Soaring on Mars

[puffnfresh]

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?

[Tim Olson]

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

[John Giddy]

"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.

[C.Fleming]

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?
>

[root]

"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.

[C.Fleming]

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

[Mike Borgelt]

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

[C.Fleming]

"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

[goneill]

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?
> >
>
>

[root]

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.

[C.Fleming]

"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

[Robert Ehrlich]

"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.

[C.Fleming]

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.

[Liam Finley]

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
>
>
>

[Mike Borgelt]

On 28 Aug 2003 15:22:32 -0700, (Lennie the
Lurker) wrote:

>Mike Borgelt > wrote in message >...
>> >
>> Not just like on Earth. The lower gravity means the density doesn't
>> drop off as quickly with altitude as on Earth.
>>
>Gravity follows an inverse square law, the further you are from the
>center of gravity the less it becomes. Mars being considerably
>smaller than earth, and much less mass, a change of several thousand
>feet still won't be considerable, but will be a greater change then it
>would be on a larger planet. The density will decrease faster than
>here on Earth. Mars equatorial radius is .5326 that of Earth, gravity
>is .379 and mass is .1074, all factors that lead to gravity decreasing
>much more rapidly than here on Earth.


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

We are talking atmospheric density vs altitude above surface not
gravity vs altitude above surface. The gravity *causes* the density
gradient so lower gravity, lower density gradient hence the density
doesn't drop off as quickly.

I might add that the sensible atmosphere of Earth ends long before the
gravity has decreased much.

Mike Borgelt

[Mike Borgelt]

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

[Liam Finley]

Before we get too excited about soaring on mars, does anyone know if
the planet has significant thermal convection?

[C.Fleming]

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?

[Lennie the Lurker]

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.

[Martin Gregorie]

On 29 Aug 2003 14:45:04 -0700, (Liam Finley) wrote:

>Before we get too excited about soaring on mars, does anyone know if
>the planet has significant thermal convection?

Judging by the huge dust devils that Mars Global Explorer has
photographed many times it's likely to have some useful thermals.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Liam Finley]

(Lennie the Lurker) wrote in message >...
> 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.

A high-school equivalency certificate with an emphasis on home-ec
would give him more standing than you Lennie.

[Mike Borgelt]

On 2 Sep 2003 16:29:44 -0700, (Liam Finley) wrote:

Liam,

My ISP had a problem with the news server the last couple of days.
Could you copy Lennie' reply to which you refer please?

Mike Borgelt

>