A mobile platform for inspecting a long hollow structure having tapered internal cavities which are difficult to access, the mobile platform comprising: a frame; a first support block fixedly mounted to said frame; a second support block that is supported by and slidable relative to said frame; a horizontal lead screw rotatably coupled to said first support block and threadably coupled to said second support block so that said second support block will move linearly relative to said first support block when said lead screw rotates; a motor coupled to said lead screw for driving rotation of said lead screw; and a first link having a proximal end pivotably coupled to said first support block; characterized by further comprising: a second link that is twice the length of the first link and having a proximal end pivotably coupled to said second support block, said first and second links being pivotably coupled to each other at a midpoint of said second link, a vertical position of a distal end of said second link being a nonlinear function of rotation of said lead screw; and a payload platform pivotably coupled to said distal end of said second link, wherein said payload platform is translated in a direction perpendicular to said lead screw during rotation of said lead screw wherein the payload platform is configured for attaching a nondestructive inspection sensor. a frame; a first support block fixedly mounted to said frame; a second support block that is supported by and slidable relative to said frame; a horizontal lead screw rotatably coupled to said first support block and threadably coupled to said second support block so that said second support block will move linearly relative to said first support block when said lead screw rotates; a motor coupled to said lead screw for driving rotation of said lead screw; and a first link having a proximal end pivotably coupled to said first support block; characterized by further comprising: a second link that is twice the length of the first link and having a proximal end pivotably coupled to said second support block, said first and second links being pivotably coupled to each other at a midpoint of said second link, a vertical position of a distal end of said second link being a nonlinear function of rotation of said lead screw; and a payload platform pivotably coupled to said distal end of said second link, wherein said payload platform is translated in a direction perpendicular to said lead screw during rotation of said lead screw wherein the payload platform is configured for attaching a nondestructive inspection sensor. a second link that is twice the length of the first link and having a proximal end pivotably coupled to said second support block, said first and second links being pivotably coupled to each other at a midpoint of said second link, a vertical position of a distal end of said second link being a nonlinear function of rotation of said lead screw; and a payload platform pivotably coupled to said distal end of said second link, wherein said payload platform is translated in a direction perpendicular to said lead screw during rotation of said lead screw wherein the payload platform is configured for attaching a nondestructive inspection sensor.