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Hole through Spar web? Ok or not?

AJ85WA

AJ85WA

Well Known Member
Hi Guys

Obviously I will double check with Vans but just wanted to get some input from guys on here.

The issue is that I have already completed all my wiring going to the wings from the panel. It goes down the centre under the tunnel cover and then through the spar web where the two spars connect and under the seats to the wings.

But when I checked out my wings (already closed and wired) the wires run in front of the spar and i am looking for a way to get it behind to meet up with the other wires from the panel.

Would it be ok to drill a small hole in either of the arrow locations? Just your opinions.

RV6SPAR_zps1dd982ff.jpg
 
I cut an opening in the center where the spars butt together

I cut an opening in the center of the spar webs only where they butt together but are not connected. All of my wiring from front to rear goes through that opening. I made a console that the wiring from the panel goes through to get to that opening so no wiring is exposed. Flying ~1,000 hrs now at high speeds.

Bob Axsom
 
Last edited:
Bob

Hi Bob

Yes This is what I have done aswell, but my wiring inside of the wings is in front of the Spar, not behind.

Cheers
 
What about using one of the outboard spar web lightening holes...

I assume you have landing light plus nav/position lights? Remove the wingtip and fish the wires through one of the existing spar lightening holes behind the leading edge. Then you can run them behind the spar. If you have enough wire, you could even bring them to the leading edge wingtip rib and then insert them in a piece of PVC pipe secured at each end behind the spar. Just a thought. I'm curious what Vans response will be. My guess is you would need a hole about 3/8 or so with a grommet.
 
See what Van's says about overall stresses, but if you keep it as close to the center of the web as possible you should be fine. The neutral axis should be approximately at the center of the web and have zero stress. Stress goes up dramatically away from the center, which is why Vans thoughtfully put all of that material out there. :)

Guy
 
Hi AJ,

I'm building a 6 and just a little behind you on my project. My wings also are complete with wiring and have the wiring run in front of the spar along with the pitot line.

I elected to drill the holes through the fueslage in front of the spar where my plans were to run the wires above the fuel lines and over to the center tunnel in front of the spar and then fore/aft as needed. You built those nice RV7 like spar covers that if you chose to do the same thing would cover the wire runs.

Just a thought - love your website and pictures. Good luck

Russ
 
Wiring Hole

AJ,

I cut an elongated hole where the spar meets at the centerline. Check out the "Spring-fast Grommet Edging" that Aircraft Spuce sells. It's a great way to insulate your wires from the sharp aluminum. I got this from someone else on this website that was dealing with the same issue as you are.

John
 
I thought about it a lot ...

I just wouldn't do it. I'm sure many have done it. But if I were to give in to the desire I would do it in the vertical center of the web and as far outboard as possible with extreme attention to deburring. Have you considered going out to the tip and looping around the spar and coming back in on the back side? I'm an old worry wart of course, you should have experienced my disbelief when I had to cut the holes in the rear spars for the aileron pushrods.

Bob Axsom
 
Vans Reply

Hi Guys

Thanks for all the replies, I'm also a bit of a worry wart and won't sleep if I did anything like this.

It was a big NO from vans

"You can not drill a hole in the location you have in your picture, this is close to the highest
stress area on the entire wing. You will need to run your wires into the center of the aircraft
and pick a location further inboard."

I think I will run some conduit secured on each side behind the spar and loop the wires around.

Thanks for the nice comments Russ, appreciate it.:)
 
Since the topic of piot lines was brought up. Back when I built my wings I ran the pitot line per plans ahead of the spar. Now that I am working to integrate systems, I realize that was a poor choice. If you plan to have an EFIS with a remote ADAHRS, do yourself a favor and run the pitot line behind the spar. I am lucky that I have enough room in my wing wiring conduit to re-run the lines, otherwise it would be a major PITA. The best location to mount the ADARS is aft, but it a paint to get the pitot lines back there when you start ahead of the spar.
 
Another good thread

AJ,

Look at the thread started by NYTOM titled Help! Wire routing over spar in a 6. There are some good photos.

John
 
Guy Prevost said:
See what Van's says about overall stresses, but if you keep it as close to the center of the web as possible you should be fine. The neutral axis should be approximately at the center of the web and have zero stress. Stress goes up dramatically away from the center, which is why Vans thoughtfully put all of that material out there. :)
Click to expand...

**** Disclaimer: I'm not an engineer. I'm a relapsed liberal studies dropout. But I've done a lot of mechanical design and simple stress analysis, and I have designed wing spars for aircraft now flying. And I did once stay at a Holiday Inn. /Disclaimer ****

It might be true that the tensile and compressive stresses due to bending are lowest along the neutral axis. However, there is still a lot of shear stress in the middle of the shear web, hence the name. Those shear stresses are greatest just outboard of the side of body where the two 1/4" bolts transfer the majority of the lifting loads into the fuselage through the F604 bulkhead. That's probably why Vans doesn't want holes in the shear webs in the indicated locations.

Thanks, Bob K.
 
Thanks for replies

Thanks for the replies guy, but I think some might be understanding me wrong, I have already run wires from my panel to the wings through the centre section where the two spars meet.

My question was that my wing wires are run in front of the spars in the actual wing,so to meet up with the wires coming out of the fuselage they need to get behind the spars again.

I might just have to open up my wings again and redo the wiring:(

Cheers AJ
 
Why not run the wing wire bundle ahead of the spar inside the fuselage and meet up with the main center bundle by the tank selector valve?
 
az_gila said:
Why not run the wing wire bundle ahead of the spar inside the fuselage and meet up with the main center bundle by the tank selector valve?
Click to expand...

I don't recommend having a bunch of electrical connections in close proximity to a bunch of fuel connections.
 
Mel said:
I don't recommend having a bunch of electrical connections in close proximity to a bunch of fuel connections.
Click to expand...

Doesn't have to be.

The center bundle is there with the fuel system per later plans, and the routing ahead of the spar can keep sufficient distance away from the fuel lines going from the selector to the wing tanks. The electrical wire to the fuel sender is in that area already.
 
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