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  #1  
Old 09-01-2018, 10:17 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 140
Default Match wits with Van's Engineering!

Woe is me, but might as well give the VAF brain trust's mechanical engineering neurons a tickle over the long weekend.

Due to a tear in the spacetime continuum, the trailing edge of my -9A's right flap was bent during pushback into the hangar when an unauthorized tool chest suddenly materialized in its path. (That's my story and I'm sticking with it! )

The T.E. distortion was limited to the most-outboard bay. (See the poor picture--in all senses of the adjective.) AEX wedge bent downwards, double-flush TE rivets in the vicinity distorted, and up visible gaps between the skins the wedge, and the outboard rib opened up. The bottom skin creased to a greater extent than the top skin in the picture. Every other part (especially the ribs) is undamaged. Nevertheless, I don't think trying to unbend the TE is likely to succeed, aesthetically or structurally.

https://drive.google.com/file/d/1amX...ew?usp=sharing

All right. Denial, bargaining, depression, and all that duly observed, comes acceptance and a plan to move forward: Instead of de-riveting the top and bottom skins and replacing them and the wedge entirely, I came up with this idea for a repair, and sent it up to the mothership for their opinion. (I know, the dwg shows the outboard end of a left flap, so please apply your mental mirror as required. Neither the dimensions nor details of the depicted ribs are to scale.)

https://drive.google.com/file/d/1zos...ew?usp=sharing

I'm not sure about the number of rivets for the joint plate. AC 43.13-1B (if I'm reading table 4.9 correctly) calls for 5.2 3/32 rivets per inch along a lap joint between 0.020" 2024-T3 sheets. That seems like a lot more than one sees in other lap joints on the RV-9A (e.g.: the wings' inboard to outboard lap joint; forward fuselage to tailcone joint). I'm also not sure about additional reinforcement of the butt joint between the new and original AEX wedge. Structural epoxy between the top skin, wedge, and bottom skin, say? I suppose a ~12" long "vee" of .020 applied to the trailing edge wouldn't be much of a disturbance to airflow over the TE. Could be match drilled to the TE rivet holes in the original skin, then dimpled in assembly with the underlying counter-sunk AEX wedge and dimpled skin serving as the female die.

Van's support got back to me Friday, 31 August, but the Chief Engineer was already out for the Labor Day holiday. They suggested two other options: (a) buy the parts to build an all new right flap; (b) buy a "factory second" QB flap. Evidently, there are cosmetically unacceptable but completely airworthy QB flaps in stock. Mr. Lock himself does the pricing, however.

So, while helpless laughter may break out at KUAO and its environs Tuesday morning, what say ye VAFers: is this an acceptable repair, and if not, what could make it so?
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Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
In final assembly...

VAF dues paid 5 Dec 2017
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  #2  
Old 09-01-2018, 10:30 PM
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az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 9,606
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The weak point created by your repair may be the spot where there is a discontinuity in the trailing edge wedge piece.
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EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
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La Cholla Airpark (57AZ) Tucson AZ
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  #3  
Old 09-01-2018, 10:53 PM
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DrillBit DrillBit is offline
 
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Location: Pleasanton, CA
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Default

Quote:
Originally Posted by az_gila View Post
The weak point created by your repair may be the spot where there is a discontinuity in the trailing edge wedge piece.
Indeed, that's my second concern.
Quote:
Originally Posted by DrillBit View Post
...I'm also not sure about additional reinforcement of the butt joint between the new and original AEX wedge. Structural epoxy between the top skin, wedge, and bottom skin, say? I suppose a ~12" long "vee" of .020 applied to the trailing edge wouldn't be much of a disturbance to airflow over the TE. Could be match drilled to the TE rivet holes in the original skin, then dimpled in assembly with the underlying counter-sunk AEX wedge and dimpled skin serving as the female die.
The "vee" would be putting extra skin, top and bottom, in either side of discontinuity, with ~ 6 rivets to either side. If the "vee" would have to be several gauges larger than .020, then one might have to put the same "vee" on the left side to even things out, roll-moment-wise?
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N748PK, RV-9A
In final assembly...

VAF dues paid 5 Dec 2017
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  #4  
Old 09-02-2018, 07:32 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,658
Default

Just build a new flap. It will take less time and a lot less cursing.

If you repair, you have a constant reminder to live with.

Carl
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  #5  
Old 09-02-2018, 07:57 AM
Mel's Avatar
Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 10,080
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Quote:
Originally Posted by DrillBit View Post
I'm not sure about the number of rivets for the joint plate. AC 43.13-1B (if I'm reading table 4.9 correctly) calls for 5.2 3/32 rivets per inch along a lap joint between 0.020" 2024-T3 sheets. That seems like a lot more than one sees in other lap joints on the RV-9A (e.g.: the wings' inboard to outboard lap joint; forward fuselage to tailcone joint). I'm also not sure about additional reinforcement of the butt joint between the new and original AEX wedge. Structural epoxy between the top skin, wedge, and bottom skin, say? I suppose a ~12" long "vee" of .020 applied to the trailing edge wouldn't be much of a disturbance to airflow over the TE. Could be match drilled to the TE rivet holes in the original skin, then dimpled in assembly with the underlying counter-sunk AEX wedge and dimpled skin serving as the female die.
Keep in mind that the flaps carry a lot of load. The flaps are the only control surface that are deflected steeply into the airstream and remain there. Other control surfaces are deflected into the airstream for only a few seconds at a time.
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Mel Asberry..DAR since last century
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<rvmel(at)icloud.com>
North Texas (8TA5)
RV-6 Flying since 1993, 172hp O-320, 3-Blade Catto (since 2003)
Legend Cub purchased 12/2017
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  #6  
Old 09-02-2018, 07:58 AM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
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As a learning opportunity, what's to be lost by drilling out the affected rivets and playing around with straightening? Find an A&P in your EAA chapter who's done 'body work' on certified planes to walk through it with you.
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  #7  
Old 09-02-2018, 08:01 AM
painless painless is offline
 
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Location: Peshtigo, Wisconsin
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Build a new flap and hang the damaged one on your wall of shame.
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  #8  
Old 09-02-2018, 08:05 AM
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airguy airguy is offline
 
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If you still have the building surface available for it, I would build a new flap since you're not painted yet. Will likely be faster, and will certainly be stronger.
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Greg Niehues - VAF 2018 dues paid
Garden City, TX
N16GN flying! http://websites.expercraft.com/airguy/
Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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  #9  
Old 09-02-2018, 12:06 PM
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RV6_flyer RV6_flyer is offline
 
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Quote:
Originally Posted by painless View Post
Build a new flap and hang the damaged one on your wall of shame.
Quote:
Originally Posted by airguy View Post
If you still have the building surface available for it, I would build a new flap since you're not painted yet. Will likely be faster, and will certainly be stronger.
Looks like I am the 3rd person with the same opinion.

Three people are thinking the same thing about RV aircraft construction and repair.
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  #10  
Old 09-02-2018, 06:52 PM
BMC_Dave BMC_Dave is offline
 
Join Date: Mar 2017
Location: Seattle, WA
Posts: 183
Default

Personally, I'd try to unbend the damaged section. The photos don't look too bad, and there are tools meant to remove such damage to sheet metal in the automotive realm.

If it bothers you that much sure, buy a whole new flap. To me... that would be a waste of money.
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