Building a wooden wing spar

[@007mwn]

Taking all the mystery out thank you for these short "how id did it videos"

[@paulliebenberg3410]

For certificated aircraft wood spars the FAA requires a scarf slope to be a minimum of 10:1 and recommends 12:1. Seems like 5:1 is flirting with danger. Is that what Fisher recommends?

[@timketcham9139]

AC43.13-1b par 140 .,..5:1

[@timketcham9139]

And I've done my own testing and the joint never breaks. At 5 to 1 ratio the wood always breaks beyond The joint regardless of where I set the fulcrum on or beyond to join

[@timketcham9139]

I've never seen a 12:1 reference. But 15:1 is the maximum slope of the grain when inspecting lumber for aircraft. But...as many sticks of lumber have a greater slope near the ends, this can be taken advantage of when scarfing longerons together. Also described with drawings.

[@paulliebenberg3410]

@@timketcham9139 when I did my A&P training AC43.13-1 was the "A" edition and that's what I was basing my comment on. I just looked up the "B" edition and there have been some changes. Spar splice scarf joints have gone from a minimum of 10:1 to a minimum of 15:1. Where are you seeing 5:1?

[@timketcham9139]

Originally I got that information from the blueprints on Fisher flying products airplanes, and the Maranda 14h Prints, actually the super koala and the storch prints also show 5 to 1 scarf joint on spar caps. But I'm one to always looking information up and do my own testing. So I found it in AC 43.13-1b. but also did my own testing building up many times of 5 to 1 scarf joints out of various woods and slow stress testing as well as drop testing them. Now I have seen references to metal spars being 15 to 1

[@stolaircraftsuyanto9728]

hello my uncle, what kind of wood are you using, is it Pine? or any other wood?

[@timketcham9139]

I use commercial white ash. It's 1.4 times the weight of Sitka spruce, but 4-6 times stronger in all of the moduluses except the modulus of elasticity. There are other woods that can be used. Northern White Pine, Yellow Poplar (not tulip poplar). NACA report 354 is a good resource.

[@stolaircraftsuyanto9728]

@@timketcham9139 thank you uncle, this type of wood is very rare here, in Asia there is fir wood but I don't know what type it is. Your plane is very beautiful, success is always for my uncle

[@timketcham9139]

@@stolaircraftsuyanto9728 find out what kind of wood it is. There are many acceptable woods that you can use. And most of them have good data on their strengths. And most important with these woods is that it has to be graded for straight grain, no knots, and specific gravity. You don't want a slope in the grain on any given board to be more than 1:15. Inspect for tight grain, 6 growth rings/25.4mm.

[@stolaircraftsuyanto9728]

@@timketcham9139 thank you uncle, glad to be able to communicate with uncle. 🙏

[@tjkoker]

Is this all comprised of spruce and 1/8" spruce plywood? Thanks.

[@timketcham9139]

It is commercial white ash for the spar caps, and the web is mil spec Norwegian Birch.

[@alpenglow1235]

What type of glue?

[@timketcham9139]

T-88

[@todpevy8952]

So what are you building ?

[@timketcham9139]

This is the main beam or "spar" in the wing of an airplane.

[@todpevy8952]

@@timketcham9139 yes i know what make ,and model

[@timketcham9139]

@@todpevy8952 oh sorry, FP202 Koala

[@timketcham9139]

@@todpevy8952 it's the black plane in some of my other videos... I flipped it, so I have to build a new wing and landing gear and a prop

[@todpevy8952]

@@timketcham9139 ok thanks .. i want to build a fisher advenger

[@marttimattila9561]

1 to 5 ? should be 1 to 10

[@timketcham9139]

Not according to AC4313.1b and NACA report 354 and several other publications.

[@seerjfly4783]

@@timketcham9139 5:1 refers to 'reinforcement plates,' AC photo on pg 1-19 shows "15:1" 10/12:1 will do, please don't let that slide.

[@timketcham9139]

@@seerjfly4783 I read the paragraph through and reviewed the illustration and only see reference to 5:1 and drawing of 5:1. Don't want to argue but please find a reference to 15:1. OR, ARE YOU REFERRING TO THE SLOPE OF GRAIN FOR GRADING WOOD?

[@timketcham9139]

@@seerjfly4783 I really am interested in your reference, but it doesn't change the 5:1 in this video as it is the design and on the prints such. Same with all the Fisher, Minimax, Ragwing... every wooden plane that I've built or restored or have plans for.

[@seerjfly4783]

@@timketcham9139 I can't post a photo here, but '15A' on the drawing pg. 1-19 means 15:1. I don't want to argue either, build as you like. We are building 'experimental's' after all.