Some of us like older aircraft homebuilt designs. There are still Pietenpols under construction, still Baby Aces ready to emerge after a scratchbuilding process or even just restoring an older bird.
The design might be aged, but there’s no reason to restrict oneself to ancient hardware standards.
I’m looking at YOU, Army-Navy. Yes, the venerable Army-Navy standards for aircraft hardware date back more than 80 years. It’s not so bad for the minor hardware like nuts, bolts, and washers. But it gets kind of ridiculous when you get to the turnbuckles.
Light aircraft, especially older homebuilt designs, use a LOT of turnbuckles. The Bowers Fly Baby, for instance, uses about 40 AN130-16S units.
Unless you’re smart. That AN standard was replaced years ago with the Military Standard (MS). Homebuilder supply houses sell those antique AN130 turnbuckles for more than $50.
Are you aware that the more modern MS equivalent sells for a bit more than half of that? They work just fine, and, in fact, do away with the need for safety wiring! The MS2125X series uses small spring clips, instead.
I did a major re-rigging effort on my Fly Baby and am quite pleased with the MS turnbuckles. Worked just fine, and they kept me from having to safety-wire eight AN units.
Below is a table that explains what components to buy.
| AN Equivalent | Strength (lb) | Barrel | Fork | Clevis Pin | Cable Eye |
|---|---|---|---|---|---|
| AN130-8S | 800 | MS21251-B2S | MS21252-2RS | 0.188 | MS21255-2LS |
| AN130-8S | 800 | MS21251-B2S | MS21252-2LS | 0.188 | MS21255-2RS |
| AN130-16S | 1600 | MS21251-B3S | MS21252-3RS | 0.188 | MS21255-3LS |
| AN130-16S | 1600 | MS21251-B3S | MS21252-3LS | 0.188 | MS21255-3RS |
| AN130-32S | 3200 | MS21251-B5S | MS21252-5RS | 0.25 | MS21255-5LS |
| AN130-32S | 3200 | MS21251-B5S | MS21252-5LS | 0.25 | MS21255-5RS |
| AN Equivalent | Strength (lb) | Barrel | Pin Eye | Clevis Pin | Cable Eye |
|---|---|---|---|---|---|
| AN135-8S | 800 | MS21251-B2S | MS21254-2RS | 0.188 | MS21255-2LS |
| AN135-8S | 800 | MS21251-B2S | MS21254-2LS | 0.188 | MS21255-2RS |
| AN135-16S | 1600 | MS21251-B3S | MS21254-3RS | 0.188 | MS21255-3LS |
| AN135-16S | 1600 | MS21251-B3S | MS21254-3LS | 0.188 | MS21255-3RS |
| AN135-32S | 3200 | MS21251-B5S | MS21254-5RS | 0.25 | MS21255-5LS |
| AN135-32S | 3200 | MS21251-B5S | MS21254-5LS | 0.25 | MS21255-5RS |
| AN Equivalent | Strength (lb) | Barrel | Cable Eye | Cable Eye |
|---|---|---|---|---|
| AN140-8S | 800 | MS21251-B2S | MS21255-2RS | MS21255-2LS |
| AN140-8S | 800 | MS21251-B2S | MS21255-2LS | MS21255-2RS |
| AN140-16S | 1600 | MS21251-B3S | MS21255-3RS | MS21255-3LS |
| AN140-16S | 1600 | MS21251-B3S | MS21255-3LS | MS21255-3RS |
| AN140-32S | 3200 | MS21251-B5S | MS21255-5RS | MS21255-5LS |
| AN140-32S | 3200 | MS21251-B5S | MS21255-5LS | MS21255-5RS |
| AN Equivalent | Strength (lb) | Barrel | Fork | Clevis Pin | Fork |
|---|---|---|---|---|---|
| AN150-8S | 800 | MS21251-B2S | MS21252-2RS | 0.188 | MS21252-2LS |
| AN150-8S | 800 | MS21251-B2S | MS21252-2LS | 0.188 | MS21252-2RS |
| AN150-16S | 1600 | MS21251-B3S | MS21252-3RS | 0.188 | MS21252-3LS |
| AN150-16S | 1600 | MS21251-B3S | MS21252-3LS | 0.188 | MS21252-3RS |
| AN150-32S | 3200 | MS21251-B5S | MS21252-5RS | 0.25 | MS21252-5LS |
| AN150-32S | 3200 | MS21251-B5S | MS21252-5LS | 0.25 | MS21252-5RS |
Question for you Ron. How do you match turnbuckle sizes to cable tensile strength? I am using 1/8” 7×19 cable that depending on reference is rated 1700-2000lbs. This falls between the -3 and -5 turnbuckles. Is there a preferred weakest link?
Don’t really know on that, Matt. The Fly Baby, for instance, specifies 1/8″ 1×17 stainless cable (rated at 2100 pounds) with AN-130-16 turnbuckles, rated at 1600 pounds.
Yet…the cable options aren’t there. The next step down in cable is 3/32″, rated at only 1,000 pounds.
Hopefully, the turnbuckle/cable combination is sized for a particular load. So if the anticipated max load is 1500 pounds, one would use a 1600-pound-rated turnbuckle with 2100-pound-rated cable (the closest above the known load).
It might be more a religious thing than anything else, but I think I’d want the cable rated higher than the turnbuckle. The cable rating depends on the quality of the terminations of the end of the cable; if the eye one makes with thimble and nicopress isn’t 100%, the capacity of the entire cable is reduced. The turnbuckle, of course, is coming from standard processes and one could expect that each one meets the minimum standard.
The fact that it’s a minimum standard should be remembered; that AN-130-16 turnbuckle is probably not going to break at 1,601 pounds. IIRC, typically, they require a failure point of TWICE the rated value. It’s certainly not something one should count on, but it should smooth out the rating differences between the cable and the turnbuckles.
Thank you sir, for your logic. My use case is in control cables, not wing bracing, so the required tensile strength is on the lower end of the scale.
Great to see you here on AvBrief, Ron!
Thanks! This place looks like fun….