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This topic is created for a specific business case: Gliders that deliver passengers and cargo to the surface of Mars from Low Mars Orbit.
The NASA Ingenuity helicopter proved that winged flight is possible, and it showed precisely what air foil velocity is needed to generate sustained lift sufficient to carry weight in addition to that of the air foil.
I asked ChatGPT to think about what it will take to land a winged vehicle on Mars. It came up with an estimate of 54 meters/second.
That is fast but well below existing aircraft on Earth.
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Post #3: Conversation with ChatGPT about landing / flight on Mars.
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This post contains a transcript of a conversation with ChatGPT about what velocity it will take to land an aircraft safely on Mars.
It came up with an estimate of 54 meters per second, based upon analysis of the Ingenuity helicopter.
Airfoil velocity on Mars - This request is relative simple compared to some we've dealt with. NASA demonstrated winged flight on Mars. Their little helicopter shows that if a wing (airfoil) is moving fast enough in the thin atmosphere of Mars, it can lift not only itself but some significant mass besides. I bring this up in the context of a discussion about design of a winged aircraft for landing on Mars. This is NOT about an aircraft for Mars. This is strictly about a winged lander. My correspondent leads off with assertion that the velocity of a wing on Mars would have to be near the speed of sound on Mars in order to sustain lift for itself and it's payload/fuselage. My understanding is that the velocity of the helicopter blades was kept below the speed of sound on Mars. Can you find the velocity of the airfoils used by Ingenuity, and by extension, how fast would a wing have to fly to remain airborne on Mars?
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Your understanding is correct. The claim that a wing on Mars must fly "near the speed of sound" to generate lift is not supported by Ingenuity's flight data.Let's work through the numbers.
What was Ingenuity's blade speed?
Ingenuity's rotor diameter was about 1.2 m, so the rotor radius was about 0.6 m. NASA reports that the rotors operated between about 2400 and 2700 RPM during flight.
The tip speed is:
V=2πR×60 RPM
Using R=0.605 m and 2700 RPM:
V=2π(0.605)×60/2700 << the equation may be missing something due to translation .. I think the missing character was slash
V≈171 m/s
NASA specifically states that Ingenuity's flight team never allowed the rotors to exceed 2700 RPM to avoid approaching the Martian sound barrier.
The speed of sound near the Martian surface is roughly 240 m/s (varies with temperature), so:
240/171≈0.71
Thus Ingenuity's rotor tips operated at roughly Mach 0.7, not Mach 1.
Why this matters
A helicopter rotor is simply a rotating wing.
Each blade section produces lift according to: <snip due to translation>
Notice that lift depends on:
air density ρ
velocity squared V
2
wing area S
lift coefficient C
LMars has only about 1% of Earth's atmospheric density, so something must compensate:
larger wing area,
higher velocity,
higher lift coefficient,
or some combination.Ingenuity compensated with:
very large rotor area relative to its mass,
extremely light construction,
high rotor speed.It did not need supersonic blade speeds.
What about a fixed-wing aircraft?
This is where your correspondent's argument becomes weaker.
A fixed-wing aircraft can have a wing area vastly larger than Ingenuity's rotor disk area. If you are designing a winged lander, you are not constrained to a 1.2-meter rotor.
NASA's various Mars airplane studies typically examined cruise speeds on the order of 50–150 m/s, depending on wing loading and vehicle size. That's fast compared with Earth aircraft of similar mass, but well below the Martian speed of sound (~240 m/s).
For example:
Speed (m/s) Speed (mph) Mach on Mars
50 112 0.21
100 224 0.42
150 336 0.63
200 448 0.83
240 537 1.0A Mars glider or winged lander would likely operate somewhere in the middle rows, not necessarily at Mach 1.
A useful comparison
Suppose a Mars winged lander has:
10 times the lifting surface area of Ingenuity's rotor disk
similar lift coefficientThen, because lift scales with velocity squared, the required speed falls by:
<snip due to translation>
So a vehicle needing 170 m/s with Ingenuity-sized lifting surfaces could achieve the same lift at roughly:
170/3.16≈54 m/s
with ten times the wing area.
This is exactly why fixed-wing aircraft are generally more efficient than helicopters.
For your discussion
A concise response might be:
Ingenuity's rotor blades were operating at roughly 170 m/s (about Mach 0.7 on Mars), not near the Martian speed of sound. Since rotor blades are themselves airfoils, NASA has already demonstrated that useful aerodynamic lift can be generated on Mars at substantially subsonic speeds. A fixed-wing lander can carry much larger lifting surfaces than Ingenuity, so its required flight speed could be considerably lower than rotor-tip speed and need not approach Mach 1.
That doesn't prove a particular winged lander design will work, but it does show that "a Mars aircraft must fly near the speed of sound to generate lift" is too strong a statement. The required speed depends heavily on wing loading and wing area, not just atmospheric density.
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The core issue in our discussion was the landing speed of the vehicle. A velocity of 54 meters/second is still pretty fast. A quick comparison is 54 m/s >> 194.4 Km/hour. It appears that a number of aircraft had landing speeds on Earth in excess of the figure you estimated.
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I’ll tighten this around landing speed, not cruise or rotor-tip speed, and separate “physically possible” from “operationally acceptable.” The key variable is wing loading: mass per wing area.Thought for 12s
Yes — 54 m/s is fast, but not exotic. It is about 194 km/h / 121 mph / 105 knots.
For landing, the useful relation is:
<snip due to translation>
So Mars landing speed is driven mostly by wing loading W/S, because Martian air density ρ is so low. NASA’s lift equation uses the same density–velocity–area relationship.
Your comparison is fair: many Earth aircraft land faster than 54 m/s. A Boeing 747 typically lands around 145–150 knots, about 75–77 m/s, though with enormous runways and strong landing gear.
So I would revise the argument this way:
A Mars winged lander does not need to approach Mach 1 merely to make lift. Ingenuity stayed below about Mach 0.7, and Mars sound speed is around 240 m/s. But a practical winged lander may still have a high touchdown speed unless it has very low wing loading, high-lift devices, powered lift, or some final deceleration system.
In other words: “not near sonic” does not mean “slow.” A plausible Mars winged lander landing at 50–100 m/s is still a serious kinetic-energy problem, but it is quite different from claiming it must land near 240 m/s.
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GW Johnson pressed ChatGPT on that 54 m/s velocity, and it accepted the correction. That figure was for a lightly loaded wing that would certainly not be designed for a Mars winged lander. In the end, we have this summary:
Thanks for your consideration of the overview of the discussion. Reliance on retropropulsion seems to be where Elon Musk and Jeff Bezos, and their Chinese counterparts are heading. I am from a generation that would regard depending upon a rocket to land as overly risky. I suppose that when thousands of flights have occurred with few failures, perhaps we humans will have more faith. It took 100 years for humans to develop trust in winged aircraft, and we are still let down occasionally. It seems that the consensus is that the winged lander in the airliner configuration is not going to work at Mars. The vehicle designed by someone that ultimately wins the competition for the Phobos/Mars circuit will include heat shield capability, tail landing capability, and a shape that proves optimum for this particular application.
I think that is the right conclusion.
The “airliner on Mars” concept is probably the wrong mental model. The winner for a Phobos/Mars circuit is more likely to be a purpose-built Mars shuttle, perhaps something like:
Entry body + lifting shape + terminal rocket lander
Not a capsule alone, not an airplane alone, and not necessarily a Starship-style cylinder either.
A plausible competition-winning vehicle might have:
a durable heat shield for repeated Mars entries,
moderate lift-to-drag for cross-range and energy management,
body lift or deployable surfaces rather than airliner wings,
high-temperature structure around the leading edges,
tail or belly landing depending on final configuration,
rocket terminal descent for the final low-altitude/low-speed phase,
and enough aerodynamic control to reduce propellant demand before landing.Your instinct about risk is reasonable. Retropropulsion is inherently dramatic: the vehicle must be actively working until the final seconds. But on Mars, the atmosphere is thin enough that pure aerodynamic landing becomes very difficult, while still thick enough to be extremely useful for braking and heating management.
So the likely compromise is:
Use the atmosphere for as much velocity reduction as it can safely provide, but use rockets for the part Mars air cannot handle well.
That may be the practical middle ground between your generation’s distrust of rocket landing and the modern trend toward propulsive terminal descent.
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