aidan
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No Turbulence In Higher Altitude?

Fri Dec 17, 2004 7:59 pm

Hi folks,

Is it true that there is no turbulence in a higher altitude? I heard once that there is no turbulence in Concorde cruising altitude, is it true?

If true, what is the altitude when there is no longer turbulence? Understand that if you go higher there is less air thus less turbulence. Go higher there will be no gravity also  Smile

Regards!  Smile
 
Okie
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RE: No Turbulence In Higher Altitude?

Fri Dec 17, 2004 10:31 pm

Is it true that there is no turbulence in a higher altitude?

Most weather related turbulence occurs at lower altitudes in the atmosphere but there are super cell thunderstorms, hurricanes, that can extend up into the higher levels of the atmosphere. So the quick answer would be there is less likely a chance of weather related turbulence.

Go higher there will be no gravity also

Earth's gravity extends Millions of miles into space, there will be only a very minor effect only 10 miles above the surface of the earth. (where the Concorde flew)

I have found gravitation multiplication produced by alcohol more of an issue. Face down on the floor without enough strength to get back up.

Okie
 
BMAbound
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RE: No Turbulence In Higher Altitude?

Fri Dec 17, 2004 11:04 pm

The troposhere (higher over the equator and lower over the poles) contains pretty much all the moisture and therefore all the weather. So yes, turbulence created by convection, subsidence and orographic (forced) mixing will not be found above the tropopause. Concorde, and every now and then regular airliners, fly above the tropopause and are therefore not exposed to all the nasty weather below them.

johan
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Starlionblue
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RE: No Turbulence In Higher Altitude?

Fri Dec 17, 2004 11:34 pm

Go higher there will be no gravity also

This is a misconception. The gravity of any object extends outwards forever (for all practical purposes) but the gravitiational pull decreases with distance according to the inverse square law (http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html). In near Earth space, the gravitational pull is pretty much equal until you get very far away.

Objects in orbit are under the influence of gravity, or they would not remain in orbit. The weightless effect is achieved since the pull of gravity is exactly balanced by the outward vector in the orbital movement. The vector is pulling the spacecraft out from the earth. Gravity is pulling in. Balance, and no weight.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
aidan
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RE: No Turbulence In Higher Altitude?

Fri Dec 17, 2004 11:53 pm

Thanks all for the explanation.

I didn't except any elaboration on the gravity though, brought it up just for a joke  Smile

Anyhow, great explanation. Which bring to other point, if regular airline can cruise in a higher altitude that have no turbulence why not keep the a/c cruise on that altitude all the time? I'm sure the pax will be much happier if the flight is smoother.

Is cost, i.e. need more fuel to cruise higher, the only consideration why a/c not cruise in higher altitude?

Regards,

aidan
 
SlamClick
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RE: No Turbulence In Higher Altitude?

Fri Dec 17, 2004 11:59 pm

Here is a simple test of logic.

Is there enough air to support the airplane?

No = no turbulence.
Yes = possible turbulence

I've had U-2 pilots as student and have been told that clear air turbulence may exist in their entire envelope.


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Starlionblue
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 12:29 am


I've had U-2 pilots as student and have been told that clear air turbulence may exist in their entire envelope.


Those guys have it tough. The U-2 (nowadays officially the "TR-2") only has a 10 knot window between overspeed and stall. I'm guessing this is due to the high cruising altitude. So I guess turbulence throws a nice wrench into the works  Wow!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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Starlionblue
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 1:35 am

Anyhow, great explanation. Which bring to other point, if regular airline can cruise in a higher altitude that have no turbulence why not keep the a/c cruise on that altitude all the time? I'm sure the pax will be much happier if the flight is smoother.

Is cost, i.e. need more fuel to cruise higher, the only consideration why a/c not cruise in higher altitude?


Disclaimer: I think I know what I'm talking about, but I may well bollocks it up...

If you want to cruise higher, you run into a phenomenon known as "coffin alley" or "coffin corner". For any given wing, the higher you go, the higher your stall speed (in ground speed). This is due to the fact that as the air gets thinner, airspeed will sink. At a certain altitude, airspeed will meet stall speed. So that's the lower end of the envelope. At the other end, as you go faster, you will encounted mach buffet. Since Mach speed decreases with altitude, the higher you go, the slower you have to go to avoid mach buffet.

Thus you have a situation where the higher you go, the smaller the window between mach buffet speed and stall speed. Big problem. Eventually you can go so high that mach buffet speed=stall speed, at which point your wing will no longer carry you. Of course, even before then any wind shear will take you past some edge of the envelope. You can solve this in two ways. Either go faster than Mach 1 (SR-71 option) or have very specialized wings (U-2/TR-2 option). But for airliners that would not be economically viable.

And I won't even start on engine issues at altitude.
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FredT
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 2:48 am

Most aircraft don't have the power to climb to anywhere near coffin corner. You want to fly as high as possible due to fuel efficiency anyway, and they already do. This is above most of the weather, but there is still turbulence. One example is CAT associated with jet streams.

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Ralgha
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 2:49 am

The U-2 (nowadays officially the "TR-2")

It's "TR-1", and that designation was reverted back to U-2R in 1991.

These days the airplanes are either "U-2R" or "TU-2R".

Also, SlamClick has it exactly right, if there's enough air to fly in, there's the potential for turbulence.

[Edited 2004-12-17 18:49:58]
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
 
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vzlet
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 2:55 am

Since Mach speed decreases with altitude, the higher you go, the slower you have to go to avoid mach buffet.

Starlionblue, what I think you meant here is that the speed of sound decreases with altitude. An aircraft maintaining a constant velocity while climbing will experience increasing Mach speed because it's getting closer to the speed of sound.

And I think this would be clearer if you specify that it's indicated airspeed that will decrease at a constant true speed:
This is due to the fact that as the air gets thinner, airspeed will sink.

(That said, I'll follow your lead and also disclaim guaranteed accuracy in this area!)

-Mark
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vzlet
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 3:07 am

And, all the U-2s are now "S" models, with F-118 engines.

This from http://www.af.mil/factsheets/factsheet.asp?fsID=129:
"In 1992 all TR-1s and U-2s were designated U-2Rs. All U-2R models have since completed engine replacement and are designated as a U-2S/TU-2S."
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vc10
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 5:41 am

Not going into all the clever stuff here about tropopause etc , but I have seen CBs going up above 60,000ft in the tropics near Singapore, so do not believe all that you read in books about it being calm the higher you go.
Yes Concorde did experience turbulence at it's higher cruise altitudes, but it normally was not the wallowing type experienced by subsonic aircraft, but more like driving fast over a cobbled road, and it seemed to be related to temperature shears.

little vc10
 
SlamClick
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 6:43 am

Hey Vc10 you are absolutely right about thunderstorms going well above the trop. A few years ago I had a group of dispatch students on a "field trip" to an airline dispatch center. While we were there they had the local stuff on Mobile Alabama because they had a charter going there. At the time we were there Mobile was not a good destination - there was a thunderstorm maybe twenty miles or more across of RED returns and it topped out at 73,000' You can have my share of that!

That was not the highest or largest I've ever seen or heard of but it was a good one.

I was mostly referring to clear air turbulence in relation to the U-2 pilots. The atmosphere, even in its upper reaches is a turbulent, chaotic environment. As so many of us know, you get "mountain wave" thousands of miles away from any mountains, far out over the ocean. If air can flow horizontally it can flow vertically too.

Consider the really big picture on the earth's climate and this becomes obvious. As a generality, air rises near the equator and descends near the poles. It is therefore also true that the flow is generally toward the equator at lower levels and toward the poles at upper levels. Now divide the air system into three separate cells, one polar, one temperate and one tropical and throw in coriolis force and yes, you can find turbulence just about anywhere.

We should be surprised when a flight is smooth.

Happiness is not seeing another trite Ste. Maarten photo all week long.
 
FredT
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 8:07 am

If you are picky, the speed of sound does not decrease with altitude. It decreases with decreasing temperature. And yes, this means that for a constant TAS the mach speed will increase.

And affirm on the stall speed. The true air speed for stall increases as the density of the air gets lower.
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Santhosh
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RE: No Turbulence In Higher Altitude?

Sat Dec 18, 2004 12:34 pm

What does it mean by 'mach buffet'. Can any explain in detail pls?

Thankfully
George
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Starlionblue
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RE: No Turbulence In Higher Altitude?

Mon Dec 20, 2004 12:40 am

IIRC Mach buffet is due to shock waves forming as parts of the airflow become supersonic when the aircraft approaches the speed of sound. Swept wings are a way to delay the onset of such shockwaves.

These shockwaves occur in the transonic regime, which starts well under Mach 1, since regions of the airflow become supersonic.

I'm sure somebody else can explain it better. Meanwhile: http://en.wikipedia.org/wiki/Mach_number
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
FredT
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RE: No Turbulence In Higher Altitude?

Mon Dec 20, 2004 5:16 am

Mach buffet is, for all practical purposes, the same as stall buffet. As the speed of the air flow over the airframe reaches sonic speeds locally, shockwaves form. Just as flow separation occurs at high angles of attack (stall), separation can be caused by these shock waves, causing buffeting and loss of lift.

Regards,
Fred
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Catatonic
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RE: No Turbulence In Higher Altitude?

Mon Dec 20, 2004 5:41 am

Mach buffet is the food they served on Concorde when it was flying supersonic.
Equally Cursed and Blessed.

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