VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 09-01-2018, 11:17 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 142
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?
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Ready for inspection...

VAF dues last paid 9 Dec 2018
Reply With Quote
  #2  
Old 09-01-2018, 11:30 PM
az_gila's Avatar
az_gila az_gila is offline
 
Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 9,740
Post

The weak point created by your repair may be the spot where there is a discontinuity in the trailing edge wedge piece.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
Reply With Quote
  #3  
Old 09-01-2018, 11:53 PM
DrillBit's Avatar
DrillBit DrillBit is offline
 
Join Date: Nov 2007
Location: Pleasanton, CA
Posts: 142
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?
__________________
Kurt Haller
P-town, CA (10 min from KLVK!)
N748PK, RV-9A
Ready for inspection...

VAF dues last paid 9 Dec 2018
Reply With Quote
  #4  
Old 09-02-2018, 08:32 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,774
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
Reply With Quote
  #5  
Old 09-02-2018, 08:58 AM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 3,196
Default

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.
Reply With Quote
  #6  
Old 09-02-2018, 09:01 AM
painless painless is offline
 
Join Date: Jan 2005
Location: Peshtigo, Wisconsin
Posts: 726
Default

Build a new flap and hang the damaged one on your wall of shame.
__________________
Jeff Orear
RV6A N782P
Peshtigo, WI
Reply With Quote
  #7  
Old 09-02-2018, 08:57 AM
Mel's Avatar
Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 10,147
Default

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.
__________________
Mel Asberry..DAR since last century
A&P/EAA Tech Counselor/Flight Advisor/Nat'l Test Pilot School
Specializing in Amateur-Built and Light-Sport Aircraft
<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
FRIEND of the RV-1
Eagle's Nest Mentor
Recipient of Wright Brothers "Master Pilot" Award
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:29 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.