Taken as a given that Vacuum pumps fail A LOT more than one encounters electrical problems, it seems to me an all-electric airplane is certainly more convenient. However, it also seems to me that in the event of any kind of electrical short/ fire / you are totally in the dark for either a few minutes while you trouble-shoot, or possibly until you get down…
In a electric/vacuum plane such as an sr-20, with an STEC rate based AP, say the 55, let’s take what statistically is a real killer of pilots, instrument failure/ partial panel / in IMC near take-off or landing. If you lose the Vacuum and the standby, your AP being rate-based is still there to keep you under control. If you have an electrical problem that necessitates a master switch off, even for a minutes, you still have the vacuum system… Seems to me like with the STEC and the dual systems you have a nice redundancy.
In the all-electric plane, you smell burning wires shortly after take-off into 500 OVC, and you properly kill the master… NOW WHAT? Four different power sources going through the same set of wires and insulation to the same electrical instruments is not true redundancy, is it?
Is there a feature about the 22 I don’t know? A standby, non-electric driven something?
And for all of you who would say, “well how often do you see that kind of failure?” I would answer probably about as often as you might need for that chute behind your heads…
I just see no safety advantage at ALL to the electric only airplane. In fact, I see a disadvantage (albeit rare) in return for added convenience.
Other than the two separate alternators and the two separate batteries, and the separate battery for the turn and bank indicator which are part of the SR22 as built, there are two items which certainly would improve safety in the event of a total electrical failure.
First, an external antenna connection for the use of a handheld nav/com should be considered essential. There appears to be ample room for an additional connector in the center console near the headset connectors.
Second, I am seriously considering installing a backup AH. BFGoodrich Avionics makes a 2 1/4" backup AH. It is described at www.bfgavionics.com under “standby instrumentation” and is the AIM520 series. If the Davtron clock/OAT/voltmeter were moved to the upper right portion of the right panel (where the suction gauge is on the SR20) this would leave a 2 1/4" open spot on the upper left of the left side of the panel. The AIM520 can be installed with a backup battery and switch similar to the turn and bank indicator. I am not sure of the specifications for the backup battery. The person I spoke with at BFGoodrich Avionics indicated that probably a gel cell battery that would be charged from the avionics bus would probably be used.
With this configuration, you would have communication and VOR navigation from the handheld and turn and bank and AH from independent electrical supplies. The AIM520 and the more expensive J.E.T. instruments are in transport catagory aircraft, installed with backup battery.
As to the possible failure points in the SR22 electrical system is concerned, perhaps someone with more detailed information regrding the two altinator and two battery system could give a detailed description of what the possibilities there are concerned. Michael’s post apparantly concerned a single generator and single battery failure. Apart from the handheld com failure, the generator and battery failure itself was apparantly pretty rare.