Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Rob L
#1841522
Josh wrote:That and the overall mass of the helicopter is only 1.8 kg!


Does the lower atmospheric pressure (and lack of lift ) on Mars make that more or less of an issue? I'm guessing more.

Rob
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By Josh
#1841529
Significantly more. I suspect @Dave W could offer a more technically adept description but basically lift is proportional to density of the atmosphere you're going for, and the Martian surface only offers 1% of the earth's. The rotor RPM of Ingenuity is also 6 times the average earthbound helicopter rotor RPM.

The shape of the rotor blades are intriguingly different to my eye too - is that to do with distribution of lift along the blade?
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By akg1486
#1841539
Josh wrote:Significantly more. I suspect @Dave W could offer a more technically adept description but basically lift is proportional to density of the atmosphere you're going for, and the Martian surface only offers 1% of the earth's. The rotor RPM of Ingenuity is also 6 times the average earthbound helicopter rotor RPM.

The shape of the rotor blades are intriguingly different to my eye too - is that to do with distribution of lift along the blade?

I just re-watched the Veritasium video (linked to in an earlier post in this thread) and the rotor blade shape isn't mentioned. What is mentioned is that the blades can be asymmetrically tilted during revolution to provide torque to move sideways. I wouldn't be surprised if the shape is optimized for that. The video does explain why there are two rotors on top of each other: the top one creates like a funnel of air that raises the local air pressure on the bottom one, thereby making the bottom rotor more effective since it has more air to accelerate downwards.

Do watch that video: all three top scientists from the JPL team share their insights.
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By Dave W
#1841557
akg1486 wrote:What is mentioned is that the blades can be asymmetrically tilted during revolution to provide torque to move sideways. I wouldn't be surprised if the shape is optimized for that.

That characteristic is traditional helicopter technology; the pitch on each individual blade is cyclicly (ie at a particular point on the revolution) changed so that the disc formed by all blades tilts in the dynamically desired direction.

The blade shape and twist will be optimised for the atmosphere in which they operate, and they look strange because no Earth-bound helicopter has operated in such low gas (atmospheric) pressure. Hence the significantly more rapid rotor speed, wider chord, and greater twist.

As PPL theory from Bernoulli tells us for a wing (hence any aerofoil, including a rotor blade):

Lift = 1/2 x rho x v(squared) x S x CL

Where:

rho = atmospheric density
v = airspeed (ie blade speed at a particular point along the blade in a nil wind hover)
S = aerofoil area (linked to chord, naturally)
CL = Lift coefficient ( driven by local aerofoil shape)

rho is very, very low by Earth terms, hence everything else needs to be higher even given an extremely light airframe hence low lift force requirement.

There is no real Earth precedent for performance at this level.

So higher rotational speed (> V), greater blade chord (> S) and unusual aerofoil with greater twist and AoA (>CL). The exaggerated twist is I suspect likely due to the higher speed and lower density hence unusual (for Earth) aerodynamic lift distribution along the blade.

The technicalities of it make it an even more impressive achievement than even it superficially seems, to my mind. JPL and NASA are rightfully ecstatic and deserve every ounce of the pride they must be feeling today.

:clap:
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By akg1486
#1841568
To put the development of human achievement into perspective: there is a Japanese woman born before the Wright Brother’s first motorized flight in North Carolina in 1903 who was still alive during the first motorized flight on another planet.
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By 602fan
#1841573
As others have said this is a tremendous achievement. The principle difficulty is the lack of blade damping in the flapping degree of freedom due to the low density, requiring some sort of mechanical or structural damping. I recollect one of the engineers mentioning early models beat themselves to death because of this.

And the speed of sound is so low that compressibility effects would, I think, have been critical, more so because they’ve had to drive rotorspeed way up because of the low density.

Twist and planform are driven by some pretty basic hover requirements and would be common to any powered rotor. Most helicopter blades approximate ideal twist by a linear distribution, and planform by a rectangular blade. But I see hints of optimum twist and planform in these blades.

I’d love to see a technical paper on the design but I’m now long out of the rotorcraft game.
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By johnm
#1841574
I've always been an admirer of craftsmen, engineers and scientists and this piece of work is a tour de force.....
By TopCat
#1841661
Dave W wrote:That characteristic is traditional helicopter technology; the pitch on each individual blade is cyclicly (ie at a particular point on the revolution) changed so that the disc formed by all blades tilts in the dynamically desired direction.

OMG, is that why the stick is called the cyclic?

I've only wondered about that on and off for about 20 years.
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