Why is ice less likely to form on the wing tip and root of a Boeing 777?

[stan19]

For eg Boeing 777 , there's only anti ice feature on mid span of wing only, while wing root and tip area are not. Anyone know the reason why wing tip and root are less likely to form ice?

 

[Danger]

This is only a guess, so don't take it as fact. I've never looked into that, because I've never heard of it before. Mechanical de-icers always used to be along the leading edge. The spray-on ones cover the whole wing.
All that I can surmise without investigating is that in flight the 'bow wave' of the nose diverts airflow outside of the root area, while the inherent flexiblility of the wings will crack off stuff trying to form on the tips. Again, that's only speculation. Can't wait to see what Fred and his ilk have to explain it for real.

 

[chroot]

I have to speculate, because I don't know for sure... Perhaps because most of the lift is generated there, perhaps a change in airfoil shape is most catastrophic there.

Structural ice adds weight to an aircraft, and this is bad -- but, even worse, ice in the wrong place can change the shape of the leading edge of an airfoil, causing it to create much, much less lift that it should.

- Warren

 

[russ_watters]

The leading edge of the wing is the laminar region and thus the flow is most unstable. A small disruption just kills the lift whereas further back, the flow is turbulent and not as easily disrupted.

 

[stan19]

The leading edge of the wing is the laminar region and thus the flow is most unstable. A small disruption just kills the lift whereas further back, the flow is turbulent and not as easily disrupted.

i agree with wat u said, but my question is comparing the leading edge of the root,mid span and tip.

 

[chroot]

AFAIK, the root and tip are not aerodynamically shaped for efficient lift -- meaning the mid-span is where most of the lift is generated, and where icing would be the most problematic.

- Warren

 

[RainmanAero]

Hi Folks,

AFAIK, the root and tip are not aerodynamically shaped for efficient lift -- meaning the mid-span is where most of the lift is generated, and where icing would be the most problematic.

I always thought that the elliptical lift distribution was the holy grail, so that most of the lift is produced at the root, with a decreasing lift profile as you move outboard. This also serves to minimize the tip vorticity.

There could be another reason that the anti-icing (wing heater) system is centered at the middle of the wing... the fact that the 777's engines are wing-mounted at about that position. And hot bleed air is generally used to heat the wings. From this website:

http://www.meriweather.com/777/over/antiice.html

"Engine Anti-Ice System uses engine bleed air to heat the engine cowl inlets. Each engine has a dual loop Anti-Ice system duct leak detection system. If a leak is detected in an Anti-Ice duct, the affected engine Anti-Ice valves close. The wing Anti-Ice System provides bleed air to three leading edge slats on each wing. Wing Anti-Ice is only available in flight. If TAT is 10° C or above wing Anti-Ice operation is inhibited until 5 minutes after takeoff."

AFAIK, if you directly heat the middle of the wing with bleed air, you can generally keep the temp of the tip and the root above the freezing point where ice will not form over the lift-producing leading edge of the wing. Another aspect is that the further away from the engine (the heat source) that you try to transport the heat, the more heat (total energy) you will "steal" from the engine. So by not running the anti ice ducts too far away from the engines (just far enough) you minimize the total thermal load on the engine due to anti-ice heat demands.

I could be wrong, however.
Rainman

 

[Danger]

Hell of a post there, Rainman. To give you an indication of how long it's been since I was flying... I didn't even know that they were using the engines for de-icing. The last that I knew of was resistance heating from inside the wing. Thanks for the update.

 

[jaap de vries]

Although more lift is created near the root of the wing, wing tip stalling is actually more dangerous because it creates a stronger rolling moment around the longitudinal axis. In most wing designs the root angle of attack is therefore larger than at the tip.