My SPA planes all fly on an OS .91 FS, and required about 1/2 to 3/4 ounce on the wingtip.

Now that I have a digital scale, (like yours), and have become aware of the importance of building light, I'm just trying to make use of it to distribute the weight where I want it. In your case with that 120 2-stroke engine, performance is not a concern, but I use my planes in SPA competition where that fixed engine increases the importance of light weight and best use of the wood.

I used to think that people who weighed each sheet of wood were fanatical, bordeing on "nuts". Then I came to like the King Altair for SPA and quickly realized that EVERY OUNCE MATTERS because you are limited in engine output, and that if your competition has a lighter plane on the same engine as you, he is going to have a vertical advantage. I know that performance in wind might aid a larger or heavier plane in some cases, but what I just stated is a general rule of thumb.

This wood is going to be part of the weight of the ship anyway, so why not distribute it in such a way in order to reduce the need for additional lateral balancing weight...at least some? It's not an "exact science"; there probably are other factors that enter in, but it seems logical to me that DISTRIBUTING THE WEIGHT properly is a factor in reducing total weight.

There is another reason I try to do this besides trying to get use out of the scale, and the fun of weighing balsa, (and it IS kind-of fun to see the difference in weights between identical-looking pieces of wood). I was told by pattern great Ron Chidgey that it matters WHERE the weight is distributed, and not just the balance. I'm told that these planes roll better if the weight is more toward the center, so when you put a chunk of lead on the wing tip, it adversely affects the rolling characteristics even though the plane is "laterally balanced". Admittedly, this is the "world of perfection" for the aerobatics elite trying to get the perfectly balanced and set-up plane, and it may not matter as much for less accomplished pilots...still why not do things in such a way as to give the best flying plane that you can have regardless?

If the weight, (that is going to be there anyway), is distributed so that the least amount of additional weight is needed, then we should probably try to do it. That's why it is better to shift the battery pack than simply add more weight...to reduce total weight to a minumum, and to distribute that weight the best possible way.

The first plane I did this on was the Simla, and I wound up actually having to add a SMALL amount of weight to the right wing, (the same side the engine leans toward). In the case of the Simla prototype, I put ALL of the heavier wood on the left side. I may not do that on my King Altair wing I'm currently building, (I just ordered the contst balsa yesterday), but I will put MORE of the heavier stuff on the left wing.

Just my take on all this...waiting for a reply from Ed to get his take.

Duane