how long would it take to clean off that filth?
Glojo,
Much as I enjoy many of your posts, this time you're mistaken. The aircraft wash takes less than an hour (depending on how many people are involved), but what does take time is the re-greasing of all the moving parts which inevitably get sprayed with water and foam as the upper parts of the airframe get cleaned.
Because of the Working At Height regulations, any work on the rotor head etc has to be done in the hangar, surrounded by staging. This is not the fault of either the RAF or the SKIOS engineers, many of whom find the WAH restrictions frustrating. If the aircraft is in the hangar surrounded by staging, it cannot be off the ground within 15 minutes - therefore the aircraft cannot be washed on 1st Standby. If both aircraft are serviceable at once, then one aircraft can be washed, but as soon as one breaks, the other one won't get washed (plus of course the engineers are busy fixing the broken one). And before anyone starts, while the aircrew could indeed help the busy engineers by washing an aircraft, noone will trust us to do the re-grease etc!
Another issue at this time of year is that the hoses etc in the aircraft wash pan can freeze meaning that washes have to be deferred. Been a bit chilly in north-east England lately, I believe? Frankly the airframe in the picture is much cleaner than many I have seen!