NASA will send tiny helicopter to Mars NASA has announced that its Mars 2020 mission will include a small helicopter. The appeal of a ‘copter is obvious: it’ll be faster than a crawling robot, see further and should be less likely to be stuck in sand. While Bernoulli’s Principle holds on Mars, the red planet’s atmosphere is vastly thinner than Earth’s so a copter …
> "Where can I look at the engineering details of the design please?"
Here is NASAs info. Including a lovely video based on what I assume to be an initial design:
https://www.nasa.gov/press-release/mars-helicopter-to-fly-on-nasa-s-next-red-planet-rover-mission
Do you always have someone google for you?
You say none of the engineers have thought of that... but some of them never thought to check orientation, or even if imperial/metric measurements are being used.
I joke. But in reality, sometimes a bad idea gets railroaded into production "because". It will be a first though, if it works. I'm having problems visualizing a 6% atmos heli though. Seeing one working in their giant vacuum chamber would be a blast!!!
Well, think about it like this.
The gravity of Mars is about one third that of the Earth and its atmosphere is about 160 times less dense. In very rough terms that means that helicopter blades have to be designed in such a way that on Earth they would have 50 times the lift they do on Mars.
That means, again in rough terms, that if we could have a blade 5 times the lift and rotating 10 times as fast as for a terrestrial helicopter, it would do the job. The power needed, of course, should be much less because of the reduced gravity.
The limitation on a rotating wing is the point at which the wing tips reach the speed of sound, which on Mars is about 240m/s.
At 3000 rpm (50 revs/sec) the wing tips reach the speed of sound for a circumference of about 5 metres which means a blade length of 0.8 metres. So if we started with a Chinook with its 9 metre blades, limited to around 300rpm on Earth... it's only going to reach around 220 rpm on Mars. The blades, in fact, would be too small and slow by a factor of around 600.
So, if I've understood it right and my back of envelope approach is even within an order of magnitude, no practical Martian helicopter is ever going to be more than a few kilos.
"The limitation on a rotating wing is the point at which the wing tips reach the speed of sound, which on Mars is about 240m/s."
On an _individual_ rotating wing.
You can increase the number, increase their surface area or even move to multiple rotor planes.
All have been done in the past on earth
My money's on the dust though. considering 6% atmosphere it has to be incredibly fine to be lifted in the kinds of quantities we see, even with 1/3 gravity.
"NASA suspects the natives are hiding behind rocks waiting for lumbering the rover to pass."
"I suspect the natives will be hiding behind rocks, armed with a shotgun, waiting to blast the drone from the sky!"
I think you're getting confused with Mars, Pennsylvania
This post has been deleted by its author
"...and the first human-designed heavier-than-air vehicle to visit another planet".
So the Mars rovers are lighter than air? Well then, I guess it's a good thing the atmosphere is so thin; Otherwise, the buoyancy would have them floating off the surface. Can't have that. ...or is the implication the rovers were designed by chimps, dolphins, or E.T.s?
Maybe they mean heavier-than-air FLYING vehicle. No, no. The Register never makes errors. It must be true, so the question is now who has NASA hired to do the design work and are they being paid a fair wage.
Oh, what am I saying. We all know the earth is flat and all this outer-space stuff is nonsense filmed in a studio somewhere. :)
Looks like one of those things you can get on eBay for when you're bored round the office.
My thoughts exactly.
In fact, I was thinking of one of these (having purchased one of these eyeball-removers from a different seller last year).
'I'd guessed really big blades moving quite slowly.'
No, if you take the lift equation
Lift = Coefficient of Lift * Density of the atmosphere * V squared * the reference area
You've decreased the Density of the atmosphere, so to still get the same lift you need to either increase the area of the wings 160 times or the V squared*. Or some compromise between the two, although in this case I'm guessing there was a limit on how big they wanted the rotors to get. For an accurate answer you have to consider Reynolds number as well but that's the broad picture.
The next problem you've got is that the rotors are now moving much closer to the speed of sound which is not ideal.
*There's a limit to what you can do with the Coefficient of lift, if you could increase that 160 times we'd do it on Earth and airliners would have tiny wings.
The next problem you've got is that the rotors are now moving much closer to the speed of sound which is not ideal.
Ahhh yes but, what is the speed of sound on Mars. Surly its a different value than Earths or?
Weight, to make them spin quick enough to still take off they need to be strong and strength adds weight. Especially as larger blades would exert more force on the rotor head needing more strength and weight. It's a vicious cycle.
Again isn't Mars considerbly smaller (in Mass), to that of Earth, wouldn't the Gravity be a bit less over there then it is here?
The speed of sound on Mars is around 240 m/s. A bit lower than the 340 m/s on Earth.
Gravity on Mars is about 2/5 that on Earth (3.7 m/s² vs 9.8 m/s²). However, in this case, the mass is important as it's rotational, rather than the weight due to gravity (semantics on the part of the original post). In the same way, a satellite in zero gravity can spin itself apart if the control systems malfunction.
"You've decreased the Density of the atmosphere, so to still get the same lift you need to either increase the area of the wings 160 times or the V squared*."
So, maybe something like DaVinci's design them?
Big blades have 2 problems;
Size... they're big. You said so yourself. That means they take up more space and weight more. Not a good thing where every gram counts.
Weight, to make them spin quick enough to still take off they need to be strong and strength adds weight. Especially as larger blades would exert more force on the rotor head needing more strength and weight. It's a vicious cycle.
However if the air is thin then the sound barrier isn't such an issue so smaller, faster blades can do the job. Especially since strengthing them to go faster would require at lot less weight to reinforce them for higher speeds.
'However if the air is thin then the sound barrier isn't such an issue so smaller, faster blades can do the job.'
It's less of an issue in terms of the dynamic force on the blade, however it will still cause issues with flow over the blades breaking down leading to a loss in lift. Roughly speaking you'll get a shock wave forming somewhere on the upper surface first* rendering the area of blade behind it ineffective.
*Where ever the relative flow is fastest.
"At some point, once humans have made contact with intelligent extra-terrestrial life, no doubt big corp will be looking at offshoring offplaneting services."
Ah but which will us earthlings be, the ones paying offworlders low wages, or the ones being paid low wages by offworlders?
You realize the myth that Bernoulli law has anything to do with flying has been busted very long time ago?
Also, RC helicopters do exceed 2000 RPM sometimes, so 3000 RPM for a helicopter this small is not that much of a feat. What is (going to be) remarkable achievement though, is a stable landing from which said helicopter can start again without human intervention.
Bernoulli's law isn't the only component to explaining aerodynamic lift effects, but it's certainly involved. Pressure differences due to changes in speed DO occur around certain wing/chord profiles, they're just not the only effect involved. Newtons 3rd and Coanda effects are important too, among others.
It's not nearly as much further to go to Mars than the Moon as you'd think...
Getting to earth obit is the vast majority of the work...
You can actually get to Mars for less dV than it takes to get to the moon (RRS Kerbal dV map assumed correct):
http://i.imgur.com/AAGJvD1.png
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