Taxi problem

T

Taoufiq

Filing Flight Plan
Joined
Jul 9, 2023
Messages
22
Display Name
Display name:
Taoufiq
Yesterday on taxi, i had to push the right rudder almost all the way to keep the plane straight. Any idea what could it be? Thanks 1966 c172
 
Crosswind? Dragging left brake? Flat left tire?
 
If a brake was dragging you would probably be able to hear it.

Put a tow bar on it and pull it. Does it want to pull to the left?
 
Greg Bockelman said:
If a brake was dragging you would probably be able to hear it.

Put a tow bar on it and pull it. Does it want to pull to the left?
Click to expand...
Dont thik so, i will test it today. If thats not the issue, what should i check next?
 
Jack aircraft and spin wheel.

Dragging brake usually gets hotter. Laser Temp Gun?

The Caliper can stick on pins from lack of lube and infrequent use.

The piston in the caliper can stick because it was serviced with

other than 5606. I don’t like to even use the term Brake Fluid

for that reason.
 
Rudder trim?
When it happens, let up on the pedal, and look at the rudder. If it's deflected, then likely trim or rigging. If not deflected, then likely brakes, nosewheel, or tires.
 
Is it your plane? Do you have a mechanic on field?
 
Half Fast said:
Check tire pressures first. Easy to check, easy to solve, and a likely culprit.
Click to expand...
Just did, the right one was at 16 psi (pilot side), and the other one was at 21.
 
Just wanted to say if you're having this much trouble on the ground with the rudder pedals then don't take off. One cross wind the wrong direction and you might not have enough nose wheel authority to correct the plane and head it on heading.
 
wheaties said:
Just wanted to say if you're having this much trouble on the ground with the rudder pedals then don't take off. One cross wind the wrong direction and you might not have enough nose wheel authority to correct the plane and head it on heading.
Click to expand...
Thanks, wasnt planning on flying before it gets fixed
 
90% sure it's a broken right rudder bar spring. They do that, though usually it's the left one that lets go and you have to hold left rudder. It's the one that gets stretched most of the time during takeoff and climb when you have to have right rudder to counter the left-turning tendency. Most likely the left spring has been replaced one or more times while the right spring has been slowly wearing and fatiguing.

Center the nosewheel and lift the nose while pulling down on the tail (DON'T push down on the horizontal stab. That cracks its forward spar.) If the rudder is off to the left with the nosewheel off, that spring is busted or the rudder system is badly misrigged.

The system. The springs are #15, but they are two different part numbers. Different lengths. They are a stinker to get at and replace.

upload_2023-7-9_18-28-34.png

Edit: One other possibility is a broken spring inside the right steering bungee. The bungees are those two rods that attach to each side of the nosewheel's steering collar. They're what give the Cessna its soft, sloppy nosewheel nosewheel steering compared to a Piper's.
 
Last edited:
It’s probably pulling to the left because your right brake is shot. Possibly due to what Dan said or maybe the right brake linings are worn to the point that the caliper piston has over extended allowing fluid loss and air into the system.
The disks look rough as a cob. Appears to be significant neglect with the tires and brakes. I would be concerned about other common problems! Especially flammable fluid hoses forward of the firewall. Might want to check the dates on those.
Did you happen to get a prebuy?
 
Dan Thomas said:
Center the nosewheel and lift the nose while pulling down on the tail (DON'T push down on the horizontal stab. That cracks its forward spar.)
Click to expand...
Hey Dan, I’ve always heard of this from fellow mechanics but never actually seen one cracked myself. I currently have a 172 horizontal stab removed (sheared rivets at the elevator stop bracket) and thought it’d be an excellent opportunity to inspect for spar cracks while it’s on the bench. Do you happen to have any pics of a 172 with this type cracking. Thanks!
 
Jdm said:
Hey Dan, I’ve always heard of this from fellow mechanics but never actually seen one cracked myself. I currently have a 172 horizontal stab removed (sheared rivets at the elevator stop bracket) and thought it’d be an excellent opportunity to inspect for spar cracks while it’s on the bench. Do you happen to have any pics of a 172 with this type cracking. Thanks!
Click to expand...
They crack outward from the center lightening hole in the forward spar, normally at 45° to the vertcal and horizontal. Cessna says that stopdrilling is OK, but I have seen those cracks continue cracking either because the stopdrill didn't clean up the end of the crack, or pilots kept pushing down on the tail.

1689006768690.jpeg

That view is looking forward through the large hole in the stab's top skin between the two long stab/fuselage fairings.

Too many folks don't understand the geometry here. That stabilizer is a unit with the elevator as far as the air is concerned, and the center of pressure is therefore just ahead of the stab's aft spar, which is a much heavier, laminated affair to take the loads. The forward spar is very light because the air loads on it are lower. Now, that control surface is intended to govern aircraft attitudes in flight, NOT on the ground, as in flight the tail forces deal only with the force couple between the CG and CP, which are relatively close together. On the ground, a person pushing down on the stab is raising the nose against the force couple between the main gear and CG, a much larger distance, and the downforce required, on the wrong part of the stab, causes that spar to flex around that hole and it fatigues and cracks. Cessna says that if a crack progresses into the flange of the spar, it MUST be repaired with a doubler kit and maybe a new spar section if the cracks have extended far enough.

We had three 172s in the flight school. I found all of them cracked. After repairs, I forbade any of our people to push down on the stab, and we had no more trouble. That's what towbars are for. Pushing down on the stab also often buckles the nose and main ribs in the spar. It's a poor way to handle an airplane.

The SB: https://ddrr17eur1111.cloudfront.net/wp-content/uploads/2020/04/21183259/document.pdf
 
Taoufiq said:
No crosswind yesterday for sure.
What s the reason for dragging brake and how to check it?
Click to expand...
In your first post you said you had to push the right RUDDER all the way to make it taxi straight, not the right brake. Which is it, now?
 
Airframe Components has an excellent video on the stab.

“ Inspection of Cessna 172 Stabilizer Spar”.
 
  • Like
Reactions: Jdm
Full right rudder on landing indicates a serious problem, possibly much worse than any broken spring. If it was a dragging left brake, the tire would have blown out on touchdown, since there is little weight on it at landing speeds. It sounds to me like the rudder bar may be failing, with the welded-on lug that actuates the cable breaking away.

That airplane needs a thorough, full inspection by a qualified and experienced mechanic. It's 57 years old and may have a long history of really cheap maintenance. I have seen this way too often, and sometimes i marvel that these things don't come apart in the air more often. That time is coming, though, for a lot of these ancient things.
 
  • Like
Reactions: Tai
It’s the Left.

Or the Right.

The other Left?

The Pilot side Right seat?

The right ( ?) brake or rudder pedal moves a lot so that’s normal?

It appears the Right Brake is not working so full Right Rudder is needed?


In my prior life I was chilling in a C-47 while the Pilot was getting recurrent.

The Left Engine was shut down via Mixture.

” Make sure you feather the Right one!” was heard .

Then became quiet followed by “excitement”!
 
Sounds like he’s compensating with right rudder (because of a bad right brake) to overcome left braking forces. Left braking could be from a dragging condition, or simply normal left brake application. Either way it’s messed up and needs attention.

Thank you fellas for the the stab information. Good stuff for sure!!
 
Excellent video Gary! Thank you sir. The bracket shown at the end of the video is exactly what I’m currently reattaching. It’s becoming a real problem area for the flight schools. I’ll try to upload a video what a loose rivet condition looks like there.
 
Well I can’t get access to the video now but basically you wiggle the elevator up and down at about the mid travel position while shining a light towards the lower base of the stop bracket. If the bracket rivets are sheared you’ll notice about 1/16” movement at the lower portion of the bracket. It’s difficult to see. Best to have a helper.
 
The issue was that the right brake was missing hydrauliq fluid, so when i was braking on both, only the left one was working, so the plane would turn left, and i had to push the right rudder to compensate…
 
  • Like
Reactions: Tai
So the next question is, where did the brake fluid go? Did you find a leak in the system? Fix it?
 
  • Like
Reactions: Tai
Greg Bockelman said:
So the next question is, where did the brake fluid go? Did you find a leak in the system? Fix it?
Click to expand...
We didnt find no leake. The amo says maybe because we brake too hard on landing (beginners) that the fluid pops out from caliper or something like that
 
Taoufiq said:
We didnt find no leake. The amo says maybe because we brake too hard on landing (beginners) that the fluid pops out from caliper or something like that
Click to expand...
Pressure in the caliper normally seats the O-ring seal more firmly and it doesn't leak. Your caliper, if it's the original 1966 caliper, is likely corroded in its piston bore and oil is escaping. If It's leaking there should be some sludge on the bottom of the caliper where the dust sticks to the oil. Other possible places include the fitting seal at the bottom of the master cylinder, and the hoses from the masters to the bulkhead fittings. There are also bulkhead fittings where the aluminum line exits the fuselage right behind the gear leg. Any of that stuff can slowly seep oil.

I bet it's been a while since a mechanic had a good look under that floor.
 
Like Dan says above, always great advise from him and Bell206.
IMO if it is missing 5606 then you can be sure it is leaking somewhere.
Also important to change that fluid every so many years. This is how I learned to do it. Pretty simple and cheap.
IMG_0616.JPG

The old being flushed out. Don't forget to lube behind the rudder pedals.
IMG_0617.JPG

IMG_0618.JPG

It sounds like your aircraft needs some love and attention?
 
Last edited:
  • Like
Reactions: Tai
The Master Cylinders should have plastic plugs installed on the top to keep fluid from splashing

and debris out. These plugs MUST have a small vent hole or the brake will malfunction.

Fingertight only! My preference is to use the “ bottom up” method per Gary as it is generally the

easiest and it also bleeds the system.. For filling from the top I have found it wise to put a rag around the

base in case you drop it. W/o the rag you may go hunting and find others!

I do fill slightly different than Gary’s m/o as I do not use a return line. Placing

a paper towel alerts me when the rez is full.

NOTE: Without covering the plugs you CAN squirt your instruments!


Placing paper towels under calipers when parked will help identify the source.
 
Dan Thomas said:
I bet it's been a while since a mechanic had a good look under that floor.
Click to expand...
Proud to say I don't cut any corners during annual inspections on my own plane. I have a clear conscience and feel good about flying it after laying eyes on it myself. It's a solid week of work, 35+ hrs on average for a 172. Not counting my IA's time.
IMG_2064.JPG

I mostly adhere to the progressive maintenance schedule all through out the year as I do fly it a lot.
(edited)_IMG_3013.png

(edited)_IMG_3042.png

That is the moon during one of many epic nights of flying trusting my bird.
IMG_2920.JPG
 
Last edited:
You must log in or register to reply here.
Back
Top