• Welcome aboard HomebuiltAirplanes.com, your destination for connecting with a thriving community of more than 10,000 active members, all passionate about home-built aviation. Dive into our comprehensive repository of knowledge, exchange technical insights, arrange get-togethers, and trade aircrafts/parts with like-minded enthusiasts. Unearth a wide-ranging collection of general and kit plane aviation subjects, enriched with engaging imagery, in-depth technical manuals, and rare archives.

    For a nominal fee of $99.99/year or $12.99/month, you can immerse yourself in this dynamic community and unparalleled treasure-trove of aviation knowledge.

    Embark on your journey now!

    Click Here to Become a Premium Member and Experience Homebuilt Airplanes to the Fullest!

Pressure Relief holes in Longerons

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

bobthebuilder

Well-Known Member
Joined
Feb 16, 2012
Messages
183
Location
Johannesburg, South Africa
Hi Guys,

I am at the point where I am almost ready to start tacking the first fuselage truss together.
Holes need to be drilled to allow the hot gasses to escape. These holes will also be used later to allow the linseed oil to traverse through the structure.

My question is ...... where do I drill these holes?







My options are:
  • Only in the longerons. (Red Dots)
  • One in the loneron, and others in the cross members. (Green Dots)
I found no reference to this in AC43, and am nervous about weakening the structure.

Any advice?
 
Drill holes in the longeron at each cross-tube junction. Of course, the holes are within the tubing intersection, not visible on the outside of the tube after welded up. I think you meant that, but the colored dots could mean otherwise.
This allows good flow of the oil through all the tubes.
And, you're right about allowing hot gas to escape. It's a bummer to make a good joint weld and then have the last bit to explode out due to hot gas trapped in the tubing.

By the way, those joints are works of art. Shame to have to weld them!

Tom H
 
Hi Tom,

Thanks for your response.

Drill holes in the longeron at each cross-tube junction.
This makes perfect sense from a structural point of view.

..... But I may have to rework my notches.

If you take a look at the first picture as an example, this means that the longeron would have three holes drilled into it. This because the centre tube is only notched to accept the longeron. The diagonals on either side were notched to accept both the longeron, and the centre tube. (Not sure If am explaining this well enough - Let me know if your want a better picture)

Should I maybe notch the centre tube to accept the two diagonals, thus creating the need for only one relief hole at the centre of the cluster?

This would save weight (i know ..... barely) but I though it would be stronger the way I have it now.

Thanks for the words of encouragement Tom.
 
Maybe I am not fully understanding what you are saying. Using your first pic as example:
- drill small hole in longeron where the perpendicular center tube intersects. The drilled hole will be enveloped by the perp. center tube.
- drill a small hole in longeron where each diag. tube intersects. Put the holes in the longeron so that the diag tubes envelope the drilled holes.
This should result in three drilled holes in the longeron, but all will be enveloped by the intersecting tubes. The drilled holes are about 3/32" dia.
From what I have seen and read, this is common practice in steel tube fuselage construction, and does not weaken the structure.
I suppose you could drill holes in the side of the center tube to allow oil to flow into the diag tubes. But, no add'l notching needed. That oil creeps anywhere it can find a path. And, I think add'l notching would weaken the structure some.
At some point you will have to have a hole in the fuselage to inject the anti-rusting oil, also used to drain the oil after you rotate/manipulate the fuselage to get the oil distributed throughout the tubing. Then plug the hole. Various methods possible, from a sheet metal screw to a welded hub for a small pipe plug.

Hope this makes sense.
Tom H
 
Back
Top