Hexakis icosahedron frame-skin vacuum lighter than air vehicle

A vacuum lighter than air vehicle (VLTAV) includes a rigid frame of rods connected together to form a hexakis icosahedron. A membrane skin covers the rigid frame and defines therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. The plurality of rods and membrane skin have weights and dimensions that result in a neutral and/or positive buoyancy for the vessel while preventing geometric instability.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Serial No. 62-439994 filed on Dec. 29, 2016 and U.S. Provisional Patent Application Serial No. 62-440003 filed on Dec. 29, 2016, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to lighter than air vehicles, and more particularly to lighter than air vehicles using an internal vacuum and associated methods.

BACKGROUND OF THE INVENTION

The idea of a vacuum lighter than air vehicle (VLTAV) was first proposed by Francesco Lana de Terzi in 1670. His concept was simply an evacuated sphere. His idea had a flaw as the concept of buckling, which is a structural instability that comes about when you load a structure in compression, was not understood. The proposed continuous layer spheres would fail due to buckling before a complete vacuum could be created.

Another VLTAV concept is disclosed in U.S. Patent Publication No. 2006/0038062 A1 to Akhmeteli and Gavrilin who proposed to construct a skin or “shell” out of multiple layers in a sandwich configuration. The structure is composed of three layers, two thin (top and bottom) layers and a relatively thick cellular core layer. The core's material properties were low density, high compressive strength in the transverse direction, high out-of-plane shear strength, high compressive modulus in the transverse direction, and high out-of-plane shear modulus. Akhmeteli and Gavrilin verified no material existed to create a thin shelled sphere that could be placed under an internal vacuum without buckling.

In 2012, Trent Metlen at the Air Force Institute of Technology (e.g. see “Design of a Lighter than Air Vehicle that Achieves Positive Buoyancy in Air Using a Vacuum,” Air Force Institute of Technology, Wright-Patterson AFB, 2013) developed the idea of using geodesic spheres covered by a membrane as the structure for a VLTAV. A geodesic sphere is an icosahedron that has its triangles divided into more triangles. When each of these divisions occur, the new vertex is place on a circumscribed sphere.

Continuing in 2014, Ruben Adorno Rodriguez again at the Air Force Institute of Technology (e.g., see “Nonlinear Structural Analysis of an Icosahedron and its Application to Lighter than Air Vehicles Under a Vacuum,” Air Force Institute of Technology, Wright-Patterson AFB, 2014) modeled the icosahedron using non-linear finite elements. A goal was to determine what material properties are necessary to make an icosahedron vacuum lighter than air vehicle possible. It was determined that an important feature of a VLTAV is utilizing a material that has a high enough specific density, E/p, to withstand the compressive forces and be light enough to float.

Thus, lighter than air vehicles (LTAV) are considered vehicles that float due to filling an enclosed or semi-enclosed volume with a gas lighter than air. A vacuum may indeed be the ultimate lighter than air “gas”, but it also requires the structure to be especially rigid for the reasons stated above. The problem with a vehicle of this nature is that previously no structure had been designed that can withstand the compressive loads due to an internal vacuum and still be light enough to float. It has been proposed that polyhedral shapes such as an icosahedron could be used as the structure, yet material limitations prevent the design from working today.

Therefore, there is a need for the design of frames and materials to achieve the goal of floating with an internal vacuum while withstanding the compressive loads produced thereby, and eliminating the need for a gas such as helium.

BRIEF SUMMARY OF THE INVENTION

With the above in mind, embodiments of the present invention are related to a vacuum lighter than air vehicle (VLTAV) including a rigid frame comprising a plurality of rods connected together to form a hexakis icosahedron. A membrane or membrane skin covers the rigid frame and defines therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. The materials of the rods and membrane skin result in the vessel having a weight and buoyant force that results in positive buoyancy while preventing geometric instability.

In certain embodiments, the rods may be cylindrical, hollow and/or pultruded rods. Additionally, or alternatively, the rods may include a carbon fiber composite material having a specific modulus of at least approximately 1.29*108m2/s2and a specific yield strength of at least approximately 1.80*106m2/s2as a zero-degree layup.

In certain embodiments, the membrane skin may be a laminate membrane skin, such as a fiber matrix reinforced laminate membrane skin material having a specific modulus of at least approximately 9.52*107m2/s2and specific yield strength of at least approximately 1.43*106m2/s2for a 0.4 mm thick segment.

In certain embodiments, the rigid frame may include joint members connecting the rods at vertices. As such, the rods of the rigid frame may be connected together at 62 vertices with 180 edges defining 120 identical scalene triangle faces.

Another embodiment may be directed to a vacuum lighter than air vehicle (VLTAV) including a rigid frame of cylindrical rods connected together at 62 vertices with 180 edges defining 120 identical scalene triangle faces. A laminate membrane skin covers the rigid frame and defines therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. The rods and membrane skin have weights and dimensions that result in a positive buoyancy for the vessel while preventing geometric instability. The cylindrical rods may include a material having a specific modulus of at least approximately 1.29*108m2/s2and a specific yield strength of at least approximately 1.80*106m2/s2as a zero-degree layup. The laminate membrane may be a material having a specific modulus of at least approximately 9.52*107m2/s2and specific yield strength of at least approximately 1.43*106m2/s2for a 0.4 mm thick segment.

In certain embodiments, the rods may be cylindrical, hollow and/or pultruded rods. Additionally, or alternatively, the rods may include a carbon fiber composite material. Also, the laminate membrane skin may be a fiber matrix reinforced laminate membrane skin.

Embodiments may be directed to a vacuum lighter than air vehicle (VLTAV) including a rigid frame of rods or a plurality of rods connected together to form a hexakis icosahedron rigid frame, and a membrane skin covering the rigid frame and defining therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. A vacuum pump may be coupled in fluid communication with the vessel and configured to control the internal vacuum therein and create vessel up thrust. The rods and membrane skin may have weights and dimensions that result in one of a neutral buoyancy and a positive buoyancy for the vessel while preventing geometric instability.

In certain embodiments, a propulsion system may be coupled to the vessel and configured to move the vessel through the air while floating.

In certain embodiments, the rods may be cylindrical, hollow and/or pultruded rods. Additionally, or alternatively, the rods may include a carbon fiber composite material. Also, the membrane skin may be a fiber matrix reinforced laminate membrane skin.

Embodiments may be directed to a method of making a vacuum lighter than air vehicle (VLTAV), the method including constructing a rigid frame by connecting rods together to form a hexakis icosahedron, and covering the rigid frame with a membrane skin to define a vessel configured to hold an internal vacuum that allows the vessel to float in the air. The method may include selecting weights and dimensions of the rods and membrane skin to result in one of a neutral buoyancy and a positive buoyancy for the vessel while preventing geometric instability.

In certain embodiments, connecting the rods may include connecting cylindrical hollow pultruded rods at 62 vertices. The cylindrical rods may include a material having a specific modulus of at least approximately 1.29*108m2/s2and a specific yield strength of at least approximately 1.80*106m2/s2as a zero-degree layup. A zero-degree layup has the majority of fibers in one direction.

In certain embodiments, the membrane skin may be a fiber matrix reinforced laminate membrane skin material having a specific modulus of at least approximately 9.52*107m2/s2and specific yield strength of at least approximately 1.43*106m2/s2for a 0.4 mm thick segment.

A concern with vacuum airships is that the required vacuum or near-vacuum inside the structure results in the atmospheric pressure exerting enormous forces, causing the structure to collapse if not supported. The structure of the present embodiments solves the problem using geometry and materials, in combination, that resist buckling at pressures needed to produce neutral and/or positive buoyancy.

Known materials commonly used as lifting gases in lighter than air aircraft present both a cost driver and a logistics burden for those aircraft designs. An advantage of the VLTAV structure of the present embodiments is the elimination of the requirement to purchase or transport a lifting gas.

Unlike known lifting gases, a near-vacuum environment is theoretically capable of approximating the full lift potential of displaced air (e.g., such that every liter of vacuum could provide lift approaching 1.28 g). Many applications exist in aerospace and related industries for vacuum airships that exhibit such lift potential.

DETAILED DESCRIPTION OF THE INVENTION

Known materials commonly used as lifting gases in lighter than air aircraft are expensive and burdensome. An advantage of the vacuum LTA structure of the present embodiments is the elimination of the requirement to purchase or transport a lifting gas.

A problem with the conventional concept of vacuum airships is that the required vacuum or near-vacuum inside the structure results in the atmospheric pressure exerting enormous forces, causing the structure to collapse if not supported.

Referring again to the prior art concept of the continuous layer copper sphere or shell, the way a sphere or shell of this type would not fail due to shell buckling would be if the material chosen had a specific modulus, E/ρ2, of approximately 4.9*105kg−1m5s−2, which did not exist in 1663. Currently, a material with a high specific stiffness, a carbon nanotube composite, has a specific stiffness value that is half of what is necessary to create a thin shell vacuum lighter than air sphere, meaning that the prior art design remains unfeasible because of limitations in the available materials. The value of 4.9*105kg−1m5s−2is computed using equation (1).

Eρs2=9⁢Pc⁢r⁢3⁢(1-μ2)2⁢ρa2(1)
Where E is equal to the modulus of elasticity (the materials resistance to being deformed elastically or linear stiffness) and ρsis equal to the materials density. If you let ρabe sea level air density (1.225 kg/m3), μ be the Poisson's ratio (0.3), and Pcrbe sea level atmospheric pressure (101,325 Pa).

The structure of the present embodiments addresses the problem using geometry and materials, in combination, that resist buckling at pressures needed to produce neutral and/or positive buoyancy.

Referring toFIGS. 1-5, an embodiment of a vacuum lighter than air vehicle (VLTAV)10will be described. The VLTAV10, such as a high-altitude balloon, for example, is configured to achieve neutral buoyancy and/or positive buoyancy using an internal vacuum.

The structure will have the ability to float. A W/B ratio, of the weight W and buoyant force B, is chosen that sets the design parameters of the structure based upon the equations discussed below. Stresses develop and then would be checked to see if the structure succeeds or fails at the desired elevation. Dimensions of the structure can be determined for a particular desired elevation. Some example materials for the rods are provided below.

With reference toFIG. 1, rods11are connected together to form a rigid frame in the shape of a hexakis icosahedron. A hexakis icosahedron is a Catalan solid with 120 faces, 180 edges, and 62 vertices. The face configuration for this shape is V4.6.10, comprising twelve vertices with four lines intersecting, twenty vertices with six lines intersecting, and thirty vertices with ten lines intersecting. This polyhedron is composed of 120 identical scalene triangles. The hexakis icosahedron is face uniform but with irregular face polygons, may also be known as a disdyakis triacontahedron, or a kisrhombic triacontahedron and would be appreciated by those skilled in the field of geometry.

In certain embodiments, the rods11may be cylindrical, hollow and/or pultruded rods, for example, as illustrated inFIG. 2. Additionally, or alternatively, the rods11may include a carbon fiber composite material having a specific modulus of at least approximately 1.29*108m2/s2and a specific yield strength of at least approximately 1.80*106m2/s2as a zero-degree layup.

A membrane skin12is covering the rigid frame and defining therewith a vessel configured to hold an internal vacuum that allows the vessel to float in the air. In certain embodiments, the membrane skin12may be a laminate membrane skin, such as a fiber matrix reinforced laminate membrane skin material having a specific modulus of at least approximately 9.52*107m2/s2and specific yield strength of at least approximately 1.43*106m2/s2for a 0.4 mm thick segment. The laminate may be designed so that the strengthening fibers within the laminate are oriented along ideal load paths to be expected when the structure is evacuated. The manufactured membrane skin12would then be stretched over the frame and seams secured together (e.g. stitched or glued). Some example materials for the membrane skin12are provided below.

The rigid frame may include joint members15connecting the rods11at vertices13as shown inFIG. 1. For example, the rods11of the rigid frame are connected together at 62 vertices13with 180 edges defining 120 identical scalene triangle faces14. It should be understood that each of the 62 vertices may include a joint member15, for example, various vertex joint members15with four, six, and ten rod inserts.

The vertex locations, surface area, and volume are necessary for modeling this structure. The62vertex locations of the hexakis icosahedron are determined by referencing the table inFIG. 3which includes various C values (C0-C8). And, a set of equations designating the C values (C0-C8) inFIG. 3are shown in the table ofFIG. 4based on an inscribed icosahedron with a unit edge length in Cartesian coordinates. The inscribed icosahedron's vertices lie on the twelve vertices of the hexakis that have ten edges connecting. The C values in the table ofFIG. 3are given for the specific coordinates for each vertex locations V0-V61. There are 62 vertices and each is located in the hexakis icosahedron with three coordinates defined by the various values of C0-C8. The values of C0-C8are defined by the equations inFIG. 4.

The edge lengths of the unit triangle T (FIG. 1) that makes up the hexakis framework can be determined by using equations (2-4) below. In which Ise, Ime, Ilerepresent the short, medium, and long leg lengths of the triangle. With the edge lengths known, the surface area is computed using equation (5) as well as the number of triangles, shown in equations (5-6) below. Finally, the volume is readily computed using equation (7) below.

To determine the frame dimensions, the independent variables that define the geometry should be computed. These variables are beam radius and thickness for the frame (e.g., hollow rods11) and skin thickness for the skin12. To determine these parameters, the sizing equation (8) may be used. Equation (8) is a general formula to compute the W/B for any frame-skin structure with an internal vacuum.

WB=Vs⁢ρs+Vf⁢ρf+(Vi-Vr)⁢ρair,i(Vi-Vr)⁢ρair,o(8)
Where, Vfand Vsare the frame and skin volume respectively; ρf, ρs, ρair,i, and ρair,oare the frame, skin, internal air, and external air density respectively; Viand Vrare the initial internal volume and the volume lost or reduced due to the structure deforming when an internal vacuum is present. The Wand B are the weight and buoyant force of the vehicle respectively.

In order to compute the frame and skin dimensions for the hexakis icosahedron VLTAV10, the first step is to set the left-hand side (W/B) of equation (8) to an initial value. For instance, if an icosahedron design was desired to float or carry a payload, the initial value of W/B in equation (8) would be set to a number less than one (indicating a positively buoyant design). Now, for this example, just because a positively buoyant vehicle can be geometrically sized may not mean the design would actually float or carry any payload. The proposed design not only has to satisfy the W/B constraint of being less than one, it also must not fail due to material and geometric instability as well. It is noted, that the W/B value can only be less than one when the weight of the vehicle is less than the buoyant force produced. Therefore, when this is performed, any amount of weight given up for buoyancy, directly reduces the design's resistance to material and geometric instability. A W/B equal to one may not produce a VLTAV that can rise, however, it does produce a VLTAV that can float (neutrally buoyant).

The next step is to specify what percentage of the designs weight (W) is to be dedicated to the frame and skin. To do this, we introduce two variables,

WBf⁢⁢and⁢⁢WBs,
frame W/B and skin W/B, where the total of these W/B's is equal to the W/B on the left-hand side of equation (8). Utilizing equation (8) and the introduction of

WBf⁢⁢and⁢⁢WBs,
the beam radius and skin thickness can be computed. The equations for the beam radius and skin thickness are shown in equations (9) and (10). The beam thickness (tbhex) is computed using equation (11) by specifying the desired c value for manufacturing.

Again, c is the ratio of the rod thickness to the rod radius. The rods11or tubes are beams of the frame ofFIG. 1.

The variables include: ρais the density of air at a given elevation; W=the weight of the system or VLTAV10; Bfis the weight of the frame; Bsis the weight of the skin12; ρfis the density of the frame; Ise, Imeand Ilerepresent the short, medium, and long lengths of the frame members or rods11making up each triangle; VHIis the total volume of the hexakis icosahedron frame; and AHIis the surface area of the hexakis icosahedron frame.

One suitable material for the frame rods11may be a carbon fiber composite extruded into hollow tubes that meet the criteria of thickness and ratio described above. A driving constraint for the present embodiments may be the need for a frame and skin material to have a high specific modulus

(Eρ)
and a high specific strength

(Eσy).
Where E is the material modulus of elasticity, ρ is the material density, and σyis the material yield strength. An example of a material for the frame that has been preliminarily analyzed using finite elements is IM10 or Hexply 8552. This material has a specific modulus of approximately 1.29*108m2/s2and a specific yield strength of 1.80*106m2/s2as a zero-degree layup. Of course, other materials can be used for the frame as long as they meet or exceed the specific properties of Hexply 8552.

One suitable material for the membrane skin is a laminate constructed by Cubic Tech, now acquired by DSM Dyneema, known as CT155 UHMWPE. This laminate utilizes ultra-high molecular weight polyethylene fibers to strengthen the membrane. This material's specific modulus is approximately 9.52*107m2/s2and specific yield strength is 1.43*106m2/s2for a 0.4 mm thick segment. Of course, other materials can be used for the membrane as long as they approximate or exceed the specific properties of CT155 UHMWPE.

These materials were used to preliminarily analyze several example design iterations for manufacturing feasibility. Two designs, one with payload or float capacity maximized, and the other with the radius of the vehicle minimized are detailed as examples of feasible structure that could be realized with the existing materials described above. Both designs total W/B were decreased until the safety factor SF constraint was reached for either the frame or skin. The results of the two feasible vehicles are shown in the Tables ofFIGS. 5A and 5B. The design (FIG. 5A) focusing on maximizing payload would have a vehicle diameter of 14 m (46 ft) and could carry a payload of 260 kg or float to 2140 m. This vehicle was able to attain a final W/B of 0.8 limited by the frame SF before the skin. The design (FIG. 5B) focusing on minimized radius had a vehicle diameter of 6.2 m (20 ft) and could carry a payload of 9 kg or float to 860 m. This design's final W/B was 0.91.

So, the rods11and membrane skin12have weights and dimensions that result in a neutral and/or positive buoyancy for the vessel while preventing geometric instability. A concern with vacuum airships is that the required vacuum or near-vacuum inside the structure results in the atmospheric pressure exerting enormous forces, causing the structure to collapse if not supported. The structure of the present embodiments solves the problem using geometry and materials, in combination, that resist buckling at pressures needed to produce neutral and/or positive buoyancy.

Various contemplated and example embodiments of a VLTAV aircraft could be used and retrofitted for propulsion, aerodynamics, energy renewal, sensors and endurance etc.

Referring now toFIG. 6, an example embodiment of an operational low-altitude VLTAV aircraft20for urban surveillance is shown. This aircraft20may either operate inside of buildings or outside of buildings without exceeding the aerodynamic coverage that the buildings provide. The aircraft20includes the frame/membrane structure of the VLTAV10discussed above, along with a vacuum port26included such that a vacuum pump25could be carried to vary the vacuum level or altitude of the vehicle20when desired. The vehicle20may also have a propeller21, control surfaces22, batteries23as a power source for the pump25and an electric turbine24for propulsion via the associated propeller21. The turbine24may have a dual use to charge the batteries23using wind. For example, the vehicle20may launch a tether to secure itself to a building and then use wind to turn the turbine24and thus recharge the batteries23of the vehicle20when necessary so that the vehicle could have increased endurance and mobility. The turbine24may also rotate 360 degrees to allow for maneuverability and to position itself with wind gusts for recharging.

An example embodiment of a mid-altitude aircraft30is shown inFIG. 7. This aircraft30may use multiple internal VLTAVs10as discussed above within an aerodynamic shroud34to attain “lift” for the aircraft30. The shroud34may be fitted with solar panels31, control surfaces32and a propulsion system33to allow the vehicle30to be controlled as a modern aircraft would. Landing gear35may also be provided. This vehicle30would be able to fly at extremely low speeds because the effect of stall would not be an issue because the flight mechanism of the vehicle utilizes the buoyancy developed from the vacuum LTAV's10. It will be appreciated, however, that in other embodiments, lift can be provided by a combination of the air speed and wing design as well as the use of multiple internal VLTAVs. In other embodiments, altitude control could be performed by having inflatable and deflate-able ballast (not shown) for which air could be pumped in or out. The array of solar panels31on top of the shroud34would be used for energy regeneration so that the vehicle may have extremely long endurance.