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Bent Side Skin from Hard Landing

DonFromTX

DonFromTX

Well Known Member
I have not seen very many RV12s, but have seen several with bent side skins from what the owners called a "hard landing". It seems to me that if one cut the portion directly over the main gear back a ways so it would not ruin a side skin during a harder than normal landing, it would be wise. Comments anyone?
 
How hard?

How many owners have had a hard landing"? It's the easiest airplane to land gently that I've ever flown. Seems like it would take a pretty high descent rate to get that gear to flex very much-- it's rigid. Wonder if the attach bolts weren't really tight (tapped down", per Van's ) on the gear legs?

Wayne 120241/143WM
 
This is clearly another example of a poor design of the RV12 aircraft by Vans engineering team. Much like the "sub standard" nose gear on the "A" model, this once again signifies a company that looks for the "quick buck" by rushing a design to market without proper analysis.


Tongue firmly in cheek!
 
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I can't speak to their reasons and design, but it seems to me that a little trip with the snips will preclude side skin wrinkle in the event of a hard landing. I know how that works, I have MADE hard landings before!
 
I'm surprised!

jthocker said:
This is clearly another example of a poor design of the RV12 aircraft by Vans engineering team. Much like the "sub standard" nose gear on the "A" model, this once again signifies a company that looks for the "quick buck" by rushing a design to market without proper analysis.
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I'm really surprised at your condemnation of Van's when your signature shows multiple builds/ownership of the worlds most successful homebuilts!

"Substandard nosegear design"? C'mon...you're blaming Van and not the pilots? Methinks that you're painting with a pretty broad brush!

You have no idea of the analysis and wing spar-to-failure testing that Van's does on our behalf.

Best,
 
Pilots are typically a very confident (cocky) group and some (many) likely may have difficulty admitting to a hard landing. Instead why not just ask how many have experienced bent side skins? (tried smiley face here, but it didn't work).
Dick Seiders
 
In private they have confided in me as to what bent the skins. Did not want to embarass anybody, just wondered if someone had decided to trim the skin which would have prevented it from happening.
What the heck, I am EAB so I guess I can trim it if I want to :D
 
Would someone post a picture or a precise description of the location of such wrinkles or the location of some skin portion to be snipped?
 
I'm trying to figure out how to land a 12 hard enough to bend anything. So far my only problem on landing has been getting it on the ground! If your speed is too high, it floats. I have yet to make a single hard landing on the mains. I have been lazy a time or two holding the nose wheel off, but never have the mains landed with a clunk. I have made my share of stinkers in a Cherokee, so I know what an arrival as opposed to a landing feels like. I guess if you flare high enough an wait for a stall the 12 will hit with a thud. This is not a design problem, this is a pilot issue.
 
Dip

I saw a guy land three times (in one attempt), on the third, the nose gear collapsed (Cherokee). His comment was "that was the first time he landed there and he did not realize that the runway had a dip in it". The only Dip around was the pilot that did not know how to land. Expensive lesson but I don't think he realized he did anything wrong, so I guess it wasn't a lesson.
 
I thought I had a photo of one, but cannot find it. If with the wings off, you look directly above the main gear leg, you will see some side skin, where a landing gear coming up would contact it. Problem is, on one all it did was wrinkle the skin directly above it, but on others it wrinkled the side skin enough to make one want to replace it
In one instance, the pilot was with his CFI for a BFR, came in high, was told to slip it to lose altitude, over did the slip and landed hard.

.
Bill_H said:
Would someone post a picture or a precise description of the location of such wrinkles or the location of some skin portion to be snipped?
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Wrinkles in the skin above the gear

I would say that with a normal landing that this will not happen. Any airplane if landed hard enough will damage it. I have 170hrs with many landings and no wrinkles in the skin above my gear. Don if you think you might make a few hard landings then trim the skin its up to you.:D
 
Something my instructor kept drilling in to me came to mind "if you don't like the landing setup go around"




DonFromTX said:
I thought I had a photo of one, but cannot find it. If with the wings off, you look directly above the main gear leg, you will see some side skin, where a landing gear coming up would contact it. Problem is, on one all it did was wrinkle the skin directly above it, but on others it wrinkled the side skin enough to make one want to replace it
In one instance, the pilot was with his CFI for a BFR, came in high, was told to slip it to lose altitude, over did the slip and landed hard.

.
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In my old age and years of not flying, I perfected a new maneuver in my Ercoupe, I rarely see anyone with the skills to do it as well as I. When coming in for landing, flare and arrest the downward movement about 3 feet above the runway! This allows you to arrive straight down instead of the floating forever to find the pavement.
 
Gear/Sideskin Clearance

Don't know if anyone else has taken the time to measure the gear to side skin clearance on their fuselage or not, but I found quite a variation between the left and right side on mine. I may relieve the close one a bit, just to be on the safe side.

Tom
 
Had not thought of that, but it made me recall, ALL THREE that I have seen wrinkled, were on the RIGHT side of the plane, don't know why. I just went out and measured mine, as near as I can tell both sides are the same. Totally unloaded fuse with no tail or seats, avionics, engine, etc, there is about 3/4 inch gap.
 
Side Skin

I did not have any hard landings but I noticed a slight 'bend' in the right side skin - small enough that it could only be seen when the light and viewing angle was just right - the best I can figure is that when using a hydraulic jack at the tie down point to raise the plane to install wheel pants brackets that somehow that flexed things enough to cause the slight damage. The 'rubber' fairing between the top of the wing and the fuselage at that point was also curled somewhat inward, suggesting the top of the wing skin was pushed upward.

As those things go, I made it worse trying to 'fix' it - am going to leave it as most people never notice it and it does no harm (except to the bulder's ego)

FWIW
 
JohnF said:
the best I can figure is that when using a hydraulic jack at the tie down point to raise the plane to install wheel pants brackets that somehow that flexed things enough to cause the slight damage. The 'rubber' fairing between the top of the wing and the fuselage at that point was also curled somewhat inward, suggesting the top of the wing skin was pushed upward.
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I can't imagine jacking a wing could be worse than flight loads. Think about it. Jacking the airplane can never be more than 1 "g". Even normal flight loads go beyond that.
 
Point Load

Mel said:
I can't imagine jacking a wing could be worse than flight loads. Think about it. Jacking the airplane can never be more than 1 "g". Even normal flight loads go beyond that.
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Mel there is a difference in uniform and point load.
I don’t think the wing received a 1 G load that far out on the spar if flight.
In reference to the dent you are correct.

Also jacking at that point may be more than I G as the center of gravity moved.

My view
 
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Not sure how to mark it, but you can see where the MLG would contact the side skin if deflected up very much. I propose to snip out that area directly above the MLG leg. This photo distorts the view actually there is about 3/4 inch between the leg and the side skin when building. The skin between the leg and the first horzontal row of rivets serves no purpose except to wrinkle the whole side in a hard landing.
2092cza.jpg
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DonFromTX said:
The skin between the leg and the first horzontal row of rivets serves no purpose except to wrinkle the whole side in a hard landing.
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I disagree.

I admit that witout a stiffening flange along the free edge, it is not a real strong load path in compression, but it is in tension. (Everyone should remember that modifications before certification are not allowed under E-LSA certification).

BTW, a 3/4" gap is huge for this location. If the gear leg is deflecting that much, that close to the top of the leg during a very hard landing, then that pilot was only a nats hair away from doing some major structural damage (my opinion anyway).
 
more clearance

DonFromTX said:
Not sure how to mark it, but you can see where the MLG would contact the side skin if deflected up very much. I propose to snip out that area directly above the MLG leg. This photo distorts the view actually there is about 3/4 inch between the leg and the side skin when building. The skin between the leg and the first horzontal row of rivets serves no purpose except to wrinkle the whole side in a hard landing.
2092cza.jpg
[/IMG]
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Don
Can you use your seam tool and bend the skin outward at the point of the possible of contact to add a little more clearance

Are you sure the gear hit the skin at that point? Scratch on the paint?

The side skin is in shear in a hard landing?

Cutting of the skin may add to the problem?

My view
 
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Common Issue

This is actually a common issue on "regular RVs". If you don't trim the skin above where the gear leg goes into the fuselage, the gear will flex up on landing and bend the skin.

Probably the worst part is that the powdercoat on the gear leg gets damaged in the process.

Hans
 
I don't pretend to know the answers, that is why I posted it, but with four known and admitted cases so far, I feel it should be addressed.. I would have no problem putting a doubler under or over the newly formed edge to replace the strength that was removed. The common solution seems to be to just ignore it after it happens, since it makes clearance when it bends up. I was hoping for an approved solution to keep it from happening.
I was never around when any of them bent, just relying on owners that related to me that it was caused by a hard landing they made. I would sure hate to replace an entire side panel because of it.
And Scott: The 3/4 inch is with no avionics, no tail cone, no engine for weight. Judging from the angle of my spindles, the distance will reduce a lot when loaded, I have none to measure fully loaded..
 
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Define the problem first

DonFromTX said:
I don't pretend to know the answers, that is why I posted it, but with four known and admitted cases so far, I feel it should be addressed.. I would have no problem putting a doubler under or over the newly formed edge to replace the strength that was removed. The common solution seems to be to just ignore it after it happens, since it makes clearance when it bends up. I was hoping for an approved solution to keep it from happening.
I was never around when any of them bent, just relying on owners that related to me that it was caused by a hard landing they made. I would sure hate to replace an entire side panel because of it.
And Scott: The 3/4 inch is with no avionics, no tail cone, no engine for weight. Judging from the angle of my spindles, the distance will reduce a lot when loaded, I have none to measure fully loaded..
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Don this seems to be something we need more information on.
Cutting or adding stiffener to solve a problem that is not described is not a good idea.
The crimple zone may be a good thing.
Pitchers of the damage would help.
If this has happened more than a few times Van should chime in.

My view
 
Another data point.....

Van's Aircrafts prototype/demonstrator (N412RV) has been checked and there is no evidence of gear leg contact to the skin (the legs are painted... it would show).

This airplane has been used quite a bit for transition training with numerous known HARD landings.
 
I will note that even 331RV's crash did not show any damage above the gear. We had them go backwards a bit (enough to slice through the brake lines), but absolutely none upwards.
 
Well they did. Vans seems to think that there is sufficient clearance for normal operations, and if you land that hard you probably hurt something else. They may be correct, maybe you need a new landing gear leg after such a mishap.
My counterpoint is why reskin the whole side of the aircraft when a little fix would make it necessary to only replace the MLG leg. I will keep looking, I had photos of two of them earlier.
 
Interesting responses. I guess it IS possible that some legs are stiffer than others? All of them bending on the right side is possible evidence as well.
 
John, I have seen dozens of -12s. I talk to several -12 owners on a daily basis. The report from Scott R. is no damage even when they know of hard landings. The owner of a damaged plane responds with no side skin damage even after an accident. I know of no damage to side skins.

Is this really an issue? :confused:
 
I agree with Larry. I have NOT seen a single RV-12 with bent side skins. This thread started stating several have been seen with this condition. Don, please post a photo of the ones with this condition. Checked mine and there is absolutely no evidence of a problem here. And there is PLENTY of clearance to allow for flex. SHOW us a photo!!
 
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Leg geometry

I checked the clearance between the gear leg and the skin on my aircraft today and the leg would have to rise at least half an inch to contact the skin. Given the close spacing of the inboard and outboard mounting points and the skin edge, the horizontal part of the gearleg would have to bend like a banana to make contact with the leg. Considering the thickness of the leg metal, I reckon a deflection like that would have to be permanent.

It did occur to me that the gear leg would be a lot closer to the skin if spacer U-1202B was accidentally left out.

Rod
 
If it doesn't exceed the design loads, there is only a momentary elastic wrinkling during the load event that causes no permanent effect.

If it exceeds the design load but not the failure load, there will be residual permanent wrinkles in the skin afterwards.

And of course if it exceeds the failure load there will be broken parts and probably a somewhat broken airframe.

Typically for general aviation aircraft, the design loads are called "limit" loads. There is usually no requirement for a higher "yield" load like there is for spacecraft. A yielding failure is usually defined as a permanent detrimental deformation, and a non-detrimental deformation is usually allowed. This might involve some permanent wrinkling in some areas which could be unsightly. You'd typically see that at the rivet lines or the frames or stringers or longerons.

The failure load is called the "ultimate" load. It is normally 150% of the limit load. It's often defined as a failure to sustain the load, in other words, something gave way.

Dave
 
So David I would guess that means that every time I put my 12 in the sun and the leading edge wing skins are popping like popcorn there is nothing to be concerned about, correct?
Dick Seiders
 
If it cools off with no wrinkles it's done no damage.

However, whether it can handle limit loads if flown before it cools off - that's a question for Van's.

Dave
 
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