The following explanations originally were written to answer questions put to SkyLifter concerning new heavy-lift omni-directional (O-D) airships that the company (formed in 2008) was promoting. The main airship featured was a dirigible Lenticular Aerostat Luffship, namely the LS-L150 as a type for 150 tonne payloads. The answers here are revised versions by their originator.
It should be noted that Luffships Ltd is a new company recently started for development of LTA aircraft designed by Charles Luffman (hence Luffships), including O-D Lenticular Aerostat types. SkyLifter, as a potential operator of Luffships, now also recognises that development and operation of airships need to be separate businesses in a similar way to the established aircraft industry; where businesses providing operating services with aeroplanes and helicopters generally are separate to the businesses that develop and provide them. This therefore frees SkyLifter to pursue other aircraft that suit its purposes and for Luffships to be developed to suit the needs of businesses anywhere who would like to acquire and operate them. It also frees the originator of Luffships to pursue other types (e.g. unidirectional – UD), which some operators may prefer or need for the particular capabilities that they have. However, UD airships are not the only way, as aeroplanes and helicopters prove, which operate to provide different services depending on their capability or suitability for the roles they fulfil.
The answers here therefore generally are for O-D Lenticular Aerostat types, which are considered to be the best way for seriously heavy lift aerial crane and outsized loads transport purposes.
What are HTA and LTA?
Aircraft typically fall into two categories, HTA (Heavier-than-air) and LTA (lighter-than-air). Types between these categories are being called Hybrids by some people, but see Q&As 2 How do airships work. HTA types are aeroplanes, rotorcraft, missiles, etc. In the LTA category there are tethered aerostats, free balloons (moving with the wind) and dirigibles (including airships). Buoyant aircraft use LTA technology, which hybrids may instead be called. LTA aircraft mainly or only use aerostatic lift (buoyancy), rather than aerodynamic lift. In other words, they can float without airspeed in the air and don’t need airflow over wings for lift. Some LTA aircraft (mainly airships) use aerodynamic lift a little bit to balance the differences between weight and buoyancy and buoyant aircraft (hybrids) may use it extensively. HTA aircraft don’t deliberately use buoyancy (a gift of nature) at all.
What makes them float in the air?
Luffships float in accordance with Archimedes’ principle by displacement of the atmosphere (air), providing buoyancy (aerostatic lift). This is a natural effect due to gravity, but acts in the opposite direction, where light vessels are pushed up by the medium they are in. Archimedes’ principle states “a body floating or submerged in a liquid is buoyed up by a force equal to the weight of the liquid displaced”. In this respect the atmosphere (air) behaves in a similar way to liquids. Indeed our own body experiences the buoying effect; where, if one weighed oneself in a vacuum chamber (not recommended), it would be found that our ‘true weight’ is a little more (about 700 gm more) than our ‘effective weight’ in the atmosphere is (generally not noticeable). In water the effect is noticeable because water has somewhat greater density.
Are they piloted?
We are designing O-D Luffships to be operable in various ways: 1) by a single pilot, 2) remotely controlled and 3) for autonomous operation. Modern avionics and navigation instruments will be used and air traffic control is similar to helicopter operations because they fly in similar ways. The flight deck is the compartment below the main module. This position gives the crew a 360 degree view of the surrounding airspace and ground operations. As well as many monitoring sensors around the aircraft, the pilot will be able to view all around via CCTV cameras (something not especially available to pilots of other aircraft) and lights.
How do O-D Luffships fly?
O-D Luffships fly in a similar way to helicopters except that they won’t tilt so much. They will remain essentially upright from pendulum stability when moving forwards, backwards, sideways, up, down or rotating around their vertical axis (precession). Due to the aerostat’s lenticular profile (like a discus) they have no apparent front, side or back. These Luffships therefore are omni-directional (able to move in any direction without turning to face that direction).
The O-D capability has great benefits because it makes geo-stationary positioning (to pickup/deliver payloads) much easier. It also is great for geo-stationary platform applications at any altitude. Thrust vectoring from multiple cycloidal propellers ensures changes to wind direction are easily countered without any need to turn and with much less chance of being blown off station. They will be good for various patrol duties, able to often float along in silence (drifting with the wind as balloons do, when desired) only using power for course corrections or to return against the wind direction.
Changes to compass heading, acceleration and slowing all happen very gradually and gently, so there will be virtually no g-forces felt – similar to free balloon flight.
Should I have concerns about 150 tonnes flying over my house?
Yes, always, but not especially from Luffships, where the LS-L150 was designed to meet SkyLifter’s need for such aircraft capability. Safety is paramount. Luffships incorporate normal aircraft practices for safety factors and fail-safe methods, and will be certified to similar standards as all other aircraft (including jetliners which, incidentally, weigh hundreds of tonnes and are accepted to fly over people’s homes). Luffships won’t behave like HTA aircraft do when their engines stop or wings fall off, falling from the sky – often crashing and burning. When a Luffship’s engines stop, intended as a routine aspect of flight, they will simply float on with the wind, as balloons do. They also don’t have so many parts (like wings and tail surfaces) that could break loose. If the aerostat gets a hole in it, the main chamber isn’t pressurised, so won’t mind – perhaps eventually (if a big hole) quietly descending to the ground with descent rate controlled by the release of ballast and vectored thrust. Besides, operators of these aircraft mainly would be over-flying uninhabited regions to fulfil the duties needed.
How do Luffships go up and down?
Ballast will be varied to trim them prior to launch (as for other airships) so that they will weigh just a little more than the buoyancy experienced, causing just a small reaction against the ground – but essentially floating (so airborne) due to buoyancy. The propellers then will be used for thrust to either hold their position against winds or move them in directions desired, including ascending and descending. The parachute effect of their aerostat will limit descent rate, even when overall weight is substantially greater than buoyancy. Luffships therefore will descend safely and gently without power due to the small excess weight.
How do the Cycloidal propellers work and what are their benefits?
See: Voith_Schneider_Propeller for a simple animation.
Cycloidal propellers look like paddle-wheels, since they have several straight blades equi-positioned around the edge of a rotating cylindrical framework. As they turn the blades pitch in a synchronised way under collective control (similar to helicopters). This enables the resulting thrust to be quickly vectored in any radial direction under full power.
The main benefit is rapid response for precision control in any 360 degree direction. Due to the way they operate and their installed position there also is reduced danger from failures, since the trajectory of freed parts is not towards the aircraft and breakaway energy is low compared with screw propellers and turbines. This makes for compatibility with the aerostat and personnel safety needs.
What is used for fuel and power?
We have sought to minimise carbon emissions and the fuel burn rate. Luffships will use (bio)diesel fuel and solar collectors to generate electricity, used to power the cycloidal propeller electric motors and aircraft systems. The aerostat design is ideal for large arrays of solar collectors because a large portion of the upper surface faces the sun at any one time (more so than cigar-shaped aerostats, hampered by the need to face the wind and there slender longitudinal form). The diesel engines and their drive-train plus water recovery systems will all be placed in an engine room on one level above the pilot’s control station. This ensures easy access, maintenance (even in flight) and much reduced outside noise. Exhaust emissions will be very low compared with airliners, perhaps comparable to a car.
How will Luffships land?
Being LTA aircraft, Luffships won’t truly or normally land, remaining airborne throughout their life (buoyed up by the atmosphere). They instead will be captured and then held, restrained by mooring lines next to the ground in a similar way to ships next to their births. O-D Luffships thus will be fixed against movement by the mooring lines – not so easy for UD types, which need to weather vane around a mast to minimise aerodynamic loads. Otherwise, similar to helicopters, Luffships will be able to stop in the air over a mooring site (controlled with thrust) and then descend vertically. No runway required!
During payload pickup and delivery an objective is that Luffships will not be restrained; instead holding station (as helicopters do) in a pseudo hover situation under autonomous control above the ground. The legs one sees under the pod are ‘fenders’ to cushion and protect the lower structures when bumping against the ground (so not landing gear).
Landing is possible by fully and rapidly venting the LTA gas in the aerostat. While this is a way for emergency use to prevent unintended breakaway from the mooring restraints or from ascent when escape is necessary, it will not be routine. If deliberate landing is necessary for other purposes (e.g. for maintenance or repair) then, while moored, the under-slung parts will first be removed. The aerostat then will be hauled down to ground level and deflated using upper vent valves, when it will collapse against the ground (so no longer airborne).
How will O-D Luffships be moored?
O-D Luffships will be moored in a fixed circular arrangement with multiple lines at equi-spaced positions around their aerostat’s perimeter to anchor points on the ground. The fixed arrangement facilitates ease of maintenance compared with airships swinging at a mast. For storm resistance the aerostat also will be drawn down close to the ground and protected with a surrounding skirt (cloak). The fixed state (no weather-vane movement) means the mooring loads will be more evenly spread across multiple anchors and the mooring site may be considerably reduced in size compared with HTA aircraft airfields and typical UD airships at their moorings.
What is the aircraft made of?
Luffship aerostats will be made from strong non-rigid laminated fabrics stabilised with mainly LTA gas and some air. The chambers inside will be made from similar materials but of lighter weight. The structures below may be metallic (typical aluminium airframe) and/or use composite mouldings. Their suspension lines are similar to ships mooring lines (strong synthetic fibre ropes). A central umbilical trunk, which looks like a rod (but is not primary structure), may be used as a service trunk for personnel, air and systems between the lower structures and the aerostat, so would be made from light laminated fabric.
How will Luffships be built?
Luffships don’t necessarily need a hangar for inflation, assembly or maintenance, where they were designed together with mooring and protection arrangements to obviate the need for them. However, hangars are convenient if available to enable build and maintenance activities in a more comfortable environment. Such hangars may be large air-stabilised or light structure fabric covered buildings, for which we have a number of designs prepared. These temporary buildings are ideal as they are low-cost and mobile. And, whereas airship designs of the past have required large hangars for maintenance work, O-D Luffship aerostats act as their own shelter when moored and fitted with a ground skirt for protection, an extra to consider.
That said, the basic parts: aerostat, nacelles, propellers, ground facilities, etc, will be built to order by specialist approved organisations who will deliver them to us for assembly, test and Luffship certification. We thus will be the technical design authority for Luffships produced (needing DOA approval by the airworthiness authority for the purpose). We don’t have plans at the moment to undertake parts production ourselves, so will be reliant on established organisations for them. This enables us to be a smallish business in a similar way to past companies like Airship Industries Ltd. We have a strategy for stepped development starting with small Luffships that are readily doable.
When checked out and approved, we then will package/box and supply them to operators who are trained and approved for the purpose. We also will provide the necessary documents, procedures, training, licensing and support necessary for operators to set up and go from there.
Where will Luffships be built?
We currently are based in Germany and the UK, where build and test arrangements are being organised. However, we also have partners for businesses in the USA and Malaysia, where arrangements are at a formative stage. We plan to expand globally when possible, which depends on enough interest from people who want the capability that Luffships provide. This needs orders or agreements for them.
Will I be able to hire an LS-L150?
If we’re successful with our development objectives then yes, eventually – so not at the moment or until we’re able to develop this rather big aircraft; which could be never if not supported. It’s not supported by outside investors at the moment! However, we know it’s possible and are confident about the design being able for the purpose, so would appreciate registered interest helping us to show them that there’s a serious market to serve, which needs it. We also think that, compared with other offerings for such capability, our proposal is the only one that can survive or could become successful, both at a price that operators would succeed with and from the way the aircraft is designed for the circumstances of operation under real weather conditions with the state of the industry as it exists today; not as ideally portrayed by others. We are realists about the objective and won’t be pursuing its further development until the spadework necessary to enable it is done.
We basically are aircraft people who have worked in the airship industry since the 1980s who have seen all the rhetoric before and know the issues – fed up with B——t! From consideration of the needs for seriously heavy lift aerial crane/transport aircraft and attempts to satisfy them, we think the LS-L150 design is the only one at the moment that could survive the treadmill of development necessary before such capability would be allowed to operate commercially.
We would work to certify it for flight in all parts of the world. However, we’re not planning to be an operator providing the services that it may fulfil, which needs other organisations to step up to the mark for that. Nonetheless, we will develop operating capability – necessary for the certification process and to train the people who become operators. They’re the people to ask about hire and who should register with us to discuss the possibilities of becoming an approved operator.
For qualified organisations, we also will offer a manufacturing license option.
In the meantime, we intend to follow our strategy for development, which starts with readily doable projects focussed on getting income to do more. A prime objective at the moment is to complete the development of the LS-L20 and provide this to operators who then may begin the process of setting up the infrastructure network of bases to ultimately enable LS-L150 operations.