How about the 12? I haven't seen many reports of nose gear failure in the 12. Is its nose gear more sturdy than the other 2 seat models?
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RV nose gear accident study results
- Thread starter Craig-RV8a
- Start date
How about the 12? I haven't seen many reports of nose gear failure in the 12. Is its nose gear more sturdy than the other 2 seat models?
bobair43
Member
RV7a nose over
My RV7a was completed 2005. 2021 I had a nose over accident at my home airport. On landing as the nose wheel came down the airplane swerved quickly to the left. The nose wheel hit the mud and the plane flipped over. I was lucky recieved no injuries. After getting the plane back to the hanger found that the bolt at the top of the gear leg had sheared and the gear rotated causing the turn to the left. I have scince repared the the plane and installed the upgraded RV14 stile engine mount with the elastimer cushion. Thinking this accident could not have happened with this mount.
I would be interested to know if there have been any accidents involving the new nose gear.
My RV7a was completed 2005. 2021 I had a nose over accident at my home airport. On landing as the nose wheel came down the airplane swerved quickly to the left. The nose wheel hit the mud and the plane flipped over. I was lucky recieved no injuries. After getting the plane back to the hanger found that the bolt at the top of the gear leg had sheared and the gear rotated causing the turn to the left. I have scince repared the the plane and installed the upgraded RV14 stile engine mount with the elastimer cushion. Thinking this accident could not have happened with this mount.
I would be interested to know if there have been any accidents involving the new nose gear.
There is a service bulletin that involves inspecting the rotation limit stop for the nose gear, fork, and assuring that it is installed correctly. Many of them are not, and if not, the fork rotation is limited to less rotation than intended, which puts a high shear load on the bolt which can cause them to fail.
RVbySDI
Well Known Member
To clarify, it is not the allen bolts that are installed incorrectly. It is the metal bracket that hits the allen stops that is being installed backwards.
It's not the allens location, it's the plate that contacts them. Was the stop mounted on the back, or the front??
The upper bolt can only shear if there in play in the gear leg. This is something that should be checked during your annual inspection. The nose gear needs to be off the ground to check for ANY play in the socket (left, right, up, and down). This is not the fault of the design.
simpkinsona
Well Known Member
Gear stop
Actually you have that backwards. The gear stop in the wrong position limits the wheel travel too much.
-Andy
Actually you have that backwards. The gear stop in the wrong position limits the wheel travel too much.
-Andy
AlexPeterson
Well Known Member
Improper installation of the bracket means a large reduction of available swivel angle. When the bracket hits the stop bolt, the result is a large torque moment on the gear leg, shearing the upper bolt.
https://www.vansaircraft.com/service-information-and-revisions/sb-14-12-22/
I agree 100%, but that’s not what he’s talking a out
Dan, we are in complete agreement.
However, this can’t be about the lower bracket SB.
Here’s what Bob wrote:
“After getting the plane back to the hanger found that the bolt at the top of the gear leg had sheared and the gear rotated causing the turn to the left.”
That’s the AN5-20 bolt that secures the top of U-603-3 Nose Gear Leg to the Engine Mount weldment and prevents gear leg rotation. I’ve never heard of that bolt shearing but it could certainly happen if there’s any looseness.
Gasman is correct about checking the nose gear for any play. I replaced all 3 of my gear legs’ upper bolts with the tighter tolerance NAS bolts on KELLI GIRL’s first condition inspection for that very reason.
Dan, we are in complete agreement.
However, this can’t be about the lower bracket SB.
Here’s what Bob wrote:
“After getting the plane back to the hanger found that the bolt at the top of the gear leg had sheared and the gear rotated causing the turn to the left.”
That’s the AN5-20 bolt that secures the top of U-603-3 Nose Gear Leg to the Engine Mount weldment and prevents gear leg rotation. I’ve never heard of that bolt shearing but it could certainly happen if there’s any looseness.
Gasman is correct about checking the nose gear for any play. I replaced all 3 of my gear legs’ upper bolts with the tighter tolerance NAS bolts on KELLI GIRL’s first condition inspection for that very reason.
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AlexPeterson
Well Known Member
Dan stated this perfectly. Not sure how to make it clearer.
The possibility that this service bulletin was not completed and subsequently caused bobair43's issue is why it was brought up.
I found that the stock bolt was too short. It has a taper just before the threads that does not allow a tight fit on the nut end. This means that the designed shear of the socket is reduced.
I just went up one size and used an added washer for a prefect fit.
I have to wonder which is a higher load:
- With an incorrect installation, hitting the stop while making a sharp turn
- With a correct installation, using the brakes while making a sharp turn
Both will apply a significant twist to the nosegear rod, and a resultant significant shear load to the bolt holding it in place.
Different solution!
While building my 6A it was popular to use an aviation taper pin in place of the bolt at the top gear mount. It was a PITA to work the tapered reamer through the spring steel leg but, patience and a lot of cutting oil got the job done. I was wondering if this is still a popular mod?
While building my 6A it was popular to use an aviation taper pin in place of the bolt at the top gear mount. It was a PITA to work the tapered reamer through the spring steel leg but, patience and a lot of cutting oil got the job done. I was wondering if this is still a popular mod?
scsmith
Well Known Member
I think all of these rod-in-socket joints should have taper pins rather than bolts. The swiveling tail wheel pivot block on the tail wheel spring is a prime candidate (I have taper pins there).
But all main gear legs and nose gear legs that have a rod in a socket should use taper pins. There is no other way to make an assembly that won't "work" in the joint. By "work" in this context, I mean small rotations within the play allowed by the clearance of a bolt through a hole.
Just my engineering opinion.
With an incorrect installation, not only is the increased twist leverage but the added load by dragging the tire to the restricted radius instead of it rolling there.
A 180* turn should only be executed with just enough power to make it happen. Never enough that you would need to use brakes to stop the turn.
For a visual, turn your nosewheel to a full stop and grab the prop (at the hub) and pull down..... A C/S prop and O360 just exaggerates it.
AlexPeterson
Well Known Member
There is essentially no twisting load on the nose gear mounting bolt when turning with one main gear locked. That is no doubt how the swivel limit stops were set. (OK, the contact patch of the nose gear does move off centerline some during pivot around a main gear, so some shear is placed on the nose gear mount bolt.) However, in the case of limited nose gear caster range (improperly installed stop), there is a large shear on that bolt when pivoting around a main, as the nose wheel tire would be skidding sideways somewhat instead of pure rolling.
The bolt at the top of the nose gear leg is the exact same diameter as the bolt used for the main gear legs on the tail dragger or the tricycle gear. There is no way that a properly operating free swiveling nose wheel can apply a higher rotational load on the nose gear leg, than is applied to the main gear legs.
If the stop is installed correctly, making a pivot turn with one brake locked will not allow the nose fork to actually hit the stop. It goes slightly beyond that when the stop is contacted. That is why if you read the service bulletin it mentions that an easy check For proper stop installation is to use a tow bar and turn the nose, fork, hard over and then move the airplane. If the stop is installed correctly, one of the wheels will actually rotate backwards while the airplane is being moved forward.
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RV-8A Incidents?
What I would like to know is if any RV-8A has fallen victim to a nose gear collapse incident. Also, does anyone know if an A fitted with an Antisplat fixture has suffered a nose gear collapse?
Thanks!
Steve
What I would like to know is if any RV-8A has fallen victim to a nose gear collapse incident. Also, does anyone know if an A fitted with an Antisplat fixture has suffered a nose gear collapse?
Thanks!
Steve
The answer to both questions is yes.
But, have any “properly flown” nosewheel RVs had a collapse? Not sure, but do understand that the vast majority of A model nosewheel collapses are due to “pilot technique.”
That is difficult to answer because without extensive amounts of recorded data, it is impossible to know exactly what happened (though there have been some accidents where the basic EFIS data showed a pretty clear picture of what likely happened ), but my personal opinion makes me agree with your "vast majority" estimate.
Until you hit the brakes to stop the turn, while your nosewheel is still turned?AlexPeterson said:
Could it be a factor that the nosegear is regularly loaded loaded back and forth from side to side as you turn, but the main gear is only significantly loaded in one direction (neglecting the in-flight condition where it's just the weight of the wheel pulling the other way)?
Does the nosegear failure data set include information as to whether the bolt is sheared or not? ie. is a failure of the bolt a contributory factor?
I am not aware of the failure of any nose gear bolts, other than instances where the fork rotation stop was installed backwards. That would indicate that the bolt is adequate for normal operation.
