Advice Requested; Heavy Balsa

[Sendhendrix]

I’m beginning a scratch build of Fred Reese’s “Golden Oldie.” I just finished stripping spar stock (1/4x1” spars) from a 3” sheet that weighed 5 ounces. According to a density calculator I found online, that’s 20lbs per cubic foot?? This sheet has been hanging around in my balsa stores for a very long time, (probably because I could tell it was ridiculously heavy) and it has a brother that weighs nearly as much that I would be using for the other wing. Now I’m having serious reservations about actually using this stuff because of how heavy it is, but this wing is the old-fashioned deep spar type design with virtually no sheeting. I’ve already cut and slotted the ribs, so it’s too late to redesign for an I-beam spar with shear webs. Advertised flying weight for this plane is 5.5 pounds. By my math, I’ll have half a pound of balsa in wing spars alone if I proceed.

I do have a few other sheets of 1/4” wood in my shrinking stash that are more in the 10 lbs/cubic foot range. Should I dig into that, and pretend this other stuff never existed? Or should I proceed in the blissful ignorance of my former non-scale-owning self?

My other question is, does anybody want me to document this build and post it? I’ve never done a build thread, and I don’t think I’d be impressing anyone necessarily, but hopefully there would be some discussion that could benefit me and others.

Thanks to anyone who responds.

 

[speedbirdted]

20 lb balsa is absolutely iron heavy. I usually shy away from using over about 10-12 lb balsa except for when the extra durability or weight is needed - this is generally considered about average weight. Usually this is good enough on tensile strength for most applications. For a wing design like the Golden Oldie has, it will probably work fine. The covering does take some load, but the spars exist for a reason.

Balsa sucks at handling a bending load, but this is because very thin pieces are effectively like having a very narrow distance between the top and bottom spar in a wing, which as you probably know can result in a wing with poor stiffness. The Golden Oldie has a solid spar which is nearly the entire wing chord; effectively what this is is basically a set of two spars with shear webbing, except the shear webbing is now integral to the spar itself.

And yes, post a build thread!

 

[Tench745]

Build threads are always appreciated.
My dad has a saying; it is not a new saying. "Do it right the first time or make time to do it over."

 

[Sendhendrix]

I ended up using much lighter balsa. After considering Speedbirdted’s description of the thick spar being more akin to the I-beam built-up style that I’d prefer to see, and noticing the thick leading and trailing edge, and realizing that the biplane wings will function as an assembly once they are mounted with struts and cabanes, I realized it was worthwhile to bequeath unto this bird some of my choicest stock. After all, this is supposed to be a high-drag, slow flying, lightly loaded affair, and I’d like to power it with my old Saito .45 Mk II, which is not known to be a screamer.

I’m not sure what I’m going to end up using this rock hard stuff for, but it’s all in the crap box now.

As far as a build thread; I have been taking pictures and notes, and will drop the first installment in a new thread once I’m far enough along to be certain the project won’t die. I’d like to have the plane completed by January 1, 2021.

A strange thing has occurred. I tend to let things slide in the privacy of my workshop that would horrify other builders, comforting myself with the knowledge that the finished product will perform and crash as adequately as any work of fine art. But since I plan to subject my work to the scrutiny of anyone who cares to see, I’m actually taking some pains to make a better account of myself. So that alone will make a build thread more worthwhile, for me, anyway.

 

[speedbirdted]

Heavy balsa has its uses! I've actually been leaning more towards using hard balsa in place of ply in some places where it's specified. I find balsa can be cut easier without splintering as you can cut with the grain at all times, plus there tend to be far fewer imperfections in balsa versus ply, such as knots or delaminated pieces. You can get the exact same strength along with saving a bit of weight if you take some time to rethink the installation and gusset accordingly.

A Saito 45 will fly it fine. From the article on Outerzone this was designed with early 80's 40 size 4-cycles in mind. I have seen one of these with an Enya 53 which is not really much of a powerhouse either and it seemed to have plenty of power to it. The guy had actually originally mounted a Hirtenberger VT49, which has about the power of a 25 2-cycle, and it seemed happy with it. (Though don't do that - the reason he changed it out is because it couldn't idle low enough to land with power on!)

 

[rockyboy]

Yes please on the build thread! And hang onto that heavy stuff - that kind of material is great when you are putting screws into balsa (servo mounts / firewalls / control horns). Probably don't want to use big pieces of it, but it can be handy!

And another vote yes on that build thread!