View Full Version : Wood vs Metal spars (ribs too?)

Crash, Jr.
10-30-2020, 01:38 PM
Okay, I know this is going to spark some debate but what the hell it's cold outside and we have nothing better to do.

So when it comes to weight and weight alone, which one is going to be lighter, metal or wood spars??

Also does anybody have numbers on if the wood ribs in the Wag Aero plans are lighter than comparable Piper ribs?

Thinking about building a set of fully wood wings and want to know if it's worth it....

10-30-2020, 02:27 PM
Here's a place to start:


I have one wood wing built with another started. But then I talked to various people and got nervous about the larger flaps I was planning. So I expect to have aluminum wings on my current project, keeping the wooden wings for the next one....

I haven't weighed mine and now it is hanging from the rafters, but without flaps and ailerons it feels in the neighborhood of Marty's wing in the 60 pound range.

10-31-2020, 09:54 AM
On the Citabrias, the wood wing weighs about 50-60 lbs less than the metal one. The metal one comes with a slight gross weight increase (100 lbs), so I guess you'd say it's a bit "stronger" since they carry the same aerobatic rating.

Many "experts" (I'm not an expert and have only flown the wood-wing variant) claim they can feel the difference in the two wings, and prefer the more "forgiving" wood wing to the "stiffer" metal one. Personally, I doubt it makes much difference in flight to the average Joe. What does make a difference is the wooden wing AD that requires annual inspection for cracks. That adds cost to the annual, and adds up eventually.

Crash, Jr.
10-31-2020, 11:37 AM
Interesting...what cracks are inspected for and where? I'm curious if there's something in the Citabria wing design that is causing the spars to crack.

Doesn't seem to be an AD on inspecting wood spars on J3's

bob turner
10-31-2020, 12:09 PM
A couple fatalities always gets the regulators' attention. Folks were hitting things with Scout wingtips, causing difficult-to-detect compression cracks just outboard of the lift strut attach. Only happened on high power birds, so they made it a one-time inspection for (I think) 90 hp and below.

The feds mandate inspecting every square inch of all four surfaces of both spars annually. It must be done with a "Bend-A-Light" and mirror. Somebody owned stock in that company, probably - a truly shitty light source - but I back that up with a really good fiber optics scope.

A moment's reflection indicates the impossibility of this inspection. Rainbow Ron even sells a special window for the critical area, which clearly indicates that even the experts think the "every square inch" part is hooey - you would have to pull the spar to do a good job, and even then use a magnifying glass.

Best to not hit anything with your wingtip. If/when you do, pull the wing apart and really look.

No fatalities due to Cub wood spars = no AD, I guess.

10-31-2020, 11:55 PM
Plus, Citabrias are aerobatic training aircraft, thus subjected to beginners potential ham-fisted flying... But from what I've seen/read, the damage on Citabrias appears to be when someone groundloops, and hits the wingtip on something, rather than just "in-flight" load-related damage. I think the concern is about those in-flight loads AFTER the cracks get started from something else...