It can be easily established that the required airship can only be conceived as a rigid structure airship. Non-rigid or semi-rigid airships only allow passenger transport in a gondola below the airship hull. The required space for 400 passengers together with a crew of 116 persons would mean a gigantic gondola even if a minimum amount of space per passenger were considered and among the many disadvantages is the very large drag. In contrast, the Zeppelin LZ 129 already with its rigid structure construction allowed accomodation of the passengers in the hull with thus favorable aerodynamic conditions and a relatively large amount of available space per passenger (although with a small total number of passengers).

In addition, the airship should possess a metallic outer skin to be resistant against light and weather conditions and have minimum maintenance costs. The only all-metal-airship that can be considered as being successful was the American airship ZMC 2. Here the outer skin additionally performed as the gas cell which had to be kept at a slight overpressure. Hence this airship has to be considered as a non-rigid airship with internal metal stiffening skeleton. For the large Zeppelins, a metal outer skin never came into consideration because the weight, governed by the elongated form and the resultant very large surface area compared to the carrying gas volume, would have been much too large. Whereas the LZ 129 had a length to thickness ratio of 6:1, the value for the ZMC 2 was only 2.83:1 and therefore much closer to the - in this respect - optimal spherical form with 1:1.

With the LC-400, for the first time a form approaching a rotational ellipsoid is abandoned where width=height=diameter. Instead, the form of the outer skin is an exact three axes ellipsoid, with the axis relationship Length L: Width W: Height H = 3:2:1, represented by the equation x²/a² + y²/b² + z²/c² = 1. Here a = L/2, b = W/2, c = H/2 and the origin of the coordinates is in the centre of the airship. x is positive in the forwards direction, y positive to the right and z positive going down.

If one were to compare this ellipsoid regarding its elongation with rotational ellipsoids, then considering the different width and height, the cross sectional areas use instead of the diameter D the value . One therefore obtains an equivalent elongation ratio of 2.12:1. This value is more favorable for the surface area to volume ratio than that of ZMC 2 and is also aerodynamically favorable as will be shown in the next section but one. Especially important for this form is the fact that for the middle level z = 0, a large oval surface with surface area F = (L/2) (W/2) is available that provides much room for accomodating the passengers, as will be shown soon.

The final dimensions of the airship can only be arrived at in a multiple iterations process approach. The carrying capacity of the helium filling is given at the cruising height. Now check whether for the given helium volume the carrying capacity is less than the weight of this helium volume plus the weight of persons, cabins, general facilities, operational equipment, operational fuel, provisions (stores), together with the weight of the airship skeleton, outer skin, motors etc. If yes, a larger dimensioning must be chosen with larger helium volume, larger motors because of larger air drag which in turn weigh more and require more fuel etc. This iteration must be carried out until the carrying capacity of the helium slightly exceeds the start weight of the airship.

As a preliminary result of this iteration process, the chosen axes dimensions are presented here without any explanation because Section 15 deals with the total weight audit for a 6 ˝ day cruise where the here presented axes dimensions proved adequate. It must be stressed that this technical description is the first draft where the weight estimate is based on industrial experience. It is surely to be expected that a construction work based on this draft after, for example, exact calculation of the statics will give an either higher or lower value, which may be compensated by probably choosing other motors or other furnishing of the cabins or any other possibilities. Under the foregoing premises, the following is defined:

	Length L = 219m	Width W = 146m	Height H = 73m
And therefore half axis	a = 109.5m	b = 73m	c = 36.5m

The volume of the ellipsoid is given as V = 4 a b c/3
Volume V = 1,222,133 m³

The surface area of the ellipsoid is numerically calculated by a three dimensional curved surface integrating computer program (Mathematica)
Surface area O = 65,123 m²

The area of the horizontal middle level (z = 0) is given by F = a b
Middle area F = 25,112 m²

With a known approximation formula, the horizontal perimeter at the middle is calculated as
Middle perimeter U = 579 m

The ellipsoid above the middle level down to z = 10 m below the middle level is completely filled with gas cells (with a spacing of 0.5 m to the outer skin and the floor). The bottom half is occupied from z = 13.5 m going down (z = 17.25) with cabin deck and panorama or promenade deck. The volume of this part due to a numerical integration is
Deck volume V_D = 157.780 m³.

The rest of the bottom half is partly filled with further gas cells which support a part of the deck weight. The rest of the volume not occupied by the gas cells is for corridors, machine rooms, supply equipment, fuel, and water. For this purpose 10,000 m³ are reserved.

The total volume available for the gas cells is thus approximately
=> Gas volume V_G = 1.048.517 m³.

The buoyancy force A in kilograms for one cubic meter of helium is equal to the weight of the air displaced by it minus the weight of the cubic meter of helium and with an added correction factor for the water vapour content for the displaced air, since damp air is lighter than dry air because the molecular weight of water (18) is smaller than the average molecular weight of air (29). This specific buoyancy force is therefore a function of the air pressure (in the following this is always equivalent to the helium pressure, which is almost always the case for the conditions here), as well as the air and the (often varying from it) gas temperature and the air humidity. The formula for this dependence is

Thus one obtains, for example, at an air pressure of 1013.25 mbar and a temperature of 15 °C, which is the International Standard Atmosphere (ISA) at sea level, and at 100% humidity a buoyancy force of A = 1.048 kg/m³, whereas at 2,000 m altitude (794.88 mbar, 2 °C) it is A = 0.864 kg/m³. For high and low pressure regions, the maximum variation of the air pressure is ± 2.5% about the normal pressure, i.e. for a travelling altitude of 2,000 m, a variation between 775 and 815 mbar. The corresponding buoyancy values are A_h = 0.886 kg/m³ and A_l = 0.842 kg/m³.

With a helium volume of 1.048.517 m³, the following buoyancy force values "A" are obtained: at sea level A_m = 1.099 t, at a travelling altitude of 2,000 m at normal pressure A_RN = 906 t, at high pressure A_RH = 929 t, at low pressure A_RT = 883 t.

Since the helium expands upon ascent, the gas cells should be filled on ground to a value so that upon reaching the maximum travelling altitude they are almost full i.e. the so called pressure height is reached. Hence one may only fill the airship at sea level at normal pressure and 15 °C for a pressure height of 2,000 m with only 82.4% (= filling factor 0.824) of the total holding capacity of 858,000 m³ i.e. 707,000 m³. This means a buoyancy force at start of A_st = 906 t, the same as at the pressure height.

The necessary alteration of the buoyancy force of ± 23 t upon traversing low and high pressure regions can be obtained by either cooling or heating a part of the lower gas cells (approx. 200,000 m³) with the equipment described in Section 8, but at any time also by dynamic positive or negative lift by changing the angle of attack by ± 5°, resulting in a lift-change of ± 50 t at cruising speed.

The gradual diffusion of the helium from the gas cells through the cell walls and leakage from feedthroughs and valves is a minor problem and may be compensated by occasional dumping of a small fraction of surplus water during the cruise.

Special attention has to be paid to the construction of the gas cells because the general reliability of the airship is essentially dependent on them. Primarily, the carrying gas volume must be distributed over a sufficient number of gas cells which are separated from each other by tightly spanned string nets to prevent their lateral displacement. This was neglected in the English airship R101, where in dynamic ascents with 3° ascent angles, the upper ends of the gas cells were pushed up to 3m in front resulting in the nose being lifted up. This had to be compensated by counter steering. Hence see-saw motion was obtained and a calm horizontal flight was hardly possible. It was also neglected in the same airship to keep the gas cells away from the struts and rings of the skeleton by string nets so that the gas cells soon scoured through (or chafed) at the points of contact resulting in loss of buoyancy of up to one ton per hour of travel. Therefore in the LC-400 it is provided for to keep the gas cells away from the outer skin at an average distance of 0.5 m by string nets.

Various accidents, especially the one of the American airship "Shenendoah", teach us that special care must be taken in the dimensioning of the overpressure valves. In this airship, the valves were designed to open at a few mbar overpressure in the gas cells to prevent their bursting if the pressure height was exceeded. Helium being very expensive at that time and the fear of excessive loss resulted in their diameter being designed much too small. Now as the ship got caught in a stormy upwind that pushed it up within a few minutes more than 500 m above the pressure height and the resulting overpressure could not be relieved fast enough by the much too narrow valve openings, several of the cells burst. After leaving the upwind region, the much too heavy ship lost height fast and the crew threw away all ballast and part of the fuel as well. The lighted ship now shot up once again above the pressure height and broke up through this overstressed dynamic load into three parts. A part of the crew was killed and only the lucky circumstance that the nose and tail still contained enough helium has to be thanked that these parts landed relatively gently with the rest of the crew.

This tragic event (and many more similar ones) teach us two things: 1) The gas exhaust valves must be dimensioned large enough for extreme cases, but be controllable for regulated gas exhaust for less extreme cases. 2) There should be no overreaction like in this case throwing away the ballast. Of course this is much easier said than done, because the delayed reaction of the ship resulting from its large inertia is very difficult to predict even for a very experienced commander.

Today´s technology and engineering allow a solution in that electrically operated valves of large enough cross-section be computer controlled. The computer program should include all important parameters like the values of the partial pressure sensors from all gas cells, the variometer readouts, the instantaneous weight of the ship and react upon them. For extraordinary situations, the commander must have the possibility to override the computer program. Moreover, the vertical actuators are then a help in providing dynamic counter-steering.

a) Air drag, Reynolds numbers
The air drag coefficient c_w values for normal ellipsoids (three different axes lengths) are not to be found in the literature. The coefficients c_w for rotational ellipsoids for flow in the direction of the long axis as function of the ratio diameter/length are to be found in S.F. Hoerner: "Aerodynamic drag", 1958, Page 3-12 as Figure 19, where this ratio ranges from 0 to 1.4 i.e. from extremely oblong to slightly oblate ellipsoids including the sphere. The measurements were made at moderate Reynold numbers around 10⁶, which is the case for smaller airships.

This function varies very slightly in its value for the range that is being considered here. For the estimate of the correct cw value, it is therefore a good approximation to replace the diameter of the rotational ellipsoid by the geometrical mean of the width and height, = D, when the frontal drag is to be calculated. Similarly for the side wind sensitivity = D, for the rise or sink resistance = D are to be used. Hence the values obtained from the diagram are c_w1=0.07 for the frontal resistance, the same c_w2=0.07 for the side wind drag and c_w3=0.10 for the vertical drag. For comparison, the front drag for the Zeppelin LZ129 according to experimental measurements was c_w4=0.06 (axes ratio 6:1), c_w5=0.07 for the side drag of the hull and c_w6=1.1 for the tail and rudder surfaces (flat board).

Now the air resistance is given by the formula W=1/2 v² F_i c_wi where is the density of air, F_i and c_wi with i=1....6 are the largest cross-sections and the corresponding drag coefficients for the cases mentioned above.

For the travel resistance, a cruising speed of V = 100 km/h = 27.778 m/s at cruising altitude of 2,000 m (air density = 1.007 kg/m³) and for the side wind sensitivity the same v = 100 km/h side wind speed is considered. For the sink and rise resistance, v = 1 m/s (shortly before the landing or immediately after start) is considered. The resultant values of the resistance for the ellipsoid airship LC-400 described here are given below; for comparison the corresponding values for the LZ 129 are given in brackets.

Frontal cross-section	FF = 8,371 m2	Frontal resistance	W100,F = 227,651N (37,187N)
Side cross-section	FS = 12,556 m2	Side resistance	W100,S = 341,459N (583,525N)
Vertical cross-section	FH = 25,112 m2	Sink resistance	W1m/s,H = 1,265N (756N)

The Reynolds Number is given by R = vl/, where v is the cruising speed (27.778 m/s), l is the length of the air ship (219 m), is the kinematic viscosity of air at cruising altitude (2000 m). With ₂₀₀₀ = 1.684 ^. 10^-5 m²/s, the Reynolds Number R = 3.6 ^. 10⁸. For investigations in a high pressure wind tunnel at 50 bar pressure and v = 30 m/s, one obtains Model Reynolds Number = 19.5 ^. 10⁶ for a model in scale factor 1 : 1000 (21.9 cm). Herewith is one already safe in the over-critical region so that the results obtained with the model can be transferred to the airship.

The first evaluations of the measurements in the wind tunnel were a surprize, exhibiting essentially lower drag coefficients than the above estimates. So c_w1 (for frontal angle of attack = 0 and angle of side-slip = 0) was measured as c_w1 = 0,028 ± 0,001 at a Reynoldsnumer Re = 35.2 ^.10⁶. Further measurements at lower Re-numbers allowed to extrapolate the relevant number for LC-400 at cruising height (2000 m) and speed (100 km/h), which is equivalent to a Re-number of 3.6 ^. 10⁸, an air drag coefficient of c_w1 = 0.027 ± 0.002.

This is valid only for the bare hull, without ampennage, motor-nacelles etc., which all increase the drag coefficient. The comparable value for the LZ129 bare hull is c_w = 0.056 (taken from the diplome thesis work of A. Litz, FH Aachen, 1994). This result alone would already have justified the expensive model and wind tunnel measurements, since now we know that the propulsion motor needs only be less than half as powerful as origionally estimated (see above).

The reason for these astonishing results is the special ellipsoidal form of the LoftyCruiser, as will be explained in a planned publication in a specialized technical journal.

b) Dynamic rise/sink
According ot our wind tunnel measurements the coefficient of lift e.g. for v = 5° was found to be C_A = 0.15 which translates to a dynamic lift of A = ± 50 t at the usual cruising speed and height.

c) Moments from gusts
(Detailed calculations to be completed after evaluating the multitude of wind tunnel measurements.)

The normal steering of an airship by the rudder attached to the tail fin has two principal disadvantages:

1.) The large surface area of the fins and rudder attached to it present a large resistance to the gusts of wind which may come either from the sides or from the top or the bottom, where the c_w value to be assumed is that of a flat board. In the history of aviation, many catastrophical accidents have been either directly or indirectly caused by this. Sometimes the tail fin together with the rudder was completely torn off, often the covering fabric was torn to shreads and the rest jammed the rudder. It has also happened that at high speed hard rudder was laid resulting in the airship breaking apart in the middle.

2.) As is very well known in shipping, the rudder works only at adequate flow; at relative speed zero to the surrounding medium the rudder is useless. This can hence present great difficulties especially at landings.

These principal disadvantages of normal steering devices can be overcome if one were to provide for manoeuvering drives which allow full manoeuveribility even at speed zero without significant increase of air resistance. With proper dimensioning, these units can also take over the position control and dampen aerodynamic disturbances in flight so that in principal the empennage can be omitted. To support the so achieved dynamic stabilisation and to allow some self-stability, relatively small retractable fins may be provided which can be steered in the range of ±15° (Fig.1).

With this dynamic regulation, the time constants of the appropiate controls are of highest importance to allow, for example, at the earliest possible time the right amount of counter-steering in case of a wind gust, resulting in a calm flight. This can be best achieved by a fully electronic control circuit where the control motors are the final regulation elements. These electrically driven control motors as regulatory elements are called actuators here.

Description of the actuators
Each of the actuators used here consists of a power unit, in whose envelope, called actuator tube here, two counter-rotating variable pitch propellers are directly driven by a frequency variable asynchronous electric motor. All actuator tubes run through the ship and end in openings which follow the contours of the ship and have aerodynamically favourable edges for the necessary intake and exhaust of air. Four vertical (parallel to the vertical axis) and two horizontal (parallel to the transverse axis) actuators are foreseen. The middle axis of two of vertical actuators cuts the long axis about approx. 80 m before and after the middle point of the ship, the other two on the transverse axis each 58 m to the left and right of the middle point. The horizontal actuators lie below the three decks at approx. z = 15 and x = ± 73. The centre of gravity of the motors for the actuators are at the level z = 15 to assure favourable centre of gravity of the airship (Fig 2 a, b, c).

All actuator tubes will be incorporated into the skeleton statics. They are lined on the inside and outside with sound-insulating or sound absorbing material.

Ascent/Descent with the vertical actuators
For the horizontal actuators, electric motors with a shaft load of 100 kW are planned, which in the peak may be overloaded by 50% for 60 s. To calculate the standing thrust, the data of the propeller and the maximum revolution must be known. Both of these can be decided upon after the final design of the complete system. For a first design, the value can be estimated from the data of available propeller types. As such, the values given in the monography from F. Dubs: "Aerodynamik der reinen Unterschallströmung", 6^th Edition, Basel, 1990, are used. Two counter-rotating twin-blade propellers with diameter of 5 m are used whose combined fullness factor (sum of the blade area divided by the propeller circular cross-section) is 0.30. The maximum speed of the blade tip was chosen to be U = 150 m/s to minimize the propeller noise. Hence the power factor K_p = 2 P/( U³ S_p) = 0.0030 where P is the motor power, = 1.0065 kg/m³ the air density at travelling altitude and S_p is the propeller circular cross-section. With this value and the fullness factor, the nomogram (Fig. 246, loc.cit.) gives the blade angle as _3/4 = 5° (extrapolated). At this blade angle, the nomogram Fig. 245 gives the ratio of the thrust factor K_F = 2 F/( U² S_p) to the Power Factor K_p as K_F/K_p = 10.0. Here F is the propeller thrust. The final stationary thrust F₀ = (K_F/K_p) (P/U) = 6,667 N. This value is based on the free stream thrust. For ducted power units, as is here the case, there is a long enough entrance duct as diffuser to give an approx. 30% higher stationary thrust => approx. F₀ = 8,600 N. It is clear that for the actuators, only the stationary thrust is of importance in the normal case because there is usually no pressure difference between the entrance and exit openings since their centre-point is located on symmetrical points of the ship. Upon gusts, the efficiency can only get better so that one can count on the value of the stationary thrust for further calculations.

Eletric motors with a rating of 300 kW are foreseen for the vertical actuators. With the already described procedure above, the propeller parameters can be once again optimized and a stationary thrust of 25,800 N for each actuator can be calculated. The four vertical actuators can thus together provide an ascent/descent force of 10 t. This is equivalent to an ascent/descent speed of 9.5 m/s at a cruising altitude of 2,000m. The large inertia of M = 741 t slows the reaction to the switching on of the actuators like, for example, at start. One obtains with h = 1/2 b t² where h is the achieved height after t seconds and the acceleration b = 4 F₀/M, the following pairs of values t/h: 0/0; 1/0.08; 3/0.7; 6/2.9; 10/8.2; 20/32; 30/65, the still low resistance of air has been neglected. It is clearly noticeable after the last pair when the ascent speed is already v = 4 m/s. At this height, the propulsion motors would generally be already switched on and deliver dynamic lift so that the cruising altitude should be reached in a few minutes.

Turning around the vertical axis by horizontal actuators
The torque D of the horizontal actuator pairs at stationary thrust F₀ = 8,6000 N and lever length l = 73 m (see above) is D = 2 x 8,600 x 73 = 1,255,600 Nm. The moment of inertia J of the airship along the vertical axis can only be roughly guessed so long as the distribution of the mass in the airship has not been finally decided. As a simple calculable model, it is assumed that the mass is uniformly distributed over a disc of radius R² = a b. Then J = 1/2 MR² = 1/2 x 741,000 x 109.5 x 73 = 2.96 x 10⁹ kgm². With the rotation angle along the vertical axis, the time behaviour (t) is given as = 1/2 (D/J) t² . A few pairs of value for t/ are 0/0; 1/0.013°; 10/1.3°; 20/5.1°; 30/11.6°; 60/81°; 133/181°. One sees that the airship can turn around a point in about two minutes.

Whereas for these turns the two actuators are blowing antiparallel, for spot landing parallel operation is a great help for making small movements parallel to the transverse axis.

Compensation of gusts by the actuators
In the "Requirements for air worthiness of airships" of the German Air Traffic Control-Luftfahrt Bundesamt (LBA), Braunschweig, the form and strength of gusts that an airship must withstand without damage are given. These gusts are represented by the formula u = (U_M/2) [1 - cos ( /H)] where

UM	= the maximum speed of the gust which is fixed at 25 ft/s at the maximum speed of the airship VH. At a lower airship speed of 0.65 VH, the gust speed is 35 ft/s.
	= penetration depth 0 < < 2H
H	= the gradiant length of the gust L/4 < H < 800 ft
L	= length of the airship

The gusts can come from any and every direction. In the case being considered, the worst condition is that the gust comes from the front at the bottom or the front at the top, because then is the risetime the shortest. In order to calculate the risetime T_A, the following values are available: L = 219 m, V_H =125 km/h = 34.7 m/s, 0.65 V_H = 22.6 m/s, 35 ft/s = 10.5 m/s, H = L/4 = 54.8 m.

One thus obtains the risetime that the gust requires to traverse from = 0 to = L/4 at an average speed of U_M/2: T_A = 54.8/(12.5/2) = approx. 10 s.

This time should be possibly larger than the time taken for the actuators to attain the maximum speed of rotation of n = 500 rpm from stand still. For the 300 kW motor, the vertical actuator rotor moment of inertia is J_R = 46.8 kgm² (basic standard version from Schorch/LDW, Berlin), its torque D = 5730 Nm. Since no data is available for the dimensioning of a counter-rotating propeller, the calculation for a 5-blade propeller from MT Propeller Entwicklung, Straubing were adapted since it has almost the same fullness factor as a 2x3 bladed counter rotating propeller with same power (300 kW), diameter (6 m), and speed of rotation n (500 rpm). This propeller has an axial moment of inertia of J_p = 137.5 kgm². Since the full torque is immediately available as a result of the frequency variable motor drives, the total moment of inertia J = (137.5 + 46.8) = 184.3 kgm² already allows the full maximum speed of rotation to be achieved after a run up time of T_H = J/D = 2 (500/60) 184.3 / 5730 = 1.68 s neglecting the air resistance. Even if the air resistance were considered and the run up time guessed at 5 s, this time is only half as large as the shortest risetime of the reference gust, so that the control system can be dimensioned to efficiently compensate the test gust.

Landing manoeuvre with the actuators
The landing of the cruise airship must be done with the assistance of the actuators since it must exactly land on an iron landing platform only 30 m long and 20 m wide, which is very difficult to perform without the actuators. The ship would be brought by the forward propulsion motors in a dynamic descent flight to an altitude of about 100 m and then to stand still above the ground. The four vertically working actuators would then press the ship to ground with a starting force of about 10 t. During the descent, downward looking radar or acoustic sensors would continously measure the height above the platform and the horizontal position of the ship relative to the platform and the data transferred to the board computer. An appropriate program would steer the power to the vertical actuators depending on the altitude and horizontal actuators in parallel operation to alter the sideways displacement, whereas minor power variation to the forward propulsion motors would adjust the forwards or backwards position. Moreover, if required, the horizontal actuators in antiparallel operation would turn the nose of the airship into the wind. About 20 m above the ground, the slow sink flight would be switched over to strong buoyancy flight so that the ship would land with a landing speed of only a few cm/s. The remaining kinetic energy would be absorbed by retractable shock absorbers to guarantee a soft landing. The electromagnetic mooring equipment (see Section 7) would then upon switching on anchor the ship rigidly to the landing platform. The propulsion and actuator motors may now be switched off.

a) Arrangement and type of the propulsion motors
Four electro-motors, each with 1,300 kW power capacity are foreseen for the propulsion. They normally run at half power and the full power should only be required at unfavourable wind condition. They must be so dimensioned that the full power of 5.2 MW is available at the normal cruising altitude. They are contained in four nacelles which hang in a quad configuration on the bottom half of the airship a few meters away from the hull, just as in the last Zeppelins.

Two counter-rotating variable pitch propellers are foreseen as thrust propellers for each motor. Their thrust can be reversed to either make a turn or brake the airship, and at the same time maintain maximum efficiency at every speed and altitude. Moreover, there is cancellation of the spin forces along the axes and a compensation of twist in the propeller slip-stream so that the air flow along the outer skin of the airship is less disturbed.

b) Cruising and maximum speed; fuel consumption
In Section 4a, the frontal resistance of the ship at 100 km/h was W_100,F = 33,870 N. The motor power required to maintain this cruising speed is P₁₀₀ = W₁₀₀ * v = 2,600 kW i.e. 50% of the installed power. Hence the maximum speed to be expected v_max = 125 km/h.

To estimate the fuel consumption at the cruising speed, one must first know the specific gasoil consumption. For a 100 h journey, one would perhaps require a fuel capacity of 118 t of the two turbines of 4.2 MW each and the conversion efficiency of the driven electrogenerators, which is only estimated at the moment.

c) Banking with help of the propulsion motors
If one were to allow the propulsion motors on both sides to run at full power, and adjust the propeller blade angle on one side to full thrust (push) and on the other side to full pull, the result is a strong torque along the vertical axis and leads to a curve being flown by the airship. The radius of the curve can be calculated once it is known what percentage of the maximum thrust at the maximum blade angle can be obtained as pull and how large is the moment of inertia of the ship around the vertical axis. Both of these would be decided upon at the final detailed design. In any case, the horizontal actuators would be switched on when a tight curve is to be flown. For very tight or sharp curves, both of the side vertical actuators must be in antiparallel operation as well so that the passengers do not notice any discomfort due to the centrifugal forces. Should an extreme evasion course be necessary (for example in front of a thunderstorm), the propulsion motors would be switched to full reverse thrust and at the same time a quick turn-around be possible by use of the horizontal actuators to take a reverse course at maximum speed for escape.

d) Cooling and condensed water production
Inspite of the streamlined jacketing of the motors by the nacelles in the Zeppelins, large air resistance was caused by the radiator and condensed water production equipment which required large air-intake openings. In case of the cruise airship, one can consider a heating and cooling water circuit running through the entire ship where the single units like cabin air-conditioning, helium gas temperature control and also the propulsion motor and condensed water production equipment are appropriately dimensioned and connected to controlled heat-exchangers. This means that the nacelles need only relatively small intake openings for the electro-motor. The reduction of the total drag should be considerable even if quantifying is not possible owing to lack of comparable data and is of little interest at this stage of development.

A still not satisfactorily solved system in the airship technology is that of landing and mooring (or anchoring) of the airship. A generally used method is that of throwing a tow-line from the airship to a necessarily large crew of ground personnel that then pulls the ship to the intended anchorage and ties it down securely to posts. Later, the ship is transferred from the anchorage to a covered hall by either the ground crew or appropriate equipment to protect it from weather conditions (especially stormy winds).

Another generally used method is either to tie the ship to a mast so that the gondola just touches the ground to allow the passengers to climb down a ladder or stairs, or a tall mast of about 50m height with snap-in equipment where the opposite part mounted in the nose of the airship snaps into. The top of the mast is freely rotatable so that the airship can sway in the wind just like a weather-vane. Passengers, crew and freight are transferred over a footbridge (or gangway) from the airship to the top of the mast and then by a lift to the ground. Both of these methods with many variants are vividly described in the book from P. Kleinhans (Editor): "Die Grossen Zeppeline", 2^nd edition, Düsseldorf, VDI-Verlag, 1996 (in German). It is clear that these methods are very expensive and dangerous as well. They are therefore unacceptable for large cruise-airships with about 400 passengers.

The method presented here of electromagnectic mooring avoids the difficulties mentioned above and as a result of the minimal necessary infrastructure as well as low number of ground personnel requirements should allow economical operation.

a) Construction and Properties
The cruise airship differs slightly in its lower part from a perfect ellipsoid form in that parallel to the middle level an elliptically shaped entrance/exit deck is to be found. Six pot-shaped electromagnets are rigidly mounted on this deck so that their pole surfaces are level with the bottom surface of the deck. The ship thus lands with these pole surfaces in contact with the iron landing platform and would be anchored by switching on appropriate direct current through the magnets (Fig. 3). The position of the six magnets is such that all the magnets with their center of pole surfaces lie on the circumference of a circle. One magnet is in front of and one behind the centre point seen in direction of travel. The other four magnets are situated on to the right and left, seperated by 45° on the circumference. The diameter of the circle is approx. 28 m.

b) Displacement and detachment forces
The magnets are commercially available lifting magnets from Wagner KG Magnetbau, D-87751 Heimertingen, Germany, and the following details are taken from their catalogue. They are 1.150 mm in diameter, 295 mm in height and weigh 1,060 kg. For lifting an iron plate of steel (e.g. St34 or St37) with a minimum thickness of 8 cm and an air gap of 3 mm between the pole surface and the iron plate, the detachment force is 241 kN, the power consumption 5.7 kW. This means that when all six magnets are switched on, the total holding force is almost 145 t. In comparison, the buoyancy is approx. 52 t when all the passengers and crew have disembarked, and approx. 100 t when all rubbish after a one week cruise is disposed away.

The magnets must not only overcompensate the buoyancy caused by the disembarkation and unloading but must also anchor the airship rigidly against sidewards working forces. According to the definition of stationary friction is this the case when the so called friction coefficient multiplied by the vertical component of the force acting on the sliding surface is larger than the sidewards working displacement (or pushing) force. The values for the coefficient of friction for steel on steel vary between 0.15 and 0.58 according to the surface properties and cleanliness of the surface. If one of the two surfaces were to be coated with a thin layer of rubber of about 2 mm thickness, the coefficient of friction is larger than 0.5 even under wet conditions. Upon further calculation, the required displacment force = 0.5 x 6 x 241,000 = 723 kN.

c) Behaviour upon gusts, loading and unloading and power failure
As already mentioned in Section 4, the side resistance of the airship at a windspeed of 100 km/h is 342 kN. This wind force is thus far away from the displacement force of around 723 kN so that the airship cannot be moved, according to this rough estimate, even by the strongest gusts. In reality, the windforces are much lower than those in free air space because the airship is at ground level on the landing platform, and the flowing air masses along the bottom side of the airship are compressed and accelerated to produce underpressure which in turn presses the airship even more so onto the platform. This effect was seen and measured in the wind tunnel investigation and will be described in detail in the above-mentioned planned publication.

The side wind gusts produce not only displacement forces but also a tip over moment which would tip the ship over on its side if an appropriate holding moment were not applied by the magnets for compensation. For a rough estimate, the pres­sure point of the side wind is at approx. half of the ship height i.e. approx. 36.5 m. Therefore the wind tip over moment is 342 kN x 36.5 m = 12,483 kNm. This must be compensated by the a moment larger than the sum of the moments from the distance between two oppositely facing magnets and the holding force of the mag­nets on the windward. Holding moment = 2 (22 m x 41 kN + 11 m x 241 kN) = 15,900 kNm i.e. approx. 30 % higher than the wind tip-over moment. In reality, here too would the already mentioned ground effect give a helping hand and support the holding force of the magnets by the underpressure present at the lower part of the ship (Fig. 3). (This effect was registered during the windtunnel measurements.)

On completely unloading the ship, one must take care that the buoyancy does not exceed the total holding force of the magnets which can easily be accomplished in that clearing of the rubbish and filling with new supply stores together with refuelling be carried out in parallel.

The safety of the electromagnetically moored airship is dependent on the fact that no power interruptions longer than one tenth of a second are allowed. For shorter interruptions, even a buoyancy of 10 t will not alter the position of the magnets by more than 3 mm due to rising of the ship, i.e. within the allowed air gap, so that when current is again available the holding force is immediately at disposal. For larger current interruptions until the emergency generator can deliver enough current, an accumulator-battery connected to each of the magnets supplies the necessary current for 5 to 10 minutes.

d) Landing platform The landing platform is an approximately circular ring-shaped iron plate which is laid together from square tiles of 2m x 2m dimension and has an outer diameter of 32 m and inner diameter of 24 m. Thus for landing on the platform, there is ranging freedom of ± 2 m which is more than enough for a program controlled landing.

Whereas the thickness of the magnetically active plate should be at least a twelfth of the magnet diameter, i.e. approx. 8 cm, the centre may be of thinner plates, for example 2 cm thickness with a concrete lower layer so that the complete platform is a flat circular surface of approx. 16 m radius. All plates would be laid edge to edge and welded together so that they are all well joined. To prevent any gaps larger than 3 mm between magnet pole surfaces and the active iron surface, the surface of the platform has to be kept clean from any dirt e.g. sand or mud. Single sand grains or pebbles less than 3 mm would be pressed in the rubber protection of the pole shoes and are therefore harmless. However, a complete coverage with a thin sand or mud layer would dangerously decrease the attachment friction. It is therefore necessary to have at every landing place a ground personnel of two to four persons who keep the platform clean and can be contacted via mobile telephone by the airship at any time.

e) Shock absorbers, ground effect at landing
To keep the landing as soft as possible, retractable shock absorbers are foreseen on the graduated circle which would be driven out about one meter in length when the ship is a few meters above ground before the landing. Because of the large sluggish mass of the airship of ≈ 900 t, even a small landing speed of 30 cm/s means a large amount of kinetic energy to be absorbed. Therefore, eight appropriately dimensioned shock abosorbers, each of which can absorb at least 2 kW during the 3 s interaction phase, are foreseen. Any ground effect due to the low landing speed is not to be expected, with the exeption of sudden gusts of wind pushing the airship down somewhat faster, according to wind tunnel measurements here of neglegible importance..

a) Arrangement of the system
To circumvent the problem of carrying of ballast to create lift and venting of helium for descending, it makes sense to heat or cool at least a part of the lifting gas. Early experiments proved to be not very promising for various reasons until the Second World War stopped these experiments.

A new solution to the problem is planned that will use the hot exhaust gases of the two gas turbines via heat-exchangers. A detailed design is under construction and will probably be explained in the next updating of this site.

b) Buoyancy change for the start, cruise and landing
Should the airship be presumably too heavy at start, the refrigerator would be switched on long enough as a heat-pump to heat the gas, for example, from 15 °C (sea-level) to about 35 °C. The additionally gained buoyancy would be then about 14 t.

Conversely, a much too light airship at the cruising altitude would cool the gas to about 20 °C to give a loss of buoyancy of about 12 t for easier landing.

As already described in Section 3, the buoyancy may vary by ± 19 t when travelling through high or low pressure regions. Also this relatively slow change can be easily accomodated by tempering the helium gas. Hereby, the travelling would be with less dynamic lift i.e. lesser resistance losses which results in less fuel consumption and higher safety. The same holds for the buoyancy force change upon travelling from warmer to colder regions and viceversa.

The electrical power plant supplies all users in the airship with electricity from an intermediate circuit of 750 V dc and also houses the current control units for the actuator and propulsion motors.

Description of the equipment
It consists of two gasturbin-driven electrogenerators, each of 4,200 kVA (4,200 kW) capacity, switched in parallel. If one of the two generators fails (or malfunctions) for a short period, all consumers with the exception of the actuators would be switched off so that the actuators still have a slightly reduced peak power available to maintain full manouverability of the airship. The rest of the vital consumers (see below) would be then supplied by an emergency generator of sufficient capability.

The equipment connected to the emergency circuits is:

Anchor magnets 34 kW

Lifts (elevators)	30 kW
Pumps	30 kW
Emergency lighting	20 kW
Others	36 kW
Emergency generator capacity	150 kW

The four decks of the airship are connected by a lift (or elevator) block whose axis is parallel to the vertical axis of the airship. The block consists of six single lifts, built back to back. Each of the cabins can accomodate 8 persons so that a single journey can transport 48 persons. The average speed is effectively 1 m/s so that in a maximum of 10 minutes all passengers and accompanying personnel can gather in front of the airship for an excursion (Deck plans Fig. 4a, 4b).

Two wide staircases in the front and rear part of the cabin deck lead down to the panaroma or promenade deck. Emergency stairs may be used by passengers in emergency to evacuate the airship fast. Two emergency circular stairs leading from the panorama deck to the entrance/exit deck allow the exit to be accessed in case the elevators (lifts) fail due to power cut.

Two push up doors (also operable by hand), to the right and the left of the elevators, lead to the outside at the exit deck.

The water supply of the airship is split up into drinking water, cleaning water, and water for flushing of the toilets.

Drinking water would be solely provided by mineral water in plastic bottles because the control of drinking water quality from taps according to health requirements would be too expensive. Only the drinking water for the kitchen is foreseen in a large receptacle with taps.

Only a small amount of cleaning water would be taken on board at start (see Section 12). A large amount of the cleaning water would be provided by the combustion water recovery equipment. The cleaning water would be used on one hand for washing and bathing, and on the other hand as heat source or sink for the helium tempering and air conditioning, as cooling water for the diesel motors and finally, in extreme emergency, as throw away ballast. An appropriate heat exchanger can be installed at any particular user. Each deck is also foreseen with hot and cold water piping leading to every user i.e. primarily to the cabins.

The used cleaning water would be collected by pipes leading to the reservoirs to be used for flushing the toilets. The various reservoirs are interconnected by pumps and tubing so that the flight attitude may be trimmed if necessary.

The normally used vacuum toilets to be found in aeroplanes would also be installed in the airship. The connected faeces collectors are continuously kept at the necessary underpressure by two underpressure pumps. A supply of toilet flushing water is only required for the first day of the cruise (see Section 12), after that it would be replenished (supplemented) by the collected used cleaning water.

The following stores are required for a 6 day cruise:

Drinking water, 5 l per person and day for 516 persons and 6 days	16 t
Washing water, for the first day, 10 l per person	5.2 t
Toilet flushing water, for the first day, 5 x 0.2 l x 490	0.6 t
Provisions	16 t
Gas oil	140 t
Total weight of the stores	ca. 178 t

An airship is inherently safer than an aeroplane. A complete loss of steering or engine failure in a modern jet plane would most often result in a catastrophy. An airship would even then float like a balloon and give the crew ample time to carry out repairs with the equipment available on board. Even additional gas loss (e.g. by leakage in a gas cell) can be compensated by throwing away a few tons of cleaning water to allow further travel like a balloon or land or water safely.

a) Fire safety
Since the non-inflammable noble gas helium is used as compared to in the past mostly used hydrogen gas, fire hazard from the carrying gas can be principally ruled out.

The skeleton and outer skin of the airship are made of aluminium alloys; all other parts with only a few exceptions are made of non-inflammable or difficult to enflame plastics. Inspite of this, all decks are equipped with an appropriate number of fire extinguishers to immediately put out any small fires (e.g. clothing or paper).

b) Emergency landing
Should the electric power plant completely fail and the airship be unsteerable, then further travel would be like a balloon until an appropriate landing place is in sight. After enough helium has been vented and a safe landing accomplished, more helium may be blown away to make the ship heavier. The foreseen approx. 5 m long ground anchors could be spiralled into the ground through the floor of the disem­barkation deck to allow a safe exit. Should the lower part of the ship be damaged so that jammed doors prevent disembarkation, an emergency exit would still be possible from the exit in the service deck using folded ladders.

c) Emergency watering
Before an emergency watering, the floor of the lower decks is to be sealed with the water-tight doors against the outside and the upper part of the airship be used as a life saving boat until rescue comes. For the extreme case, a life preserver for every passenger and crew member, and enough life rafts and emergency slides are to be foreseen.

Precautions against terrorist attacks
At start, identity control and baggage check are the most important safety measure to be carried out. After every excursion, each passenger is to be identified by face control (automatic) before entry into the airship.

Quick retreat and fast altitude increase are best strategy when being shot at upon flying over unsafe regions. Since all survival important parts are redundantly laid out, the danger of a catastrophy is reduced considerably. Moreover the volume of the ship is mostly filled with the gas cells. The leakage of helium from between one to three gas cells can be compensated by either throwing away ballast or dynamic ascent flight. A thorough checkup at the next landing place and appropriate repair of the damage is then to be carried out. Injured can be treated by the airship´s doctor on board, and be flown out by the already ordered helicopter at the next landing place.