Building a Biplane
Fri, 01 Dec 2017
A Minor Setback
I have been slowly but surely building up my stack of ribs in the
Charger project. I'm up to rib #33 (out of 44), with each taking about
2 hours, plus about 6 hours to produce all the parts to support every
15 or so ribs. So, slow but steady progress.
The wings are built up of ribs, some metal bits and pieces, and
spars. These are the long pieces of solid wood that
stretch out from the fuselage, and provide the foundation of the wings.
The plans call for aircraft-grade Sitka Spruce, which basically means
wood with straight, tightly-packed grain and a minimum of flaws and
defects. The spars are a bit under 12' and a bit under 11' long,
depending on whether you're talking about the top or bottom wing.
In June of this year, I placed an order for my spars with Wicks
Aircraft Supply. I knew they would take months to actually ship, so I
figured that by the time they shipped, I'd probably have all my ribs
done, and everything would move along hunkey-dorey.
We have encountered a small snag in that plan.
Wicks called today and
said that, effectively, they can't get high enough quality wood any
more, and they're quitting the Spruce spar business. My order is
canceled, so sorry, have a nice day. They were very kind about it, and
I understand, but this still leaves me in a bit of a lurch. I still
Fortunately, I have some alternatives:
- Laminated Spruce: just because Wicks can't find any 12' lengths
of aircraft-quality Spruce doesn't mean there's no aircraft-quality
Spruce to be had. It just means that finding it in 12' lengths is no
longer possible. Shorter, smaller pieces of Spruce carefully laminated
with high quality glue can make up a spar, and there are distinct
advantages. Laminated wood is stronger (see plywood vs. a plank of the
same thickness), fails more gracefully, and is not prone to warping.
Because it's made up of a lot of small pieces of wood, you get to
preview the wood for defects that would be hidden in larger pieces. I
can do the lamination myself, which sounds both enjoyable and
inexpensive. Steen Aero Lab sells laminated spars, and I have a
request in to them for a quote.
- Douglas Fir: Fir is about 20% stronger than Spruce, and is
about 20% heavier (rough numbers from memory, don't hold me to them).
I can't change the shape of my spars, that ship has already sailed
unless I want to remake all 33 of the ribs and re-calculate a bunch of
other stuff. So, I'd add 20% to the weight of the spars, which would
amount to probably 5-10 lbs at a guess. Douglas Fir is much easier to
find in plain old lumberyards, so I'd be looking at cheaper lumber,
- Aircraft Spruce still sells spars: the cost is about the same
as Wicks, and at least on the phone when I asked, there was no
suggestion that they would have trouble finding the wood I was asking
for. I have a request for a quote in to ACS to see how long their
leadtime would be, and what shipping would cost.
So I've got some options, but it's a bit disappointing that my
well-planned order fell apart like this, putting me further behind on
my construction plans than I already was. We'll see what Steen and
Aircraft Spruce have to say, and that may determine the way forward.
Posted at 15:21
Building a Biplane