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re-polishing leading edge skin

re-polishing leading edge skin

(OP)
While in HMV environment one customer requested re-polishing of all nose skins on L/E slats, Vertical Stabilizer, Inlet Cowls, to improve appearance (no damage, such as scratches/gouges/nicks, have been noted).
L/E slat nose skin: 0.063" thick, chem milled to 0.040", 7075-T6.
Inlet Cowl lip skin: 0.092" thick, 2219-T62.
Vertical Stabilizer: composite metallic structure, Outer skin is 0.100" thick chem milled, 2024-T3 Clad.
I am looking for a technical argument not to do the re-polishing.

RE: re-polishing leading edge skin

Out of my league, but, there was an article several decades ago about providing a 'pebbled' surface that reduced drag by affecting the point of flow separation...

Dik

RE: re-polishing leading edge skin

polishing L/Es is an issue. Many a/c have nice pretty L/Es. The OEM MM should include limits for polishing as it removes material and so reduces birdstrike strength.

If the airplane usually has polished L/Es then there should be MM limit on polishing. Maybe the OEM didn't anticipate owners wanting to polish the L/E and so never investigated this ? If there is no limit in the MM you could ask the OEM. Possibly your plane has "after-market" (STC) installed L/Es that are nice and pretty. Then ask the STC holder.

This should give you guidance to go ahead or not.

another day in paradise, or is paradise one day closer ?

RE: re-polishing leading edge skin

I recall 30 years ago some pilots had the great idea of Polishing their DC-3. They obviously been watching some old movies & thought that this would make their aircraft 'standout in a crowd'. Never to dissuade ambition - we provided the rags, polish & ladders for the exercise .. After a long 10 hour day .. they managed to get the nose cone of the aircraft looking pristine. This was the last of 'Polishing' we had to listen to ..
- If you are a HMV - 3rd party .. what is the issue ? Mucho billable hours & employing relatively low skill manpower.
- If HMV is part of the same company then the polishing crew will start discovering all types of issues such as pitting, loose rivets, dents, cracks, & will make a mess of the hanger during the exercise - because polishing is messy!
- just indicate to upper management a 'generous' amount of Manhours & Out-date departure delay .. & the problem will go away ..

RE: re-polishing leading edge skin

didn't one of the US airlines swap to a no paint finish to save weight ? and then switched back to paint ??

another day in paradise, or is paradise one day closer ?

RE: re-polishing leading edge skin

There is also the little matter of polishing away the pure aluminum after several polishing's and getting increased corrosion on the remaining duralamin.
B.E.

You are judged not by what you know, but by what you can do.

RE: re-polishing leading edge skin

B-52s and KC-135s early on were kept polished to survive in a nuclear environment.

After several years of polishing, the cladding was worn thru and rampant corrosion became a maintenance nightmare.

As I recall, most Boeing jets with unpainted/polished leading edges do NOT have aluminum... they are stainless steel or titanium.

Many turbine engine inlet lips [heated] that were anodized aluminum also do NOT survive very long due to atmospheric abrasion. A special heat/abrasion resistant 'lip-skin' coating [AMS3604] is applied to eliminate corrosion and maintain a clean/decorative appearance for a extended length of time... at the cost that when this coating is properly applied... it is for all practical purposes permanent.

I THINK that it MIGHT be possible to polish aluminum, then quickly apply a clear conversion coating... such as MIL-DTL-5541 class 3... or a B-52s and KC-135s early on were kept polished to survive in a nuclear environment.

After several years of polishing, the cladding was worn thru and rampant corrosion became a maintenance nightmare.

As I recall, most Boeing jets with unpainted/polished leading edges DO NOT have aluminum skins... they are stainless steel [or titanium?].

Many turbine engine inlet lips [heated] that were anodized aluminum also do NOT survive very long due to atmospheric abrasion: abrasive pitting wears away all anodize finishes sooner or later. A special heat/abrasion resistant 'lip-skin' coating [AMS3604] is applied as a primary [or post-production repair] coating to eliminate corrosion and maintain a clean/decorative appearance for an extended length of time... at the cost that when this coating is properly applied... it is for all practical purposes permanent [touch-up only... stripping VERY difficult].

I THINK that it MIGHT be possible to: [a] polish the aluminum; then [b] quickly apply a clear conversion coating such as MIL-DTL-5541 class 3... or a [clear/un-tinted] silane-based surface prep such as s 3M AC-130 or -131 or PRC-DeSoto EAP-9 or -12; then [c] apply a clear polyurethane topcoat. But I couldn’t fathom a guess as to how-long this coating would maintain the sparking-bright appearance. At least this coating would look polished AND be sorta maintainable.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

RE: re-polishing leading edge skin

Looks like you repeated things WKTaylor, smile

RE: re-polishing leading edge skin

KS... dohooooo... rednosemy fingers were faster than my brain this morning.

OK, I admit it... I tend to go-off-line [into MS word] for longer posts simply because I have 'lost several long drafts' due to computer glitches and unforeseen aws*ts, my part. In this case my haste to cut/paste W/O editing kicked my butt kicked my butt kicked my butt kicked my butt.

Here is what I actually meant to say...
----------
B-52s and KC-135s early on were kept polished to survive in a nuclear [flash] environment. After several years of polishing, the cladding was worn thru and rampant corrosion became a maintenance nightmare [all skins].

As I recall, most Boeing jets with unpainted/polished leading edges DO NOT have aluminum skins... they are stainless steel [or titanium?].

Many turbine engine inlet lips [heated] that were [thick] anodized aluminum also do NOT survive very long due to atmospheric abrasion: abrasive pitting wears away all anodize finishes sooner or later. A special heat/abrasion resistant 'lip-skin' coating [AMS3604] is applied as a primary [or post-production repair] coating to eliminate corrosion and maintain a clean/decorative appearance for an extended length of time... at the cost that when this coating is properly applied... it is for all practical purposes permanent [touch-up only... stripping VERY difficult].

I THINK that it MIGHT be possible to: [a] polish the aluminum; then [b] quickly apply a clear conversion coating such as MIL-DTL-5541 class 3... or a [clear/un-tinted] silane-based surface prep such as s 3M AC-130 or -131 or PRC-DeSoto EAP-9 or -12; then [c] apply a clear polyurethane topcoat. But I couldn’t fathom a guess as to how-long this coating would maintain the sparking-bright appearance. At least this coating would look polished AND be sorta maintainable.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

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