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#26 2016-12-30 17:26:00

SpaceNut
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Re: Scouting Mars by Helicopter

GW Johnson wrote:

I would do your lift fan explorations as part of the generalized category retropropulsion.  I have doubts that the same configuration would work in both subsonic and supersonic slipstreams,  and I have doubts about practical levels of disk loading in "air" that thin, even at the surface,  much less 10 km+ up.  Nevertheless,  it needs a thorough look. 

GW

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#27 2016-12-30 17:31:49

SpaceNut
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Re: Scouting Mars by Helicopter

More copying of OT post on helicopter use to scout mars:

kbd512 wrote:

GW,

I agree with most of the points you're making, but I still think the best way to visit multiple sites in a single mission is to figure out how to make aircraft fly on Mars.  If it's possible to make practical electric aircraft work on Mars, then there's virtually no point on the planet that couldn't be accessed in a matter of hours.  More importantly, the same technology that would make powered flight practical also makes soft landing substantial payload tonnages feasible without resorting to dumping truckloads of propellants through a rocket engine.  Every kilogram of payload delivered to the surface of Mars has a substantial price tag attached to it, so there's a clear incentive to limit EDL mass to what is minimally required to soft land.  I could be wrong, but I think the best way to do that is a two stage supersonic compressor combined with a conventional two or three stage lift fan.

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#28 2016-12-30 17:33:35

SpaceNut
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Re: Scouting Mars by Helicopter

GW Johnson wrote:

Well,  let's just say I'm skeptical but intrigued by the notion of some sort of aircraft on Mars.  Some sort of helicopter would really help,  at least up to a few 100 km.  But the density is so bloody low,  I have to be very skeptical of any sort of airplane or helicopter projects for Mars.  You still need very,  very low landing speeds not to crash.  Almost regardless of the scenario you are looking at.

With densities that low (fraction of a percent of that here),  dynamic pressures are minute at such speeds,  and you can only build so much area before the square-cube weight growth eats you up on Mars,  even at the lower gravity.   Aero coefficients are the same there as here,  they have no density or pressure or velocity effects in them.  Those went to dynamic pressure.

I know much less about helicopters,  but small airplanes that land on dirt strips here need to touch down between about 30 and 60 mph to be reliably not crashed by your ordinary pilots.  No one has built a large dirt-strip airplane in a lot of years now,  but landing touchdown speeds on them (I'm thinking of the B-17) were under 100 mph,  even with specifically-trained pilots. 

At 60 mph here on Earth at sea level,  dynamic pressure is around 9.2 psf,  and not-quite-stalled lift coefficients on straight,  subsonic wings are about 1.1 or thereabouts,  with little or no flaps.  (Not much higher with flaps.)  Your wing loading W/S is then limited to just about 10 psf max at 60 mph touchdown.  Significantly worse in thinner air at altitude or on a very hot day.

For the same touchdown speed on Mars (a simple kinematic requirement to avoid a rough field crash,  nothing to do with actual aircraft design otherwise),  CL is no different,  and the density is about 0.7% that here.  Dynamic pressure is then about 0.064 psf.  That limits your wing loading to about 0.07 psf,  those being Mars pounds at 38% of corresponding Earth pounds,  of weight.  100 sq.ft can carry ~7 lb Mars weight,  which is about 18-19 lb Earth weight. 

Wing structure weight typically is the 0.58 power of aspect ratio.  My C-170 has aspect ratio near 7,  and its wings (without fuel) weight about 100 pounds (Earth) each.  Their total of 200 lb here is about 76 lb there on Mars.  Even if advanced carbon composite,  they would still be about 30 lb there (2.5 times lighter).  Higher aspect ratio might lower that ~10-20% before you push structural limits too far on the materials.  Looks like a losing proposition to me. No payload,  no fuselage,  no power supply,  no propulsion.  Just the wing. 

Why would a helicopter (or any other subsonic lift fan) be any different?  They're not different here in any significant respect. 

GW

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#29 2016-12-30 17:35:43

SpaceNut
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Re: Scouting Mars by Helicopter

GW Johnson wrote:

I probably should have based my numbers on ~150 sq.ft of wing area,  not 100.  But it makes no real difference to the conclusions.

GW

Unless we find means to reduce parts used in the helicopter mass we will somehow need to find a way to create more lift.

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#30 2016-12-30 17:36:47

SpaceNut
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Re: Scouting Mars by Helicopter

GW Johnson wrote:

You cannot find more lift,  unless you can tolerate supersonic blade speeds aerodynamically,  structurally,  and from a lethal noise standpoint.  The blade tips on the Tu-95 Bear are just-supersonic at full power,  and it can be heard from a shallowly-submerged sub if flying at low altitude.  A supersonic prop was tried in the 1950's on an experimental variant of an F-84 Thunderjet.  It was not found attractive at all.  The Nazis also tried it,  and abandoned it,  during WW2.

You can add extra blades,  but there's interference from blade-to-blade that starts robbing you of your improvements.  Conventional wisdom says about 6 blades is max,  but I really suspect that number is actually up around 13-15,  for a rotational tip speed under 0.9 Mach,  and a well-subsonic slipstream.  Spin faster or fly faster,  and it starts looking like ~6 blades max again.

So,  limited to subsonic tip speeds,  it is well-known that you want as much of your blade length operating as near to best L/D as you can achieve.  That gets you the most disk thrust for the power required to spin it,  something very important to a practical design.  Best L/D speed is not fastest-feasible speed,  it's usually in the lower third of the feasible speed band with more wing-like airfoils,  with the exception being the very thin-section (easily-stalled) airfoils out at the tip. 

And absolutely none of that known propeller technology is compatible with more than about a 0.8 Mach slipstream speed.  Remember,  we've had dive experience to just-supersonic speeds with propeller airplanes since the P-38 just before WW2.  Props that work sbsonically simply quit working at all as effective thrusters as you hit the sound barrier,  because you are spinning subsonic airfoils at vector-addition supersonic speeds,  even if the rotational component is still subsonic. 

As far as I know,  there is no way around that.  That "barrier" is precisely why jet engines were invented.  They make supersonic flight possible,  not some "trick" propeller design.

GW

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#31 2016-12-30 17:41:42

SpaceNut
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Re: Scouting Mars by Helicopter

RobertDyck wrote:

The objective here appears to be bringing the vision from the TV show to life. NatGeo showed a swarm of drones covering vast area quickly to look for resources. If helicopter blades don't work on Mars, could a jet engine? If there's an issue with the CO2 atmosphere of Mars, could a ducted fan?

aeo-rc-30mm-ducted-fan-combo-w-9000kv-brushless-motor-9.gif

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#32 2016-12-30 18:20:49

SpaceNut
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Re: Scouting Mars by Helicopter

GW Johnson wrote:

The lift fan or helicopter problem looks an awful lot like the static performance problem for the propeller.  The stream tube is very wide at low speed from which the disk draws air,  trending from wide to disk size at the disk plane,  to about half the disk diameter at the achieved final exit jet velocity,  several disk diameters downstream.  That's from actuator-disk theory.  Interrupt that exit jet (as with the surface,  and you get less thrust. 

There's some,  but not a lot,  of stream velocity at the disk plane.  This stream velocity adds vectorially to the rotational tip speed,  for an absolute tip velocity that really needs to stay subsonic.  You can get away with up to about 0.9 or 0.95 Mach,  because the sections there are so very thin.  This thinness delays the transonic drag rise to such high speeds. 

None of that depends on anything but speed,  and speed of sound.  The lift and drag forces per unit blade area depend upon dynamic pressure,  and the lift and drag coefficients.  These get integrated root-to-tip along with the chord length and twist distributions to get the net blade lift and drag.  Thrust comes from the axial component of lift.  Torque comes from the vector addition of the other lift component,  and both components of the blade drag.  It's just the geometry,  but it gets a bit complicated to book-keep.  That's blade element theory. 

Technically,  you need to simultaneously solve the blade-element and actuator-disk models,  to get a reliable solution. 

Ignoring any blade-to-blade interference problems,  you just add this up for your total number of blades.  That thrust,  distributed over the circular disk area,  is the "disk loading".  (Disk loading is what you converge to make the two models solve together.)  At max feasible pitch,  that's all the lift there is,  and it's usually associated with a lot of power (torque),  because the max-thrust aerodynamics are not the most efficient.  Murphy's Law,  but a very real effect.  Your efficient disk loading is less;  that's where you usually want to fly. 

Disk loading will be proportional to some reference dynamic pressure.  That means for Mars,  at the same speeds otherwise,  disk loading is proportional to density,  which on Mars is around 0.7% that here on Earth.  For a given disk diameter,  area x disk loading is all the Mars weight you can hold up.  That's Mars weight units,  which would be a larger number of Earth weight units,  due to the 38% gravity.  Earth weight is weight on Mars / 0.38. 

What that really means is a disk design that would load to "X" weight/area disk loading here on Earth,  will only load to 0.007 "X" /0.38 weight/area on Mars.  The low density factor greatly overwhelms the reduced gravity factor.  The resulting reduction in disk loading is about 0.02 that on Earth,  or about factor 50 times less.  That's just way out of the ballpark for what you can compensate with high strength/weight composite materials,  which is nearer 2.5:1. 

The 48 foot diameter 2-blade rotor on a Bell model 205 helicopter picks up a max gross weight of 9500 lb here on Earth.  The same rotor could only hold up about 190 lb on Mars.  If you can design around that kind of lowered disk loading (and you'll need a lot bigger rotor diameter and more blades),  then helicopters on Mars are feasible. 

People looking at little drones flying around here on Earth,  then at how similar the landscapes look on Mars to some here on Earth, and then just make the leap to thinking that those same kinds of drones could easily fly around on Mars.  They know about the lower gravity making things easier.  But few realize just how close to vacuum that "air" really is.  It only has significant dynamic pressures at supersonic and hypersonic speeds. 

To get the same dynamic pressures we use here,  wind speeds have to be just about factor 12 larger there.  A 60 mph speed that produces 9.2 psf here at sea level,  requires a 720 mph wind speed there. And THAT's the problem with helicopters,  airplanes,  or lift fans,  on Mars.  And parachutes. 

GW

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#33 2017-01-06 23:40:03

SpaceNut
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Re: Scouting Mars by Helicopter

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#34 2017-05-17 22:48:22

SpaceNut
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Re: Scouting Mars by Helicopter

No forgotten yet.... How a Helicopter Drone Could Fly on Mars

We've gotten pretty smart at telling rovers what to do when they're working on Mars. NASA has more than a decade's experience in directing these machines on the Red Planet, asking them to image rocks, drill into the surface, or drive over varying surfaces. The Curiosity rover is so smart that in some cases, it can identify targets by itself to analyze.

But rovers have a big limitation: They stay on the ground. Aerial imaging is only available through satellites that orbit several miles above a rover. While this can provide a large overview of the site, it makes it difficult to anticipate what's just over the next hill or crater.

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#35 2017-06-07 18:56:20

SpaceNut
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Re: Scouting Mars by Helicopter

Helium or hydrogen lift would be a way to augment the blades lifting capability.

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#36 2018-05-06 14:31:55

SpaceNut
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Re: Scouting Mars by Helicopter

Thanks for the topic link:

Void wrote:

I pick on SpaceNut quite a bit.  So I will support SpaceNut this time.

https://en.wikipedia.org/wiki/NASA_Mars … pter_Scout

Nothing against you either Robert.


Wiki indicates soon we will hear on its potential for mars....

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#37 2018-05-12 18:30:48

SpaceNut
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Re: Scouting Mars by Helicopter

Engineers at JPL began working on the Mars Helicopter in 2013 and spent four years coming up with the final design.
NASA plans to deploy the helicopter for a 30-day flight test campaign with up to five flights covering progressively greater distances. Once there, it will use solar cells to charge its batteries and operate a built-in heater to combat frigid nighttime temperatures.
The will not pilot and Earth will be several light minutes away, so there is no way to joystick this mission in real time which means the helicopter has to fly itself autonomously once it receives its instructions relayed from the rover to it for each flight.

The space agency announced the decision on Friday to add a small helicopter — about four pounds with a fuselage the size of a softball and blades that span just over three and a half feet, tip to tip — to its Mars 2020 mission, which is to launch in July 2020 and arrive at Mars the following February.

A Helicopter on Mars? NASA Wants to Try

The thin air at the surface of Mars is the equivalent of being 100,000 feet above Earth — well beyond the limits of terrestrial helicopters — although the weaker gravity helps. Two pairs of rotor blades will spin in opposite directions at nearly 50 revolutions per second. A prototype has been tested in a chamber that mimics the Martian atmosphere at NASA’s Jet Propulsion Laboratory.

How hard is it to fly a helicopter on Mars? NASA will soon find out

AMQ454A3M5GB3BOKANEVDGR7MI.jpg

To get airborne, the four blades on the Mars Helicopter will make nearly 3,000 rotations per minute. That means they will spin about 10 times faster than a helicopter built for our skies.

NASA plans to fly the craft up to five times over a span of 30 days. For its maiden voyage, the goal is to hover 10 feet above the ground for about 30 seconds. If all goes well, its final flight will cover a distance of several football fields over a period of 90 seconds.

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#38 2018-05-15 11:37:21

elderflower
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Re: Scouting Mars by Helicopter

This thing will be a drone with autonomy. It can carry a camera but how will it decide what to photograph? There's no getting away from the need to put a human on Mars or in Mars orbit so that it can be operated directly, like a drone on Earth.
I'd like a man capable flying machine on Mars, but proportionating Earth helicopters for the Mars environment gives you a big machine scarcely able to get it's own Mars weight off the ground. I can't see it being done at all unless a supersonic rotor can be developed. I have some thoughts in this direction but I need to give it a lot more consideration before I post it.

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#39 2018-05-15 17:21:59

SpaceNut
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Re: Scouting Mars by Helicopter

The unmanned drone hopefully still functional once man does arrive could be converted to a telerobotic controll arial egress planner for crews wish to plan out exploration around the site.

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#40 2018-12-09 16:58:46

SpaceNut
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Re: Scouting Mars by Helicopter

Repost:

elderflower wrote:

I did consider a tip jet arrangement for a possible Mars helicopter. I couldn't make an enormous rotor produce sufficient lift for expeditionary purposes with a tip speed of M=0.85. The very low density of the atmosphere was the main problem here. Nonetheless, putting a diffusion device on each end of a long, centre pivoted arm rotating at high speed would be possible. All the structural problems for this have been solved. However you would use a lot of the pressure you generate just getting the product to flow back up the arm to the centre where it can be tapped off and quite a bit of power overcoming the windage of the arm.

Such that the tip of the blade would have a vent that is angled to push the blade at speeds that is greater than a motor might be able to do. If that vent can gimbal then we can also create lift in addistion from pushing the Helicopter upward as well.

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#41 2019-03-13 20:31:21

SpaceNut
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Re: Scouting Mars by Helicopter

http://www.marsdaily.com/reports/NASA_i … s_999.html

Martian atmosphere. At the surface where the Mars 2020 rover is targeted to land, the atmospheric pressure is equivalent to about 100,000 feet above the Earth's surface. No helicopter has ever reached even half that distance above Earth.

Yet the Mars Helicopter will be able to fly as high as about 15 feet above the Red Planet thanks to its two sets of rotor blades - each four feet long, tip-to-tip - spinning at 2,400 rotations per minute, which is about 10 times faster than an Earth helicopter.

The smallness of the main helicopter body helps too. It's only about the size of a softball and will weigh just under four pounds.

The plan at Mars is to attempt up to five flights, each one flying just a little farther and each lasting up to 90 seconds. A solar array on the top of the vehicle will recharge the batteries, which will be used both to rotate the blades and to keep the vehicle warm, especially at night.

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#42 2019-03-14 03:12:06

louis
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Re: Scouting Mars by Helicopter

Another good example of NASA wasting funds on marginal projects rather than concentrating them on the  central task - in stark contrast to Space X. If you have a base on Mars then maintaining a helicopter becomes possible. 

SpaceNut wrote:

http://www.marsdaily.com/reports/NASA_i … s_999.html

Martian atmosphere. At the surface where the Mars 2020 rover is targeted to land, the atmospheric pressure is equivalent to about 100,000 feet above the Earth's surface. No helicopter has ever reached even half that distance above Earth.

Yet the Mars Helicopter will be able to fly as high as about 15 feet above the Red Planet thanks to its two sets of rotor blades - each four feet long, tip-to-tip - spinning at 2,400 rotations per minute, which is about 10 times faster than an Earth helicopter.

The smallness of the main helicopter body helps too. It's only about the size of a softball and will weigh just under four pounds.

The plan at Mars is to attempt up to five flights, each one flying just a little farther and each lasting up to 90 seconds. A solar array on the top of the vehicle will recharge the batteries, which will be used both to rotate the blades and to keep the vehicle warm, especially at night.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#43 2019-03-14 05:50:05

elderflower
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Re: Scouting Mars by Helicopter

Tip speed of the proposed rotor will exceed Mach 1. Good luck to whoever is trying to solve the structural and control issues that that raises!

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#44 2019-03-14 09:37:51

tahanson43206
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Re: Scouting Mars by Helicopter

For elderflower .... You have provided a learning opportunity for anyone (like me) who would like to pursue it.

I am hoping you are willing to invest a bit more time into this topic.

I'll continue after the quote:

elderflower wrote:

Tip speed of the proposed rotor will exceed Mach 1. Good luck to whoever is trying to solve the structural and control issues that that raises!

First, thanks for the impetus to ask Mr. Google about helicopter tip speed and the speed of sound.  There are LOTS of citations, and while I only scanned a few, I saw plenty of confirmation of your warning.  However, what I did NOT see was a satisfying explanation of how (or why) the speed of sound in a gas has the effect that it (by observation) does.

The speed of sound (as I understand it) is a function of pressure and temperature of a gas, and it represents the rate at which individual molecules bump into each other in the ordinary course of their working day.  According to a source I found, the speed of sound on Mars is noticeably lower than the speed of sound on Earth, but I also found a reference showing that the speed of sound decreases on Earth with altitude.  I did not attempt to confirm this, but I am making a guess that the speed of sound on Earth at 100,000 feet might be the same as the speed of sound at the surface of Mars.

Second ... I am wondering (and would appreciate guidance) if the mass of a gas (eg, at 100,000 feet on Earth) might allow for a reduced effect of acoustic shock on equipment. 

Third ... the purpose of advancing the tip of the helicopter blade (or any part of the blade) is to interact with gas molecules, and to impart momentum to them in a downward direction, so that the blade can react by bouncing upward.   I am having difficulty understanding why the natural rate of bouncing of the gas molecules has anything at all to do with the propelling action of the blade.  If the blade advances upon an individual molecule faster than it is moving with respect to its peers, I would expect it to deflect downward at a rate which might well exceed the natural rate of movement.

Back to you at this point ...

(th)

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#45 2019-03-14 17:30:25

SpaceNut
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Re: Scouting Mars by Helicopter

https://en.wikipedia.org/wiki/JPL_Mars_Helicopter_Scout

The helicopter will undergo a 30-day test campaign and fly up to five times early in the rover's mission, as it is primarily a technology demonstration. This helicopter will fly no more than 3 minutes per day at altitudes ranging from 3 m to 10 m above the ground, and cover a maximum distance of about 600 m (2,000 ft) daily.

The inconsistent Mars magnetic field precludes the use of a compass for navigation, so it will use a solar tracker camera integrated to JPL's visual inertial navigation system. Some additional inputs might include gyros, visual odometry, tilt sensors, altimeter, and hazard detectors. It will use solar panels to recharge its batteries, which are six Sony Li-ion cells Batteries: 273 g with a nameplate capacity of 2 Ah.

Nice amount of flights made possible by Revolutionary Vertical Lift Technology (RVLT) project.and hopefully when no dust devils are around as that would be a problem for the helicopter...
Hopefully the power remaining in the batteries will keep them from freezing during the mars night.
Remnant fields...for no compass using sun orientation for flight.

Some workhorse computer tools to characterize and better understand how well the Mars Helicopter would fly in the Red Planet’s atmosphere were used in the RVLT project.

https://ntrs.nasa.gov/archive/nasa/casi … 006746.pdf

https://www.nasa.gov/aeroresearch/programs/aavp/rvlt/

https://rotorcraft.arc.nasa.gov/Publica … TechMx.pdf

Mars 2020 will launch on a United Launch Alliance (ULA) Atlas V rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida, and is expected to reach Mars in February 2021.

https://spaceflightnow.com/2018/03/15/n … 020-rover/

Jim Watzin, director of NASA’s robotic Mars exploration program at the agency’s headquarters, said last month that an engineering model of the helicopter has completed 86 minutes of flying time in a test chamber configured to simulate the Martian atmosphere.

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#46 2019-03-14 17:54:44

tahanson43206
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Re: Scouting Mars by Helicopter

Thanks to SpaceNut for the numerous links relating to the helicopter on Mars initiative.

I scanned the pdf (6746 ) and found the highest Mach number expected/evaluated was .5

At that point, I went back to look at the speed of the tips, and got:

Given 1.21 meters diameter: 3.8 meters circumference (rounded down)

2800 rpm / 60 * 3.8 meters >> 177.4 meters per second (rounded up)

That number is well below the figure from Wikipedia for Mach 1 on Mars: about 240 meters

However, it is above the Mach number I found of .5, so I probably missed something.

(th)

Last edited by tahanson43206 (2019-03-14 17:56:39)

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#47 2019-03-14 18:33:30

SpaceNut
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Re: Scouting Mars by Helicopter

https://www.universetoday.com/77077/how-fast-is-mach-1/

Mach 0.8 to 1.2 is 273-409 m/s which is quite a range and if the atmosphere is thinner or thicker that number changes quite fast with the formular

Mathematically, this can be defined as M = u/c, where M is the Mach number, u is the local flow velocity with respect to the boundaries (i.e. the speed of the object moving through the medium), and c is the speed of sound in that particular medium (i.e. local atmosphere, water, etc).

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#48 2019-03-14 19:30:41

GW Johnson
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Re: Scouting Mars by Helicopter

Airfoils that make good fans or propellers are subsonic airfoils with a nose radius and curved contours.  Drive one supersonic,  and it forms a shock wave top and bottom.  Because of the nose radius,  this is a detached bow shock wave. 

Even if you make the supersonic portion of the airfoil sharp-edged wedges,  you still get a shock wave top and bottom,  just attached to the leading edge. 

The presence of a shock wave thickens the boundary layer,  leading to instability and stall separation.  That is loss of lift (and an increase in drag) on the airfoil.

And THAT is why supersonic propellers fundamentally cannot work very well.  They cannot,  and they never have.  Many have tried,  all have failed.

All that being said,  if the Mars helicopter tip speed is under Mach about 0.9 or so,  the airfoil shock problem is more-or-less avoided,  at least for thin sections typical of rotor blade tips.   

Then the disk loading is limited.  You get factor 0.38 relief on the weight,  but you get hurt by factor 0.007 on density. That's about factor 54 lower disk loading capability on Mars. 

We'll see if NASA can pull this off.  Consider me an open-minded skeptic about the feasibility of this.  Capitalize the "skeptic" part of that statement. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#49 2019-03-15 18:36:49

kbd512
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Re: Scouting Mars by Helicopter

GW,

Has anyone ever attempted to use supersonic propellers shaped like this?:

WhalePower - The Science

Never is a very strong word to use.  Nature seems to have a solution to the problems you just described.

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#50 2019-03-15 20:43:58

tahanson43206
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Re: Scouting Mars by Helicopter

For kbd512 re #49 ...

I tossed the question you posed into Google, and got back immediate confirmation of application of the whale fin discovery to helicopter blades.
This report is dated 2012, and I saw hints that there are other reports.
https://newatlas.com/humpback-whales-ro … des/21332/

However, to this point, I have not found an answer to your specific question, regarding "supersonic propellers"

The research discussed at the link above is reducing turbulence as helicopter blades complete the retreating part of their cycle.

Edit: A subsequent search found an article about a company founded by the whale fin researcher to develop improved propeller blades for a wide variety of applications.

https://www.technologyreview.com/s/4097 … -turbines/

One thing I find curious is that all the top citations Google showed are from 2008 or 2012.

I would have expected such a discovery to yield results for some time.

Edit(2): This is more like it, but I still have not found evidence of work on supersonic operations. The link is from 2018:

https://www.newswire.ca/news-releases/c … 49041.html

(th)

Last edited by tahanson43206 (2019-03-15 21:03:29)

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