NASA Will Send Helicopter To Mars To Test Otherworldly Flight (bbc.com) 103
NASA is sending a small, autonomous rotorcraft to Mars via the agency's Mars 2020 rover mission, currently scheduled to launch in July 2020. NASA says the goal of the mission is to "demonstrate the viability and potential of heavier-than-air vehicles on the Red Planet." BBC reports: Its design team spent more than four years shrinking a working helicopter to "the size of a softball" and cutting its weight to 1.8kg (4lbs). It is specifically designed to fly in the atmosphere of Mars, which is 100 times thinner than Earth's. NASA describes the helicopter as a "heavier-than-air" aircraft because the other type -- sometimes called an aerostat -- refers to aircraft like balloons and blimps. The helicopter's two blades will spin at close to 3,000 revolutions a minute, which NASA says is about 10 times faster than a standard helicopter on Earth.
Wow (Score:1, Interesting)
Nah, they managed to make it 10-20 times heavier (Score:2)
The fine summary says it's the size of a softball, which is inches in diameter (9cm). It's also four pounds (1.8kg). A typical hobby shop drone of that size would be maybe 100 grams.
My hobby shop "heavier than air" vehicle is 100cm and 500 grams. Keep in mind mine is 10x longer, 10x wider, and 10x taller, so it should be about 1000x the weight.
3.5 inches (Score:2)
That should say "3.5 inches".
Mine is nearly 10 times that length, and ten times the width,
so presumably around 10x the height, yet weighs 75% less.
Apparently they made theirs from solid lead or something.
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Helis would. Here's why (Score:5, Informative)
I'm not the one who said that, but I do have enough understanding of the physics of props to explain why it should likely be largely true for helicopters. "Drones" (quadcopters) would likely run into a problem.
You have probably played around with sticking your hand out a car window and angling it so that it flies up. You've probably noticed that if you angle it too much toward the vertical, the airflow pushed your hand backward with considerable force. Props are of course angled similarly, so that some of the oncoming air is forced downward, creating lift, and the greater the angle, the more drag, or backward force is created. It is the job of the motor to overcome that drag. A more dense fluid has more drag, and so requires more motor power to maintain the same speed. So the required motor power is equal (and working opposite to) the drag.
You may have noticed that the same thing happens in water. Because water is more dense and vicious than air, water creates a greater force at a given angle - both greater lifting force and greater drag force.
We call the drag created by the angle "induced drag". There are complex formulas for drag and lift, which involve something called the Reynolds number, but as it happens when calculating the ratio of drag to lift the other numbers cancel out and drag is directly proportional to lift for a given foil, as density and speed changes. You can intuitively imagine that if you hold a flat board in a flow, at exactly 45 degree angle to the flow half the force will be up and half drag backward. That isn't exactly correct due to flow separation and complex stuff, but the intuitive understanding is that the magnitude of the forces is related is true. Something more dense, like water, will have more force - more drag and more lift. Lower density will give less drag and less lift.
Lower density means less lift AND less drag, proportionately. The required motor power is exactly equal to the drag. So the required motor power is reduced as drag and lift are reduced. Thus required power is directly proportional to lift - the thin atmosphere gives less lift, and needs less motor to overcome drag.
So just moving a helicopter from Earth to Mars we find that the lift (at a constant RPM) is too small, and the Earth motor is way oversized for the need. To make it fly on Mars, we need the prop to generate more lift BUT we don't mind a lot more drag - we have plenty of motor to overcome drag. We can easily generate more lift (and drag) by making the prop larger, spinning it faster, or increasing its "pitch" (the small dimension of the prop, from top to bottom on a helicopter). In particular, larger props generate a lot more lift and So it's easy to get lift equal to the weight of the craft - our motor was designed to overcome the proportional drag. drag. Larger props are also considerably more efficient, having a better radio of lift to drag.
Quadcopters have a problem when you want to make the props bigger. Quads of course have four props, and if they are large enough to be efficient the ends of the props nearly touch at the center of the craft. You can't go larger without the ends of the props hitting each other. To put much larger props on a quad, you'd need them at different heights, going over and under each other. Even if you do that, the prop can't be longer than the width of the frame, because the tip of one prop would hit the axle of the others.
This is just a first approximation to show it is generally a reasonable idea to simply put bigger or props on for lower density atmosphere, or just let the same props spin faster since they have less drag. Practical issues arise such as building the prop to be stiff enough given the extra length.
Re: Helis would. Here's why (Score:1)
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AFAIK, partly from the simulated Mars in X-Plane, you can add more blades to any given prop.This helps reduce the supersonic tip issue with longer blades, which is especially true with a low density atmosphere. Consider the development of fighter aircraft props from two blades, up to five in 1945, and counter rotating, for six, and paddle blades.
One of the features that most late-war (ww2) fighters (and many others as well) also had were variable-pitch propellers. Helicopters rely on varying the main rotor pitch to control vertical lift and horizontal motion/thrust when the main rotor is tilted by the main rotor control stick, and a variable-pitch tail rotor to control yaw.
I doubt that any drone the size of a softball that is capable of doing anything useful would have the spare room or mass available for a pitch-controlled rotor system, however. A
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Consider the development of fighter aircraft props from two blades, up to five in 1945, and counter rotating, for six, and paddle blades.
And then there was Thunderscreech. https://www.youtube.com/watch?... [youtube.com] F84H .
This is all pretty simple for NASA to simulate except for the gravity. So I expect if they can get one flying here, it will do okay on Mars.
Taking the matter in a different direction, this should be a tremendous enhancement to a rover. An eye in the sky to scan for interesting things to examine, elimination of some of the guesswork involved in moving the rover around. Then a return to the rover to sip some of that nice electrici
You forgot it's on Mars, and that induced drag is (Score:2)
Might be time to take said book down off the shelf again and refresh your memory.
The drag equation is:
D = Cd * A * .5 * (r * V^2)
R is density. Density on Mars is 1/100 that on Earth, so when you say:
>To get the airfoils rotating at 10x speed ... the motor is required to be outputting up to 100x the normal power.
That would be correct if density were constant. Reduce density by 99% and you also reduce drag (and therefore power) by 99%. Required motor power is therefore increased by 100x to get additional v
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Longer arms have to be thicker for the strength (Score:2)
> This is nonsense. If you want to fit larger props on a quad, you make the mounting beams longer.
A longer beam must be thicker and wider in order to have the same strength. An arm twice as long, twice as thick, and twice as wide is roughly eight times heavier. The longer arm also is a longer moment arm producing a larger bending force at the point of attachment. That requires the central part of the frame to be stronger, and therefore heavier. You just end up making the entire craft bigger and heavier
You're quite missing the point (Score:2)
> What part of "Of course there are other problems with larger props, such as larger weight" wasn't clear t
What apparently isn't clear to you is that cubed is quite a bit larger than squared.
2x longer props on 2x longer arms require 4x the weight. 4x the weight in turn requires props double in size again. Longer props on longer arms can't be a solution to the thrust to weight ratio being too low because longer arms make the problem WORSE, not better.
To paraphrase what you said:
Too much weight for a give
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It's not just very thin, most of the distance to Mars is a total vacuum. I'm not sure how they're planning to fly it to Mars.
Also, the batteries will give out long before it gets there.
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Your hobby shop drone could probably not even withstand the rocket liftoff, never mind the rest of the trip and the landing.
Re:Wow (Score:5, Insightful)
Is your hobby shop model going to have to survive being launched at 25,000 mph into space, then travel for months in an absolute zero cold vacuum, then be dropped from orbit onto the surface of a frigid cold planet with almost no atmospheric pressure?
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Oh and I forgot: All the while bathed in intense radiation
Re: Wow (Score:5, Funny)
No, but if there are trees on Mars mine will find them ... and get subsequently stuck just high enough to not be able to reach.
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Mine will utilize an Illudium Q36 Explosive Space Modulator to blow up the Earth so it would no longer obstruct the view of Venus.
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you win!
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Shock/Vibe/Thermal (Score:1)
Launch acceleration and shock are not negligible. A typical "enveloping" test would be about 14 grms for 1 minute (actually, they typically give you a acceleration spectral density curve that has a flat top at 0.16 g^2/Hz from 50-800 Hz). A typical shock spec might be 2000g.
Then, you also need to design for launch loads (i.e. the acceleration of the rocket) which is something like 6-10 g in the direction of motion.
Heaters cost mass and battery capacity (which is also mass). You're not going to put a RHU on
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Re:Wow (Score:5, Informative)
Re:Wow (Score:4, Funny)
They spent 4 years developing something that I walked into a hobby shop and purchased lot more that 4 years ago.
I'll call NASA immediately and get this straightened out. Thanks!
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I love NASA threads for comments like this: I love the displays of angry ignorance form armchair engineers people who have no clue about actual engineering or anything to do with space.
Yo umight be called an engineer, but writing dubious javascript code doesn't actually make you knowledgable about, well, any of these things as is abundantly clear from your post.
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They spent 4 years developing something that I walked into a hobby shop and purchased lot more that 4 years ago.
Does yours fly up to about 60km, where the pressure is comparable to the one on Mars?
...
Does it recharge itself in a cloudy day?
Can it operate in about -100 degrees?
Ignorance maybe is a bliss, but it's a danger for the others.
strange summary (Score:2)
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Ridiculous (Score:1)
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This one is actually a rotating solar sail design... Why have a stationary sail when it can spin?!?!?!?
And how's it going to fly when it gets there? (Score:2)
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Sincerely,
A NASA Intern Wannabe
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You see the landing gear? The four balls splayed out
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An wing on a plane generates lift in a very simple way: It is moving forward in the air. Note that the wing is moving here, while the air is (generally) not, and only tends to be accelerated as a result of the forces imparted upon it by the wing. The shape of the wing is such that molecules of air are relatively easily pushed above and below the wing. The masses of air pushed both up and down here is the same, so no lift is actually generated from this.
The asymmetrical shape of the wing, however, in n
Increase in Dust Storms Predicted for Mars (Score:1)
I can just imagine all the dust being blown around by this and how long it will take to dissipate.
Fake math bullshit again (Score:1)
You cannot multiply and get a lower result. You cannot have "the atmosphere of Mars, which is 100 times thinner than Earth's"
100 times thinner is bullshit. Multiplying anything gives you a higher number, not lower. The way to say it might be "a hundredth as dense as Earth's" or some other creative wording. Not just saying 100 times thinner because it's easy to write.
Then it goes on to actually to do the math the right way here "The helicopter's two blades will spin at close to 3,000 revolutions a mi
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You cannot multiply and get a lower result. You cannot have "the atmosphere of Mars, which is 100 times thinner than Earth's"
You can, if you're doing it in the context of saying that Earth's atmosphere is already thin. Like, "Jupiter's atmosphere is thick, and Earth's is only a hundredth as thick. Mars' atmosphere is a hundred times thinner than that."
That's the only way that annoying convention makes sense. Foo is Bar, and Alice is even more Bar. It's possible for Foo's Bar to be bigger than Alice's, but it's an awkward way to use that construction. It only makes sense if being "a hundred times thinner" is in relation to som
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Only taking the pressure (which is actually closer to 6hPa if memory serves, instead of ~1000hPa on Earth) is only part of the story. It depends on where they land since the pressure varies between 300hPa to ~1155hPa. I suspect that they will land in a high pressure (low altitude) area.
Gravity, i.e. the thing you have to fight against, or compensate, is only 1/3 of the Earth's, which helps quite significantly.
Also Mars atmosphere is mostly composed of CO2, its mean molecular mass is 44 instead of 29 on Eart
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You cannot multiply and get a lower result.
While I appreciate your single-minded dedication to the natural numbers, you should probably know that a while back, some people discovered fractional numbers which have the amazing property that if you multiply by one you can get less than the number you started with!
The world has of course moved on since then (we're well out of the stone age now) and understand them a lot better, bht the basics are the same.
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Phrases like a hundred times smaller and a hundred times thinner are implicitly implying division.
a hundred times bigger means multiply by 100
a hundred times smaller means divide by 100
In a few million years (Score:4)
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In a few million years, Marsians will wonder if the initial bacteria they came from a few million years ago were brought from outer space.
But I'll bet they'll appreciate their rotors.
Sheesh... (Score:2)
How is it going to get there since there's no air for the blades to push against in space. Dumb idea.
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Only dongs will know (Score:2)
10 times faster than a standard helicopter on Eart (Score:1)
pretty cool, but need balloons as well (Score:2)
Um (Score:2)
Who us gonna sit it upright after it gets blown over by a sudden burst of wind?
Well if it doesn't get there (Score:1)