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Soaring on Mars



 
 
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  #11  
Old August 28th 03, 05:08 PM
C.Fleming
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"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


  #12  
Old August 28th 03, 06:05 PM
Robert Ehrlich
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"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.
  #13  
Old August 28th 03, 07:40 PM
C.Fleming
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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.


  #14  
Old August 28th 03, 10:09 PM
Liam Finley
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I'm sure all these problems would be solved by going to a flying wing
design.

Any minute now a post will appear saying the Marske Pioneer has been
tested on Mars and it would not spin and got 100:1 L/D and the proof
will be up on the website as soon as the Martians give back the video
camera...

"C.Fleming" wrote in message ...
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



  #16  
Old August 28th 03, 11:59 PM
Mike Borgelt
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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
  #17  
Old August 29th 03, 10:45 PM
Liam Finley
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Before we get too excited about soaring on mars, does anyone know if
the planet has significant thermal convection?
  #18  
Old August 30th 03, 12:00 AM
C.Fleming
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It has the largest mountain ridge in the solar system!


"Liam Finley" wrote in message
om...
Before we get too excited about soaring on mars, does anyone know if
the planet has significant thermal convection?



  #19  
Old August 30th 03, 04:37 AM
Lennie the Lurker
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Mike Borgelt wrote in message . ..
:

Now apply that to a neutron star. The Cheela disagree with you. So do
the inhabitants of "The Integral Trees".

Mssrs. Skilling and Richardson seem to agree with me, at least that's
where I got my info, not pulled out of my ass. Take it up with them.
They're only professional astrophysicists, if they're still alive.
Your qualifications?

ps. BS degree in electronics doesn't cut it.
 




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