One criticism continually levied against airships is perceived “vulnerability” to attack. However, this perception needs balance with regard to, “vulnerable 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 afterwards, so wasn’t a great concern. They don’t normally pop 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. However, 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, airships don’t just fall from the sky like rocks, as heavier-than-air (HTA) aircraft may do.
Today’s airships are much less vulnerable than previous designs. If serving destitute people in war-torn regions, large airships would only look like big optical targets at close range. However, against the brightened sky and from afar, they’re very difficult to locate; so much so that Navy and Air Force pilots in experimental interceptions at the time with airships had great difficulty in sighting them at altitude (normally below 10,000 ft – 3050 m, near cloud level), having been directed to within half a mile (0.8 km) of their location. The very light colour that is standard for airships today and the potential use of colour schemes reduces their optical signature further. This can result in concern that large, hard to see airships, then pose a hazard for fast aircraft with unsuspecting pilots when transiting their operational area – an issue for the military, but not necessarily for civil airliners that generally fly at much higher altitudes.
Also, while airships look large at close range, they inherently have very small 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 HTA aircraft fuselages, can easily be shaped to reflect such radar signals in directions away from receiving antenna. Simple low cost techniques also exist that may be used to reduce airship signal strength reflection for surveying sensors. These things aren’t necessary for civil aircraft and transponders normally are used by them for identification purposes – to make them visible!
Airships also have very low infrared signatures, as most of their heat sources are for avionics operation rather than to fly. In addition, engines used may be diesels housed within nacelles away from the open environment, preventing detection by IR sensing systems. Such engines also are fuel efficient. For long endurance applications, their exhaust gas also may be condensed to capture water for ballast, compensating for expended fuel weight and further reducing IR signature. Excess heat may then be pumped into the aerostat, where helium conducts heat five times better than air, making the airship’s overall IR signature similar to that encountered by a sunlit cloud; hardly the type of signature that a sophisticated IR missile would be able to easily target. Even if a missile did hit the airship’s aerostat it probably then would just pass straight through (making holes) without exploding (due to not recognising it had made a hit), allowing the airship to safely continue and take counter measures – making them good to help people and deliver aid in war torn regions.
With regard to envelop holes, see the answer to What happens if an airship gets a hole in it? Nonetheless, it should be noted that in 1985 the SKS500-04 whilst flying at about 1000 ft (305 m) altitude suffered failure of an elevator surface, which broke away and then hit the aerostat’s rear envelope, causing a tear about 15 ft (4.6 m) long. After a while the pilots noticed poor control response followed by pitching down and diving towards the ground as gas vented, eventually crashing into a corn field at parachute decent rate. Both pilots (no one else onboard) walked free from the incident, such is the nature of LTA aircraft; where a similar incident involving an HTA aircraft most certainly would have been fatal. The airship subsequently was repaired and re-enveloped with a bigger aerostat, becoming the first SKS500 HL to enter service.
Also, the true story about a tethered aerostat operating in the Middle East that broke free should be noted; where it then drifted away with expensive sensitive electronic systems aboard that weren’t for others’ eyes to see, so became a problem to recover. An Apache helicopter was sent after it to shoot it down, which they tried to do. However, after emptying their barrels it continued to freely drift for many miles – eventually (hours later), after loosing 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!
Airships thus are not easy to find (unless in your face) plus are capable, robust and not necessarily 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 HTA aircraft, other 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 6:19 mins through it when the ability of fabric structures is revealed:
- From hot air balloons to blast-resistant shelters: Interview with Founder, Harold Warner (8:05 mins)
Fabric structures today (aerostats) are made with high strength, high tenacity fibres that weren’t available for airships of old, now also used for armour and bullet proof vests!