BC12 ribs vs F21 ribs

[Hank Jarrett]

Had no idea that was how ply rating worked, and I was an aircraft landing gear engineer at one time which included wheels, tires and brakes!

Hank

[n6346m]

Just a note on tires. When our airplanes were built, tires were rated in plies. The more plies, the stronger the tire. Quite some time ago aircraft tires switched from plies to ply rating. A 4 ply rating tire may only have two plies, but with the newer stronger material it is as strong as an old 4 ply tire. If you choose wisely you can find a fairly light 4 ply rated tire that is fairly light weight. You can save even more weight by having it polished smooth, but I wouldn't suggest that unless you will be primarily on grass.

Funny how this thread went from ribs to spars to tires. Is going from spruce to fir allowed as per the factory drawing or is it considered material substitution, which requires FAA engineering approval?
I also went from brand X 8.50 tires to the Desser Aero Classic 8.50 slicks and saved 3 1/2 lbs per tire. I don't think the FAA cares about ply ratings anymore. Like skis and floats, it's the weight bearing capability of the tire that matters to them.
Bob

[3Dreaming]

Funny how this thread went from ribs to spars to tires. Is going from spruce to fir allowed as per the factory drawing or is it considered material substitution, which requires FAA engineering approval?
I also went from brand X 8.50 tires to the Desser Aero Classic 8.50 slicks and saved 3 1/2 lbs per tire. I don't think the FAA cares about ply ratings anymore. Like skis and floats, it's the weight bearing capability of the tire that matters to them.
Bob

The weight bearing capacity is the same as ply rating. As far as the wood substitution I think it is covered in AC-43, but I have not dug into it to be for sure.

[Hank Jarrett]

Has been "Just a bit" of topic drift on this thread!

[skip]

The weight bearing capacity is the same as ply rating. As far as the wood substitution I think it is covered in AC-43, but I have not dug into it to be for sure.

I must have too much time on my hands, but I was just checking something else in 43.13 anyway...

43.13-1B section 1.2 Page 1.1 and 1.2 right up front.

b. Substitution of Original Wood. The
wood species used to repair a part should be
the same as that of the original whenever pos-
sible; however, some permissible substitutes
are given in table 1-1. Obtain approval from
the airframe manufacturer or the Federal
Aviation Administration (FAA) for the re-
placement of modified woods or other non-
wood products with a substitute material.

And from table 1.1:

Species of Wood	Strength proper- ties as compared to spruce	Maximum permissible grain deviation (slope of grain)	Remarks
Spruce(Picea) Sitka (P. Sitchensis) Red (P. Rubra) White (P. Glauca).	100%	1:15	Excellent for all uses. Considered as standard for this table.
Douglas Fir (Pseudotsuga Taxifolia).	Exceeds spruce.	1:15	May be used as substitute for spruce in same sizes or in slightly reduced sizes providing reductions are substantiated. Difficult to work with handtools. Some tendency to split and splinter during fabrica- tion and considerable more care in manufacture is necessary. Large solid pieces should be avoided due to inspection difficulties. Gluing satisfactory.

Several other wood types are mentioned.

There is, of course, a lot more about quality, but I think this is the applicable statement of approved data.

Skip Egdorf
BC12D-4-85 N34237

[N96337]

ANC-19 is where you really get into the nitty gritty about wood and aircraft construction using wood. It's available online, free, and well worth having in the library!
John

[astjp2]

https://vb.taylorcraft.org/forum/taylorcraft-technical-topics/reference-documents/11661-anc-19

[Ragwing nut]

F-21 front spar taller, ribs are the same on F-21. Not sure about -21A models.