MS2125X Turnbuckles and You

I'm doing a complete replacement of the flying wires, turnbuckles, shackles, and anchor plates on my Fly Baby.

Pete designed the airplane 60 years ago, back when men were men, airplanes were taildraggers, and all hardware complied with the Army-Navy (AN) standard. The Fly Baby uses 16 AN-130-16 turnbuckles in its flying and landing wires.

The AN standard for turnbuckles was cancelled fifty years ago, replaced by the MS21251-MS21255 series of parts (barrels, eye ends, cable eye ends, clevis pin ends, pin ends). Now, the AN130 turnbuckles are still available, but the MS turnbuckles have a clip-wire safety system rather than doing the endless double-wrapping of the AN types. When you're talking 16 turnbuckle on the Fly Baby wing bracing ALONE (41 total turnbuckles on the entire airplane) that's a lot of extra work. Especially when you're replacing existing flying wires and may have to remove the safetying and tweak the turnbuckles to get the plane flying straight.

While an AN130 turnbuckle order gets you an assembly of barrel, clevis pin end, and cable eye end, there's no "standard" package for the MS turnbuckle set. I was especially concerned about the clevis pin ends...I was redesigning the plates they attached to, and needed to know whether to include edge margin for 3/16" or 1/4" clevis pins.

So...I researched the MS2125X turnbuckle system, and this is what I came up with.
Attachment 9131
One point of confusion... the spec for the Clevis pin end includes 2200-pound rated unit (-4 type), but the barrel spec and cable eye ends DON'T.

The 2200-pound units are threaded 1/4-28, which can be accepted by the B5 barrel...which is rated for 3200 pounds. The -2200 versions of the old AN spec were eliminated in 1944! That's why the MS spec version doesn't include barrels or cable eye ends that size.

The BIG difference: The -4 clevis pin ends take a 3/16" clevis pin, like the AN130 turnbuckles, and the -5 pin takes a 1/4" pin. So if you're replacing existing turnbuckles, you order -5 barrels and -5 cable eye ends, but -4 clevis pin ones.

If you're REPLACING an existing AN130 turnbuckle, your combination would be:
Barrel MS21251-B5S
Clevis Pin End MS21252-4RS
Cable Eye End MS21255-5LS

Or is there significance in the left/right selection of the turnbuckle ends, other than making sure they're in opposite directions?

Ron Wanttaja

Ron: Just want to make sure that each assembly you specify has one end that is left threaded and one that is right threaded. Only place you need to be super careful is if you were using the same style ends on a single assembly.

One thing to note, is the MS21251 specification has a call out to use a -5 on 1/8 diameter wire due to breaking strength issues. It's listed as Item 6 under the Requirements section of the specification.

BTW, it pays to shop around on hardware. Skygeek is one of my go-to's. They don't always have everything, but it's worth checking. I've found some killer deals on hardware for my shop at times.

Thanks Craig. Thought that was the case, but it's good to get confirmation.

I did notice the call out for the -5 for 1/8" wire. My aft flying wires will be 1/8", and the wires are rated at ~2,000 pounds. With the -4 units rated at 1,600, I can see the reason for the call out.

However, Pete specifies AN130-16S turnbuckles, which, of course, are ALSO rated at 1600 pounds (e.g., less than the wire. So, using -3 of the MS variety would still be within the Bowers "specs." "Specs" in quotes, of course, since Pete didn't really do that many calculations on the airplane.

I'm inclined to order all the -5 units, just to make parts management easier.

Thanks for the Skygeek reference, I'll see what they've got.

Ron Wanttaja

Ron: I would agree with staying with the -5's for the 1/8" cable. Something I noticed, either in the spec or one of the two amendments, was a notice to not use any of certain barrels made prior to a specific date, due to a change in process standards that put their strength limits too close to the specification, if not under the limits.