Why isn't the sheeting on the top of the fuse between F3 and F4 applied cross-grain?

I just recieved a Chrysalis and have been reviewing the construction instructions and had a question. Why isn't the sheeting on the top of the fuse between F3 and F4 applied cross-grain? I can understand that it might be easier for a beginner to apply that way, but the increase in strength with no weight penalty seems to run against the grain of your "light is right" philosophy. I know you guys are very careful in your designs and you may have a specific structural reason for doing it that way, so I figured I'd ask before doing this.

It's because in this case it's actually stronger to apply it with the grain lengthwise. The idea that cross grain is stronger isn't necessarily correct.

One thing that cross grain would help with is crack propagation. It would crack easier, but the cracks couldn't go as far before something stopped them. Another way to accomplish the same thing without the strength loss of cross grain is to put fiberglass straps around the tail boom every 4-6 inches. 3/4 oz. glass is fine for this, but the 1" Sig brand fiberglass tape is easier to use, and doesn't have too much of a weight penalty. If you plan to stall a lot on landing flair while still 5' high, you might want to add these. We've had a few reports of lengthwise fuselage cracks (usually from this particular scenario), but it's usually isolated cases. Most folks don't see this problem, but a few folks see repeat occurances. This is usually a dead giveaway that there's a flying technique problem with those individuals. The glass straps will help in this case, but the best solution is to develop better flying technique.

The stock fuselage is very strong without any mods, in my experience as tough or tougher than other typical balsa HLG'S. I've spiked mine in vertically from 40' into hard sod (Rx failure) with nothing more than a few small cracks in the battery compartment cover, just in front of the hatch. BTW, this is also a good place for a fiberglass strap, and on the next plans revision I plan to add it as standard.

On wing spar shear webs, one of the primary jobs of the webs is to prevent the spar caps from buckling. This is the main reason for installing them with the grain vertical. There are shear loads in both the spanwise and thickness directions, so you can make a valid argument for either direction if you ignore the buckling issue.

BTW, the web page with the Q&A section is the most useful resource for your models. I really appriecate the effort to have that on there as a place to get the most up to date info/construction tips.

Thanks, it's been a fun endeavor. It takes a lot of our time, but it also helps us find potential improvements, and helps us see our designs through the eyes of our customers. It's been a great learning exercize for everyone involved. I learned a long time ago that the best way to find out if you really understand something is to try to explain it to someone else!

Don Stackhouse @ DJ Aerotech