Sheared the nosewheel attachment bolts

[SixPapaCharlie]

Had an interesting occurrence last week. I apparently started the year off with too much money in my bank account and my plane caught wind of this.
Freshly overhauled carb installed and I went to do some test runs. I pulled the plane out of the hanger, started it up and pressed the right rudder pedal.
Heard a loud pop and my right foot went to the floor.

Both rudder pedals moved freely. I shut it down thinking I had somehow detached the pedals from the entire rudder connection.
Opened the door and confirmed the rudder moving along with associated pedal input.

Opened the cowl and the nosewheel attachment plate was now just sitting on top of the structure rather than bolted on.
Apparently there is a known issue with the original bolts that hold this on can shear off.










The Piper Comanche nose gear is a very simple machine. Strut tube goes through a housing. The housing is bolted to the engine mount.
The tube at the top has a cap held on with 3 bolts. the cap has "wings" that stick out.
Rudder pedals are attached to a bar that connects behind this and that bar simply pushes on the "wings" of the cap on the strut tube, turning the nose wheel.





Turns out this is a known issue and I have ordered the High Strength bolts along with parts to go ahead and overhaul the nose wheel since it is now at an A&P in Grand Prairie TX.







Any thoughts on what would have happened if these bolts snapped upon landing / takeoff?
I wonder if the wheel would stay aligned or possibly turn. I wonder if there would have been a chance for a nose gear collapse.

 

[Jim K]

Good question. Is there any caster built in to the nose gear fork?

How did you end up tying the tail down?

 

[Tarheelpilot]

I wonder how many original fasteners are still on your airplane holding critical components.

Our GA fleet is old.

 

[SixPapaCharlie]

Good question. Is there any caster built in to the nose gear fork?

How did you end up tying the tail down?

I went to TSC and got a 4 foot Earth Anchor and screwed it into the ground. It took 2 hours and every ounce of energy to get the damn thing in the ground.
As expected, Right before walking away I said "That's not going anywhere".

Tied the tail with 2 1000lb rachet straps

 

[SixPapaCharlie]

I wonder how many original fasteners are still on your airplane holding critical components.

Our GA fleet is old.

Especially given everything planes have taught me about shear force and why wings can be attached with a couple bolts...
Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

 

[Jim K]

I went to TSC and got a 4 foot Earth Anchor and screwed it into the ground. It took 2 hours and every ounce of energy to get the damn thing in the ground.
As expected, Right before walking away I said "That's not going anywhere".

View attachment 137070 View attachment 137071View attachment 137072

I mean, it's too late now, but I bend a piece of rebar into a question mark shape and chuck it into my big drill. You have to be careful not to break your wrist, but it beats doing it by hand.

 

[Let'sgoflying!]

Glad it happened stationary.
If on the runway besides the much worse damage, the ntsb prob try to blame pilot error.

 

[SixPapaCharlie]

Good question. Is there any caster built in to the nose gear fork?

How did you end up tying the tail down?

I have the fork and wheel in my garage and there doesn't appear to be any castor. It is dead center like a unicycle.

 

[Doc Holliday]

"Known issue"? Then why hasn't it been addressed previously?

 

[Bell206]

Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

Post a pic of the cross-section of the broken bolts. That should reveal more on why they sheared. As to why, if they were over torqued or under torqued then that would have set up a fatigue schedule which takes time to break. Or one was broken for a period then the other two finally fatigued out an broke. Thats way proper torque is so important even in shear applications.

 

[SixPapaCharlie]

Glad it happened stationary.
If on the runway besides the much worse damage, the ntsb prob try to blame pilot error.

It would be chalked up to pilot failing to maintain, such and such.
We pulled the assembly apart and found some things that were not neglected but out of spec.
The AD is 1000 hrs and 10 years. A lot of wear can happen between those times. I still have 3 years left on the gear AD.
Annuals don't require disassembling these things. There are some things on these planes that I wonder how a pilot would even know.

I did make lingering eye contact with the plane and say "One more issue and I am selling you" as I left the hangar yesterday.
That's a lie but I need the plane to know like a parent counting to 3, that I am on 2 so it better behave.

 

[nauga]

Any thoughts on what would have happened if these bolts snapped upon landing / takeoff?

You presumably still have rudder and brakes, even if the nosewheel doesn't caster. Still might be a handful, but not necessarily catastrophic.

Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

I'd bet a reasonable amount that if some of the bolts weren't at least partially sheared they were certainly weakened considerably before failing completely.

Nauga,
not shear genius

 

[SixPapaCharlie]

Post a pic of the cross-section of the broken bolts. That should reveal more on why they sheared. As to why, if they were over torqued or under torqued then that would have set up a fatigue schedule which takes time to break. Or one was broken for a period then the other two finally fatigued out an broke. Thats way proper torque is so important even in shear applications.

Bolts are in the hangar. I will be out there in a couple hours. I will snap a pic.
My MX believes they were loose. He said there is wear on the gear aligner with slightly elongated holes that makes him think they were shifting / rubbing, leading to the failure.

 

[Checkout_my_Six]

Pilot error…..does it every time.

 

[Jim K]

I did make lingering eye contact with the plane and say "One more issue and I am selling you" as I left the hangar yesterday.
That's a lie but I need the plane to know like a parent counting to 3, that I am on 2 so it better behave.

I have bad news for you...

 

[X3 Skier]

Took the USAF Aero Club Cherokee to Arnold AFS once. The USAF Ground crew moved it for some reason and broke the pivot bolt for the nose wheel steering. Similar to your set up. When I did the preflight, the rudder pedals didn't feel right. Upon further examination, I found while the rudder moved, the nose wheel didn't. Not my plane, not my monkey. Hitched a ride home in an Aero Commander for my first AMEL Time. Same plane that swallowed a valve one time over downtown Cincinnati.

 

[SixPapaCharlie]

You presumably still have rudder and brakes, even if the nosewheel doesn't caster. Still might be a handful, but not necessarily catastrophic.


I'd bet a reasonable amount that if some of the bolts weren't at least partially sheared they were certainly weakened considerably before failing completely.

Nauga,
not shear genius

Actually, it has tow stops preventing it from turning too far. I was thinking it might turn completely sideways and skid or collapse.
Maybe would have just turned to the limit one way or another. Ugly still but likely not bent metal.

 

[nauga]

I was thinking it might turn completely sideways and skid or collapse.
Maybe would have just turned to the limit one way or another. Ugly still but likely not bent metal.

If it's properly designed (and I assume it is) the contact patch is behind the steering rotation axis to prevent exactly that.
OTOH, even with that it might be sporty for a bit if you landed with it cocked.

Nauga,
pivotal

 

[455 Bravo Uniform]

Collapse, even if you kept the ship centerline on the runway, could have resulted in a prop-strike and that expense. 3 bolts and labor are cheap! Thank your plane for talking to you. Go back and apologize.

 

[eman1200]

I have no idea what could have cause that

 

[Dave Theisen]

Especially given everything planes have taught me about shear force and why wings can be attached with a couple bolts...
Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

Obviously, you don’t skip leg day.

 

[luvflyin]

I have the fork and wheel in my garage and there doesn't appear to be any castor. It is dead center like a unicycle.

That doesn’t mean there isn’t caster. If it is vertical when extended then there wouldn’t be, but it is ‘tilted’. Think motorcycles. They all have caster.

 

[DaleB]

Especially given everything planes have taught me about shear force and why wings can be attached with a couple bolts...
Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

I doubt that you did. I suspect (and a close inspection might confirm or disprove) that two were already broken, and you just broke the third.

 

[SixPapaCharlie]

I doubt that you did. I suspect (and a close inspection might confirm or disprove) that two were already broken, and you just broke the third.

Yeah, that actually makes way more sense.

 

[mondtster]

Hopefully the bolt holes and mounting surfaces are checked before new bolts are just slammed in and the gear reinstalled. If things are tore up enough it might not take long to be in the same position again.

 

[X3 Skier]

Actually, it has tow stops preventing it from turning too far. I was thinking it might turn completely sideways and skid or collapse.
Maybe would have just turned to the limit one way or another. Ugly still but likely not bent metal.

Those stops are no match for the tug that broke mine

 

[texasclouds]

That Piper almost looks like a real plane with the tail dragging in proper form. Maybe it’s time to ditch the training wheel.

 

[Dan Thomas]

Especially given everything planes have taught me about shear force and why wings can be attached with a couple bolts...
Its a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

As Bell says, if those bolts aren't properly torqued, that bellcrank will slam against them until they're cracked. If there's any nosewheel shimmy, they really get hammered.

I have the fork and wheel in my garage and there doesn't appear to be any castor. It is dead center like a unicycle.

If it's properly designed (and I assume it is) the contact patch is behind the steering rotation axis to prevent exactly that.
OTOH, even with that it might be sporty for a bit if you landed with it cocked.

Yup. If you look at the strut and fork in this shot of a Comanche, you can see that the strut is angled forward about 5 or 6 degrees. Draw a line through the strut axis and you'd see that it intersects the ground near the front of the tire's contact patch. That's the caster.


Look at the typical bicycle. Let's draw a line through the steering pivot and see where it contacts the ground:


It intersects the surface just ahead of the contact patch. If those forks were straight like the Comanche's nosewheel fork, the large wheel radius of that bike would put the contact patch so far behind the axis that the caster would be too extreme and steering would become difficult.

That doesn’t mean there isn’t caster. If it is vertical when extended then there wouldn’t be, but it is ‘tilted’. Think motorcycles. They all have caster.

Yup. As above.

 

[Magman]

Some thoughts:

Why would you NOT want High Strength Bolts in areas like Landing Gears?

Most light aircraft have Steering Stops. However; very few have the

Limits depicted for Line Crew guidance.

Some Insurance Companies will not cover maintenance failures. They may

be doing you a favor by saying “ Pilot Error”. At least until Renewal Time.

 

[Tarheelpilot]

Especially given everything planes have taught me about shear force and why wings can be attached with a couple bolts...
It’s a little scary now that I managed to shear off 3 bolts at once with the push of a single pedal.

I try not to think about it…

 

[bentmettle]

arguably the biggest benefit of the higher strength bolts is that the endurance limit usualy goes up with it.

Is there any link between tensile strength and endurance limit for steel ?

I'm designing a shaft, and i have to choose a material. I deal with cyclic stress in my machine, so i set up an expression for all the possible stresses and combined it with von Mises criteria for

engineering.stackexchange.com

Did the bolts shear across the thread roots?

 

[SixPapaCharlie]

 

[bentmettle]

Textbook. Annoying I'm sure.

thanks for the photos!