Tech Log The very best in practical technical discussion on the web

Jetstream

Old 26th Oct 2008, 22:41
  #1 (permalink)  
Thread Starter
 
Join Date: Feb 2001
Location: europe
Posts: 53
Likes: 0
Received 0 Likes on 0 Posts
Jetstream

Flew Northbound yesterday and crossed a Jetstream at 90 degrees that had a core speed of 220kts. That's a personal record. Watching the HDG change was unreal as we went through and out the other side.
It was pretty smooth too. Not what we expected. The FO said she had a 190 kt tailwind earlier in the week heading Eastbound.

Tom
wxjedi is offline  
Old 26th Oct 2008, 23:39
  #2 (permalink)  
 
Join Date: Jul 2007
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
I guess the force was strong in that one
PPRuNeUser0183 is offline  
Old 26th Oct 2008, 23:40
  #3 (permalink)  
 
Join Date: Feb 2000
Location: Limbricht
Posts: 2,193
Received 6 Likes on 5 Posts
Tom, just for my personal info, do you encounter any sudden turbulence as you penetrate a jetstream at an angle, or is the wind change gradual?
Avman is offline  
Old 28th Oct 2008, 17:17
  #4 (permalink)  
 
Join Date: Jan 2003
Location: Northampton
Posts: 516
Likes: 0
Received 0 Likes on 0 Posts
Avman,

From a purely physical point of view, I should imagine it would be a pretty smooth ride, albeit noticeable. My reasoning behind this is to think of an aerofoil moving through the air - consider the surface of the aerofoil and the boundary layer of air to be the jetstream core. Now think how this affects air for some distance away from the aerofoil itself, right up until a point of sufficient distance from the aerofoil that it is no longer affected. So it would seem the logical answer to me is that it would be a gradual change.

Of course I stand to be corrected

Jack
Halfbaked_Boy is offline  
Old 28th Oct 2008, 17:38
  #5 (permalink)  
Warning Toxic!
Disgusted of Tunbridge
 
Join Date: Jan 2005
Location: Hampshire, UK
Posts: 4,011
Likes: 0
Received 0 Likes on 0 Posts
Shows how little you know! Lad, you dinna know what yer talkin' aboot! Try piloting in a jetstream before you tell us the theory!
Rainboe is offline  
Old 28th Oct 2008, 22:02
  #6 (permalink)  
 
Join Date: Jan 2008
Location: The Smaller Antipode
Age: 89
Posts: 31
Received 17 Likes on 10 Posts
Once asked to hold at F/L 200 at a VOR/DME fix ( wot's FMS ? ) approaching Tokyo from the South, wind in the region of 180 kts abeam, turned outbound and was swept far, far, away. Eventually held at right angles to the required airway, 10 secs outbound, 5 minutes inbound - or something - interesting anyway.

Before anyone tells me that you don't get jet streams at that altitude - it was still a bl**dy strong blow, and remember what downed the 707 on Fuji - winds of 200 kts recorded around the mountain that day.

Last edited by ExSp33db1rd; 28th Oct 2008 at 22:17.
ExSp33db1rd is offline  
Old 28th Oct 2008, 22:18
  #7 (permalink)  
 
Join Date: Dec 2001
Location: Here 'n' there!
Posts: 586
Received 10 Likes on 6 Posts
HBB, next time watch what happens when you land and the wind drops and backs (assuming you are in the Northern Hemisphere) from 30kts to, say, 15kts in about 1500 ft! The aircraft will be all over the place in the windshear!!! Now, try that at FL350 with a 220 kt wind with appropriate windshear thrown in! Mmmmm, the coffee goes everywhere! Not much fun! If you suddenly fly into an updraught of +50 kts the Boundary Layer has nothing to do with it - you are in a "lift" plain and simple! You are going up - or down - at huge speeds! By the way, check out the texts on CB's! Avoid them as well if I were you! Alas, "windshear" and updraughts/downdraughs in CBs can cause significant damage! So, please, stay safe! And learn from others!

Cheers, H 'n' H!

PS Not patronising you in any way - just be aware that any change in windspeed, for whatever reason, can spoil your day.
Hot 'n' High is offline  
Old 29th Oct 2008, 15:11
  #8 (permalink)  
 
Join Date: Jan 2003
Location: Northampton
Posts: 516
Likes: 0
Received 0 Likes on 0 Posts
H 'n' H,

Thanks for the clarification. No, my only reasoning was thinking that a jet core travelling at 200 kts will then affect the air in near proximity to it, and so on and so forth. 'My' theory was that if this process happens over, for example, 30 nms or so (laterally speaking) then although the change would be noticeable, it would cause no caffeine spillages as you said! But as I suspected, I do stand corrected!

Mind you, I'm sure that, like universal black holes, jetstreams come in all shapes and sizes, some 'shallower' than others so to speak. After all, as wxjedi mentioned, it was a smooth ride for him

Rainboe, thank you for your enlightening contribution also

Cheers, Jack
Halfbaked_Boy is offline  
Old 29th Oct 2008, 20:55
  #9 (permalink)  
 
Join Date: Dec 2001
Location: Here 'n' there!
Posts: 586
Received 10 Likes on 6 Posts
HBB, no problems. As you note, sometimes there is a very smooth gradient and the coffee remains where intended! Other times .!!!! Often, there is no logic behind the outcome. I have always adopted the approach where I expect the worst. After all, one can only be pleasantly surprised by a potential bad event not taking place! Far better than being caught unawares. With Jetstreams in particular, there is no reason to assume a constant change in velocity as you approach the core. Why? If you ever find out, please do let me know!!!! LOL!

Cheers, H n H
Hot 'n' High is offline  
Old 31st Oct 2008, 21:21
  #10 (permalink)  
daf
 
Join Date: Jan 2007
Location: in the cockpit at 11km height
Posts: 28
Likes: 0
Received 0 Likes on 0 Posts
dual jetstreams

did anyone ever try to cross a "dual jetstreams" at an angle at aprox 90 deg ??

What i mean is 2 jetstreams that follow the same way, as seen on the sign.chart.

I did, and tell u what, we had to wear shoulder harnesses just to fell safe. **** it was turbulent.
Anyone has a good explanation on why it is so violent with 2 jetstreams?
My cpt, gave me an explanation, that i didnt really understood at that time.

regards

D
daf is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.