Volcanic ash / Saharan dust

[Sober Lark]

Why wouldn't Saharan dust plumes affect aviation in the same way as the widely dispersed volcanic ash we are currently experiencing?

Waking up to find your car covered in the reddish Saharan dust is quite a regular occurrence here at 53° N but to the best of my knowledge it has never inconvenienced aviation operations here.

[redsnail]

Volcanic ash is very abrasive whereas dust is not nearly as abrasive.

[flapassym]

Nearly but not quite. Saharan dust is made of sand, blunted by many years of rubbing up against other dust particles. It has a melting temperature of around 1350 C.

Most turbine engine tgt's are around 850 C.

Volcanic ash has a melting temp of around 600 C. it melts all over the cooling ducts of turbines thereby blocking them causing overheating and eventual failure.

The abrasive properties are an issue but not the main one.

[redsnail]

Thanks for that, I'll use it tomorrow explaining to the pax. (If we go flying...)

[Sober Lark]

Many thanks for your informative reply

[wascrew]

worked in the middle east many years ago and rumour was their engines cleaner/ better than european carriers due to the abrasiveness of the sand

maybe someone more clued up could elaborate

[dubh12000]

If you look at the turbine section, then yes they "look" cleaner but then again the sand would have had a detrimental effect on the gas path coatings. Airlines flying over deserts would always have indications of sand ingestion, generally showing up inside the cooled blading itself with silica deposits etc.

From a serviceability and repair perspective, sulphidation is a much more serious problem. It won't stop an engine, but it will scrap out a lot of blading at overhaul.

[PRD Area]

Regarding the abrasive properties of Sand vs. Volcanic Ash, if you had an electron microscope handy with samples of both available, you would be able to tell the difference in abrasiveness simply by looking at them. Fortunately, such images are also available online.

First, Sand:
http://www.futuretimeline.net/21stcentury/images/sand_grains_electron_microscope.jpg

Second, Volcanic Ash:
http://www.geo.mtu.edu/%7Eraman/Ashfall/Syllabus/Entries/2009/6/21_Formation_of_Ash_files/1137793565_1_11.jpg

However, as previously mentioned, the abrasion on the airframe and compressor blades in the engines is a secondary consideration to the melting of ash in the combustion chamber and turbine blades in the engines.