Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Very Strong Gusty Crosswind Landings In A Quad Vs A Twin

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

Very Strong Gusty Crosswind Landings In A Quad Vs A Twin

Old 3rd Nov 2014, 15:01
  #1 (permalink)  
Thread Starter
 
Join Date: May 2010
Location: Eyjafjallajokull
Age: 32
Posts: 20
Very Strong Gusty Crosswind Landings In A Quad Vs A Twin

Recently a junior colleague posed this question to me and I was stumped...I couldn't give her a definitive answer.

According to her, based on personal observations and you tube videos, quads seem to handle better, stable and land reasonably well in strong crosswinds.

Twins tend to rock and roll all over the place. I gave her the answer a former instructor in the Far East told me years ago when I posed a similar question. He opined that the quads like the B747 and A380 have very good " wing loading " on account of the outboard engines, and hence are stable in gusty crosswind conditions. He elaborated on further with other reasons but I only remeber the " wing loading " part as I thought it was BS, good for a laugh. Well, it sounded like wing loading because he explained about the geometry, moments of force and engine weight effects on the wing. Well, I didn't buy it then but I found myself regurgitating the same to my colleague! It's embarrassing!

Anyone with a better explanation?
Kilda Ste Hilda is offline  
Old 3rd Nov 2014, 15:21
  #2 (permalink)  
 
Join Date: Jun 2014
Location: Mordor
Posts: 304
Never flown a quad, but perhaps it has to with inertia, ie 2 engines on the wing give a a higher moment of inertia, thus better resisting rolling moments induced by turbulence?
Sidestick_n_Rudder is offline  
Old 3rd Nov 2014, 15:26
  #3 (permalink)  

Do a Hover - it avoids G
 
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 86
Posts: 2,206
The initial (NB initial) response of any aircraft to a lateral gust will be determined by two factors:

1 The rolling moment due to sideslip (or if you prefer it the amount of ‘dihedral effect’ present in the design).

2 The rolling inertia of the aircraft.

It is likely that the roll inertia of a quad is greater than a twin so for a given similar dihedral effect in both categories the quad will be less likely to bank quickly compared to the twin.

I have stressed initial response because very rapidly other factors come into play. The main ones being any control input following the gust arriving and the aerodynamic roll damping term present in the wing design.

(BTW if anybody wonders why I write about ‘dihedral effect’ rather than dihedral angle it is because several aspects of aircraft design introduce the same effect as dihedral angle)
John Farley is offline  
Old 3rd Nov 2014, 15:27
  #4 (permalink)  

Do a Hover - it avoids G
 
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 86
Posts: 2,206
Sorry S n R you made the point better than me!
John Farley is offline  
Old 3rd Nov 2014, 16:58
  #5 (permalink)  
 
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 84
Posts: 474
It would be interesting to hear the views of pilots who have flown both the A330 and A340!
Owain Glyndwr is offline  
Old 3rd Nov 2014, 17:17
  #6 (permalink)  

Dog Tired
 
Join Date: Oct 2001
Location: uk
Posts: 1,675
It does not matter if you are in a magnificent Airbus.

Nothing matters.
fantom is offline  
Old 3rd Nov 2014, 18:55
  #7 (permalink)  
 
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 84
Posts: 474
I was hoping for something more interesting!
Owain Glyndwr is offline  
Old 3rd Nov 2014, 19:11
  #8 (permalink)  

Do a Hover - it avoids G
 
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 86
Posts: 2,206
Owain

Both the A330 and A340 are FBW. This means control inputs will be made by the FBW system as soon as the aircraft starts to roll and so if we assume both FBW systems are equally competent the two aircraft will both subsequently respond in the same way to the same gust regardless of any roll inertia differences. That is what FBW is all about.

Last edited by John Farley; 3rd Nov 2014 at 19:12. Reason: Spelling
John Farley is offline  
Old 3rd Nov 2014, 19:20
  #9 (permalink)  
 
Join Date: Apr 2006
Location: Front right seat
Posts: 274
I've flown B727, B747, A320, A340-200/300/600 and A330. There is no difference. The only significant point with the big Airbus's is that over active sidestick handling will get you into the poo very quickly. Other than that, fly them like a C172.
divinehover is offline  
Old 3rd Nov 2014, 19:36
  #10 (permalink)  
 
Join Date: Jun 2014
Location: Mordor
Posts: 304
Hi John,

It was good to read a more technical explanation, than mine

Could you elaborate a bit on the factors affecting aerodynamic damping?

Regarding the Airbus FBW - my personal opinion is that its handling in gusty crosswinds is pretty appalling. Lots of rolling, partly due to slow response of the FBW and partly due to overcontol (one can argue that this is due to poor piloting technique, but the system is IMHO quite conductive to it).
Sidestick_n_Rudder is offline  
Old 3rd Nov 2014, 21:19
  #11 (permalink)  
 
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 84
Posts: 474
Thanks John.
Point taken, but I just didn't know if AI had tuned the gains for each machine or not. If not theremight have been a difference
Owain Glyndwr is offline  
Old 3rd Nov 2014, 22:58
  #12 (permalink)  

Do a Hover - it avoids G
 
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 86
Posts: 2,206
S n R and Owain

I have no knowledge of Airbus aircraft but have an old CTP mate at Dunsfold who very much does. He says the trick is not to try and correct the aircraft as soon as it rolls due to turbulence but let the FBW do what it designed to do. Non intuitive and maybe easier said than done for many pilots.

Re roll damping as we all know the upgoing wing loses AoA and the down going wing has an increase. This produces asymmetric lift in the sense needed to reduce the roll rate. This effect is enhanced by increasing the aspect ratio. It is also greater the steeper the lift curve slope of the aerofoil concerned.
John Farley is offline  
Old 3rd Nov 2014, 23:25
  #13 (permalink)  
 
Join Date: Jan 2014
Location: glendale
Posts: 822
maybe its because the "quads" go senior and the senior guys know what they are doing?

glendalegoon is offline  
Old 4th Nov 2014, 00:00
  #14 (permalink)  
 
Join Date: Jun 2001
Location: Chicago, IL, USA
Posts: 518
I've flown both the 747 and 767.

No big difference as far as I'm concerned.

The sight picture is different due to cockpit height and length of fueslage (i.e. the 747 cockpit is higher and farther from the centerline--closer to the runway edge--during big crabs).

But the physical handling of the aircraft is pretty much the same.

...for whatever my opinion is worth...
zerozero is offline  
Old 4th Nov 2014, 04:38
  #15 (permalink)  
 
Join Date: Apr 2008
Location: nowhere
Posts: 0
Originally Posted by Kilda Ste Hilda View Post
According to her, based on personal observations and you tube videos, quads seem to handle better, stable and land reasonably well in strong crosswinds.
About 20 years ago I was on a vacation in LA on a very windy November day. It was a direct 30 knot crosswind. I decided to watch some aircraft land in LAX. There were many go-arounds but all were narrowbody and mostly 737. Some mentioned windshear. Not one of the 747's went around and there were quite a few.

The most interesting aircraft that made it in while I was there and I kid you not....A Beech 18.
JammedStab is offline  
Old 4th Nov 2014, 08:44
  #16 (permalink)  

Do a Hover - it avoids G
 
Join Date: Oct 1999
Location: Chichester West Sussex UK
Age: 86
Posts: 2,206
I have stressed initial response because very rapidly other factors come into play. The main ones being any control input following the gust arriving and the aerodynamic roll damping term present in the wing design.


As I said the behaviour after the initial response will be modified by any control input.

Don't forget autostabs as well as FBW will move the controls.

So I reckon the original notion that quads would be steadier than twins is probably most likely to be true if you have manual controls and no stabs or dampers! Those were the days.
John Farley is offline  
Old 4th Nov 2014, 09:21
  #17 (permalink)  
 
Join Date: Jun 2013
Location: Or-E-Gun, USA
Posts: 327
I Can Only Guess, So I Will...

In no particular order, the Big Quads have 2x-3x or more mass and thus are more stable, especially when already on a ~stable course. One responder notes that the Big Quads are usually driven by older, more experienced pilots. Those older, more (often FAR MORE) experienced drivers 'tend' to fly with a much lighter hand and, where appropriate, allow the embedded FBW systems to do their auto-correction before the human interface can react. Most recognize that current FBW systems react faster - and with a lighter hand than does the human.
That convoluted mouthful said, in a difficult, gusty x-wind approach, I'd much prefer to be in a heavy quad. Why? That older, more mature, more experienced driver is far more likely to call "Go Around and Divert," and simply get the heck out of Dodge City that is the light-weight driver. He did not become 'old' or accumulate 20K+ hours because he took risks just to keep the schedule intact. I'll always prefer to ride behind the light-handed, experienced 'old farts,' in a difficult situation. Ahem - just my two cents' worth. (I too am an old fart. I drive, but only little stuff. I've NEVER found it necessary to land under questionable conditions and yes, I've spent more than one night away from home, waiting for the weather to improve. The decisions to divert must have been good ones, because I'm still here to talk about it.
No Fly Zone is offline  
Old 4th Nov 2014, 09:27
  #18 (permalink)  
 
Join Date: Aug 2005
Location: fl
Posts: 2,561
"The most interesting aircraft that made it in while I was there and I kid you not....A Beech 18."

Now why doesn't that surprise me? It would be fun to watch most of these new age pilots land a Beech 18 in a 30 knot crosswind. I didn't get to fly one of these new generation planes with the tail wheel in the front until prepping for my PPL. They said I needed a plane with fancy instruments, radio and a battery for the check ride.

I still find learning in a tail dragger made all these fancy Boeing planes quite easy to land in 30 knot gusty crosswinds. The Beech 18 and Boeing 767 both land quite well using the same technique.
bubbers44 is offline  
Old 4th Nov 2014, 18:12
  #19 (permalink)  

Aviator Extraordinaire
 
Join Date: May 2000
Location: Oklahoma City, Oklahoma USA
Age: 72
Posts: 2,394
I still find learning in a tail dragger made all these fancy Boeing planes quite easy to land in 30 knot gusty crosswinds. The Beech 18 and Boeing 767 both land quite well using the same technique.
I landed a DC-3 in a 30kt crosswind one day, which was not planned trust me, and had more of a problem taxing in than I did landing.
con-pilot is offline  
Old 5th Nov 2014, 17:52
  #20 (permalink)  
PGA
 
Join Date: Dec 2003
Location: Europe
Posts: 253
I have flown 319 / 320 / 330-200 / 340-300 / 340-500 / 380-800 and I find in a crosswind they all handle almost exactly the same, must be the FBW. The 319 was easily over controlled, once again due to the FBW sometimes being a bit slow, but in essence there is no difference as far as I'm concerned.
PGA 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 - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.