This is how I did mine during construction but I think itcould be done to a finished aircraft by being careful not to cut anything besides the web in the gear leg tower .
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We've never reviewed or analyzed any of the ways that people mod the gear towers (usually with removable panels?)
We've never heard of any failures either, so it seems unlikely to cause problems however it's been done, but we don't have the engineering bandwidth to devise, study or test alternative construction methods if the plans method works. Bear in mind that most builder are not testing the gear to limit loads, as we would do, unless they are really bad pilots...
So the response is typically that for all "I don't like the plans way, I want to do it this way" questions. This is experimental aviation, you can do what you want. Just don't go crazy.
Van's Aircraft, Inc.
14401 Keil Rd NE
Aurora, Oregon 97002
503.678.6545
Van's said that they have not seen any reported failures. I didn't make the mod, and since I have such big hands, I just didn't put much in there, only routed a few cables through the towers. Pretty easy to snake things through with a bit of guidance....
Habe there once been reported failures due to this modification? I could not find any...
Have to agree with Mel, those square corners look like the source of cracks beginning in a pretty stressed area.
My plan is 20 to 25 countersunk #8 screws. I still have to work out spacing and minimum edge distance, all that fun stuff. Is there a recommended hardware AN507 or AN509?
As an update, I've decided against countersunk screws. Too afraid of the #8 screw head dimples stretching the material with on the gear tower and messing up the pre-punched rivet hole locations. It also seems like unnecessary work for little gain.
AN 525 at 1/2" long are "washer head" structural screws with a smooth grip that's just the right length using a standard washer.
How about using .063 for the cover plate, and you can machine countersink the holes for the screws?
Dan, thank you for taking the time to post. Those pictures along with that #4 pic reinforce what I thought - that the tower is strong enough with whatever mod you chose. I don't need my airplane to to withstand more G-forces than I can handle.....Lot of field experience at this point, many airframes. Personally, I've probably landed as hard as anyone.
Well, maybe not. IIRC Mike Stewart did the "whole panel" mod, and he was slamming a 540 powered -8 into a small grass strip.
The "oval access" mod is way less invasive. It removes a connecting strip 2.625" wide and replaces it with a solid panel.
Matt Dralle suffered what may be the best documented groundloop:
http://www.matronics.com/forums/viewtopic.php?t=97483&sid=137bd43fdb569e8ae0d19279e8047f21
The failure appears be in compression, originating at the outer skin. The oval mod would not affect this failure (fourth photo). Not that it matters, as the entire fuselage is shot.
From the wayback machine, original thread:
https://vansairforce.net/community/showthread.php?t=13079&highlight=tower