Spars

[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.

[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!

[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

[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.

[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

[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

[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.

[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/

[astjp2]

Re: Spars

If your labor is free you still can't, spend the money and get an approved part.

Wag Aero has front and rear spars availiable in either spruce or douglas fir.By the pictures they are varnished,plates glued,and drilled.Fir spars are listed for 675.00 and spruce for750.00.Not my choice at this time as I think I can reproduce them myself considerbly less cost.

[woodmw]

Re: Spars

What is the source of "Taylorcraft News", i.e., who publishes it and how does one obtain a copy? Google doesn't seem to be able to find it.

[mike lutz]

Re: Spars

Wag Aero has front and rear spars availiable in either spruce or douglas fir.By the pictures they are varnished,plates glued,and drilled.Fir spars are listed for 675.00 and spruce for750.00.Not my choice at this time as I think I can reproduce them myself considerbly less cost.

[astjp2]

Re: Spars

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

Close (very close), but the Spruce actually has a better strength to weight ratio so you are actually better off from that perspective to use a full size spruce spar. From a COST perspective the Doug Fir is better since there is very LITTLE difference in strength to weight (a little, but not much, stronger AND heavier).

You CAN change the dimensions and design of the spar, BUT, the time and cost would be huge compared to the improvement in strength and weight. The proof that your spar is safe to the FAA would be a mess to do.

Real world, use a Spruce spar, or use a MUCH stronger, dimensionally the same Doug Fir one with the proper FAA paperwork done BEFORE you build the wing. The reference I sent can be used to calculate the total weight gain for Douglas Fir spars. Takes a little time, but not that hard. If someone can tell me the weight of a bare Spruce one a thumb nail estimate of the increase in weight pretty easy.
Hank

[Hank Jarrett]

Re: Spars

Close (very close), but the Spruce actually has a better strength to weight ratio so you are actually better off from that perspective to use a full size spruce spar. From a COST perspective the Doug Fir is better since there is very LITTLE difference in strength to weight (a little, but not much, stronger AND heavier).

You CAN change the dimensions and design of the spar, BUT, the time and cost would be huge compared to the improvement in strength and weight. The proof that your spar is safe to the FAA would be a mess to do.

Real world, use a Spruce spar, or use a MUCH stronger, dimensionally the same Doug Fir one with the proper FAA paperwork done BEFORE you build the wing. The reference I sent can be used to calculate the total weight gain for Douglas Fir spars. Takes a little time, but not that hard. If someone can tell me the weight of a bare Spruce one a thumb nail estimate of the increase in weight pretty easy.
Hank

[astjp2]

Re: Spars

You can substitute Doug Fir with spruce, it is referenced in some aeronautical bulletin that I have on wood structures. Its 15% stronger and 15% heavier but you are not allowed to change the size of the structure to reduce the weight to match a spruce one.... Tim

[mike lutz]

Re: Spars

another spar source is in the Taylorcraft News,vol.139 first quarter 2013 publication,page 10.It has a source listed as:,Precision AeroMarine.Their web site is--www.precisionam.net ----(WI) no phone or address listed.I know nothing about them,although I am sending a e-mail this coming week after I measure my front and rear spars.I have a 1939 bc-65 with factory float fittings welded on I am planning to restore soon.