Stringer wall thickness

[Zzz]

Any opinion on the stringer tubing wall thickness? How much rigidity is really gained from the .032 to the .050? How much weight?

[Mark Goldberg]

Certainly thicker stringers add weight. The benefit is less chance the shrinking fabric will be stronger than your stringers. I have seen fabric shrunk to where it deformed structure. The other scenario is at an airshow when some BIG SOB leans against the side of your fuselage and bends your stringer. Bob Barrows likes the stronger stringer material. But on my BH I have wood and thin bent over (not extruded) aluminum stringers and they have held up OK. Mark

[Battson]

When you pick up the bundle of stringers in the kit - yes they feel HEAVY...
The heavier material is still quite flexible with the long lengths involved, but they are important too, I would be worried about them getting bent by some careless ramp jockey, the fabric shrink, or a branch flick-up on a backcountry strip - if I had used a lighter material - the 0.050" wall is heavy duty.

Edit - I did a back of the envelope calculation, there seems to be about 4 lbs extra weight in the heavier 0.050" stringers. Seems a small price to pay for rugged durability. I would tent to think Bob has a good reason if he of all people recommends a heavy solution

[Glenn Patterson]

We used the Avipro stringer material in BH727. The stringers make a good solid structure for the fabric with nice lines. We will operate on skis and sometimes a plane has to be muscled around to break it free. If someone accidentally pushes against the fuselage when lifting the tail then it should not harm it.
I saw a set of photos with the wood stringers inside a BH that snaked about & it may have been the humidity. Up to that point I thought wood was easy but the photos set me looking for a different material. May be it is an engineering mindset that I like straight clean lines. Aluminum is not affected by humidity. The extruded rectangular section is a lot sturdier than the aluminum window screen frame that is used in other models of kitplanes & is competitive. I looked at Steen Aero and other sources of formed sheet metal stringers before settling on the extruded aluminum.
Bob Barrows put these stringers on his drawings and to say he is weight conscious is an understatement as no one builds them any lighter.
Glenn

[Glenn Patterson]

One quick check on weight would be to quickly add up the lengths of stringer used. The left side middle ends at the window and the RS ends at the baggage doors. I think the rigidity is worth it.
Glenn

[Zzz]

Thanks for the replies everyone.