pear shaped lightening holes in the rear of the main rib---

[fairchild]

I tried last night scribing these out on my master rib using the 4 holes there as center points. I have my plans page of that blown up 2X.
First I used my compass to draw the set for the .032 ribs (solid line). I used a diameter which seemed to match the diameter on the 2X plans.

I noted that the dashed circles and the solid circles seemed to touch at the 12 O-Clock points on the plan. So I re-set my compass to draw the dashed circles so they touched
the solid ones at 12 O-Clock (and on their centers) . That kind of "set" the diameters of the dashed circles.

I then compared my drawn dashed line diameter to the one on the plan---- and both of mine were over 1/2 inch smaller. Some where I am doing something incorrectly.

I e-mailed Bob/Maria …….. but no reply so far. (they may have to research the problem a little ?)

does anyone know what the CORRECT diameters for both sets of circles SHOULD be ?????? did anyone else notice this seeming discrepancy ?

Thanks for any thought ----
Tim B.

[Chris In Milwaukee]

Looks like 4-1/4” and 3-3/4” for the big pear, and 3-1/2” and 3” for the little pear.









Note these are Patrol wings, but there are only a few differences between the Bravo and Patrol wings.

You have an engineering scale like this one? Pop over to Office Max and grab one if not. Solves a lot of those measurement problems. Just read the scale on the plan sheet, flip the ruler, and measure away.

[fairchild]

That's funny---- I have a drawer full of those "antique" scale rulers and for some reason I never thought to get one out. I will measure my regular plans page and see if it agrees with
my 2X blown-up page. Another possible inconsistency in my plan--- the mylar shows 4 centering holes for those 4 circles--- and the plans page only shows 3 of them.
I have glued my mylar to a sheet of 1/2 inch MDF- and that forms my master rib. Im sketching my circle on the mylar lightly in pencil. Good thing mylar erases well !
I will go out and see how your measurements compare to mine---- and let you know.....
Thanks a lot !
Tim

I took the mylar ---- traced out the 4 center holes and then took my tracing over to plan and made a pinhole where the missing center hole should have been.
Then I used my that center to get my rear dashed radius. Then I re-drew all 4 circles again on the mylar and got----
Big = 4=1/8, 3+3/4 small = 3+3/8, 2+7/8

Still smaller than yours....

Took my 2X blown up plan and compared it to the hight and length of the center rib vs. master rib form. My 2X print is undersize slightly---
.4% in the horizonal and .7% in the vert. That works out to 1/8 inch less in the 32 inch rib length and 1/16 in the 8+ inch rib height. Not a huge amount
but that's enough to not count on using that 2X plan for any fine ,important measurements...… some of that could be changes in humidity affecting the
paper---- remembering silkspan shrinks more one way than the other because of the linear nature of the rolled paper pulp.

These measurements MAY NOT be critical at all---- if there is nothing important routed through those holes. The flap torque tubes seem to have
their own holes. The aerolon cable has its own hole...… anyone see why those holes wernt round ? I had kind of assumed that they were
pear shaped for something to pass through...… (maybe your arm holding a bucking bar ?????? :-) )

Tim

PS
I just did my scale ruler on my plans---- front big hole I get very slightly less than 4 (you got 4+1/4) and the other 3 were pretty close to the same.
(within ruler reading error---)

[Chris In Milwaukee]

I noticed that, too. The Mylar has the right center holes.

[fairchild]

I have all most convinced myself that the exact size of the holes may not be critical in that there not much around or in it to cause any interferences.
It LOOKS like the reason for the there being 2 different hole sizes/shapes is the torque tube hole below--- so the inner rib holes were made smaller to keep
a generous amount of material width between the tube hole and the lightening hole---- that is the lightening hole was shrunk down until he was happy with the
strength/size of the septum area. Also I saw Mswain's ribs have a round hole there instead of pear shape. So I guess pear shape was picked just to take better
advantage of the available space there which could be removed.

So I think --unless I hear from Bob/Maria...… I will just take my best guess at the holes and drive on. I well may have been stressing about a non-issue--
but this structure is new to me-- so its harder to tell that without being able to see one in person. ( I just have the 3-D model in my head--- which could be
messed up---- )

T

[Chris In Milwaukee]

Theres some wiggle room in these ribs, so you don’t have to worry too much if you’re off by a tiny bit in the hole diameters. It’s not a Gulfstream, so it’s all good If it looks right, it probably is.

[fairchild]

OK--- lowering the screws back into the water and bringing the steam boiler back on-line---- Damn those torpedoes !