Ups. I missed this thread.
I have one of only 2 hotshot commanders in Europe. The other is flying in Norway.
Robin Miley designed this system im 1988 and it got STCed in 1991.
He is sick and sold the whole business to Carl Lee. He is a nice and approachable chap.
I spend 17k on the kit and £8325 on installation. (just checked invoices)
It is a lot of money, but well worth it with my long range mission profile.
I’m very happy with the turbo, my commander is a complete different machine.
It turned from an anaemic plane that barely reached FL130 to doing 750fpm at FL 150.
In practice, in Europe, almost nobody achieves this.
That’s difficult indeed. A multi-aircraft syndicate probably comes closest, there are quite a few here with a very wide variety of aircraft, from microlight to multi-engine. But you won’t find a single-engine turbine on a larger syndicate, insurance costs would be prohibitive. But under certain conditions, German authorities allow “non commercial revenue flights (nichtgewerbliche Flüge gegen Entgelt)”. And I know of several JetProps (or similar) aircraft that can be hired from their corporate owners under such terms, usually much cheaper than a syndicate could offer them, because a lot of basic costs will be deducted from the owner’s taxes and not calculated into the flying hours. The downside is that the owner or his pilot will usually be PIC, but the ones I know would let you handle the controls, which saves you the time and cost for the annual IR checkride for the class rating.
to hire something else for the rare occasions when it might be required
The problems with that are
In an ideal world (cheap and plentiful hangarage, cheap landings, pilot colleagues who are nice reliable and have an excellent cheque book withdrawal-from-pocket reflex) one would keep a TB20 or whatever for short trips and have a Jetprop or a TBM syndicate with say 10 members. In practice, in Europe, almost nobody achieves this.
You volunteer to clean the toilet after somebody has done a “number two” on it, WN…
Been there, done it. But it would really be only for emergency use and passengers try to avoid it on their own as there is only a curtain for privacy…
…purely on improving your plane which you already (it has to be assumed) basically like and which you plan to keep for a long time.
Yes, sure, I understand that. But my approach, instead of dumping six figure numbers into that aeroplane trying to convert it into something that it will never be, to use it within it’s limitations and to hire something else for the rare occasions when it might be required. Just like my car: Many years ago, I investigated having a trailer hitch fitted so that I could haul some bricks with it or my horse in case it needs to be taken to the doctor. After doing the maths, I decided to leave the car as it is and hire a minivan or other suitable vehicle whenever I need it…
money does not have a cost these days.
Pass that one by me again….? 
They (and their passengers!) will love legroom, reclining seat backs, a toilet,
You volunteer to clean the toilet after somebody has done a “number two” on it, WN 
I was once reliably informed by a 421C owner that that is a real no-no.
But, seriously, just about all upgrades to aircraft cannot be justified financially and cannot be justified on the resale value, and the case for them hangs purely on improving your plane which you already (it has to be assumed) basically like and which you plan to keep for a long time.
The other option is you do it and fund it and own the STC
The third option would be to take the money for the STC and one turbo conversion and buy a Cessna 421 with that. Then generate income by renting it to TB20 owners around ypu for their longer trips in possible bad weather. They (and their passengers!) will love legroom, reclining seat backs, a toilet, no oxygen masks, no noise-reduction headsets, de-icing, weather radar, luggage space, no w&b issues and a few extra knots (not many though) – just kidding of course, but the amount of money required will be about equal, twin ratings for three pilots included.
The other option is you do it and fund it and own the STC. Then you market the STC via your trip reports (i.e. change it from “after 2h of climbing with 10fpm at 60kts” to “after passing FL250 10 minutes into the flight”) and find enough buyers to recover your costs.
Remember, interest rates are zero so money does not have a cost these days.
The main job would be to find 10 TB20 owners who are willing to stick their hands in their pockets.
If you can do that, the job is straightforward
The reasons one would not simply dump their TB20 and buy a TB21 include
You might also give Gomolzig in Germany a try. Have seen quite some heavy structural mods from them. They also make and design exhaust systems and are DOA, so they might be able to do the work. I don’t know if they do FAA as well, but you might be able to use the bilater agreement the other way around.
According to the website RCM uses exactly the same equipment as the TiO540 of my 114TC.
That means automatic wastegate.
