Simple balloons with a bulbous rotund form (spherical, pumpkin or pear shaped) are omni-directional (OD) aerostats with a payload unit below – keeping them upright from low weight as a pendle. As such they easily can be launched and captured vertically, rising or descending directly from/to points on the ground, where they are restrained. They also can
easily use a tether to an anchor position and/or a fixed winch to control height, easier for LTA gas filled types. They normally are inflated with hydrogen (H 2 ) that is released after flight, which also involves special safety measures to prevent fire. Gordon Bennet balloonists do it regularly!
Provided winds are low and steady, they are not difficult to manage at ground level, generally quickly deflated and then folded/packed into a fabric carry bag (valise) with handles for transport. Flights thus normally are limited to forecast good weather days.
Otherwise, ground anchoring methods with screw pickets and/or suitable heavy ballast methods are necessary, as their bulbous forms have high aerodynamic drag, needing restraint.
To manage higher wind strengths (which increase with height) and wind-direction changes, tethered aerostats traditionally have been provided with a teardrop form that is unidirectional (UD). This reduces drag but needs tail fins to steady their heading and face the wind. These tethered aerostats thus have greater complexity and cost, also needing
special ground facilities involving automated turntable methods to hold and orient them for wind alignment.
This is from need for the tether to align with the UD aerostat’s centre of buoyancy (to restrain excess buoyancy and aerodynamic forces without upset) requiring its nose to also be mast fixed, holding it against aerodynamic drag. However, where the combination of the two restraint positions prevents normal weathervane action. The result is an arrangement
that is both expensive and difficult to install at needed ground sites as well as difficult to relocate.
Alternative lenticular aerostats that retain OD characteristics, enable reduced drag, and can be fixed in a similar way to simple balloons without need for turntables. They now are being offered by new developers instead – such as those designed by Luffships. These OD types reduce costs and can quickly be relocated, so are regarded as the way forward for the industry to adopt.
Photo by engin akyurt
