Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Gloss Loss  
User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Posted (5 years 1 month 2 weeks 1 day 13 hours ago) and read 2399 times:

When unpainted aircraft flight surfaces (wings, fuselage, fairings, etc) age and lose their gloss over 20 years of operation, what typical % drag increment do they generate? Does anyone know of any technical studies of this matter?

Faro


The chalice not my son
11 replies: All unread, jump to last
 
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (5 years 1 month 2 weeks 22 hours ago) and read 2303 times:



Quoting Faro (Thread starter):
When unpainted aircraft flight surfaces (wings, fuselage, fairings, etc) age and lose their gloss over 20 years of operatio

Most of those surfaces are painted. The normal repaint schedule should take care of it. For the case of bare aluminum fuselages, they polish them on a periodic basis.

Tom.


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 2, posted (5 years 1 month 2 weeks 13 hours ago) and read 2262 times:



Quoting Faro (Thread starter):
When unpainted aircraft flight surfaces (wings, fuselage, fairings, etc) age and lose their gloss over 20 years of operation, what typical % drag increment do they generate? Does anyone know of any technical studies of this matter?

The reason they lose there gloss (shine) is because the operators don't take care of them. Look at AA MD-80's:


View Large View Medium
Click here for bigger photo!

Photo © Gabriel Widyna



User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 3, posted (5 years 1 month 2 weeks 12 hours ago) and read 2252 times:

Which is funny since shiny surfaces are slicker and therefore generate less drag, I would have thought it a priority to shine up the surfaces relatively frequently...

Faro



The chalice not my son
User currently offlineKlemmi85 From Germany, joined Mar 2009, 210 posts, RR: 0
Reply 4, posted (5 years 1 month 2 weeks 12 hours ago) and read 2235 times:

Well, I might be wrong, BUT....

the AA livery doesn't look like someone goes out after every flight and makes em shiny. I rather suspect it to be some kind of chrome layer?!

Additional paint = additional weight = additional fuel burn. As for the wings for example, well... I don't believe they polish the wings, do they? That oughta be some ugly job. Imagine you had to polish a 744 / A380 wing, would be some work to do  Smile


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 5, posted (5 years 1 month 2 weeks 11 hours ago) and read 2224 times:



Quoting Klemmi85 (Reply 4):
the AA livery doesn't look like someone goes out after every flight and makes em shiny. I rather suspect it to be some kind of chrome layer?!

The skins are polished aluminum. No chrome, no plastic coating, just 2024 alclad aluminum.


User currently offlineOly720man From United Kingdom, joined May 2004, 6685 posts, RR: 11
Reply 6, posted (5 years 1 month 2 weeks 11 hours ago) and read 2221 times:

If you can get hold of a book called Boundary Layer Theory, by Schlichting, there are graphs that relate the skin friction coefficient to the Reynolds number for different roughness heights. The effect on drag (skin friction coefficient) is highest when the roughness height is comparable to the height of the boundary layer (or laminar sublayer) which is on the wing leading edge and on the nose of the aircraft where the boundary layer is very thin. Further down the aircraft, the roughness is considerably smaller than the boundary layer and the surface (drag wise) behaves as if it is smooth.

Other work has been done, e.g. A.D. Young, The drag effects of roughness at high subcritical speeds, J Royal Aeronautical Society, V18, p534, 1950, that looked at the roughness of camouflage paint and the conclusions agreed with the graphs indicated above.

As for an absolute value for the change in drag, it would be necessary to integrate the change in skin friction coefficient over the whole surface to get an idea. I'd imagine it's in the 0-1% range, if that, i.e. in the noise of operational variation. I'm sure the bean counters watch each aircraft's performance and if the drag rise was that apparent, in terms of fuel use, for example, more planes would be polished more often.



wheat and dairy can screw up your brain
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (5 years 1 month 2 weeks 10 hours ago) and read 2209 times:



Quoting Faro (Reply 3):
Which is funny since shiny surfaces are slicker and therefore generate less drag, I would have thought it a priority to shine up the surfaces relatively frequently...

Simply loosing the gloss is probably not a big enough impact on fuel burn to notice since, as Oly720man very nicely pointed out, the boundary layer is way thicker than that over most of the airplane. That's one of the reasons you can get away with button-head rivets at the back.

Duration-of-gloss is one of the specifications on aircraft paint, and aircraft do have a periodic paint/wash schedule (or polish schedule for bare fuselage).

Quoting Klemmi85 (Reply 4):
the AA livery doesn't look like someone goes out after every flight and makes em shiny. I rather suspect it to be some kind of chrome layer?!

Nope, just pure aluminum. 2024 clad is mostly 2024 with very thin layers of pure aluminum sandwiched to the surfaces.

Quoting Klemmi85 (Reply 4):
Additional paint = additional weight = additional fuel burn. As for the wings for example, well... I don't believe they polish the wings, do they? That oughta be some ugly job. Imagine you had to polish a 744 / A380 wing, would be some work to do

The wings are painted, not bare.

Tom.


User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 8, posted (5 years 1 month 2 weeks 10 hours ago) and read 2207 times:



Quoting Oly720man (Reply 6):
If you can get hold of a book called Boundary Layer Theory, by Schlichting, there are graphs that relate the skin friction coefficient to the Reynolds number for different roughness heights. The effect on drag (skin friction coefficient) is highest when the roughness height is comparable to the height of the boundary layer (or laminar sublayer) which is on the wing leading edge and on the nose of the aircraft where the boundary layer is very thin. Further down the aircraft, the roughness is considerably smaller than the boundary layer and the surface (drag wise) behaves as if it is smooth.

Other work has been done, e.g. A.D. Young, The drag effects of roughness at high subcritical speeds, J Royal Aeronautical Society, V18, p534, 1950, that looked at the roughness of camouflage paint and the conclusions agreed with the graphs indicated above.

Many thanx, I'll try to get a hold of that. I was also guessing around 1% maximum drag increment, I would also guesstimate that most of that is "frontal" drag on the nose section and wing/empennage leading edges.

Quoting Oly720man (Reply 6):
I'm sure the bean counters watch each aircraft's performance and if the drag rise was that apparent, in terms of fuel use, for example, more planes would be polished more often.

I'm sure they do, being a bean counter myself albeit not of the aeronautical genus. I understand that their monitoring also takes into account those minute skin surface undulations which tend to develop over time and especially on the fuselage skin due to pressurisation cycles.

Faro



The chalice not my son
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 9, posted (5 years 1 month 2 weeks 10 hours ago) and read 2199 times:



Quoting Tdscanuck (Reply 7):
The wings are painted, not bare.

Only the wing box and composite parts, the slats, flaps and aluminum (honeycomb) panels are polished.


View Large View Medium
Click here for bigger photo!

Photo © John Muzic



User currently offlineFaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 10, posted (5 years 1 month 2 weeks 10 hours ago) and read 2195 times:



Quoting 474218 (Reply 9):
Quoting Tdscanuck (Reply 7):
The wings are painted, not bare.

Only the wing box and composite parts, the slats, flaps and aluminum (honeycomb) panels are polished.

Reminds me of an article I had read some 20 years back: European types were quoted as being highly resistant to corrosion because they were painted over almost everywhere whereas American airliners were deemed not as resistant because they showed more bare metal in the undersides. I guess by now corrosion resistance is pretty much the same on both sides of the pond.

Faro



The chalice not my son
User currently offlineKlemmi85 From Germany, joined Mar 2009, 210 posts, RR: 0
Reply 11, posted (5 years 1 month 2 weeks 7 hours ago) and read 2162 times:



Quoting Tdscanuck (Reply 7):
Nope, just pure aluminum. 2024 clad is mostly 2024 with very thin layers of pure aluminum sandwiched to the surfaces.

Always learning something more, thanks  Wink


Top Of Page
Forum Index

Reply To This Topic Gloss Loss
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Hull Loss Incidents With No Fatalities posted Tue Jun 10 2008 15:19:28 by Askr
B752 Slat Loss Sensor posted Sat Apr 12 2008 02:54:41 by HAWK21M
Implications Of Total Avionics Loss T7--- posted Thu Jan 17 2008 10:43:30 by ImperialEagle
Trip Profit + Loss Computation posted Thu Sep 13 2007 14:28:26 by Faro
Severe Loss Of IAS During Cruise Flight posted Tue Apr 17 2007 06:59:51 by Fly727
Loss Of Cabin Pressure, Why No Masks? posted Wed Apr 4 2007 22:45:35 by Boston92
Partial Loss Of Wing posted Thu Feb 2 2006 20:48:32 by EGGP
Loss Of Pilot's License posted Sat Oct 29 2005 21:00:01 by Airfoilsguy
Loss Of Air Pressure posted Mon May 9 2005 15:52:55 by Eatmybologna
B767 Exits With Complete Power/hyd Loss? posted Sun Apr 3 2005 14:02:28 by Geoffm

Sponsor Message:
Printer friendly format