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Wing junction photo request

Paragon

Active Member
RV-12 builders...

To satisfy my curiousity, I'm wondering if someone here can post photos of the RV-12 wing junction area.

I'm particularly interested in seeing how the wing structurally attaches to the fuselage. I understand there is a long, protruding spar on each wing that inserts into a fuselage slot, and gets secured by the large, secured pin.

What I'm curious about is if there is any rear spar attachment, or, if not an attachment, at least a rod of some sort that inserts into a hole, such that the wing forward/aft bending moments are reacted against something.

Also curious how the flaperon controls and wing lights are connected.

(Thanks as always to the VAF.net community for supplying so much useful information to builders and potential builders.)

-Paragon
Cincinnati, OH
 
Paragon,

we are in jackson, oh

let us know if you want to visit or we can make a trip to sporty's sometime. There is a -12 in Xenia too.
 
One at Greene County

Xenia, OH, and another at Mad River airport just north of Springfield. There was (may be) one in Middletown, to, but he's not on the forum.

Wayne 120241/143WM at I19
 
All,

Thank you for the replies.

I've seen the wing removal video before - it doesn't really show the wing root area in any detail. (The smugmug site, unfortunately, does not work with my computer security settings.)

Rgmwa's description of the stub spars is what I was interested in. Thank you. I wonder about the length of these and whether over time they will sort of chafe their receptacles and become looser, if there are no bolts or pins securing them.

(It would be nice to see pictures or the relevant plans page, but no hurry - I may be able to see an RV-12 locally at some point in the future.)

I was at Sporty's when they raffled off the 2014 RV-12, and, given the crush of onlookers, I didn't really want to ask them to take a wing off just so I could have a look. I did get to sit in it and verify that I fit reasonably well.

Sadly, I did not win the raffle aircraft. But I suppose there is always 2015!


Best Regards,

-Paragon
Cincinnati, OH
 
Ah...

It looks like they are only an inch or two long, and rounded on the far end to boot. Coated with anti-sieze so you can get them on and off in the future.

But with anti-sieze they would not mechanically grip very well during fore/aft wing bending, which is certainly what I would want them to do...

I guess one could argue that the forward one hits hard stop during forward bending, and the aft one hits hard stop during aft bending, and therefore everything is fine. The stress due to fore/aft bending, like during a hard landing, is therefore converted to tension at the spar in addition to existing tension due to vertical bending loads, rather than some compression cancellation if it were bolted.

I think I would prefer bolts in those locations...


Thanks again, Rgmwa,

-Paragon
Cincinnati, OH
 
Bolts are not necessary. Correctly fitted, the stub spars fit snugly in the receptacles and will resist both fore and aft loading on the wing (rearward forces by aft stub compression and main spar tension and forward forces by forward stub compression and main spar tension) and also wing torsion for which an ability to rotate in the socket is important (as it is for bending, which is resisted by the main spar but will result in rotation of the stub spars. Torsion is resisted primarily by shear in the stub spars).
 
Last edited:
Sheer

Good Design
It works fine

The front and back stub spars stop rotation of the wing by going into compression in sheer ( top or Bottom ) The main Spar takes the Load

Ah...

It looks like they are only an inch or two long, and rounded on the far end to boot. Coated with anti-sieze so you can get them on and off in the future.

But with anti-sieze they would not mechanically grip very well during fore/aft wing bending, which is certainly what I would want them to do...

I guess one could argue that the forward one hits hard stop during forward bending, and the aft one hits hard stop during aft bending, and therefore everything is fine. The stress due to fore/aft bending, like during a hard landing, is therefore converted to tension at the spar in addition to existing tension due to vertical bending loads, rather than some compression cancellation if it were bolted.

I think I would prefer bolts in those locations...


Thanks again, Rgmwa,

-Paragon
Cincinnati, OH
 
Ah...

It looks like they are only an inch or two long, and rounded on the far end to boot. Coated with anti-sieze so you can get them on and off in the future.

But with anti-sieze they would not mechanically grip very well during fore/aft wing bending, which is certainly what I would want them to do...

I guess one could argue that the forward one hits hard stop during forward bending, and the aft one hits hard stop during aft bending, and therefore everything is fine. The stress due to fore/aft bending, like during a hard landing, is therefore converted to tension at the spar in addition to existing tension due to vertical bending loads, rather than some compression cancellation if it were bolted.

I think I would prefer bolts in those locations...


Thanks again, Rgmwa,

-Paragon
Cincinnati, OH

The basic principals of this design on the RV-12 are exactly the same as has been used on high performance sail planes for decades.

There is no mechanical griping necessary because in case where if the wing were to move for or aft, a stub can not move outward because the other stub is already all the way in... it can not move in further.

They are rounded because wings do flex under load. The radius allows a slight amount of flex but still maintain a wide contact area.
The antiseize isn't for easing install/removal, it is for this minute amount of movement that occurs.
 
All,

Thank you for your replies.

Aluminum is a material that has no fatigue "endurance limit" under cyclic loading. (Steel, by contrast, will never fail under cyclic loading as long as the cyclic stress is kept below the endurance limit stress level, which may be, say, 30 ksi for certain structural steels.)

At low stress levels, Aluminum may require a very large number of cycles to fatigue failure, say 10^6 or 10^8 cycles, but it will eventually fail in fatigue.

So aircraft structural design with aluminum becomes an exercise in designing with sufficient margin to prevent fatigue failure during the expected lifetime of the airframe. This is difficult to do because the loading history to be expected in service may be unknown. (A good airplane design process would design to fatigue limits for expected service cyclic loading conditions, as opposed to just designing to one-off g loads.)

For a Beechcraft Skipper trainer, the plane I trained in, the hard landings came frequently, maybe several times a week, including several of my own I will admit... The landing gear and general structure were designed appropriately, and the wing was given a life limit of 12,000 hrs. After that, the wing must be replaced. The Skipper is similar in size & capacity to an RV-9 sporting an O-235, but empty weight is several hundred pounds heavier, probably due to more structural margin.

Since nobody ever fatigue tests GA airplanes to failure, we have to find out when things start to develop fatigue cracks in the field via observation and repair. An example is the VS and HS Service Bulletins on the RV series empennage. The empennage design presumably passed static load tests. Folks assumed that it was a good design right up until the parts started cracking prematurely in service.

Since the only thing we have to go on for GA airplanes is that at some point a static load test was done, we can say the design can take the POH limit g loads successfully with margin when new, but we can say little about the fatigue life of the airframe.

To me, the RV-12 wing root is a design that I would want to keep an eye on. Inspect periodically for issues at the wing/spar junction. Conveniently, the wing can be removed for inspection.

It may well be a very good design for general use, with a long expected service life.

Conversely, given that the design is different than any I'm familiar with in GA airplanes, if it is subjected to flight school level repeated hard landings, it may at some point develop problems. Any such potential problems should be caught if we habitually inspect in the right locations.

Thanks again for all the replies to my inquiry.

-Paragon
Cincinnati, OH
 
Issue at wing spar...

See Service Bulletin SB14-11-03...

Smoking rivets at the skin/spar junction on the bottom of the wing - the fix is to add a doubler over the skin that extends fwd and aft of the spar a little bit, and circa 8-10 inches long.

I would have guessed the top of the wing would have issues, based on hard landings, but apparently this issue is on the bottom, which would be due to positive g flight loads.

I congratulate Van's for keeing on top of this aircraft, but an ongoing flow of SB's is concerning.

Keep safe and keep flying...


Best Regards,

-Paragon
Cincinnati, OH 45238
 
the on going SB's is a comfort to me. I know that Vans is keeping up with their development Over here Jabiru aircraft refused to issue sbs or accept that they had problems with their engines until the regulator CASA threatened to ground them all then they eventually started to Issue SB's but by then the damage to their reputation had been done and anything Jabiru powered is now almost worthless
 
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