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Jane-DoH
24th Feb 2011, 03:02
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?

rigpiggy
24th Feb 2011, 06:25
http://www.avsim.com/pages/0409/FCS/7%20Wimpy%20Brooklands.jpg

enicalyth
24th Feb 2011, 14:22
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.

DERG
24th Feb 2011, 14:36
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.

stevef
24th Feb 2011, 15:15
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.

rigpiggy
25th Feb 2011, 02:35
the hurricane is/was a semi conventional steel tube fuselage, with wooden formers, and fabric covering
Hawker Restorations Limited Restoration of Hurricane G-ROBT (http://hawker-restorations-ltd.co.uk/_images/_articles/aeromar05.html)

Mechta
26th Feb 2011, 22:19
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 (http://media.photobucket.com/image/wellington%20cutaway/chris7421/Cutaway.jpg)

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.

bearfoil
27th Feb 2011, 02:01
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

mike-wsm
27th Feb 2011, 09:43
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
(bd^3)/12
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!

DB6
27th Feb 2011, 09:50
You learn something every day. I always thought it was geodetic. Well well.

Genghis the Engineer
27th Feb 2011, 15:02
Barnes Wallis' original patents for fuselage (http://www.google.co.uk/patents?hl=en&lr=&vid=USPAT2060387&id=jX5CAAAAEBAJ&oi=fnd&dq=Wallis+Geodetic+aircraft+construction&printsec=abstract#v=onepage&q=Wallis%20Geodetic%20aircraft%20construction&f=false), wings (http://www.google.co.uk/patents?hl=en&lr=&vid=USPAT1985649&id=Iop5AAAAEBAJ&oi=fnd&dq=Wallis+Geodetic+aircraft+construction&printsec=abstract#v=onepage&q=Wallis%20Geodetic%20aircraft%20construction&f=false) and airframe (http://www.google.co.uk/patents?hl=en&lr=&vid=USPAT2115504&id=R2c_AAAAEBAJ&oi=fnd&dq=Wallis+Geodetic+aircraft+construction&printsec=abstract#v=onepage&q&f=false) 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

mike-wsm
27th Feb 2011, 16:03
But his US Patent 1,956,480 (http://www.google.com/patents?id=_4hkAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false) line 10 says geodesics.

Jane-DoH
27th Feb 2011, 20:04
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?

mike-wsm
27th Feb 2011, 20:59
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..

Speedbird48
27th Feb 2011, 21:00
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

Landroger
27th Feb 2011, 23:47
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?

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

Jane-DoH
28th Feb 2011, 03:07
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?

bearfoil
28th Feb 2011, 04:15
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.

Jane-DoH
28th Feb 2011, 04:59
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?

mike-wsm
28th Feb 2011, 12:12
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?
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:

http://www.magworks.co.uk/Harrington/Photo%20large/Wellington%20Bomber.jpg

bearfoil
28th Feb 2011, 12:32
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.

mike-wsm
28th Feb 2011, 17:49
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?

DERG
1st Mar 2011, 11:07
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.

mike-wsm
1st Mar 2011, 21:08
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.

DERG
2nd Mar 2011, 09:36
WOW MIKE!

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

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

TURIN
2nd Mar 2011, 10:03
The Wellington took a lot of (wo)man-hours to build,

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

Wellington in a Day (http://www.bbc.co.uk/news/magazine-11107561)

mike-wsm
2nd Mar 2011, 21:13
They did assemble one in less than 24hrs though....
All they did was "slot the frames together like Meccano". Just final assembly. They didn't make all the components and assemble the frames.

mike-wsm
2nd Mar 2011, 21:16
...thanks for the heads up! http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/cool.gif
Nice shades, fox-hunter. :ok:

stevef
2nd Mar 2011, 22:02
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

mike-wsm
3rd Mar 2011, 01:03
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.

Jane-DoH
3rd Mar 2011, 20:38
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

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

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

bearfoil
3rd Mar 2011, 21:27
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??

Genghis the Engineer
3rd Mar 2011, 21:41
I'd never thought of a tortoise as being semi-monocoque before.

G

bearfoil
3rd Mar 2011, 21:57
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!!

DERG
4th Mar 2011, 02:51
Robyn
Oh yes..indeed.

enicalyth
4th Mar 2011, 09:38
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?

mike-wsm
9th Mar 2011, 23:23
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.

Jane-DoH
18th Mar 2011, 03:45
bearfoil

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

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?

Without proper materials, Geodesic looks wonderful, it has lightweight, and superior strength. No need for all that work when up jumps polymer.

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

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".

I never thought of it that way...


mike-wsm

The problem with a vacuum is that it takes such an incredibly long time to make.

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...

It is beneficial to start heating the interior as the pressure drops

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

bearfoil
18th Mar 2011, 04:21
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.

Jane-DoH
19th Mar 2011, 21:59
bearfoil

Geodesic is a method, architecture is a volume.

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?

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.

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

bearfoil
19th Mar 2011, 22:27
As Mike has noted, a compound curve is quite strong. The geodesic is an amalgam of strong linear shapes, the triangle being the most elegant. There are two considerations in three dimensions, compression and tension. A cylinder (fuselage) has terrible compressive strength, marginally better tension. The strongest three dimensional fuselage (section) would be the triangle, basically three trusses fastened on edges. This shape would be strong in bearing, tension, and in torsion (twisting). To gain volume (but lose strength) the "Tube" is born.

The modern aircraft is robust, and impossibly weak, depending on the stresses, and weight.

I am no engineer, so you know, my background has been in design and fabrication. I still am unsure what you want to accomplish with Fullerine dogma v/v a/c. ??

boguing
20th Mar 2011, 00:08
BearF.

Understand what you're saying,but I'm having difficulty with this 2d/3d thing.

As I see it, the least number of finite elements needed to construct a 3d shape would be 6 - in the form of a 'triangular' pyramid.

From there, an Infinite number of elements can describe anything. So put enough 2d shapes together and you get a bumpy 3d. The more you add the smoother the surface.

The thing I'm stuck on is where you say that a tube is better in tension than compression. Hilberts' Regression suggests otherwise, or have I got that wrong?

bearfoil
20th Mar 2011, 00:26
boguing

bear with me, I am utilizing the "tube" as a fuselage, eg. frames, stringers, skin.

Suspended in space from either end, my visual and intuitive opinion is that it will resist "rupture" (separation) underneath, and foster "crumpling" (accordion), above. This of course requires 'loading', (eg 1G), so I haven't a clue as to the contribution of the existing stress.

Seen as: Tension, resistance to rupture, and Compression, resistance to wrinkling.

boguing
20th Mar 2011, 00:53
I'm with you on the tube thing completely.

So, taking two tubes, one plain vanilla ring frames and longitudinal stringers, the other Geode(s/t)ic and both hung vertically from an end, you seem to imply that the geo structure will (under identical Gravitational constants) undergo less stress than the former. When Hilbert is applied to the resultant strain, I think that the strains would be equal. Or am I missing something? As usual...

bearfoil
20th Mar 2011, 01:52
I think it is I who am missing something. Given equal weight, and suspended vertically from an end, the strain is equal. An engineer (amicus?) would have to input here, for stress is only a factor insofar as it is spread, yes? If I had a choice of material but was limited in mass, and was free to design the tube, I would select a composite, for intrinsic in the shape is the inclusion of geo- stringer, skin- etc. Incorporating the frame with the consolidating skin gives strength and weight saving. Strength (Stress) is always best when distributed, rather than focal??

edit. Did you see that I proposed suspending the "tube" from "both" ends, to simulate dynamic load?

And, if not for drag, perhaps a helix !!

Nick Thomas
20th Mar 2011, 03:04
It is interesting that the the original definition of "geodesic" is related to "geodesy" which is concerned with methods of defining the shape and size of the earth. In fact "geodesic" is a part of a great circle, therefore a great circle route could also be descibed as a geodesic route.

As I understand it the first geodesic structure was a planetarium for the Carl Zeiss co designed by Wather Bauersfeld just after the end of the first world war.

Geodesic structures are used by architects and structural engineers to enclose any curved space. An example would be the geodesic sphere that forms Spaceship Earth at Walt Disney world.

As mentioned earlier an American engineer called Buckminster Fuller designed many geodesic domes after the end of the second world war and was awarded the US patent for geodesic structures.

Bearfoil as an Architect I find your definition of Architecture interesting.

boguing
22nd Mar 2011, 22:56
BF.

Sorry not to get back to you sooner. I'm having a bit of trouble trying to keep up with the thrust of your posts. At first you said that Geodes/tics were very similar to more modern CFRP, which, in laymans' terms is close enough. You then thought that I might be falling for 'Fullerine Dogma'.

Where was dogma in Fuller? Of course a composite allows far more elegant solutions than geodetics ever can. But, how can (and more's the pity) a football get made out of 2d fabrics without linking planar surfaces in clever ways.

Just need to clear my mind a bit before launching in to the Maths.

ps. What kind of things do you design? I'm currently busy in automotive dynamics, but have had fun with boats and 'planes too. Did a few houses too!