Rod ends Selecting alternatives to unobtainable/unaffordable originals

[IanLaw]

The drawings for my Boredom Fighter project call for Fafnir RE 43 10 double row ball bearing rod ends at the forward, bell crank end of the two aileron push rods. These bearings have a 1/4" bolt hole and are hollow shafted, to fit over the 1/2"OD x 0.35" wall steel pushrod. These are no longer available via A/Spruce and were quite pricey, several years ago. The MS equivalent seems to be MS21152-3 and the only ones I can find on the web are in the region of $350+ each. Way over my budget.
At the other end of the push rod, "F45-19" rod ends are used and these still seem to be available via Aircraft Spruce, although they were also expensive when I last looked. These have a 1/4" bolt hole and 5/16" internal threads.

I guess the double row ball bearing type will always be pricey, but maybe they are over specified for what is needed? I want to retain as smooth a feel as reasonably possible for the ailerons but without sacrificing too much and without gaining any weight, at a price I can afford. Any alternative would have to be acceptable to the U.K. L.A.A. engineering dept. and it would be up to me to convince them. They may require a formal modification application, if less than convinced.


The aircraft is non aerobatic in the U.K. and the VNE is around 115mph, AUW about 750lbs.

Can anyone suggest where I may be able to find alternative parts and some advice on how to approach this?

Thanks!

Ian

[VP1]

Any alternative would have to be acceptable to the U.K. L.A.A. engineering dept. and it would be up to me to convince them. They may require a formal modification application, if less than convinced.



Ian

Would the LAA really know if you substituted the fancy rod ends for standard Heim units? I don't see how they would. If you agree, then get to searching- https://www.mcmaster.com/Rod-Ends

[Mike M]

"While Fafnir earned a reputation over the years as a high-quality manufacturer of precision ball bearing products, nowadays, engineers and designers find it easy to interchange Fafnir model numbers with a wide range of other high-quality, yet less expensive, alternatives. Contact us (https://www.astbearings.com/contact-us.html) to find out which high-quality alternatives products interchange with Fafnir ball bearings."

https://www.astbearings.com/fafnir-ball-bearings.html

[martymayes]

The drawings for my Boredom Fighter project call for Fafnir RE 43 10 double row ball bearing rod ends

That's a very specific part description. Unless you think you can pull a fast one on the governing authority, may have to fess up and say you did a part substitution. Just curious, what would the penalty if you did a part substitution, didn't tell anyone but later got caught?

[cluttonfred]

Here are some sources that may turn out cheaper: https://www.controller.com/parts/aircraft/search?PartNum=MS21152-3

[IanLaw]

Thanks everyone for the great suggestions and I'll look into them all. I also have to convince my local "LAA" Inspector, as well as the LAA itself, so have to tread a bit carefully.

I flew our group Aeronca Chief today and the aileron rod ends, at least at the aileron end, are very weedy looking things, with a 3/16" bolt. That aircraft is twice the weight of the Boredom Fighter. The next door Vagabond in our hangar seems to have a cable exiting from the back of the wing, with a thimble and nicopress sleeve to the arm on the aileron.

Happy New Year to all.

Ian

[DaleB]

Sometimes -- I'm not saying this is the case with the current example, but sometimes -- parts get included on plans and in a BOM not because that exact item is required, but because that's what the original designer/builder used. Maybe he had some on hand from another project or a past job, or they were commonly available as cheap surplus at that time, or whatever. Tough to imagine the Boredom Fighter would actually require super high spec rod ends, isn't it?

[martymayes]

Or, because Don Wolf was an engineer perhaps it was normal for him to spec a part down to the dash number. That's one of the things that impressed me with the Boredom Fighter, it's a well designed airplane!

[IanLaw]

Thanks Dale & Marty. I'm sure you're both right and I suspect the parts may well have been Grumman surplus. Don was a great guy and always patient and helpful when I started my project many years ago. I asked his advice on what now seem very stupid questions, but he always welcomed my inquiries and replied at length, by hand written letter.

Ian

[BoKu]

...I suspect the parts may well have been Grumman surplus...

I've seen this exact thing in the Dick Schreder HP-series kit gliders that I support in addition to the HP-24. Dick evidently picked up a thousand or so Fafnir RE3M6-2N two-row ball bearing rod ends after the war, and designed them into the control systems of all the HPs in places where 1/4" spherical rod ends would probably be perfectly adequate.

--Bob K.

[IanLaw]

Good to hear that Bob and all is "evidence" to plead my case for the cheaper options, provided they do the job.

Have tried all suggested options and I may be able to buy a pair of the ball bearing MS21152-3 rod ends via Atlanta Air Exchange ( listed in https://www.controller.com/parts/air...tNum=MS21152-3 (https://www.controller.com/parts/aircraft/search?PartNum=MS21152-3) - see Matthew's post above ). They have quoted me $30 each (?) for new surplus, but I'm awaiting confirmation and postage to the UK, which could be a problem. Another reply from the same listing quoted me $600 for a pair(??) and I'm hoping the lady at Atlanta hasn't missed a zero off the end of her quoted price!

I'm extremely grateful for all your suggestions and will post the eventual outcome, in the unlikely event anyone else has the same problem in future.

Thanks again.

Ian

[DaleB]

postage to the UK, which could be a problem.
It shouldn't be. It's NOT that expensive to ship stuff internationally. Some vendors complicate things needlessly. I ran an electronic kit business for roughly 15 years and shipped packages to most of the free world. I sent packages to the UK at least weekly. USPS First Class is cheap. Priority Mail is a few dollars more. The tracking, honestly, is really no better either way. Once in a while the UK RP will want their import duties and such, but it's not terribly expensive. The Customs form takes five minutes to fill out by hand, but I always let my Endicia software print out a combined shipping/Customs label.

On the other hand, if you have it shipped by UPS, FedEx, or DHL -- be prepared for truly outrageous shipping cost and a lot of paperwork. There's nothing more irritating than finding a great deal from a vendor who can't comprehend something as simple as dropping it in the mail instead of insisting on FedEx or UPS.

[WLIU]

For what its worth, if the certificating authority wants an engineering justification for substituting a different rod end, the math is not that hard. The aileron control system is loaded in simple tension and compression, the bell cranks have known mechanical ratios, and the limit case is an aileron instantaneously deflected to the max angle at Vd. That load is simple trig with the surface area of the aileron known. And multiple that value by a 1.5 safety factor. Write up your math and the specs for the available rod end(s).

Best of luck,

Wes

[IanLaw]

Many thanks for that Dale and Wes. I feel as though I may be on the home run now!

Ian