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Tugging the Mooney


rotorman

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I had noticed that my airplane was getting harder to push into the hangar with the tow bar deflected. The push requires that for part of time I have to deflect the tow bar to far right position. At this point, it becomes nearly impossible to move it by myself. I couldn't come up with a good mechanical reason for this problem so I tributed it to my age even thought I started noticing it about 3 years ago. Consequently I bought a Sidewinder. Using this devise I have found that in fact there is significantly more resistance when I deflect the Sidewinder in the same direction as with the manual tow bar. So much resistance that the Sidewinder, which can move a Citation, cannot move the Mooney. Additionally, when the force is applied the right wheel area emits a groaning sound each time the tug attempts to move the airplane. When deflecting the wheel to the left, I get the same groaning sound on the left wheel but not as loud and the tug can overcome the additional force. 

Yesterday, after a 1.5 hour flight, I did a few turns both left and right with the pedals fully deflected. I did them from a standstill to evaluate if it required more power to turn left or right. There was no difference and the airplane responded as it should.

During the last annual performed at a Mooney shop in September the gear area and wheels were inspected, greased and the shock donuts replaced   Has anyone else experienced anything like this? 

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41 minutes ago, M20Doc said:

It sounds like the brakes are somehow being applied at the limits for steering travel.

Clarence

Interesting idea. It would be an easy check to have someone in the cockpit watch the pedals when someone swivels the nose wheel. 

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Thanks for all the input. The ones about checking for the spinning of the wheels, I would hope, was taken care of during the annual when both wheel bearings were greased.

But the brakes may be the culprit.  In reviewing the logbook and digging further into my memory, both brake masters were replaced in 2016 which is when I first noticed the problem. I also have a recollection that the original part number was not available but the logbook gives no clue as to what the replacement part number is. I do remember that the installer told me, and I later observed, that the new masters have an external spring that the originals did not have.  During the Sept annual the calipers were disassembled and O-ring seals replace so the brakes were inspected at that time. 

Can some speculate how the brakes would come on when the nose wheel is cocked to it's max deflection? With no deflection the airplane moves with normal resistance.

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This should be easy to figure out. I’d remove the cowling and left exhaust cavity (yes, I know there’s no exhaust pipe on the left side, but that’s what it’s called). This will expose the master cylinders and linkages. Then I’d put the plane on jacks to get the nose wheel off the ground so that it is easy to move and observe the action of the mechanism while moving the nose gear from stop to stop. 

SkIp

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4 hours ago, PT20J said:

This should be easy to figure out. I’d remove the cowling and left exhaust cavity (yes, I know there’s no exhaust pipe on the left side, but that’s what it’s called). This will expose the master cylinders and linkages. Then I’d put the plane on jacks to get the nose wheel off the ground so that it is easy to move and observe the action of the mechanism while moving the nose gear from stop to stop. 

SkIp

No jacks available at the moment.  But why would turnin nose wheel left or right to the limit apply brake in the direction of the turn? Can someone elaborate on the logic?

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30 minutes ago, rotorman said:

No jacks available at the moment.  But why would turnin nose wheel left or right to the limit apply brake in the direction of the turn? Can someone elaborate on the logic?

I’ve no idea how or why, but why else would the plane become impossible to move?

Clarence 

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30+ hrs ago I was a line tech at a multi line Motorcycle dealer, Service Manager asked if I would work on a Honda self propelled push mower, my reply was give it to the guy (can’t remember his name) that does the power equipment, as he walked away he said I thought you’d like it seeing how it won’t turn to the left. Wait, what? It’s a push mower why wouldn’t it turn turn left? .... long story short, there a sprague type bearing in the rear wheel that had failed. The point to this is that anything mechanical can and will do odd things, like @M20Doc said, somehow the brakes are being applied as the nose wheel is turned.... after all the rudder pedals are connected to it. 

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1 hour ago, rotorman said:

No jacks available at the moment.  But why would turnin nose wheel left or right to the limit apply brake in the direction of the turn? Can someone elaborate on the logic?

Well, obviously it shouldn’t. But you said the master cylinders were replaced with parts that are different than the original so maybe something got messed up then since the brakes are attached to the rudder pedals. 

The point is that something unusual seems to be going on and it’s pretty hard to guess what it might be. But if you open it up and look at the motion it should be immediately obvious it it’s something to do with the brakes.

Skip
 

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Continuing with the logic of the brakes being applied at the turn limits:  is it possible that somehow there’s an obstruction in the floorboard rudder pedal slots that is working against the backside of the brake actuator linkage?

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Since you are in there...

Check the size of the feet that are on the rudder pedals...

It takes enough force to push the rudder pedal to the floor...

Does the brake get hit at the same time...?

Use extra care, with some very light shoes, so you can really feel the difference...

Other than that... chasing the control rods under the belly to see what is misbehaving... if there is interference going on, there will be some pretty shiny metal indicating where things are rubbing...

Interesting situation with respect to unknown parts in the system... it is quite possible that there is some unknown side affect caused by the parts... the easy part would be identifying the parts to make them known...

PP thoughts only, not a mechanic...

Best regards,

-a-

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Further troubleshooting. I went to the the hangar this afternoon (Christmas day. Am I obsessed or what?) and confirmed that the brake is coming on when the nose wheel reaches its limit. The other thing that is present in the brake pedals is virtually no free play. It is hard to gage but when I step on the brakes they are totally firm in less than 1/2 in of travel. Maybe as little as 1/4 in. When I put my hand on the brake and have an assistant turn the nosewheel, I do not feel pedal movement nor movement in the brake rod attached to the pedal. The problem is worse with nose wheel left versus nose wheel right, but it is occurring in both directions. There may be be some small force applied to the brake pedal rode when the pedal goes to its max position which normally would not be enough to pressurize the brake but since I have almost no freeplay my brake go on.

I noticed this lack of free play after the brake masters were changed about 3 years ago and that corresponds to the same time the airplane became hard to push. I was pleased at how good the brakes felt since before the new masters I was unable to bleed them and the air gave me too much freeplay.  Is there a brake pedal free play spec? Is there any way to adjust the free play. I think not but I can hope.

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There is an adjustment to the lengths of the master cylinder piston rods. There is no description of it I could find in the S&MM for my M20J when I had to tweak mine to get the pedal angles right after installing the 3" pedal extensions. There should be some free play in the pedal before the brakes go solid.

If you remove the left exhaust cavity an examine the linkages it should be fairly obvious what's gone wrong.

IMG_2868.thumb.JPG.c3cdcc6ba0f7fd39905b178fe7ed8cdd.JPG

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20 hours ago, PT20J said:

There is an adjustment to the lengths of the master cylinder piston rods. There is no description of it I could find in the S&MM for my M20J when I had to tweak mine to get the pedal angles right after installing the 3" pedal extensions. There should be some free play in the pedal before the brakes go solid.

If you remove the left exhaust cavity an examine the linkages it should be fairly obvious what's gone wrong.

IMG_2868.thumb.JPG.c3cdcc6ba0f7fd39905b178fe7ed8cdd.JPG

That nut and washer on the rod with the spring looks like a spring tension adjuster and not a length adjuster. Am I wrong. I'll be getting in there shortly and have a look. Thanks for posting the photo.

 

23 hours ago, M20Doc said:

Possibly something with the pedal geometry.

Clarence

3C6C5447-57A4-4976-B7CE-765F52470E58.jpeg

Thanks for posting that. Do you know if any of those rods leading to the master are adjustable?

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I believe the rod (#5) between the pedal and the bellcrank is fixed length.  Adjusting the fork end in the master cylinder will change the pedal angle.  The spring pushes on the check nut, so it’s length shouldn’t be affected.

Clarence

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