Lightening Hole specs - where are they?

[maniago]

Searching around I'm coming up empty with the rules on lightening hole spacing, sizing, flange requirements etc.

Been through the ACs, my A&P books and various aircraft mfg searches on the net. Zippy. Best I get is "..size of lightening hole and width of the flange...are determined by design specifications." No duh.

Obviously, I'm missing it. Anyone point me to the right publication or in the right direction?

Thanks

Mick

[David Paule]

There aren't any specs for them - the designer designs them individually where appropriate, so it isn't an A&P choice, it's an aeronautical structural engineer's choice.

A decent reference is Bruhn's "Analysis & Design of Flight Vehicle Structures." If you have the 1973 edition, look for article C10.18.

Dave

[maniago]

Well at $175+ for an old copy, not really what I'm looking for. Did get a hit on Bruhns 300 page (!) errata document that took me to two NACA papers from the 40's. Oh joy.

Really looking for the simple info like Bingelis gives us for rivets.

Anyone?

[RVDan]

I have a Glen L Martin aircraft company structures design manual from the 40's and they make no mention about lightning holes. That is my go to manual that I thought would have something for sure.

[maniago]

Its here....
http://ntrs.nasa.gov/archive/nasa/ca...9930093371.pdf

....for anyone who wants to read it. Requires knowing the load required to be carried, then use of charts, graphs, and some other ratios I'm not gonna bother to figure out. See page 19 for examples.

I think I'll just call the factory and get their rule of thumb.

[David Paule]

Well, engineering isn't always simple. Imagine trying to do it with a deadline and a budget.

Hope you enjoy this.... it's from xkcd.com, and this is number 277.



Dave

[maniago]

Haha good one. Ref engineering, budgets etal, been there done that. But I worked for the govt. Keeping to budgets and timelines is strictly optional....except for a war need. Then only budgets were optional.....

[rvbuilder2002]

There are a lot of locations that correctly adding a lightening hole would not be detrimental.
There are also a lot of places were adding them (even if done right), would be.

For anything other than simple structure (radio tray supports, etc) it is best to have a direct understanding of the loads involved with the structure before adding them if the plans don't mention it as optional.

One exception to that would be material in the center of factory stiffening beads.

[wirejock]

When someone complains about the length of the red light my response is, "run it, I know the guy that put it up".
By the time they contemplate the response, the light changes. Back in TX I actually did know the guy that put up a few.