Spar thickness

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builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Spar thickness

Post by builderwannabe »

All, I know I will get a lot of varied responses on this one. I ordered some wood to build the wings and have been informed that the wood that has been found for the spars is just a shade(1/32-1/16th of an inch) under 1 inch thick. I am away from home for work but am pretty sure i remember the plans calling for 1 inch thick wood. That being said the question would be is wood that is a shade under 1 inch a problem. I know it will by necessity be less strong but can it really be that much less and is 1 inch really required for the weight and type of flying done in piets. Any thoughts?
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taildrags
Posts: 378
Joined: Tue Mar 07, 2017 10:39 pm

Re: Spar thickness

Post by taildrags »

Wannabe- there are Piets flying with 3/4" thick spars, although I don't recommend that without some knowledge of what you're doing and what type of wood it is. However, I would consider "a shade thinner" than 1" to be just fine. Just be sure to compensate for that if you decide to route out sections of the spar web, because it could get a little too thin if you don't. If you plan to use solid (non-routed) spars, you should be fine.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Re: Spar thickness

Post by builderwannabe »

Taildrags, thanks for the reply, i don’t have a degree in aero so really cannot run any numbers to tell what the minimum thickness would need to be. That being said my “spidey sense” indicated that it should be fine but its always good to run ones ideas across someone else to make sure they are not too off the mark. Do you think there will be a problem fitting the ribs on the spar if they are built per the plans or is a little “slop” ok with the fit?
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taildrags
Posts: 378
Joined: Tue Mar 07, 2017 10:39 pm

Re: Spar thickness

Post by taildrags »

Wannabe- the ribs should slide onto the spars but they need to be a snug fit. The best way to do that is to cut off some short stub ends of your spar stock (assuming that you've got a little to spare... and the ends usually have a little checking or scuffing anyway)- and when you build your rib jig, cement those stubs in place on your jig and then build the ribs around the spar stubs. That way, the rib openings will be sized the same as your spars are, whatever thickness they end up being "just a shade thinner" than a full 1". You can cover the stubs with clear packing tape so the ribs and adhesive don't stick to them when you're gluing up the ribs.

-Oscar
builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Re: Spar thickness

Post by builderwannabe »

Copy all, thanks. I am a hand tool wood worker so in my mind i was seeing myself doing lots of hand planing to get the ribs onto the spars.
at7000ft
Posts: 33
Joined: Mon Mar 06, 2017 3:06 pm

Re: Spar thickness

Post by at7000ft »

I used 3/4 spruce for my spars, which I think is specified in the three piece wing plans (no routing needed). 160 hours and haven't fallen out of the sky yet.

Rick H
builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Re: Spar thickness

Post by builderwannabe »

Thanks Rick, I need some motivation to get back to the basement and do some more work on the plane and getting some hours on the airframe will do it.
at7000ft
Posts: 33
Joined: Mon Mar 06, 2017 3:06 pm

Re: Spar thickness

Post by at7000ft »

A couple pictures of my 3/4" spars, notice that I epoxied 1/8" ply pieces to spar where the ribs attached so the ribs were built to plans with the 1" openings to slide on the front and rear spars.

Image

Image

RH
builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Re: Spar thickness

Post by builderwannabe »

Rick, unable to see pics, could be on my end though, the older i get the less i know(and wanna know) about electronics and computers, explains my choice in experimental aircraft.

Sean
builderwannabe
Posts: 21
Joined: Mon May 13, 2019 8:05 pm

Re: Spar thickness

Post by builderwannabe »

Thanks for the pics Rick, it really helps me to see how others have solved things.
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