pierre smith

pierre smith

Well Known Member
Say Mel, Vic and other A@P's, I read the attached report of Sean Tucker's elevator pushrod failure in 2006 and was surprised to read that the rod end bearing broke completely out! As you know, he jumped out and totalled the airplane but we use a very similar rod end in our RV's. The one in my hand has "Aurora GMM-3M 670" part numbers on them and came with a -7A we're building. Any idea if this is a TSO'd part?

I'm not overly concerned but if a Fafnir product is safer, I think we might consider them. What say you?

The link: http://www.ntsb.gov/ntsb/brief.asp?ev_id=20060405X00398&key=1

Thanks,
 
I was thinking that a bigger rod end bearing [bigger thread and bearing] would be considerably stronger. It might weigh a bit more, but a huge safety factor. I suppose at what point is enough ,.enough
 
I think you need not worry, I'm sure the loads that poor rod end had to endure on Sean's airplane in one flight are far greater than ours see in a lifetime.
 
No... bigger is not better...

rv72004 said:
I was thinking that a bigger rod end bearing [bigger thread and bearing] would be considerably stronger. It might weigh a bit more, but a huge safety factor. I suppose at what point is enough ,.enough
Click to expand...

...if you read the report.

"Fafnir" and not "Federal" marked on the part seems to be a much more important factor. Sounds like a bad batch (2 out of 4 tested) were made with a sub-standard material, and a subsequent failure of QC inspections.

Parts used for a design load rating of 1500 pounds that fail at 850 pounds are just outright dangerous!

There is a premium for Mil-Spec parts, but they are better controlled - I think the rod-end business has gone to commercial standards...:rolleyes:

UPDATE CALCULATION

For the RV-6 control system, the bearing at the elevator has about a 3.5 : 1 mechanical advantage over the control stick "pull". My old 60's "standards" book specifies a 150 pound max. design force on the stick, giving a 525 pound force at the elevator rod-end. It seems like the weak 850 pound parts would be OK in our RVs - but I personally would prefer parts made to specification that fail around 3000 pounds...:)
 
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rocketbob said:
I think you need not worry, I'm sure the loads that poor rod end had to endure on Sean's airplane in one flight are far greater than ours see in a lifetime.
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+1. The forces he puts on it in one flight is more than mine would see in a life time. :eek:
 
Not as much margin...

rocketbob said:
I think you need not worry, I'm sure the loads that poor rod end had to endure on Sean's airplane in one flight are far greater than ours see in a lifetime.
Click to expand...

...as you might think... see my calculations above.

Bad parts are just bad parts...:(
 
Wow - scary stuff!

I had a pushrod bellcrank come partially detached once, but still had enough control to land.

Don't assume! Check these things regularly...
 
And this..........

....the ones we use cost around $5.00 and the certified Fafnirs $30+. There are 4 on the elevator pushrods and 8 in the wings, plus 4 more as elevator hinges and 3 on the rudder....19 X $30 + $570 compared to $95.

Regards,
 
Wonder where the bad bearings, not meeting specs, were made.

Give you three guesses and you should be able to get it in one!

Ted
 
According to the NTSB report, similar bearings were tested that failed at around 800lbs. The report stated very clearly that the weak bearings they tested were made in the USA.
 
FWIW, a typical Pitts-type elevator control system places the rearmost pushrod in tension for up elevator. Our RV's have a large diameter pushrod back there because up elevator places the pushrod in compression.

The NTSB report says Sean's rod end failed in tension (outer race fracture). That particular failure mode isn't possible in an RV unless you push real hard while inverted.

Regardless, I'll do a shop inventory audit this weekend. Any Federal brand rod ends will be getting a flotation test.
 
The report stated they were marked Made In The USA, that doesn't mean they are.

Copy cat merchandise is being brought in by the shipload. Some recent cases come to mind.
1) Niki shoes that were not NIki, these were at least caught at the docks and confiscated. They later were donated to a third world country.
2) Construction bolts marked with proper ASTM specification markings and failed in use because they didn't meet the spec.
3) As I recall there was some AN hardware that went into Military planes that failed.
Interesting point of the Military AN hardware is that most all US Government contracts are supposed to be Domestic Supplies.
4) Marine gauge manufacturer who started getting their gauges back for warranty after failure. After disassembly come to find out it was not their gauge. Had their name and logo on it but not thier internals

I run into this alot in my business. Purchase steel or stainless steel that is supposed to be a certain ASTM spec. Make parts, send out for heat treat and the part will not heat treat to the proper tensile and yeild. Have the material anylized and find out it did not meet the spec even though you have a certificate that says it does. I no longer buy import alloy metals because of this. To costly in the end.

This is one incident(Sean Tucker's) that would have taken lives if it wasn't for the skill of the pilot.

Ted
 
Does anything...

Ted RV8 said:
......I run into this alot in my business. Purchase steel or stainless steel that is supposed to be a certain ASTM spec. Make parts, send out for heat treat and the part will not heat treat to the proper tensile and yeild. Have the material anylized and find out it did not meet the spec even though you have a certificate that says it does. .....
Ted
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...happen to whoever signed the certification paperwork when this happens?

I know that 50,000 odd employees were I used to work all had to take yearly ethics training when some hardware was delivered with bad certifications.
Interestingly, the boss who ordered it kept his job...:rolleyes:
 
Rod end bearing

Pierre,

Recently an RV-6 went down in the Sarasota area of Florida. I have not seen anything on the forum or Van's site reference same.

Pilot was killed, passenger survived. Passenger said he heard a loud snap on a low approach and airplane went into the trees.

Cause: Elevator rod end bearing sheared off right at the lock nut, elevator horn end. You know Woody down here. He saw the wreckage just today and confirmed the rod end bearing failure.

Y'all know anything about this????............Joe.
 
HelioJoe said:
Pierre,

Recently an RV-6 went down in the Sarasota area of Florida. I have not seen anything on the forum or Van's site reference same.

Pilot was killed, passenger survived. Passenger said he heard a loud snap on a low approach and airplane went into the trees.

Cause: Elevator rod end bearing sheared off right at the lock nut, elevator horn end. You know Woody down here. He saw the wreckage just today and confirmed the rod end bearing failure.

Y'all know anything about this????............Joe.
Click to expand...

Is this the one?

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20090404X71345&key=1
 
That would be this...

HelioJoe said:
Pierre,

Recently an RV-6 went down in the Sarasota area of Florida. I have not seen anything on the forum or Van's site reference same.

Pilot was killed, passenger survived. Passenger said he heard a loud snap on a low approach and airplane went into the trees.

Cause: Elevator rod end bearing sheared off right at the lock nut, elevator horn end. You know Woody down here. He saw the wreckage just today and confirmed the rod end bearing failure.

Y'all know anything about this????............Joe.
Click to expand...

...one.

http://www.vansairforce.com/community/showpost.php?p=315926&postcount=15

April 4 was a bad day...:(

http://www.heraldtribune.com/article/20090405/ARTICLE/904051061/0/NEWS

[speculation ON] a broken elevator control might explain the "aerobatics" that witnesses saw, but couldn't actually describe [speculation OFF]
 
HelioJoe said:
Pierre,

Recently an RV-6 went down in the Sarasota area of Florida. I have not seen anything on the forum or Van's site reference same.

Pilot was killed, passenger survived. Passenger said he heard a loud snap on a low approach and airplane went into the trees.

Cause: Elevator rod end bearing sheared off right at the lock nut, elevator horn end. You know Woody down here. He saw the wreckage just today and confirmed the rod end bearing failure.

Y'all know anything about this????............Joe.
Click to expand...

Well, it sounds like the rod end failed - but when did it fail?

The loud snap the surviving passenger reported could have been the airplane hitting the trees and the rod end may have failed when the pilot tried to fly out of the tree.

All this points to the need to wait for an official report on what happened. We sure don't need to go out a replace rod end bearings just yet.

Another observation relative jumping to any conclusions, it was my experience (having wrecked an airplane) that the wreckage was impounded under lock and key and NO ONE was permitted near it unless cleared by the NTSB and/or FAA until the wreckage was released after the investigation was completed. This is so to prevent anyone from altering the evidence. And even after the NTSB does their thing, an insurance company can do the same thing until all claims are settled. This guy Woody may have seen the wreckage but maybe not.
 
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David-aviator said:
Another observation relative jumping to any conclusions, it was my experience (having wrecked an airplane) that the wreckage was impounded under lock and key and NO ONE was permitted near it unless cleared by the NTSB and/or FAA until the wreckage was released after the investigation was completed. This is so to prevent anyone from altering the evidence. And even after the NTSB does their thing, an insurance company can do the same thing until all claims are settled. This guy Woody may have seen the wreckage but maybe not.
Click to expand...

The wreckage is in a hangar a few rows down from mine. I have not seen it, but I know some airport "bums" who have. Hopefully the passenger will recover and be able to shed some light on the accident. My understanding is that he works for Sarasota Avionics here in Venice. So, hopefully his information will be more factual than the 11 year old witness the newspaper quoted as saying "he did a loop-de-loop".
 
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DanH said:
The NTSB report says Sean's rod end failed in tension (outer race fracture). That particular failure mode isn't possible in an RV unless you push real hard while inverted.
Click to expand...

What about the pushrod between the stick and the elevator bellcrank?
I still doubt we (normally) place that much tension or compression force on our bearings. I'd be more afraid of the bearing freezing/stiffening up and putting a bending load on the shank, right at the locknut. Wiggle-check those pushrods and keep 'em lubed.
 
Yeah.....

....and don't lay on the jamb nut with a huge wrench and stress the bearing threads with an overabundance of preload.
Methinks this would also be a good place for blue Loctite.

Regards,
 
<<What about the pushrod between the stick and the elevator bellcrank?>>

Oops....good point.
 
az_gila

Does anything...happen to whoever signed the certification paperwork when this happens?

To answer your question:

In the past when this has happened I would get either replacement material or a refund. Nothing to cover machining expenses. I suppose you could sue your supplier but this seems to just make money for the lawyers. Best to just move on and learn from the experience, which is why I will not buy import alloys anymore.

The problem is when the certificate comes from a foreign country is just a piece of paper, not much behind it. The purchaser(steel supplier) can elect not to buy from that steel mill again.

Ted
 
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pierre smith said:
....and don't lay on the jamb nut with a huge wrench and stress the bearing threads with an overabundance of preload.
Methinks this would also be a good place for blue Loctite.

Regards,
Click to expand...

Very well said Pierre. Maybe a piece of heat shrink or rubber tubing on the remaining threads between the jamb nut and bearing would also help it[pushrod] not screw in. If one side does loosen, it wont allow the pushrod to rotate very far before it stops .
All this things might seem a bit extreme, but it sure makes me feel better and doesn't take a whole lot of effort.

FWIW, the Glasairs had some undercarriage failures due to failing rod end bearings. They failed on the threaded portion. They issued a SB where you had to take a tapered cylinder with inside thread ,and cut it [shorten]on the fat end of the tapper ,to the exact length of the exposed thread.
This in effect allowed the bending forces of the bearing to be concentrated on the housing instead of the threads. As far as I remember this solved the rod end bearing failures. I think the SB can be found on their site at Newglasair.
 
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