tapered wing spars

Since a lot of us are asking questions about why we do or don't do certain things in building our planes thought I'd throw one out and then duck.
Most real aircraft have tapered spars from the center to tip of the wings. This works because the forces decrease along the semi-span of the wing and saves weight. Since we use extra weight in one wing tip, and basically hang the plane on the other tip, and the speed along the span isn't constant this doesn't seem applicable for our planes.
I'm not aware of anyone using tapered spars. Do any of you know if this has been done? If it hasn't been done what reasons, other than the points I noted, are there for not doing it?

Red Reinhardt's "International Stunt Winner" had the entire D-box tapered, and yet had a constant chord wing. See photo, with builder/flier "Conrat", aka Mike Conner. It isn't done a lot, because it's more work, but light extremeties is ALWAYS good. Less weight in the wing means less tip weight, and lower total weight. IMO. Steve

Carl,

I am aware of the stresses place on wings during high "G" maneuvering, but don't use tapered spars. They add too much complexity to wing building. Instead, I typically use multiple spars. They vary in length with the main spars full length, medium spars from gear bay to gear bay and stub spars out to a rib or two beyond the fuselage to help with wing root bending moments and distribution of bellcrank loads into the wing structure. These are easier to apply than tapered spars but accomplish exactly the same purpose.

I taper combat plane spars.

Ares, Argus, Cobra and most other "I" beam wings have a tapered spar.
By tapered, I assume you mean higher at the root than at the tip.

Right about now would be a good time for someone to post a really neat, easy way to cut or plane a set of matching tapered spars. It's easy enough (in CompuFoil, at least) to plot the ribs with the spar slots decreasing in depth towards the tip (decreasing in width too if so desired!) The daunting task of making tapered spars has always kept me outta that design process!

Seems like I saw a TV documentary a while back about making bamboo fly rods that had some tricks but boy, did that process ever look laborious!

>Ares, Argus, Cobra and most other "I" beam wings have a
>tapered spar.
>By tapered, I assume you mean higher at the root than at the
>tip.

Nope..those Reinhardt spars are wider-chordwise at the root,
and taper towards the tip. My Combat models had over-under spars,
each of which tapered depthwise toward the tips.
Tony G

I can't understand why anyone would want to take time to taper spars. Many full size airplanes handle the load distribution problem by using laminated spars with more laminations at the root tapering to just one at the tip. This type of spar is readily adaptable to stunt ships. Just make deeper spar notches inboard to accommodate extra layers of spar stock.

Al, do you taper the laminations across rib bays to reduce stress risers?

On the drawings of full size spars that I've seen, there are more laminations so the % change in stress distribution at the end of each lamination is small and they can be cut square or at 45º.

No, the system is overstrength anyway. In any case I don't use laminated spars. As I said before I use multiple spars of different length.

Two things come to mind. On "D" tube wings and most "C" type wings it's the ribs that "taper" towards the tips. The spars are just not that heavy in our models. The only model that I can think of with an actual tapered main spar, a sheet spar, is the very pretty, small fast and one thousand rib plane called the "A Bomb". It came out in MAN in the late 50's. Lots and lots of ribs. On the other side of the sheet plan is the VETO. Neeto, that one.

Identical tapered pieces are a snap, if you have a table saw.

Take a look at any tapering jig for a table saw. Making single purpose ones out of scrap wood only takes a couple minutes. I just made one to make tapered back slats for an adirondak chair I built, worked perfectly.

To get taper in both dimensions, two passes are needed, perhaps two different jigs. A similiar sort of jig can be made and the stock can be passed through a thickness sander or planer, but generally much more time is required and many passes.

As I remember, Tom Morris' "New Millenium" wing uses a sheet balsa spar, which is easily tapered in depth toward the tips. I have never built a wing like the "Ares" with sliced ribs, but that is also an easy way to get thickness taper.