2H4
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Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 1:05 am



A couple of days ago, cnn.com reported that a new planet has been discovered that is very similar to Earth. Much remains unknown, of course, but early findings indicate a habitable environment with temperatures and atmosphere like our own.

One of the differences is the gravity. It's reported to be 1.6 times that of our own planet. In other words, a 100-pound weight would weigh 160 pounds on the new planet.

My question: Assuming all other factors are equal to Earth, how would aircraft design/usage change in light of the stronger gravitational pull?

More specifically:

Would we simply fly airliners around half-full with yards of legroom?

Would ranges drop as fuel is left behind in favor of payload? Perhaps turboprops and UDFs would quickly replace jets, as less fuel weight would need to be carried for a given range requirement.

Would new designs incorporate a large wing and sacrifice cruising speed?

Would maximum (structural) load factors be cut in half? How would this affect certification/operations?

Would helicopters even be usable?

Would people still fly gliders?

How long would runways/taxiways last?

Could we still utilize aircraft carriers?

Would landing distances decrease as a result of even more weight being placed on the gear when the spoilers are raised?

60% more gravity. It would be interesting to see the industry rise to the challenge.


2H4


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N231YE
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 1:45 am

Quoting 2H4 (Thread starter):
Would helicopters even be usable?

Helicopters will always defy gravity, whether its Earth at 1.00Gs or "Planet X" at 1.60Gs. They do this because no matter what planet they are on, they will always fly by repelling the ground due to the ineluctable ugliness of their design   

[Edited 2007-04-25 18:50:05]
 
KELPkid
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 2:19 am

Actually, I remember hearing a while back that NASA had designed a solar cell/electric motor powered UAV specifically for flying on Mars...must be an interesting machine  Smile I wonder how you'd deploy such a machine...probably the reason it hasn't been sent to Mars yet.
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futurecaptain
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 3:55 am

Interesting to think about. My thought is firstly we all can agree that lift must overcome gravity. This leads me to believe that we would need more lift to move the same amount of mass through the atmoshphere on the other planet. AFAIK the two ways to do this are fly faster or increase wing span. If we took our current airliners and bumped the speed up a bit then more air moving over the wings would create more lift which is what we agreed we needed to overcome gravity. Or on the other hand we can increase wingspan and give more area for the air to pass over, at a slower speed, to increase lift.

Yes, as far as we know helicopters are so ugly even alien worlds repel them so they will fly. The A380 uses the same principle to achieve flight.  Smile

I assume landing distances would increase if the planes flew faster. even though more weight is put on the wheels the airplane is moving much faster. It would take awhile to stop all the weight. If we go with the increase wingspan theory then landing distances would still increase if we consider cruise speeds comparable to Earth. A 777 flying at the approach speed on a planet with 1.6 times the gravity of Earth will be that much heavier and harder to stop. Not only that but with the increased wingspan more area to the sides of runways and taxiways would need clearing.

Just my $.02
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KELPkid
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 4:09 am

F=ma, so the mass would be the same on our extraterrestrial world with 1.6x the gravity...and assuming the air density is relatively close to what we have down here on Terra, drag wouldn't change all that drastically...it seems as 2H4 pointed out, that a somewhat scaled-up wing would be in the works (to convert a terrestrial aircraft design), probably with increased thrust to overcome the excess induced drag from a larger wing

Quoting Futurecaptain (Reply 3):
I assume landing distances would increase if the planes flew faster. even though more weight is put on the wheels the airplane is moving much faster. I

Once again, F=ma. Mass doesn't change...however, on account of the larger wing and bigger engines, I guess mass would go up...

I wonder if on E*1.6 (Earth world 1.6 times the size of Earth) you would encounter the coffin corner sooner than you would on Terra Firma..  scratchchin  Your wings are going to be called upon for 60% more lift than they would have to be here on our home world.
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airfoilsguy
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 4:15 am

I would think the air density would be grater on a planet with a higher gravity. Because the gravity would pull down more gas making the air density greater.
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GAIsweetGAI
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 4:19 am

I don't think we'd have to change anything.

The A/C's weight would increase, true, but the air's weight would increase as well. The air would be denser than here on Earth.

We'd still find the same lift to weight ratio.

Then again, I may be wrong, as I'm no expert on this.
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KELPkid
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 4:23 am

Quoting GAIsweetGAI (Reply 6):
The A/C's weight would increase, true, but the air's weight would increase as well. The air would be denser than here on Earth.

Which would lead to a lower speed of sound on our Earth Mark II...which could present some problems.
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Blackbird
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 5:19 am

No... higher air density will equate to a higher sound-speed.

Andrea Kent
 
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Jetlagged
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 5:21 am

Quoting KELPkid (Reply 7):
Which would lead to a lower speed of sound on our Earth Mark II...which could present some problems.

a = SQRT(gamma * R * T)

where gamma is the ratio of specific heats (Cp and Cv), R is the gas constant and T is absolute temperature.

For air gamma is 1.4, R is about 287 (in SI units)

For planet Earth II, who knows?

So the speed of sound is related to atmospheric temperature, but not density. It will certainly be different though.
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Yellowstone
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 6:26 am

Quoting Futurecaptain (Reply 3):
A 777 flying at the approach speed on a planet with 1.6 times the gravity of Earth will be that much heavier and harder to stop.

Not quite. Stopping distances, which relate to momentum, depend on mass, not weight. (Although adding the necessary extra wingspan would add mass.) Friction, on the other hand, does depend on weight, so that could affect landing distances.

For those who don't know the difference: Mass is the amount of matter in an object; it is invariant under changes in gravitational field, and is measured in kilograms or slugs. Weight is the strength of the force exerted on an object by gravity, and hence it varies directly with the mass of the planet, the mass of the object, and inversely with the square of the distance between them. Like all forces, it is measured in newtons or pounds.
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DavidT
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 6:45 am

The amount of energy needed to accelerate the plane to however fast it travels will be the same as on earth, as kinetic energy is just (1/2)mv^2.

However more energy (read: fuel) will be needed to raise the aircraft to cruising altitude, as the work done against gravity will increase 1.6-fold.

At cruise, to keep the aircraft level, the downwards gravitational force pulling the aircraft towards the ground will be 1.6 times larger than on earth, meaning that the wings must provide 1.6 times the lift they normally do on earth meaning bigger wings.
 
2H4
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 6:51 am




Quoting DavidT (Reply 11):
At cruise, to keep the aircraft level, the downwards gravitational force pulling the aircraft towards the ground will be 1.6 times larger than on earth, meaning that the wings must provide 1.6 times the lift they normally do on earth meaning bigger wings.

And with more lift comes more drag.....which increase the thrust required.....which increases fuel burn.....which either reduces range or payload. It seems that the net effect on operations would be extreme.


2H4


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Mir
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 3:10 pm

Quoting KELPkid (Reply 2):
Actually, I remember hearing a while back that NASA had designed a solar cell/electric motor powered UAV specifically for flying on Mars...must be an interesting machine

Despite Mars' lower gravity, the thin atmosphere would make flying difficult. You'd have to have a plane like the U-2 designed to operate in those conditions, but because of the air density, the true airspeed would be much higher, which would lead to inertia problems.

-Mir
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rwessel
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 4:53 pm

Assuming this planet were just like earth, except that someone cranked the gravity knob to "1.6", and things like air density and composition did not change, then an aircraft will fly exactly as it would on earth with a 60% extra load hung on.  weightlifter 

IOW, you could take a 160klbs MTOW 737-700, and load it to an earth equivalent of 100klbs (that's only 16klbs above the OEW - so only pilots and a minimal amount of fuel), and it would fly on this new planet exactly like a grossed out '700 would here. One pesky detail is that it would be above the MLW in all cases, though.

In short, you'd need more wing, more structure, more power and more fuel to move the same amount of payload, which may impact other operational parameters (you might need longer runways if you accept higher takeoff speeds, for example), and which certainly have structural implications (leading directly to more weight), but there are no mysteries here.

And sailplanes? Sure, you'd nearly halve the effective L/Ds, and without some reinforcement, they'd be a bit overloaded, but they'd fly fine. It's just that unless the thermals get a lot stronger, your spiffy 50:1 ASG29 on planet X would perform a bit worse than a clunky old 30:1 SGS 1-36 would here. Although it would still not have that lovely oil-canning sound in turbulence...

You will, however, need to upgrade the towplane.  stretch 
 
Legs
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 5:11 pm

Think about it from the perspective of the little green aerospace engineers that live on Planet X. They would be looking at our planes specs and marveling how on earth we get so much weight into the air on such ludicrously undersized wings and airframes. Imagine combining the materials engineering that Planet X's inhabitants would have probably developed with our (relatively) sparse gravity, the possibilities are mouth watering!
 
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Jetlagged
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RE: Aircraft Design/Operations On Another Planet

Thu Apr 26, 2007 9:14 pm

Since the theme seems to be generally high weight and more drag, Antonov would appear to be ideally qualified to design an Earth II aircraft. NASA should put them under contract straight away. Or perhaps this might be a few centuries premature?
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hangarrat
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RE: Aircraft Design/Operations On Another Planet

Fri Apr 27, 2007 5:41 am

Quoting Airfoilsguy (Reply 5):
I would think the air density would be grater on a planet with a higher gravity.



Quoting DavidT (Reply 11):
the downwards gravitational force pulling the aircraft towards the ground will be 1.6 times larger than on earth, meaning that the wings must provide 1.6 times the lift they normally do on earth meaning bigger wings.

It seems like everyone is skirting the very simple answer to the question. Aircraft would be optimized for the conditions on that planet. An aircraft designed to fly in E1.6's atmosphere would be horribly inefficient on Earth 1.0.
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SP90
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RE: Aircraft Design/Operations On Another Planet

Mon May 07, 2007 1:08 am

This might be a bit off topic but with the gravity being 1.6x that of Earth, can humans even live there for extended periods of time? You would have to be in good physical shape just to walk around empty handed. Imagine your a 150 lb person on Earth and someone just strapped on an extra 90 lbs to you and made you walk around with it 24/7.  weightlifter 
 
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Starlionblue
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RE: Aircraft Design/Operations On Another Planet

Mon May 07, 2007 3:31 am

Quoting SP90 (Reply 18):
This might be a bit off topic but with the gravity being 1.6x that of Earth, can humans even live there for extended periods of time? You would have to be in good physical shape just to walk around empty handed. Imagine your a 150 lb person on Earth and someone just strapped on an extra 90 lbs to you and made you walk around with it 24/7.

Good question. Most people would probably have heart problems, back problems, muscle problems and other fun stuff very fast.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
rwessel
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RE: Aircraft Design/Operations On Another Planet

Mon May 07, 2007 4:05 pm

Quoting SP90 (Reply 18):
This might be a bit off topic but with the gravity being 1.6x that of Earth, can humans even live there for extended periods of time? You would have to be in good physical shape just to walk around empty handed. Imagine your a 150 lb person on Earth and someone just strapped on an extra 90 lbs to you and made you walk around with it 24/7.

The total kit being carried by our infantry running around Afghanistan and Iraq weighs more than that. The old standard for various exploratory expeditions was that you carried your own weight in supplies.

1.6G would undoubtedly be hard on knees, backs and a few other body parts, and significantly increases the odds of injury from falls and whatnot, but a decade or two should be endurable by most semi-fit humans in the 15-55 age range. And if you were only semi-fit at the beginning of that, you'll probably be quite fit at the end.

Mind you there's a dearth of experimental evidence involving humans on this point. Mouse studies have been done where mice have lived multiple life cycles (birth, growth, reproduction, repeat), under 2G, with minimum ill effects, although bigger bones and musculature develops, as one would expect.
 
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Starlionblue
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RE: Aircraft Design/Operations On Another Planet

Tue May 08, 2007 4:08 am

Quoting Rwessel (Reply 20):

The total kit being carried by our infantry running around Afghanistan and Iraq weighs more than that. The old standard for various exploratory expeditions was that you carried your own weight in supplies.

Agreed, but in a high G environment it's not all on hips, shoulders and knees. Even breathing would be harder due to he extra weight of the ribcage.

Quoting Rwessel (Reply 20):

1.6G would undoubtedly be hard on knees, backs and a few other body parts, and significantly increases the odds of injury from falls and whatnot, but a decade or two should be endurable by most semi-fit humans in the 15-55 age range. And if you were only semi-fit at the beginning of that, you'll probably be quite fit at the end.

Mind you there's a dearth of experimental evidence involving humans on this point. Mouse studies have been done where mice have lived multiple life cycles (birth, growth, reproduction, repeat), under 2G, with minimum ill effects, although bigger bones and musculature develops, as one would expect.

All good points. The interesting thing would be looking at pregnancy and developing children. Larry Niven had Jinxians becoming very stocky and short. Hmm...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WSOY
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RE: Aircraft Design/Operations On Another Planet

Wed May 16, 2007 7:36 am

Quoting Starlionblue (Reply 21):
Even breathing would be harder due to he extra weight of the ribcage.

Since the "air" would also be heavier, less breathing of air would supply the needed oxygen. The effort required for getting air to the alveoli in the lungs would be more, but the alveoli could count less. It's complicated.
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rwessel
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RE: Aircraft Design/Operations On Another Planet

Wed May 16, 2007 3:24 pm

Quoting WSOY (Reply 22):
Since the "air" would also be heavier, less breathing of air would supply the needed oxygen.

Just because the gravity on a new planet might be higher (or lower), does not mean the atmosphere will be denser (or less dense) at ground level. The planet in question could simply have less (or more) total atmosphere, and of a different composition.

Consider Venus, for example: it has about 90% the surface gravity of Earth, and about 90 times the atmospheric pressure.
 
WSOY
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RE: Aircraft Design/Operations On Another Planet

Wed May 16, 2007 6:07 pm

Quoting Rwessel (Reply 23):
Quoting WSOY (Reply 22):
Since the "air" would also be heavier, less breathing of air would supply the needed oxygen.

Just because the gravity on a new planet might be higher (or lower), does not mean the atmosphere will be denser (or less dense) at ground level. The planet in question could simply have less (or more) total atmosphere, and of a different composition.

Yes quite, but I thought the idea here was just that everything else but the gravity will be the same as on the planet Earth. Pardon me.
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Starlionblue
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RE: Aircraft Design/Operations On Another Planet

Thu May 17, 2007 10:06 am

Quoting WSOY (Reply 22):
Since the "air" would also be heavier, less breathing of air would supply the needed oxygen. The effort required for getting air to the alveoli in the lungs would be more, but the alveoli could count less. It's complicated.

So it is. Like breathing in scuba gear. At depth the air is so dense it starts to feel "heavy".
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