yoke freeplay

How to keep the Cessna 170 flying and airworthy.

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cmsusllc
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yoke freeplay

Post by cmsusllc »

What is a reasonable amount of freeplay in the u-joint on the yoke? Mine has about 1/4" of free play at the outside of the yoke-no freeplay fore and aft. I landed in some nasty winds the other day and it felt loose.
Scott 53B
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Brad Brady
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Re: yoke freeplay

Post by Brad Brady »

cmsusllc wrote:What is a reasonable amount of freeplay in the u-joint on the yoke? Mine has about 1/4" of free play at the outside of the yoke-no freeplay fore and aft. I landed in some nasty winds the other day and it felt loose.
Scott 53B
In my opinion (which is is just that) that is too much play......They are worn out. you need to look at the chain in the rear of the yoke and make sure the slack isn't there.....other wise the U-joint (3/8 inch type of unit used on a ratchet/socket ) is probably suspect. I know that you know what a U-joint is.....I just put it in parenthesis so every one knew what we were talking about......
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johneeb
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Re: yoke freeplay

Post by johneeb »

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Bruce Fenstermacher
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Re: yoke freeplay

Post by Bruce Fenstermacher »

Hey Scott I have no comment on whether your u-joint is shot or not. When holding the co-pilots yoke still and moving the pilot yoke I have more play than that. Of course that would be taking into consideration any play in both u-joints, the sprockets and chain. And yes mine is probably on the limit for sloppiness.

But in any case I've never felt the controls were loose. Maybe I don't know any better but I don't think so. My point is that maybe the play you felt was not in the control system itself but aerodynamic.
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GAHorn
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Re: yoke freeplay

Post by GAHorn »

Scott, the reference earlier to the "3/8 inch type" was Brad's caricature of the units....not a specific size to obtain, should you decide to change yours. These are PN 0411257 which, if prescribed from Cessna, will cost you around $320 each. The generic units (MS 20271-B10 ...for a 5/8" shaft) may be obtained from Spruce for about $80 each.
http://www.aircraftspruce.com/catalog/a ... joints.php

These things almost never wear out, although it is possible. Most of your "slack" will probably exist at the sprocket/chain and perhaps at the throughbolts that hold them in place (which unfortunately, if they are loose, end up damaging the u-joints anyway.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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KG
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Re: yoke freeplay

Post by KG »

I've seen a couple of airplanes with one control wheel cocked at an angle and have been told it was due to the improper installation of a u-joint. Is this the same u-joint?

I've seen it on two different airplanes so am wondering if this is an easy thing to get off-center during the installation.

Keith
53 170B
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GAHorn
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Re: yoke freeplay

Post by GAHorn »

KG, while that MAY be the problem, I doubt it. It's most likely a wheel that is "mis-clocked" at the sprocket/chain.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
cmsusllc
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Re: yoke freeplay

Post by cmsusllc »

The freeplay I was refering to is strictly the u-joint. Both yokes are about the same which is why I'm asking as I would think the left would show more wear. The airframe has about 5500 hours and all the controls beyond the u-joint are snug. Thanks George for the part numbers.
Scott 53B
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N2255D
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Re: yoke freeplay

Post by N2255D »

When my u-joint on the left side of my C140 started to get sloppy I swaped with the right side. That way you get change both at the same time. :P
Walt Weaver
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DWood
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Re: yoke freeplay

Post by DWood »

McFarlane Aviation shows one in their catalog for 120 thru 185 Cessnas part number MC0411257 which appears to be an identical replacement. You might call them as the p/n is not coming up on line. 866-923-2741 I saw it on their display board at OSH.
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c170b53
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Re: yoke freeplay

Post by c170b53 »

Mismatch at wheels if not due to wear would of course be cable rigging. I've placed a piece of rubber tubing over my joints to keep them clean ,lubed and most importantly to provide support.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
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Brad Brady
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Re: yoke freeplay

Post by Brad Brady »

gahorn wrote: These things almost never wear out, although it is possible. Most of your "slack" will probably exist at the sprocket/chain and perhaps at the throughbolts that hold them in place (which unfortunately, if they are loose, end up damaging the u-joints anyway.)
Well George, maybe I'm just to annal....I have had many people change out the U-joints....( my criteria is holding the right side.....if you can move the left more than an a half of an inch (Outside control wheel).....I'll change both......( after I am certain that the chain and cables are correct) there is no reason to change just one side......
markeg1964
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Re: yoke freeplay

Post by markeg1964 »

My mechanic is about to install a new u-joint in my 170. He suggested swapping the left with the right but after looking closely we decided it was better to just replace the left one with a new unit. I didn’t measure my movement but I would guess it is close to one half inch if not more. My right side has very little free play. I’ve been putting off fixing it due to the cost but finally got tired of noticing the free play while on x-countries with nothing to do.
Mark

Twin Oaks Airpark
1950 170A N5528C
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Senior Chief
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Re: yoke freeplay

Post by Senior Chief »

Cut a piece of 5/8 inch garden hose into two 3 inch pieces. Slide them over your u-joints and keep on trucking.
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GAHorn
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Re: yoke freeplay

Post by GAHorn »

Brad Brady wrote:.....my criteria is holding the right side.....if you can move the left more than an a half of an inch (Outside control wheel).....I'll change both......( after I am certain that the chain and cables are correct) there is no reason to change just one side......
I can appreciate what you are thinking, but to be slightly more cheapskate..... what I believe is a better method is to lay under the panel and, while looking up at the u-joint, and while holding the sprocket in one hand,... operate the yoke to determine the freeplay in that one side, then compare it to the other. In that fashion, one is actually determining the relative looseness in each yoke/u-joint assy rather than the total looseness. (If one were very loose and the other tight, would you want to replace both?)

Also, don't forget that the u-joint also transmits push/pull inputs to the control system. Simple twisting movement is not it's only ...in fact is not even its most stressful.... function. Make certain there is no excessive fore/aft looseness in the system which might indicate wear. While under there, look for any indication of wear or runout in the bronze bushing inside the "T".

What actually causes looseness, anyway? Well, certainly wear does, but what causes the wear? This is a low-stress system and that u-joint does not operate at high speed or high-operating stresses, so what wears it out?

I believe that two things contribute most of the wear over the years. The first contributing factor is vibration. That u-joint sits on the end of a long arm (the shaft) and with the vibration of engine/airframe being magnified by that long arm, wear is accelerated at any point of contact that has materials-change and/or attachment. That u-joint is just that sort of device.
While the bearings are hardened against that wear, they receive the benefit of that vibration nonetheless, and our hand resting-on-the-yoke at the opposite end adds upward pressure to the joint which may increase the hammering effect of vibration. (It may also be that a yoke that is completely free to vibrate at the end of the shaft, such as the copilot's side normally does, might receive wear from this factor.) Either way, things are going to get loose eventually. When the original u-joints are replaced with modern equivalents, they are usually replaced with the MS 20271 types which have protective covers incorporated, which provide some of the benefits Jim and SeniorChief may be seeking. I'm reluctant to endorse garden hose unless it met traceability requirements. :wink:

Another factor is the type of control locks that most light Cessnas have. Most Cessna control locks hold the control wheel/yoke and the rudder pedals. If you think about it, that means the control surfaces, when deflected by wind or other input, pass their movement on to the control cable system, which ends up at the cockpit control wheel/rudder pedals. While the factory method may protect the control surface from banging against it's stops....all that abuse from wind also abuses the entire control system....the cables, pulleys, each bearing, every contact point,.... and each u-joint.
Even the C-170 whose owner uses the seat belts to hold the yoke (like me), suffers similarly. The best systems use a method of holding the control surface externally. (However, as most of us know, do NOT lock the rudder to the vertical stabilizer at the counterbalance area or you risk serious damage to your rudder. Use a bungee or rope system that holds the rudder at it's trailing edge, instead.)

Another method by which the system receives wear is through ill-informed lubrication methods. The aileron control-chains are normally not lubricated with oil, so that they do not attract dust/grit to cause wear. They are normally only wiped with a clean dry cloth, unless the airplane lives in a really humid or coastal environment. (I consider outdoor storage in most of the U.S. to be that sort of environment. In such cases, a light spray of lube oil such as LPS-1, followed by wiping with a dry cloth is what I'd recommend.) The early u-joints had exposed bearing/joints and should be lubed with light oil. Same thing for the bronze bushing whithin the control "T" thru which the sprocket driveshaft passes. The oil recommended is Mil-7870, but any light oil such as 3-in-One, sewing-machine, or gun-oil is suitable.

Anyway, I was just provoking some thought on how our systems actually receive wear through 60 years of service.

I do not plan to use any different lock-system on my aileron/elevator system, but I do inspect my control system thoroughly at each annual.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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