Airplane for Mars

tahanson43206 · 2025-06-23 11:16:11

To my surprise, only two topics existed in the NewMars forum in June, 2025, with "airplane" in the title.

We have a number of discussions about heavier-than-air vehicles for Mars (and many other locations)

This one is offered for NewMars members who might like to add links, images and text specifically about airplanes on Mars.

The Ingenuity helicopter demonstrates that flight on Mars is possible.

In demonstration, it was shown that a rapidly moving propeller can force molecules of atmosphere down in sufficient quantity, and at a sufficient velocity, so that there is a net upward force delivered to the air frame.

I note that the lift generated is a consequence of Newton's First Law. Molecules from above the helicopter are caught by the moving propeller blade and given a downward motion. It is the upward force exerted on the propeller blade that is communicated back to the air frame to sustain the flight.

The question I have in opening this topic is: What is the absolute maximum availability of molecules on Mars at the mean surface altitude, per square meter?

The molecules available can flow downward to the moving blade no faster than they would if a perfect vacuum were formed at the location of the moving blade.

The air pressure at the location described would (presumably) deliver molecules into a perfect vacuum at a rate that should be knowable.

Whatever that rate may be, that is the maximum possible flow that is available to a moving propeller blade.

However, ** lift ** is a function not only of the supply of mass to accelerate downward, but of the velocity given to the molecules when they are "treated".

I'm hoping we might have a NewMars member who would like to address this physics problem.

In the absence of such a person, if there is a reader who is not a member and who would like to contribute to this topic, please see the Recruiting Topic for procedure.

(th)

tahanson43206 · 2025-06-23 11:17:28

This post is reserved for an index to posts that may be contributed by NewMars members over time.

Index:

kbd512 on Raymer design for a manned aircraft for Mars (2021)
https://newmars.com/forums/viewtopic.ph … 89#p232389

(th)

GW Johnson · 2025-06-23 12:54:07

The weight of "air" above an area is literally the atmospheric pressure. On Mars that varies with elevation, but seems to be near 6 millibars on the kinds of plains where the Viking landers landed. That's 0.006 bars of pressure, when a bar = 100,000 N/sq.m. So at any location where the pressure is 6 millibar, there are 600 N weight of air above 1 sq.m. At .38 gees and 1 gee = 9.80667 m/s^2, using W = mg, I calculate that to be 23.5 kg mass of "air" above that same sq.m.

Compare that to Earth at 1.01325 bars sea level pressure and 1 full gee of gravity. That's 101,325 N weight of air above 1 sq.m, corresponding to 10,332 kg of air above that same sq.m.

GW

Last edited by GW Johnson (2025-06-23 12:54:20)

tahanson43206 · 2025-06-23 13:35:49

For GW Johnson re #3

Thank you for helping with the inquiry I have launched here!

If we assume a square meter of propeller area for convenience, then we have 23.5 Kg of mass directly above the square meter.

If we open that square meter to a pure vacuum, the molecules directly above the opening will fall through due to two factors:

1) The gravity of Mars will pull the molecules toward the center of the planet.

2) The pressure of the electron shells of the molecules above will push them down.

However, more molecules than just the ones directly above will be involved. Molecules some distance away will be pressed toward the opening, due to that same electron shell interaction.

I don't know the answer to this question, but I assume it must be possible to calculate the total mass of air molecules that can be measured flowing through that opening in some period of time, such as one second.

It is that mass, and not one gram more, that is available for a propeller to push downward on Mars.

I expect that it will be possible to compute precisely the amount of lift generated by the Ingenuity propellers as equal to the mass of the vehicle when hovering. From this we might be able to calculate the amount of air mass being driven downward.

However, the actual thrust is a function of the velocity given to the molecules passing through the blades, so we may not be able to determine the air mass flow precisely, because we do not know the velocity given to the molecules.

All we can know with precision is the lift produced.

However, we ** should ** be able to predict the lift that would be produced by a given mass of air given a specific velocity.

(th)

kbd512 · Yesterday 03:17:39

This topic comes up again and again...

The ultimate answer is that it's possible to create a practical crewed aircraft on Mars, but far from easy.

The Raymer Manned Mars Airplane: A Conceptual Design and Feasibility Study

Concept Aircraft Presentation Slide Deck:
AIAA Aerospace Sciences Meeting, January 2021

A large collection of beautifully rendered concept artwork showcasing the Raymer Manned Mars Plane Concept:
The Raymer Manned Mars Plane (RMMP)

My personal opinion on this matter is that we require the strongest composites money can buy, an energy-dense monopropellant, such as Hydrazine, fed through a gas turbine to maximize energy extraction while minimizing engine / propellant / propellant tank mass, and a multi-wing design to prevent the wings from becoming impractically large to transport to Mars or mandating risky VTOL maneuvers. My variation on his original concept uses 6 foldable / stowable wings instead of 1 giant wing, similar to dragonfly wings, in order to transport the aircraft to Mars.

Dr Raymer's concept plane has a wingspan of 105.136m, tip-to-tip, which is longer than a football field. Simply put, that's an impractically large wing which is driving airframe mass, at 848.8kg. If we had 6 stowable wings, then each wing is about 17.523m long, and therefore fits inside the payload bay of a Starship. This should also result in iighter / stiffer wings that don't weigh as much. His design used IM7 fiber, but I think we need T1200 fiber, which is roughly 50% stronger and about as stiff. These are still very long wings, each one about 4.725m longer those of the Perlan II high altitude glider. However, fabricating such wings is not outlandish since Perlan II's total wing length is 25.55m and I believe it was fabricated as a single piece design.

His design used 8X CO/O2 rockets for vertical takeoff and landing, plus 2X horizontally mounted rockets for acceleration to flying speed. I think that's a kluge, which is what I think about all VTOL aircraft that are not helicopters. Stall speed for his concept was 115 knots. C-130 approach speed is 130 knots and landing speed is around 110 knots. C-130s are proven capable of performing rough field landings, and their minimum rotation speed is around 97 knots. Most of the time you're going to rotate closer to 110 knots when fully loaded. Therefore, a 120kt to 130kt rotation speed is not outlandish. Takeoff and landing at that speed is fine, provided you have very large / low-pressure tires that can roll over large rocks.

His design uses 500Wh/kg Lithium-ion batteries, which we actually have now (yay!), but even future projected battery technologies are pitiful when compared to Hydrazine's gravimetric energy density.

500Wh/kg Lithium-ion batteries: 1.8MJ/kg
1,000Wh/kg Lithium-O2 batteries: 3.6MJ/kg
CO combustion with O2: 10.1MJ/kg
Hydrazine decomposition over a catalyst: 19.5MJ/kg

HAN or AF-M315E monopropellant is considerably denser than Hydrazine, with much lower toxicity and no concern over it freezing in the tank.

Dr Raymer's design requires 200hp, provided by 4X 50hp electric motors, 2 inboard and 2 outboard, presumably with 2-bladed props for maximum efficiency. Motors are fantastic when it comes to power-to-weight, better than anything except a rocket engine, but their battery power source is pathetic.

Space Shuttle Hydrazine-fueled APUs weighed about 40kg each, less gearbox, and produced 135hp. RCC vs superalloy components would reduce mass by a factor of about 4, so only 10kg per APU. At 80,000rpm, the gearbox would need to provide a 110:1 reduction to swing a 4m diameter prop, since local Mach 1 is only 788fps. Max prop rpm is therefore ~725rpm. The Shuttle APUs could generate up to 150hp for short periods of time. Regardless, fuel flow was 3lbs/min, so 810lbs for 4.5hrs, meaning less than the battery mass for the same 4.5hrs of flight. Deleting the electric motors, power conditioning equipment, photovoltaics, rocket engines, and CO/O2 propellants and tanks will save quite a bit of mass. HAN provides a healthy energy density increase over Hydrazine, plus 45% less volume than Hydrazine for the same total energy storage. This is starting to look doable with a more or less "conventional" design. 95 gallons of Hydrazine buys us 4.5 hours of flight time. Since we deleted so much mass elsewhere, all the rest of our components can become smaller and lighter- a virtuous circle.

tahanson43206 · Yesterday 06:10:07

This post is about the hypothesis that the lift available on Mars (or any planet with an atmosphere) is knowable.

The Ingenuity helicopter flown on Mars demonstrates what I suspect is the best possible lifting mechanism for a planet with a thin atmosphere.

The airfoil wing design reported by kbd512 in Post #5 is able to obtain lift by driving molecules down, just as the helicopter blades do. The difference is that the velocity of the wing is less than the velocity of the helicopter blade.

I am hoping that a NewMars member might be interested in this subject, and both able and willing to perform the analysis needed.

My thesis in a nutshell is that the maximum lift obtainable in any atmosphere is a function of the mass that can be obtained from the atmosphere in a given area, such as a square meter.

The effectiveness of any mechanism at obtaining lift might be compared to the theoretical mass that is available from the atmosphere if a pure vacuum were (magically) provided in the area of interest. The function of a helicopter blade is to create a partial vacuum in the area it sweeps, by collecting molecules from the volume immediately ahead of the blade, and directing those molecules down.

The atmosphere above the swept area will attempt to fill the low pressure area, thus providing more mass to be swept.

It should be possible to calculate the effectiveness of a particular wing/propeller blade design, with respect to the theoretical vacuum.

Update: Once the mathematics of the concept are solid, it should be possible to calculate the maximum theoretical lift available on Earth.

The application of interest is flying vehicles that can hover.

(th)

kbd512 · Yesterday 08:51:16

tahanson43206,

This post is about the hypothesis that the lift available on Mars (or any planet with an atmosphere) is knowable.

Atmospheric density is knowable, therefore atmospheric buoyancy for something like an airship to rise off the surface is also knowable. The aerodynamic lifting force generated by a wing (a conventional fixed wing, a helicopter's main rotor blade, or an aircraft propeller) is not readily knowable because the Coefficient-of-lift (Cl) and Coefficient-of-drag (Cd) are empirically determined values which are produced through the use of wind tunnels and numerical integration done by CFD programs. More to the point, Clmax, which is the maximum lifting force any particular wing design can generate before it stalls, is not simply and easily "knowable" without a modern CFD program using appropriate codes and backed by empirical testing. This applies to Earth as well as Mars.

As the presentation from Dr Raymer indicates, at Mars Sea Level, the amount of lifting force that an appropriate airfoil can generate, relative to the same airfoil at Earth Sea Level, is approxiamately 23.13X LESS. Mars local Mach 1 is 240m/s or 788fps. You're not going to drag a wing / rotor blade / aircraft propeller through the Martian "air" as fast as you can at Earth Sea Level as a result.

My thesis in a nutshell is that the maximum lift obtainable in any atmosphere is a function of the mass that can be obtained from the atmosphere in a given area, such as a square meter.

Lift Coefficient | Glenn Research Center | NASA
The lift coefficient is determined by dividing the lift force by the dynamic pressure of the airflow multiplied by the reference area of the lifting body, such as a wing. This coefficient is a dimensionless value that allows for comparison of lift-generating capabilities of different objects, regardless of their size or speed.
...
Dynamic pressure (q) is calculated using the air density (ρ) and the velocity (V) of the airflow: q = 0.5 * ρ * V^2.
...
The lift coefficient (Cl) is then calculated using the formula: Cl = L / (qS)

That quaint explanation may make it seem as if there's a simple equation for determining Cl and Clmax. However, that is very misleading. There isn't one single simple value for an actual real world wing shape moving through a real fluid. For a 2D shape, you can express Cl using an equation which provides Cl for a given air density, velocity, and angle-of-attack. For a 3D wing shape, which is the only kind of "shape" that real world wings come in, the only way you can arrive at the Cl for the wing as a whole is to integrate, and the easiest way to do that is to use an appropriate CFD program and a wind tunnel. Notice the word "and" between the words "CFD program" and "wind tunnel". You need both. I'll let GW explain why you need both.

GW is going to reply with a very similar answer if you ask him the right question. He's going to tell you about the basics and the theory first, because most people don't even know that much, which means they have no basis for greater understanding until he teaches people the fundamentals.

tahanson43206 · Yesterday 09:31:33

Thanks to all who've contributed to this topic so far! It appears that we might need to restate the proposition:

[header]
The molecules available can flow downward to the moving blade no faster than they would if a perfect vacuum were formed at the location of the moving blade.[/header]

This proposition has nothing to do with airfoils or equations of performance of airfoils.

It is a very simple question that is (obviously) difficult to answer.

GW Johnson has provided a running start by setting out the weight of a column of air above a square meter area at the surface of Mars.

The question I am asking is:

If we use magic to create a pure vacuum under that square meter, what is the rate of mass flow through that opening.

Clearly the gravity of Mars is the main player in this scenario. Mars is pulling on the air above the opening, and it is pulling on all the air around the planet.

When we open the vacuum port, the air immediately above the port will enter, because electron shells in adjacent molecules are constantly bouncing against them, and when the port opens, they will be pushed through.

The question I am asking (repetitive, I know) is:

What is the mass flow we can expect to occur if we keep that vacuum port open for some period of time.

I offer as a hypothesis that whatever that mass flow is, that is the entirety of the mass available to a propeller or other device whose purpose is to accelerate mass downward in order to generate lift upward.

In other words, I expect to find that for a given area on the surface of Mars (or any planet) the absolute maximum lift that can be obtained is a consequence of the available mass at that point.

(th)

kbd512 · Yesterday 10:09:42

tahanson43206,

Magic notwithstanding, airfoils are used to create pressure differentials in real world aircraft and engines. The compressor and expansion stages of a gas turbine immediately come to mind. The mass flow rate for this theoretical device is going to correlate back to air density (the pressure differential), inlet area, volume, local speed of sound, and compressibility effects, which differ for CO2 vs "air". Gravity, at least over the range of acceleration rates for planetary bodies such as Mars and Earth, doesn't really have much effect here.

Google is your friend:

Q: How fast does air fill a vacuum?
A: Air rushes into a vacuum at a speed related to the speed of sound, approximately 343 meters per second (767 mph) at 20°C. However, the actual time it takes to fill a vacuum depends on the size of the space and the pressure difference. In a small volume, like a 1cm³ cube, the air would fill the space in microseconds.

How fast does air fill a vacuum? If on atmospheric pressure at sea level there is a imaginary vacuum sphere and then the sphere suddenly disappears, how fast will air fill that space?

This response from Physics Professor (since 1977) Jess H. Brewer, to a similar question, is even more in-line with your question about this magical device:
What would happen if a sphere of air 2 meters in diameter were to somehow disappear, roughly instantly creating a perfect vacuum?

Atmospheric pressure is 101 kPa (p=1.01×105 kg⋅m−1⋅s−2) and the density of air is about ρ=1.225 kg/m3. The volume of a 2 m sphere is V=33.5 m3, so the work done to push the air out of such a volume would be W=pV=3.385×10^6J. About the same as required to lift a 34.5 metric ton block 10 m high. Now, whatever is at the center of that initially empty space is going to receive roughly that amount of energy in the form of a pressure front moving in at the speed of sound. It probably wouldn’t be as bad as having a 34.5 metric ton block dropped on you from 10 m, but I suspect the difference would be academic.
If two identical volumes or air where suddenly superimposed, the outcome would depend entirely on how instantaneous the superposition was. If it were absolutely instantaneous, some of the nuclei (probably not many, but it wouldn’t take many) would overlap, causing at least fission and (if really absolutely instantaneous) some quark-gluon plasma generation. In that case the explosion due to the overpressure would be the least of your worries.
Fortunately this is just a fantasy scenario.

Note how no mention of gravity is made in the response, because this is mostly about the effects of a pressure differential.

tahanson43206 · Yesterday 20:14:19

For kbd512 re #9

Thanks for an interesting review of the question at hand. The example of a vacuum sphere is particularly interesting, because such spheres have been constructed and excavated to the extent humanly possible at the time.

However, the scenario painted for a fixed volume such as a sphere is not the same as would apply if the "magic" were a worm hole that opened up on the surface of a planet (Earth or Mars or any other ) ... the flow of gas through the opening would be unlimited.

What I expect would happen is that a vortex would form, similar to the swirl we observe on Earth when we let water out of a sink, or when we observe a tornado. My guess is that Nature is telling us a vortex is the most efficient way to evacuate gas or a fluid through an opening that presents no resistance.

I understand the concept I am trying to get across is not at all intuitive, so I'm having to cast about for ways to explain what should be a simple concept but obviously is not.

The point I'm trying to make is that the supply of mass that a machine (propeller or similar mechanical device) can accelerate downward is limited by the supply that is available above the surface of the machine, and by the rate at which the atmosphere can deliver the available mass. You have brought up an interesting point. The velocity with which the air may be supplied may be limited by the speed of sound of the gas mixture.

In recent posts, GW Johnson has looked at the velocity of the tips of the Ingenuity helicopter, and his analysis indicates that the velocity chosen by the NASA engineers was comfortably BELOW the velocity of sound on Mars at the altitude where the machine flew. My recollection is that GW computed .74 as the approximate percent (74 %) of the speed of sound.

I bring this up because NASA has been working on the next version helicopter, and it has chosen (and tested) a 10 centimeter greater diameter, and an 800 rpm increase to 3500 rpm. GW has not yet done the analysis, but i expect he will report the NASA engineers are ** still ** going to be operating below the speed of sound on Mars.

Your analysis includes the possibility that the speed with which air flows through an opening to a worm hole might limit the rate of flow.

What I'm looking for is the flow rate of mass (molecules of air) that are available for a flying machine ( a helicopter to be specific) if we consider the pressure of the atmosphere at the location of the machine and the area swept by the machine.

Your point about gravity is interesting. Gravity is the prime mover, but the manifestation of gravity in this instance is the pressure experienced by the gas molecules as they jostle each other while waiting for something else to do.

(th)

kbd512 · Today 15:09:15

tahanson43206,

What I'm looking for is the flow rate of mass (molecules of air) that are available for a flying machine ( a helicopter to be specific) if we consider the pressure of the atmosphere at the location of the machine and the area swept by the machine.

Generating lift in a bulk fluid is a matter of generating a pressure gradient through relative motion of a lifting device moving through that fluid. The fluid's density, viscosity, compressibility, the shape of the lifting device, angle-of-attack relative to the oncoming flow, and its relative velocity all affect the magnitude of the generated pressure gradients. For any reasonably well-designed lifting device, velocity has an outsized effect on the lifting force being generated.

Asking someone to "just throw out a number" for a given fluid density, without specifying all of those parameters, is simply not possible, because the magnitude of the lifting force depends on all of them. If we further bound the answer to this question by specifying that the lifting device only works when the fluid flows over or through it at subsonic velocities, then we're more constrained in what our answer will be. However, there are in fact examples of wings that, at least at reduced velocities relative to much faster cruise flight, will generate substantially more lift than prototypical airfoil shapes (slats, fowler flaps, flaps on the top of the wing rather than only hinged to the trailing edge to enable lift generation at much higher AoA before significant flow separation occurs, vortex generators, blown lifting surfaces, and shape morphing surfaces that use aeroelastic materials):

Wings that will ordinarily only achieve Cl between 1 and 2 in cruise flight can use those various aforementioned lift-enhancing devices to increase Cl to as much as 4 or even 5 without a corresponding increase in Cd.

tahanson43206 · Today 18:53:15

For kbd512 re #11....

Thank you for this post which appears to me to be a valuable addition to a collection about flight on Mars, although it appears to be applicable in any atmosphere dense enough to support flight at all.

In this post, I'm intending to attempt to collect facts about Ingenuity, in hopes they may be useful at some point:

Question to Google: What is mass of Ingenuity when deployed on Mars

Search Labs | AI Overview
Ingenuity Mars Helicopter - NASA Science
The Ingenuity helicopter's mass was approximately 1.8 kilograms (4.0 pounds) on Earth and about 1.5 pounds (0.68 kilograms) on Mars. This difference is due to the lower gravity on Mars, which would make the helicopter weigh less.

I would offer the suggestion that when hovering, Ingenuity's propellers generated a total lift of (point(68)) kilograms in the Mars atmosphere.

I asked Google for the area swept by the propellers of Ingenuity on Mars. It calculated the area for just one propeller:

Rotor Diameter: 1.2 meters
Rotor Radius: 1.2 meters / 2 = 0.6 meters
Area: π * (0.6 meters)² ≈ 1.13 square meters
Therefore, the area swept by the Ingenuity helicopter's blades when deployed on Mars is approximately 1.13 square meters.

From this I would conclude that the rotating blades created (point)68 kilograms of lift while hovering.

The air molecules that were being collected and accelerated downward would have had a mass such that when flung downward by the turning blades, they imparted a total of (point)68 kilograms of lift to the vehicle.

From science.NASA.gov I found this about Ingenuity:

Takeoff
Unlike many consumer drones, Ingenuity is not controlled by changing the rotor speeds. Instead, we control our Mars Helicopter in the same manner as full-scale terrestrial helicopters: by changing the pitch angle of the blades, which affects the airfoil “angle of attack” and thereby determines how big a “bite” the blades take out of the air. The bigger the bite, the more lift (and drag) is produced. Like a traditional helicopter, we can change the pitch angle in two ways: by using “collective control,” which changes the blade pitch uniformly over the entire rotation of the blade, and by using “cyclic control,” which pitches the blade up on one side of the vehicle and down on the other.
When Ingenuity takes off, the rotor is already spinning at the setpoint speed of 2,537 rpm. We take off with a sudden increase in collective control on both rotors, which causes the vehicle to “boost” off the ground. During this initial takeoff phase, we limit the control system to respond only to angular rates (how quickly the helicopter rotates or tilts). The reason for this is that we don’t want the control system to be fighting against the ground, possibly resulting in undefined behavior.
The initial takeoff phase lasts for only a split second; once the helicopter has climbed a mere 5 centimeters, the system asserts full control over the helicopter’s position, velocity, and attitude. At this point we’re accelerating toward a vertical climb rate of 1 meter per second.

The fixed rate of rotation is not something i'd seen before. It is the pitch of the blades (collective) that determines lift during flight.

(th)

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