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Old 01-16-2018, 05:42 PM
rgmwa rgmwa is offline
Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,622

Notwithstanding the problems the OP is having, every time I have to remove the wings I'm still amazed that Vans can fabricate and kit wing spars and fuselage with holes that line up so accurately that you can slide (OK, maybe with some persuasion) two pins through four bushings with practically zero tolerance. Very impressive.
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Old 01-16-2018, 07:08 PM
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engineerofsorts engineerofsorts is offline
Join Date: Mar 2009
Location: Austin, Texas
Posts: 300
Default Definition of sloping seat pan

Originally Posted by magiccarpet View Post
What part do you mean with the "sloping seat pan" ?
I was using the wrong name--the proper name is seat ramp cover--this is the inspection plate with an aggravatingly large number of screws between the
F-1226-R and -L seat ramp floor parts. I couldn't find the part number. The part you are checking for buckling is the F-1203A bulkhead. The center portion of the bulkhead exposed when you remove the seat ramp cover is what will be buckling
Rob Reese
RV-12 #120332 N73HR
Austin, TX
TangoFlight Mentor

Last edited by engineerofsorts : 01-16-2018 at 07:13 PM. Reason: added information
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Old 01-16-2018, 08:54 PM
deene deene is offline
Join Date: Jan 2005
Location: Georgetown, TX
Posts: 382

I work on the student built 12's mentioned above in addition to my 12 and a friend's.

We have pretty well established that after gross errors like skin trimming, wrong parts in the spar channel, etc, the stub spar(s) fit is behind tight pin fit.

And as Rob described, removing the seat pan allows the front bulkhead to clearly show the stub spar misfit (bulkhead deforms to unload the stud spar stub misfit by being too wide) is behind the tight pins.

And as mentioned by earlier posters, taking a slow process as described by Madmaveric works.
Deene Ogden.
N399AD RV-12...flying
N299AD RV8 QB, IO-390X, BA prop...SOLD
N199AD One Design...SOLD
N99AD BD4, flew for 22 years...SOLD
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Old 01-16-2018, 11:54 PM
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magiccarpet magiccarpet is offline
Join Date: Feb 2013
Location: Switzerland, Europe
Posts: 168

Originally Posted by engineerofsorts View Post
I was using the wrong name--the proper name is seat ramp cover--this is the inspection plate with an aggravatingly large number of screws between the
F-1226-R and -L seat ramp floor parts. I couldn't find the part number. The part you are checking for buckling is the F-1203A bulkhead. The center portion of the bulkhead exposed when you remove the seat ramp cover is what will be buckling
Hi Rob
Thank you for clarification. This helps
Chris, RV-12 S/N 120832, HB-YSC
Phase I


=VAF= dues paid for 2019
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Old 01-17-2018, 04:22 AM
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madmaveric madmaveric is offline
Join Date: Dec 2014
Location: somewhere, earth
Posts: 118

Just to add to the earlier fix for mine. There is a benefit to having a tight spar stub as you can make the fit be more uniformly, meaning more wear would be needed to make it a lose fit.

When I first started marking my stubs, there was only one or two small points that it was touching in the socket.

As I gently removed a bit of the high points each time, the high spots became wider, until I was pretty much having to skim a small amount off the complete radius.
It made it more difficult to 'rub' the ink off as I got further into it as it was now more like a ball and socket, meaning more rubbing was needed to show where it was touching.

In some ways I'm glad it happened as it means the spars are secured with more of a mating surface now, rather than a couple of high spots.

So if you do have to do the procedure, think of it along the lines that you are making a better fit rather than correcting a mistake, it a makes the extra work a bit easier.

In some ways I'm surprised this isn't the standard method of getting these to mate fully (i.e. the stubs start out all oversized) but I guess VAN's has enough data to show it isn't going to cause issues later, and it is a bit of a tedious job on your own.

A correctly fitted wing with high spots would need less wear to become a lose fit as you only need to wear off the high spots, so having to do this gives more wear tolerance in future. whether the extra tolerance is needed or not is a different question.
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Old 01-20-2018, 07:28 PM
Tacco Tacco is offline
Join Date: Jan 2017
Location: White Salmon, WA
Posts: 86

An update. It was indeed the over-sized rear spar stub. Pretty much used the procedure Madmaverick mentioned above. Built a wheeled cart for my saw horses to make the wing removal and refitting a one man operation to facilitate the multiple times I had to do this. Used a dry erase marker to "paint" the ends of the spar to highlight the high spots. I ended up having to remove a fair bit of material - about .025 (not surprisingly). Left the fit a bit tight as I expect things to loosen up after a few landings.

Thanks to all for the help. Every input was valuable.
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Old 01-21-2018, 06:59 PM
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rswalden rswalden is offline
Join Date: Mar 2005
Posts: 94

Good advice on the Muffler Expander .....

Our spar pins were VERY stubborn going in. This is what we suggest....

1. Grind down/smooth the ridge on the end of the pins to make it more of a bullet shape.
2. Grease the pins liberally using lithium grease or similar.
3. Insert the muffler expander in one spar hole and use a socket wrench to expand the radius of the muffler expander. That will produce a PERFECT alignment on that side.
4. Now move the wing tips up and down to bring the opposite bushings into alignment (feel the inside with your fingers).
5. Fabricate a shim and wedge it between the spars and the white plastic block in order to bring it into alignment. Ours required a .064 shim.
6. Twist and turn your greased pin into the bushing hole, tapping it with a plastic tipped mallet to until the pin is in place. It gets easier each time.
7. Remove the muffler expander..... and twist/turn/tap the pin into place on that side. Wear shop gloves so you don't slice your hands on the sides.

After inserting/removing the pins a few dozen times, it actually become easy. We use a banquet table with the legs sitting on Harbor Freight moving casters to support a wing when removing it from the fuselage. We fit two RV-12s in one T-hangar.... That requires one wing to be removed from one airplane. Easy enough to do with one person.

I hope this helps.....
Bob Walden (Waldo), CFII-ASMEL
KFFC "Falcon RV Squadron" Peachtree City, GA
RV-7A Tip-Up, IO-390, 450+ Hours
RV-12 (Sold)... RV-12 Transition Training
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Old 10-21-2018, 07:30 PM
Tacco Tacco is offline
Join Date: Jan 2017
Location: White Salmon, WA
Posts: 86

Originally Posted by engineerofsorts View Post
On our student-built RV-12 completed last spring, we force-fit (don't force it, get a bigger hammer ) the spar pins and had a painful time removing them. One method we found for determining whether the REAR spar stubs need trimming was to remove the sloping seat pan and then check the spar pin fit. As you tap the pins in, if the vertical bulkhead (where the 12-volt jack is) starts buckling, its a good indication of the spar pins being too long. We marked the edges of the pins with a marker pen, inserted and wiggled a bit, and kept filing the high points off until the pins could be inserted with minimal distortion of that bulkhead. If the FRONT spar stubs are too long, I suspect you would not see the distortion of the bulkhead, so I would start filing the front stubs first in that case. We measured progress by putting a straightedge across the bulkhead and measured the amount of distortion with calipers to verify progress in getting the proper fit.
Rob, I thought this problem was solved, it isn't. I'm seeing exactly what you describe above. Question is: how did you decide which stubs to file down. Did you actually end up filing the front spar stubs?
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Old 10-21-2018, 09:00 PM
RFSchaller RFSchaller is offline
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,470

Mine needed skin trimming. About a year later I noticed a click when climbing on the wing to enter the cockpit. I also noticed a slight fore-aft play at the wingtip and ended up using 0.025 shim plates on the spar tongues to eliminate the problem. My shims were shaped like the tongues and wrapped around the bottom edge of the tongues so on end they looked like Ls.
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Old 10-22-2018, 04:40 AM
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mike newall mike newall is offline
Join Date: Jan 2005
Location: Yorkshire, England
Posts: 1,752

On both of ours (2016 kits) the fitting of the wings required some gentle effort. We used contact crayon on sub spars, filed the stubs where touching, then had a minor skin issue and then - thunk - the pins fit.

It is a high precision assembly really with some variability due to size and construction. The instructions should include a work through for issues so that guys don't end up grabbing the larger mallet and potentially doing damage.

#1 aeroplane is just waiting for paperwork so we can test fly, #2 had it's first ships power up last night - smoke stayed inside the wires which was a bonus

Both first flights will end up on YouTube as per normal on my Trent772 channel.
"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q

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