tell me if I am thinking right ?

[fairchild]

Got all my nose ribs done. Seems clear NOW --- that when it comes time to attach the nose ribs to the front spar with the attach angles---- I imagine I will stretch a wire down the wing
with the wire running through the front jig pin hole---- and adjust the exact position of the wire to match the hole position on the mylar master template. That should assure that the nose
ribs are in the correct position and duplicate the shape of the master form.

NOW--- I am making the tooling blocks for the main center ribs. I see that the mylar master form shows NO jig pin holes on that rib. I BELIEVE I need to make two 3/16 holes in the
diagonal corners to function as jig pin holes for the big rib. I will need those holes ALSO when I hydroform them to prevent the sheet from sliding on the form during the pressing.
Seems like the holes could also perform the same "locating" function later when riveting them in.

I have looked at other peoples center ribs and see jug pin holes at the diagonal corners. (N3UF- mr. Snap in his video)
Does this sound logical ? I guess I will have to drill 2 additional holes in my master form and transfer them to the cutting jig and forming blocks. Does this sound right ?

Tim

[Ray Strickland]

Your center ribs will be located by your spars.

[Chris In Milwaukee]

I drilled the holes just for purposes of holding the routing form sandwich together with the aluminum in between. So naturally, they’ll all be in the same location. You could potentially use them as a guide hole, not unlike the nose ribs. As mentioned above, the spars are your primary guide there, such that the transition from the bend in the spar channel transitions smoothly to the rib. As long as the spars are perfectly rigged/aligned, either should do the trick.

[N3UW]

I did the same as Chris. The Jig holes were for holding the material for routing. Bob used hand sheers so he did not need any. As others have said, the front and rear spars are used to locate the center ribs after the spars are locked into the building jig.

[fairchild]

YES---- I will ALSO need the two holes for routing the blanks as well as the forming process.

IF I am reading the plans correctly---- the cap strips on the rear spar are NOT graduated (stepped) - and are the same on both sides----
where the cap strips on the main spars ARE stepped (less beefy toward the tip) on both sides and slightly different on each side.

This LOOKS like it would mean that when you are fitting the center rib in between the two spars-- the rear edges of the main ribs would
all be the same length-- and maybe all most touching the cap strips (with minimal variation at each station)
where as the fronts of the main ribs would be different lengths by station location- and I would guess you might have some fudge factor
on the attach angles-

would I want the rear edges of the main ribs TOUCHING the rear spar cap strips ? OR- would I want to hold them off about 1/32 to avoid
chafing on the cap strips ? It appears that you would want the center ribs located precisely front-to-rear --- because if you had some
variation station to station--- the wing thickness would undulate spanwise...... so I suppose that would mean I want to size the rear edge
of the main rib to be 2 cap strips from the rear spar web surface ...... (plus maybe 1/32 clearance-)
Does that sound right ? and if all lines up correctly---- a wire stretched through the jig holes SHOULD line up all the way down if the spar
is straight----

Do I have a roughly correct mental 3-D mental picture of the spar/rib interaction ? If I am about to make the tooling for the main ribs- NOW
is when I need to clear up any mis-interpretations of the plans....

Also one other point------
On page 3B --- I see a 1/2 inch hole in the upper rear corner of the main rib where an aerilon cable passes through. However - the next
page shows the other piece of the cable running near the front of the main rib---- however I DONT see a matching hole for it to run through....
What am I missing there ?

Tim

[Chris In Milwaukee]

IF I am reading the plans correctly---- the cap strips on the rear spar are NOT graduated (stepped) - and are the same on both sides----
where the cap strips on the main spars ARE stepped (less beefy toward the tip) on both sides and slightly different on each side.

This LOOKS like it would mean that when you are fitting the center rib in between the two spars-- the rear edges of the main ribs would
all be the same length-- and maybe all most touching the cap strips (with minimal variation at each station)
where as the fronts of the main ribs would be different lengths by station location- and I would guess you might have some fudge factor
on the attach angles-

would I want the rear edges of the main ribs TOUCHING the rear spar cap strips ? OR- would I want to hold them off about 1/32 to avoid
chafing on the cap strips ? It appears that you would want the center ribs located precisely front-to-rear --- because if you had some
variation station to station--- the wing thickness would undulate spanwise...... so I suppose that would mean I want to size the rear edge
of the main rib to be 2 cap strips from the rear spar web surface ...... (plus maybe 1/32 clearance-)
Does that sound right ? and if all lines up correctly---- a wire stretched through the jig holes SHOULD line up all the way down if the spar
is straight----

I'd leave a little wiggle room, although the wing "shouldn't" vibrate enough to chafe anything. You *can* make each rib a different length if you want to in order to compensate for the depth of the cap strips on the main spar. But I made the ribs all the same length and will use a wider attach angle to compensate. Regardless of the length of the rib, the five rivets (or so) that attach the rib to the angle are where the physical connection is made. The 1/8" of material on the rib is insignificant, IMO. Keeping spars square and parallel are the important things.

Do I have a roughly correct mental 3-D mental picture of the spar/rib interaction ? If I am about to make the tooling for the main ribs- NOW
is when I need to clear up any mis-interpretations of the plans....

Yes, you do. I used six jig holes on the center ribs, one in each corner and two in the center, to make sure that nothing slips in the forming jig when I was bending metal. That 2024 is some rigid stuff, so if it's not firmly attached while bending, you'll definitely drag it around.

Also one other point------
On page 3B --- I see a 1/2 inch hole in the upper rear corner of the main rib where an aerilon cable passes through. However - the next
page shows the other piece of the cable running near the front of the main rib---- however I DONT see a matching hole for it to run through....
What am I missing there ?

The forward aileron cable passes through the front lightening hole, so no extra hole required. Here's a good series of photos that show it:

http://www.mybearhawk.com/wings/assembly5.html

[fairchild]

Thanks Chris---- That helps a lot. So I can do as many jig holes as I want. Might do about 5 since its a pretty big part-- and I will have to
hydroform it in overlaping sections in the press since its so big. I can slip bolts and nuts into the holes that aernt under the press/rubber.

Since the .032 ribs dont get a bent edge lightening hole--- maybe I will bend those FIRST--- BEFORE I cut a 45 degree bevel around
the lightening holes on the forming block. Once done with those--- then bevel the form block and form the other remaining .025 ones.

Cable goes through front BIG hole. Thats simple enough.

Sounds like the attach angles kind of "save the day" and alleviate any problems of exact length issues for the ribs.

Looking at the plans--- it looks like the rear spar has only 1 layer of cap strips(1 layer on each side) (as opposed to 2-layers stacked on front spar) ---
is that correct ????? --- so I only need 1/8+ inch clearance in the rear-----
I was thinking of leaving about 1/16 extra for fudge factor. Maybe I will make my attach angles about 1/8 wider. someone made them wider
on the spar side too (at least some of them-) and said that they had come rivet set clearance issues and edge distance problems--- and that fixed both issues. A little extra on the front ones on the rib side would seem a good CYA. :-)

Tim

[Chris In Milwaukee]

Looking at the plans--- it looks like the rear spar has only 1 layer of cap strips(1 layer on each side) (as opposed to 2-layers stacked on front spar) ---
is that correct ????? --- so I only need 1/8+ inch clearance in the rear-----
I was thinking of leaving about 1/16 extra for fudge factor. Maybe I will make my attach angles about 1/8 wider. someone made them wider
on the spar side too (at least some of them-) and said that they had come rivet set clearance issues and edge distance problems--- and that fixed both issues. A little extra on the front ones on the rib side would seem a good CYA. :-)

That's correct. Only one layer on the aft spar (on each side). If you're talking about leaving an *extra* 1/16" of material on the ribs, I think you'd find that a bit of a pain if you find that you have to trim it off. Getting snips around that bend corner isn't an enjoyable experience, and it'll usually leave a sharp burr. You can certainly file it off, but then that flange ends up looking less awesome than it did when it came out of the routing form and freshly bent, with it's beautiful pristine router cut edge being replaced with a serrated mangling a la hand shears.

If you're a perfectionist, then take off (.032 + .125 + .125) from the front edge and (.032 + .125) from the aft edge of the center ribs and you'll have the perfect wiggle room between the spars you need to make minor adjustments and keep your spars parallel without the front or back of the ribs from touching the spars (original chafing concern - you'll have about .016 clearance on both front and rear).

[fairchild]

NO- ! Not leaving 1/16 extra on ribs----- I was suggesting SUBTRACTING OFF 1/16 the rear of the ribs so as to not quite touch the spar.
Maybe the same on the front of the ribs too)
Equivalent to your .016 clearance. I just picked 1/16 ---- maybe 1/32 would be a better number--- (.032)
Since I will be cutting these with the router--- I could -in theory- get as precise and repeatable as I want.
What you were suggesting was what i was suggesting ! :-) I just maybe had a number bigger than I needed there......

I was also wondering this---- when you go to attach the rib to it's attach angle --- does the rib material on the face of the attach angle thats
the inside of the bend (on the angle) or the face thats the outside of the bend. I would hope it goes on the outside of the bend so that the
end of the rib does not make contact with the radius of the bend line of the attach angle. The difference in position for the rib would only
be the thickness of the attach angle. (if they had to go on the inward bent side-- you would either have to trim the rib back or bend a matching
radius in the end...... cant imagine any of that would be going on ...... )

Sounds like I have the basic geometry ---- so i will proceed tonight in making the MDF blank routing sandwitch and the form block.

Thanks for the followups Chris---- I kind of wish the plans had drawings of both sides of the spars. Little more on the paper and a bit
less in my head ! Maybe less chance of a goof up that way.

Tim

[Chris In Milwaukee]

Yeah, I’d say outside. More wiggle room that way. Glad to see we were saying the same things, only differently!

The plans do show both sides of the spar, but in a more “legacy draftsman” sort of way. The caps with the dashed (hidden) lines are the caps in the back. The solid lines are in front.

Sure glad I took those mechanical drafting classes in High school

[fairchild]

Chris---- I was just looking at your build log--- and I gotta say what you are doing is very impressive. Be neat to see a 400hp m-14 on it !

When you get done with that---- :-) ------- how about this for an idea. Take the patrol and kind of do to it what was done to the monocoupe.
Shrink all the surfaces by about 20%----- make the wings stiffer----- higher Vne------ a more complicated flap to keep stall speeds down---
maybe a laminar wing (?) ------- make say-- the outer 1/2 span of the wings eliptical....... I wonder how that would work..... maybe someone
could do it in X-Plane and see what happens :-) Culp did the mullicoupe with an m-14........ apparently that worked OK though it was a much
heavier thing than the patrol.

Looks like you are making ribs the same as me except I am using about 4 inches of soft rubber in the press and 30 tons of jack. This is bending
in my lightening holes AND bending my outer flanges to about 70 degrees. It seems like the extra thickness of the rubber allows the part to submerge deeper into the rubber and that helps the rubber push the outer flange over. It couldnt do that when I used the same but thinner rubber.

I hope you get your new shop set up soon so we can have more blog pics. !

Tim