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Soaring on Mars



 
 
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  #1  
Old August 23rd 03, 12:40 AM
puffnfresh
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Default Soaring on Mars

Given the lesser density of air on Mars what would be the glide ratio of
a PW-5 starting at an altitude of say 5000 feet? (lesser gravity, too)
Is it worth book a trip in next few years?

  #2  
Old August 23rd 03, 02:37 AM
Tim Olson
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In article , puffnfresh
wrote:

| Given the lesser density of air on Mars what would be the glide ratio of
| a PW-5 starting at an altitude of say 5000 feet? (lesser gravity, too)
| Is it worth book a trip in next few years?

The X-Plane flight simulator has an option of flying on Mars,
implementing the correct gravity, air density, etc. Air is about 1% as
dense as on Earth, with 1/3 the gravity. I was able to start the
included SH-Cirrus sailplane at about 20000' AGL and dive it to get
enough airspeed to sort of glide, but IAS never got above 40 knots, even
though groundspeed was scary fast. Landing would be a *big* problem...

-- Tim Olson
  #3  
Old August 23rd 03, 03:48 AM
John Giddy
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"puffnfresh" wrote in message
...
| Given the lesser density of air on Mars what would be the
glide ratio of
| a PW-5 starting at an altitude of say 5000 feet? (lesser
gravity, too)
| Is it worth book a trip in next few years?

My first impression is that since both Lift and Drag include
density in the same way:
Lift = Cl x 1/2 x rho x v x v
Drag = Cd x 1/2 x rho x v x v
The ratio is independent of density.
However, you would have to fly very fast (large v) to
generate even 1/3 of the weight on earth, and the poor
glider would probably flutter to bits.
You would then need a *huge* parachute to get you down in
one piece.
I think you could put your money to better us !!
John G.

  #4  
Old August 23rd 03, 05:49 AM
C.Fleming
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Said another way, the air is so thin on Mars, you might as well be trying to
soar on the moon. It doesn't matter that the gravity is less; without air,
you're going to have a 0:1 glide ratio!

Chris




"puffnfresh" wrote in message
...
Given the lesser density of air on Mars what would be the glide ratio of
a PW-5 starting at an altitude of say 5000 feet? (lesser gravity, too)
Is it worth book a trip in next few years?



  #5  
Old August 26th 03, 03:37 PM
root
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"C.Fleming" wrote:

Said another way, the air is so thin on Mars, you might as well be trying to
soar on the moon. It doesn't matter that the gravity is less; without air,
you're going to have a 0:1 glide ratio!


I would rather think the opposite. As long as you have air, even with low
density, you keep the same glide ratio, but at a higher speed. A higher
speed is closer to satellisation speed, i.e the contribution of the centrifugal
force due to the curvature of the ground is higher, so the glide ratio
should be a little higher. But this is only true provided the increased best glide
speed remains under the speed of sound, which is unlikely, near or above this
speed aerodynamics changes completely and glide ratio becomes very low.
  #6  
Old August 26th 03, 08:41 PM
C.Fleming
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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





  #7  
Old August 26th 03, 11:45 PM
Mike Borgelt
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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
  #8  
Old August 27th 03, 12:05 AM
C.Fleming
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"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




  #9  
Old August 27th 03, 07:58 PM
goneill
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I have just been to a presentation on the Perlan project which at it second
stage goal of 100,000ft height is
about mars ground level air pressure.
The aircraft would have 29-30 metre wings (ETA size) and be designed to fly
in the range of 0.6-0.7 mach .The convergence into "coffin corner" occurs at
108,000ft .
The l/d of the design at sealevel would be 50:1 and at the altitude would
drop to 25:1 (source, Nasa supercomputer flight simulations)
The designer of the ETA has been asked to provide some data on large span
composite wing structures at the reynolds numbers required for this project
gary
"C.Fleming" wrote in message
...
Said another way, the air is so thin on Mars, you might as well be trying

to
soar on the moon. It doesn't matter that the gravity is less; without

air,
you're going to have a 0:1 glide ratio!

Chris




"puffnfresh" wrote in message
...
Given the lesser density of air on Mars what would be the glide ratio of
a PW-5 starting at an altitude of say 5000 feet? (lesser gravity, too)
Is it worth book a trip in next few years?





  #10  
Old August 28th 03, 01:36 PM
root
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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.
 




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