“Nothin’ but blue skies,” but why?

December 2023

Q: True or false and why: On a sunny day, the blue sky overhead results from the same principle of molecular absorption that exoplanet researchers rely on to determine the atmospheric composition of planets too dim to be imaged even by the James Webb Space Telescope.

Send a response of up to 250 words that someone in any field could understand to aeropuzzler@aerospaceamerica.org by noon Eastern Dec. 11 for a chance to have it published in the next issue.

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FROM THE NOVEMBER ISSUE: Coaxial conundrum

We asked you whether it’s true or false that coaxial helicopter blades are separated by a good distance only so they don’t contact each other.

WINNER: False. The top and bottom rotor blades of a coaxial helicopter are separated vertically by a good distance for two simple reasons: 1) To reduce aerodynamic interference between the two rotors. When two rotors are close together, the airflow from one rotor can interfere with the airflow from the other rotor, which can reduce efficiency and increase noise. 2) To reduce the risk of blade contact, especially during maneuvers. When a helicopter is maneuvering, the rotor blades can fl ex and deform. If the blades are too close together, they could contact each other, which could cause a catastrophic failure. The distance between the two rotors is typically between 10% and 15% of the rotor diameter. This distance is enough to reduce aerodynamic interference and blade contact risk, while still allowing the rotors to interact with each other in a beneficial way. For example, the coaxial rotors on the Russian Kamov Ka-50 helicopter are separated by 15% of the rotor diameter. This separation distance allows the rotors to work together to generate more lift and reduce drag, which improves the helicopter’s performance.

Sudarshan Gnanvendan

AIAA student member

sudarshan.g2021@vitstudent.ac.in

Sudarshan is studying mechanical engineering at Vellore Institute of Technology in India.