"OIL CAN"

[phugoid]

RE PRIMARY ALL METALLIC FLIGHT CONTROL SURFACES, SUCH AS AILERONS, ELEVATORS, RUDDERS OF AN AGING LARGE TRANSPORT FLEET AND PROVIDED INTERNAL AND EXTERNAL STRUCTURAL INTEGRITY HAS BEEN CONFIRMED/ASSURED BY CLOSE VISUAL INSPECTION AIDED BY BOROSCOPE AS REQUIRED; WHAT CONSTITUTES IF ANY, AN ACCEPTABLE LEVEL OF SKIN "OIL CAN"?

DOES SKIN "OIL CAN" CONDITION APPRECIABLY EFFECT OR SHIFT DESIGN SPEED (CONFIRMED BY FLT TEST) THRESHOLD AT WHICH FLUTTER WILL OCCUR?

SHOULD "OIL CAN" CONDITION BE INTERPRETED AS LOSS OF CONTROL SURFACE RIGIDITY/STIFFNESS, ALL ELSE BEING EQUAL AND INCLUDING PROPER MASS BALANCING, PARTICULARLY AND WHEN OPERATING AT SUBSONIC MACH NUMBERS?

DOES CONVEX VS CONCAVE "OIL CAN" MAKE A DIFFERENCE RELATIVE TO RIB CAPS TO WHICH SKINS ARE FASTENED?

DOES CLICKING OR RECOILING "OIL CAN" WHEN DEPRESSED BY MODERATE FINGER/HAND PRESSURE CONSTITUTE LOSS OF SURFACE INTEGRITY?

DOES "OIL CAN " PERPENDICULAR (PARALLEL TO RIB(S)) OR TRANSVERSE TO CONTROL SURFACE SPAN, EFFECT FLUTTER PROPENSITY?

DOES "OIL CAN" APPRECIABLY AFFECT CONTROL SURFACE DESIGN ENVELOPE AND THEREBY AEROELASTIC STABILITY?

IN GO, NO-GO REPAIR CONTEXT, MUST "OIL CAN" BE CONSIDERED A POTENTIAL FLUTTER EXCITER IN ALL CASES, REGARDLESS OF "OIL CAN" AREA SIZE?

TO DATE, BOEING AND FORMER MDC SRMs ONLY ADDRESS "OIL CAN" CONDITION IN 2360 PRESSURE BULKHEAD, KEEL BEAM AND NOSE WHEEL PRESSURE BULKHEADS. MAINTENANCE MANUALS AND COMPONENT MAINTENACE MANUALS DO NOT ADDRESS THE CONDITION FROM EITHER AN INSPECTION CRITERIA AND OR REPAIR REQUIREMENT STAND POINT.

 

[rb1957]

NO NEED TO SHOUT ...

oil canning is permanent buckles in the thin sheet metal skin; in our case, of a control surface.

the buckles significantly weaken the skin and reduce the shear stiffness of the sheet and the control surface.

the flight tests that confirmed the design speed would certainly have been unbuckled.

the OEM documentation for control surfaces doesn't mention oil canning 'cause none is acceptable.

i'd prefer that you didn't poke the buckles through, nice though the "clicking" sound maybe, as you're just weakening the structure further.

 

[WKTaylor]

phugoid...

WHAT TYPE AIRCRAFT ARE YOU REFERING TO????????????? PLEASE BE SPECIFIC!!!!!!!!!!!!!

Also... what is the unsupported skin thickness and worst case W x L of the skin bay?????

Most large acft that I deal with have a skins with a very high percentage of surface area reinforced with bonded-on or riveted-on stiffeners/doublers or have honeycomb construction [etc]. VERY few large or high performance aircraft will have open areas of unsupported skins in flight control surfaces, for reasos You cited... and more.


Regards, Wil Taylor

 

[phugoid]

TAYLOR,
PER YR RQST:

DC10-10,-30 SERIES

REF. DAC DWG NRC6041 OUTB AILERON ASSY
REF. DAC DWG ARC1111 SKIN ASSY

SKIN .016" 2024-T3 CLAD SHEET
FINGER DOUBLER .012" 2024T3 CLAD SHEET

FINGER DOUBLER BONDED PER DPS 1.950 TO SKIN PRIOR TO AILERON ASSEMBLY

SKIN BAY IS 5.0" WIDE X APPROX 36.0" LONG, DEPENDING ON SPAN LOCATION

OILCANNED AREA SPANS FROM STA XOA 902.750 TO APPROX STA XOA 949.853

PROGRESSES FROM FORWARD OF TRAILING EDGE WEDGE TO APPROXIMATELY MID SPAN.

 

[rb1957]

is the surface waviness within the aerodynamic tolerance ?

as with most things, how did this happen ? could something else (under the surface?) also be bent ??

i suspect that the strength of the aileron is still sufficient, i'd worry more about the stiffness (aero-elasticity).

what do the "boys at (douglas)boeing" have to say ?

 

[WKTaylor]

Phugoid..

Does the oil-can effect travel across the ribs... or does each bay display it's on effect? IE: when You cycle one bay by hand, does an adjacent bay respond?

Are there any loose rivets? Any cracks discovered, anywhere on the surface(s)?

Is this confined to one side or both sides (top, bottom or both) and is this confined to just a few, or all, DC-10 ailerons?

How long has/have the aileron(s) been in service? Any known overstress? If confined to one aileron, has it been checked for overall alignment (distortion)?

Are You absolutely CERTAIN the internal doublers are not disbonded??

Have You contacted Boeing-LGB service engineering with this question???

Regards, Wil Taylor