I marveled at the two flight videos today on YouTube by Perseverance helicopter flights during Ingenuity mission.

Got me thinking.

Why aren’t the helicopter blades wider? I would like to think that in order to compensate for Mars’ thinner air.

Doesn’t increasing the area of wing surfaces equal bigger lift?

Video 1, Video 2

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    $\begingroup$ Hey, welcome to Drones.SE! Could you please explain what dimension you are referring to when you say "wider"? Do you mean span, chord, camber, or something different? $\endgroup$
    – ifconfig
    Nov 20 '21 at 20:21
  • $\begingroup$ that’s a good question. i was thinking about the width of the blade. $\endgroup$ Nov 28 '21 at 14:35

Increasing blade chord can give more lift, but only up to a point. Helicopter blades are pushing a column of air downwards, accelerating it from stationary to whatever speed is necessary. Each time a blade passes the same point, it gives that part of the column a push downwards. If the air hasn't really slowed down from the previous blade, then the blade adds nothing useful. So there's a limit to how much air each blade can push before it interferes with the next blade - and pushing a fat blade around causes drag and requires power, even if it's not doing anything useful.

For maximum efficiency, you want long, narrow, slow moving blades, so that each one is in 'clean' air.


Longer blades are more efficient, but it's only practical to a point. Blades have to withstand high RPM, be balanced, and be light. Also the linear velocity of the tip of the blade increases a ton if u have a long prop. At the same RPM, every rotation the tip travels 2pi*r meters, so more r means more distance in the same time.

This may not seem like an issue, however propellers really don't work very efficiently close to or above the speed of sound. Having the tips go supersonic can lead to compression and other issues. This is why there haven't been any successful supersonic propeller planes. The speed of sound is even lower on mars.

Here is some reading on that if you are interested, that explains it very well: https://mars.nasa.gov/mars2020/participate/sounds/ https://www.highskyflying.com/can-propeller-planes-go-supersonic/

  • $\begingroup$ this is a good answer. Since it is a close call vote-wise, I will give it a 30 day wait before accepting the highest vote. $\endgroup$ Nov 28 '21 at 14:36

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