Airfoil elevator rib profile and thickness

[B-Spot]

I am making a materials list for the elevator and rudder and I have come across some things that seem to conflict in the drawings on my 4 place model B.

The Tubing size chart calls out T25 as .032"

Drawing 23B shows horizontal stabilizer ribs as T25 with an asterisk, asterisk states see drawing 24B.
The elevator T25 ribs do not have an asterisk but are shown on 24B also.

Drawing 23B shows cross section C-C as typical T25 with 1/8" turn downs on the open part of the channel.
Drawing 24B shows cross section A-A witch is effectively the same as C-C with no 1/8" turn down.

Drawing 24B shows horizontal stabilizer rib cross section B-B as .025", cross section A-A for the elevator does not have a thickness.

So are the ribs for the horizontal stabilizer and elevator .032" as T25 states in the tubing size chart or .025" as the print shows on 24B?
I assume the profiles are what is shown on 24B so what is the 23B C-C profile for?

[geraldmorrissey]

I can't answer specifically but the Patrol ribs, both horizontal stab and elevators are .032 with the 1/8" down flange on the edge. I know the 4 place origionally had stab ribs with no upper or lwr contour and now builders have added that feature. Somebody with specific knowledge, help this guy out.

[alaskabearhawk]

Look carefully at all the notes on the two plans sheets. I have an A model so I'm not much help. But I suspect that Bob is giving you the builder an option for either a flat rib or a profiled rib on the stab. if you use the standard flat rib on the stab and elevator, the note to see 24B doesn't apply. If you decide on an airfoil-shaped rib 24B applies. What does the note to the right of Section A-A on 24B say?

If all else fails, just give Bob a call.

[B-Spot]

The note is about using a form block to create the airfoil ribs.
My assumption is that the profiled ribs are .025" and do not have the edge turned down.
The 1/8" turn down on the edge would be very hard to create after forming the rib in a curved shape, and forming .032" material would also be difficult to work with. The sheet shows material as 4130A again to make forming easier.
But I try to verify my assumptions because given enough rope I can justify a lot.

[B-Spot]

I assumed the turn down edge was to prevent exposing the fabric to the hard edge. Where did you purchase your tubing from?

[alaskabearhawk]

The downturned edge I *think* was for strength, but I really don't know. The downturned edge makes rib stitching a pain. As far as steel goes, I got all mine from Dillsburg Aeroplane Works. Unfortunately they went out of business in 2013.

All the questions would be good to run by Bob.

[B-Spot]

I watched your rib videos thanks for taking the time to make them. I found them informative.