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  #221  
Old 09-14-2012, 08:56 AM
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DonFromTX DonFromTX is offline
 
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I too had puzzled over that gap between the lower bracket and the channel. I suppose the possibility exists that the end of the bracket is bending under unusual forces, creating the loose bolts, or as stated, the channel is being deformed by proper bolt torque, or both.
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  #222  
Old 09-14-2012, 10:43 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DonFromTX View Post
I too had puzzled over that gap between the lower bracket and the channel. I suppose the possibility exists that the end of the bracket is bending under unusual forces, creating the loose bolts, or as stated, the channel is being deformed by improper bolt torque, or both.
It is not likely that the U-1202PC bracket bends causing loose bolts. The bosses on the ends (where the bolts pass through the holes), fit tightly against the edges of the gear leg. The gear leg would have to deform to allowing the brackets to bend.

I am assuming you meant to write improper bolt torque causing deformation of the channel. Properly torqued bolts would never have the tension load required to cause the cracking seen in the channel. I am doubtful that over torquing could do it either. I am pretty sure the threads would fail long before you caused any damage to the channel...
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  #223  
Old 09-14-2012, 12:16 PM
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joedallas joedallas is offline
 
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Location: Spring Hill Fl
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Default Excessive Breaking

It takes a 100HP and 700 feet to get the aircraft flying.

Trying to stop it in 200 feet takes a lot more energy

The kinetic energy required to stop an aircraft is a function of the weight (mass) of the aircraft multiplied by the square of its speed.

If the bolts are tight and the breaks are applied after the aircrafts drag slows the aircraft a little there would be no problem.
.
If vans adds reinforcement to this connection it will be only to help with excessive hard breaking. (Tradeoff strength for useful load )

Remember this is a Light sport Aircraft Not a Army Tank

My View
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Last edited by joedallas : 09-14-2012 at 12:28 PM.
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  #224  
Old 09-14-2012, 04:30 PM
J.Coles J.Coles is offline
 
Join Date: Apr 2010
Location: Auckland New Zealand
Posts: 99
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Quote:
Originally Posted by DaveLS View Post
RV-12 Gear Leg Attachment Cracks

After studying this thread, I made a few notes for myself.

Symptoms:

Cracks radiating from forward outboard landing gear attach bolts in the center section aluminum ?C? channel web

Cracks more likely on right side.

Skin deformations about the landing gear

Crushed brake lines from contact with aft skin where gear leg passes through skin


*

Possible causes/contributing factors:

Hard landings

Heavy braking

Excessive touchdown speeds

Grass runways

Loose gear attach bolts

Powder Coat

Gear legs that are longitudinally stiff

*

Failure Mode Thoughts:

Two different mechanisms, one for skin damage another for crack formation.

Skin damage, crushed brake lines:

Hard landings, a torque stress? *Mechanism(s) is possibly the tail cone rotating down due to momentum and/or gear legs rotating aft due to impact.

*

Possible solution to skin damage:

Land better

Cracks:

Repeated impacts could be the mechanism of these failures. *Each individual impact could be less that that required to deform the skin, but could over time work harden (and thus more brittle) and eventually crack the ?C? section web. *The source of these impacts is probably pulsating longitudinal forces on the wheels. Loose attachment bolts (facilitate impact transfer of energy), higher landing speeds (more energy), heavy braking (that causes shutter), not smooth runway surfaces, and gear legs that do not absorb longitudinal forces, would all contribute to impact forces being applied to the ?C? section web.

Possible solution to Cracks:

Redesign landing gear to deal with longitudinal impact forces. Out of the builders hands.

Add reinforcements to ?C? section web to mitigate impact forces.

Fully seat gear attachment bolts. *Ream holes, lube bolt shafts, seat (hammer?) bolt heads fully, remove powder coat (insure metal to metal contact). Add in non-thread resistance to torque values and torque to high end of range. Check bolts regularly.

Land slower.

Operate only on smooth surfaces.

Use minimal braking and insure that braking does not induce wheel shutter.

Ultimate Plan:

Follow Van?s recommendations when offered.


-Dave
Hi Dave,

This is a good summary of the situation so far. The only thing I can see that is missing at this stage, is the number of aircraft with the damage that the pilots feel they were operating within the normal range.

Does anyone have a count on this?

Cheers

Julian 120316
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  #225  
Old 09-14-2012, 06:08 PM
rgmwa rgmwa is offline
 
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Location: Perth, Western Australia
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Quote:
Originally Posted by rvbuilder2002 View Post
Properly torqued bolts would never have the tension load required to cause the cracking seen in the channel. I am doubtful that over torquing could do it either. I am pretty sure the threads would fail long before you caused any damage to the channel...
I have not installed my gear legs yet, but am almost at that point in the build. What concerns me is that, on my channel at least, the flange cutouts for the outer bolts do not finish flush with the top surface of the channel web. There is a small lip probably not much more than 1/32" high which passes through the edge of the bolt hole. Clearly, this means the nut and washer will not have a full bearing surface, and there will be a non-uniform stress concentration around the bolt hole at this point. The lip is visible in this photo.



I certainly have some concerns that this could potentially contribute to cracking of the channel web, so I'm considering using longer bolts and putting a 1/8" packer under the washer to spread the load better.
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Last edited by rgmwa : 09-15-2012 at 01:54 AM. Reason: clarification
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  #226  
Old 09-14-2012, 06:18 PM
E. D. Eliot E. D. Eliot is offline
 
Join Date: Dec 2005
Location: San Pedro
Posts: 1,013
Default I'd like a little reinforcement designed by Van's

In the fuselage area of concern IF it wouldn't lead to other yet unseen problems.

In LSA and the RV-12 in particular we have a maximum weight that we can legally fly at. Let's say that the reinforcement that is designed by Van's weighs 10 pounds. Though that is probably high, I'll incorporate it into my 12 build as a 'just in case' beef up.

It is beginning to look like these structural problems are caused by hard braking and??? No one wants to stomp on the brakes but if I must, as in the case of an emergency, I don't want to have to be weighing the cost of repairs as I try to avoid whatever it is that is ahead of me on the runway.

I'm not shooting at anyone here but in my opinion, the best way to reduce the 'gross weight' that you fly at in the 12 is to go on a diet and exercise. There are few of us over the age of 50 who couldn't stand to loose some weight. I'll speak for myself and my wife who have in the last two years lost a bunch of weight and now, with both of us in an airplane, we have a total combined weight of 325 pounds. All you have to do is to change the way that you eat - again, not shooting at anyone in particular. Shoot at me if you want, I'm a man.

Last edited by E. D. Eliot : 09-14-2012 at 10:07 PM.
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  #227  
Old 09-14-2012, 06:42 PM
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DonFromTX DonFromTX is offline
 
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For some reason, I guess since I started this thread, owners have been reluctant to share their damage with others on the VAF, so they confided in me, in some cases only after I am sworn to secrecy. I am personally aware of three cracked channels (photos of all three are in this thread) and a total of 9 wrinkled side skins. That in itself is meaningless, since I have no way of knowing how many more (if any) are out there, nor how many have been reported to Vans.

.
Quote:
Originally Posted by J.Coles View Post
Hi Dave,

This is a good summary of the situation so far. The only thing I can see that is missing at this stage, is the number of aircraft with the damage that the pilots feel they were operating within the normal range.

Does anyone have a count on this?

Cheers

Julian 120316
__________________
A&P, PP-SEL, Pathological Flier, EAA Technical Counselor
EAA Chapter 595 President,http://www.595.eaachapter.org/index.htm
Retired US Army Officer
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  #228  
Old 09-14-2012, 08:49 PM
NASA515 NASA515 is offline
 
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Location: Hansville, Washington
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"I'm not shooting at anyone here but in my opinion, the best way to reduce the 'gross weight' that you fly at in the 12 is to go on a diet and exercise. There are few of us over the age of 50 who couldn't stand to loose some weight. I'll speak for myself and my wife who have in the last two years lost a bunch of weigt and now, with both of us in an airplane, we have a total combined weight of 325 pounds. All you have to do is to change the way that you eat - again, not shooting at anyone in particular. Shoot at me if you want, I'm a man."

Consider yourself "SHOT". BANG!

Bob Bogash
N737G
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  #229  
Old 09-14-2012, 08:59 PM
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Bill_H Bill_H is offline
 
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Location: Marshall TX (KASL)
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OK, no plane is expected to fall 20 feet to the runway and not sustain damage. But ANY plane must be expected to be able to use maximum braking after touchdown and not damage itself in the process! I have trust in Van's engineering that they got that right and this problem has to do with something other than the use of maximum braking. I mean, that would be Structures 101.
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  #230  
Old 09-15-2012, 12:05 AM
Michael Seager Michael Seager is offline
 
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Posts: 52
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Quote:
Originally Posted by DonFromTX View Post
For some reason, I guess since I started this thread, owners have been reluctant to share their damage with others on the VAF, so they confided in me, in some cases only after I am sworn to secrecy. I am personally aware of three cracked channels (photos of all three are in this thread) and a total of 9 wrinkled side skins. That in itself is meaningless, since I have no way of knowing how many more (if any) are out there, nor how many have been reported to Vans.

.
It also seems too that not many have reported their damage through the proper channels to Vans. Which leads me to believe that pilot error may have been to some extent a lot of the problem.
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