Why Do Blimps and Airships Sound Like Loud Light Planes?

In the world of aviation, the sounds associated with blimps and airships can often confuse the public, leading to frequent comparisons to the noise generated by light aircraft. This confusion is typically rooted in the similarity of their propulsion systems. Let's delve into the reasons why these massive, floating craft often sound a lot like their smaller, ground-based counterparts.

Propulsion Systems and Similarities

Most blimps and airships you've ever seen were equipped with piston-powered engines and propellers, just like many light aircraft. The sound that makes them recognizable is a direct result of these similar propulsion systems. The reason for the slightly louder sound can be attributed to several factors, including their speed, altitude, and operational durations.

Slower Speed and Louder Sounds

Unlike high-speed aircraft that rapidly take off and fly at high altitudes, blimps and airships move more slowly and tend to linger in areas for extended periods. As a result, the sound of their propeller-driven engines lingers longer and is more noticeable, leading to the perception that they are louder.

Altitude and Sound Travel

Another crucial factor is the altitude at which these aircraft fly. Blimps and airships typically operate at much lower altitudes, meaning that the sound travels a greater distance before it dissipates. By comparison, at higher altitudes, the sound of an aircraft is more attenuated, making it less noticeable from the ground.

Current Fleet and Propulsion Systems

The current fleet of Zeppelins, flown by Goodyear, primarily uses Lycoming engines, a design proven in light aircraft such as the Cessna 200, 300, and 400 series. These engines are powerful and reliable, but their performance can be enhanced at higher altitudes through turbocharging. However, for the operational altitudes where dirigibles typically cruise, naturally aspirated fuel-injected versions provide sufficient power without the need for additional modifications.

These engines run without mufflers, and the straight pipes allow for the full conversion of fuel (avgas) into noise rather than speed and altitude. This results in a higher decibel level, which might explain why blimps and airships sound like louder light planes.

Future Developments and Quieter Propulsion

The next generation of airships, like the HAV AirLander being built for passenger service, will use diesel engines optimized for the task. These engines are expected to operate more silently, with claimed noise levels lower than those of a jet, although they are not completely silent.

Additionally, there are innovative projects involving advanced fuel cell technology for dirigibles, designed to power big brushless electric motors. These electric motors are likely to be much quieter than the diesel or piston engines currently in use. A Spanish company is developing such power packs, intending to create airships that can be electrically propelled, thereby achieving a quieter operation.

Comparison Between Hydrogen-Powered and Lofted Airships

It’s worth noting the difference between hydrogen-powered and hydrogen-lofted airships. The old Hindenburg, for example, used Maybach diesel engines located on the keel, accessible during flight. This design presented safety risks, especially considering the explosive nature of hydrogen lifting gas.

Modern dirigibles use fuel cell technology, which can efficiently sip hydrogen from safe containers. Helium and air are managed using high-speed pumps to adjust trim and buoyancy, reducing the risk of gas leaks. These advancements not only enhance safety but also pave the way for quieter operations.

Although electric propulsion might not be entirely silent, the quieter motors in these new airships are expected to make less noise than their gasoline-powered predecessors.