The blog post explores the physics behind the distinctive "whoosh" sound created by passing objects like airplanes. It explains how this sound isn't simply the object's engine noise, but rather the Doppler-shifted frequencies of ambient noise—like wind, traffic, or conversations—being compressed as the object approaches and stretched as it recedes. This effect, similar to how a siren's pitch changes as it passes by, is most noticeable with fast-moving objects in relatively quiet environments. The post further delves into how our brains perceive these shifting frequencies, potentially misinterpreting them as the sound of the object itself and sometimes even creating phantom whooshing sensations when no physical source exists.
GPS jamming and spoofing are increasing threats to aircraft navigation, with potentially dangerous consequences. A new type of atomic clock, much smaller and cheaper than existing ones, could provide a highly accurate backup navigation system, independent of vulnerable satellite signals. These chip-scale atomic clocks (CSACs), while not yet widespread, could be integrated into aircraft systems to maintain precise positioning and timing even when GPS signals are lost or compromised, significantly improving safety and resilience.
HN commenters discuss the plausibility and implications of GPS spoofing for aircraft. Several express skepticism that widespread, malicious spoofing is occurring, suggesting alternative explanations for reported incidents like multipath interference or pilot error. Some point out that reliance on GPS varies among aircraft and that existing systems can mitigate spoofing risks. The potential vulnerabilities of GPS are acknowledged, and the proposed atomic clock solution is discussed, with some questioning its cost-effectiveness and complexity compared to other mitigation strategies. Others suggest that focusing on improving the resilience of GPS itself might be a better approach. The possibility of state-sponsored spoofing is also raised, particularly in conflict zones.
The author recounts their visit to the National Museum of the U.S. Air Force in Dayton, Ohio, specifically to see the XB-70 Valkyrie. They were deeply impressed by the sheer size and unique design of this experimental supersonic bomber, describing its presence as awe-inspiring and otherworldly. The post focuses on the aircraft's visual impact, highlighting features like the drooping wingtips and massive size, alongside numerous high-quality photographs showcasing the plane from various angles. The author emphasizes the privilege of witnessing such a rare and significant piece of aviation history, capturing their personal sense of wonder and the enduring legacy of the XB-70.
HN commenters generally express awe at the XB-70's ambitious design and capabilities, with several noting its stunning appearance and sheer size. Some discuss the technical challenges overcome in its creation, like the unique compression lift generated by its wingtips and the complex fuel system needed for Mach 3 flight. Others lament the project's cancellation, viewing it as a missed opportunity for advancements in supersonic flight. A few commenters offer personal anecdotes about seeing the aircraft in person, highlighting the visceral impact of witnessing such a large and unusual plane. The impracticality of the XB-70 as a bomber due to advancements in surface-to-air missiles is also mentioned, along with its later contributions to supersonic research. A recurring theme is the romanticism surrounding the project, representing a bygone era of ambitious aerospace engineering.
Summary of Comments ( 32 )
https://news.ycombinator.com/item?id=43713524
Hacker News users discuss various aspects of the "whoosh" sound phenomenon. Several commenters offer additional examples of sounds exhibiting similar characteristics, such as the Doppler shift observed with passing cars or the sound of a large truck passing a house. Some discuss the physics behind the phenomenon, including the role of air pressure changes and the shape of the object creating the sound. Others delve into the subjective experience of these sounds, noting how perception can be influenced by factors like background noise and individual sensitivity. One compelling comment highlights the prevalence of this effect in movies and its potential exaggeration for dramatic effect. Another interesting observation is the comparison to the "sonic boom" of a supersonic aircraft, contrasting the continuous whoosh with the sharp crack of the boom. Finally, a few commenters mention the psychological impact of these sounds, including their potential to be unsettling or even anxiety-inducing.
The Hacker News post titled "Passing planes and other whoosh sounds," linking to an article on windytan.com about the physics of whooshing sounds, has generated a modest discussion with several interesting comments.
One commenter shares a personal anecdote about experiencing the Doppler effect with the sound of a passing plane, noting the distinct drop in pitch as the plane moves away. They also connect this experience to the sound of cars passing by, highlighting the commonality of the phenomenon in everyday life.
Another commenter delves into the specifics of the Doppler effect, explaining how the frequency shift is dependent on the relative velocity between the source and the observer. They then raise the question of why the sound of a passing plane seems to "whoosh" down rather than up, even though both rising and falling frequencies are involved. They hypothesize that this perceived downward shift is due to the greater change in frequency occurring as the plane moves away, alongside the general decrease in loudness as the source recedes.
A subsequent comment builds on this hypothesis, suggesting that the human ear is more sensitive to downward frequency changes and that the decreasing volume of the receding sound source might contribute to the perception of a downward whoosh.
Another commenter links to a Wikipedia page about the sonic boom, a different phenomenon associated with supersonic aircraft, distinguishing it from the Doppler effect discussed in the original article. This comment helps clarify the different types of sounds generated by moving aircraft and their underlying physical principles.
One user mentions their experience with sailplanes, explaining how the quiet nature of these aircraft allows for a clearer perception of the Doppler shift and a more pronounced "whoosh." This adds another real-world example to the discussion and highlights how the surrounding environment can influence the perception of these sounds.
Finally, a commenter with a background in audio engineering provides a more technical explanation, mentioning how the perceived pitch of complex sounds like those produced by aircraft engines is not solely determined by the fundamental frequency but also influenced by overtones and harmonics. They suggest that the Doppler effect's influence on these different frequency components might contribute to the complex nature of the perceived "whoosh."
In summary, the comments on the Hacker News post provide a range of perspectives on the physics and perception of whooshing sounds, from personal anecdotes to detailed explanations and related phenomena, demonstrating a shared curiosity about the acoustic world around us.