Graf Project Photo (WIP)

[JoeVanCleave]

Folks;

Here is an earlier shot of the front-half of my Graf project, taken with my older, very lo-res Jam Cam. Front half hull length is 72", max diameter 16". The framework is constructed of 1/16"x1/8" balsa longitudinals, and 1/16" square balsa for ring members, and all panels and mainrings are braced with thin polyester/cotton thread as tension members. All joints are assembled using CA glue with accelerator.

In this shot, the front nose is being worked on, after a latex balloon in the fore-most gas bay exploded during inflation and the shock wave broke several balsa pieces.

The mid-ship portion of this hull section (towards the rear) are covered in ultrafilm in this shot; since then I've also covered another section with condensor tissue. I'll get some new photos soon, including construction details.

The intent of this model project is to build a model rigid airship, using the general principles of the Zeppelin design (i.e. compartmented gas cells, radially braced mainrings, diagonal bracing of side panels, outer covering seperate from internal gas cells, etc), that will fly, indoors, under RC. Although not to scale, it's intended to illustrate the principles used in the design and construction of the big rigids.

~Joe

[Stephen Cunha]

You have a very impressive piece of work here. One question I have about the structure, I don?t see signs of the keel; will the longitudinal section be strong enough to prevent the ship from folding?

[toddk]

I should think that a braced frame should be more than adequate. I know that Barnes Wallis omitted it entirely in either the R100 or the R80.

[JoeVanCleave]

At the scale of size of the model, and considering the minuscule lift forces involved, the model is more rigid than it needs to be, so a keel is unnecessary.

If I had true indoor ultralight model building experience, perhaps this model would be much lighter - and more fragile - hence necessitating a keel. As it is, it's strong enough to handle without it breaking.

Attached are several more pictures. The first is a closeup of the side of the hull, where you can see the section covered in condensor tissue. The second shot is a side view of the nose section, which has yet to be covered. I have a small cone, carved from balsa, with a tiny wire loop on the end, as the nose anchor cone. In practice, I probably will not anchor the model from a mast via the nose; rather, I'll distribute the anchoring forces along the hull using several anchor threads.

The third picture is an axial view, looking from amidships forward. This shot reminds me of some old photos I've seen of the Graf during construction. You'll note that this design uses 16-sided rings. The Zeppelins used odd-number sided rings, allowing the bottom facet to be used as the keel, supported from the upper vertices by suspension wires. Since there's no real crew in this model needing access to all parts of the ship, and considering the minuscule weight of any potential control car, its simply not needed. Using even number sided rings - especially 16-sided - makes design and construction much easier.

The fourth shot is the model sitting on the hangar box. You can see the radial bracing wires of the mid-ships mainring.

My Dad has been kind enough to let me use portions of his garage to build the workbench, and store the hangar box.

The next part of this project is to start a model 18" in diameter, the largest that will allow two hull sections to fit inside the hangar box nested in a diagonal orientation. Each hull section half will be one large gas cell, so I will have to dispense with the radially braced mainring design and go with self-braced ring corners. I will not use the "deep ring" concept of the ZRS-3 & 4; for model purposes, it's simply overkill regarding framework weight, and getting the triangular girders to fit together accurately is a model-builder's headache. I've already tested several self-braced corner designs, where each vertice of the transverse ring has a strut of thin balsa triangulating each corner. Destructive tests show that these self-braced corners are plenty strong enough: the balsa pieces fail before the corner does. The main issue is really rigidity of the rings during assembly; the radially braced rings proved to be quite rigid.

Assembly will involve building a horizontal assembly fixture, where each ring section will be supported in space along the longitudinal axis, allowing the longitudinal girders to be attached.

[Stephen Cunha]

Toddk

Did you really mean R80? Actually she had a keel. Wallace’s big contribution here was the improved aerodynamic shape over other British airships and the earlier German ships. You are right about R100; however R100 had massively built frames and a shape that resisted bending.

Mr. Van Cleave

You may be correct. Stress on your model my not require longitudinal bracing. Flying indoors will not create giant down drafts, thunder storms or gale force winds to contend with. I will be watching your posts intently and whishing you the best. Regards Stephen