Longeron Repair

[HatSwitch]

I picked up an old abandoned project a few years ago. The original builder was an engineer and to my eye the workmanship and his attention to detail on the tub and spar reflects that. Then, there is the hole that was punched into the left lower side of the fuselage for a retractable step. The hole virtually severs the lower left longeron on the aft or cockpit side of the IP. I haven’t seen a plan for the flush/retractable step but I personally wouldn’t place it clean thru an unreinforced longeron the way this hole was positioned and drilled even if it was called out that way.

 

This longeron needs to be/will be repaired. Any input?

 

Anyone have details for the flush/retract step mod?

 

 

My Open-EZ project had to be put on hold for more then a year but work was resumed in December. When I get my Open project caught up or close to the other OEs in progress on the board, I’ll try to bring these two up together.

Feels good to be back in the shop.

Hat

[Kent Ashton]

You can make holes in these things and they are still pretty strong. See the hole in the side of Klaus's Varieze, here

http://lightspeedengineering.com/News/News.htm

 

The thing I'd fret over is spreading out the load on the step mechanism so that your weight doesn't break the structure. If the end result is strong enough to hold your weight, I'd consider it OK. It's not like cutting an aluminum longeron.

[HatSwitch]

I think I started this thread the day before the CZ entered what we all know turned out to be a 5 year black-out. So it took some time to see Kent’s reply J

The hole repair needed on the tub of my second Long-Ez project hasn’t been performed yet, but as a follow on to this thread, I have spoken with a few folks over recent years concerning how to do it.

Like many of us still building and happen to reside more than a 1000 miles afar of Oshkosh, going to AirVenture every year just isn’t practical. I think making at least one build-era-pilgrimage to Oshkosh is worth doing and Osh-11 was the one for me for a few reasons. First, as just about everyone knows, Osh-11 served in part to celebrate Burt’s career and mark the year of his official retirement. Second, there were a lot of other Canardians, builders in particular, from this forum going that I wanted to meet personally. So we went. While there, I ran into Terry S. and Gary H. while they were conducting an interesting group discussion and line inspection of some of the grazing Canards parked on the grass. After everyone dispersed, I introduced myself and described the project and the retractable boarding step hole that came with it. Terry explained in essence, the longerons are important structural elements and though used as hard points for mechanical attachments, shouldn’t be fully compromised, ever. Ref the photo above: (The hole drilled in the left side of the tub is flush to the interior floor and the aft face of the IP. The hole left the longeron nearly severed with only about 20% of the spruce intact along the bottom edge)

Terry and Gary both graciously suggested a fix: IIRC, They suggested to further remove the existing longeron material sloped at approx’ 60-degrees-to-daylight on both sides of the hole. Flox-in a shaped to fit replacement length of with-the-grain spruce, followed by a standard glass repair of affected areas as needed.

Lots of work and will probably be what I do when the time comes. It was great meeting both of them and I fully appreciated the generosity of their time and in-put.

 

For the sake of relighting an old thread. I’d personally appreciate hearing some qualified opinions, from a structural perspective, what limitations should be adhered to regarding penetrations and mechanical attachments to the longerons, Long-Ez in particular? What should we avoid? What degree of material compromise of the longeron/s would be cause to ground the plane for structural reasons?

As Kent pointed out, these little birds are pretty strong and there are lots of big holes cut in the sides of some.

 

 

Hat

[Jon Matcho]

I am not a structural engineer, but...

 

That appears very fixable to me.  However, I can't see what the inside looks like, but I wouldn't cut the outside anymore than is already done to preserve the contour -- I am betting that everything you need to do can be done from the inside.  Also, if those lower longerons are anything like the Cozy longerons they're just tiny triangular lengths of wood.  

 

I would plug the outside hole (for later) and then cut everything out from the inside and do as Terry suggested, either that 60 degree business, or any wood-type butt joint (tongue and groove, or dovetail inserts).  Cut and trial fit the wood pieces before mixing epoxy.

 

Make sure the wood is wet with epoxy and use flox in the area to fill all anticipated voids.  Insert the replacement wood puzzle piece, and then cover with 1 or two layers of bid/uni according to the repair section in chapter 3 (?)  For the outside, do a standard repair per chapter... 3 (wherever that is) and use peel ply to ensure no ridges between glass layers.

 

Go for it.  You'll be fine.  Have you done the practice layups and stuff (excuse me, but you haven't posted here in 4+ years so I've forgotten where you're at ;-)  Sorry!!! Kidding of course.    

[Jon Matcho]

Also, check this unique EZ-type aircraft out (a modified three place based on the Long-EZ or possibly Cozy III).  The builder cut and replaced about 4 feet of the upper longerons so that his canopy could be made to go lower than flush to the original longeron waterline.  

 

http://www.airport-data.com/aircraft/photo/001013603.html

 

The point is that longerons are not some sort of super structures that must absolutely be straight and cannot be compromised.  You'll be fine.