Building light vs. durability & Wing Loading vs. Stability

[payne9999]

I am building some scale civilian aircraft in the 50-54" range. They are quite light by design weighing in at 17-20 oz. They are stick construction like the typical Comet balsa models of days gone by but much better designed and thought out.

The plans are masterfully designed but are so light that I am breaking a lot of stringers and other fuselage and tail parts just handling it during the build. No disrespect intended to the designer because his work is incredible. However, it occurred to me that if the plane is that delicate now how will it ever survive one of my landings. I typically land quite nicely but every 8-10 landings is kind of ugly and it is often due to having unpredictable winds, cross wind landings or just dumb thumbs.

After building the fuse and stab, elevator fin and rudder I wondered: Should I rebuild and make the more critical structural pieces from light Engelman spruce (in this case 1/8" square and 1/16X1/8" bracing) or would that make the weight a critical issue?

The planes will be covered in Doculam with a light coating of acrylic or thinned latex.

Also, I have a wood and Monokote covered ARF that is the same size that is about 36oz. that flies nice and is reasonable on wing loading although I really pay when it comes to flight times. I am comparing it to my Mountain Models L-4 that is 17-19 oz. The L-4 is quite bouncy and less stable especially in a light breeze but gets incredible flight times.

So, I am wondering about the trade offs between weight and strength as well as weight and stability/wind penetration.

Tonight I started building a second fuse with some light Engelman spruce to check the difference in actual weight. I know it will be stronger and the Titebond glue joints will be a little better that brittle CA.

Also, I am ordering a pack of Paulownia wood. I will re-saw it into model size strips with a thin kerf table saw blade. Paulownia appears to have about twice the strength to weight ratio of balsa and is only 15-25% heavier.

I am curious about other builders out there and your trade-offs with weight vs. strength and material choices. I have built hundreds of balsa/tissue models and many glow planes but these ultra light electric models are fairly new to me.

Thanks,

Dave