Spars

[M Towsley]

Re: Spars

Mike,

It used to be a newsletter you could purchase through Bruce Bixler of Alliance, Ohio.

Steve Krog took over the newsletter, he does the Cub one and maybe some others. Some folks like them, some say they are a re-hash of some of the Cub stuff. Some people on here get them. Try searching Steve's info.

Here is the link: http://taylorcraftclub.org/

[waltermrich]

Re: Spars

Sounds like Tim said it correctly using Douglas Fir is not a major alteration just a major repair, Of course spruce would be preferable but its cost is prohibitive, I know I can go to a local lumber supplier here and get klin dried Douglas Fir that meets the Mill specs for aircraft use, in the right lenghts for about $200 as opposed to Spruce for about $1000 for all spars, not to mention the hassel of getting it. I probabbly would be sold on Fir if I can find an aggreeable AP IA, that would be part of it. The EAA has a lot of good info on the use of wood in aircraft.

[astjp2]

Re: Spars

Sounds like Tim said it correctly using Douglas Fir is not a major alteration just a major repair, Of course spruce would be preferable but its cost is prohibitive, I know I can go to a local lumber supplier here and get klin dried Douglas Fir that meets the Mill specs for aircraft use, in the right lenghts for about $200 as opposed to Spruce for about $1000 for all spars, not to mention the hassel of getting it. I probabbly would be sold on Fir if I can find an aggreeable AP IA, that would be part of it. The EAA has a lot of good info on the use of wood in aircraft.

Do you know the #of grains per inch? What about the slope of the grain? Can you verify if the wood was quater sawn? I paid $145 for 2x6 rough doug fir, the grain was on the edge not on the face and I went through half a bunk to find 2 that had acceptable grain and slope. They made the best stringers but I made them 5/16" instead of 1/4"Tim

[Hank Jarrett]

Re: Spars

If you read what I said carefully we are saying the same thing. YOU, (an IA) can NOT change the design shape or cross section of the spar (you can change the material to another one that is approved, but you can't change the shape). It CAN be done (changing the dimensions), but it would have to go through a full engineering process and be approved. It could then be implemented as an STC. It would be a mess to do and in my opinion not worth it.
If you were the factory engineer it "might" be worth the trouble if there was a production run to spread the cost over, and with the price of aircraft spruce might be a good idea.
Hank

Hank, as an IA, I cannot change the spar dimension and I can substitute the doug fir for spruce as a direct replacement, its not a Major alteration, just a major repair. Tim

[waltermrich]

Re: Spars

The wood supplier I visited in Iowa city had many types of speciality woods. Kiln dried Douglas Fir was available to at about 10% moisture content with the gain slope of about 1inch in 15 or what ever the requirement was with no knots 4 quaters thick, which can be cut into 3/4 inch thick pieces and planed into the right thickness for spars, some work involved but it might make you glad you did it yourself if you know how to do it.

[astjp2]

Re: Spars

The wood supplier I visited in Iowa city had many types of speciality woods. Kiln dried Douglas Fir was available to at about 10% moisture content with the gain slope of about 1inch in 15 or what ever the requirement was with no knots 4 quaters thick, which can be cut into 3/4 inch thick pieces and planed into the right thickness for spars, some work involved but it might make you glad you did it yourself if you know how to do it.

You will need it to be 7/8" for the front spar, what was your grains per inch? Was it quarter sawn? Was the parallel grain on the face or the edge? Do you know if there are any pitch pockets? These are questions that need to be answered BEFORE you buy. Tim

[Hank Jarrett]

Re: Spars

Absolutely right! I saw a set of Cub spars that were cut from White Pine with the grain 90* out and were FULL of small knots! It was supposed to be just a re-cover job, but ended up being a full rebuild. There are some really STUPID people out there. Make sure your mechanic approves of the stock BEFORE you buy it! Also make sure you meet the moisture content requirement. Over or under moisture will change the strength of the wood. You also need to make sure the tree wasn't felled over another tree which would induce compression failures in the grain. They are VERY hard to detect and you might want to test the spar stock in bending prior to doing all the milling on it. Better to break it in a fixture than in the air. Aircraft grade spruce trees are held up by a crane and cut, then laid down to avoid damage. The wood isn't so expensive just because we are easy to take advantage of. It is EXPENSIVE to properly harvest aircraft grade wood.
Hank

Al Jenkins and Joe Mathias had those spars hanging from the ceiling for YEARS at Custom Antique Aeroplanes. Great conversation pieces!

[waltermrich]

Re: Spars

In the FAA published manual43.13-1B Aircraft Inspection, Repair& Alterations are the requirements for use in aircraft with a table od acceptable woods along with the specifics of the grain slope moisture content and other specs, I had the reqirements with me when I visited the wood store , The owner of the wood store was very aware of what my requirements were and assured me we would be able to find pieces in his supply of wood, I did not get the pieces off the rack bring them down and inspect them, as they were high on a shelf long and heavy and I was only inquiring but He assured me it would be available.