Massive new US spy airship 'could be used to carry big cargoes'
Mighty Brit-designed vessel could swap height for grunt
The huge LEMV* surveillance airships now being built by British designers for the US Army may be able to carry substantial cargoes as an alternative to sky-spy equipment, according to reports.
Might not just be a spy-eye but a sky truck, too.
Aviation Week, in an update on the LEMV programme, quotes project chief Alan Metzger as saying that the vast airships are designed so that "mission and fuel modules can be removed and replaced with cargo modules".
In their standard configuration, the LEMV ships ("up to three" were ordered in June for $517m) would carry a 2,500lb payload of sensors and communications equipment on unmanned missions lasting up to 21 days. The 300-foot-long ships are "optionally manned" – they will be piloted where this is a legal requirement, as for example when transiting civil-controlled airspace, but for long surveillance missions they would normally be controlled from a ground station.
Swapping out the mission equipment would permit a LEMV to carry just 2,500lb of cargo to start with – not all that much. But three-week missions as standard indicates that the ships could spare a lot of fuel space for shorter flights of just a few days or less, suggesting that larger cargoes could be carried.
Then, an airship's lifting capacity decreases sharply as its maximum operating altitude increases. An airship's ceiling is set by its "pressure height" – the altitude at which its helium lifting gas has expanded to fill all available space inside the envelope. In order to have a higher pressure height, less gas must be put into the ship to start with, meaning that it will lift less stuff off the ground.
Next page: Then there's the matter of ballast
Answers to some comments on HAV's.
Some rather odd comments that need a few answers so here goes:
Firstly the HAV 304 is a hybrid air vehicle, which means it is a cross between a blimp and a flying wing plus a hoverskirt undercart. It does not need wings and a layer of PV panels would not justify their weight or work too well in Afghanistan. The amount of Helium is fixed and it does not need to be changed unless there was a big configuration change such as changing from medium altitude surveillance to low altitude heavy lift. Then the Helium would be topped up to increase payload, otherwise almost no Helium is required after initial inflation. All military aircraft have to use JP8 fuel which is a cross between jet fuel and diesel. Hydrogen could be used in a civil version but the present engines are Centurion 4.0 diesels which are very efficient anyway.
Secondly the 517 million dollars was for 3 HAV's not one and half the cost is for the special surveillance payloads. Initial prototypes are always expensive but a production HAV will cost less than an equivalent aircraft and far less to operate in fuel terms.
Thirdly forget about storing or compressing Helium and other research programs as they are all too heavy to be useful at present. Due to it's high static weight capability an HAV does not need such systems.
Fourthly the ballast question only applies to normal airships not to HAV's as they can take off heavy enough to avoid a light landing. Even if an extreme condition did arise then sandbags can always be loaded into the cargo bay.
Regards JB ( www.hybridairship.net )
All that technology...
It always amazes me that simplistic solutions always seem to be adopted, even when they compromise the outcome.
Rather than trying to manage the quantity of the gas by setting it at launch, why not have a small compressor and pressure vessel on board? As the craft gains height, helium could be extracted from the envelope and stored in the cylinder.
As the craft descends, the stored helium can simply be added back to the envelope to re-establish buoyancy,
This is just the same sort of control that a diver uses in water - except that divers vent gas from the buoyancy cell(s) on ascent, rather than trying to scavenge it. But that's because carrying a compressor would not be feasible. We're not airships...
Option 2 - I hear they have some sand over there, equip it with an industrial sized "no-loss-of-suction" dyson, along the lines of that capital ship in Spaceballs ;-)