Nothing beyond what I wrote in post # 60.
I own an "A" model of my own.
I have no intention of using a different fastener (but I do carefully inspect the attachment of the nose gear leg on an annual basis).
Van's Air Force
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Nose Gear Bolt Failure. Argh!
- Thread starter Kahuna
- Start date
Nothing beyond what I wrote in post # 60.
I own an "A" model of my own.
I have no intention of using a different fastener (but I do carefully inspect the attachment of the nose gear leg on an annual basis).
AlexPeterson
Well Known Member
Weldment backwards
I'm a little amazed that almost no discussion, save for RVbuilder2002, has resulted from my earlier noting that the weldment was installed backwards on the plane which had the mishap earlier this year.
That mystery aside, please note that the weldment circled is incorrectly installed, and is very likely a direct cause of the bolt's failure. When this weldment is installed backwards, the swivel limit of the nose wheel is limited to less travel than when correctly installed. The design allows one to literally pivot on one main gear when turning. Obviously, if the swivel is limited, the result is torque applied to the gear leg when doing pivots around a main.
It would be interesting to know if the weldment on the plane from the 1st post was correctly installed. It is not uncommon - I've caught it on a couple planes that were about ready for first flight.
I'm a little amazed that almost no discussion, save for RVbuilder2002, has resulted from my earlier noting that the weldment was installed backwards on the plane which had the mishap earlier this year.
That mystery aside, please note that the weldment circled is incorrectly installed, and is very likely a direct cause of the bolt's failure. When this weldment is installed backwards, the swivel limit of the nose wheel is limited to less travel than when correctly installed. The design allows one to literally pivot on one main gear when turning. Obviously, if the swivel is limited, the result is torque applied to the gear leg when doing pivots around a main.
It would be interesting to know if the weldment on the plane from the 1st post was correctly installed. It is not uncommon - I've caught it on a couple planes that were about ready for first flight.
flytoday
Well Known Member
Thanks Alex
I appreciate your notes on the weldment Alex, thanks! When my bolt failed in Feb., and I started a VAF thread, there were many posts and views but I don't recall anyone commenting on the weldment orientation. My thanks to you!
Perhaps there is more attention to the bolt/pin because that is what actually breaks, is difficult to access, inspect, changeout, etc.
IMHO the diagram that comes with the REV3 nosewheel kit and engine mount does not include an obvious depiction of the proper weldment orientation. I'd recommend all -A owners check the orientation (should be notches forward, in the direction of flight, leading the strut tube). It wasn't caught on my plane for almost 20 years of maintenance and operations.
Carl
I appreciate your notes on the weldment Alex, thanks! When my bolt failed in Feb., and I started a VAF thread, there were many posts and views but I don't recall anyone commenting on the weldment orientation. My thanks to you!
Perhaps there is more attention to the bolt/pin because that is what actually breaks, is difficult to access, inspect, changeout, etc.
IMHO the diagram that comes with the REV3 nosewheel kit and engine mount does not include an obvious depiction of the proper weldment orientation. I'd recommend all -A owners check the orientation (should be notches forward, in the direction of flight, leading the strut tube). It wasn't caught on my plane for almost 20 years of maintenance and operations.
Carl
Walt
Well Known Member
I believe I brought this up initially back in post #54 and RV2002 commented on it in post #55, but we still have not seen pics of the OP leg to know if this was the case.
Kahuna
Moderatoring
We wont be back at the plane for another week or so to ferry it home. We will report additional findings.
BSwayze
Well Known Member
I went with a tapered pin on my nose gear leg and engine mount.
Search the forums here for various threads and details on the installation.
I went with a tapered pin on my nose gear leg, too. I'm surprised there hasn't been more discussion in this thread about using it as an alternative to the AN-5 bolt. I'm very confident in this installation.
Here's the page on my website describing my work on this:
Installing Tapered Pin in Nose Gear Leg
And here's a picture:
As Bruce Hill mentioned, there are threads here on VAF about using the tapered pin. Here's one of them. Others turn up with a simple search:
http://www.vansairforce.com/community/showthread.php?t=105870&highlight=tapered+pin
but what would you do if it were loose?
I've read this whole thread and have, in particular, paid attention to the posts from rvbuilder2002. What I haven't seen yet is how the factory would have us respond to looseness in the nose gear leg.
I'm interested because at last annual I detected a *very* small amount of fore-aft (no rotational) play in that leg. I removed the bolt and the leg, inspected for any elongation (found none), and with the approval of my A&P, tightened it so there was no movement and returned it to service.
I have to believe that this looseness will return, however, and would like to know how the folks that designed this would have us fix it.
I've read this whole thread and have, in particular, paid attention to the posts from rvbuilder2002. What I haven't seen yet is how the factory would have us respond to looseness in the nose gear leg.
I'm interested because at last annual I detected a *very* small amount of fore-aft (no rotational) play in that leg. I removed the bolt and the leg, inspected for any elongation (found none), and with the approval of my A&P, tightened it so there was no movement and returned it to service.
I have to believe that this looseness will return, however, and would like to know how the folks that designed this would have us fix it.
bret
Well Known Member
Any one have experience with these folks for a reamer, to do the taper pin mod? about half price of ACS.
http://drillsandcutters.com/7-hss-straight-flute-taper-pin-reamer/
http://drillsandcutters.com/7-hss-straight-flute-taper-pin-reamer/
That would be somewhat similar to answering the question.... "What should I do to fix the vibration in my engine?".
So a proper response to the question depends on what the actual problem is, and how bad it is.
Any rotational movement on the bolt is very bad.
Up and down movement of the leg at the bottom of the socket isn't good, but it is far less critical. It usually seems worse than it really is because of the long arm length. I.E., .001 movement at the base of the socket translates to .006-.007" (which would feel like quite a bit) at the fwd end of the gear leg.
Many times, drawings issued with design changes are not meant to be comprehensive. They are meant to supplement the full set of drawings.
It has always been stressed that the construction manual is for building and maintaining an RV. That is why it is always stressed that when a buyer purchases an RV from someone else, they be sure to get all of the construction documentation as part of the sale.
Curious if any of these broken bolt incidents occurred on planes where the nose wheel stops were absent. We have been operating ours from day one with no stops to make it easier to maneuver when parking or pushing it back into the hangar. Without stops the nose wheel is free to fully swivel, reducing any possible twisting load that could shear the bolt. I don't know if a locked wheel turn in a plane with stops causes the nose wheel hit the stops or not, but if it does, that would not be good for the bolt. (Note: If the stops are removed you have to be sure never to let the nose wheel be positioned 180 degrees with the engine running or the prop will hit the pant.)
LeRoy Johnston RV-6A Esperanza 880 hours
LeRoy Johnston RV-6A Esperanza 880 hours
so then is a tiny bit of fore-aft movement ok? And, once again, what's the proper response when it gets worse?
BTW I really appreciate you engaging in this discussion ...
AlexPeterson
Well Known Member
Yes you did indeed, Walt! We all missed it in the earlier thread, apparently.
Of the three RV-As involved two are confirmed as having the the stop limiter installed backwards,the third we will hear about next week when Kahuna reports back.This has been a great thread bringing a lot of new issues and possible remedies to light. I don't know anything about the Kiss NGL,but this may also share a Vans limiter,perhaps Galin can add some light on that failure. I'd like to thank Brad,Carl,Len,Galin for sharing there misfortune here so we can all learn and avoid the same fate.
RHill
RHill
I would think any movement would be a cause for concern to be addressed at the next service or annual. Options would depend on what you have
Ream to the next size AN bolt,up grade to NAS bolt or BACB30US Inconel.I wouldn't do it to a new mount but to a hogged out hole The Tapper Pin solution.IMHO
rhill
GalinHdz
Well Known Member
My KIS nose gear did not have a stop limiter while my new nose gear assembly has stop limiters. I wonder if this is the actual cause of the failure and the bolt is just the result.
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If it was me, I would do it for sure. It cost very little, it is very little work and the return of investment is a lot of peace of mind.
Walt
Well Known Member
I would definately recommend changing the bolt!
yes. At least you'll know and won't wonder
OMG! Saying it out loud, you've just invited the bad Juju upon your plane.
Now you *must* replace the bolt!
Malndi
Well Known Member
OMG! Saying it out loud, you've just invited the bad Juju upon your plane.
I am ordering the bolt Monday. Is a firm commitment to replace the bolt sufficient to keep evil spirits at bay until it's done?
Geico266
Well Known Member
I am ordering the bolt Monday. Is a firm commitment to replace the bolt sufficient to keep evil spirits at bay until it's done?
Absolutely!
Yes replace the bolt, I'd say go with the NAS6200/NAS6600 bolt in place of the AN bolt for consistent shoulder diameter as the AN's are prone to get drawn out at the start of the threads,a washer or two under the head and under the nut will help even out the uneven bearing surfaces of the socket.Some photos of what you find would be appreciated.
RHill
shear chamfers
Anyone who has used a metal shear knows how much a small dull spot (essentially a chamfer) on the cutting edges makes it harder to shear metal plate.
Well-reasoned post, Alex!
Roger
Anyone who has used a metal shear knows how much a small dull spot (essentially a chamfer) on the cutting edges makes it harder to shear metal plate.
Well-reasoned post, Alex!
Roger
I was going to wait till we hear back about the third RV to bring this up.Yes this leg and socket is set up as a shear,having high temp grease can only add to that effect.The steel of the tube is thin compared to the leg that is held from rotation by this single bolt passing through them.The top OD and bottom OD of the tube would benefit from a mounting boss welded in place to give the bolt head&nut a flat bearing surface to seat against.Chamfer lies between Deburr and Countersink,there just isn't enough steel on the socket to do anymore then deburr without added reinforcement.Chamfer the Leg not the socket would be my call.Use of a higher grade bolt with a consistent diameter,long enough to terminate the shank clear of the socket OD,reamed to a close tolerance fit.Of course,Vans should be consulted before any deviation from the plans.IMHO
RHill
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shear terror
Interesting thoughts, RHill... please consider these ideas.
Even without the lateral forces caused by the improperly installed caster limiting plate, the factor of safety calculation is worrisome. At maximum caster angle, the normal force betwen the tire and the pavement has an 8 inch moment arm about the axis of the gear leg. Spiking the brakes to stop a pivot turn can easily double the normal force at the nose wheel on a short wheelbase plane.
Experience with metal shearing shows that even a very small chamfer (dullness) makes it much harder to shear metal.
The failure mode caused by excess chamfer thinning of the socket tube is progressive loosness, not a catastrophic failure like that caused by the the bolt shearing.
Grease certainly doesn't help the situation. Retaining compound probably helps, but I have no proof yet.
As was pointed out 11 pages ago, for whatever reason it appears that A-model owners have been .... asked to solve these problems for themselves.
Interesting thoughts, RHill... please consider these ideas.
Even without the lateral forces caused by the improperly installed caster limiting plate, the factor of safety calculation is worrisome. At maximum caster angle, the normal force betwen the tire and the pavement has an 8 inch moment arm about the axis of the gear leg. Spiking the brakes to stop a pivot turn can easily double the normal force at the nose wheel on a short wheelbase plane.
Experience with metal shearing shows that even a very small chamfer (dullness) makes it much harder to shear metal.
The failure mode caused by excess chamfer thinning of the socket tube is progressive loosness, not a catastrophic failure like that caused by the the bolt shearing.
Grease certainly doesn't help the situation. Retaining compound probably helps, but I have no proof yet.
As was pointed out 11 pages ago, for whatever reason it appears that A-model owners have been .... asked to solve these problems for themselves.
Can we classify it a problem that needs to be solved, if two of the three examples discussed in this thread have been shown to have been assembled incorrectly?
We can see from searching the archives of VAF that there is not a long history of this occurring.
Based on the large number of "A" models that are flying (many since the early 90's), it is not unreasonable to speculate that some specific issue may have caused it in just a few airplanes.
A specific detail has been identified in 66.6% of the known incidents. Is that the complete cause? Only time will tell for sure, but I think we can say that at least a small wisp of smoke is visible from the gun.
I intend to propose that an official notification be issued at Van's, so that at least non builder owners may find the problem while they or their A&P inspector research service info while doing a condition inspection.
The biggest problem is the people who still own the RV they built. They are far less likely to check the Van's web site, and because they know they assembled everything correctly when they built it
, they are not likely to catch it during an inspection they are doing themselves.The best thing the RV community can do regarding this issue is spread the word regarding how the stop bracket is supposed to be installed.
Scott, just thinking out loud here, but is there an easy way to check that the stop bracket is installed correctly? For example, if you lower the tail and swing the nosewheel to one side, should it go 90 degrees if installed correctly, but stop at 60 degrees if it's in backwards?
I don't know if those numbers are right, just wondering if there's an easy way to check.
I don't know if those numbers are right, just wondering if there's an easy way to check.
Yes.
Good question (to make it easy to check without wheel fairing removal)
I cant give you a deflection distance / angle value, but it can be checked by moving the airplane with a tow bar.
If the stop bracket is installed correctly, when you pull the airplane fwd with the nose wheel at full deflection left or right, the airplane will pivot about a point that is somewhere between the two main wheels. Meaning, one wheel will roll backwards and the other fwd (the yawing axis is somewhere between the two main wheels)
If the bracket is on backwards, both main wheels have to roll fwd or aft when at the turn stop ( the yawing axis is outboard of the main wheels).
Does that description make sense?
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Don't get me wrong here,I want an Iconel alloy bolt for my gear. This one bolt stands between the Prop and the ground,between a great flight and total disaster. Chamfering the NGL removes the blade from the equation,by adding the two boss mounts strengthens the tube socket and gives the nut and bolt a flat bearing surface,Chamfering the tube would be a non issue with these welded in place. Anything that inhibits rust I would think is fine,grease is probably not the best option but better than unprotected steel. A small subtle improvement. Of the three RVa's involved, all three were involved with air show formation performances with repeated flank turns,two are confirmed as having the stop installed backwards.Given the troubled history of the A gear I hope the factory doesn't blow this off as builder/pilot error.
RHill
I am confused.
Your your self said two have been confirmed to have a construction error (third... unknown at this point).
Why then would it be wrong to blame it on builder error?
Should the wing structure be designed so that in case someone makes a mistake and forgets to install some of the wing spar bolts, that the wing should still meet the claimed design load factor?
Sorry to be so blunt, but the one thing I hate about our country is we have trained up a whole society of people to believe that everything is always someone else's fault.
I was thinking exactly the same thing. I could not have said it any better.
As of now, Yes Two out of Three.
It is builder error,in both cases so far with a third yet to be reported.
https://www.vansaircraft.com/pdf/sb12-08-14.pdf , Well it helps....
I take full responsibility for any confusion,I suspect 3pm Low blood sugar and my maker may have left a few bolts out. What I meant is.I hope this opportunity to improve the NGL attach point doesn't get overlooked because of builder error. This is the best thread I've read in a wile,I appreciate everyone's involvement,especially yours Scott,Thank you.
RHill
Yes, that makes perfect sense to me. I'll make a note next time I see the -A models at my home airport. Thanks!
tomhanaway
Well Known Member
bolt length for rv-8/8a
Just to clarify, post #33 spoke of using a -27 length bolt. Note that the builder was specifically working with the 7A.
As I read the construction plans for the 8/8a (dwg 49), the nosegear calls for a -20 length bolt.
I'm planning to order NAS bolts for both main gear (-22) and nose gear (-20).
Unfortunately, this makes ordering something like the Iconel bolts, which need a minimum order, that much more difficult.
If my numbers are wrong, please let me know.
Thanks,
Tom H.
Just to clarify, post #33 spoke of using a -27 length bolt. Note that the builder was specifically working with the 7A.
As I read the construction plans for the 8/8a (dwg 49), the nosegear calls for a -20 length bolt.
I'm planning to order NAS bolts for both main gear (-22) and nose gear (-20).
Unfortunately, this makes ordering something like the Iconel bolts, which need a minimum order, that much more difficult.
If my numbers are wrong, please let me know.
Thanks,
Tom H.
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pa38112
Well Known Member
I have gotten a new quote for a quantity of 10 for the Inconel bolts- $85 each, so probably $90 delivered to everyone who wants one. I have 4 interested people, so just need 5 more. from the post above, we should confirm the size for each model.
There are lot of varied thoughts on if this bold is necessary or appropriate. I am sure we are fine with the standard bolt if it is installed properly and regularly inspected or replaced.I have worked with Inconel in the past and find it to be tough as nails. For me, flying off of grass, this bolt gives a higher margin of safety if the fit starts to work its way loose. That is worth $90 to me.
There are lot of varied thoughts on if this bold is necessary or appropriate. I am sure we are fine with the standard bolt if it is installed properly and regularly inspected or replaced.I have worked with Inconel in the past and find it to be tough as nails. For me, flying off of grass, this bolt gives a higher margin of safety if the fit starts to work its way loose. That is worth $90 to me.
I don't think that the factory is blowing this off.
The third plane belongs to a friend of mine and I have flown with him a lot.
So, when I had a chance to discuss this one on one with Van, we talked about the **operational** aspect of the turns an additional loading that MIGHT be placed on the bolt repeatedly, FAR GREATER than what 99.??% pilots would experience. He even tried to calculate the loads in his head in real time but decided to wait and do it at home (we were headed into a meeting). And he offered to analyze further the bolt (if it could be recovered) to better understand what was at the root of the failure. I asked by friend to hold on to whatever broken bolt parts he could.
The fact that there may be some rare circumstance here does NOT mean do nothing. But it might mean that the best solution is as was posted earlier (I think it was by Kahuna), inspect often (annually or some number of hours) and replace at some interval.
When there is a problem, as rvbuilder2002 says, lets make sure that we are attacking the right problem with an appropriate to the use case and problem, solution.
James
P
paul mosher
I going to get one made of diamond! Harder and more expensive. Seriously I'm using a nas bolt for the tighter dimensional tolerance.
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LettersFromFlyoverCountry
Well Known Member
I'm a little amazed that almost no discussion, save for RVbuilder2002, has resulted from my earlier noting that the weldment was installed backwards on the plane which had the mishap earlier this year.
That mystery aside, please note that the weldment circled is incorrectly installed, and is very likely a direct cause of the bolt's failure. When this weldment is installed backwards, the swivel limit of the nose wheel is limited to less travel than when correctly installed. The design allows one to literally pivot on one main gear when turning. Obviously, if the swivel is limited, the result is torque applied to the gear leg when doing pivots around a main.
It would be interesting to know if the weldment on the plane from the 1st post was correctly installed. It is not uncommon - I've caught it on a couple planes that were about ready for first flight.
Can we get this original image cropped down to this spot and reposted at actual size?
rightrudder
Well Known Member
Me too....I just drilled & reamed the mount, and there's a tiny bit of slop. I think the NAS bolt will be just the ticket. I think I'll bolt the gear leg to the mount before I bolt the mount to the firewall for ease of installation.
BillL
Well Known Member
Doug, If this thread is any indication of the loading and issues, what are you going to do when (not if) this bolt needs to be replaced? Do you have a firewall access plate?
The assumption being that it is checked until loose, then replaced. Repeat as needed. Reasoning: after the bolt is loose, there is a possibility of the initiation of a crack, the replacement would eliminate that possibility. You might, just might, be able to retorque once given the possibility that the paint has relieved the initial torque.
flytoday
Well Known Member
Maybe
Maybe I can crop, zoom, enlarge some. What detail or component are you looking for?
Carl
Maybe I can crop, zoom, enlarge some. What detail or component are you looking for?
Carl
Nope. VERY important bolts on VERY large aircraft can cost magnitudes more than that.
I agree, both the bolt and the cost thereof are excessive for RVs.
Inconel alloy bolt
One bolt stands between your $30,000 to $60,000 dollar engine&prop and the ground,on a nose gear with a very troubling history,and your thinking $90 is too much to spend on one bolt made of Unobtainium..........Well I guess your right,you'll need that extra $87.50 to put towards that custom $20 thousand dollar paint job or the $50 thousand dollar Avionics package.And what are you going to say at the next fly-in when you get razed for having a training wheel up front,"Hey Guy,I'll have you know that gear is held in place with a bolt made of pure Unobtainium Alloy,So there!" Not if you don't have that bolt. All fun aside,this Great Thread was started by Kahuna at the expense of three of our own for Safety reasons.Anything that improves Safety of the nose gear should be first priority,so please check your stop limit plate for correct instillation and NGL for play and encourage everyone else to do so too. I can't help to think Allen is sitting in his comfy chair enjoying his favorite libation,chuckling to himself over this thread.
RHill
One bolt stands between your $30,000 to $60,000 dollar engine&prop and the ground,on a nose gear with a very troubling history,and your thinking $90 is too much to spend on one bolt made of Unobtainium
..........Well I guess your right,you'll need that extra $87.50 to put towards that custom $20 thousand dollar paint job or the $50 thousand dollar Avionics package.And what are you going to say at the next fly-in when you get razed for having a training wheel up front,"Hey Guy,I'll have you know that gear is held in place with a bolt made of pure Unobtainium Alloy,So there!" Not if you don't have that bolt. All fun aside,this Great Thread was started by Kahuna at the expense of three of our own for Safety reasons.Anything that improves Safety of the nose gear should be first priority,so please check your stop limit plate for correct instillation and NGL for play and encourage everyone else to do so too. I can't help to think Allen is sitting in his comfy chair enjoying his favorite libation,chuckling to himself over this thread.RHill
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