Geodesic Airframes
 

As I understand it, a geodesic structure is based on straight lines drawn along a curved surface. There were a couple of British bombers based on this design concept by Barnes Wallis and they were remarkably sturdy though the skeleton looked like some kind of metal basket.

Did they use conventional stringers/longerons and spars? Also is there any commonality in concept between a geodesic frame and a honeycomb structure?

DN de G Allen
 

Try and find a slim book called the Systematic relaxation of Constraints by D N de G Allen. Written in the 1930's for airship designers this is the tour de force and succinct with it.

the frames were made of wood at first...this is where they used a two pack glue, plyurethane of the fist time. Now I am guessing here but the airframes specically using this process was the Halifax and also the Hurricane but not sure. The wood used was ASH...as from an ash tree.

An interesting Barnes Wallis design of fabric-covered duralumin channel section. Used by Vickers (in no date order) on the Wellesley, Windsor, Warwick and, most famously, the Wellington. The earlier R100 airship also utilised the helical weave construction.
Amazing structural strength.

the hurricane is/was a semi conventional steel tube fuselage, with wooden formers, and fabric covering
Hawker Restorations Limited Restoration of Hurricane G-ROBT

The Wellington had external stringers to give a smooth surface for airflow. Despite the incredible ability to absorb battle damage, geodesic construction was dropped on later designs as fabric ripple at speeds over 300mph increased drag.

This gives a pretty good idea of the structure:

Wellington cutaway image by chris7421 on Photobucket

It appears that there were spars, longerons and formers, although they look smaller than one would expect to find on a semi-monocoque structure.

I made an experimental geodesic leading edge for a large, ultra-lightweight UAV using 0.6mm pultruded carbonfibre rod. The resulting structure was very stiff and weighed almost nothing. It is definitely worth revisiting for appropriate applications.

Honeycomb structures use the inner and outer skins to transmit loads. The honeycomb converts gives each skin depth to resist buckling. I would say that they are quite different.

Hmm. It is not difficult to imagine that not only are geodesics and CFRP similar, for purposes of discussion here, they are identical.

Strength/Weight was always a driver in Aviation, hence Spruce rather than Fir, and Titanium rather than Steel. When the paradigm became Moot, we went back to solids. Howard Hughes developed an early form of prepreg using Birch veneer and Urea or Phenolic shear layers, enormously strong, and absent the need to "relieve" structure to minimum weight to maintain Strength.

The "Skeleton" of steel tube covered with fabric became obsolete when prestressed Aluminum panels and minimal structure could provide a three dimensional operant of what the Tube Fabric structure only "suggested".

Inside every solid and shaped prepreg panel of Carbon reinforced Plastic is a ghost of the Honeycomb, and the "Geodesic".

The secret to strength has always been "Two Phase", being a matrix enveloped in some solid. Bamboo is a perfect analogue in Nature of Rutan's best efforts.

eg: Fibrous/Lignin and Carbon Fibre/Resin. Same-o same-o.

bear

Looking at the Wellington cutaway, it is a lattice, two-dimensional in some areas and curved into a cylinder in others. Neither is truly geodesic in the sense of being a self-defining surface of linked rods. It is only in two-way curved surfaces that the geodesic structure becomes rigid.

The added rigidity in the Wellington comes from having a very thick skin, anyone with mechanical knowledge will recognise
which is the moment of inertia of a beam of width b and depth d, the stiffness being proportional to the cube of d.

In the context of a lattice structure Bearfoil is quite correct in drawing a parallel with honeycomb materials where the separated skins provide the stiffness and the honeycomb simply defines the gap between skins.

PS - Apologies for lapsing into lecturer mode, will try not to in future!

You learn something every day. I always thought it was geodetic. Well well.

Barnes Wallis' original patents for fuselage, wings and airframe all use the word "geodetic", and personally I'm inclined to go with his version. He was cleverer than me!

I think he first published a journal paper on the science of it sometime in the mid 1930s, probably in "aircraft engineering", but I can't find a reference to that - I have seen the paper whilst browsing in a university library some years ago.

Wouldn't it be nice if we could all access old British patents and RAE TNs online in the same way we can US papers and NACA reports.

G

But his US Patent 1,956,480 line 10 says geodesics.

So the reasons geodetic airframes were abandoned were because the skin would ripple at high airspeed? Why didn't they just use a metal skin over a fabric skin?

Were there any other reasons why geodetic airframes were abandoned?

The use of 'geodesic' design was very much a Barnes Wallis personal mission. He used geodesics in the design of airships around 1930, aircraft like the 1935 Wellesley and 1938 Wellington, and a radiotelescope in 1955. Other designers did not go that route.

Another more practical reason is tooling. Geodesic aircraft structures require special production tooling. Once a factory has invested in geodesic production tooling they would be more willing to incorporate geodesics in further similar designs.

Interesting to note that the two aircraft mentioned above are named for the same man. It was a Mr Arthur Wesley b1769 who changed his name to the more impressive sounding Wellesley in 1798, and, as his career advanced, changed his name again, this time to Wellington, around 1810 and became Duke of Wellington a few years later..

Jane-DoH,

The original geodetic arframes, Wellington, Watwick etc; were all covered in fabric and as has already been said the fabric would start to pant at higher speeds.
The early Vicker Vikings had a conventional fuselage of stressed skin, but the wings were fabric covered. They then came out with a modification (Mod 508???) where the fabric was removed and sheet metal riveted on. The later ones and the Vallettas all had sheet metal over the same structure but from the factory.
Speedbird48

Jane-Doh
 

It may not be the reason and the story may well be apocryphal, but I always understood that when a Wellington was tested as a potential glider tug for D-Day, it worked well. However, when they measured the fuselage on its return ....... they found it to be considerably longer and somewhat slimmer than before the test.:eek:

Roger

mike-wsm,

What kind of tooling do they require that is not required for traditional aircraft fabrication? Is it hard stuff for an aircraft manufacturer to procure in those days?

The application for this approach was narrow, dependent entirely on the radius of the Sphere needed, and Airframes are not conducive to "round". One needs a tube, a planform or two, and some cruciform slabs. The flatter the structure, the more strength was sacrificed by the shallow curve needed, and the material and intense labor needed to assemble became disqualifying. Each triangle needed to close itself with gusseting shared by its partner, and the edges of the tri were supposed to be mitred as "compound" surfaces. This is an enormous amount of work, and by the time methods caught up with demands, Howie was pressure cooking Birch trees and Phenolics into compund panels of immense strength.

One of my favorite a/c besides the Largest a/c ever made (The Birch Goose) is the Mosquito. If God had wanted Plastic airplanes, he would have made Carbon Fibre trees.

bear

Please don't use the word "Geodetic" here, it is an entirely different animal. Bucky would not approve.

If you think Hughes was no genius, walk through IKEA and see his brilliant application of Duramold with Baltic Birch (FinnPly) shapes made into nomadic furniture, wagons, and pieces that are their own shipping crates before they become Cabinets.

Phthallates, acrylates, and God's own laminates. Go bang on the skin of an F-16 where the wing blends into the Fuse. 'A' Sharp, if it passed QA. Geodesic construction was retro less than ten Years after the Wrights flew, imo.

bearfoil,

is it possible to have a geodetic fuselage and a non geodetic wing? Or would the whole hybridization not work?

As for Howard Hughes pressure cooking birch trees and phenolics into compound panels -- is this a very very primitive composite?

There is a reference to this in wiki under Barnes Wallis. Tooling in this context would include assembly jigs, generally made in-house to meet the needs of any design. It is part of the cost and time-scale of any project, you don't just build the product, you have to produce the tools and the jigs to hold things as they are assembled.

The Wellington took a lot of (wo)man-hours to build, you can see the complexity in this pic:

Jane-Doh

A very simple concept is spread. Distribution of stress allows for lower weight, crucial in the aviation application. At some point, the adoration of complexity for its own sake must be sacrificed to make money. The military application of wildly expensive formats is crazy apparent.

Variable geometry, "Stealth", "Flying Wing", too many more to bring up. Skeletal frames covered in skin go back to the first of the Chordata, animals with "Bones".

Almost Anything is possible, and being possible, welcoming of discussion. The most efficient Space vehicle currently is made of CFRP, has no bones, and burns Rubber in "pops" that make it sound like a "Buzz" engine. Sometimes I think Rutan does what he does just to make fun of the dinosaurs who think with old Brains, and use technology that was old when Mother Nature had her "A-Hahs".

The Helical Frames in those old bombers were copies of the "Chinese Finger", not some marvel of Human Intellectual innovation.

How about a vehicle whose body work doubles as its energy tankage??

Li-Poly/ Plastic as Electrode, and formed into Fender, and coachwork.

The newest Airframe is virtually indistinguishable from early Post WW2 bombers.

The secret to making money is not to make things complex, but to make them simply.

Having no understanding of why Geodesics interest you so, I may be missing your point here. Sorry if that is the case.

I think Jane may be wishing us to refer to geodesic carbon C60 molecules, known as Buckminster Fullerene or Bucky:mad:s. Well, I wasn't going to say it in front of a lady, was I?

Nah she wants to suss us men out. Wants to know what kinda figures we prfr. I prfr size 7 shoes and 31 inseam myself.

Alas all too true, though I am honour bound not to reveal the content of pms that may have passed between herself and myself. You might wish to ask her to look at test pilots and express opinions.

WOW MIKE!

You saying she is a real life version of the lady on Top Gun!

Adds up...thanks for the heads up! :cool:

They did assemble one in less than 24hrs though....

Wellington in a Day

All they did was "slot the frames together like Meccano". Just final assembly. They didn't make all the components and assemble the frames.

Nice shades, fox-hunter. :ok:

You might be slightly under-estimating those Vickers workers, mike-wsm! :)
Fair enough - each assembly section had its seasoned experts but it was still quite an achievement to put a large aircraft together in 24 hours, especially considering the fabric doping procedure.A lot of flying/engine control & undercarriage rigging involved there as well.
I've done a bit of that on older aircraft - respect to those men and women :D

stevef

I was quoting directly from the reference cited by TURIN.

My original statement was "The Wellington took a lot of (wo)man-hours to build" and by implication I was comparing it with other contemporary aircraft.

bearfoil

I just found geodesic airframes fascinating because they were very sturdy and the use of the vanished after WW2.

To be clear the geodetic airframe was helical in nature, not using angled frames (at first my impression was that each frame was simply angled forward -- take a hula-hoop, hold it in front of you and tilt it forward) one angled forward and backward to intersect?

Regardless, the geodesic design seems to have some overlaps with trusses (as there are a lot of intersections and produce a lot of quadrilateral and triangular shapes, and the image inside the Wellington did seem to have a series of truss-structures in them).

I know modern composites are far more effective than this design, and I'm not actually a proponent of excessive complexity (my general attitude is: If you're given the choice between simplicity and complexity; use simplicity unless complexity is needed to accomplish the task).


DERG

I wouldn't say that, but I do have some skill with remembering figures and such.

Hi Jane

The problem with geodesic architecture is its rapid loss of strength in planar shapes.

Without proper materials, Geodesic looks wonderful, it has lightweight, and superior strength. No need for all that work when up jumps polymer. Even some time spent on the English wheel will give Aluminum sheet practical Strength/Weight. In every cube of Granite lives a David. Leonardo is not exactly on speed dial on the shop floor, however.

Inside the shell of a Tortoise are what look like Vestigial "Ribs". They are not ribs, though, they are frames, giving Mr. Slow's carapace some "Trusswork". The finest architecture is found in the Natural World. Human beings can get so full of themselves when the focus is narrow. Pride goeth before the Fall, eh??

I'd never thought of a tortoise as being semi-monocoque before.

G

Entomology trumps Boffinology??

Insecta have completely monocoque design. Exoskeleton. Body/Exo, Wing/Skeletal

In the scheme of things, Boeing and Bus are basically just monstrous honeybees.

Engineer, get thee not overprecious!!

Robyn
Oh yes..indeed.

airships
 

Back to airships. The lifting gas must be lighter than air. The ultimate lifting gas would be none at all, a vacuum. But atmospheric pressure would crumple this envelope. But if it was a geodesic shape with tension bonds attached to enough nodes to prevent crumpling of the inner bag, could the outer ends be fastened to another geodesic frame such that all it members wre in compression?

The problem with a vacuum is that it takes such an incredibly long time to make. It's quite easy to pump out the first bit, but the less air there is in there, the longer you have to wait for the molecules to whizz around enough to reach your outlet and get pumped away. It is beneficial to start heating the interior as the pressure drops but there are limits to how much heat you can apply and still retain structural integrity.

bearfoil

What kind of architecture goes well with planar shapes? From an academic standpoint is it possible to integrate a geodesic fuselage with other types of architecture in the wings?

Academically speaking, is it possible to create a geodesic frame out of polymers? :}

I never thought of it that way...


mike-wsm

You'd almost certainly need a hard-shell for this, but if you had a series of access panels, few hundred let's say all over the surface of the blimp. That way you could stick pumps in and suck out the air more rapidly than if you had one hole and one pump. You could also rig a network of porous tubes through the frame to amplify the effect, if they were sturdy enough they could provide some load bearing functions allowing you to reduce strength in other parts of the blimp to keep the weight in line. I'm not sure I'm explaining this right...

LMAO! That was the exact idea I was thinking of as I read what you were writing about the pressure dropping and the time to drain out everything increasing -- as the pressure drops increase the temperature which does increase the pressure, but because the atoms are moving faster they'd all fly out of the vessel quicker even as the pressure gets very low, and once there's nothing left you still have no pressure so you just seal everything up and then either cool it down while on the ground or just lift off and let the outside air temperature cool you down

Hi Jane

Geodesic is a method, architecture is a volume. Which brings up the best way to create a vacuum. Two discs of strong metallic construction are welded together at their shared rim. From either side, and at the center, the discs are separated, mechanically. Theoretically, there being no space between the discs at the start, the more one can separate the two, the larger the "perfect" vacuum one creates. This is the theory that propels us through the air and across the land.

But. There is no such thing as a 'vacuum'. It is an artful way of saying 'less pressure', migrating to none.

Vacuum must have a mate, existentially. We call it 'Pressure'.

A 'Geodesic' of polymer? Simples. Start with a CFRP Soccer ball, and start drilling. In mechanics, this is called 'relieving', exchanging strength for light weight. If you like, pattern your relief on the hexagon, pentagon, etc. Imagine a 'wiffle ball', then.

The beauty of polymer is that it takes so little work to attain marvels of strength and resilience. Polymer is frame and skin at one with whatever shape one wishes. In airframes, or sailboats, structure is pleasant when it has few components. A mold, some A, some B, some woven matrix, and a 'vacuum cleaner', voila, a 44 foot Marples prime for the single handed TransPac.

bearfoil

I apologize for my incorrect terminology. Regardless, what I meant was is it possible to design a tubular structure with a geodesic construction method, then where planar shapes form to shift to some other structural design method? Also is it possible to create tubular geodesic spars instead of the traditional spar configuration?

I would have never thought of a wiffle-ball that way