the bulkhead;
• mechanically attaching a flange of the bulkhead to the monolithic lipskin at the inner edge of the annular plate, wherein the flange is located at an inner edge of the bulkhead, opposite the outer edge of the bulkhead;
• mechanically attaching the flange of the bulkhead to a fan cowl having a front edge abutting the inner edge of the annular plate;
• and
• dividing the annular plate into two or more segments after the step of spin-forming, wherein the protrusions include joint flanges formed at edges of the segments of the spin-formed annular plate, wherein the joint flanges have holes formed therethrough, the method further comprising a step of mechanically attaching the segments of the spin-formed annular plate back together by inserting mechanical fasteners through the holes in the joint flanges.