The Physics of NASA’s New Mars Helicopter – NEWPAPER24
1 week ago
The Physics of NASA’s New Mars Helicopter
Sending a rover to Mars is cool—however sending one to Mars together with a helicopter is even higher. Sure, that’s the plan for the following NASA Mars rover, scheduled for 2020. The concept is to have a driving rover that brings alongside a small coaxial helicopter. The helicopter shall be self-powered and fly for a couple of minutes a day. The primary benefit of the helicopter is that it may possibly scout forward of the rover and take photos and stuff—possibly some epic rover selfies. However actually, it must be an enormous benefit over earlier rovers.
In addition to being a cool Mars mission, this Mars helicopter can be excellent for some physics questions. Listed below are some questions and solutions concerning this flying robotic.
Why would not it have a tail rotor?
The Mars helicopter shouldn’t be your conventional helicopter. For a helicopter with a single rotor (like those you normally see on Earth), the tail rotor is required to counteract the change in angular momentum (and the frictional torque from the air) because of the important rotor spinning. With out the tail rotor, the helicopter would spin uncontrolled and crash—or at the very least get the passengers very dizzy. A coaxial helicopter has two counter rotating blades. For the reason that two rotors are spinning in reverse instructions, the entire angular momentum is zero and there’s no want for torque from an additional tail rotor.
Eliminating the tail rotor additionally does one thing else—it saves house. You may make a smaller helicopter by utilizing a coaxial rotor. Smaller is best—particularly with the restricted house on board the rover. Getting an even bigger helicopter on the rover can be like making an attempt to suit an overstuffed rolling suitcase within the overhead bin in your final cross-country flight. Additionally, I ought to level out that the Mars helicopter would not return to the rover, however it does begin there.
Will a helicopter work on Mars?
With reference to helicopter flight, there are two large variations between Earth and Mars. First, the density of the environment on Mars is considerably decrease than on Earth (solely about 1 p.c of our atmospheric density). Second, the gravitational discipline can be decrease on Mars (simply 38 p.c of the gravity on the floor of the Earth). The decrease atmospheric density makes it tougher to fly a helicopter, however the decrease gravity makes it simpler.
The true query—how do helicopters fly? In a really primary mannequin of helicopter thrust, the rotors take air above the helicopter and throw this air down. For the reason that “thrown” air has a rise in momentum, this requires a drive—which is the carry drive. Additionally, we are able to think about this mass of air is within the form of a cylinder with the radius of this air-cylinder the identical as the realm of the helicopter rotors.
The momentum of the downward thrown “air” (I’ll use air for the stuff on Mars and Earth) is dependent upon the pace that it is transferring down and the mass. However what about this mass of air? For the reason that thrust drive is dependent upon the speed of change of momentum, I do not really have to know the peak of this cylinder of air.Nonetheless, the speed of change of air-mass does certainly rely upon the scale of the rotors and the density of air. From that, I can get the next tough approximation for the thrust drive from a helicopter.
You possibly can in all probability guess that the A is the rotor space and v is the pace the air is pushed down. The density of air is represented by the Greek letter ρ. However what about gravity? Nicely, if the helicopter is to hover then the thrust drive have to be equal to the burden. We will calculate the burden because the product of mass (m) and gravitational discipline (g).
For the reason that air density on Mars is simply 0.01 that of on Earth however the gravitational discipline is 0.38 as a lot, the decrease gravity profit doesn’t match the loss in air density. It is tougher to hover on Mars than on Earth. Oh, please discover that that is only a tough mannequin for the thrust drive from a helicopter. Please don’t use this calculation to try to construct your individual human-carrying helicopter. Nonetheless, you possibly can use it to calculate the proper dimension of the S.H.I.E.L.D. helicarrier rotors.
Really, here’s a fast homework query for you. Primarily based on the recognized mass and dimension of the Mars helicopter, what’s the air pace from the rotors in an effort to make this factor hover?
What concerning the flight time?
NASA says that the Mars helicopter will be capable of fly for about two to 3 minutes per day. The remainder of the time, it should use its photo voltaic panel on the highest of the car to recharge the battery. So, how large of a battery does this factor want? There are literally two methods to estimate the battery dimension (aside from asking NASA—that is the boring manner).
The primary methodology considers the charging time. Mainly, this factor will recharge for a complete day. On Mars, every day is nearly precisely the identical as an Earth day (however 37 minutes longer). However the complete day would not matter—what issues is the size of daylight time. Similar to on Earth, the size of daylight on Mars modifications with the seasons. So, let’s simply estimate that the solar is seen of 10 hours a day (I simply picked that for enjoyable).
The subsequent factor to find out is to consider the photo voltaic irradiance. That is the ability per unit space that the is within the mild reaching the floor of the planet. For Earth, this has a most of about 1,00Zero Watts per sq. meter. On Mars, it is solely about 2590 Watts/m2—however keep in mind that’s the most. Over the course of a day, the solar seems to vary place. When you have a static going through photo voltaic panel, the typical irradiance shall be smaller. I am simply going to go along with 295 Watt/m2. For the reason that dimension of the photo voltaic panel seems to be roughly the scale of the dice a part of the robotic, I’ll estimate its radius (it seems to be round) at 7 cm. With this dimension, irradiance, size of a day, and an effectivity of 25 p.c, that will give a complete power of about 40,00Zero Joules. That is very near the power saved within the battery of the iPhone X—word, there are some tips going from items of mAh to Joules.
Now for the second methodology. How a lot energy would it not take for the Mars helicopter to fly for 3 minutes? How do you calculate flying energy? Nicely, consider it this fashion. Energy is the speed at which you utilize power. What’s the helicopter doing with its power? It’s taking air above it and rising its pace (a rise in kinetic power). I am skipping some steps, however from that I can get an expression for the ability wanted to hover—you will discover all the main points in my calculation of the ability wanted for a human propelled helicopter (sure, that is an actual factor).
To calculate the flying energy, I have to know the rotor dimension (14 cm diameter) and the helicopter mass (about 1 kg). From this, I can calculate the thrust air pace wanted to hover. And with the pace, I can calculate the speed of change of air kinetic power—which is the ability. With these values (together with the density of air and the gravitational discipline on Mars), I get a flying energy of 374 Watts (word: listed here are my calculations in python).
However wait. NASA has already launched the ability requirement for the helicopter at 220 Watts. Personally, I contemplate this to be shut sufficient for a win-win. Win for me for doing this and win for you since you learn it.
If I am going with the NASA energy of 220 Watts I can calculate the power required to run for 3 minutes since energy = power/time (do not forget to transform the time to seconds). This offers an influence utilization of three.96 x 104 Joules. Increase. Proper across the power worth for the opposite calculation.
I in all probability ought to have left this complete factor as a homework drawback—however I could not assist myself. I needed to see if the numbers labored out.
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Uber EMEA head hopes agency will hold London license – NEWPAPER24
4 mins ago
May 24, 2018
Uber EMEA head hopes agency will hold London license
Uber has taken steps to enhance its enterprise mannequin and is hopeful it’s going to regain its license to function in London, the agency’s head of EMEA stated Thursday.
Transport for London, however the firm has been combating to maintain the precise to function within the British capital by way of an enchantment. It lately appointed Jamie Heywood, a former Amazon govt, as its new U.Ok. boss.
The agency is presently making an attempt to reshape its picture underneath the tenure of Chief Govt Dara Khosrowshahi. Below former boss Travis Kalanick, Uber was hit with a collection of scandals, from sexual harassment complaints in opposition to the corporate, to the usage of software program, to allegedly blocking regulators from gaining full entry to the Uber app.
On Thursday, Uber introduced it was opening a middle in France dedicated to growing its flying taxi know-how. A day earlier, it stated it was increasing insurance coverage protection for drivers throughout Europe.
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