Airships are big and slow; where people generally know this but ask developers, “Aren’t they vulnerable to hostile action?” The answer is, “Yes, they are, just as all things are; where people devise ways to destroy most things created – including our planet!”.
Perceived “vulnerability” to attack is a criticism often levied against them. However, this perception needs balance regarding, vulnerability to what and under what circumstances? Also, following a hit, how survivable are they?
Regrettably, it’s not just a military problem, as commercial operators also find that irresponsible people (e.g., some farmers or hunters) take pot shots at airships; evidenced by aerostat damage found during normal maintenance a little while later – so wasn’t of great concern. They don’t pop from pin pricks like party balloons!
Vulnerability thus should be considered with a range of values on a movable cursor-scale denoting the threshold of acceptability. Everything is vulnerable if hit often and hard enough (but see later), and nothing is immortal! Also, when used for peaceful purposes, such as delivering aid to war-torn destitute people, vulnerability may be an issue. Nonetheless, good design precepts coupled with survivability considerations and sensible operation justify the usefulness of vulnerable vehicles that must over-fly dangerous regions. During World War II, few ships proved to be as vulnerable as aircraft carriers; and few ships proved to be as useful. One thing’s for sure, once hit by hostile fire, buoyant aircraft don’t just fall from the sky like eggs that smash as nonbuoyant aircraft do.
Today’s buoyant aircraft are less vulnerable than previous designs. Large types only look like big optical targets at close range. However, against the brightened sky and from afar, they’re difficult to locate; so much so that Navy and Air Force pilots in experimental interceptions with airships had difficulty to see them at altitude. It also was after being directed to within half a mile (0.8 km) of their location. This was because airships’ flight ceiling usually is low and they normally fly at about 1,000 ft (305 m) altitude – often near cloud level. Their very light colour and use of colour schemes also reduces optical signature. This instead causes concern that large, hard to see buoyant aircraft, then pose a hazard for fast aircraft with unsuspecting pilots when transiting their operational area; an issue for the military, but not for civil airliners flying at much higher altitudes.
While buoyant aircraft look large at close range, they have very low radar cross sections. Their large aerostats mainly are just fabric, which doesn’t show up on radar screens. It’s only their gondola and/or radar antenna that may present a return for surveying radar systems. Airship gondolas, similar in size to nonbuoyant aircraft fuselages, can easily be made to reflect radar signals in directions away from receiving antennae. Simple low cost techniques also exist to reduce buoyant aircraft signal strength reflection. These things aren’t necessary for civil aircraft, where transponders normally are used by them for identification purposes – to make them visible!
Buoyant aircraft also have low infrared signatures, as most of their heat sources are from avionics rather than to fly. Engines used may be diesels housed within nacelles, preventing detection by IR sensing systems. Such engines are fuel efficient. Also, for long endurance applications, their exhaust gas may be condensed to capture water for ballast (compensating for expended fuel weight) further reducing IR signature. Excess heat may then be pumped into the aerostat, where helium conducts heat five times better than air, making their overall IR signature similar to that of sunlit clouds; hardly the type of signature that a sophisticated IR missile would be able to easily target. Besides, new electrical propulsion systems now will be used instead.
Even if a missile did hit an airship’s aerostat it probably then would just pass straight through (making holes) without exploding from not recognising it had made a hit, allowing flight to safely continue and to take counter measures. This makes them good to help people and deliver aid in war torn regions.
With regard to aerostat envelop or gas cell holes, see the answer to What happens if an airship gets a hole in it? It also should be noted that in 1985 the SKS500-04, whilst flying typically at about 1000 ft (305 m) altitude, suffered failure of an elevator surface that broke away and then hit the aerostat’s rear envelope – causing a tear about 15 ft (4.6 m) long. The pilots later noticed poor control response followed by pitching down and diving towards the ground as LTA gas vented, eventually crashing into a corn field at a parachute decent rate. Both pilots (no one else aboard) walked free from the incident, such is the nature of buoyant aircraft. A similar incident involving a nonbuoyant aircraft probably would have been fatal. The airship subsequently was repaired and re-enveloped with a bigger aerostat, becoming the first SKS500 HL to enter service.
The true story about a tethered aerostat operating in the Middle East that broke free also should be noted; where it then drifted away with expensive sensitive electronic systems aboard not intended for others to see, so became a problem to recover. An Apache helicopter was sent after it to shoot it down, which they tried to do. After emptying their barrels, it continued to freely drift – eventually (hours later), after losing sufficient buoyancy, it descended (slowly) to the ground when it was recovered (still intact but extensively damaged by the gun fire). It was filled with helium, which it still contained when recovered, so incendiary bullets also would have been useless!
Buoyant aircraft thus are not easy to find (unless in your face), are capable, robust and not easy targets to bring down. Their actual vulnerability from attack thus should be re-thought. They also can be armed, if necessary, with similar missiles – but that do work against nonbuoyant aircraft, missiles and their ground operators – who reveal their location by their nasty attacks.
If the story isn’t believed, watch the following video. However, wait at least until 3:00 mins through it when the ability of fabric structures is revealed:
- From hot air balloons to blast-resistant shelters: Interview with Founder, Harold Warner.
Fabric structures today (aerostats) are made with high strength, high tenacity fibres that weren’t available for buoyant aircraft of old, now also used for armour and bullet proof vests!