Braking with full right rudder

How to keep the Cessna 170 flying and airworthy.

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Bruce Fenstermacher
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Re: Braking with full right rudder

Post by Bruce Fenstermacher »

pkissel wrote:Hi guys

Do you think this could be something bent in my rudder pedal linkage?
or My rudder degree of travel on each side being off - mechanic said he got 16 degrees on right side and maybe a touch less on left side.
IF the longer screw/stop fixes the issue is that acceptable or should I be tearing into all of the linkage?

Left rudder and brake is fine.

Thanks for any advice and help!
Linkage bent? Anything is possible.

But chances are your rudder cables are not rigged correctly. Both rudder cables must be sufficiently short that the pedals are X amount from the fire wall. I will find the thread with the x amount and discussion why this is important. The short story is that if the pedal assembly is allowed to move to far forward, the linkages force the brake on.

You check this X measure with the rudder in neutral. And then you set your rudder stops so the rudder can not exceed max travel according to rigging procedure for the 170.

Added: The X measurement is 6" measured from the firewall to the rudder pedal hinge line. This is posted and described in this thread: viewtopic.php?f=5&t=7530&hilit=rudder+cable+adjustment, in this post: viewtopic.php?f=5&t=7530&hilit=rudder+c ... ent#p68362
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pkissel
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Re: Braking with full right rudder

Post by pkissel »

Wow thanks for the help Bruce!
This makes total sense in my head now and I will check that measurement today.

I will let you know what I find.
1951 - C170A - N1787D
pkissel
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Re: Braking with full right rudder

Post by pkissel »

Well you were right Bruce!
My rudders measured from the firewall to the top of the "T" are about 5 and 3/8 inches... There was a B model in the hangar and I measured it and it was just a hair over 6 inches.

SO i put in the extra washers on the stop by the rudder (how I previously had it) and it doesn't actuate the brake. Monday I will have my mechanic adjust the rudder pedals to a hair over 6 inches and I suspect this will fix the problem!

I appreciate it
1951 - C170A - N1787D
pkissel
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Re: Braking with full right rudder

Post by pkissel »

So I adjusted the turnbuckle on the right rudder as much as we could - I believe we got 3 turns out of the right side and it did improve the pedal distance and made the braking actuation much less or non existent ( I did not get to taxi around and be certain no brake was being actuated since we had a snow storm here - but it did not appear the master cylinder was moving at all.)
We also adjusted the left rudder to keep the pedals centered - we then tested the tension weight on the cables and the book says 20-40lbs. Mine were maybe 14 on the left and maybe 18 on the right. We continued turning the left turnbuckle but were not seeing any improvement on the cable tension weight and continued turning - not sure how many turns.

When I went to test the rudders the left clearly has less amount of travel than the right to apply full rudder deflection.

Is this normal? The other 170 in the hangar feels similar when I test those rudders out. The left being stiffer and shorter where the right is softer and as you get to the end of the travel the bottom pushes in.


There was mention of a clevis on the master cylinder that can adjust for the pedal position. Maybe tomorrow I will look into that and see if there is a difference.


Regardless it seems my rudder cables will never be able to reach the specified 20-40lbs they must have been REALLY loose before looking into this because now the left especially feels very firm.

I am hoping we can get this figured out tomorrow. Thanks for any help
1951 - C170A - N1787D
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GAHorn
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Re: Braking with full right rudder

Post by GAHorn »

pkissel wrote:So I adjusted the turnbuckle on the right rudder as much as we could - I believe we got 3 turns out of the right side and it did improve the pedal distance and made the braking actuation much less or non existent ( I did not get to taxi around and be certain no brake was being actuated since we had a snow storm here - but it did not appear the master cylinder was moving at all.)
We also adjusted the left rudder to keep the pedals centered - we then tested the tension weight on the cables and the book says 20-40lbs. Mine were maybe 14 on the left and maybe 18 on the right. We continued turning the left turnbuckle but were not seeing any improvement on the cable tension weight and continued turning - not sure how many turns.

When I went to test the rudders the left clearly has less amount of travel than the right to apply full rudder deflection.

Is this normal? The other 170 in the hangar feels similar when I test those rudders out. The left being stiffer and shorter where the right is softer and as you get to the end of the travel the bottom pushes in.


There was mention of a clevis on the master cylinder that can adjust for the pedal position. Maybe tomorrow I will look into that and see if there is a difference.


Regardless it seems my rudder cables will never be able to reach the specified 20-40lbs they must have been REALLY loose before looking into this because now the left especially feels very firm.

I am hoping we can get this figured out tomorrow. Thanks for any help
WHERE… did you get that “20-40 lbs” tension on the rudder cable tensions…??

The rudder cable system on a 170 is not interconnected….and cannot be changed from other than whatever tension the rudder-pedal-return springs apply.
You will NEVER affect rudder-cable tension by adjusting the turnbuckles.

Adjust them to achieve the 6” distance from the firewall and that is all.
'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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c170b53
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Re: Braking with full right rudder

Post by c170b53 »

100 series pre 1962 172 rigging I’ll guess, as AJ would say v-ery interesting.
Jim McIntosh..
1953 C170B S/N 25656
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Re: Braking with full right rudder

Post by GAHorn »

c170b53 wrote:100 series pre 1962 172 rigging I’ll guess, as AJ would say v-ery interesting.
Are we discussing a 172..?? …or a 170-A…??
'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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c170b53
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Re: Braking with full right rudder

Post by c170b53 »

WHERE… did you get that “20-40 lbs” tension on the rudder cable tensions…??
Just a wag, the info was taken from that material.
170 rudder rigging couldn’t be easier but while they are at it check the aft fairleads and cable condition
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
voorheesh
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Re: Braking with full right rudder

Post by voorheesh »

It might be a good idea to have a qualified aviation mechanic have a look at this airplane if one is available. Diagnosis by distant on line messages could lead to misunderstandings and other problems.
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Re: Braking with full right rudder

Post by voorheesh »

I need to add to my above comment. It’s not intended to criticize the communications on this site which are invaluable, plus the experience and expertise of many members. All of which are greatly appreciated. In this case the question about the rigging procedure and the description of the problem by the OP seemed to call for a hands on approach to make sure it’s properly understood and resolved. That’s where an experienced airplane mechanic, in person, is worth his or her weight in gold if they can get it right for you the first time. I also realize that help may not be readily available in your location. I’ve seen minor problems like this go the wrong way a few times. Not a discrepancy you want to be guessing on.
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c170b53
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Re: Braking with full right rudder

Post by c170b53 »

I don’t see the last comments as negative, nor should the recent individual with the tension issue. Obviously there’s been a com issue somewhere and a bit of diplomacy can’t hurt to get back on track. Its a wide audience in 170 land or maybe a small one here but it’s always been difficult to know the entire situation behind a post, only the end user knows the big picture or should. Hopefully common dog prevails.
Jim McIntosh..
1953 C170B S/N 25656
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Bruce Fenstermacher
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Re: Braking with full right rudder

Post by Bruce Fenstermacher »

As pointed out, the rudder system is not a closed loop system. The major parts look like this in order front to back.

Pedal Pedal
Return spring Return spring
Cable Cable
Turnbuckle Turnbuckle
Rudder bellcrank-----Rudder bellcrank

The only place the left and right side are connected is at the bellcrank. Any cable tension is caused by the return spring to the limits of the sprint tension no matter how far the turnbuckle is adjusted. Total tension, assuming a frictionless system would be the sum of both springs what ever that is.

With the rudder centered, adjust each turnbuckle so that the pedal hinge line is 6" from the firewall. There is no other adjustment of the cable length in this system. Then adjust each rudder stop so the rudder has 16° movement right and left. There is no specific cable tension. However if you have no tension on one side mostly you likely have a broken return spring.

Things that might have changed from the factory that can make this simple adjustment harder. We will assume all the pulleys are in good shape but all should be visually inspected. Have the cables been replaced? If so are they the correct length? Do you have the correct length turnbuckle parts? With a quick visual inspection, you should have on short and one long eye. The cable links, those flat plates held together with the AN-3 bolts, should be the same length both sides.

On my plane I found modified cable linkage and one turn buckle had both short eyes and the other both long eyes. On my plane I would have liked to pull the peddles a little farther from the firewall but was limited by how short I could adjust the turnbuckles and still have enough room for a legal safety wire wrap around the short eye. On my airplane, adjusted as best I could, at extreme right pedal the master cylinder plunger was starting to move but not enough to create pressure and apply the brake.

You should have an IPC and you can see the entire rudder cable system in figure 49.
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DWood
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Re: Braking with full right rudder

Post by DWood »

I am aware of a parking brake being activated on full rudder. Are your parking brakes still connected?
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GAHorn
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Re: Braking with full right rudder

Post by GAHorn »

Bruces’ comments describe the assembly as depicted…the only cable tension which occurs is the result of the tension-springs which pull the rudder pedals/cables taut. (Addt’l Note: It has been occasionally observed that incorrect springs are installed… Springs which resemble “screen-door springs” have been found in this installation on some of these old airplanes. Presumably the common hardware springs have been installed because of the reputation of Genuine Cessna parts-Prices…. However, in the case of these special springs (actually different between Left/Right)…these USED to be some of the most affordable and reasonably priced Genuine Cessna Parts you might find…about $8 ea. Now PNs 0310196-4 and -3 (left and right) are priced at $34 and $54.)
B34FD8AC-0B82-4AEC-8D05-8DE88C9CDF65.png
3D5E988E-13C9-40B3-A470-D5A6C4953FBA.jpeg
DWoods’ comment refers to the possibility that contact between the firewall-blanket and the brake-master-assembly can activate the parking-brake latching-lever into the “latched” position. Subsequently, if a gusting cross-wind is encountered, the application of full-rudder-pedal may inadvertently apply the toe-brake and can result in the parking brake being “latched” into the “parked” position. A landing (or any further operation such as taxying, etc) will present the pilot with the problem of a braked-wheel on that side.

Dan is pointing out the common recommendation to DIS-Able the parking brakes on Cessna 170s permanently by removing the locking-lever on top of the brake Master Cylinders. (This might be considered as a “Minor Alteration” but the legality probably includes Placarding the Parking Brake as “INOP”. In my own instance, the lower-end of the Bowden-Cable has its’ solid-control-wire bent securely Back onto the sprial-sheath…which prevents anyone from being able to Pull the Park Brake Knob….not even a “smidgeon” …. giving a pretty obvious indication that the operator is Not Able to Apply the Park Brake at all. Hope this helps.)
'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. ;)
pkissel
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Re: Braking with full right rudder

Post by pkissel »

Thanks everyone

I was away from the computer for a while - we got it all sorted based on all your info and help. I did have a mechanic involved and unfortunately he didn't have much time working on 170s....I am also not great at this stuff but it seems like and is a pretty basic set up, especially after reading your comments, frustrating that it took so much effort to figure this out.


Now to fix my left wing "heavy" problem.

again thanks for all the knowledge.

PK
1951 - C170A - N1787D
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