Introduction
The following explanations originally were written to answer questions about heavy-lift omni-directional (O-D) dirigible buoyant aircraft being promoted from 2008 onwards called SkyLifters, still a Luffships Ltd (LSL) objective. The main aircraft featured then was the large LS-L150, a Transport Category type for 150 tonne underslung payloads as an evolving design for point to point heavy-lift services anywhere.
LSL also pursues unidirectional (UD) types, which some operators may prefer or need for the particular capabilities they have. However, as for aeroplanes and helicopters, they suit different duties because of the different way they operate – needing airflow alignment.
LSL’s main goal thus is to develop the LS-L150 as soon as possible. However, after reading our responses to the following questions, see the answer to the last question about the LS-L150’s availability for service.
What are HTA and LTA?
These acronyms are technical terms that just mean heavier-than-air and lighter-than-air. A third term: as-light-as-air (ALAA) or as-heavy-as-air (AHAA), perhaps also is needed to complete the set. The terms are used to describe aircraft as well as their: parts, systems, materials and substances, where their weight relative to the weight of air they are immersed in is important with regard to the way the atmosphere (air) acts on them under the influence of gravity. General aviation aircraft fall into three categories:
- Nonbuoyant types, which are substantially HTA aircraft displacing little air for buoyancy, usually needing high airspeed and associated high power to fly. They take off from runways after becoming airborne from enough aerodynamic lift to overcome their all-up-weight (AUW) weight and later land with weight transferred to the ground for support when airspeed is lost.
- Buoyant types near ALAA displaced, already essentially airborne from atmospheric displacement before launch. When LTA they can instead launch directly from excess aerostatic lift (buoyancy) and fly using zero to low airspeed aerodynamics/power and later return to the ground for capture while remaining afloat. Otherwise, when HTA, they launch with a short impulse of thrust to gain momentum and then fly as previously explained.
- Types between these categories are semi-buoyant aircraft (falsely called Hybrids by some people because HTA & LTA are not separate sciences) needing a combination of aero-dynamic and -static lift to become fully airborne with moderate power to maintain airspeed.
HTA relates to aeroplanes, rotorcraft, missiles, etc that don’t use an aerostat for significant buoyancy. In the ALAA category there are tethered aerostats, free balloons (moving with the wind) and dirigibles (i.e., airships), all buoyant aircraft with an aerostat (filled with LTA-gas to puff them out, which causes air displacement) functioning as a flotation aid to support overall weight (including the LTA-gas). Semi-buoyant aircraft are new types yet to enter service and prove their worth. They use a smaller aerostat unable to support max AUW in the air but don’t need so much aerodynamic lift as HTA types to then fly.
What makes them float in the air?
Buoyant and semi-buoyant aircraft use an aerostat that enables floatation in accordance with Archimedes’ principle to displace the atmosphere (air), developing buoyancy (aerostatic lift) proportional to the weight of air displaced as a result. 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, generally not noticeable) than our ‘effective weight’ in the atmosphere. In water the effect is noticeable because water has somewhat greater density.
Are they piloted?
LSL’s dirigible buoyant aircraft will be operable in various ways: 1) by a single pilot, 2) remotely controlled and 3) autonomously flown. Modern avionics and navigation instruments will be used and 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 pilot a 360 degree view of the surrounding airspace and ground operations. As well as many monitoring sensors around the aircraft, the pilot also will be able to view in all directions via CCTV cameras (something not especially available to pilots of other aircraft).
How do O-D airships fly?
LSL’s O-D airships will 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 airships therefore will be able to move in any direction without turning to face the flight direction.
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 float 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 will happen 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 buoyant aircraft, where the LS-L150 was designed to meet heavy-lift needs for such capability. Safety is paramount.
LSL will comply with normal aircraft practices for safety factors and fail-safe methods, and our buoyant aircraft 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). Our airships won’t behave as nonbuoyant aircraft do when their engines stop or wings fall off, falling from the sky – then crashing and burning. When our O-D airship’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 vertical thrust. Besides, operators of these aircraft mainly would be over-flying uninhabited regions to fulfil the duties needed.
How do your airships 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. Our airships 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 radial 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 obviate carbon emissions and minimise the fuel burn rate. Our airships will use H2 as 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 voltaic cells 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 their slender longitudinal form). The H2 fuelled engines or fuel cells 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, mainly steam (which is an LTA gas that also is useful).
How will your airships land?
Being buoyant aircraft, our O-D dirigible types (airships) won’t truly or generally 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. They thus will be fixed against movement by the mooring lines – not so easy for UD types, which need to weathervane around a mast to minimise aerodynamic loads. Otherwise, similar to helicopters, our O-D dirigibles 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 these dirigibles should 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 rapidly venting the LTA-gas in the aerostat. While this is a way for emergency use to prevent unintended breakaway from 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 your O-D airships be moored?
Our O-D dirigible buoyant aircraft (airships) will be moored in a fixed way with multiple lines at equi-spaced positions around their circular aerostat’s perimeter to anchor points on the ground. The fixed arrangements ease maintenance compared with UD 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?
Our aerostats will be made from strong non-rigid laminated fabrics stabilised with mainly LTA-gases 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 your airships be built?
Our dirigible buoyant aircraft (airships) 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 sheds to house 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 relocatable. And, whereas airship designs of the past have required large hangars for maintenance work, O-D airship 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 airship certification. LSL thus will be the technical design authority for buoyant aircraft 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 suppliers for them. This enables us to be an SME in a similar way to past companies like Airship Industries Ltd. We have a Strategy for stepped development starting with small airships that are readily doable.
When checked out and approved/certified, 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 your airships be built?
We are based in the UK, where initial prototype build, test and type certification arrangements are being set up. However, we also have partners in Germany, the USA, Canada, Malaysia and Australia, where further arrangements are in hand. We plan to expand globally when possible, which depends on enough interest from people who want the capability that LSL provides. This needs orders or agreements for them. As our various aerostat and airship designs gain type certificates we will enable further build arrangements to suit international demand. Interested parties should register with us as a first step for collaboration.
Will I be able to hire an LS-L150?
When LSL fulfils our development objectives then yes, eventually – so not at the moment or until we are able to develop this rather big buoyant aircraft. 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 there’s a serious market to serve and that it’s wanted.
Compared with other offerings for such capability, we think our proposal is the only one that can survive or could become successful, both at a price 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 development until the spadework necessary to enable it is done.
We will 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 manufacturing license options.
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-L5, LS-LT15, Patroller 3 & LS-L20 and provide them to operators who then may get on with setting up the network of bases to ultimately enable LS-L150 operations.
