Aileron Pocket Rib Notch Critique

[SpruceForest]

Working through all the rib routing and pressing/forming the extras to get the process debugged before committing to numbered parts. May be nothing, but seems like the flange notches should start a little deeper into the rib to avoid what seems to me to be a compound bend. These ribs seem to mostly be mounts for the 0.016 closeout skins, so not primary structure, but seems like moving the rout another 0.1" in would avoid that two-way bend. In terms of layout, seems like I should have moved the 3/16" diameter hole fully onto the web surface rather than splitting it per the plans.

Critique?

Thanks,

Todd

[Frank]

LSA plans are pretty clear on the subject.

[SpruceForest]

Thanks for your time and the look. At the sketch-level of detail, I agree, but note that with the interior bend radius added at the aft edge and underside (this is the current Patrol plan, seemingly identical in terms of flange notch layout to the LSA you posted), the 3/16" base diameter notches are squarely in the interior radius bend zone, which produces the distorted bend (i.e., the peaks) shown in my original photos. In other words, layout per the plans generated the as-seen in my opening shots.

Options would appear to be a) bend at a tighter radius (4t for 0.020" gains 0.020" allowance) or b) move the base of the notch to clear the bend area the inner surface of the material. Moving to an 0.080" bend radius still has the base of the notch either in or on the edge the inside radius bend zone, while moving the base of the notches in a bit seems like it comes with a slight reduction in rib stiffness (on the order of the alignment pin holes). A third option is a little quick file work to ease the base of the notch back just enough to avoid the peaked effect which would avoid the re-rout on the ribs, but I'm guessing that time-wise it is a wash versus modd'ing the jig and a quick rout touch-up.

My guess is that it does not matter much. My pilot right-side brain says not to worry - to quote every mechanic that ever released a bird to me after being unable to duplicate the squawk - "fly-it-and-watch-it." My semi-OCD aero-engineer left side brain says to eliminate avoidable stress concentrations where possible so as to avoid the structure necessary to distribute them or more frequent inspections. The arguments between them keep me up at night (voices? what voices?).

So what I think is happening is that the higher stress on the material with that slight compound bend is relieved by some distortion of the notch, which - unless it peaks and noticeably reduces the bend radius - is not going to be much of an issue.

AsDrawnWithBendLine_AileronPocket_P471.jpgAs Drawn_Annotated_AileronPocket_P471.jpg

[Frank]

Yeah that extra inner line would have thrown me off too. Looking at other builders pocket ribs helped.
I have left the bottom little flange unbent for now. Will bend those on assembly, thinking I shouldn't necessarily go for final dimension yet.

[SpruceForest]

Yeah..not a bad idea to hold off on that bottom flange until you get the final rear spar numbers. Just retooled my router templates for lunch and got about half way through trimming up my already-cut ribs. I think the fix here is to move the notch not the inner bend line... drawing is marked up below, and I'll trial this tonight on the press.

[Frank]

The way I read it is the double line which goes thru the hole represents the bend. Cut the hole and notches exactly as drawn, do not move the 3/16 hole, ignore the single line which touches the hole.

[Frank]

Also, measure in 1/2 from the dotted line of the flange. Should bring you to the double line.

[SpruceForest]

This is what I mean about some of the details being sketch-level versus accurate 3-view... it can lead to some interesting discussions ;-).

This is a full-scale drawing, so the double line is the edge-view of the 0.020" flange. The flange bend radius is 0.1", so has to extend that distance beyond the inside line of the pair - that is the third line I drew in on the rib plan in the shot...I went back and labeled it for clarity in the attached shot.

I don't think we can count the double line as the flange AND bend allowance because that suggests a zero-radius bend at the inside of the flange. And if we want the flange notch to originate outside of the bend, that suggests to me that the 3/16" diameter hole that starts the notch has to originate at least 1/2 the hole diameter beyond that the beginning of the flange bend.

The sketch I attached shows what I think Bob wanted (if my engineering judgement is accurate) and what he drew. May be time to pick up the phone and suss out whether it is a) important, and b) correct. As I mentioned, I think that unless the material yields in the bend, it probably is not an issue where the notch is started.

AsDrawnVsDesired_AileronPocket_P471.jpgAileronPocketMarkup_P471.jpg

[SpruceForest]

Just got the revised pocket rib out of the press and cleaned up... definitely less distortion in the notches with move of the notches a little deeper into the rib. Feeling good enough about these to rout the remainder and press them off.

AileronPocket9_P471.jpgAileronPocket8_P471.jpg

[Frank]

I'm skeptical of fabricating what the plans want versus what the plans show. But the bottom line may be how well the pocket ribs fit vertically into the rear spar, and how much clearance there is with the aileron nose ribs. On this same page of LSA plans is an Aileron and Hinge Mount Layout detail in which the clearance is measurable.

[Frank]

BTW your Rev 2 looks great!

[SpruceForest]

Thanks... agree that the fit issue on these ribs is way more important!

FWIW, I have not done sheet metal development since the 80's when I was at the composite aerostructures lab at UMD, and that was for sensor mounts and gear racks. Not sure whether Bob intended the drawing to be used as a sheet metal development, because real aluminum gets pulled in a couple different directions in forming, so the view provided in the plans may be pretty accurate for the 'already bent/as seen' component, but not that accurate in terms of the flat pattern.

[nborer]

I believe you are correct. I read Bob's drawings as what it should look like when formed - it's up to the builder to develop the flat pattern.