Nosewheel Steering Disconnection on Retraction

[moosebreath]

How is the steering disconnected when the nose wheel retracts?  I can not find a narrative description and it is not clear, to me at least, in the parts manual drawings.  Thanks.

[N201MKTurbo]

It is kind of hard to describe, but it is all in the steering horn. It is easier if you see it in action. With gear down the steering pushes the pivot back and forth  and steers the nose wheel. With the gear up, the steering just spins around the pivot. Clear as mud, right….

[EricJ]

+1 to the description above, but if you get underneath the airplane and just look up at the steering horn, and see where the nosewheel pivots on the vertical axis for steering, and then see where it pivots for retraction, you can kinda figure out how it works.    It seems like a really oddball system to me and I always wonder what it does while the gear is retracting, but it seems to work fine.   It's fairly easy to see how it works with the gear down, and how it does nothing when the gear is retracted, though.

I helped a hangar neighbor with the nose gear on his Comanche, and that's the most dirt-simple retractable nosewheel steering system I think I've seen.   Comparing the two makes me wonder what sort of life events the guy was going through that designed the Mooney nosewheel steering.

[PT20J]

This probably won’t help — but just in case

When the gear is down, link 27 connected to the rudder rotates the steering horn 30 about the pin attached to the structure 10 and this turns the nose gear leg 35 to steer. When the gear is retracted, the gear leg rotates up and back about the shaft 31 and any rudder movement just rotates the steering horn around the bolt 34 at the top of the gear leg 35.

Besides the limited movement of the steering mechanism that makes it easy to damage the leg when towing, there is also the fact that the steering is rigidly connected to the rudder so that when landing in a slip in a strong cross wind, the nose wheel will be off center when it touches down and you need to let it center the pedals by releasing pressure or you head for the rough.

[Fly Boomer]

9 hours ago, N201MKTurbo said:

It is kind of hard to describe, but it is all in the steering horn. It is easier if you see it in action. With gear down the steering pushes the pivot back and forth  and steers the nose wheel. With the gear up, the steering just spins around the pivot. Clear as mud, right….

I'm not the OP, and I can't say I understand how it works, but it's just another example of what an engineering marvel these airplanes are.

[A64Pilot]

10 hours ago, EricJ said:

 Comparing the two makes me wonder what sort of life events the guy was going through that designed the Mooney nosewheel steering.

Ever taken an old school automatic transmission valve body apart and tried to figure out fluid flow? New ones may be the same I don’t have any experience with those.

Some hydraulic flight control servos remind me of the transmission valve bodies.

I guess we have to stop calling then trannie’s now huh? How about XMSN?

[Flyler]

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

[Skyland]

Genius example.  Thanks for sharing your model.

[1980Mooney]

33 minutes ago, Fly Boomer said:

I'm not the OP, and I can't say I understand how it works, but it's just another example of what an engineering marvel these airplanes are.

Like everything else in aviation, it is a trade-off.  It works but with highly restricted and unequal turning angle (11 deg. left and 13 deg. right) which results in a large turning radius and its fragility during towing operations.  Per POH long body turning radius (without brakes) is 40 ft to the right and 48 ft to the left.(outer main gear radius).  By comparison a Bonanza (outer main gear - no brakes) can turn in under 16 ft. either way.

[Greg Ellis]

1 hour ago, Flyler said:

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

Thank you for posting this.  That goes such a long way to explain how this system works.

[haymak3r]

2 hours ago, Flyler said:

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

This is probably the best thing I will see on the internet for the next 10 years. Well done!

[Slick Nick]

I learned more from a 3 second video of a cardboard model, than I did reading the description over and over and looking at parts diagrams. Thank you!

[EricJ]

2 hours ago, Flyler said:

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

Brilliant!   Yeah, that's it. 

Does it bind when the gear is partially retracted?

[N201MKTurbo]

You will also notice it straightens out the nose wheel as it retracts and holds it in the center.

[Hank]

3 hours ago, Flyler said:

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

Screwdrivers and packing tape! That's wonderful. 

[Flyler]

19 minutes ago, N201MKTurbo said:

You will also notice it straightens out the nose wheel as it retracts and holds it in the center.

Yup!  That is another smart part of the design.  Not only does it "disconnect" the steering (not really of course) but it also straightens the wheel.  I would say that is so the wheel well can be narrower in the cabin, but knowing Al Mooney, it's probably in case there is some slight errant breeze in the wheel well, he would want nice smooth airflow over the wheel 

Here's a better example of the "self centering" action:

 

[EricJ]

5 minutes ago, Flyler said:

Yup!  That is another smart part of the design.  Not only does it "disconnect" the steering (not really of course) but it also straightens the wheel.  I would say that is so the wheel well can be narrower in the cabin, but knowing Al Mooney, it's probably in case there is some slight errant breeze in the wheel well, he would want nice smooth airflow over the wheel 

Here's a better example of the "self centering" action:

 

That makes sense.   The binding I was worried about just self-centers it.

[Flyler]

Just now, EricJ said:

That makes sense.   The binding I was worried about just self-centers it.

If it helps, this joint has to be a spherical joint.  Often called a ball joint, tierod end, or heim joint.  It works in the cardboard because, well, it's made out of cardboard  

[EricJ]

2 minutes ago, Flyler said:

If it helps, this joint has to be a spherical joint.  Often called a ball joint, tierod end, or heim joint.  It works in the cardboard because, well, it's made out of cardboard  

I was puzzled about whether there's binding at the other end of that piece of cardboard, but it makes sense that it's relieved by the nosewheel moving to center itself.   Something wears out the steering horn/bushing, and airplanes don't spend much time driving around on the ground, so I had a suspicion that maybe there was bind on it during retraction/extension.   I just never thought about it enough to figure out what it did mid-cycle, but your model helps, for sure!   Very cool.   

[PT20J]

I read somewhere that Leroy Grumman worked out the folding wing mechanism for the Wildcat with a pink pencil eraser and a paperclip.

[Flyler]

When I was a green engineering intern, I had an idea for a 4 bar linkage.  Using some cardboard cutouts and simple push pins, I brought my idea up to the Chief Engineer.  We could move the push pins around to adjust the linkage length to get it to do what we wanted, and it was 1:1 scale.  He was really happy about how stupid yet effective the cardboard method was.  After some praise, he looked at me for a while, then looked at the cardboard.  Then he looked at me again.  His smile turned to a frown.

"Tyler, where did you get this cardboard?"

I shrugged and said I had found it downstairs in engineering, just a big box laying around.

"Tyler, this the triple wall cardboard from GM.  I know it sounds stupid, but this is a prototype packaging cardboard that we paid many thousands of dollars for.  You cut up that box?!?!"

 

Fortunately they had already made a determination about the cardboard and there wasn't any collateral damage, but I certainly lost some sleep over that 

[Fly Boomer]

4 hours ago, 1980Mooney said:

By comparison a Bonanza (outer main gear - no brakes) can turn in under 16 ft. either way.

Wow!  Huge difference -- never taxied a Bonanza.

[N201MKTurbo]

As elegant as our nose gear design  is, it is more delicate than most and has a poor turning radius.

[moosebreath]

Amazing!  Thanks for the most complete demonstration of how this works.

 

[0TreeLemur]

10 hours ago, Flyler said:

As a "Mechanical Design Engineer" this interests me too, so I made a cardboard model.  I know its nutty, but I am a nutty person.  This is just a basic simplification of how the steering works in the extended and retracted position.  It has the same strength properties as the gear in my Mooney 

 

I nominate this for the best post of the year!   I think we need another button!