Aircraft ice protection method

1. A method of protecting an airfoil from undue ice accumulation during flight, said method comprising delay-rectifying steps for removing delay-induced ice accumulation and routine-deicing steps performed after the delay-rectifying steps;

wherein the delay-rectifying steps and the routine-deicing steps are performed by an electrothermal device comprising a parting strip (PS) and at least a first set of spanwise-aligned deicing zones, the parting strip (PS) being positioned to heat the leading edge region of the airfoil, the first zone set comprising an upper fore zone (UF 1 ), a lower fore zone (LF 1 ), an upper aft zone (UA 1 ), and a lower aft zone (LA 1 );

wherein the delay-rectifying steps comprise:

for a first time period (t 1 )

continuously heating the parting strip (PS),

continuously heating the first upper fore zone (UF 1 ),

continuously heating the first lower fore zone (LF 1 ),

not heating the first upper aft zone (UA 1 ),

not heating the first lower aft zone (LA 1 ),

wherein the routine-deicing steps comprise:

continuously heating the parting strip (PS),

intermittently heating the first upper aft zone (UA 1 ),

intermittently heating the first lower aft zone (LA 1 ).

2. A method as set forth in claim 1 , wherein the routine-deicing steps further comprise:

intermittently heating the first upper fore zone (UF 1 );

intermittently heating the first lower fore zone (LF 1 ).

3. A method as set forth in claim 1 , wherein the electrothermal device further comprises a second set of spanwise-aligned deicing zones, the second zone set comprising an upper fore zone (UF 2 ), a lower fore zone (LF 2 ), an upper aft zone (UA 2 ), and a lower aft zone (LA 2 );

wherein the delay-rectifying steps further comprise:

for a second time period (t 2 ) after the first time period (t 1 ):

continuously heating the parting strip (PS),

continuously heating the second upper fore zone (UF 2 ),

continuously heating the second lower fore zone (UL 2 ),

not heating the second upper aft zone (UA 2 ),

not heating the second lower aft zone (LA 2 );

wherein the routine-deicing steps further comprise:

intermittently heating the second upper aft zone (UA 2 ),

intermittently heating the second lower aft zone (LA 2 ).

4. A method as set forth in claim 3 , wherein the routine-deicing steps further comprise:

intermittently heating the first upper fore zone (UF 1 ),

intermittently heating the first lower fore zone (LF 1 ),

intermittently heating the second upper fore zone (UF 2 ),

intermittently heating the second lower fore zone (LF 2 ).

5. A method as set forth in claim 3 , wherein the delay-rectifying steps further comprise:

during the first time period (t 1 ), not heating the second set of zones (UF 2 , LF 2 , UA 2 , LA 2 );

during the second time period (t 2 ), not heating the first set of zones (UF 1 , LF 1 , UA 1 , LA 1 ).

6. A method as set forth in claim 5 , wherein the routine-deicing steps further comprise:

intermittently heating the first upper fore zone (UF 1 ),

intermittently heating the first lower fore zone (LF 1 ),

intermittently heating the second upper fore zone (UF 2 ),

intermittently heating the second lower fore zone (LF 2 ).

7. A method as set forth in claim 3 , wherein the electrothermal device further comprises a third set of spanwise-aligned deicing zones, the third zone set comprising an upper fore zone (UF 3 ), a lower fore zone (LF 3 ), an upper aft zone (UA 3 ), and a lower aft zone (LA 3 );

wherein the delay-rectifying steps further comprise:

during a third time period (t 3 ) after the second time period (t 2 ),

continuously heating the parting strip (PS),

continuously heating the third upper fore zone (UF 3 ),

continuously heating the third lower fore zone (LF 3 ),

not heating a third upper aft zone (UA 3 ),

not heating a third lower aft zone (LA 3 );

wherein the routine-deicing steps further comprise:

intermittently heating the third upper aft zone (UA 3 ),

intermittently heating the third lower aft zone (LA 3 ).

8. A method as set forth in claim 7 , wherein the routine-deicing steps further comprise:

intermittently heating the first upper fore zone (UF 1 ),

intermittently heating the first lower fore zone (LF 1 ),

intermittently heating the second upper fore zone (UF 2 ),

intermittently heating the second lower fore zone (LF 2 ),

intermittently heating the third upper fore zone (UF 3 ),

intermittently heating the third lower fore zone (LF 3 ).

9. A method as set forth in claim 7 , wherein the delay-rectifying steps further comprise:

during the first time period (t 1 ), not heating the second set of zones (UF 2 , LF 2 , UA 2 , LA 2 ) and not heating the third set of zones (UF 3 , LF 3 , UA 3 , LA 3 );

during the second time period (t 2 ), not heating the first set of zones (UF 1 , LF 1 , UA 1 , LA 1 ) and not heating the third set of zones (UF 3 , LF 3 , UA 3 , LA 3 );

during the third time period (t 3 ), not heating the first set of zones (UF 1 , LF 1 , UA 1 , LA 1 ) and not heating the second set of zones (UF 2 , LF 2 , UA 2 , LA 2 ).

10. A method as set forth in claim 9 , wherein the routine-deicing steps further comprise:

intermittently heating the first upper fore zone (UF 1 ),

intermittently heating the first lower fore zone (LF 1 ),

intermittently heating the second upper fore zone (UF 2 ),

intermittently heating the second lower fore zone (LF 2 ),

intermittently heating the third upper fore zone (UF 3 ),

intermittently heating the third lower fore zone (LF 3 ).

11. A method as set forth in claim 1 , wherein the electrothermal device further comprises chordwise strips (IP) isolating adjacent inter-set zones, and wherein these zone-isolating strips (IP) are heated continuously during the routine-deicing steps.

12. A method as set forth in claim 11 , wherein the zone-isolating strips (UPS, LPS) are continuously heated during the delay-rectifying steps.

13. A method as set forth in claim 1 , wherein the intermittent heatingsteps are performed so three or less zones are intermittently heated at the same time.

14. A method as set forth in claim 13 , wherein the intermittent heatingsteps are performed so two or less zones are intermittently heated at the same time.

15. A method as set forth in claim 14 , wherein the intermittent heatingsteps are performed so only one zone is intermittently heated at a time.

16. A method as set forth in claim 1 , wherein the delay-rectifying time period (t 1 ) is based on an outside air temperature reading.

17. A method as set forth in claim 1 , wherein the parting-strip continuously heating steps are performed at a temperature T delay during delay-rectifying steps and at a temperature T deicing during routine-deicing steps,

wherein the delay-rectifying temperature T delay is greater than the routine-deicing temperature T deicing .

18. A method as set forth in claim 17 , wherein the delay-rectifying temperature T delay is greater than the routine-deicing temperature T deicing by at least about 30° F. and/or about 11° C.

19. A method as set forth in claim 1 , wherein the parting strip (PS) has a width of between about 0.5 inch to about 1.0 inch and/or about 12 mm to about 26 mm.