JPL tweet links to mars.nasa.gov's Flying on Mars Is Getting Harder and Harder which explains that seasonal changes are lowering the density of the local atmosphere, presumably due to warmer seasonal temperature.
When we designed and tested Ingenuity on Earth, we expected Ingenuity’s five-flight mission to be completed within the first few months after Perseverance’s landing in February 2021. We therefore prepared for flights at atmospheric densities between 0.0145 and 0.0185 kg/m3, which is equivalent to 1.2-1.5% of Earth’s atmospheric density at sea level. With Ingenuity in its sixth month of operation, however, we have entered a season where the densities in Jezero Crater are dropping to even lower levels. In the coming months we may see densities as low as 0.012 kg/m3 (1.0% of Earth’s density) during the afternoon hours that are preferable for flight.
Later it warns:
A speed increase like this comes with a number of potential issues. One of these has to do with aerodynamics: A rotor speed of 2,800 rpm, in combination with wind and helicopter motion, could cause the tips of the rotor blades to encounter the air at nearly 0.8 Mach – that is, 80% of the speed of sound on Mars. (The speed of sound on Mars is somewhat lower than we are used to – about ¾ the speed of sound on Earth.) If the blade tips get sufficiently close to the speed of sound, they will experience a very large increase in aerodynamic drag that would be prohibitive for flight. For Ingenuity’s rotor we do not expect to encounter this phenomenon until even higher Mach numbers, but this has never been confirmed in testing on Earth.
It sounds like a remote concern but nonetheless it's important to know about both typical peak wind speeds and their daily variation, and about random, unexpected excursions which can be of concern for perseverance; both for takeoff/navigation/landing and for those peak tip speeds.
Question: How does the wind behave throughout the day in Jezero Crater? (worried about Ingenuity)
We know that the weather station on Insight has solid-state anemometers, but I don't know if Perseverance has one as well. It seems like it should considering it's partnering with an experimental aircraft that may try to push the hairy edge of its operational envelope.
- How does InSight measure wind speed?
- this answer to How can I find a daily record of the temperature on Mars?
example from the linked question: