I would like to add two things in response to Jake's comments. I have found that the best place to buy "hard" balsa of densities over 15# is at craft stores such as Michaels and Hobby Lobby. And, yes, I do bring my scale to my local Hobby Lobby. The local hobby shop has a good selection of very good sheet balsa but not much of the hard stuff. Because of the density and strength variations throughout a sheet, one needs to check each individual cut piece before using it for a dummy motor, just as one checks out the weight and stiffness of each part for the airplane itself.
Basswood has good stiffness and tensile strength properties as well as excellent uniformity and a fine grain structure. However, the inital yeild strength is much less than the ultimate tensile strength. This means that basswood is "soft" in that it takes a permanent set when moderately bent or twisted rather than springing back completely. This is good in that one does not see sudden (brittle-like) breaking when there are severe strains. One gets some warning before breakage, unlike some balsa. So, to each her/his own when choosing a dummy motor material.
Leo
--- In Indoor_Construction_at_yahoogroups.com, Jake Palmer <82.jake@...> wrote:
>
> Balsa can be strong enough, but it's usually not consistent. I have sheets
> and sticks with huge variations in strength and density. Basswood on the
> other hand tends to be very consistent. It's also not easy to find 15-20#
> wood in a hobby shop unless you bring a scale and a calculator. I find it
> easier to grab a few 3/32 square basswood strips without having to bother
> with calculating density.
>
> That said, if you have good 15# balsa it will work fine.
>
> On Mon, Jul 16, 2012 at 3:33 PM, Leo Pilachowski <leop_at_...> wrote:
>
> > **
> >
> >
> > I use balsa dummy motor sticks for all of my indoor planes, including
> > Science Olympiad and LPP which get wound to over 1 oz-in of torque. While
> > 5# balsa is too weak, balsa above 15# is just fine although I do use 20#+
> > balsa for the LPP dummy sticks. I use 1/8" for the SO planes but everything
> > else now 3/32". This is plenty strong enough in my experience. Balsa is an
> > amazing material. For a given density, it has the best Young's modulus and
> > strength of just about all the available woods, including Sitka Spruce.
> >
> > Leo
> >
> >
> > --- In Indoor_Construction_at_yahoogroups.com, "John Kagan" <john_kagan@>
> > wrote:
> > >
> > > --- In Indoor_Construction_at_yahoogroups.com, Jake Palmer <82.jake@>
> > wrote:
> > > >
> > > > I'm not John, but I'm also in the process of building new partial
> > sticks.
> > > > I had a balsa stick break during unwinding at the Kibbie Dome this
> > year so
> > > > my new sticks are 3/32 square basswood with .015 wire. They're much
> > more
> > > > durable and require virtually no clay.
> > >
> > > ^^ this
> > >
> > > Balsa is too weak
> > >
> >
> >
> >
>
Received on Mon Jul 16 2012 - 20:23:34 CEST
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:47 CET