A 3:00 gour flight through icing is no problem as far as capacity is concerned.
However, if you buy the fluid at the standard aviation price, you will be spending as much on the fluid as in IFR route charges when flying a TBM900 
I also think that a 3hr flight through IMC / icing conditions will be long enough to encounter the sort of hazards for which a radar is worth having. Debatable, of course… I can see it happening if you don’t have an IR and have to fly VFR OCAS … one spends a lot of time in IMC when doing that (been there, done it).
Nope
Killfrost 25L drum is Euro 121,- ex VAT. This is the real stuff.
I do not need 25l for a 3 hour flight.. A lot less.
Also … anybody who wants to undertake a 3 hour flight in a light single with 3 hours of real icing better book a hotel. I have flown flights where the tks system was running continuously. However this was more light rime than icing.
I suppose it depends upon what you are trying to achieve and the specific aircraft. From my perspective, I’m talking about a DA42 undertaking aerial work. At best you will get about 2:15 from 30l of TKS and, if the amount of icing is significant, this number could reduce to as little as 0:20! Importantly, the equipment is described by Diamond as an anti-icing system rather than a de-icing system. There is also the question of replenishment whereby you have to ensure stocks are available.
Our other aircraft, a PA31 Chieftain, will go on forever in icing (apart from rain ice) although there is an obvious disadvantage in that it burns 160l of AVGAS an hour as opposed to the DA42’s 40l of Jet!
Chieftains put in a good effort in icing, I’ve spent hours in icing in one also without much bother. Have had a couple of ‘moments’ though when the aircraft got heavy enough that it was towards blue line to remain level, that was go home time.
This is a more generic comment on TKS so I am posting it here rather than in the TB20 TKS thread.
The funny observation is that the TKS system burns money faster than the engine.
Both get through something like 40 litres per hour, and TKS fluid is roughly 2x more expensive than avgas
Also one thing, which may be obvious to old-timers with TKS, is that you really cannot plan to need it for enroute flight. You cannot even cross the Alps in IMC (e.g. prob90 icing conditions) with it.
I always said it that it is potentially expensive. First of all, you really need to find the lowest possible €/l solution there is. I have been brewing my own TKS fluid for many years, with good results.
But the bigger factor is the usage of the system. I use it really little. The trick is to really continue to fly as if you didn’t have the system, i.e. ALWAYS find VMC / non icing conditions. No way I would accept to fly an enroute/level flight portion of a flight in icing conditions. All I use the TKS for is to avoid ice build up when puching through clouds during climb and dscents. I use very little TKS fluid.
[Thermawing] … is only just warm enough, so the water can run off and freeze further back.
Not quite. Thermawing does not have enough power to keep the leading edges warm and ice free. Instead, ice is allowed to accumulate. it cycles sections of the leading edge so they warm up very quickly to liquify the boundary ice layer, and the airflow is then carrying the ice off.
Also thermawing never got any STCs, AFAIK, other than the Cessna 400, and there were loads of problems on that one in the early days. Whereas TKS has always worked since the beginning.
I have been brewing my own TKS fluid for many years, with good results.
How do you do it?
Someone very kindly gave me a load of TKS fluid (the pricey branded stuff) for my 60th birthday and later I bought an even larger amount from a guy who crashed his plane (but survived; not sure if he will fly again, sadly). The latter was blended by some chemical outfit and came from Far North in Scotland. That lot was originally bought for quite a bit less than the branded version. I am now about halfway through it and in a year or two will need to source maybe a 200 litre drum.
I have a 1 micron filtration setup which makes sure that no crap ends up in the TKS tank and ends up bunging up the filters at the pump, which like everything from CAV are no doubt very pricey. This also makes it very convenient to move the stuff because any container bigger than about 10 litres is too heavy to move about easily. I just pump the stuff into 5 litre containers, via the filter.
Well, the ingredients / mixture recipe is public, and very simple. I didn’t brew it myself, but gave the instructions to a chemical laboratory and ordered 100 litres. Again, it’s very simple stuff.
I am in the process of installing TKS. I will report on it when its done, target is mid June. Order time for the kit was about 5 months.
The process looks like this:
http://www.flyabonanza.com/TKS_Deice.html#grid
