Author Topic: Mars Helicopter  (Read 7299 times)

Offline speedevil

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Re: Mars Helicopter
« Reply #20 on: 04/05/2017 07:09 PM »
I suppose another reason to minimize blade length would be the physical size of the craft....

Packaging too.
Go much longer, and you can't avoid blades being required to fold in multiple ways.
The required power may go down, in principle per watt if you increase area, but the torque also rises, meaning you need a more capable gearbox, and probably swash plate and related unreliable mechanisms.

Plus, the above can cope with expected winds - more blade, and you're going to have to fold on landing them to avoid the sail area meaning you get blown over.

Fun optimisation problem.

Offline Rei

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Re: Mars Helicopter
« Reply #21 on: 04/05/2017 10:32 PM »
So, for fun I pulled up my prop calculator spreadsheet.  Plugging in 220W, air density 0,02kg/m, prop diameter 1,1m, 4 blades, prop cord 6cm, prop lift coefficient 0.7, prop drag coefficient 0.03, air viscosity 1.42e-5, etc.... I get static thrust of 9,5N, versus gravity on Mars of 3,7m/s... so 0.6G (earth-g) acceleration. Sounds like a perfectly reasonable design spec  :)  RPM is high (20k RPM).

If we change the prop to 2m, prop chord 12cm, everything else the same, the power req for the same static thrust goes down to 120W. and RPM down to 5.8k.  Contrarily, you could hold the power constant and get 14,2N thrust, and thus 4,7N more, enough to hold an additional  1,27kg mass.

Note that this is just for static thrust.  Efficiency drops as airspeed increases.  Also, my spreadsheet isn't very good at converging for static thrust (since I don't use it for that), so it's leaving a bit of residual flight speed (so real efficiencies would be a bit higher) - about 0,15m/s.  I could tweak it to get rid of the residual but... meh.  ;)
« Last Edit: 04/05/2017 10:36 PM by Rei »

Offline as58

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Re: Mars Helicopter
« Reply #22 on: 04/05/2017 10:48 PM »
So, for fun I pulled up my prop calculator spreadsheet.  Plugging in 220W, air density 0,02kg/m, prop diameter 1,1m, 4 blades, prop cord 6cm, prop lift coefficient 0.7, prop drag coefficient 0.03, air viscosity 1.42e-5, etc.... I get static thrust of 9,5N, versus gravity on Mars of 3,7m/s... so 0.6G (earth-g) acceleration. Sounds like a perfectly reasonable design spec  :)  RPM is high (20k RPM).

If we change the prop to 2m, prop chord 12cm, everything else the same, the power req for the same static thrust goes down to 120W. and RPM down to 5.8k.  Contrarily, you could hold the power constant and get 14,2N thrust, and thus 4,7N more, enough to hold an additional  1,27kg mass.

Note that this is just for static thrust.  Efficiency drops as airspeed increases.  Also, my spreadsheet isn't very good at converging for static thrust (since I don't use it for that), so it's leaving a bit of residual flight speed (so real efficiencies would be a bit higher) - about 0,15m/s.  I could tweak it to get rid of the residual but... meh.  ;)

Blade tip speed seems to become a bit... excessive.

Offline Rei

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Re: Mars Helicopter
« Reply #23 on: 04/05/2017 11:58 PM »
Hmm, yeah, it does (the spreadsheet doesn't check for the prop going supersonic, it's just basic blade element theory). I'm sure they're not designing for a supersonic prop, so their parameters must be different somehow. Probably a different angle of attack than I used.
« Last Edit: 04/06/2017 12:02 AM by Rei »

Offline scienceguy

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Re: Mars Helicopter
« Reply #24 on: 04/06/2017 04:19 AM »
Maybe a helicopter on Mars shouldn't be called a helicopter. Maybe it should be called an ornithopter.
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Offline as58

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Re: Mars Helicopter
« Reply #25 on: 04/06/2017 01:47 PM »
Maybe a helicopter on Mars shouldn't be called a helicopter. Maybe it should be called an ornithopter.

I'm not following. Ornithopter is a completely different type of flying machine and making one work on Mars seems to me (much) harder than a helicopter.

Offline scienceguy

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Re: Mars Helicopter
« Reply #26 on: 04/06/2017 08:32 PM »
Maybe a helicopter on Mars shouldn't be called a helicopter. Maybe it should be called an ornithopter.

I'm not following. Ornithopter is a completely different type of flying machine and making one work on Mars seems to me (much) harder than a helicopter.

I was just thinking of the book Dune, where they flew around in ornithopters. The planet Arrakis is like Mars.
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Offline ChrisWilson68

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Re: Mars Helicopter
« Reply #27 on: 04/06/2017 09:05 PM »
Maybe a helicopter on Mars shouldn't be called a helicopter. Maybe it should be called an ornithopter.

I'm not following. Ornithopter is a completely different type of flying machine and making one work on Mars seems to me (much) harder than a helicopter.

I was just thinking of the book Dune, where they flew around in ornithopters. The planet Arrakis is like Mars.

Yeah, I remember that from Dune.  But "ornithopter" isn't just a made-up name.  It has an actual meaning -- it means a machine that flies by flapping its wings, like a bird, not like a helicopter.  So, in Dune, Frank Herbert was imagining a future civilization that had developed flying machines with flapping wings.


Offline ChrisWilson68

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Re: Mars Helicopter
« Reply #28 on: 04/06/2017 09:09 PM »
Being able survey a route from air for rover should speed up exploration. NASA can download flight information and use it to plot a route for rover. Load rover with 100m route and leave it to it.

Ideal for scouting lava caves.

I would agree if I hadn't already seen how detailed the pictures we can get from orbit already are, and how well autonomous vehicle driving software already works.  With today's technology, anything too small to be seen from orbit can easily be handled by autonomous software on the rover.

So, while a helicopter on Mars might have value as a rover in its own right, I don't think it has value in finding a path for a ground rover.

Offline hop

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Re: Mars Helicopter
« Reply #29 on: 04/06/2017 09:27 PM »
I would agree if I hadn't already seen how detailed the pictures we can get from orbit already are, and how well autonomous vehicle driving software already works.  With today's technology, anything too small to be seen from orbit can easily be handled by autonomous software on the rover.
The people who actually build and operate Mars rovers do not appear to agree with this. For current rovers, the range visible in the navcams is a significant limiting factor. It only takes a small dip or rise to completely obscure what's ahead.  Autonomous driving is much slower and less efficient. On could certainly argue that more advanced autonomy would be a better trade than longer range imagery, but it's definitely a trade.

Online TrevorMonty

Re: Mars Helicopter
« Reply #30 on: 04/06/2017 09:48 PM »
In ideal terrains rover can see and travel 120m and considerable less than <120m in lot of terrain. Helicopter increases that to 400m in most terrains.

The video had great example of rover spending days finding a safe route into a crater. Helicopter survey would have saved days of precious rover time plus wear and tear in this case.

It is not just about route survey but also locates points of increase kms away.

Offline speedevil

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Re: Mars Helicopter
« Reply #31 on: 04/07/2017 12:15 PM »
So, for fun I pulled up my prop calculator spreadsheet.  Plugging in 220W, air density 0,02kg/m, prop diameter 1,1m, 4 blades, prop cord 6cm, prop lift coefficient 0.7, prop drag coefficient 0.03, air viscosity 1.42e-5, etc.... I get static thrust of 9,5N, versus gravity on Mars of 3,7m/s... so 0.6G (earth-g) acceleration. Sounds like a perfectly reasonable design spec  :)  RPM is high (20k RPM).
The quoted blade speed in the other video is 2200RPM.
Prop chord of 6cm is reasonable as a limit for a 11cm prop, but you're probably looking at more like 60cm, especially with a coax.
This drops the rotary speed a lot.

Offline speedevil

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Re: Mars Helicopter
« Reply #32 on: 04/07/2017 12:29 PM »
In ideal terrains rover can see and travel 120m and considerable less than <120m in lot of terrain. Helicopter increases that to 400m in most terrains.
The range of the helicopter is several hundred meters - but it's at ~40m altitude at those ranges.

You are going to get (over the whole flight) useful stereo images of much of the surrounding flattish terrain out to several hundred meters from the flightpath, enough to say you can probably, or probably can't navigate over it.

Combining a couple of flights, or selected images over one orthogonal to a path, you get information over a much longer baseline, but at this point, you're bumping up against orbital terrain models possibly being more useful.

Offline hop

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Re: Mars Helicopter
« Reply #33 on: 04/07/2017 05:24 PM »
The range of the helicopter is several hundred meters - but it's at ~40m altitude at those ranges.
Right, the higher altitude is a big deal. Some early MSL designs had cameras on a second arm to get further reach, e.g. https://twitter.com/elakdawalla/status/601596999704666113

Again, a helicopter isn't the only possible solution, but it is a solution to a problem that has a significant impact on operation of current vehicles.

Offline speedevil

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Re: Mars Helicopter
« Reply #34 on: 04/08/2017 04:03 PM »
Again, a helicopter isn't the only possible solution, but it is a solution to a problem that has a significant impact on operation of current vehicles.

Even treating it as a one-shot 'which is the best way out of this canyon' tool, it may well entirely pay off its 1kg mass budget in one flight.
I also wonder about landing.
For obvious reasons, these may not need to be on the 'soft landed' part of the structure.
What if you throw them out 500m up, before final braking, saving some on mass.

Offline Asteroza

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Re: Mars Helicopter
« Reply #35 on: 04/10/2017 12:00 AM »
Lasermotive was working on a power/data over fiber solution for tethered surveillance UAV's, which could easily fit the bill here if the UAV need not land away from the rover.

Other options include using a thick inflatable rotor blade, perhaps using a sublimating substance for inflation gas. You could get a much larger rotor than packaging would allow for fixed hard rotors.

Offline CameronD

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Re: Mars Helicopter
« Reply #36 on: 04/10/2017 06:56 AM »
Again, a helicopter isn't the only possible solution, but it is a solution to a problem that has a significant impact on operation of current vehicles.

Even treating it as a one-shot 'which is the best way out of this canyon' tool, it may well entirely pay off its 1kg mass budget in one flight.
I also wonder about landing.
For obvious reasons, these may not need to be on the 'soft landed' part of the structure.
What if you throw them out 500m up, before final braking, saving some on mass.

If that's all you're trying to achieve, use a balloon on a string.  When finished, deflate, rewind and re-use.  ::)

The helicopter idea only starts to makes sense if you're wanting to survey a long way away from the rover ..and even then I'm not so sure:

http://www.gaerospace.com/space-exploration/planetary-balloons/mars-balloons/



« Last Edit: 04/10/2017 07:06 AM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Asteroza

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Re: Mars Helicopter
« Reply #37 on: 04/10/2017 08:19 AM »
Again, a helicopter isn't the only possible solution, but it is a solution to a problem that has a significant impact on operation of current vehicles.

Even treating it as a one-shot 'which is the best way out of this canyon' tool, it may well entirely pay off its 1kg mass budget in one flight.
I also wonder about landing.
For obvious reasons, these may not need to be on the 'soft landed' part of the structure.
What if you throw them out 500m up, before final braking, saving some on mass.

If that's all you're trying to achieve, use a balloon on a string.  When finished, deflate, rewind and re-use.  ::)

The helicopter idea only starts to makes sense if you're wanting to survey a long way away from the rover ..and even then I'm not so sure:

http://www.gaerospace.com/space-exploration/planetary-balloons/mars-balloons/

Running with the evacuated theme, NIAC phase 2 had one for a vacuum airship. Deploy tethered from a rover?

https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Evacuated_Airship_for_Mars_Missions

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