Buzzing off course

November 2020

Q: It’s the near future, and you’re aboard the Amazon International Space Station. You need to head over to the nearby Bayer Sustainability Lab to check on your crops, so you don your spacesuit and voice-controlled Human Maneuvering Unit, the latest iteration of which has achieved perfect navigation control. You tell the unit to make a straight beeline for Bayer. The unit laughs. “You’d better let me drive.” You demand to know what’s so funny. What will the unit say?

Draft a response of no more than 250 words and email it by noon Eastern Nov. 9 to aeropuzzler@aiaa.org for a chance to have it published in the December issue. For a head start … find the AeroPuzzler online on the first of each month and on Twitter @AeroAmMag.

FEELING THE PRESSURE: We asked you whether your ears would pop if you were flying within a perfectly sealed aircraft passenger cabin. Asteris Apostolidis, innovation strategy manager at Air France-KLM, and Clint Balog of Embry-Riddle Aeronautical University helped choose the winner.

WINNER: If you were inside a perfectly sealed aircraft passenger cabin, your ears would indeed not pop at all! The pop is just from the difference in air pressure from inside your ear to outside. The reason we design airplanes that maintain higher altitude pressure than sea level is to save weight and thus save fuel. If you were to maintain sea level air pressure (1 atm) on the inside of your airplane cabin, the air inside the fuselage would be “pushing outward” because of the much lower air pressure outside. For example at a cruise altitude of 35,000’, the outside air pressure is only 0.24 atm, which would result in a differential pressure of 0.76 atm (about 11 psi) pushing out. By allowing the cabin air pressure to drop to a still breathable 8,000’ pressure altitude (0.74 atm), you bring down the differential pressure to only about 0.5 atm, drastically reducing the thickness of the airplane skin and supporting structure required to keep the air in. One benefit of switching to carbon fiber fuselage on the Boeing 787 was the ability to have a lower cabin altitude of 6,000’ without increasing the weight compared to a traditional aluminum fuselage, and thus less ear popping.

Sean Bell
AIAA senior member
Wentzville, Missouri
Test program integration engineer at Boeing