Patent Description:
One possibility to provide a zero-emission aircraft is to power the aircraft with hydrogen. Compared to kerosene, hydrogen requires approximately four times more tank volume. Aircraft having a fuselage and an aircraft tank for storing hydrogen in an upper area are known from <CIT>, <CIT>, and <CIT>.

The object of the invention is to provide an aircraft tank providing more tank volume for storing cryogenic hydrogen.

To address this problem, the invention provides an aircraft according to claim <NUM>.

Advantageous embodiments of the invention are identified in the dependent claims.

The invention provides an aircraft witch an aircraft tank for storing cryogenic H2, wherein the aircraft tank is configured as non-circular dorsal tank.

Preferably, the aircraft tank is configured as conformal fuel tank fitted to an outer contour of an aircraft fuselage.

Preferably, at least one outer or inner skin segment of the tank has a cross section formed as a circular segment or elliptical segment.

Preferably, first and second outer and/or inner skin segments are connected with a transition area having a stronger curvature compared to the curvature of the first and second skin segments.

Preferably, a lower side of the tank to be arranged near to the aircraft fuselage has several skin segments connected by concave connection areas.

Preferably, a lower side to be arranged near to an aircraft cabin has first to third skin segments with a convex curvature with concave connection areas therebetween.

Preferably, the aircraft tank includes a series of reinforcement ribs connecting several skin segments of the tank in the interior of the tank.

Preferably, the ribs have perforations enabling cryogenic H2 flow.

Preferably, the ribs have several orifices for weight reduction.

Preferably, the aircraft tank comprises an inner skin side reinforced with at least one of the reinforcement structures of the group consisting of flanges, stringers, orthogrid stiffeners, and isogrid stiffeners.

Preferably, the aircraft tank comprises a flat or plate shaped bulkhead for closing a forward and/or backward end of the tank.

Preferably, the aircraft tank comprises a closure bulkhead with at least one reinforcement structure.

Preferably, the aircraft tank comprises a closure bulkhead reinforced with at least one of the reinforcement structures of the group consisting of longitudinal stiffeners, transversal stiffeners, orthogrid stiffeners, and isogrid stiffeners.

Preferably, the aircraft tank comprises a bird-strike resistant forward closure bulkhead.

The aircraft tank comprises an inner skin defining an inner tank volume and an outer secondary skin enclosing the inner skin and defining an isolation chamber between the inner and outer skins.

Preferably, a distance between the inner and outer skins is at least <NUM>. Preferably, the outer skin has an aerodynamic smooth outer surface and/or a fairing function.

Preferably, the aircraft tank has an elongated tank body with a non-circular cross section. Preferably, a tank wall assembly of the tank body comprises at least one inner skin and at least one outer skin.

The invention provides an aircraft, especially passenger or cargo aircraft, comprising an aircraft tank according to any of the preceding embodiments. Preferably, the aircraft is a single-aisle or double aisle aircraft.

According to the invention, the aircraft has a fuselage containing a passenger cabin and/or a cargo space, wherein the non-circular H2 cryogenic dorsal tank is arranged on the top of the fuselage.

Preferably, the aircraft tank is configured as conformal tank of the aircraft. According to the invention, the outer skin of the aircraft tank has aerodynamical smooth transitions to the outer skin of the fuselage.

One possible concept for a zero-emission aircraft is to power the engines of a turbofan aircraft with hydrogen. With this concept, classical aircraft configurations can be used wherein fuel tanks are configured to store hydrogen. The most promising storage concept for hydrogen is the cryogenic storage of liquid hydrogen at low temperatures. At the present, cryogenic H2 tanks are normally cylindrical tanks or spherical tanks with a circular cross section. This has advantages with regard to a small surface enclosing a large volume, and correspondingly low weight of the tank, better thermal isolation and better handling of higher pressures within the tank.

Preferably, the aircraft is a turbofan hydrogen-powered aircraft. Due to the powering with hydrogen, the aircraft produces zero CO2 emissions and can substantially reduce air pollutants such as nitrogen oxide, as well as helping prevent contrail formation. However, a larger tank volume is needed for storing H2 compared with kerosene.

In current classical passenger and cargo airplanes, tanks inside the wing do not provide volume which suits all needs of an hydrogen-powered aircraft. Therefore, embodiments of the invention provide, as (additional) tank position option, the dorsal tank configuration.

Previous and current studies show that for a classic aircraft configuration the dorsal tank configuration is a good option. Some challenges with these configurations are:.

Therefore, the invention proposes a non-circular tank; especially, a non-circular tank which follows the shape of the fuselage. One target of some embodiments is to make best use of the available cross-sectional area between dorsal tank and fuselage, avoiding unused space.

By a circular tank, which is common for actual concepts of cryogenic H2 aircraft tanks, this unused area would need to be covered by the fairing, increasing the fairing area and weight significantly.

Preferred embodiments of the invention provide at least one or several of the following advantages:.

The invention proposes an aircraft with a fuselage and a non-circular cryogenic H2 dorsal tank arranged on the top of the fuselage. Preferably, the tank follows the shape of the fuselage and reduces the fairing wetted area.

Most preferred embodiments aim to make best use of the available cross-sectional area between dorsal tank and fuselage, avoiding unused space.

Preferred embodiments provide a dorsal tank arrangement comprising several non-circular H2 tanks.

Preferably, the H2 tank or all H2 tanks are filled with liquid hydrogen and dimensioned for a maximum pressure of <NUM> bar.

Preferably, the selected tank material is light metal such as an aluminium alloy, especially aluminium AL <NUM>. Composites may be an option. According to several embodiments, some of the areas of the tank wall or of skin segments thereof may be made from metal while other areas may be made form composite material. According to further embodiments, skins of the tank can be made, at least partially from fibre reinforced plastics such as CFRP.

Preferably, vacuum is assumed in between tank skin and outer aerodynamic tank skin for best isolation.

Preferably, the temperature inside tank is < <NUM> (-<NUM>).

Preferably, the tank follows outer contour of the fuselage.

Preferably, the tank has circular outer skin segments.

Preferably, the tank has perforated ribs inside to enable cryogenic H2 flow.

Preferably, the tank has ribs including weight reduction orifices.

Preferably, the tank inner skin side is reinforced with flanges/stringers, orthogrid or isogrid stiffeners.

Preferably, the tank has a flat reinforced closure bulkhead, especially reinforced e.g. by longitudinal, orthogrid or isogrid stiffeners.

Preferably, the tank has a bird-strike resistant forward closure bulkhead.

Preferably, the tank's secondary outer skin providing the thermal insulation chamber is at a distance of <NUM> from tank skin.

Preferably, the tank's secondary outer skin is at a distance of minimum <NUM> from tank skin providing the aerodynamic smoothness (no need of a fairing around the tank).

Embodiments of the invention are described in more detail with reference to the accompanying drawings in which:.

<FIG> and <FIG> show cross sections through a fuselage <NUM> of an aircraft <NUM> according to a first and second embodiment of the invention, while <FIG> shows a similar cross section through the aircraft 12a according to a first comparative example. <FIG> and <FIG> show different views of a further aircraft 12b according to a second comparative example, while <FIG> and <FIG> show similar views of the aircraft 12a according to the first comparative example, and <FIG> and <FIG> show similar views of the aircraft <NUM> according to the first embodiment of the invention, a cross section thereof is also shown in <FIG>.

<FIG> and <FIG> show a conventional aircraft 12b (second comparative example) with turbofans <NUM> as engines powered by kerosine. The kerosine is stored in aircraft tanks within the wings. <FIG>, <FIG> and <FIG> show an aircraft 12a according to the first comparative example having turbofans <NUM> as engines which are powered by hydrogen. In order to provide a larger tank volume compared to the kerosine tanks of the conventional aircraft of <FIG> and <FIG>, the aircraft 12a according to the first comparative example comprises a dorsal tank arrangement 16a including several cylindrical aircraft tanks 18a which are configured to store cryogenic hydrogen. These cylindrical hydrogen aircraft tanks 18a according to the first comparative example are also referred to as reference tanks in the following. The aircraft 12a according to the first comparative example has, as visible in <FIG>, a fairing <NUM> with a supporting substructure for the cylindrical aircraft tank 18a. Hence, a large unused space <NUM> is present.

The aircraft <NUM> according to the first and second embodiments of the invention as shown in <FIG>, <FIG>, <FIG> and <FIG> have a dorsal tank arrangement <NUM> with several aircraft tanks <NUM> according to a first and second embodiment of the invention. In the embodiments shown, the dorsal tank arrangement <NUM> includes a forward first aircraft tank <NUM>-<NUM> and a rear second aircraft tank <NUM>-<NUM>.

The aircraft tanks <NUM>, <NUM>-<NUM>, <NUM>-<NUM> are configured to store cryogenic hydrogen and have an elongated tank body with non-circular cross section as shown in larger detail in <FIG> and <FIG>. Especially, the aircraft tanks <NUM>, <NUM>-<NUM>, <NUM>-<NUM> are configured as non-circular dorsal tanks. As visible from <FIG> and <FIG>, the aircraft tanks <NUM>, <NUM>-<NUM>, <NUM>-<NUM> are conformal fuel tanks fitted to an outer contour of the fuselage <NUM>.

The aircraft tank <NUM> has a lower side <NUM> with a recess <NUM> which receives the top of the fuselage <NUM>. The lower side <NUM> comprises first to third (lower) skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> that are curved outwardly - convex curvature - connected by concavely curved connection areas <NUM> there between.

The upper part of the inner skin <NUM> of the aircraft tank <NUM> may be circular or elliptical in cross section as shown in <FIG> or may comprise several convexly curved (upper) skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>. The curvature of this fourth to sixth skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> may be circular or elliptical, as shown in <FIG>. Transitions areas <NUM> between the upper skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> have a stronger curvature compared to the curvature of the upper skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>.

As visible from <FIG> and <FIG>, the non-circular cryogenic H2 aircraft tank <NUM> makes best use of the cross-sectional area avoiding large fairings <NUM> and an unused space <NUM>.

As visible by a comparison of <FIG> and <FIG> the wetted area of the aircraft tank <NUM> according to the embodiments of the inventions is significantly reduced compared to the reference tank 18a of the aircraft 12a of the first comparative example. The non-cylindrical aircraft tank <NUM> has a reduced wetted area with improved aerodynamics and reduced fairing weight.

<FIG> show details of the structural concept of the inner skin <NUM> of the aircraft tank <NUM>. The inner skin <NUM> defines a tank volume <NUM> in its interior. The inner skin <NUM> is a reinforced tank skin. Especially, the inner skin <NUM> is reinforced by longitudinal stiffeners <NUM>. As shown, all skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> comprise the longitudinal stiffeners <NUM> in the interior thereof (especially at the inner side of the inner skin <NUM>). According to other embodiments, the skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> could also be reinforced by orthogrid or isogrid structures (not shown).

Referring to <FIG>, the forward and rear ends of the aircraft tank <NUM> are closed by closure bulkheads <NUM>; an example thereof is also shown in <FIG>. The closure bulkhead <NUM> can be a flat, plate-like structure with reinforcements. The bulkhead <NUM> has an orthogrid structure <NUM> for reinforcement. The closure bulkhead <NUM> closes the tank <NUM>, wherein stresses at the orthogrid structure <NUM> are below the allowable material stress. Especially, the forward closure bulkhead <NUM> is reinforced in such way that it is resistant against bird strikes.

As visible in <FIG>, <FIG> and <FIG>, the interior of the aircraft tank <NUM> is provided with a series of reinforcement ribs <NUM>. The ribs <NUM> connect the skin segments <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM> to each other. The ribs <NUM> are preferably plate-shaped structures. The ribs <NUM> inside have mainly the functions to keep the outer shape and minimise deformation and keep the skin stress below the allowable material stress. Preferably, the ribs <NUM> are evenly distributed over the longitudinal direction within the interior of the aircraft tank <NUM>. Preferably, the ribs <NUM> have orifices <NUM> at lowest points to enable a flow of (liquid) hydrogen. Further, the ribs <NUM> have several larger openings <NUM> in order to reduce their weight. For example, a number of three to forty ribs <NUM> are provided within the interior tank. Preferably, the distance between the ribs <NUM> is less than one meter.

As shown in <FIG> and <FIG>, the aircraft tank <NUM> further comprises an outer skin <NUM>. The outer skin <NUM> of the aircraft tank <NUM> has an aerodynamic function. The outer surface of the outer skin <NUM> is provided with aerodynamic smoothness, further, the outer skin <NUM> provides smooth transitions to the fuselage <NUM>.

Between the outer skin <NUM> and the inner skin <NUM>, an isolation chamber <NUM> is established. Hence, the outer skin <NUM> has the further function of tank isolation. The gap between the skins <NUM>, <NUM> is selected such that a good isolation is possible. For example, the gap is at least <NUM>. The isolation chamber <NUM> is evacuated and/or contains isolation material as this is generally known for cryogenic H2 tanks.

The aircraft tanks <NUM> according to the embodiments of the invention have been modelled in a finite element analysis to get a weight estimate and to estimate the stresses on the tank walls during use as liquid hydrogen tanks. The outcome was that the weight penalty of choosing a non-circular tank is compensated by the reduced fairing weight when compared with the first comparative example. Hence, surprisingly, the aircraft tanks <NUM> according to the embodiments of the invention provide overall a smaller weight compared to the comparative example with the cylindrical aircraft tank 18a. Further, the material stresses at the skins <NUM>, <NUM> and the ribs <NUM> are much smaller as the allowable material stress.

As shown in <FIG> and <FIG>, the aircraft <NUM> is preferably a passenger aircraft wherein the fuselage <NUM> contains a passenger cabin <NUM> and a cargo space <NUM>. Further embodiments using a similar fuselage <NUM> are configured as cargo aircrafts. Especially, the aircraft <NUM> is a narrow-body aircraft or a wide-body aircraft.

Claim 1:
Aircraft (<NUM>), comprising a fuselage (<NUM>) containing a passenger cabin (<NUM>) and/or a cargo space (<NUM>) and an aircraft tank (<NUM>) for storing cryogenic H2, wherein the aircraft tank (<NUM>) is configured as non-circular dorsal tank arranged on the top of the fuselage (<NUM>) and comprises an inner skin (<NUM>) defining an inner tank volume (<NUM>) and a secondary outer skin (<NUM>) enclosing the inner skin (<NUM>) and defining a thermal insulation chamber (<NUM>) between the inner and outer skins (<NUM>, <NUM>), wherein the outer skin (<NUM>) of the aircraft tank (<NUM>) has aerodynamical smooth transitions to the outer skin of the fuselage (<NUM>).