Spars

[Bird]

Now I know I should use spruce but fir is being pushed now also. Yes I understand it is a little heavier and I might get a splinter but the FAA says it's cool so looking for your thoughts

[cvavon]

Re: Spars

Bird why don't you drive down to Atlanta to AC spruce and get spruce blanks and plywood for doubler 4 years ago that cost me $900.00 you are closer then i am to spruce 5 hr trip one way and they will let you pick out your wood from stack the ones we got were grate

[Bird]

Re: Spars

That is why I am asking around, I have just started to reasearch and am only seeing prices of just over 2 grand for a set at the cheapest.

[cvavon]

Re: Spars

The $900.00 was the 4 slabs of wood ply wood for doublers spar varnish rib nails and 2 qts of primer now it was 4 or 5 years ago but if the price doubled thats 1800 less then 2000

[otrcman]

Re: Spars

Now I know I should use spruce but fir is being pushed now also. Yes I understand it is a little heavier and I might get a splinter but the FAA says it's cool so looking for your thoughts

Could you provide some reference in which the FAA is pushing the use of fir ? This would not be consistent with the published guidance in the FAR's or in advisory circular AC 43.13.

In your FAR/AIM book you will find paragraph 43.13(a), which states in part, "Each person preforming maintenance, alteration, or preventative maintenance on an aircraft, engine, propellor or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual...." So, step one in any repair is to follow the manufacturers type design data.

What if there is no data available from the manufacturer? FAA provided for this possibility with the publication of advisory circular AC 43.13. The front page of AC 43.13 (para 1. PURPOSE.) states, "This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when when there are no manufacturer or maintenance instructions."

AC 43.13 does contain a table of wood properties, including those of spruce and fir. But that does not imply an open license to make such substitutions.

The FAR's tell us to follow the manufacturer's data. In the case of Taylorcraft spar replacement, we do have manufacturer's data. None of this says that you CAN'T use fir for a spar, but you would need a valid reason for doing so and would have to receive approval for the design change via an approval from your FSDO.

Dick

[crispy critter]

Re: Spars

I need material for one rear spar blank.....around $200ish for the wood and nearly twice that for shipping!

[cvavon]

Re: Spars

Kevin get external load permit fly to spruce with dad's 170 and hall it back to ky

[Hank Jarrett]

Re: Spars

Check out NACA report No. 354. http://ntrs.nasa.gov/archive/nasa/ca...1993091423.pdf

To make a long story short,
Spruce is lighter per cubic foot than Doug Fir (DF)
DF is STRONGER per cubic foot than Spruce
DF is HEAVIER than Spruce
DF is LESS EXPENSIVE than Spruce by volume, strength and weight

None of this matters. What matters is you can make a DF spar the same dimensions as a Spruce spar and it will be much stronger (and heavier).

You can REDUCE the size of a DF spar so that it has the same strength as Spruce and it will only be a LITTLE heavier, but the ribs and other parts won't fit on it.

You can SELECTIVELY shape a DF spar so that it fits in the same space as a Spruce spar and it will be the SAME STRENGTH AND WEIGHT, but you better be ready for the FAA with a good analysis showing how you removed the wood in the right places. This is possible because COST drove Taylorcraft (and almost everyone else building light planes) to use PLANKS for spars. If you MILL the spar to an "I" beam shape by removing wood from the web area you don't loose any significant strength, but reduce the weight A LOT. The machining costs would be outrageous for a factory without CNC milling machines, but with modern tools it might be worth it so you could use much less expensive materials.

OH BOY! A trade study! Who wants to finance it?

Hank

[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.

[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

[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

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

[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.

[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.

[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.