First, avoid buying spar 'sticks'. Cut spars from sheet stock.
Most spars will need to be spliced (butt or scarf) at least at the center because balsa is so variable in density, strength, and stiffness. Splicing two adjacent spars cut from the same sheet and butting at the same point will yield matched spars (think of an archery bow). That's one reason why you have 12" hobby wood from an indoor supplier.
Be sure to follow this procedure when making prop spars--even doing deflection tests and match spars with the same deflection. They resist a lot of force.
To know which spars are matched you need to mark the sheet being cut. When cutting spar stock from a sheet, first *lightly* mark an end face surface with a diagonal line using a felt-tipped pen to avoid denting the wood. You can then match up the spars as they were cut.
You can get very good wood, if not better than online specialties, at a hobby store or one catering to multiple interests. Indoor modelers rarely use wood over 7# density. Most model hobby stores cater to outdoor modelers who rarely want anything under 6#. You can usually find balsa in the 5# to 7# range. But you have to hunt for it.
Note: most indoorist's refer to density. = pounds per cubic foot = 3.81 x Weight (grams) divided by volume. If you use ounces, change 3.81 to 108. It's a good idea to get used to knowing density of each sheet of stock.
It's probably better to buy from a source specializing in indoor wood until you want to venture out and look in hobby supplies. Few online sources sell light (4# - 6#) contest balsa.
When I shop for balsa I look for the straightest grain, lack of warp, and lack of checks (hairline fractures), and as uniform a texture or color over the sheet as possible. If I can get a 12" to half a 36" sheet with these characteristics, it's stacked with those I set aside from a bundle of matched size wood that is the least heavy. Then pick out the least heavy with the best desirable characteristics from that set-aside stack.
Unless you have a postal scale, or the shop has a weighing scale, AND know weight range for the density of each sheet size, you will have a collection of wood too heavy for indoor use.
hbm
--- In Indoor_Construction_at_yahoogroups.com, "Ren" <nmonllor@...> wrote:
>
> Hello again,
> I went along and glued the ribs to the front and rear center sections of the wing using the ambroid/acetone/DOP mixture.
> Is it the norm to get 12" spar sticks from IMS and the wing calling for more than 18" wings?? It just seems odd to me...
>
> I weighed the sticks on a digital scale I purchased for the hobby and the sticks that I have here at home (old stock) are heavier by about .10g, so I opted not to use them.
>
> Who else beside IMS is there to purchase indoor balsa from , say in 20" to 36" lengths?
>
> Thank you,
> Ren
>
Received on Sun Jan 17 2010 - 10:00:47 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:45 CET