Even Airbus and Boeing use it in case everything else fails ...
Update:
This extract http://peter-ftp.co.uk/aviation/misc-euroga/IO-540-C4D5D-Series-Parts-Catalog.pdf from the IO-540-C4D5D shows that it has a very different accessory gearbox to the IO-540-C family.
The -C can have the alternator installed using the 71675 hydraulic pump adapter – a standard Lyco part which is about $1500. The -C family have a big hole for the spare accessory point, just for this sort of thing.
This pic shows the B&C alternator and the hydraulic pump adapter together
But the -C4D5D’s spare accessory drive point can’t take that adapter. Instead it has a standard size vacuum pump drive, which seems great because that’s exactly what the B&C alternator needs, but to save a few bucks Lyco fit a blank shaft in there, as per item 25 here http://peter-ftp.co.uk/aviation/misc-euroga/IO-540-C4D5D-Series-Parts-Catalog.pdf. Had they fitted item 17 in place of item 25, the alternator could be fitted directly!
I might still take off the accessory drive blanking plate and see what is behind it but unless somebody at Lyco was feeling charitable on the day, I know what I am going to find…
So this is a job for when the engine comes out – probably an overhaul in a few years’ time.
Doesn’t stop me going for the 337 field approval in the meantime however…
It’s bizzare that despite about 30 emails with a Lyco “engineer” (not as intelligent as this one http://goo.gl/AV7BOS) nobody there seems to know anything about this. They could have just told me straight…
But unless you are going for TKS with heavy power consumption or planning to cross the Atlantic why do you need two alternators? You can get enough standby power for basic navigation to get you down…either with portables or a plug-in battery pack…no need for any mods….seems like a waste of time and money to me….what is your motive?
Why would anybody want two alternators?
To continue a flight to the destination, without much concern, if the main one packs up.
One can fly on with a handheld radio and GPS etc but one can’t fly an ILS with those, unless I suppose you have that handheld which does that also…
But yes I am not pulling out the engine just to do this. Too much hassle.
TKS doesn’t need significant power. You may be thinking of the system that electrically heats the leading edges – that one has a second alternator which outputs a few kW, just for that purpose.
A lot of people have looked at this project, on the TB20, and all have failed. There is some “information” around suggesting that e.g. the crankcase needs to be machined, which as far as I can tell is nonsense and the solution is much simpler.
I have just spent four days in a rented hangar, doing (with an A&P/IA) the mother of all Annuals.
We took the opportunity to finally open up the mysterious 3rd accessory drive point.
As suspected, Lyco put a blank shaft in there…
So the only solution to this is to wait till the engine overhaul, because removing the accessory gearbox case in situ is a big and risky job, and may be impossible.
The B&C standby alternators that I have been benchtesting, deliver far less output power than advertised, about 6/7 Amps @ 3500 RPM, which is only about 1/3 of the rated output.
I aswell think that an emergency battery would be a better and more affordable solution. Only if it is possible to use two large alternators I would prefer an alternator. This is done on some Cirrus and Rockwell Commander for example.
Far most important I reckon is to make sure you have a good warning system, which actually measures bussvoltage. With older Cessna’s an alternator failure is very easy to go undetected. This is also true for some Piper’s. Early detection will give you possibility to reduce load at an early stage.
From my memory the warning on the TB is also a warning based on buss voltage.
What alternator model was it, and was the 3500 the engine RPM or the alternator RPM?
Yes – the TB20 warning detects the bus voltage.
Don’t remember exact P/N, but was B&C generator used on Cessna 210 and Beech Bonanza. The idea is good, but this things just don’t seem to make up their promise. You will still drain your battery.
Another things is that bearings wear out. This might be better now, as they advertise now that they use a balancing machine). Although B&C says thay they are the only one who do this, that is defenitly not true, also other manufacturers have dynamically balanced rotors.
The 3500RPM is alternator RPM used on the test bench, according their specs. Output for alternators and generators is typically the rotor RPM, not the engine RPM, as the gearing might be different of different engines.
There are also (regular) alternators which perform better than specified.
B&C make some tiny generators, which are about 1/3 of the length of the one described in the earlier parts of this thread.
The “life” of the one I have is 1800hrs, which slightly annoyingly is less than the usual engine TBO of 2000hrs, but it’s easy enough to pull it out.
AFAIK the only options for a vac pump drive mounting are the B&C units, and the “vapourware” GAMI “Supplenator” which looks very clever in that it delivers smooth DC without needing a battery to act as a smoothing capacitor.
I have the B&C unit here, on a loan until I get the paperwork sorted. It is marked as a “mockup” but is probably fully functional. However I don’t have a voltage regulator for it. However… it would not be hard to make one, for test purposes, and then spin up the alternator to see what comes out. 28V x 20A is about 0.75 HP i.e. quite a lot of power would be needed. I have a turret mill which can go up to 10000rpm so could use that 
Wonder if you have tested it, and what output you have measured.
