Soaring on Mars

Correction:

Before any of you nit-pick over one word, change "airspeed" to simply
"speed."

The revised text should read:

Your assumption is that the air density is adequate to provide sufficient
lift -- which it's not. The speed which would be required to produce
enough lift would be extremely fast -- well over the speed of sound (many
times over) -- which would rip a conventional glider apart.

The air density on Mars is only 1% of Earth's (1) -- at the Martian
equivalent of MSL. Just like on Earth, air density rapidly decreases with
altitude, so the air density just a few thousand feet above the Martian
surface may only be 1/10th of 1% of Earth's (I don't know the exact number,
I'm not a rocket scientist for JPL). So, as I said: you might as well be
trying to soar on the moon.

-Chris

(1)
"Bill Daniels" wrote in message
Air is about 1% as dense as on Earth

On Tue, 26 Aug 2003 15:41:42 -0400, "C.Fleming"
wrote:

Correction:

Before any of you nit-pick over one word, change "airspeed" to simply
"speed."

The revised text should read:

Your assumption is that the air density is adequate to provide sufficient
lift -- which it's not. The speed which would be required to produce
enough lift would be extremely fast -- well over the speed of sound (many
times over) -- which would rip a conventional glider apart.

The air density on Mars is only 1% of Earth's (1) -- at the Martian
equivalent of MSL. Just like on Earth, air density rapidly decreases with
altitude, so the air density just a few thousand feet above the Martian
surface may only be 1/10th of 1% of Earth's (I don't know the exact number,
I'm not a rocket scientist for JPL). So, as I said: you might as well be
trying to soar on the moon.

-Chris

Not just like on Earth. The lower gravity means the density doesn't
drop off as quickly with altitude as on Earth.

The glider wouldn't be ripped apart by flying at high TAS(q is still
low) unless there was a flutter problem which could be induced by the
shockwaves you are going to get by flying at some large fraction of
the local speed of sound or supersonically unless your aircraft design
takes care of this, which can be done.

The folks at NASA are doing studies on Mars airplanes. It isn't that
easy but obviously someone thinks it is doable.
1% density means the TAS/IAS ratio is 10.

Mike Borgelt

"Mike Borgelt" wrote in message
...
On Tue, 26 Aug 2003 15:41:42 -0400, "C.Fleming"
wrote:

Not just like on Earth. The lower gravity means the density doesn't
drop off as quickly with altitude as on Earth.

Air density decreases with altitude. Both here and on Mars. The already
thin air on Mars at the surface is even thinner aloft. That's my point.


The glider wouldn't be ripped apart by flying at high TAS(q is still
low) unless there was a flutter problem which could be induced by the
shockwaves you are going to get by flying at some large fraction of
the local speed of sound or supersonically unless your aircraft design
takes care of this, which can be done.

That's what I said. Flying supersonically would rip the glider apart.


The folks at NASA are doing studies on Mars airplanes. It isn't that
easy but obviously someone thinks it is doable.

That's why I clearly said 'conventional glider.'

1% density means the TAS/IAS ratio is 10.

Mike Borgelt

Mike Borgelt wrote:
...
The folks at NASA are doing studies on Mars airplanes. It isn't that
easy but obviously someone thinks it is doable.
1% density means the TAS/IAS ratio is 10.
...

And also that the same glider on Mars has to fly 10 times faster in
order to obtain the same lift, balancing the same weight. But due to
the lower gravity on Mars, its weight would be lower, so the normal
(best L/D) speed on Mars would be less than 10 times this speed on the
earth. This speed can further be reduced by reducing the wing loading,
which provides some benefits on the earth that are no more valuable on
Mars, like speed, which is rather to high, and penetration, which makes
little sense. So it is not unbelievable that soaring may happen on Mars
at speeds between mach 0.5 and 0.7.

"root" wrote in message
...

And also that the same glider on Mars has to fly 10 times faster in
order to obtain the same lift, balancing the same weight. But due to
the lower gravity on Mars, its weight would be lower, so the normal
(best L/D) speed on Mars would be less than 10 times this speed on the
earth. This speed can further be reduced by reducing the wing loading,
which provides some benefits on the earth that are no more valuable on
Mars, like speed, which is rather to high, and penetration, which makes
little sense. So it is not unbelievable that soaring may happen on Mars
at speeds between mach 0.5 and 0.7.

Most of that sounds ok -- except your guess at mach speeds. Where do you
come up with 0.5 to 0.7 mach? Remember that as air density decreases, so
does the indicated airspeed at which we reach 1.0 mach. From memory (of
many hours staring at airspeed/mach indicators), on Earth: 340 knots ias =
0.8 mach at approx. 28,000 ft., while at 39,000 ft., the ias drops to 260
knots while maintaining 0.8 mach. On Mars, with an air density of less than
1% of Earth's, it appears clear to me that because mach 1.0 will be reached
at a very low indicated airspeed, a conventional glider (the original post
referenced a PW-5) wouldn't have a chance.

On a lighter note: what a view of Mars! I live in Manhattan, and even with
a clear sky, we rarely can see more than the moon. But Mars is there for
anyone who chooses to look up! While crossing the North Atlantic, Mars is
so bright, you almost need to wear sunglasses as it comes over the eastern
horizon! Some flight attendants refused to believe me that it was Mars,
they thought it was another airplane!

-Chris

"C.Fleming" wrote:

"root" wrote in message
...

And also that the same glider on Mars has to fly 10 times faster in
order to obtain the same lift, balancing the same weight. But due to
the lower gravity on Mars, its weight would be lower, so the normal
(best L/D) speed on Mars would be less than 10 times this speed on the
earth. This speed can further be reduced by reducing the wing loading,
which provides some benefits on the earth that are no more valuable on
Mars, like speed, which is rather to high, and penetration, which makes
little sense. So it is not unbelievable that soaring may happen on Mars
at speeds between mach 0.5 and 0.7.

Most of that sounds ok -- except your guess at mach speeds. Where do you
come up with 0.5 to 0.7 mach? Remember that as air density decreases, so
does the indicated airspeed at which we reach 1.0 mach. From memory (of
many hours staring at airspeed/mach indicators), on Earth: 340 knots ias =
0.8 mach at approx. 28,000 ft., while at 39,000 ft., the ias drops to 260
knots while maintaining 0.8 mach. On Mars, with an air density of less than
1% of Earth's, it appears clear to me that because mach 1.0 will be reached
at a very low indicated airspeed, a conventional glider (the original post
referenced a PW-5) wouldn't have a chance.


Sorry, your calculations with weird units don't have an obvious meaning to
my metric educated mind. I never thought of indicated airspeed, only tried to
evaluate the ratio of true airspeeds on Mars and the earth to ensure similar
(e.g. best L/D) flight conditions. My idea was that the speed of sound, while
affected by the change in conditions, should not be affected by a very important
factor. The factors involved are absolute temperature, molecular weight of the
gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I don't
know exactly what are the components of the martian atmosphere, I guess it is
not methane or CO2, but rather diatomic gases with molecular weigth near O2 and
N2 as found on the earth. As all this is under a square root, changes must be
huge to become significative, same thing for temperature. Halving the temperature
on earth only decreases the speed of sound by a factor 0.7, and this is pretty
cold.

So 10 times the gliding speed on the earth is about the speed of sound on the earth,
if the reduction of gravity and wing loading gives a factor that overrides
the change in the speed of sound, subsonic soaring may be possible on Mars.

Mach, Knots Indicated Airspeed (kias), and Feet: weird aeronautical units?
Last I checked, those were standard on both sides of the ocean, unless
you're in Russia.

Indicated airspeed and mach ratios are the two most important factors to
consider! The glider needs to reach a specific Indicated Airspeed in order
to produce adequate lift, which in the extremely thin Martian air would be
an extremely fast True Airspeed. The minimum Indicated Airspeed needed is
open for debate, but it certainly is significantly faster than 40 kias, due
to slow-speed-buffet limits in the extremely thin air. We are also limited
by the Mach Ratio, which for a conventional high-aspect ratio glider is
quite low, nowhere close to 0.85 Mach-limited swept-wing subsonic jets. So,
without asking a Boeing-McDonnell-Douglas Engineer to help me with the math,
I think it's pretty safe to say that the minimum speed required of our PW-5
would be significantly faster than the maximum allowable speed; Hence, our
glider no worky-worky.

-Chris




"Robert Ehrlich" wrote in message
...

Sorry, your calculations with weird units don't have an obvious meaning to
my metric educated mind. I never thought of indicated airspeed, only tried
to
evaluate the ratio of true airspeeds on Mars and the earth to ensure
similar
(e.g. best L/D) flight conditions. My idea was that the speed of sound,
while
affected by the change in conditions, should not be affected by a very
important
factor. The factors involved are absolute temperature, molecular weight of
the
gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I
don't
know exactly what are the components of the martian atmosphere, I guess it
is
not methane or CO2, but rather diatomic gases with molecular weigth near
O2 and
N2 as found on the earth. As all this is under a square root, changes must
be
huge to become significative, same thing for temperature. Halving the
temperature
on earth only decreases the speed of sound by a factor 0.7, and this is
pretty
cold.

So 10 times the gliding speed on the earth is about the speed of sound on
the earth,
if the reduction of gravity and wing loading gives a factor that overrides
the change in the speed of sound, subsonic soaring may be possible on
Mars.

On Thu, 28 Aug 2003 17:05:10 +0000, Robert Ehrlich
wrote:

. My idea was that the speed of sound, while
affected by the change in conditions, should not be affected by a very important
factor. The factors involved are absolute temperature, molecular weight of the
gas(es) and gamma (Cp/Cv). Gamma depends only on the atomicity. While I don't
know exactly what are the components of the martian atmosphere, I guess it is
not methane or CO2, but rather diatomic gases with molecular weigth near O2 and
N2 as found on the earth. As all this is under a square root, changes must be
huge to become significative, same thing for temperature. Halving the temperature
on earth only decreases the speed of sound by a factor 0.7, and this is pretty
cold.

So 10 times the gliding speed on the earth is about the speed of sound on the earth,
if the reduction of gravity and wing loading gives a factor that overrides
the change in the speed of sound, subsonic soaring may be possible on Mars.


The Martian atmosphere is mostly CO2. Anyone have a number for the
speed of sound in CO2 at say 220 degrees K ? Then we can do the real
numbers.

Mike Borgelt