Hovercraft on Mars

Calliban · 2021-04-19 08:09:28

I have been through the planetary transport topic and no one appears to have raised this concept, much to my surprise. I was interested in a concept that could allow rapid transportation to sites of scientific interest for early Mars missions. This would need to allow navigation over rough, bolder filled terrains at high speeds.

The relative easy compressibility of air on Mars (CO2 exists as a gas at a temperature far beneath its critical point) makes it possible to compress gas using a funnel mounted on the front of a fast moving vehicle. The gas can then be heated to a temperature above its critical point at 31°C and used to inflate a skirt, that would levitate the hover craft above the ground. A portion of the same compressed CO2 stream would enter a jet engine, providing thrust. The low speed of sound of CO2 relative to air and water vapour, should reduce the rate of expansion and loss of CO2 out of the skirt.

I would propose the use of silane to power the hovercraft. It will burn in carbon dioxide, so would appear to offer the best energy density of chemical fuels on Mars.

The hovercraft would need to be relatively lightweight, as the dynamic pressure that is achievable in the Martian atmosphere at subsonic speeds, is limited. With an air density of 0.02kg.m-3, and a velocity of 100mph (44m/s), dynamic pressure would be 20Pa.

The total lift force provided by a hovercraft (N) is provided by:

F = 0.5 x air density x intake area x (intake entry velocity^2 - intake exit velocity^2).

If intake area is 100m2 and exit velocity is twice entry velocity, i.e. 88m/s, then total lift force is 1936N, or 526kg on Mars. On this basis, a hover craft travelling at 100mph on the surface of Mars, with an inlet area of 100m2, must weigh no more than 526kg.

The lift is limited by the exhaust velocity achievable by a Martian jet engine and the temperature that the skirt material and frame can withstand. Exhausr velocity for a pure silane rocket engine would be on the order of 3km/s, which would provide excellent lift, but would be far too hot to be workable.

Last edited by Calliban (2021-04-19 09:19:46)

tahanson43206 · 2021-04-19 09:12:44

For Calliban re new topic!

Congratulations, and best wishes for success with this new topic.

You are the ** only ** resident ** real ** engineer in the present active membership of (about) 15 ...

Captain J. Torriani is in academic preparation for a career in design of machines (including robots), so eventually (if we are fortunate) he may have some time to contribute to the accumulation of knowledge and practical wisdom in the archive of this forum.

However, for the time being, you are the person upon whom the entire field of (human) engineering depends!

Here I offer a nod to GW Johnson, who remains active in practical engineering, from the vantage point of consultancy.

***
You have noted my interest in persuading Mars Society management to support investment in a repository of information that can be consulted by someone like Noah, as he prepares plans for actual settlement of Mars, or for support of settlement by organizations on Earth.

In the case of your proposal ... this appears to me to be a viable concept. Hovercraft are successful on Earth, and I see no reason at all why they should not be even more successful on Mars, despite the challenges you have already noted.

Since you ** are ** a working engineer, you know very well what information storage systems are needed to support accumulation of knowledge that is needed to design and build a hovercraft for Mars.

Please share some ideas for us (existing members) to consider, and for Mars Society management to evaluate.

I have proposed use of DropBox (as just one example) if we are unable to win support from Mars Society, but (so far) SpaceNut has held out for a solution that Mars Society can (and will) support.

An "in house" data storage solution would most certainly be better, because the members of the Society can be enlisted to support it.

Plus! If the concept is successful, some portion of new members to this forum may be able to afford membership in the Society, and the enterprise can become self-sustaining.

(th)

Calliban · 2021-04-19 09:26:10

tahanson43206 wrote:

For Calliban re new topic!
Congratulations, and best wishes for success with this new topic.
You are the ** only ** resident ** real ** engineer in the present active membership of (about) 15 ...
Captain J. Torriani is in academic preparation for a career in design of machines (including robots), so eventually (if we are fortunate) he may have some time to contribute to the accumulation of knowledge and practical wisdom in the archive of this forum.
However, for the time being, you are the person upon whom the entire field of (human) engineering depends!
Here I offer a nod to GW Johnson, who remains active in practical engineering, from the vantage point of consultancy.
***
You have noted my interest in persuading Mars Society management to support investment in a repository of information that can be consulted by someone like Noah, as he prepares plans for actual settlement of Mars, or for support of settlement by organizations on Earth.
In the case of your proposal ... this appears to me to be a viable concept. Hovercraft are successful on Earth, and I see no reason at all why they should not be even more successful on Mars, despite the challenges you have already noted.
Since you ** are ** a working engineer, you know very well what information storage systems are needed to support accumulation of knowledge that is needed to design and build a hovercraft for Mars.
Please share some ideas for us (existing members) to consider, and for Mars Society management to evaluate.
I have proposed use of DropBox (as just one example) if we are unable to win support from Mars Society, but (so far) SpaceNut has held out for a solution that Mars Society can (and will) support.
An "in house" data storage solution would most certainly be better, because the members of the Society can be enlisted to support it.
Plus! If the concept is successful, some portion of new members to this forum may be able to afford membership in the Society, and the enterprise can become self-sustaining.
(th)

Thanks Tom. That is a sobering thought. Kbd is also an active engineer from what I gather. Gary is retired, but still active in his own way, contributing to discussions on various topics. So I am certainly not the only engineer present.

I think a Mars wiki is a good idea. If Zubrin and Co are concerned about its content, then why don't they volunteer to oversee it and provide a level of technical peer review? That would appear to be the most resource efficient option from what I can see, as they have people willing to produce a knowledge store free of charge from this end.

Last edited by Calliban (2021-04-19 09:28:14)

kbd512 · 2021-04-19 11:10:10

Calliban,

I'm not an engineer. I work in supply chain management on forecasting / statistical analysis software, the business of figuring out how to either manufacture a good at minimum cost or to get people and materials from Point A to Point B for minimum cost and time invested.

Aviation is a personal interest of mine, so in the course of "figuring out" how to design my own plane, I've learned a handful of relevant things about structures and aerodynamics from the books I've read, example problems, and my own amateur attempts to apply what I've learned. The more I learn, the more I realize that I've barely scratched the surface of the body of knowledge required. I have also had some help from real aerospace engineers and one aerodynamicist. Finding an aerodynamicist who will even speak to you is a challenge, BTW, but one of the engineers I spoke with "knew a guy who knew a guy", so to speak, and he was kind enough to tell me what books to read and what concepts to focus on; another Canadian man, actually, and a nice guy but very busy, as you would expect. At best, I could be considered an "enthusiastic amateur" who barely knows enough to be dangerous. I'm sure I give the real engineers like GW a good chuckle here and there.

Anyway, many of these unique issues that we encounter with power or weight or other key performance criteria tie back to "simple math" kind of problems that must be addressed. It's surprising that some people still refuse to accept the results, but I guess I shouldn't be too upset over it. I never viewed any of the problems or solutions as "magic", though- merely another problem to be solved with a little ingenuity and a lot of hard work. Maybe that's the difference.

tahanson43206 · 2021-04-19 11:56:59

For all ... What looks promising for Mars ** ought ** to find application on Earth ...

There are plenty of swaths of uncluttered desert on Earth. A means of fast transport over such terrain might turn out to be economically competitive with wheeled transport due to speed advantage, and airborne systems such as helicopters due to (potentially) greater load carrying potential vs energy expended.

In addition, and ** this ** may be a selling point ... (I'm thinking of suggestions from Louis here) a hovercraft might (?) be able to pull power from an "unimproved" roadway (ie, not-paved dirt/sand road).

There is still a ** lot ** of unimproved roadway on Earth.

***
Here is a question that perhaps only computer modeling can address ... the ground under such a vehicle is likely to be occupied by small objects which can (and will) respond to voluminous flows of gas to git-up-and-go wherever the gas is going.

I'll leave that observation as "the question"

(th)

kbd512 · 2021-04-19 13:14:20

Calliban,

Assuming all the other technical issues could be resolved, how far could you possibly get with a hovercraft of that size?

Is this for transporting a person or small parcels, perhaps repair parts, at speed?

The Navy hovercraft I'm familiar with don't go over boulders, they go around them. Rocks tear up the skirt, and then you don't have a hovercraft anymore.

What if we took the same Silane jet engine and used it to power a "Trophy truck"?

Those things are a lot faster than most people think, and can negotiate terrain at speeds that would destroy most other vehicles, at the cost of continual chassis / suspension / engine maintenance. As long as you can keep the wheels warm, Trophy trucks routinely top 100mph over incredibly rough terrain, sort of like Dukes of Hazzard, except that the vehicle isn't destroyed every time it lands. It's a jarring ride to be sure, but these are what we use for off-road racing here on Earth. Some types of off-road military trucks are equipped with a "seat suspension system" to make the ride more tolerable to the occupants.

louis · 2021-04-19 13:15:51

Hovercraft are generally used on water, rather than rough terrain, and I suspect for a very good reason, namely that if they were travelling over rocks and stones their skirts would get cut to pieces pretty quickly.

I would also add from my recollection of crossing the Channel to mainland Europe in a hovercraft, they are incredibly noisy, so certainly not ideal for human exploration compared with a nice quiet electric engine rover.

That said, we should explore all transport options and maybe after a way was cleared, hovercrafts might have some advantages over flat ground - though I doubt it.

Calliban wrote:

I have been through the planetary transport topic and no one appears to have raised this concept, much to my surprise. I was interested in a concept that could allow rapid transportation to sites of scientific interest for early Mars missions. This would need to allow navigation over rough, bolder filled terrains at high speeds.
The relative easy compressibility of air on Mars (CO2 exists as a gas at a temperature far beneath its critical point) makes it possible to compress gas using a funnel mounted on the front of a fast moving vehicle. The gas can then be heated to a temperature above its critical point at 31°C and used to inflate a skirt, that would levitate the hover craft above the ground. A portion of the same compressed CO2 stream would enter a jet engine, providing thrust. The low speed of sound of CO2 relative to air and water vapour, should reduce the rate of expansion and loss of CO2 out of the skirt.
I would propose the use of silane to power the hovercraft. It will burn in carbon dioxide, so would appear to offer the best energy density of chemical fuels on Mars.
The hovercraft would need to be relatively lightweight, as the dynamic pressure that is achievable in the Martian atmosphere at subsonic speeds, is limited. With an air density of 0.02kg.m-3, and a velocity of 100mph (44m/s), dynamic pressure would be 20Pa.
The total lift force provided by a hovercraft (N) is provided by:
F = 0.5 x air density x intake area x (intake entry velocity^2 - intake exit velocity^2).
If intake area is 100m2 and exit velocity is twice entry velocity, i.e. 88m/s, then total lift force is 1936N, or 526kg on Mars. On this basis, a hover craft travelling at 100mph on the surface of Mars, with an inlet area of 100m2, must weigh no more than 526kg.
The lift is limited by the exhaust velocity achievable by a Martian jet engine and the temperature that the skirt material and frame can withstand. Exhausr velocity for a pure silane rocket engine would be on the order of 3km/s, which would provide excellent lift, but would be far too hot to be workable.

tahanson43206 · 2021-04-19 13:38:24

Louis, it is good to see your contribution to Calliban's innovative topic here!

Your pessimism is warranted, if we assume an unimproved "roadway"

However, your persistence in advocating for solar panels is your reward, in this situation!

I would like to try to put everything together here ...

1) Calliban's idea
2) Louis solar panels
3) Ingenuity flight
4) kbd512's question about distance

Let the roadway consist of Louis' flat solar panels, rolled out as he has described in previous posts, and connected with suitable fittings to handle the conditions of Mars day/night cycle.

The passing hovercraft will handily remove any Mars dust that might meander onto the roadway.

A power feed arrangement using electromagnetic induction insures supply to the passing vehicles.

Range is limited only by the length of the roadway.

This concept has the distinct and attractive advantage that it will work on Earth in climates with lots of sun and limited amounts of rain.

The Earth has a ** lot ** of those, and it is going to have a ** lot ** more, because it is highly unlikely that humans are capable of organizing themselves to sacrifice short term profit for long term survival of the entire race.

I don't like to leave pessimism lurking at the bottom of a post, so I'll wrap up with the (slim) possibility that humans ** can ** solve the climate change problem before extinction looms. There will ** still ** be lots more dry unvegetated land than there is now, and there is plenty now.

(th)

Calliban · 2021-04-19 13:52:39

louis wrote:

Hovercraft are generally used on water, rather than rough terrain, and I suspect for a very good reason, namely that if they were travelling over rocks and stones their skirts would get cut to pieces pretty quickly.
I would also add from my recollection of crossing the Channel to mainland Europe in a hovercraft, they are incredibly noisy, so certainly not ideal for human exploration compared with a nice quiet electric engine rover.
That said, we should explore all transport options and maybe after a way was cleared, hovercrafts might have some advantages over flat ground - though I doubt it.

I think I am inclined to reach the same conclusion. The Martian atmosphere is just too diffuse to provide adequate lift. To achieve the required dynamic pressure, speed needs to be at least 100mph, probably double that looking at realistic mass per unit area. Unless the ground is flat and free of rocks, the skirt will be damaged quite rapidly. The high compressibility helps and so does the lower gravity, but not by enough.

Never mind. Sometimes it can be valuable to find out what won't work and then narrow down our options to what will. The hyperloop is basically a hovercraft mounted on a track. The speed of the train is such that the air beneath the vehicle is trapped by its own limited speed of sound. It would work even better on Mars, because the CO2 is colder and beneath its critical point, so there would be less drag and the the lower speed of sound would make it efficient at lower speed. But the hyperloop needs a track and an investment in infrastructure. So it isn't suitable for early exploration phase.

Last edited by Calliban (2021-04-19 13:56:05)

kbd512 · 2021-04-19 14:11:51

Louis,

The noise you experienced is the result of a compressible fluid (primarily air at 14.7psi) to transfer the pressure waves from the exhaust of the engine to your ears. There simply isn't very much atmospheric density on Mars to transmit pressure waves, although close proximity to a combustion engine will be "louder" than an electric motor. That said, commercial aircraft cabins are still remarkably quiet at cruising altitude. Given an atmospheric pressure less than 1/10th the density of Earth's atmosphere at 10,000m, there will be very little noise.

The primary advantage of a hovercraft over water is the ability to travel at speed using less energy than if it the hull of the vehicle was partially submerged in another fluid (water) 1,000 times denser than air. Hydrofoils work on the same basic principle, wherein a very small airfoil shaped "wing" is submerged in the water, rather than the much larger hull of the entire ship. Both have some pros and cons. The Navy hovercraft that we use to land troops and vehicles are "over the beach" short range vehicles most at home in shallow littoral waters and smooth seas. They guzzle down fuel at an alarming rate, but still manage to provide a smoother ride, astonishingly smooth given the speeds they attain, than small speed boats and their ability to disembark on land following a high speed run onto the beach. If you tried to run a small boat onto the beach at the same speed, you'd either destroy the hull or never get it off the beach again without a tugboat. For that reason, the Navy really frowns on beaching ships and boats, and even the purpose-built landing ships are not truly "beached" (more like the ramp is on the beach while the hull and propellers remain in the water). The beaches used tend to be flat and clear of large obstructions like boulders for the reason you noted about rocks not playing well with the delicate rubberized skirt of the hovercraft. If the skirt is tall enough, many lesser obstacles can also be successfully "flown" over as well. The operators are trained not to attempt to go over something that would damage the craft, although accidents still happen infrequently.

Anyway, long story short, I agree with your sentiment about a hovercraft being difficult to use over rough terrain and that in an ideal world, we'd use an electric motor attached to a vehicle with a monster suspension system to soak up the bumps. As you said, though, all options should be explored and the most practical options selected for further development.

My question to Calliban is whether or not the machine can scale up to carry enough payload to make it a practical form of transport. Over a smooth sandy desert with few sharp rocks, it seems like a good way to cut down on energy usage associated with heavy off-road vehicles sinking into fine powdery sand.

Calliban · 2021-04-19 16:00:41

kbd512 wrote:

Louis,
The noise you experienced is the result of a compressible fluid (primarily air at 14.7psi) to transfer the pressure waves from the exhaust of the engine to your ears. There simply isn't very much atmospheric density on Mars to transmit pressure waves, although close proximity to a combustion engine will be "louder" than an electric motor. That said, commercial aircraft cabins are still remarkably quiet at cruising altitude. Given an atmospheric pressure less than 1/10th the density of Earth's atmosphere at 10,000m, there will be very little noise.
The primary advantage of a hovercraft over water is the ability to travel at speed using less energy than if it the hull of the vehicle was partially submerged in another fluid (water) 1,000 times denser than air. Hydrofoils work on the same basic principle, wherein a very small airfoil shaped "wing" is submerged in the water, rather than the much larger hull of the entire ship. Both have some pros and cons. The Navy hovercraft that we use to land troops and vehicles are "over the beach" short range vehicles most at home in shallow littoral waters and smooth seas. They guzzle down fuel at an alarming rate, but still manage to provide a smoother ride, astonishingly smooth given the speeds they attain, than small speed boats and their ability to disembark on land following a high speed run onto the beach. If you tried to run a small boat onto the beach at the same speed, you'd either destroy the hull or never get it off the beach again without a tugboat. For that reason, the Navy really frowns on beaching ships and boats, and even the purpose-built landing ships are not truly "beached" (more like the ramp is on the beach while the hull and propellers remain in the water). The beaches used tend to be flat and clear of large obstructions like boulders for the reason you noted about rocks not playing well with the delicate rubberized skirt of the hovercraft. If the skirt is tall enough, many lesser obstacles can also be successfully "flown" over as well. The operators are trained not to attempt to go over something that would damage the craft, although accidents still happen infrequently.
Anyway, long story short, I agree with your sentiment about a hovercraft being difficult to use over rough terrain and that in an ideal world, we'd use an electric motor attached to a vehicle with a monster suspension system to soak up the bumps. As you said, though, all options should be explored and the most practical options selected for further development.
My question to Calliban is whether or not the machine can scale up to carry enough payload to make it a practical form of transport. Over a smooth sandy desert with few sharp rocks, it seems like a good way to cut down on energy usage associated with heavy off-road vehicles sinking into fine powdery sand.

The classic hovercraft works as a result of dynamic pressure from a gas being forced into the gap between the vehicle and ground. The skirt is there to keep the rate of gas loss manageable, for an acceptable clearance between the fuselage and the ground, in order to limit the amount of fuel expended to provide lift. I think the problem with trying to do that on Mars is that the speed of the hovercraft would need to be extremely high by normal standards for any frontal scoop to be able to collect enough gas to provide sufficient lift. The skirt would not survive impact with jagged rocks as that speed.

One possible alternative would be a sort of ground effect vehicle - a hovercraft that flies at a height of a few metres without a skirt.
https://en.m.wikipedia.org/wiki/Ground_ … odynamics)

We would scale the hovercraft up so that its dimensions are say 100m wide and 200m long. The craft would be fashioned as a lifting body. Next, we fly it at speeds approaching sonic in the local Martian atmosphere - say 200m/s. The wing shape would be curved and would trap air beneath the lifting body, in a thin layer between the craft and the ground. The CO2 rich Martian air would escape from the edges, but the cold, heavy CO2 would have a lower speed of sound than air at Earth sea-level. So it would have a relatively high stagnation pressure that the vehicle can ride upon.

We could enhance the effect by attaching a ram scoop type device to the front of the vehicle and run the CO2 through a high bypass ramjet engine, with an exhaust temperature of about 100°C, that vectors the thrust downward. The warm, high pressure CO2 would expand between the ground and the fuselage of the vehicle and would escape at the edges. However, it cannot expand faster than its own speed of sound. As the vehicle is travelling at 200m/s, the rate at which new CO2 is forced between the vehicle and the ground would balance the rate at which it escapes from the edges at a relatively high equilibrium pressure.

Taking off and landing would be problems that would appear to necessitate runways of some kind. Or alternatively, rocket power using stored propellant could levitate the craft and accelerate it to a speed where the combined lift of the lifting body and ram jet, are sufficient to keep the craft at least a few metres above the surface. At the destination, reverse rocket power and stored propellant would slow the vehicle down and keep it airborne until forward speed were neutralised. A ground effect vehicle is essentially an aeroplane that flies so close to the ground that its own downdraft is trapped between the ground and its own moving wing. An Earth based example, is the Ekranoplan. What I am proposing here, would probably look more like a magic carpet, with a large intake on the top and jet engines mounted on the back.

I am not an aeronautical engineer. However, dynamic pressure for an incompressible moving fluid is given by:

P = 0.5 x rho x v^2.

If the vehicle is traveling at 200m/s say and local rho of Martian Air is 0.02kg.m-3, then dynamic pressure is 400N/m2. That is 108.7kg lift per square metre of wing area under Martian conditions. So our 100m x 200m ground effect craft could have total mass of 2175 tonnes. My guess is that this would be sufficient for both structure, engines, at least a couple of hundred tonnes payload and enough fuel for a range of thousands of km.

The mass lifted would be a function of the area of the ground effect wing. So a 10m x 20m ground effect craft would have total lift 21.75 tonnes at 200m/s. One advantage with scaling the aircraft up, is that the vehicle can exploit ground effect at greater height and is therefore less effected by vortex shedding and other local fluid effects resulting from rocks and other obstacles exposed to the high speed air stream. Even so, the amount of dust the ground effect vehicle would kick up would make it easily visible from space.

I may need Gary to check that I haven't overlooked something here, as it sounds too good to be true. If we can assemble the vehicle from a lightweight frame and use CFRP to cover the frame, then ground effect vehicles should allow even early missions to reach targets thousands of km from the landing site, within travel times of a few hours.

Last edited by Calliban (2021-04-19 16:58:35)

louis · 2021-04-19 17:05:47

As I recall, the noise was shuddering through the cabin of the hovercraft I was on. A lot of it was vibration I imagine going through the cabin structure. Of course you have to have air in the cabin (unless everyone's in space suits) so I am sceptical that they would be much less noisy on Mars.

Off topic re hydrofoils I've seen a few people on the Thames in recent months using individual board hydrofoils. They must have electric motors because they are very quiet. The riders are standing on a small board about 50 centimetres above the water level. It's quite spectacular. I'd estimate their speed at at least 20 MPH which is fast for craft on the Thames...It's the sort of thing that could keep people amused on Mars on an indoor lake.

kbd512 wrote:

Louis,
The noise you experienced is the result of a compressible fluid (primarily air at 14.7psi) to transfer the pressure waves from the exhaust of the engine to your ears. There simply isn't very much atmospheric density on Mars to transmit pressure waves, although close proximity to a combustion engine will be "louder" than an electric motor. That said, commercial aircraft cabins are still remarkably quiet at cruising altitude. Given an atmospheric pressure less than 1/10th the density of Earth's atmosphere at 10,000m, there will be very little noise.
The primary advantage of a hovercraft over water is the ability to travel at speed using less energy than if it the hull of the vehicle was partially submerged in another fluid (water) 1,000 times denser than air. Hydrofoils work on the same basic principle, wherein a very small airfoil shaped "wing" is submerged in the water, rather than the much larger hull of the entire ship. Both have some pros and cons. The Navy hovercraft that we use to land troops and vehicles are "over the beach" short range vehicles most at home in shallow littoral waters and smooth seas. They guzzle down fuel at an alarming rate, but still manage to provide a smoother ride, astonishingly smooth given the speeds they attain, than small speed boats and their ability to disembark on land following a high speed run onto the beach. If you tried to run a small boat onto the beach at the same speed, you'd either destroy the hull or never get it off the beach again without a tugboat. For that reason, the Navy really frowns on beaching ships and boats, and even the purpose-built landing ships are not truly "beached" (more like the ramp is on the beach while the hull and propellers remain in the water). The beaches used tend to be flat and clear of large obstructions like boulders for the reason you noted about rocks not playing well with the delicate rubberized skirt of the hovercraft. If the skirt is tall enough, many lesser obstacles can also be successfully "flown" over as well. The operators are trained not to attempt to go over something that would damage the craft, although accidents still happen infrequently.
Anyway, long story short, I agree with your sentiment about a hovercraft being difficult to use over rough terrain and that in an ideal world, we'd use an electric motor attached to a vehicle with a monster suspension system to soak up the bumps. As you said, though, all options should be explored and the most practical options selected for further development.
My question to Calliban is whether or not the machine can scale up to carry enough payload to make it a practical form of transport. Over a smooth sandy desert with few sharp rocks, it seems like a good way to cut down on energy usage associated with heavy off-road vehicles sinking into fine powdery sand.

kbd512 · 2021-04-19 17:32:09

Calliban,

How do you avoid having the dusty "air" sand blast the hell out of any kind of turbine type compressor without a massive and highly effective air filter?

You've seen what happens to our AGT-1500s operated in Iraq, haven't you?

Those supposedly have a highly effective air filtration system, but it still looks a lot like a dog chewed up the turbine blades after a few hundreds hours of operation or even less in severely dusty environments. We're going to need some next-level Dyson technology to develop the "proper amount of suction", if you know what I mean.

I know that we have a handful of high speed land vehicles on our salt flats reach high subsonic or low supersonic speeds, but how practical would those be for going over rough terrain, or simply over terrain with a bit of variability to it?

Many of those vehicles are routinely destroyed making high speed runs here on Earth over nearly perfectly flat terrain, even the ones with computer control systems to adjust the suspension and aero control surfaces, so this is going to require significant testing. That said, it would be very cool to have "land airliners", if such a thing is feasible.

If you can make a vehicle fly at all, then why not use big wings and big slow-turning props powered by a small monopropellant-fueled "exit only" turbine to get you away from the ground, where it will hopefully be a little less dusty (certainly not a given on Mars), so you can fly at higher than practical ground speeds above all the dust?

Even at that, you'll still sandblast the hell out of the prop, but it should be operable for at least a few hundred hours before resurfacing is required. The composite props that get sandblasted have the exterior lamination of CFRP chemically removed and replaced with a fresh lamination at the prop shops here on Earth. It's much easier and faster to repair one of those than a gas turbine, although still time consuming and expensive.

If Mars had a lake or ocean anywhere on it, or any other place without tons of dust, then I could see a hovercraft as a distinct advantage. If there are vast open desert areas between settlements that are pancake-flat, or can be made so by "making a trail", then a hovercraft of some kind does away with the need for roads and tracks and other infrastructure, and drastically cuts down on heavy duty off-road vehicle suspension wear and tear.

kbd512 · 2021-04-19 17:52:16

louis wrote:

As I recall, the noise was shuddering through the cabin of the hovercraft I was on. A lot of it was vibration I imagine going through the cabin structure. Of course you have to have air in the cabin (unless everyone's in space suits) so I am sceptical that they would be much less noisy on Mars.
Off topic re hydrofoils I've seen a few people on the Thames in recent months using individual board hydrofoils. They must have electric motors because they are very quiet. The riders are standing on a small board about 50 centimetres above the water level. It's quite spectacular. I'd estimate their speed at at least 20 MPH which is fast for craft on the Thames...It's the sort of thing that could keep people amused on Mars on an indoor lake.

Louis,

Well, I dunno then. It could very well be and probably is the vibration issue you noted. I can tell you that I've been aboard gas turbine powered US Navy frigates / destroyers / cruisers, as well as boiler and nuclear powered aircraft carriers, but the noise from the power plants is far less objectionable as compared to large diesels on the tugboats, which you can clearly hear over the noise coming from the ships when they tow the ship away from port. One feature that all US Navy ships have for the gas turbines and other large pieces of equipment, is shock mounts- great big loops of steel wire wound through holes on the edges of two steel plates. Navy ships have quite a bit of sound-deadening materials on the inside of their hulls as well. Inside the ship, all you hear is the sound of ventilation and electrical equipment, unless you go into the main spaces. I can also relate from experience that large diesel backup generators inside the ship always produce an incredible racket, easily audible over the power plant unless you dog the doors to the generator compartment and are a ways away from them. All of the high speed hydrofoils I'm aware of are powered by gas turbines, although some of them are probably hybrids.

Calliban · 2021-04-19 18:05:51

I think any air inlet on the craft would need to be mounted on the front, ahead of dust cloud stired up by the ground effect turbulence. Closed jet thrust engines using monopropellant would avoid the issue of shock blasting the turbine blades. But they would suffer low propulsive efficiency. So I think either a high bypass turbofan or turboprop type arrangement would be needed. From what you have described, the second option sounds better.

The craft is not really a land vehicle. Depending on its size, it would fly at heights of somewhere between a quarter and half of its wingspan. So, a vehicle with dimensions 200m x 100m, would fly at a height of 50m, or 160'. The rougher the terrain, the more beneficial it would seem to be to scale up.

Last edited by Calliban (2021-04-19 18:10:30)

kbd512 · 2021-04-19 19:03:50

Calliban,

Maybe I'm missing something in the units conversion, but 400N/m^2 is more like 40.79kgf/m^2, is it not?

SELECT ROUND(((0.5 * 0.02 * POWER(200,2)) / 9.807),2) AS "kgf/m^2"; -- That's what I did, but maybe I messed up a conversion or unit

SpaceNut · 2021-04-19 19:35:59

Ya I got some of it so maybe the stuff I am going to put here in references will help

air cushions mean pressure and rate of air escape to hole the item above the surface.

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

https://ijabe.org/index.php/ijabe/artic … 1468/pdf_1
Control design of an unmanned hovercraft for agricultural applications

https://www.ijert.org/research/stabiliz … 121264.pdf
Stabilization and Design of a Hovercraft Intelligent Fuzzy Controller

https://www.sccs.swarthmore.edu/users/1 … zapiro.pdf
Design and Construction of a Passenger Hovercraft

https://drc.libraries.uc.edu/bitstream/ … sequence=1
HOVERCRAFT THRUST SYSTEM AND DRIVETRAIN

Calliban · 2021-04-20 06:37:37

kbd512 wrote:

Calliban,
Maybe I'm missing something in the units conversion, but 400N/m^2 is more like 40.79kgf/m^2, is it not?
SELECT ROUND(((0.5 * 0.02 * POWER(200,2)) / 9.807),2) AS "kgf/m^2"; -- That's what I did, but maybe I messed up a conversion or unit

Remember that on Mars, 1kg weighs 3.68N. So 1kg-force will lift 2.67kg.

kbd512 · 2021-04-20 07:14:12

Calliban,

Yep, that was what I forgot.

GW Johnson · 2021-04-20 12:39:54

The hovercraft idea works on most surfaces, as long as the roughness (boulders) is quite small. Big ones punch a hole in your skirt, which is usually an inflatable structure. On Mars, blowing out a giant dust cloud will be a real problem with hovercraft, just like in sand deserts here.

What I have difficulty with is the compression ratio required to pick up the weight of the vehicle. Fans have extremely limited pressure-rise ratios on the order of 1.05. That times 6 mbar air pressure is 6.3 mbar inside the shroud, for a 0.3 mbar pressure rise, times planform area, = the weight it can lift.

Axial flow turbine technology, with multiple stages, has pressure rise ratios in the 3-15 class. Say, 10. For 60 mbar inside the shroud, 6 mbar outside. That's 54 mbar times planform area = weight it can support on Mars.

But multistage compressors are very, very heavy, compared to fans! So there is a very definite diminishing-returns limitation here, somewhere. I don't know exactly where it is, but it is there.

GW

Last edited by GW Johnson (2021-04-20 12:41:08)

Calliban · 2021-04-20 14:39:23

The hovercraft clearly could not work on Mars using fans for lift. If it were travelling at 100m/s, then it could pressurise the skirt using a ram scoop.

P = 0.5 x y x rho x v^2 = 0.5 x 1.3 x 0.02 x 10,000 = 130N/m2 = 35.3kg-lift per square metre on Mars. But the first rock that the skirt hits would be it's last, as 100m/s is 224mph.

My next question is: would a ground effect aeroplane (Ekranoplan) be any more successful?

SpaceNut · 2021-04-20 18:19:07

No need to fret as you can do several things to make it viable.
1. use helium / hydrogen to give the vehicle buoyancy while stationary...
2. make use of composite materials which can be usually lighter and just as strong for many applications.
3. make use of the liquid co2/ Lco/ ect tanks and supper heating so as to force pressure under the skirt to rise giving lift. Heating source could be RTG or engines or a vat of molten salt.
4. make use of the high speed prop designs of Ingenuity rather than the slow speed fans.

Mars_B4_Moon · 2023-08-16 05:30:55

Why the Army’s 1950s hovercraft platform failed
https://www.militarytimes.com/off-duty/ … rm-failed/

Russia's Zubr-class: Meet the world's largest hovercraft
https://interestingengineering.com/tran … hovercraft

tahanson43206 · 2023-09-10 10:44:40

For Calliban re topic...

I had forgotten this topic from 2021, when I was searching for prior work on ground effect machines ...

Mars_B4_Moon was kind enough to find and show the link to your topic.

I'd like to (at least try to) renew your interest in the topic, but I'd like to invite you to leave the ram scoop idea back in the early part of this topic, and concentrate instead on a hovercraft design suitable for Mars.

The NASA Ingenuity helicopter proves beyond doubt that a vehicle that is light enough, and which spins it's prop fast enough, can lift itself above the surface of Mars. Here is an opportunity, not available to you in 2021, to design a hovercraft for Mars.

I am confident it will look different from the same vehicle on Earth.

(th)

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