Electric mechanical mini gyros are great, but
I also have lusted at those little Jet or Peanut gyros.
I looked into it. The small Gyros I have seen run on 24VDC or 400Hz AC, mostly AC. If small light 12V ADI gyros where plentiful or cheap you would see them in RV's, so I looked at 24 V DC and Three phase (400Hz).
I figured out a way to convert 12 V to 24 V at a reasonable cost, but it does cost more and adds weight, however most small elect ADI's are AC.
Next I looked at the AC power. Well most inverters DC-AC start at 24V. So you have to convert 12V to 24V and than to AC. To make 12V DC to 110V (400Hz) can be done but again it weighs more and is not cheap. The Radio Shack 12V to 110V(60Hz) inverter will not work.
I know they are cool. I was just like you, but I got it out of my system (pun intended).
I found it is just not practical. If you must have an electric mechanical gyro look at a 3.25 12V unit from with a name brand (about $2000). Stay away from the cheap China made electric ADI $800 units.
Do you want to fly behind a surplus used Gyro with unknown service history? Also if it needs repair it will be hard to impossible to fix and the cost would be very high. Also they have special connectors (expensive) and are heavy little hunks of metal. I lost my lust for them long ago. Also when you do find them people want a mint for them.
Now Trutrak offers a solid state ADI with a mechanical display for a little over $1000. They also just came out with of a version of this ADI with the autopilot combined (with or without altitude hold). Even with a mechanical electric gyro you are still relying on electrical ships power.
Not sure if you want the small electric mechanical gyro as a primary unit for actual IFR or as a back-up. If you want a primary IFR gyro I would consider electronic Glass (Dynon, GRT, etc.), if you have not already. The days of mechanical gyros are coming to an end. Whether you can trust the experimental glass is another issue. The fact is since the early 80's commercial aircraft have used glass cockpits, not with out some issues. OF course comparing the avionics in a 30-140 million jet to ours is not realistic, but it is getting better and cheaper.
As a back-up to the solid state gyros you can add a second solid state gyro (Mix a GRT with one Dynon) or use a small electric DG (they are cheaper than an electric ADI). A last choice for a back-up is an electric T&B or TC. I understand the elect DG or elect T&B/TC back-ups will not give you pitch, but keeping wings level is key. To be honest I am not a big fan of just a T&B or TC as the sole back-up, but an electric DG with airspeed and VSI should get you back on the ground. Not to mention IFR in a RV single pilot should have an autopilot. So the autopilot is a back-up safety net.
Try to hand fly, partial panel (needle-ball-and-airspeed) in a fast plane like a RV in turbulence and in solid IMC. Actually most pilots don't do well partial panel in real IMC in any plane, which results in sad statistic bore out by the accidents after vacuum gyro failures. However the solid-state gyros should be more reliable.
I was thinking a good back-up to glass would be something not electrically powered. Sigma Tek just came out with a new design vacuum pump? If it proves to be reliable (2000 hour TBO not 200) and not crazy cash, I thought that might prove to be a good back-up. Of course vacuum gyros themselves don't last doing, especially doing Aerobatics. I remember how much my vac mechanical gyros cost me, so glass is the future for the experimental market. Vac works but is has it's limits. The best thing you can say about mechanical gyros is known history, back to Doolittle's 1st blind flight in 1929.
Even the small back-up gyros on jets are also now going to solid-state/glass.
Good Luck, If you find 2.25" 12V ADI for $200, let me know.
Cheers George
