Another thing to keep in mind is to make sure that the same edge of the material is in the same plane as the other stringers.  A sheet of "A" grain balsa has "C" grain on the thin edge - different bending characteristics.

One way to make 'banana' fuselages less likely is to strip your stringers/longerons from a sheet of balsa and keep the ends identified. Use the same length and orientation from separate strips that are adjoining. It is more likely that they have the same density and bending characteristics this way.
ian

pb_guy wrote on Oct 15^th, 2018 at 11:10pm:


I've been trying to put my thoughts together on this question and I think Ian captured a good bit of them in his post above.  The T-28 has the former-on-box fuselage construction, and I really like the way it came out.  The box lets you keep the fuselage interior open all the way to the corners, which gives room for lots of wound-up rubber from a long motor without getting things hung up on structure.  The former segments can all have the grain long-wise, which makes the fuselage much more crush-resistant (and as Ian said I think you can use much thinner and lighter wood for the formers).  I also think the combination of the inner box and outer stringers makes each quadrant of the fuselage something of a box beam, more rigid than curved stringers over half-shell formers.

However, the box fuselage requires more thought during design and more steps during construction.  The designer and builder have to be very careful to get the box accurately sized or the formers won't come together properly at the corners, and if the builder likes to use glue liberally it may come out heavier than a half-shell fuselage because you've got more and longer glue joints.

I've got a couple of aircraft in the back of my mind for design-build candidates, and based on how the T-28 went together I'm leaning towards box-former construction for them.  That said, there are a lot of plans and kits on my bucket list that use half-shell construction...

Mike

There is nothing that prevents building a basic box structure and then adding formers to create the body shape. That is the way a lot of Joe Ott's models were done - using the 'Ott-O-Matic' formers.
The main advantage of the keel and former method is that it builds the fuselage in one step instead of two.
One advantage of the box structure is that it can be lighter if you use lighter wood for the formers, since all the strength is built into the box. With the 'keel' method, you seem to use heavier formers than are really necessary for strength to keep from breaking them while adding stringers.
YMMV
ian

Is there an advantage (structural or otherwise) to using the box building method rather than a keel/former method?