There are allegations that ACF-50 is not as good; specifically that it does not meet some US MIL spec which C-X meets.
However, C-X is almost unavailable in the UK. I tried to buy it a while ago (after I bought a used C-X spray kit which came with a load of the stuff still inside) but never got anywhere with the supposed UK distributor.
ACF-50 is much more available here.
So I used the old stuff up for lighting fires and put ACF-50 in there and used that ever since. It seems to work very well, remaining in place for a good 2 years plus where there is no strong airflow (e.g. inside the wings).
C-X was developed by Ed Kollin who also did Camguard, which works brilliantly.
This topic came up in relation to the new and infamous Socata horizontal stabiliser SB which requires drilling some holes, an endoscope inspection, and corrosion proofing using a specific (but unheard of) substance. Socata have also approved C-X for this and it is believed they also approve ACF-50.
I still think the SB is misguided and they should have gone for two holes in the end caps which would allow the entire HS to be treated with a simple spray nozzle. The current SB doesn't allow for the liquid (or mist) to reach the whole HS. I asked Socata about this a number of times but got no comment.
My 1979 aircraft has factory corrosion protection (the green chromate coat). Now the question is whether I should be applying ACF-50 / Corrosion X or not.
The shop tells me it's not really necessary given that I have the factory protection and no apparent corrosion.
The shop tells me it's not really necessary given that I have the factory protection and no apparent corrosion.
That is really bad advice.
The green primer will not last for ever, and there will be plenty of trigger points e.g. rivets which were not primed.
I use ACF-50 and it works well.
That is really bad advice.
Well, the advice isn't bad, it's true that it further protects the aircraft but is less urgent for an aircraft with factory corrosion protection than for an aircraft without.
I've been reluctant so far because from what I gathered, the stuff is quite nasty and the aircraft will smell and drip that stuff for some time after being treated. I wanted to first gather some firsthand experience about the stuff before I have it applied to my aircraft.
How often do you do it? How bad is the smell / contamination / drip? How much do you pay for it?
Obviously one does not spray it into the cabin cavity.
I spray the cavities of the wings, the vertical and horizontal stabilisers, the belly, and the engine compartment.
ACF-50 does smell a bit but not within the cockpit, even though there are obviously air paths into the cockpit from the wings etc.
The plane does drip with the stuff for some days afterwards, but not much because the stuff that goes in should be just mist (vapour).
About 1 litre does the whole TB20.
If you do the engine, don't start it for a few hours 
And avoid the exhaust pipes, alternator belt, and brake disks.
It's great stuff. I cannot see corrosion ever starting where this has been.
Factory corrosion proofing is just the green primer. It's not even 2-pack epoxy primer but even if it was there are many places where corrosion can start. Most factories rivet components after priming them separately...
Also most GA airframe structures are riveted dry i.e. no sealant inside skin mating surfaces so water can get in and stay in. Some of the TB20 was done wet (they use skin clamps until the stuff dries and then they put in the rivets - quite cunning) but most of it is still dry riveted.
Location makes a big difference on corrosion. My plane spent most of its life on the seeside (Shoreham), Achim's is kept far away from sea most of its time.
I think I remember seeing your Commander at Shoreham, many times. If it is the same one, it was grounded by ADs for many months at a time, when I was looking at what to buy.
Sure being parked outdoors at Shoreham would be a very bad idea.
The alternative point of view which I heard mentioned was that the saving on hangarage (say £6k/year) can pay for a respray every 2 years, and you get total access. But that doesn't address the avionics, and internal corrosion.
Location makes a big difference on corrosion.
Oh yes. My second home is on the Red Sea and that is the most corrosive environment you can imagine. Ordinary steel rusts within less than a week, the common Russian steel within a day. Stainless steel made in Russia lasts a few months, the European V2A maybe a year and only European V4A (316) lasts. Aluminium rusts quickly, too, similar to V2A. Unfortunately it is very difficult to get good stainless steel in Egypt and people take any kind of rubbish and sell it with a V4A sticker. I often use my luggage allowance to transport V4A steel plates. They are also not that easy to get in Germany because V4A is simply not needed here outside the food processing industry. My car (Japanese) rusted within a year while here we have cars that are 80 years old without any significant rust.
The Cessna special instructions (SIDs) have a corrosion map and set the inspection intervals based on where you are on that map. The size of the map is very small and it is of bad quality so one is quite flexible in determining the local corrosion level
I think I remember seeing your Commander at Shoreham, many times. If it is the same one, it was grounded by ADs for many months at a time, when I was looking at what to buy.
It is was this one. Previous owner ran short on money. He used to bimle only, which is not proper use of this kind of aircraft.
The alternative point of view which I heard mentioned was that the saving on hangarage (say £6k/year) can pay for a respray every 2 years, and you get total access. But that doesn't address the avionics, and internal corrosion.
The way they respray for this sort of money is not quality respray and 6k is too much for a year. I pay less.
