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.

[David Dagenais]

I was able to speak with Bob Borrows recently concerning the same question; .032 vs. .025 thickness for the tail feather ribs. Bob did say that the information that should have accompanied those dimensions between sheet 23B and 24B is that T25 as .032 thick material should be either 1018 or 1020 sheet. The .025 thickness dimension is for using 4130A material. My current quandary is trying to locate some 1018 or 1020 sheet at 22 gage as 21 gage it seems is not be produced.
Thanks,
David

[marcusofcotton]

I was able to speak with Bob Borrows recently concerning the same question; .032 vs. .025 thickness for the tail feather ribs. Bob did say that the information that should have accompanied those dimensions between sheet 23B and 24B is that T25 as .032 thick material should be either 1018 or 1020 sheet. The .025 thickness dimension is for using 4130A material. My current quandary is trying to locate some 1018 or 1020 sheet at 22 gage as 21 gage it seems is not be produced.
Thanks,
David

Welcome to the group David!
I hope you're deep into looking at a specific cg issue for your specific airplane... if not, why are you striving for the option that is 28% more weight for airplane parts?

[fairchild1934]

I have NOT been able to locate 1018 sheet ANYWHERE .... I don't think it is being produced anymore as sheet. If anyone has found it please tell us.
I used 1007 or 1008 .030 as a substitute. it DID for very nicely in the hydroforming press. No work hardening.

pS--- several ads for steel claim 1018 -- but when you dig a little deeper is it is not---- it is 1007 or 1008.

[alaskabearhawk]

We might be talking apples and oranges here. I called Triple S Steel in Richmond VA and asked about 1018 sheet in 22ga. The CS person said the ASTM spec 1018 refers to bar stock only, not sheet steel. The sheet spec is 1008. A call to Bob may be in order.

[Steve W]

Not to be off topic here, but I know a guy who built all his profiled tail ribs by tig welding the three strips together. They were a work of art. 4130 was used.

[SpruceForest]

That's what we did for the LG ribs on aft legs of both Patrols... a heat sink helps, as well as patience.

[SpruceForest]

FWIW, 4130N is not too bad to work in .025 or .032... just finished the U-shaped closeouts on the landing gear legs next to the fuse, and the .032 U got bent with the 16g brake and the returns finished on the bench with an oak mandrel clamped into the channel... a dead blow hammer makes short work of the return, and the compressed oak allows the mandrel to be knocked out using a vise and hammer. The oak is sacrificial, but four pieces of 1-1/4" x 5/8" x 22" (after dimensioning) from the QS white oak in the scrap pile made some additional starter for the fireplace this fall.

[spinningwrench]

Speedy Metals has 1008 steel in all gage sizes. Might be acceptable, just lower carbon content.

[jaredyates]

Just thinking out loud here, but if you aren't heat treating the part after you make it, doesn't an easy-to-form material also mean it's easy to deform in service?

[SpruceForest]

Also worth considering 4130A - annealed 4130, versus the roughly half-hard 4130N. If you have a heat treating shop around or can send it out, you'll get 4130N back after heat treating... usually not too bad for a batch, but there can be a setup charge that makes piecemeal a real pain.. McC and Grainger sell it dear, while Spruce says they can sub 4130A for 4130N if the normalized is not available, so I assume they can get 4130A for customers that ask and likely much less expensive than McC and Grainger.

I do not believe that 1008 is 1018 in thin sheet... spec is very different on carbon content, alloying, etc. and generally lower physical values of the type we get concerned about. From an engineering point of view, either get a chop from Bob on the substitution being allowable or save some weight (~22%...) and go with the 4130. Added pounds in the tail are not where you want them, right?

[Steve W]

Not to be the devils advocate here but hasn’t it been mentioned at one point in the last 15-20 years that anything from 1010 to 1025 is acceptable for a mild steel call out off the plans?
That may have been for a specific part.