Spar Dimensions

[Tom Eggert]

Does anyone have the exact dimensions for the BC12? I need to order spar stock for both wings and the two ailerons. My original spars seem to be 1/32th beyond standard (or common) sizes (21/32 and 25/32). If anyone has drawings I'd love to get a copy.

[Guest]

Re: Spar Dimensions

Hi Tom,

I don't think that you will ever find drawings.

When I made my spars for my bc12d I measured my spars and also an F21 spar.

After measuring and pondering I ordered these pieces;

4-7/16" x 5/8" x 196" + 1/32"/ -0" rear
5-15/16" x 3/4" x 196" + 1/32"/ -0" front

That was in 1992 finished it in '98 and been flying it since 1998.

I can't find my notes but I am sure that all I did was measure my old aileron spar and order another piece to match.

Dave

[Robert Lees]

Re: Spar Dimensions

Can't help you with the main spar drawings, but when I remanufactured my aileron spars on my BC12D (note the "D"), I used my old ones as pattern and compared them to the L2B drawing D-A8202, which states (to the best of my eyesight):

Length: 192 and 7/8 +/- 1/16

Height: 4 and 3/8 +1/32 -0

Thickness: 5/8 + 1/32 -0

Further, drawing D-A8251 describes the bevel (slope) of the upper aileron spar edge as 1/16 across the spar width, and the lower being 1/32

It does beg the question how in the USA owners are expected to repair broken items if either:

a) new parts are not available from the TC holder or suitable FAA-PMA source, or
b) drawings are not available from the TC holder.

How does the FAA expect owners to comply with current FAA regulations?

[Mark Julicher]

Re: Spar Dimensions

How does the FAA expect owners to comply with current FAA regulations?

The current motto is "Nothing happens until something happens." That may be interpreted as; We are not trying to do prevention style safety, but rather we will hammer anyone that appears to have transgressed if we should find anything suspicious during an investigation.

So it is more like putting an ambulance at the bottom of the cliff instead of a guard rail at the top.

Y'all be careful out there.

[Guest]

Re: Spar Dimensions

Here is a snippit from AC43.13-1B chapter 1;

1-41. SPAR REPLACEMENT. Replacement
of spars is a major repair. Spars may be
replaced by new parts made by the manufacturer
or the holder of a Parts Manufacturer Approval
(PMA) for that part. Owner-produced
spars may be installed providing they are made
from a manufacturer-approved drawing. Also,
a spar may be made by reference to an existing
spar providing sufficient evidence is presented
to verify that the existing spar is an original
part, and that all materials and dimensions can
be determined. The dimensions and type of
wood used are critical to the structural strength
of the aircraft. Care should be taken that any
replacement spars accurately match the manufacturer’s
original design.



Seems to me that you do not need a drawing and have no issues replacing a spar by duplication.

Dave

[N96337]

Re: Spar Dimensions

Drude said it perfectly. It's not a huge deal....quit trying to make it one. There's provisions set in place already, and have been for many many years, to take care of this. It takes some knowledge of the FAR's (which any mechanic should have) and a bit of "reverse" engineering. It would be great if we could access all these "drawings" that we're supposed to be able to, but that's not going to happen anytime soon. Maybe a table of dimensions of this sort could be placed in a "sticky" on the site???
John

[Tom Eggert]

Re: Spar Dimensions

Thanks guys! All I needed was confirmation of dimensions; I have the original spars in reasonably good condition for a pattern.
New PMA'd spars are available from Wag Aero, but I would prefer Sitka Spruce and they only offer Douglas Fir. And before anybody jumps on the 'cost' bandwagon, I think the price from Wag Aero is very reasonable considering the paperwork required to get the PMA approval. My only desire is to use spruce, and as pointed out in on of the posts, it's not that difficult to comply with the FAA - you just have to be patient and understand the rules.

[woodmw]

Re: Spar Dimensions

I'll show my ignorance on the subject by asking:

When I dismantle my wings for rebuild, how do I determine if the spars are indeed original?

[Robert Lees]

Re: Spar Dimensions

You should find a little aluminium data plate with the serial number (4 digits) nailed somewhere (the serial number may well not correspond to that of the fuselage).

Also (at least on the spars I've seen) there is an inked inspection stamp about 2 inches square under the varnish.

Rob

[Guest]

Re: Spar Dimensions

I'll show my ignorance on the subject by asking:

When I dismantle my wings for rebuild, how do I determine if the spars are indeed original?

Hi Mike,

Well...

What Rob said plus your aircraft records should indicate a change or replacement.

BTW I don't think that all the spars have serial number plates.

Dave

[N96337]

Re: Spar Dimensions

Mine didn't have the serial number plate either...but they were signed in pencil, under the varnish, by 2 guys from Taylorcraft on June 9, 1946....and a friend of mine that was working at Taylorcraft at the time my plane was made, knew them both!
John