PrusaSlicer 2.9 seems to ignore bridge direction.  

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

It should. Would you please upload a 3mf project file (zip compressed, or the forum software will silently ignore it) so we we can see your settings and the model topology? Use the Attach file button below the post edit window.

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

cover-PTest.3mf
In this test, it doesn't seem to matter what I set the Bridging angle to... the result is the same..

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

@nanoplane

         If you add at least one bottom layer, I'd recommend more if your project can afford it.

Print Settings>Layers and perimeters>[Horizontal shells] Solid layers: Bottom: (set to at least one layer)

Then go to Print Settings>Infill>[Advanced]Bridging angle: and set it to 135 degrees

I would also recommend turning on "Detect bridging perimeters:" and if your going  to be using FLEX material you may want to give consideration to enabling "Avoid crossing perimeters:"

Good luck, I hope this helps

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

The lack of a bottom layer was intentional.. wanted to get as close as possible to a simple shell. I've tried changing the bridging angle but it seems to have no effect.. hence the post 🙂

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

From the preview it looks like the slide doesn't see it as a bridge but infill. 

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

It wont.  Without a bottom layer, by definition it can't be a bridge.  At least as far as PS is concerned.  It only bridges the bottom of a shell, and even then only when it can do so.  At least on the exterior of objects.  

Id use a modifier to set the bottom layers to zero on the actual bottom but still have 1 or more on that top section to allow bridging to be generated.

RE: PrusaSlicer 2.9 seems to ignore bridge direction.

So, depending on what you do, you can get weird results ... PS wants to print some internal fill floating in the air.. not sure how that's supposed to work.  🙂 

I think I do have what I want.. here's my final result:

cover.3mf

At the top of the cavity is the bridge, properly oriented across the cavity, not along the length of the cavity..
There's a few "extras" on this:  it's printing with a single perimeter for the vertical and top layers, no bottom layer; There are modifiers to make the overhang on the left and right sides of the shell 2 vertical perimeters; and, there's a modifier to max sure the top of the cavity is solid / no infill.

RE:

@nanoplane

Your side (left and Rt) modifiers are causing a problem the way you implemented them you may notice they are cutting thorough your model in the intersecting areas.

The top modifier is creating an extrusion of overhanging "solid fill" (not good) with not much Infill/perimeters overlap: (also not good) this would be prone to failure with PLA and will almost certainly fail using a FLEX filament.

Once again I recommend:

Print Settings>Layers and perimeters>[Horizontal shells] Solid layers: Bottom: (set to at least one layer)

I would also recommend setting "Detect bridging perimeters:" and if your going to be using FLEX material you may want to give consideration to enabling "Avoid crossing perimeters:" set to Zero, not 30.

Then remove the bottom most layer using a "Height range modifier" set to a range of 0.00-0.35mm with the property Bottom solid layers: set to zero

This avoids all the problems  and removes the bottom most layer you wanted gone. The upper area will then bridge properly as well

Good luck