The edge of the atmosphere

[sleddriver]

Indeed. One of the major differences between our planet and Mars: The later has no molten core, and no magnetic field, thus most of its atmosphere escaped over time. While some is still left, it's not very dense. A 150mph hurricane on Mars is very different from one on Earth.

Quote:
I am always amazed at our tiny little planet hurtling through space with its micro thin layer of atmosphere barely held in place.

Not wishing to start an argument here, but "micro thin layer of atmosphere" more aptly describes Mars, not Earth. So does "barely held in place." After all, Earth still has a dense enough atmosphere for us to breathe. Even to 14,000ft. After billions of years. That's pretty robust to me.

It is in a near perfect balance though to sustain life. Gravity, atmospheric pressure, humidity, density at sea level, and enough oxygen to sustain life, but not enough to turn us into a fireball when a volcano goes off.

 

[Astro14]

Don't forget the role of the Moon...4.5 billion years of it taking major hits and sweeping Earth orbit free of most junk that could wipe us out...

Were it not for the Moon, mass extinctions, like the one 66 million years ago, at the end of the Cretaceous, would be a common event...and Earth's evolution would not have had the long, uninterrupted runs that allowed the complexity of life we now enjoy...

 

[Cujet]

I know it's not a great pic because it came from my old phone and I texted it to myself.

However, it is from 51,000 feet in our Gulfstream G550. I have all the originals and they are pretty cool.

51,000 feet is way up there, but it's not at the edge of the atmosphere. The G550, when light and when operated with engines in alternate mode, will achieve about 65,000 feet in experimental category.

But, note that the curvature of the earth is visible at 51,000. To see it clearly, you must place your nose on the window. Otherwise the effect is too minor to be noticed.

 

[CT8]

Cujet is alt mode the mil injector position? I am not exactly sure the nomenclature is proper though.

 

[Cujet]

Originally Posted By: CT8
Cujet is alt mode the mil injector position? I am not exactly sure the nomenclature is proper though.


Alternate mode is a way to control the engines, via FADEC (full authority digital engine control) . The selection is made on the display controllers. In normal mode, the engines have additional limits. In alt mode, the engines limits N1, N2 RPM and TGT (RPM and exhaust gas temperature) are the limiting factors. The bottom line is that in some aspects of flight, there is slightly more power available in alt mode. Mostly during mid climb, where the engine would otherwise be operated at reduced power.

Mil power is not something a corporate jet has. However, we are not lacking for power

I used my G-Tech to measure 1/4 mile performance of our G550 on take off. 11.67 seconds at 144MPH. And, we were not able to spool up the engines fully prior to brake release! (it will skid all 4 tires at full power) .

 

[JetStar]

To Cujet's point, alternate mode is reduced control law function. FBW flight controls that I'm familiar with also have an alternate mode. Typically it's reserved for operating when the primary mode has faulted.

 

[Astro14]

While not the beast that the mighty G550 is, I did manage to coax a feeble old F-14 up to 60,000 feet and saw much the same view. Perhaps a bit darker.

Very cool view.

I would have kept climbing (it was still giving me 1,500 FPM at 60,000) but ran out of airspace. We were 1.5 IMN and rapidly approaching the shoreline...and Washington Center has such a poor sense of humor...

While it might not be the edge of the atmosphere...it sure looked like it!

 

[sleddriver]

Indeed. Our Moon greatly stabilizes our planet and orbit. Farther out in the solar system, we owe a big thank-you to a colossal big-sweeper: Jupiter. It's tremendous gravity-well attracts lots of objects, preventing them from coming in closer, them smashes them to bits! Remember Shoemaker-Levy-9?

 

[Cujet]

Originally Posted By: Astro14
While not the beast that the mighty G550 is, I did manage to coax a feeble old F-14 up to 60,000 feet and saw much the same view. Perhaps a bit darker.


Hahahaha. That G550 luxury yacht simply has a 100 foot wingspan and ample power. The F-14 is one of America's finest military aircraft.

 

[Oldmoparguy1]

Originally Posted By: Astro14
While not the beast that the mighty G550 is, I did manage to coax a feeble old F-14 up to 60,000 feet and saw much the same view. Perhaps a bit darker.

Very cool view.

I would have kept climbing (it was still giving me 1,500 FPM at 60,000) but ran out of airspace. We were 1.5 IMN and rapidly approaching the shoreline...and Washington Center has such a poor sense of humor...

While it might not be the edge of the atmosphere...it sure looked like it!


Astro, I am just in aw of the F14. When your at 60k, do you still have full control authority? Not sure I'm asking the right question...

 

[Astro14]

Originally Posted By: Oldmoparguy1
Originally Posted By: Astro14
While not the beast that the mighty G550 is, I did manage to coax a feeble old F-14 up to 60,000 feet and saw much the same view. Perhaps a bit darker.

Very cool view.

I would have kept climbing (it was still giving me 1,500 FPM at 60,000) but ran out of airspace. We were 1.5 IMN and rapidly approaching the shoreline...and Washington Center has such a poor sense of humor...

While it might not be the edge of the atmosphere...it sure looked like it!


Astro, I am just in aw of the F14. When your at 60k, do you still have full control authority? Not sure I'm asking the right question...


The airplane still maneuvers...but not in the same way that it did at lower altitude or speed...at 1.5 IMN and that altitude, I think our indicated airspeed was about 300 KIAS...but while Indicated Airspeed determines lift, and control authority, the true airspeed is far, far higher at 1.5 IMN than the true airspeed when maneuvering at low altitude. And it's true airspeed that determines the flight path...it's pure physics...the flight controls/wings apply force to change the path of the body in motion.

The control authority of the F-14 is still pretty good at those altitudes and speed...but while you might be able to pull 4 G...the airplane is going so fast that 4 G won't change the path much...and given the thin air, that G, and the thrust to sustain it, isn't really there...so, you're not making any tight turns...

You've got to descend to thicker air to make sustained, tight maneuvers...

 

[expat]

The closest I have come to flying an aircraft (thank goodness) has been Google flight simulator.

I's interesting to fly around Mount Everest, the controls get very mushy at high altitude, try to go higher and you find yourself in a nose-up situation, not really going anywhere, until you fall into a spin.

Would that be a realistic scenario?

 

[Astro14]

Originally Posted By: expat
The closest I have come to flying an aircraft (thank goodness) has been Google flight simulator.

I's interesting to fly around Mount Everest, the controls get very mushy at high altitude, try to go higher and you find yourself in a nose-up situation, not really going anywhere, until you fall into a spin.

Would that be a realistic scenario?


Depending on the particular airplane, and its performance, yep. Makes perfect sense.

Even an airliner, designed to operate at 35,000 feet (depending on weight, temperature, etc.), is mushy up there. The engines are putting out a fraction of their low altitude thrust, and the indicated air speed (IAS) is quite low.

A stall/spin is a classic loss of control, from flying at too high of an AOA. if you're near the ceiling of the airplane, and your try to maneuver, you'll bleed airspeed. Pull back on the yoke to maintain altitude, and you get to a higher AOA....then it's stall, spin, and you're done...

I've linked this previously, but it's a great read (not a casual read, a serious, take it a chapter at a time, kind of read) and explains everything I'm talking about. I read it in flight school nearly 30 years ago, and I still keep a copy on my iPad.

http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf

Aerodynamics for Naval Aviators. Free from the FAA.

 

[HerrStig]

As I recall, Supermarine made at least three versions of the Spitfire for low, medium, and high altitude work.

 

[Astro14]

Originally Posted By: HerrStig
As I recall, Supermarine made at least three versions of the Spitfire for low, medium, and high altitude work.


My understanding is that Packard developed the two speed supercharger for the Merlin Engine when they built it under license. That second speed (high blower) made all the difference for the Mustang at high altitude. Can't change the wing, or the air, but getting better power up there sure helps...and that innovation was retrofitted to later versions of the Spitfire.