Answers to questions relating to the core technology and operation of SkyLifters.
Why are SkyLifters not the usual cigar shape of airships and blimps?
When you have to design an aircraft to do a job, it is best to start with a list of what you want the aircraft to do, not with a pre-conceived idea of what it should look like. Top of the list is the ability to pick up and put down payloads safely. Second, is the ability to do that in variable wind and weather conditions. Third, is the need for the aircraft to be practical to build and to operate; and so the list goes on… In summary, you start to realise that the usual cigar/torpedo shape is not the ideal shape, and in fact, those shapes cause you more problems that then need to be solved with yet more engineering.
How do SkyLifters fly (float)?
SkyLifters use aerostatic lift to remain airborne and propellers are used to direct their flight. There is no need for aerodynamic lift, but the aerostat is shaped to minimise drag. Indeed, there is no need for wings, fins or control surfaces. The aerostat’s envelope (a balloon) contains Lighter-Than-Air (LTA) gas that enables buoyancy, derived from the surrounding air according to Archimedes’ principle.
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 like the liquid.
What is HTA and LTA?
As illustrated below, aircraft can be grouped into two categories, HTA (heavier-than-air) and LTA (lighter-than-air). Generally, HTA aircraft use aerodynamic lift and/or thrust to fly, whereas LTA aircraft use aerostatic lift for flying and only use thrust for moving through the air. SkyLifters are 100% LTA.
Is LTA better than HTA?
As illustrated above, LTA technology enables three unique capabilities. For some payloads, LTA is the only solution:
- Flight duration greater than 24 hours (with a useful payload).
- Ability to remain airborne without power (enabling endless, sustainable flight with no additional energy expended).
- Vertical pick-up and flight of payloads well over 20,000 kg (which is the maximum payload limit for the largest helicopters).
100% aerostatic lift is essential for vertical lifting; being able to hover in un-moving air. During flight it may be useful to create some aerodynamic lift (as an HTA/LTA hybrid), but this usually requires additional items on the aircraft and that adds weight and maintenance and control issues, all of which need engineering solutions, certification and maintenance.
Below, are two simple graphics to illustrate the unique economic advantages of LTA over HTA.
Do SkyLifters have pilots?
Although many of SkyLifter’s aircraft will have two pilot positions, we are designing them to be operable by a single pilot. Some smaller types may be radio controlled from a ground station if desired. Flight clearances are similar to those of helicopter operations, because they fly in a similar manner. The flight deck is the circular room seen under the main pod module. This position gives the crew a 360-degree view of the surrounding airspace and ground operations.
How big are SkyLifters?
The diameter of the aerostat of the largest concept design SkyLifter (150 tonne payload) is 150 metres, with a height in the middle of around 40 metres. The overall aircraft height is around 130 metres, incorporating a 70 metre vertical access tube and a 12 metre high under-slung control pod.
What is the rod connecting the aerostat to the pod on the larger aircraft?
The central umbilical trunk seen on the larger SkyLifters – which looks like a rod up the middle – is not a primary structure. The pod and payload weight is carried by the suspension cables seen located around the circumference of the aerostat. The trunk is a two-way passage for air and a conduit for aircraft systems. It also serves to provide access for personnel by means of a small elevator.
What are SkyLifters made of?
A SkyLifter’s aerostat is an inflated envelope made from strong, laminated ‘gas-tight’ fabric. The chambers inside are made of similar materials, but are of lighter weight. The pod below – the underslung module – is mostly metallic, a typical aluminium airframe, and incorporates composite mouldings. The suspension lines, which are strong synthetic-fibre ropes, are similar to ships’ mooring lines.
How will SkyLifters be built?
The hangars in which SkyLifters are assembled will be large air-pressure stabilised domes, as seen in a video on the Technology page. These temporary buildings are ideal, as they are low-cost and mobile. Additionally, while designs of the past have required large static hangars for maintenance work, the SkyLifter aerostat acts as its own shelter when moored and fitted with a ground skirt.
How do SkyLifters move forwards and backwards?
Cycloidal propellers will thrust in any direction desired. The aircraft remains upright when moving forwards, backwards, sideways, up, down or rotating around its vertical axis. Due to the aerostat’s lenticular profile it has no apparent front, side or back. Therefore, SkyLifters are omni-directional.
This omni-directional characteristic has benefits (over the common cigar-shape airship) because it makes geo-stationary positioning (and the ability to pickup or deliver payloads) much easier. Without a front or back, the aircraft is always facing into wind. Vectored thrust from the 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. It is ideal for applications at any altitude.
Changes to compass heading, acceleration and slowing all happen very gradually and gently, so virtually no G-forces are felt.
How do SkyLifters move up and down?
Ballast is adjusted so the SkyLifter weighs (including any payload) a little more than the buoyancy created by the aerostat. Then, the cycloidal propellers on the pod provide some vertical thrust to ascend or assist descent. The effect of the SkyLifter’s aerostat-shape limits descent rate, even when overall weight is substantially greater than buoyancy. This means it will descend safely without power if desired.
How do the Cycloidal propellers work and what are their benefits?
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.
Safer too. Due to the way the propellers operate and their installed position, there is also reduced danger from failures since the trajectory of freed parts is away from the aircraft and breakaway energy is low compared with screw propellers and turbines. This allows for compatibility with the aerostat and provides for personnel safety needs.
What is used for fuel and power?
We design to minimise carbon emissions and so SkyLifters are designed to use solar collectors to generate electricity, which powers the cycloidal propellers 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, which can be hampered by the need to face the direction of flight).
As a safety backup, a small (bio)fuel engine and generator may be used. This system includes a water recovery system on the exhaust.
All these systems are located in one level of the pod. This ensures easy access, maintenance (even during flight) and much reduced outside noise.
How will SkyLifters land?
Being an LTA gas-filled airship, a SkyLifter never truly lands, remaining airborne throughout its life, buoyed up by the atmosphere. However, it can be grounded when it is restrained by mooring lines to the ground. Otherwise, similar to a helicopter, SkyLifters are designed to hold a stationary position in the air over a landing site and descend vertically.
No runway is required. During payload pickup and delivery SkyLifters will not be grounded; they will float (like a hover situation) close to the ground. The legs, seen under the pod, are ‘fenders’ to cushion and protect the pod when SkyLifters eventually land.
How is the mooring of a SkyLifter different to a conventional airship? (Parking a SkyLifter)
SkyLifters will be moored in a fixed circular arrangement with lines at equi-spaced positions around the edge of the aerostat to anchor points on the ground. The fixed arrangement facilitates ease of maintenance compared with conventional airships,which swing and bounce at a mooring mast.
For storm resistance the aerostat can be drawn down close to the ground and protected with a surrounding skirt (cloak). The mooring site is considerably reduced in size compared with HTA aircraft airfields (runways and aprons) and in particular when compared with airships that rotate around their masts.
Should I have concerns about large payload aircraft flying over my house?
Yes, but it should be no more concerning than a winged flying over your home. Safety is paramount with SkyLifters. The aircraft will incorporate 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. If an HTA aircraft’s engine stops or its wings fall off, it will decend from the sky, often crashing and burning.
If a SkyLifter’s propulsion system stops, it will simply contune flying, floating with the wind (like a common gas balloon). If the aerostat gets a hole in it (the main chamber is not pressurised), there is no cause for concern – it will eventually quietly descend to the ground with its descent rate controlled by the release of ballast and vectored thrust.
I am looking for information regarding the following…
- operational cost models
- finance and insurance arrangements
- certification and compliance requirements
- weather and environment tolerance
- flight characteristics
- aerodynamic and stress models
- propulsion & fuel statistics
- load exchange procedures
We understand there is a keen and active community of aviation enthusiasts who would like to examine the technical data but the information is commercially sensitive so will not be published at this stage of development. If you are a potential customer or operator, please feel free to contact us for this information.