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Why are geodesic airframes no longer produced? Do they cost more than conventional structures? Are they not as strong as conventional structures? I assume it is insufficient cost benefit ratio, but how does that work out?

Vickers Wellington bombers under construction. Wellingtons under construction. Photo: Royal Air Force

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    $\begingroup$ Probably because the skin will take a lot of the load. especially in a pressurized craft $\endgroup$ – ratchet freak Jan 31 '15 at 21:34
  • $\begingroup$ A search for "isogrid & aircraft" shows interesting (including current) applications. Isogrid structures are considered for composite airframes too, but at the moment they are not cost-efficient compared to state-of-the art manufacturing concepts. $\endgroup$ – yankeekilo Feb 2 '15 at 7:27
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Geodesic (sometimes also spelled geodetic) designs were used in aviation as early as 1909, in the Schütte-Lanz SL1 airship. It had a wooden structure with fabric covering, and Professor Johann Schütte, the scientific head of this design, used the most efficient method conceivable. However, planning the shape of all structural members was an enormous amount of work, and stretching an existing ship by inserting a new section was almost impossible. For those reasons, the late Schütte-Lanz airships used aluminum frames with conventional design, just like Zeppelin did from the beginning. Diagonal wire bracing was used to take up shear loads.

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Geodesic frames are good in transferring both bending and shear loads. This is helpful when the aerodynamic covering is not stiff enough to contribute any shear stiffness, as in the case of fabric covering. However, when the skin is made from the same material as the frame, it can carry shear loads and a geodesic frame would not improve matters. Now it is better to carry longitudinal loads in longerons and shear in the skin.

But geodesic constructions are not dead. CAD makes the design effort manageable, and in some cases they give a weight advantage. Look at the casing of the EJ200 engine: It uses a geodesic reinforcement to make the casing light and strong and to prevent harmful vibrations. In the end, a jet engine casing is a big pressure vessel and needs to be strong, stiff and light.

Eurojet EJ200 for Eurofighter Typhoon photo by Julian Herzog, CC-BY

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The switch from internal frames to structural skin airframes -- called monocoque construction -- is fairly well covered in Wikipedia:

Early aircraft were constructed using internal frames, typically of wood or steel tubing, which were then covered (or skinned) with fabric3 such as irish linen or cotton. The skin added nothing to the structural strength of the airframe and was essentially dead weight beyond providing a smooth sealed surface. By thinking of the airframe as a whole, and not just the sum of its parts, it made sense to adopt a monocoque structure and it did not take long for various companies to adopt practices from the boat industry such as laminating thin strips of wood

That being said, we are still producing tube and fabric airplanes, particularly taildraggers based on classic designs, such as this American Champion Citabria and this Super Cub:

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    $\begingroup$ dat little Cubbie's got such a cute face! $\endgroup$ – FreeMan Nov 9 '15 at 17:20
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It started when the usual way of building was a steel-tube frame, with wooden formers attached to carry the skin. Early geodetic planes were still fabric covered, but the entire airframe structure was now in the skin, leaving the interior open for payload like people or ordnance. It was much lighter and stronger, though patented and many builders simply don't want to license-build as much of their plane from somebody elses' ideas.

Once metal skins were being used, it wasn't the only monocoque option, though it was still superior to the usual orthogonal structures. Still more expensive though.

"Geodesic" should refer to the field of mathematics itself. Geodetic applications of it work for space-frame structures or mapping a globe, etc.

Advanced Lattice Structures for Composite Airframes

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Geodesic airframes are useful for purpose-built crop dusters, built from 4130 stainless steel tubes. The chemicals on board could easily react with aluminium, which is still used for skin panels but not as a structural member: the skin plates are only for covering, not for taking any of the prime loads. The construction method is one of the reasons why they look unlike any other plane, with the angular cockpit shape and all.

Other than that, monocoque construction has completely taken over from geodesic frame construction - when the skin plates are the main load bearers the airframe is lighter.

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    $\begingroup$ Is that the only reason they look different? I would think the requirement for good visibility in low-level flying is pretty important. $\endgroup$ – jamesqf Aug 23 '17 at 6:23
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    $\begingroup$ I was under the impression that the odd shape of dusters had more to do with the need to keep the CG forward by inserting the chemical tank between the engine and the cockpit. $\endgroup$ – AEhere Aug 23 '17 at 9:25
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    $\begingroup$ You say "Crop dusters have..." as a fairly blanket statement covering all crop dusters. Would that be better stated as "Some crop dusters have..."? $\endgroup$ – FreeMan Aug 23 '17 at 12:56
  • $\begingroup$ @jamesqf - you mention visibility. To me (IANAP) the visibility out of that looks terrible with that very long hood and the pilot sitting directly over the wing, though I'm willing to be convinced that I'm very wrong. $\endgroup$ – FreeMan Aug 23 '17 at 12:58
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They ARE still produced. See for example the EU research project from 2013 here: http://www.transport-research.info/project/advanced-lattice-structures-composite-airframes

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    $\begingroup$ Welcome to Aviation.SE! Please consider adding more details to your answer, to make it more qualitative. $\endgroup$ – Noah Krasser Aug 22 '17 at 21:19
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    $\begingroup$ There is an interesting PDF if one searches a bit on the linked page. However, it seems the subject is research, not yet production. $\endgroup$ – DeltaLima Aug 23 '17 at 13:25

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