Tie Rod Double Lug Fitting Bushing Holes 3

[Kristina Sornikova]

Dear experts,

I notice tie rod end double lug fitting has two lugs, one lug has a smaller hole and other a biggger hole for two size bushings, then pin go through center or all bushing, and nut on other side to clamp tie rod end in middle. But why two different sized holes for two different size bushings?

 

[Kristina Sornikova]

@SparWeb, I think it makes sense, but the slide bushing can pass from left side through same size hole if it can fit the same size hole right side right?

 

[Kristina Sornikova]

@tbuelna, why flange of bushing inside?

 

[tbuelna]

Kristina Sornikova-

One consideration with the type of joint shown, a spherical rod end and clevis, is constraining (axial clamping) of the spherical bearing inner race so that any rotation in the joint occurs at the interface between the inner and outer spherical bearing race surfaces. This interface is designed for accommodating rotation in the joint. Below is an example of an aircraft control system spherical rod end and clevis joint from SAE ARP 5770.

 

[rb1957]

I think the point to the inside flanges on the bushings is to protect the clevis from wear, in case the spherical bearing is thicker than the bushing wall so the sph bearing "could" rotate against the clevis leg. Other variations would replace the left flanged bush with two flanged bushes, one on the inner face and the other on the outer. To my mind I can't much point to the plain bush (making one clevis hole bigger than the other) other than assembly sequence (the same rotations happen on the other leg).

another day in paradise, or is paradise one day closer ?

 

[berkshire]

tbuelna,
In figure 67 what stops the NAS538B bushing, on the right hand side of the picture, from sliding into the fork and fouling the bearing seal on the double row ball joint? It would seem that the bushing would have to be a press in fit.
B.E.

You are judged not by what you know, but by what you can do.

 

[Sparweb]

@Kristina,
Yes, I was noting how the bushing for the right-hand lug can pass through the left hand hole.

@tbuelna / rb1957,
The guidance in the BDM tells me that the bushing flange on the inside makes a more effective bearing surface against the inner race of the bearing, when the bolt is tightened against these bushings.
This is less of an issue for CRES bushings than it is for bronze bushings. As shown in your example above, one of the bushing flanges is completely unclamped even though the bolt is clamped to the inner bushing stack. It occurs to me that the neutral axis of the fork's two lugs are farther apart, as a result of having the bushing flanges on the inside. That may offer a slight improvement to the design.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[berkshire]

Sparweb,
It is that un clamped bushing I am talking about. It that is not a press fit in the fork, it can float out of place and foul the rod end.
B.E.

You are judged not by what you know, but by what you can do.

 

[Sparweb]

Berkshire,
I tried comparing that lug with the types recommended in BDM1520, but BAC would put the flange on the outside.
Both have the clearance to keep the lug forks from being squeezed, just arrive at it differently.
I do agree with you that right-side flanged bushing would have to be press-fit in order to behave itself.

Tbuelna,
Can you tell us more about the specified for this joint by the SAE paper? I don't have a copy of that one.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[tbuelna]

SparWeb,

Here is what SAE ARP5770 states on p.84, "In Figure 69 the slip-fit bushing is retained by segment staking of the exterior side."

You can find more details of bearing/bushing staking procedures in NAS 0331.

If you don't want to pay $78 for a copy of ARP5770, with a bit of digging you can find public source aircraft mechanical control system design handbooks from NASA, DoD and FAA. They will probably provide similar design guidance for this type of joint when used for aircraft primary flight control applications.

 

[Sparweb]

Thank you for the NAS 0331 tip. I probably have a copy of that. Ability to stake the outer edge is sufficient reason to orient the bushing that way, so I will compare with the BDM way and see which has the advantage.

It always seems to be like this: I have a bunch of stuff in a library to refer to, and maybe it's enough, but then I find something like this, or you show me just 1 more option, and it throws up so many more questions!

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[WKTaylor]

For grins... Some ancillary documents [not mentioned in ARP5770] worth a look...

SAE
AIR1594 Plain Bearing Selection for Landing Gear Applications
AIR4094 Aircraft Flight Control Systems Descriptions
AIR5875 Methodology for Investigation of Flight Control System Anomalies

MIL-HDBK-1599 + N1 Bearings, Control System Components, and Associated Hardware Used In the Design and Construction of Aerospace Mechanical Systems and Subsystems

NOTE. I am not wild about the double bushing [plain bearing] system shown in tbuelna’s last post. The concept of having asymmetrical holes [two different sizes] in a symmetrical dual lug system tends to create a design/stress/maintenance asymmetry in the lugs at the holes. From my experience, this is NOT elegant/simplistic/durable/repairable as it looks.

NOTE. Any time a lug/clevis system is assembled like this, without means/methods to shim the single clevis lug to the center of the double clevis lugs, there will be a load eccentricity in the double clevis system... even a few thousandths of an inch toward one lug has a noticeable added/subtracted load affect; and in a highly loaded structure can induce significant secondary loading/bending that has to be accounted for.

NOTE. Chrome-plate bolts [shanks only] are often used in these type joints where 'bolt/pin shank-wear' is a potential issue within the bore of a hardened steel bearing inner-race.... leading to looseness.

NOTE. MANY years ago [1980], a friend who had worked for Boeing thru the 1960s into the early 1970s] ... and was ‘pink-slipped’ along with hundreds more engineers en-mass... walked-out with his mini design manual. He gave me his mini-BDM to photocopy ~1979. Best gift I ever received... It was loaded with structural and mechanical design insights, tips, lessons-learned, examples and general knowledge that kick-started my life my life-long quest/thirst for knowledge.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

This a deeeep rabbit hole, Wil!

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[rb1957]

hey will, care to scan that ?

another day in paradise, or is paradise one day closer ?

 

[Sparweb]

RB,
Why would you need access to a second copy?
If you don't know what I mean, you should phone our mutual friend, "SAITAETGrad"

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[rb1957]

He's got Will's early BDM ?

another day in paradise, or is paradise one day closer ?

 

[WKTaylor]

RB...

I have corresponded/exchanged data-with one E-T member... CoryPad... several years ago... thru Dave... but I am on a mission to accumulate/document my massive library and take care of injured/recovering wife... so spare time for such an endeavor is very sparse, right now. Perhaps I'll make some stuff available after retirement.

WHOAAAAA........

I just realized that I had not seen any forum entries from CoryPad in awhile. I just check his profile... he hasn't logged-in since Nov 2017!?!?! Anyone know his status?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Sparweb]

He's got Will's early BDM ?

At least 2 versions, maybe a third vintage now.
BTW, he's back on the payroll of your company now.

Wil,
CoryPad has made many contributions that were of value to me, too. I'm another who will miss him if he's gone.
But there is always hope it's something good keeping him away... like a world tour on a cruise ship.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[rb1957]

thx steve ... "a nod's as good as a wink to a blind bat" ... found it (copied it !)

another day in paradise, or is paradise one day closer ?