9/11/2015robin lafever 1 air supported structures for ground-based em applications a study for...

04/19/23 Robin Lafever 1

Air supported structures for ground-based EM applications

A study for Berkeley EM


The following is a quick study of some of the options for adapting air-supported structures to E. M. field survey systems.

The concepts presented all have feasibility, at first glance, and most of these structures have been built and used for other purposes.

Each concept assumes a specific manufacturing technique, which in turn, defines the engineering constraints and limits to size, mass, and materials.

In all cases, I assumed a typical Transmitter coil cross-section to be 6 turns of 10 mm dia. Copper.

Thermal issues were ignored.

A goal was to get maximum transmitter planar cross-section.

Another goal was to consider only systems that could be handled by a 2-man crew; could be set up, operated, and taken down in one day; and would fit into a pickup truck or van.


10’8 X 10 Coil set

8’

Starting with a typical Coil,~80 SF included Area,6 Turns, 10mm Litz wire,For example….

X 2..

Perpendicular to each other.


8 X 10 Coil set

Coil elements are fabricated onto a substrate so that they can be installed onto an inflated structure.( Zipper pocket )


8 X 10 Coil set

Inflated structure with coils.

Fabricated using inflatable boat manufacturing techniques.


8 X 10 Coil set

This model is 8’ high X 10’ long in each axis.

Shown here, it has an 18” diameterCross-section and will require a 5-10 psiInternal pressure to remain stable.

It can be inflated with compressed air or a hand-pump.

It will weigh < 100 lbs.

Inflatable boat fabrication technology will result in a robust structure well suitedTo fieldwork.


8 X 10 Coil set

Stability can be enhanced by adding features and geometry


8 X 10 Coil set

This version uses 12” dia. Tubes.It will need 5-10 psi, and will still be floppy at the corners


8 X 10 Coil set

Additional features will help.

The web could be realized as struts, or cables as well.


8 X 10 Coil set

75 sq. ft.

…and, you get ~75 sq. ft. per transmitter plane.


Scaling Up……..


Scaling Up……..

Same fabrication technique, twice as big.

This 16’ X 20’ model may be near a practical limit for the ‘Inflatable boat’ technique


16’ X 20’ cross form

This is getting to be >200 lbs,but might still be within thepractical envelope of the inflatable-boat technique.

At this scale, however, WIND is a consideration.

This will certainly have to be tethered to the ground.


16’ X 20’ cross form

..And you get 310 sq. ft.


16’ X 20’ cross form.. Another take.

This model is built like an Inflatable Boat;Heavy, durable fabrics, and requires 5-10 psi to remain stable

This model is fabricated like a ‘Bounce House’ Light flexible fabrics, requires <1 psi to remain stable

Inflated with a hand pump or compressed air

Inflated with a fan



This is still pretty light.~100 lbs

And it will roll up and fit into a pickup truck



Coils are shown way oversized.

In real life, they cannot get too heavy



311 sq. ft.


Scaling Up another notch…..


25’ X 30’ X 70’ multi coil

These both may be made using the same techniques and materials, but there are other options at this scale.


25’ X 30’ X 70’ multi coil

I have built several of these, at this scale, over the years. They work.

A range of materials are appropriate here, from High-strength air-tight fabrics to low-cost industrial films.

It is even feasible to considerdesigning the inflation envelopeas a short-life, disposable unit.

Inflation pressure is very low, < 1 psiThe fan shown is actually too much.


1195 sq. ft.


490 sq. ft.


Scaling up some more…

These are all thin-membrane, low-pressure structures.Again, at this scale, wind is a consideration.These must all be tethered to the ground.

I have built these, at this scale.

I have built some at this scale, but not this shape.

I think this is way too big to handle in this shape.


20’ X 20” Cube , and 30’ X 30’ Cube

The cubes are not very stable.They get mushy at the corners And try to become spheres.

Internal webs will help, as will higher pressures, and light Tx cables


20’ X 20” Cube , and 30’ X 30’ Cube

1244 sq. ft.

537 sq. ft.

In any event, you get:


Even further…..

Special note:

At this scale, the internal air temperature begins to make a difference. If it gets high enough relative to the outside air, the bodies will begin to unload, or even take off.


Even further….

I’m sure you saw this coming ..a hot-air lifting body.

This is about the smallest scale that this might be practical.

I have built some of these at smaller scale, with thin film membranes.

The volume has to be large enough to overcome the weight of the fabric its made of, plus payload. Fabric strength drives you to larger volumes


Hot-air Lifting body


Hot-air Lifting body 30’ wide X 130’ long

Conceived as a modified Hot-air balloon envelope,This can also be rendered as a thin-membrane structure.

Tethered to the ground, of course, and inflated with heated air.


Hot-air Lifting body 30’ wide X 130’ long

1104 sq. ft.


And finally….

Yer basic Hot-air balloon.


Tethered Hot-air Balloon

Yer basic Hot-air balloon.Pretty much right out of the factory with a few modifications.

This one is 50’ dia. and could be made bigger and in more defined shapes.





It is tethered to the ground, inflated by heated air from a fan, and will still stuff into a medium sized van.

Since there is no airworthyness requirement, you can get used ones cheap.





It is tethered to the ground, inflated by heated air from a fan, and will still stuff into a medium sized van.

Since there is no airworthyness requirement, you can get used ones cheap.

~1800 sq. ft. / plane


Summary

~1800 sq. ft.

1104 sq. ft

1244 sq. ft.

537 sq. ft.490 sq. ft.( SHORT AXIS )

1195 sq. ft.( LONG AXIS )311 sq. ft.

310 sq. ft.

75 sq. ft.

All of these, in final form, could be handled by a 2-man crew, or less.

They will fit into a truck.

The envelopes could easily be in the 75 lb. to 200 lb. range..for all of them!

Materials and manufacturing techniques fall into three groups defined, approximately, by scale:

Inflatable Boattechnology

‘Jump House’technology

Hot-air Balloontechnology


Processes / fabrication technique / material / scale

The notions explored here fall into three neat categories, with overlap.

1. High pressure, heavy tough materials, inflated by compressed air.Made using Inflatable Boat technology

2. Low-pressure, light fabrics or films, inflated by fan.Made using ‘Jump House technology’

**Can also me made using thin-film technologies,.

3. Very low pressure, specialized fabrics, inflated by fan with hot air assistMade using Hot-air Balloon technology


Next steps

A simple next step is to match the capabilities implied by these concepts to an application that needs that capability. We already have several, lets test them against these ideas.

A more specific, application driven conceptual design is an easy next step. It will provide detailed raw info to the Vendors and Clients for reality checks, quotes, and schedules.

A Proof-of-concept demonstration is an obvious first tangible article for further development of any field device. We have already done some of the homework in this direction. Focusing on an application will allow us to capitalize on that and proceed to real hardware.

It may be possible, in some cases, to do effective POC demos before we commission a field prototype.

I’ll explain on the next page.


Next steps with detail

We have already explored the feasibility of Boat-tech structures at similar scales for our Airborne EM study, gotten reality checks from prototype fabricators and pronounced the feasibility good.

A next step would be to show the Vendor a concept design.

Jump-house vendors seem to be in abundance, and I am familiar with the basic geometry and fabrication constraints. Specific reality checks could be

straightforward.

**Jump-Houses are available for rent, in approximately the scale and shape we want.

A next step could be to rig a temporary POC demo by draping coils

onto an existing Jump-House.

Hot-air Balloon vendors are also in abundance, including homebuilders. Custom designs are common. Again, reality checks could be straightforward.

**Used Balloon envelopes, and whole systems, are available at low-cost, especially since we have no airworthiness requirement.

A next step would be to attach coils to an envelope, rig a temporary

POC demo.

Homebuilt prototypes are within our scope.


Another Option

Availability of industrial films and tapes make it feasible to hand fabricate structures like these, as long as the shapes remain simple.

As mentioned earlier, I have made and used many of these.At this scale.

Two people can fabricate this envelope in one day for < $1000 in materials.Upgrades in materials and craftsmanship will extend the useful life.


Conclusions

All these concepts, in some form, could be feasible as ground-based E. M. platforms.

All of these concepts already exist in similar forms for other uses.

All of these forms have a clear path to design, fabricate, and test field models.

Some of these could be taken to the Proof-of-concept stage for surprisingly modest effort and cost.

A few we should keep for ourselves.

Robin LafeverMarch 2010


Jump-House

http://www.myjump4joy.com/jumpers.html

These are 13’ X 13’, rent for < $100/ day.Design and fab your own < $10 K ?


Other stuff

I didn’t look into domes, tents, and display structures at all,but they are out there….

9/11/2015robin lafever 1 air supported structures for ground-based em applications a study for...

Documents

robin lafever

corners slide

geometry slide

high x

typical coil

coil elements

berkeley em slide

zipper pocket slide